1

Electrospray IonizationEfficiency Scale of Organic

CompoundsIvo Leito Merit Oss Anneli Kruve Koit Herodes

University of TartuInstitute of Chemistry

Estonia

ivoleitoutee

14th Nordic MS Conference Uppsala Aug 18-20 2010

2

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

2

3

ESI Ionization

bull The most widely applied ionizationmethod in MS

bull Ionization viabull Protonationbull Deprotonationbull Adduct formation

bull Complex mechanismbull Ion Evaporation Model (IEM)bull Charged Residue Model (CRM)

4

ESI in action (Positive ions)

Image by K K Murray (via Wikipedia)

Positivelychargeddroplets

3

5

ESI mechanism according to IEM

B SH++

H-B+

+

Polar slightly acidified solvent egWater-MeCN (+ HCOOH)

S

Dropsurface

Gas phase

H-B+

H-B+

Dropinterior

We assume the IEM model for small

molecules

We study onlyionization by

monoprotonation

6

Efficiency of ion formation in ESI

bull Not all molecules in a droplet are converted to gas-phase ions

bull Ionization efficiency what proportion of the molecules (or ions) present in thesprayed solution are converted to gas-phase ions

4

7

ESI Ionization Efficiency (IE)bull IE depends on

bull Molecular structurebull Solventbull ESI and MS Conditions

Different molecules have vastlydiffering ionization efficiencies in the

ESI source

Being able to predict ionizationefficiencies of molecules would be

very useful

8

What determines ionization efficiency of a molecule

bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip

Howeverthere is still a long way to go to gain

complete understanding

5

9

How to measurequantifyexpressionization efficiency of a molecule

bull For applying the scientific method to a phenomenon its extent needs to bemeasured

There is currently no generallyaccepted way to measurequantify

ESI IE

10

Goals

bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment

bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions

bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure

6

11

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

12

Defining ionization efficiencybull Fundamental

bull n in the gas phase is very difficult todetermine

molecules) phase-solution()ions phase-gas(

lfundamenta nnIE =

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

2

3

ESI Ionization

bull The most widely applied ionizationmethod in MS

bull Ionization viabull Protonationbull Deprotonationbull Adduct formation

bull Complex mechanismbull Ion Evaporation Model (IEM)bull Charged Residue Model (CRM)

4

ESI in action (Positive ions)

Image by K K Murray (via Wikipedia)

Positivelychargeddroplets

3

5

ESI mechanism according to IEM

B SH++

H-B+

+

Polar slightly acidified solvent egWater-MeCN (+ HCOOH)

S

Dropsurface

Gas phase

H-B+

H-B+

Dropinterior

We assume the IEM model for small

molecules

We study onlyionization by

monoprotonation

6

Efficiency of ion formation in ESI

bull Not all molecules in a droplet are converted to gas-phase ions

bull Ionization efficiency what proportion of the molecules (or ions) present in thesprayed solution are converted to gas-phase ions

4

7

ESI Ionization Efficiency (IE)bull IE depends on

bull Molecular structurebull Solventbull ESI and MS Conditions

Different molecules have vastlydiffering ionization efficiencies in the

ESI source

Being able to predict ionizationefficiencies of molecules would be

very useful

8

What determines ionization efficiency of a molecule

bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip

Howeverthere is still a long way to go to gain

complete understanding

5

9

How to measurequantifyexpressionization efficiency of a molecule

bull For applying the scientific method to a phenomenon its extent needs to bemeasured

There is currently no generallyaccepted way to measurequantify

ESI IE

10

Goals

bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment

bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions

bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure

6

11

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

12

Defining ionization efficiencybull Fundamental

bull n in the gas phase is very difficult todetermine

molecules) phase-solution()ions phase-gas(

lfundamenta nnIE =

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

3

5

ESI mechanism according to IEM

B SH++

H-B+

+

Polar slightly acidified solvent egWater-MeCN (+ HCOOH)

