column selection - restekblog.restek.com/wp-content/.../2013/11/...column-selection-handout.pdf ·...

Copyrights: Restek Corporation

Column Selection“there is more to life than a boiling

point column”

Column Selection“there is more to life than a boiling

point column”

Jaap de Zeeuw

Restek Corporation,

The Netherlands


• Retention of a compound can be related to boiling point or solubility

• The solubility of a compound in the stationary phase is a better predictor of retention than boiling point..

Stationary Phase SelectivityBoiling Point versus SolubilityStationary Phase SelectivityBoiling Point versus Solubility

So.. what do we mean with “boiling point” separation columns and where are they used as such?


2,3

1. acetone 56oC bp2. pentane 36oC3. propanol 97oC4. MEK 80oC5. hexane 69oC6. butanol 118oC7. 3-pentanone 101oC8. heptane 98oC9. pentanol 138oC10. octane 126oC

Run Conditions: Rtx-1

Dimensions: 30m, 0.32mm ID, 1.0 μm

Temperature: 70oC Isothermal

Carrier Gas: Helium at 20 cm/sec

Flow: 0.989 mL/min

Head Pressure : 5.91 psig

Injection: Split

Detector: FID

Rtx-1 100% polydimethyl siloxaneRtx-1 100% polydimethyl siloxane Alkanes


2,3






Flow: 0.989 mL/min


Injection: Split

Detector: FID

Rtx-1 100% polydimethyl siloxaneRtx-1 100% polydimethyl siloxane Ethers


2,3






Flow: 0.989 mL/min


Injection: Split

Detector: FID

Rtx-1 100% polydimethyl siloxaneRtx-1 100% polydimethyl siloxane Alcohols


2,3






Flow: 0.989 mL/min


Injection: Split

Detector: FID

Rtx-1 100% polydimethyl siloxaneRtx-1 100% polydimethyl siloxane


Separation is according to boiling point …

Need to add something..

.. “within a certain class of compounds”..


What about “polar” phases?


Run Conditions: Stabilwax




Flow: 0.989 mL/min


Injection: Split

Detector: FID

2 35

1. pentane 36oC bp2. hexane 69oC 3. heptane 98oC 4. octane 126oC5. acetone 56oC 6. MEK 80oC7. 3-pentanone 101oC8. propanol 97oC 9. butanol 118oC 10. pentanol 138oC

PEG 100% poly ethylene glycolPEG 100% poly ethylene glycol

Polar phases also separate according to boiling point..Polar phases also separate according to boiling point..


Where are “boiling point” separations used?Where are “boiling point” separations used?

Simulated Distillation

• Improved characterization of crude leads to better control of final product

• Increased gas oil yield


Simulated DistillationSimulated Distillation

• Chromatographic procedure designed to mimic (simulate) the physical process of distilling petroleum products

• Establishes a FAST correlation between retention time and boiling point

• Results are used to control refining operations

• Results are also an indicator of the range of products that can be produced from a starting material and their potential yield


1 2 3 4 5 6 7 8 9 10

Simulated Distillation Simulated Distillation

• The chromatogram of the sample is divided into time slices• The software determines the area count for each slice

• The chromatogram of the sample is divided into time slices• The software determines the area count for each slice

Retention time


Retention Time vs Boiling Point Retention Time vs Boiling Point


Simulated Distillation: ASTM methodsSimulated Distillation: ASTM methods

D2887 C6-C42 0.88 - 3 um PDMS 10/0.53 concentr.D7213 (2887-ext) C8-C60 0.15-1.2 um PDMS dilutedD3710 gasoline up to C14 2.65 um PDMS 10/0.53 concentr.D5307 crude up to C42 0.2 um PDMS, 5/0.53 dilutedD6352 C10-C90 0.1-0.2 um PDMS, 5/0.53 dilutedD7500 C7-C110 0.2 um PDMS, 5/0.53 dilutedD7169 C5-C100 0.2 um PDMS, 5/0.53 diluted

ASTM nr Range Column Injection

Methods can be classified by Boiling Point and Hydrocarbon rangesMethods can be classified by Boiling Point and Hydrocarbon ranges


