Secrets to Successful GC-MS/MS Pesticide Method Development

Transcription

1 Secrets to Successful GC-MS/MS Pesticide Method Development Katerina Mastovska Nutritional Chemistry and Food Safety Covance Laboratories

2 QuEChERS vs. Traditional Methods Quick, Easy, Cheap, Effective, Rugged, and Safe Lower cost of chemicals and consumables Minimum waste disposal (no chlorinated solvents) Basically no glassware washing and storage Faster turn-around-times Less training Larger scope of analytes (including modern, polar pesticides) Directly compatible with GC-MS(/MS) and LC-MS(/MS) Suitable for analysis of other contaminants Many labs have implemented QuEChERS BUT some are still hesitant or are having problems

3 Problems with QuEChERS Implementation Major problem: Compatibility of QuEChERS extracts with old GC methods Why? Acetonitrile as the GC injection solvent Matrix co-extractives Solutions: Optimize GC injection conditions, ideally use PTV in solvent vent mode to eliminate acetonitrile Use GC-MS or GC-MS/MS for improved detection selectivity Transfer more polar (troublemaker) pesticides to LC-MS(/MS) Use column backflushing to remove less volatile matrix components from the GC system Use analyte protectants to deactivate GC system in every injection

4 GC-MS/MS Reference Guide 4

5 Acetonitrile as the GC Injection Solvent Solvent M r (g/mol) (g/ml) b.p. ( C) P p v (kpa) V vapor ( L) V inj max ( L) psi psi 4 psi 6 psi Acetonitrile Acetone Ethyl acetate Hexane Toluene Isooctane M r... molecular mass... solvent (liquid) density (at C, p atm ) b.p.... boiling point (at p atm ) P... polarity index p v... V vapor... vapor pressure (at C) vapor volume generated by L injection (V inj = L) of the given solvent at psi (a pressure close to a head pressure in typical GC-MS pesticide analysis without a pressure pulse) and injection temperature t inj = 5 C; calculated from the following equation: V vapor =.4 ( /M r ) [(t inj + 7)/7] [p atm /(p i + p a )] V inj where p atm = 4.7 psi ( kpa) and p a is ambient pressure, usually taken as p atm V inj max... maximum safe injection volume for the 8 L liner used at different column head pressures (,, 4, and 6 psi) and t inj = 5 C, i.e. injection volume that generates 6 L of vapors (75% of the liner volume) K. Mastovska, S.J. Lehotay, J. Chromatogr. A 4 (4)

6 Acetonitrile as the GC Injection Solvent Large expansion volume Not compatible with relatively non-polar GC stationary phases Forms droplets rather than a continuous film upon recondensation in the GC column, causing peak distortions for early eluting analytes Splitless injection: the initial oven temperature has to be at or above its boiling point (e.g. at 9 C) to prevent acetonitrile condensation in the GC column PTV (programmable temperature vaporizer) with solvent vent ideal to eliminate acetonitrile from the inlet prior reaching the GC column Alternative approach: solvent exchange into toluene (or adding toluene to the acetonitrile extract) 6

7 PTV Solvent Vent Injection Injection at a lower temperature less discrimination, better results for thermally-labile analytes, reduced matrix effects Solvent elimination large volume injection (LVI), better peak shapes of early eluting peaks in acetonitrile: Dichlorvos HCH isomers Better column protection better long-term performance, reduced matrix effects K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 ()

8 PTV Solvent Vent Injection Important inlet parameters: Solvent vent period: vent temperature vent time vent flow vent pressure Analyte transfer period: inlet temperature program splitless time Post-transfer period: purge flow gas saver flow and time Dimpled liner, mm i.d. 8 8

9 Matrix Co-Extractives in GC () Non-volatile - Keep them in the liner! () Volatile Improve selectivity by using GC-MS/MS x +EI MRM CID@. (84 -> 49) 49_spike A.D x +EI MRM CID@. (74 -> 88) 49_spike A.D 5 x +EI MRM (7 -> 7) 49_spike A.D Use analyte protectants to deactivate Backflush less volatile matrix 9