S

Dropsurface

Gas phase

H-B+

H-B+

Dropinterior

We assume the IEM model for small

molecules

We study onlyionization by

monoprotonation

6

Efficiency of ion formation in ESI

bull Not all molecules in a droplet are converted to gas-phase ions

bull Ionization efficiency what proportion of the molecules (or ions) present in thesprayed solution are converted to gas-phase ions

4

7

ESI Ionization Efficiency (IE)bull IE depends on

bull Molecular structurebull Solventbull ESI and MS Conditions

Different molecules have vastlydiffering ionization efficiencies in the

ESI source

Being able to predict ionizationefficiencies of molecules would be

very useful

8

What determines ionization efficiency of a molecule

bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip

Howeverthere is still a long way to go to gain

complete understanding

5

9

How to measurequantifyexpressionization efficiency of a molecule

bull For applying the scientific method to a phenomenon its extent needs to bemeasured

There is currently no generallyaccepted way to measurequantify

ESI IE

10

Goals

bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment

bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions

bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure

6

11

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

12

Defining ionization efficiencybull Fundamental

bull n in the gas phase is very difficult todetermine

molecules) phase-solution()ions phase-gas(

lfundamenta nnIE =

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

4

7

ESI Ionization Efficiency (IE)bull IE depends on

bull Molecular structurebull Solventbull ESI and MS Conditions

Different molecules have vastlydiffering ionization efficiencies in the

ESI source

Being able to predict ionizationefficiencies of molecules would be

very useful

8

What determines ionization efficiency of a molecule

bull The main influence factors are knownbull Ionizabilitybull Surface activitybull hellip

Howeverthere is still a long way to go to gain

complete understanding

5

9

How to measurequantifyexpressionization efficiency of a molecule

bull For applying the scientific method to a phenomenon its extent needs to bemeasured

There is currently no generallyaccepted way to measurequantify

ESI IE

10

Goals

bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment

bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions

bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure

6

11

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

12

Defining ionization efficiencybull Fundamental

bull n in the gas phase is very difficult todetermine

molecules) phase-solution()ions phase-gas(

lfundamenta nnIE =

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

5

9

How to measurequantifyexpressionization efficiency of a molecule

bull For applying the scientific method to a phenomenon its extent needs to bemeasured

There is currently no generallyaccepted way to measurequantify

ESI IE

10

Goals

bull Devise a parameter and measurementmethod that can be widely used forquantifying ESI IEbull Measurable with routine MS equipment

bull Determine this parameter for a wideselection of molecules of diverse structureunder the same conditions

bull Relate the ESI IE data to molecularstructurebull Ideally predict ESI IE from structure

6

11

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

12

Defining ionization efficiencybull Fundamental

bull n in the gas phase is very difficult todetermine

molecules) phase-solution()ions phase-gas(

lfundamenta nnIE =

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

6

11

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

12

Defining ionization efficiencybull Fundamental

bull n in the gas phase is very difficult todetermine

molecules) phase-solution()ions phase-gas(

lfundamenta nnIE =

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

7

13

Defining ionization efficiencybull Practical

bull RBH+ ndash MS Response of the BH+ ion inthe mass spectrum

bull CB ndash molar concentration of the base B in the mass spectrum

B

BH

CR

IE +=

14

Agilent XCT ion trap MS with ESI Source

Effluent fromHPLC

Nebulizationgas (N2) inlet

Nebulizerneedle

Sprayshield

Capillary

Skimmer

Octopole 1 Octopole 2

Split lens

Ring electrodeDrying gas(heated N2) flow

Lens 1 Lens 2

High energydynode

ElectronmultiplyerEnd capsCapillary

entrance

Capillaryexit

Atmospheric pressure(spray chamber)

Vacuumpartition

38 mbar 015 mbar 00016 mbar 5 x 10-6 mbar (without helium)

Ion generation Ion transport and focusing Mass analyzer(ion trap)