Challenges in Simulated DistillationChallenges in Simulated Distillation

• Columns Break (fused silica)

• Columns loose stationary phase by bleed• Need to do often calibrations (time)• Replace columns (price per analysis, time)• Reduced accuracy (reliability challenge)

• Columns are not efficient• Do not meet resolution requirements


High temperature separations: column materialsHigh temperature separations: column materials

Aluminium coated Glass Capillary

MXT CapillaryHigh temperature Polyimide coated


Problem with fused silica columns used for High temperaturesProblem with fused silica columns used for High temperaturesOperation at temperatures of 400ºC or higher will result in polyimide damage

• Column life time is dictated by the OUTSIDE coating;

• Column life time not predictable

• Coupling with PressTight connections is not possible


Special High temperature polyimide was developed for highest temperature stability


Better solutions MXT metal tubing: extreme strongBetter solutions MXT metal tubing: extreme strong

• Virtually unbreakable, self straightening

• Stable up to 450ºC

• Can be bended / coiled on small radius

• Stabilizes the stationary phase

• winded on standard column cages

For Simdist a MUST to use 0.53mm


Bleed comparison using different surface deactivationsBleed comparison using different surface deactivations

Normal deactivation

Siltek-deac surface

SAME stationary phase,

DIFFERENT surface..

SAME stationary phase,

DIFFERENT surface..

Siltek coated surfaces bleed a factor 4-5 less


• Silphenylene stabilized phases cannot be used for “simdist”separations

• The Sil-phenylene will provide some polarity, which causes deviations of calibration curve..

• Need to use 100% PDMS, to be able to use historical reference values.

• Stabilization done by increase of X-links in PDMS chain

Use of “Sil phenylene” phasesUse of “Sil phenylene” phases Si

CH3

CH3

O Si

CH3

CH3

O Si

CH3

CH3

X Y


Simulated Distillation: ASTM methodsSimulated Distillation: ASTM methods

D2887 C6-C42 0.88 - 3 um PDMS 10/0.53 concentr.D3710 gasoline up to C14 2.65 um PDMS 10/0.53 concentr.D7213 (2887-ext) C8-C60 0.15-1.2 um PDMS dilutedD5307 crude up to C42 0.2 um PDMS, 5/0.53 dilutedD6352 C10-C90 0.1-0.2 um PDMS, 5/0.53 dilutedD7500 C7-C110 0.2 um PDMS, 5/0.53 dilutedD7169 C5-C100 0.2 um PDMS, 5/0.53 diluted

ASTM nr Range Column Injection

Methods can be classified by Boiling Point and Hydrocarbon rangesMethods can be classified by Boiling Point and Hydrocarbon ranges


Column Performance-ASTM D7169Column Performance-ASTM D7169

Column : 5m x 0.53mm MXT Simdist, 0.1 μm Oven : 40°C → 430 °C, 1 min, 30°C/min

Column : 5m x 0.53mm MXT Simdist, 0.1 μm Oven : 40°C → 430 °C, 1 min, 30°C/min

C104


Restek MXT columns show low bleed, because Silteksurface stabilizes the PDMS phaseRestek MXT columns show low bleed, because Silteksurface stabilizes the PDMS phase

Each column is tested with this test to guarantee performance..


Oil spill Mississippi Canyon Block 252 Oil spill Mississippi Canyon Block 252


Analysis of Tar balls/crudeAnalysis of Tar balls/crude


Basic rule in GC stationary phase selection..Basic rule in GC stationary phase selection..

Solubility of sample component in the stationary phase based upon “likes dissolve likes.”


“ choose a stationary phase that “looks like” the components you want to separate..”

Hydrocarbons 100% PDMS type phase: Rtx-1

ASTM 6730: detailed hydrocarbon analysis;Many components (>500)


GC-FID Hydrocarbons on Rtx-DHA-100GC-FID Hydrocarbons on Rtx-DHA-100C

3n-

Cn-

C

n-C

n-C

n-C

8

n-C

9

n-C

10

0 50 100 150

Column : 100 x 0.25 mm Rtx-DHA 100

Oven : 5°C, 10 min -> 50°C, 5°C/min, 54 min, --> 200°C, 1.3 °C/min

Carrier gas : He, 24 cm/s, 39.3 Psi; Injection Split, 1 : 150; Detection : FID;

Column : 100 x 0.25 mm Rtx-DHA 100

Oven : 5°C, 10 min -> 50°C, 5°C/min, 54 min, --> 200°C, 1.3 °C/min

Carrier gas : He, 24 cm/s, 39.3 Psi; Injection Split, 1 : 150; Detection : FID;


Compensate by using Selective detection..Compensate by using Selective detection..

