mass spectrometry for pesticides residue analysis- l1
TRANSCRIPT
MASS SPECTROMETRY for
pesticides residue analysis
Lecture(1)
“Pesticides classification with an introduction to mass spectrometry& vacuum system for GC MS/MS and LCMS/MS”
Contents Lecture 1: Pesticides classification with an introduction to mass spectrometry& vacuum system for GC MS/MS and LC MS/MS
Lecture 2 : Electron ionization and Chemical ionization
Lecture 3 : Electrospray Ionization and Atmospheric pressure chemical ionization
Lecture 4 : The commonly used mass to charge analyzer for pesticides residue analysis
• According to the United States Environmental Protection
Agency (EPA), Pesticides are defined as any substance or
mixture of substances intended for:
preventing, destroying, repelling, or mitigating any pest
• The increment in population induce a parallel increment in pesticide usage, especially in agriculture field. Since pesticides protect crops and improve its productivity
• Therefore, the probability of finding our food, water, … contaminated with residues of such pesticides is increased also.
• This situation is twofold when applying uncontrolled pesticides practices.
http://www.misrjournal.com/685945
Pesticides
P. Schreinemachers, P. Tipraqsa, Agricultural pesticides and land use intensification in high, middle and low income countries, Food Policy 37 (2012) 616-626.
Pesticides classification by its chemical composition
Triazine
Aryloxy phenoxy propionate
Dinitroaniline
1-Herbicides
N N
NCl NHCH2CH3
NHCH(CH3)2
Atrazine
O CH
CH3CO2(CH2)3CH3
NF3C O
fluazifop-butyl
CH3
NO2
NHCH(CH2CH3)2
NO2CH3 Pendimethaline
British Crop Production Council (BCPC), C.D.S. Tomlin, E-Pesticide Manual – Version 3.1: A World Compendium of Pesticides, sixth ed., British Crop Production Council, United Kingdom, 2004–2005.
Pesticides classification by its chemical composition
2- Insecticides
DDT
Diazinone
Cl CH
CCl3
Cl
Dichloro-diphenyl trichloro-ethane
NN
CH3
(CH3)2CH
OP(OCH2CH3)2
S
SCH3CCON(CH3)2
NOCNH
O
CH3
NCl CH2
N
NN
NO2
H
imidacloprid
Oxamyl
Organochlorines
Organophosphorus
Carbamate
Neonicotinoid
British Crop Production Council (BCPC), C.D.S. Tomlin, E-Pesticide Manual – Version 3.1: A World Compendium of Pesticides, sixth ed., British Crop Production Council, United Kingdom, 2004–2005.
Pesticides classification by its chemical composition
3- Fungicides
Boscalid
Flusilazole
Oxathiin
TriazoleF
SiF
CH3
CH2
NN
NBritish Crop Production Council (BCPC), C.D.S. Tomlin, E-Pesticide Manual – Version 3.1: A World Compendium of Pesticides, sixth ed., British Crop Production Council, United Kingdom, 2004–2005.
• In order to obtain a safe environment from pesticides residues
Monitoring programs (Food, water, soil..) & Controlling the pesticides practices
Which are carried out by proper analysis of pesticides residues and require a proper legislation.
• Pesticides legislation have been improved after preventing the usage of DDT (1980)dangers of DDT was highlighted by Rachel Carson (1962)
• Different worldwide legislation have been harmonized to introduce maximum residue limits (MRL) for effective control of various pesticides practices and assist in food, feed and environmental monitoring for pesticides residues.
Handford, A review of the global pesticide legislation and the scale of challenge in reaching the global harmonization of food safety standards, Integr. Enviro. Assess. Manage (2015)
Pesticides Legislation
http://www.panna.org/resources/ddt-story
Pesticides residue analysis
• One of the most used sample preparation method for the extraction of pesticides from fruits and vegetables is The QuEChERS method (Quick, Easy, Cheap, Effective, Rugged and Safe)
http://www.weber.hu/PDFs/QuEChERS/AOAC_2007_01.pdfhttp://www.restek.com/Technical-Resources/Technical-Library/Sample-Preparation/fff_FFAN1796A-UNV
Pesticides residue analysis
• Combination of chromatography with mass spectrometry (MS) techniques are the best choice for the analysis of pesticides residue mixture in different matrices
• In the last 10 years most of the introduced analytical methods for pesticides analysis were carried out simultaneously by both GC MS/MS and LC MS/MS ( these
techniques will be discussed later in details). To cover the huge number of available pesticides
• So, we will foxing on GC MS/MS and LC MS/MS techniques for pesticides residue analysis.
• In general : Low or nonpolar and volatile pesticides are analyzed by GC MS/MS (DDE, …..) polar or highly polar and thermo-labile pesticides are analyzed by LC MS/MS
(Carbaryl,…)
Pesticides residue analysis
MASS SPECTROMETRY• Mass spectrometry is the science of the qualitative and/or quantitative analysis
of molecules (analytes) by measuring its Mass to charge ratios (m/z).
• Measuring the m/z, which is a finger print for each molecule, make mass spectrometry techniques is the most accurate and precise technique of analysis. especially, for a mixture of compounds.
• Mass spectrometry can be used also for the chemical structure identification of the new organic compounds.
• Mass spectrometry technique consist mainly from three steps :ions production, that are subsequently separated and detected or determined step.
• A plot (record) of the relative abundance of the generated ions as a function of the m/z is defined as a mass spectrum.