Detector

End plate

Meshelectrode

Not all ionsreach theentrance

Ion lossesduring iontransport

Responsedepends on

trapping efficiency

Conclusion R does not measure just ESI IE but the efficiency of the whole

system

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

8

15

Dependence of RBH+ on conditions

bull KBH+ partition coefficient of BH+ between drop surface and interiorbull [BH+] equilibrium concentration of BH+ in the dropbull KE+ generalized partition coefficient of all other ions between drop surface

and interiorbull [E+] equilibrium concentration of all other ions in the dropbull f the fraction of droplet charge that is converted into gas-phase ionsbull P ldquosampling efficiencyrdquo of the mass spectrometerbull [Q] excess charge in the drop

][]E[]BH[

]BH[

EBH

BHBH

QKK

KPfR ++

+

++

+

+

+=

C Enke Anal Chem 1997 69 4885

16

Assumptions (I)

bull Drop surface and interior are two distinct phasesbull Excess charge is on the drop surface

bull Drop interior is neutral

bull Ion partition between these phases is rapidbull The amount of BH+ on the surface is small

compared to the interiorbull RBH+ is proportional to the amount of BH+ on the

drop surface

C Enke Anal Chem 1997 69 4885

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

9

17

Two Compounds simultaneously

bull Ifbull the assumptions holdbull And if two ions B1H+ and B2H+ are infused in the

same solution at significantly lower concentrationthan buffer electrolytes

bull then the following holds

]HB[

]HB[

1HB

2HB

HB

HB

2

1

2

1

+

+

+

+

+

+

=R

R

K

K

18

Two Compounds simultaneously

bull Considering that

bull We get

12

21

22

11

BHB

BHB

HBHB

HBHB

CR

CR

K

K

+

+

++

++

=α

α

+

+

+

=HB

1HB

1

1

]HB[C

α+

+

+

=HB

2HB

2

2

]HB[C

α

==)B()B()BB(

2

121 IE

IERIE

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

10

19

Relative Ionization Efficiency of B1 and B2

bull It is more convenient to use logRIE values

bull Measured by infusion of a solution containingtwo analytes B1 and B2 into ESI MS

bull Concentrations of B1 and B2 are knownbull R are measured from mass spectra as peak

heights (areas)

12

21

BHB

BHB

2

121 )B(

)B()BB(CR

CR

IEIERIE

+

+

==

I Leito et al Rapid Comm MS 2008 22 379

20

Compound B1 Diphenylaminebull M = 169 N

H

NH2+

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

11

21

Compound B2 Acridinebull M = 179

N

NH+

22

Mixture of B1 and B2

logRIE = -034

20050913 T=500 T=170 T=180Compound DPhA akridiin I I I IsotopicC(ppm) 06 08 correctionM(gmol)= 16922 1792173C(M) 3018E-06 3925E-06Infusion rate 03 02 170 1611978 2128693 2162743 1143C(M) in spray 1811E-06 157E-06 180 3754692 3990029 4142303 1154

akridiin

180 corr 4332915 4604493 4780218sum corr 4332915 4604493 4780218

DPhA

170 corr 1842491 24330961 24720152sum corr 1842491 2433096 2472015

K_rie (frag) 0369 0458 0448log(K_rie) -0433 -0339 -0348

1700

1800

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

12

23

Assumptions (II)

bull Linearity RBH+ ~ [BH+]bull Holds if the concentration of BH+ in the drop interior is in the

range of 1middot10-6 M

bull Compounds B1 and B2 do not suppressenhanceeach otherrsquos ionization or do that in a proportionalway

bull Equal transmission efficiency and detectorsensitivity for B1H+ and B2H+

bull Transmission efficiency is more importantbull In the used MS system transmission efficiency of different mz

ions can be tuned with a parameter target mass

I Leito et al Rapid Comm MS 2008 22 379

24

Advantages of relative measurement

bull All experimental parameters (Numerousvoltages in the MS gas flow rates temperatures solution composition) are automatically thesame for both compoundsbull Many of them difficult to control