10 Column Backflushing Backflushing can eliminate less volatile matrix components from the GC column by reversing the column flow at a pressure junction point: Flow Flow Inlet MS Flow Flow Inlet MS

11 Column Backflushing Post-Run Backflushing - begins after the last analyte has been detected - the entire column is backflushed - typically uses a short restriction capillary installed at the column outlet Concurrent Backflushing - begins after the last analyte has eluted from the first column - different options: retention gap = a short uncoated capillary mid-column set-up (e.g. two 5-m columns) short column = a short coated capillary Column : HP 5-MS UI, 5 m x.5 mm x.5 µm Column : HP 5-MS UI, 5 m x.5 mm x.5 µm K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 ()

12 Column Flow Program A) Elution of the analytes from the first column Column 5 m EPC Column 5 m Inlet Time: 5.8 min. ml/min. ml/min MS/MS B) Backflushing of the first column to remove less volatile matrix components Column 5 m EPC Column 5 m Inlet Time: min 8.6. min.5 ml/min 5. ml/min. ml/min.4 ml/min K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 () MS/MS

13 Elimination of Less Volatile Matrix Components Dandelion root powder full scan (m/z 45-65) analysis with backflushing x 9.5 Last analyte RT = 8.45 min Deltamethrin (m/z 5>7) x Run time = min x Backflushing starts (after deltamethrin safely elutes from the first column) Acetonitrile blank analysis (no backflushing, additional 5 min at 9 C) after the dandelion root powder analysis with backflushing No matrix peaks from the previous injection observed! K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 ()

14 Elimination of Less Volatile Matrix Components Dandelion root powder full scan (m/z 45-65) analysis without backflushing x 9 Run time = min x 9 Acetonitrile blank analysis after the dandelion root powder analysis without backflushing and run time of min Matrix peaks observed in two subsequent blank injections! x 9 Run time = 5 min (additional 5 min at 9 C) K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 () Additional min at 9 C needed to elute the less volatile matrix components (e.g. sterols). 4

15 Benefits of Column Backflushing Elimination of long baked out at a high temperature to remove less volatile, late eluting matrix components Reduced analysis time Increased column life time Prevention of the MS source contamination Less frequent MS source maintenance Improved ruggedness Overlays of GC-MS/MS chromatograms obtained within a.5-day sequence of 5 dietary supplement injections: Dichlorvos m/z 85 9 Malathion m/z 7 99 Ethion m/z 9 Phosalone m/z 67 8 Deltamethrin m/z 5 74 K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 ()

16 Sample Preparation and Analysis Samples: 5 dietary supplement matrices representing root powders (ginseng and dandelion), fruit (freeze-dried) powders (saw palmetto berry and mangosteen) and full-plant powdered extracts (scutellaria) Spiking level: 5 ng/g = lower limit for the majority of pesticides listed in the European Pharmacopoeia monograph.8. - corresponding matrix-matched standards (MMstd) and standards in acetonitrile (solvent std) were prepared at 5 ng/ml (equivalent to 5 ng/g) 6

17 Sample Preparation and Analysis Sample extraction and clean-up: - based on the QuEChERS method Long-term GC-MS/MS system evaluation: 5 injections (incl. 5 matrix injections) consisting of: 5 repeated sets of runs, which included the following 6 injections for each of the 5 matrices: () solvent std () MMstd () spike (4) spike (5) spike (6) MMstd.5-day uninterrupted sequence (no maintenance) to mimic an over-the-weekend run 7

18 Long-term System Performance Overlays of GC-MS/MS chromatograms for selected analytes in spiked samples obtained within the sequence of 5 matrix injections (sets:,,, 4, 5): Dichlorvos m/z 85>9 Malathion m/z 7>99 Ethion m/z >9 Phosalone m/z 67>8 Deltamethrin m/z 5>74 Ginseng Root Powder x x x x x Saw Palmetto Berry Powder x x x x x Scutellaria Powdered Extract x x x x x

