2. AOACRIChemContMethods-2018Awards

Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015  1435

Table 2014.09D. SRM acquisition parameters by GC/MS/MS analysis for the 20 pesticides of interest Group Start time, min Monitored ion transitions, m / z

Dwell time, ms

1 2 3 4 5 6 7 8 9

14.76 15.87 18.06 19.26 20.07 21.87 22.60 23.59 26.71 27.88 28.96

306/264, 306/206

50 50 50 25 50 50 50 50 25 50 50

177/127, 177/101, 200/199, 183/102 173/145, 173/109, 238/166, 238/96

230/154, 230/111, 287/272, 287/242, 267/252, 267/93

290/233, 290/125 353/282, 353/263

359/331, 359/303, 318/248, 318/246

335/303, 335/173, 318/248, 318/246, 283/96, 283/255 148/105, 148/79, 408/363, 408/59, 237/208, 237/182

10 11

266/246, 266/218, 181/166, 181/165

341/185, 341/183

( 4 ) Centrifuge at 2879 × g for 5 min at room temperature. ( 5 ) Transfer the supernatant into a pear-shaped flask. ( 6 ) Re-extract the sample with 15 mL acetonitrile, homogenize, centrifuge, and combine the supernatants from the two extractions. ( 7 ) Concentrate the extract to approximately 1 mL in a rotary evaporator (or TurboVap) in a 40°C water bath. ( 8 ) Place a pear-shaped flask in the vacuum manifold. ( 9 ) Mount a Cleanert TPT cartridge onto the manifold. ( 10 ) Add anhydrous sodium sulfate (approximately 2 cm) onto the Cleanert TPT packing material. ( 11 ) Add 10 mL acetonitrile–toluene (3 + 1, v/v) to activate the cartridge. ( 12 ) Stop the flow through the cartridge when the liquid level in the cartridge barrel has just reached the top of the sodium sulfate packing. ( 13 ) Discard the waste solution collected in the pear-shaped flask and replace with a clean pear-shaped flask. (b) SPE cleanup .—( 1 ) Load the concentrated extract from F ( a )( 7 ) into the conditioned Cleanert TPT cartridge collecting the eluate into the clean pear-shaped flask. ( 2 ) Rinse the pear-shaped flask that contained the concentrated extract with 3 × 2 mL acetonitrile–toluene (3 + 1, v/v). ( 3 ) Load the rinse into the cartridge when the level of the loading solution in the cartridge reaches the top of the anhydrous sodium sulfate packing. ( 4 ) Connect a 30 mL reservoir onto the upper part of the cartridge using an adapter ( see Figure 2014.09A ).

( 5 ) Elute the cartridge with 25 mL acetonitrile–toluene (3 + 1, v/v). ( 6 ) Evaporate the eluate to approximately 0.5 mL using a rotary evaporator (or TurboVap) in a 40°C water bath. For GC/MS and/or GC/MS/MS analysis only: ( 7 ) Add 40 μL heptachlor epoxide (internal standard; ISTD) working standard solution to the sample in F ( b )( 6 ). ( 8 ) Evaporate to dryness under a stream of nitrogen in a 35°C water bath (or Turbo Vap). ( 9 ) Dissolve the dried residue in 1.5 mL hexane, ultrasonicate the samples to mix, and filter through a 0.2 μm membrane filter. The sample is ready for GC/MS or GC/MS/MS analysis. For LC/MS/MS analysis only: ( 10 ) Add 40 μL chlorpyrifos methyl (ISTD) working standard solution to the sample prepared in F ( b )( 6 ). ( 11 ) Evaporate to dryness under a stream of nitrogen in a 35°C water bath (or Turbo Vap). ( 12 ) Dissolve the dried residue in 1.5 mL acetonitrile–water (3 + 2, v/v), ultrasonicate the samples to mix, and filter through a 0.2 μm membrane filter. The sample is ready for LC/MS/MS analysis. G. Qualitative and Quantitative Analysis (a) Criteria for qualitative and confirmation .—( 1 ) Measure the retention time of the monitored peaks and match them with the same peaks in the pesticide standard chromatograms. identification

Table 2014.09E. Gradient elution conditions for LC/MS/MS analysis

Mobile phase A (0.1% formic acid in water, %)

Mobile phase B (acetonitrile, %)

Step

Time, min

Flow rate, μL/min

0 1 2 3 4 5 6 7

0.00 3.00 6.00 9.00

400 400 400 400 400 400 400 400

99.0 70.0 60.0 60.0 40.0

1.0

30.0 40.0 40.0 60.0 99.0 99.0

15.00 19.00 23.00 23.01

1.0 1.0

99.0

1.0