bull Ion losses cancel to a large extentbull Similar transmission efficiencies

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

13

25

Experimental details

bull Solvent MeCN 01 HCOOH 8020bull Concentrations n10-7 hellip n10-5 Mbull For every concentration ratio ca 250

spectra were averagedbull Infusion rate 05 mlhbull Transmission efficiencies made as similar

as possiblebull Using the Target mass parameter

of the Agilent XCT IT MSbull Other MS parameters at default

values

26

QA of the resultsbull In all pairs parallel measurements were

done with different concentration ratiosusually differing by more than 10x

bull Every measurement is ldquocircularlyvalidatedrdquo by at least one additionalldquopathrdquo

bull A ldquovalidationrdquo pair of compounds (DMS vsDMG) is measured every now and then tomonitor the MS system

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

14

27

Circular validation

)B()B(log)BB(log

2

121 IE

IERIE =

)BB(log)BB(log)BB(log 231312 RIERIERIE minus=

logRIE(B2B1)

logRIE(B3B2)

logRIE(B3B1)

28

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

15

29

Compounds

bull 62 compounds from the families ofbull Aliphatic and aromatic aminesbull Amidines guanidinesbull Phosphazenesbull tetraalkylammonium saltsbull Heterocyclesbull Amides Esters Acidsbull some others

30

Compounds (I)

N

N

N

NH2

N

NH

NO2

NH2NH2

NO2O2N

NH2

NO2

NO2

NH2

F

N NH2

O2N

NH2

Cl

NO2

N

Aliphatic amines Aromatic amines

NH

NH

N

NH2

NH

NH2

NH2

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

16

31

Compounds (II)

NH

NH

NH

N PN

NN

N

F

F

F

PN

NN

NCl

Cl

PN

NN

ClN P N

N

NPN

NN

Phosphazenes

N N

NH

NH2

NH

NH2

Guanidinesamidines

+NN+

N+

N+

N+

Tetraalkylammonium

N

N

N

N

N

32

Compounds (III)

COOMe

COOMe

COOMe

COOMe

COOMe

COOMe

COOPh

COOPhO

O

O

O

O

O

O

O

F

F

F

Carbonyl compounds

NH2

O

OH

O

O

COOMe

COOMe

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

17

33

Compounds (IV)

N

O

ON

Cl

N N N

N

OHN

S NO N

H

O

S

O NH

O

SN

O NH

O

NCl

N

O

NN+

NN+

OthersHeterocycles

N

NH2

SO

O NH2

34

ResultsESI IE Scale

bull 407measurements

with 250compound pairs

bull Only 116 measurements

are indicatedon the scale

No Compound logIE a Directly measured logRIE values

1 2ClPhP2(pyrr) 615

2 tetrahexylammonium 565

3 4CF3PhP1(pyrr) 555

4 25Cl2PhP1(pyrr) 552

5 PhP1(NMe2)3 518

6 tetrabutylammonium 513

7 tetrapropylammonium 497

8 phenyl tetramethylguanidine 486

9 tributylamine 483

10 hexyl-methylimidazolium 466

11 diphenylguanidine 461

12 tripropylamine 456

13 acridine 442

14 246-trimethyl pyridine 390

15 diphenylamine 418

16 diphenyl phthalate 410

17 1-naphthylamine 404

18 DBU 396

19 tetramethylguanidine 389

20 tetraethylammonium 395

21 methiocarb 388

22 triphenylamine 367

23 NN-dimethylaniline 372

24 ethyl-methylimidazolium 368

25 4-fluoro-3-nitroaniline 365

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 3 25

M Oss et al Anal Chem2010 82 2865

For better view of the scalesee poster No 21

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

18

35

ESI IE Scale(contd)