“Only see what I want to see”..MS-SIM, SClD/FPD/PFPD, AED, NPD, ECD, O-FID,..

• Can use non-polar columns, also shorter in length

• Efficiency / selectivity less important

Challenges:• Quenching / Bias

• Stability and Cost of ownership

• Need qualified people


GC-MSGC-MS

In GC-MS 95% of the applications are done with a non-polar type stationary phases:

• 100% poly dimethyl siloxane (Rxi-1ms)• Arylene modified equivalent of 5% diphenyl /95%

dimethyl siloxane (Rxi-5ms and Rxi-5Sil MS)

If there is a co-elution, the MS will deconvolute if the mass spectra have clear different m/z fragments

If there is a co-elution, the MS will deconvolute if the mass spectra have clear different m/z fragments


For the best quantitative result you need to optimize the separation first..

It s always better to quantify the individual analyte as matrix effects are eliminated

Selective detection is “nice” but we always have to think of the “possible” bias..


2001 Las Vegas ISCC2001 Las Vegas ISCC


Column SelectionColumn Selection

Back to Basics.. Rudi Kaiser


When need Selectivity?When need Selectivity?• If there are limited nr of plates available;

• If components have to be separated by non-selective detection

• If components have same fragments in MS or cause a bias

• if selective detection is not “selective” enough..

• In multi dimensional separations


Limited nr of Plates

When need Stationary Phase Selectivity?



Limited number of platesLimited number of plates

Using packed columns.. 2000 -10.000 plates;

Lots of different stationary phases


No deed for glass columns as metal is more inert due to Siltek deactivation

No deed for glass columns as metal is more inert due to Siltek deactivation


If components have to be separated by non-selective detection




Use of non selective detectorsUse of non selective detectors

FID is widely used: Cheap detector, but requires chromatographic separation

Column selectivity is very important: need to use tools available:

• Use literature search

• Use Chrom databases on the web from suppliers (Agilent, Restek, Sigma..)

• Use Chrom calculators and Optimization

Chrom calculators


Example of Chromatogram CalculatorExample of Chromatogram Calculator

On-line EZ-GCChromatogram modeler

http://www.restek.com/chromatogram/ezgc/


Shortest time analysis

Uses available databases


Compound structure information + Physical constants

Compound structure information + Physical constants

Mass spectra dataMass spectra data

SynonymsSynonyms


On-Line Method translator Flow calculatorOn-Line Method translator Flow calculator

Will also be a windows application

This will be available SOON.. Watch for the Restek news


If components have same fragments in MS or cause a bias




• When components are isobaric, and show similar mass spectra

• When component forms many similar ions (PCB, Dioxins, BFRs, PAH)

GC separation is essentialGC separation is essential


Separation of PAH in foodSeparation of PAH in foodNIST SRM 2260a on 40m x 0.18mm x 0.07µm Rxi‐PAH

EPA


PAH in Food: Chrysene-TriphenylenePAH in Food: Chrysene-Triphenylene


PAH in Food: Benzo fluoranthenesPAH in Food: Benzo fluoranthenes


Complex sample using GC/MSComplex sample using GC/MS

• Environmental method, TO-15• 70 components, 4 retentive phases

1-ms 5-ms5Sil MS VMS

Bias:-1ms : ethyl acetate and hexane overlap; share some of the same ions.-5ms/5SilMS : MEK and hexane overlap, share some of the same ions.

VMS separates all


If Selectivity of Detector is not “selective “ enough..




Selective DetectionSelective Detection

Is not always possible as “selectivity” has limitations.

“Only see what I want to see”..

Impurity in main product

If main component elutes together with Target analyte

Quenching:

signal of target is impacted by main analyte


COS in propylene/propaneCOS in propylene/propaneFor trace sulfur, 100% PDMS is preferred.