Concept of MS Spectrometry
Mass Scan
OB
Ionization
NO
ON
Mass Filter
O
O
CollisionMass Filter Mass Filter
Mass Detection
http://community.asdlib.org/activelearningmaterials/introduction-to-mass-spectrometry/
2x10
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
+EI Scan (18.481 min) Chlorpyrifos_SCN_c.D
196.9
313.997.0
257.8
207.8285.8
214.9125.0
169.0 243.7 275.8108.9 179.965.0
Counts (%) vs. Mass-to-Charge (m/z)30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400
M+
5x10
00.20.40.60.8
11.21.41.61.8
22.22.42.62.8
33.23.43.63.8
44.2
+EI TIC Scan Chlorpyrifos_SCN_c.D 1 1
Counts vs. Acquisition Time (min)6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
(Q1 Scan) 5 μg/ml Chlorpyrifos
NCl
Cl Cl
OP(OCH2CH3)2
S
M-HCl, PS, 2CH2CH3
Mass SpectrumBase Beak
Molecular ion
GC Total Ion Chromatogram
History
• Eugen Goldstein (1886) discovered the Canal rays: Light appeared when placing a canal in the cathode in a discharge tube (applying a large voltage on a gas at low pressure a vessel.
https://www.uni-ulm.de/fileadmin/website_uni_ulm/nawi.inst.220/lehre/Atomphysik_SS2008/Francis_Aston.pdfhttps://en.wikipedia.org/wiki/Anode_ray
• Willy Wien (1898) elucidated that these rays is positively charged:By deflection using a magnetic filed
History
• Joseph John Thomson (1907) measured the masses of the positive rays particles (positive ions of the discharged gas) by its deflection under electric & magnetic fields.
• The deflected rays were received on a photographic plate
http://thomson.iqm.unicamp.br/iframes/iframe_thomson.htmlhttps://www.uni-ulm.de/fileadmin/website_uni_ulm/nawi.inst.220/lehre/Atomphysik_SS2008/Francis_Aston.pdf
The First Mass Spectra
History• Francis William Aston (1919) built his mass spectrograph with two electric and magnetic fields in different regions along the path of the particles which result in a focused beam. Leading to the usage of finer slits to be used, which finally improve the resolution and accuracy of the instrument.
https://www.uni-ulm.de/fileadmin/website_uni_ulm/nawi.inst.220/lehre/Atomphysik_SS2008/Francis_Aston.pdf
Mass spectra obtained by Aston, 1919–1920, of (a)Ne (b) Cl
• Mass spectrometer was modified largely (Second World War ) to be able for analyses of volatile petrochemicals
• Gas chromatography coupled with mass spectrometry (GC MS) was introduced at 1960.
Brian S. Middleditch (Practical mass spectrometry)
1970s spectrometers
History
http://www.nist.gov/mml/bmd/spectra-072914.cfm
Vacuum System MS Spectrometry
• Mass spectrometry deal with charged ions (+ve or -ve), so we need first an ionization step.
• Vacuum in the ionization unit increase the selectivity by restricting the un ionized molecules, fragments, it also restrict carrier gas (GC MS/MS) or solvent (LC/MS/MS).
• In order to separate specific charged ions (according to their m/z) free from any other ions, it is necessary to analyze them in a vacuum. This means that the ions must be in the gas phase.
• The distance that a particle travels without collision is defined as Mean free path
• Vacuum system increase the mean free path of produced ions to reach the detector of the mass spectrometer without any collision with any other forms of matter, which may result in loosing its charge (neutralization collision), changing its direction or increase its eternal energy leading to fragmentation (changing the m/z) .
Vacuum System
J. Throck Watson, Introduction to Mass Spectrometry, willy (2007)
Vacuum System
E.Hoffmann, Mass Spectrometry Principles and Applications, John Wiley & Sons Ltd, England (2007)
• L (distance/cm) = 4.95/ P (m torr) for 10 E -4 torr (0.1 mtorr) L = 49.5 cm
• High vacuum also protects the metal and oxide surfaces of the ion source,
analyzer, and detector from corrosion by air and water vapor.• The atmosphere and the bar
are both equal to 760 Torr
• 1 pa equal 0.007 torr
Agilent 7000A Triple Quadrupole GC/MS System, Agilent GC/MS Portfolio
Since the phase of the entrance sample is gas, The vacuum system in the GC MSMS is more easy to be established than LC MS/MS.
The vacuum system in GC/MS/MS include the ion source outlet, the collision cell, and both analyzers, with nearly fixed pressure along these stages (5-20 E-5 Torr at ion source and 8 E -5 Torr at Mass analyzers)
Vacuum System GC MS/MS
Vacuum System LC/MS/MS
Attainment of a vacuum system in LC/MS/MS have been carried out through different vacuum stages. Since, the phase of the entering samples is liquid.
The vacuum system consists of the vacuum interface, vacuum control system, and vacuum chamber. The vacuum interface includes the Curtain Gas plate, orifice plate, and skimmer cone.
The vacuum control system includes the turbo pumps, vacuum gauge, solenoid gas controller, and analog gas controllers. (Turbomolecular pumps or turbo pumps are the standard high vacuum pumps in mass spectrometry)
The vacuum chamber or ion path chamber includes quadrupoles, the collision cell, and the channel electron multiplier (CEM) detector system.
API 4000™ LC/MS/MS System Hardware Manual
The vacuum interface
differentially pumped interface, first low pressure stageatmospheric pressure ion source to the low-pressure vacuum chamber
Curtain Gas flow of heated, dry N2 (outside ) in addition to the vacuum at the interface remove the unionized molecules from entering the vacuum champer
Part from curtain Gas flow and ions are drawn from the Curtain Gas interface into the differentially pumped region by the pressure differential across the orifice plate. Curtain gas
(more out)
API 4000™ LC/MS/MS System Hardware Manual
Vacuum pumping system
API 4000™ LC/MS/MS System Hardware Manual