26 26-dimethylpyridine 341

27 dimethyl phthalate 354

28 triethylamine 353

29 3-nitroaniline 352

30 benzylamine 343

31 sulphanilamide 340

32 methomyl 325

33 aldicarb 322

34 piperidine 316

35 benzophenone 325

36 2-methyl pyridine 302

37 aniline 304

38 N-methyl piperidine 301

39 4-nitroaniline 296

40 pyridine 294

41 dimethyl glutarate 288

42 benzamide 274

43 pyrrolidine 270

44 diethylamine 266

45 phenylbenzoate 244

46 2-nitroaniline 244

47 4-chloro-2-nitroaniline 232

48 dimethyl succinate 214

49 tetramethyl ammonium 215

50 guanidine 195

51 trimethylamine 181

52 dimethylmalonate 146

53 2-cyano phenol 125

54 benzoic acid 122

55 24-dinitroaniline 114

56 26-dimethoxy pyridine 112

57 ethylamine 112

58 2-methoxy pyridine 099

59 3-chloro pyridine 100

60 2-chloro pyridine 097

61 ethyl benzoate 053

62 methyl benzoate 0

bull Values assignedby least-squares

minimization

bull Anchored tomethyl benzoate

IE(MB) = 0

M Oss et al Anal Chem2010 82 2865

36

Compd logIE Compd logIE Compd logIE Compd logIE

2ClPhP2(pyrr) 615 1NaNH2 404 Aldicarb 322 Me4N+ 215

Hex4N+ 565 DBU 396 Piperidine 316 Guanidine 195

4CF3PhP1(pyrr) 555 TMG 389 Benzophenone 325 Me3N 181

25Cl2PhP1(pyrr) 552 Et4N+ 395 2MePy 302 DMM 146

PhP1(NMe2)3 518 Methiocarb388 Aniline 304 2CNPh 125

Bu4N+ 513 Ph3N 367 NMP 301 PhCOOH 122

Pr4N+ 497 NN-DMA 372 4NA 296 24DNA 114

PhTMG 486 EMIM+ 368 Pyridine 294 26DMeOPy 112

Bu3N 483 4F3NA 365 DMG 288 EtNH2 112

HexMIM+ 466 26MePy 341 Benzamide 274 2MeOPy 099

DPhG 461 DMP 354 Pyrrolidine 270 3ClPy 100

Pr3N 456 Et3N 353 Et2NH 266 2ClPy 097

acridine 442 3NA 352 PhB 244 EtB 053

246TMePy 390 BA 343 2NA 244 MB 0

DPhA 418 sulfA 340 4Cl2NA 232

DPhP 410 Methomyl 325 DMS 214

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

19

37

Consistency of the scale

bull s = 030 logRIE units

bull 143 measurements deviate by more than 02 logunits

bull Their exclusion almost did not change logIE valuesbull Therefore no measurement was excluded

cm nnSSsminus

=

38

Reasons of deviationsbull Too different molecular masses of B1 and B2

bull 25-Cl2PhP1 (pyrr) (M = 400) vs DPhG (M = 211) deviation -0001602units

bull Sulfanyl amide (M = 172) vs Et2NH (M = 73) deviation 004054 unitsbull aniline (M = 93) vs pyridine (M = 79) deviation 0401235 units

bull Differences due to different concentrations of B1 and B2bull DMP vs DMG logIE

bull 681 ppm ja 1371 ppm 050bull 061 ppm ja 681 ppm 050bull 2319 ppm ja 789 ppm 052bull 2319 ppm ja 10 28 ppm 056bull 1119 ppm ja 653 ppm 044bull 988 ppm ja 938 ppm 053

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

20

39

Reasons for deviationsbull Loss of linearity RBH+ ~ [BH+]

bull Mutual ionization suppression of B1H+ and B2H+bull Additional processes

bull Should be independent

bull Long-term drift of theinstrument

40

Additional processesbull With O-protonating compounds Na+

adductsbull Not taken into account on the assumption that

Na+ adduct formation does not significantlydecrease [B]

bull With many compounds fragmentationbull Taken into account on the assumption that

fragmentation occurs in the gas phase after theESI processbull Intensities of fragment ions were added to that of