19 Analyte Protectants = compounds that strongly interact with the active sites in the GC system, thus protecting susceptible analytes against adsorption and/or degradation M. Anastassiades, K. Mastovska, S.J. Lehotay, J. Chromatogr. A 5 () 6-84 matrix + analyte protectants solvent + analyte protectants matrix solvent 9

20 Analyte Protectants Combination of analyte protectants for GC pesticide analysis HO OH O ethylglycerol ( g) HO Signal enhancement: moderate strong HO HO O O OH gulonolactone ( g) HO OH OH OH OH sorbitol ( g) retention time K. Mastovska, S.J. Lehotay, M. Anastassiades, Anal. Chem. 77 (5) 89-87

21 Normalized peak area Calibration without AP MeCN R =.9894 Fruit R =.9966 Vegetable R = Concentration (ng/ml) o-phenylphenol K. Mastovska, S.J. Lehotay, M. Anastassiades, Anal. Chem. 77 (5) 89-87

22 Normalized peak area Calibration with AP MeCN R =.9997 Fruit R =.9995 Vegetable R = Concentration (ng/ml) o-phenylphenol K. Mastovska, S.J. Lehotay, M. Anastassiades, Anal. Chem. 77 (5) 89-87

23 AP = Deactivation in Every Injection! response diminishment lindane phosalone o-phenylphenol.4 higher response 6.5 higher response K. Mastovska, S.J. Lehotay, M. Anastassiades, Anal. Chem. 77 (5) 89-87

24 Use of Internal Standards ISTD p,p -DDT p,p -Methoxychlor Accuracy (%) RSD (%) Accuracy (%) RSD (%) None TPP C - p,p -DDT K. Mastovska, Agilent Application Note EN 4

25 Why Triple Quadrupole GC-MS/MS? Selectivity Sensitivity Ruggedness 4>58 4>86.5 ng/ml chlorpyrifos in ginseng root extract (5 ng/g in the sample) MS/MS is TARGETED ANALYSIS Analyte-specific conditions required We don t see what we don t look for! 5

26 GC-MS/MS Selectivity: Selection of Ions Fonofos S P S O (mainlib) Fonofos 7>9 7>9 46>7 -fold higher signal 46>9 46>9 46>9 6

27 GC-MS/MS Selectivity: Selection of Ions Atrazine EI-MS spectrum (NIST) HN 5 N N 5 58 HN N Cl (mainlib) Atrazine 7 7

28 GC-MS/MS Selectivity: Selection of Ions m/z 5 > m/z 5 > 58 Analysis of atrazine (RT = 7.9 min) in flour (at 5 ng/g) using MS/MS transitions m/z 5 > and m/z 5 >

29 GC-MS/MS Selectivity: Selection of Ions Malathion O O O 5 O 58 S S 99 P O 4 O (mainlib) Malathion 7>7 7>7 58>47 7>99 7>99 7>99 K. Mastovska, P.L. Wylie, J. Chromatogr. A 65 ()

30 MS/MS Optimization - Example Etridiazole: Full scan EI MS spectrum Etridiazole (mainlib),,4-thiadiazole, 5-ethoxy--(trichloromethyl)- 4 Cl O N Cl S N Cl

31 MS/MS Optimization - Example Etridiazole: Overlay of product ion spectra of m/z for CE = - 6 V

32 MS/MS Optimization - Example Etridiazole: Overlay of m/z > 8 chromatograms at CE = - 6 V Optimum CE = V

33 MS/MS Optimization - Example Etridiazole: Pesticides and Environmental Pollutants MRM Database (G95AA)

34 Secrets to Rugged GC-MS/MS Method Well optimized injection conditions (PTV solvent vent for direct analysis of QuEChERS extracts) Suitable internal standard(s) Column backflushing Analyte protectants Well optimized MS/MS transitions (evaluated in target or worst-case matrices) 4 4

35 Thank you for your attention! Your questions?