On this phase COS elutes together with Propane/propylene


0 2.5 5 7.5 100 2.5 5 7.5 100 2.5 5 7.5 100 2.5 5 7.5 10

Propylene elutes with propane on the Rt-UBOND

H2S

COS, 1 ppm

Expected position of ethylene

Need selective phase to separate COS from propylene/propaneNeed selective phase to separate COS from propylene/propane

propane

ethane

Polar Porous polymer, type „U“, 30m x 0.32mm ID x 10 μm Polar Porous polymer, type „U“, 30m x 0.32mm ID x 10 μm


Multidimensional Separations




Where else do I need selectivity?Where else do I need selectivity?

• If I do not get “enough” separation on my non-polar column..

• Very complex samples, need high peak capacity..

• Use column switching Valves

Deans (live)

Valves

Deans (live)


Every major Instrument supplier offers a “flow”

switching solution


Biodiesel fuel dilution in Lube oil by Flow Heart cut GCBiodiesel fuel dilution in Lube oil by Flow Heart cut GC

PDMS columnPDMS column

WAX columnWAX column


Where else do I need selectivity?Where else do I need selectivity?

• If I do not get “enough” separation on my non-polar column..

• Very complex samples, need high peak capacity..

• Or use column switching


GC x GC Enhanced peak capacityGC x GC Enhanced peak capacity

Peak capacity in GC xGC = 1000 x 30 = 30.000Peak capacity in GC xGC = 1000 x 30 = 30.000

To get equal peak capacity, we would need a 10 km column:

Analysis times > weeks


Need to use “selectivity” to separate components that co-elute in the first dimension

Typical GC x GC SetupTypical GC x GC Setup

• Primary column (1st dimension)• Typical 30m x 0.25mm, film of 0.25-0.5um• Non-polar

• Modulator• Focuses effluent from primary column• “Injects” this effluent onto secondary column

• Secondary column (2nd dimension)• Typical 1-2m, 0.15-0.18mm, 0.15/0.18um• Polar or Selective


Selectivities mostly usedSelectivities mostly used

First dimension: Non-Polar : Rxi-1ms, -5ms, -5Sil MSPolar : Rxi-17Sil MS

Second dimension: Liquid phases- Rxi-1ms- Rxi-5Sil MS- Rxi-XLB- Rxi-17Sil MS- Rtx-200- StabilWax- Cyano

Shape selective phases• Cyclodextrin modifications

• Liquid crystal

• Ionic Liquids

Major Challenge: temperature stability


Nigerian Crude on GCxGC-TOF-MSNigerian Crude on GCxGC-TOF-MS

30m x 0.25mm x 0.25 μmnon-polar 5Sil MS

1.1m x 0.15 mm id. x 0.15 μm-17Sil-MS Range -60 - 360ºC


Rxi-XLB

Rxi

-17S

il M

S

Rxi-17Sil MS

Rxi

-5m

s

Rtx

-1m

s

Rtx

-200

Rxi-5Sil MS

Rxi-17Sil MS

BFr’s en PCB’s

Hydrocarbon oils

cannabinoids

Terpenes cannabinoids

Pesticides

First column : non-polar

Second column : polar


Rxi-XLB

Rxi

-17S

il M

S

Rxi-17Sil MS

Rxi

-5m

s

Rtx

-1m

s

Rtx

-200

Rxi-5Sil MS

Rxi-17Sil MS

BFr’s en PCB’s

Hydrocarbon oils

cannabinoids

Terpenes cannabinoids

Pesticides

First column : polar

Second column : non-polar


Basic rule in GC stationary phase..Basic rule in GC stationary phase..



“ choose a stationary phase that “looks like” the components you want to separate..”