BH+

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

21

41

Dimethyl phthalate vs diphenyl phtahalate

O

O

O

OH+

O

O

O

OH

Ph

Ph

+

O

O

O

ONa+

O

O

O +

O

O

O

Ph

+ O

O

O

ONa

Ph

Ph

+

42

Usefulness of the scale

bull Classifying compounds which would aid in predictingESI ionizability of structurally similar substances

bull Semiquantitative determinations to be made without the need to calibrate with each analyte

bull logIE as a descriptor in QSARQSPRbull Better understanding of the ESI mechanism at the

molecular level

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

22

43

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

44

ESI IE and molecular structurebull Likely to be important

bull Basicity of B (in water acetonitrile GP)bull Polarity of BH+ (dipole moment polar surface

area)bull Hydrophobicity of BH+ (logPsolventhexane)bull Size of BH+ (M MV surface area)

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

23

4545181

367

456

483

logIE

353

∆172

∆027

∆089

∆014

M = 59pKa_H2O = 99GB = 2190 kcalmollogP = -537

M = 143pKa_H2O = 107GB = 2295 kcalmollogP = -006

M = 101pKa_H2O = 107GB = 2270 kcalmollogP = -146

M = 245pKa_H2O = -64GB = 2095 kcalmollogP = -174

M = 185pKa_H2O = 99GB = 2313 kcalmollogP = 061

45N

N

N

∆103N

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

N

4646

000

122

244logIE

053

∆053

∆122

∆069

46

O

O

OH

O

O

O

O

O

M = 136 gmolpKa_H2O = -75GB = 1957 kcalmollogP = -57

M = 122pKa_H2O = -78GB = 1888 kcalmollogP = -142 M = 150 gmol

pKa_H2O = -73GB = 1941 kcalmollogP = -48

M = 198 gmolpKa_H2O = -89GB = 1996 kcalmollogP = -500

∆191

Part of the parameters have beencomputed using COSMO-RS

See poster No 21

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

24

47

Attempt to predict ESI IE Training setbull Training set of 42 random compounds

bull Scaled and centered parameters

bull Only pKa and logMV statisticallysignificant

bull R2 = 067 s = 086 log units

ssa

s MVpKIE log)0934063590()0934041090(log plusmn+plusmn=

M Oss et al Anal Chem2010 82 2865

48

Attempt to predict ESI IE Test setbull Test set of 20

compoundsbull Differences between

measurement andprediction rangefrom -16 to 11

M Oss et al Anal Chem2010 82 2865

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

25

49

ESI IE and molecular structurebull Certain trends are seen

bull Size mattersbull Hydrophobicity mattersbull Basicity matters

bull But compounds protonated to a negligible extentin solution may well ionize

bull Prediction ability still lowbull Several parameters are computationalbull Strong correlation between some molecular

parameters can distort the picturebull It would certainly work better within compound

familiesbull More data are needed

50

Outlinebull ESI Ionization

bull Mechanismbull Defining the problem

bull Quantifying ESI ionization efficiencybull Definitionbull Assumptionsbull Method

bull ESI ionization efficiency Scalebull Compounds and their IE-sbull Consistency

bull ESI ionization efficiency and molecular structurebull Still to be done

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

26

51

Still to be donebull Measurements with different MS systems

to test the universality of the approachbull In principle similar IE order should be obtainedbull Different MS systems have different tuning

parametersbull Preliminary attempts were unsuccessful

52

Still to be donebull More thorough investigation of influence

of ESI and MS parametersbull Possible mass discriminationbull Linearity RBH+ ~ [BH+]

bull Different solventsbull Preliminary results show that with common LC-

MS solvent mixtures the picture is similar

Your ideascommentscriticism ismost welcome

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379

27

53

Thanksto all these

people

Funding ESF grant 7127 HTM project SF0180061s08

54Thank you for your attention

bull This talk is available frombull httpterachemutee~ivoChrom_MS

bull Papersbull M Oss et al Anal Chem 2010 82 2865bull I Leito et al Rapid Comm MS 2008 22 379