Hydrocarbons 100% PDMS Rtx-1

Aromatic subst. Phenyl subst. PDMS Rtx-5, 17Sil, 35Sil

Halogenates Arom. Fluorimated-phenyl Rtx-440, Cl-Pesticides, Rtx-200

Solvents Cyano /phenyl Rtx-1301/624Sil

Alcohols,diols,glycols PEG Stablewax/Rtx-wax

Double bonds Cyano propyl Rt 2330, 2460


(GC-MS) Presence of Diethylene Glycol and Ethylene Glycol in Toothpaste (GC-MS) Presence of Diethylene Glycol and Ethylene Glycol in Toothpaste

Phase: PEG

Dissolves : ‘likes like”


Important note on Selectivity behavior: It changes with temperature

Important note on Selectivity behavior: It changes with temperature

Liquid phases: By lower elution temperatures the phase behaves LESS polar

Solid phasesBy lower elution temperatures the phase behaves MORE polar

This effect is the biggest with POLAR stationary phases.. Peak elution can change..This effect is the biggest with POLAR stationary phases.. Peak elution can change..


5 6 7

1-m Nap30 C/min

m8 10 12

10 C/min

5 C/min

7 min

12 min

19 min

2 C/min

1 C/min

0.5 C/min

33 min

50 min

72 min

Non-Polar phase: 100% PDMS column; different temperature programs: Analysis of a Naphtha mixtureNon-Polar phase: 100% PDMS column; different temperature programs: Analysis of a Naphtha mixture

Some components are very sensitive for changes in elution temperature..

Some components are very sensitive for changes in elution temperature..

155ºC

68ºC

81ºC

95ºC

115ºC

130ºC


Medium polarity: Optimized phase for Cl-PesticidesPeak elution reversalMedium polarity: Optimized phase for Cl-PesticidesPeak elution reversal

At 8.9 psi, u = 22 cm/sAt 8.9 psi, u = 22 cm/s

At 26 psi, u = 61 cm/sAt 26 psi, u = 61 cm/s

Tel. = 250ºCTel. = 250ºC

Tel. = 210ºCTel. = 210ºC

4,4’-DDE

4,4’-DDE

Endosulfan I

Endosulfan I


Polar column: TCEP Relative elution of benzene to C11 and C12 Polar column: TCEP Relative elution of benzene to C11 and C12

C12

C12

C12

C12

C12

C12

C11

C11

C11

C11

C11

Benzene

RI=1090

benzene

benzene

benzene

Benzene

RI = 1240

30ºC

50ºC

70ºC

90ºC

110ºC


Temperature effect on selectivity using Al2O3/Na2SO4Temperature effect on selectivity using Al2O3/Na2SO4


Impact of Flow rate on separation; Rt Alumina BOND / MAPDHigher flow = lower elution temperatureImpact of Flow rate on separation; Rt Alumina BOND / MAPDHigher flow = lower elution temperature

100kPa100kPa

200kPa200kPa

150kPa150kPa

acetylene

acetylene

acetylene

propadiene

propadiene

propadiene

C4

C4

C4


Relative position of CO changes with temperatureRelative position of CO changes with temperature

40 ºC

80 ºC

120 ºC

CO

CO

CO

CH4

CH4

CH4

0.8 min

1.4 min

4 min

Column : 1m x 0.53mm MXT Molsieve 5A 80/100 mesh

Carrier : He, 180 kpa

Split : 1 : 30; Injection: 15 μl; Sample: 2-5% in He

Detection : micro-TCD

Column : 1m x 0.53mm MXT Molsieve 5A 80/100 mesh

Carrier : He, 180 kpa

Split : 1 : 30; Injection: 15 μl; Sample: 2-5% in He

Detection : micro-TCD


Summary Summary

A boiling point column will only separate according to boiling point if the same class of compounds are considered

Columns with different selectivity’s will be essential for running many applications even using selective detection systems

Choosing selectivity will remain a challenge as we depend on data. More tools will be developed in future to help us.

Additional, selectivity is temperature dependent which means there is another factor that plays a role.


If you want to learn Chromatography?If you want to learn Chromatography?Visit the Restek ChromaBLOGraphy..A LOT of information shared by Restek scientists that allow you to

get better in your chromatography.. www.restek.com


Use the Search option..Use the Search option..

If you want to know about: “what do chromatograms tell us?”

Just search on “ what do chromatograms..” and you can get a full list with links..


Thanks you for participating

If your any question, please drop me an email

[email protected]

column selection - restekblog.restek.com/wp-content/.../2013/11/...column-selection-handout.pdf ·...

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