AOAC Final Action Methods in 2018

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

( 10 )  Ion spray voltage .—4000 V. ( 11 )  Dry gas temperature .—350°C. ( 12 )  Dry gas flow rate .—10 L/min.

F. Extraction and Cleanup Procedure (a) Sample extraction.— ( 1 ) Weigh 5 g dry tea powder (accurate to 0.01 g) into an 80 mL centrifuge tube. ( 2 ) Add 15 mL acetonitrile. ( 3 ) Homogenize at 13500 rpm for 1 min. ( 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).

( 13 ) Monitored ion transitions, collision energies, and fragmentation energies for the 20 pesticides and chlorpyrifos methyl are shown in Table 2014.09F , and SRM acquisition parameters by LC-MS/MS for the precursor and product ion transitions monitored are shown in Table 2014.09G . (d) Homogenizer .—Rotational speed higher than 13 500 r/min (report also in g -force units; T-25B, Janke & Kunkel, Staufen, Germany), or equivalent. (e)  Rotary evaporator .—Buchi EL131 (Flawil, Switzerland) or equivalent. (f)  Centrifuge .—Centrifugal force higher than 2879 ×  g (Z320; B. HermLe AG, Gosheim, Germany), or equivalent. (g)  Nitrogen evaporator .—EVAP 112 (Organomation Associates, Inc., New Berlin, MA, USA), or equivalent. (h)  TurboVap .—LV Evaporation System (Caliper Life Sciences, Hopkinton, MA, USA), or equivalent. (i)  Visiprep 5-port flask vacuum manifold .—RS-SUPELCO 57101-U (Sigma-Aldrich Shanghai Trading Co., Ltd). See Figure 2014.09 . (j)  Variable volume pipets .—10 μL, 200 μL, and 1 mL. (k)  Balance .—Capable of accurately measuring weights from 0.05 to 100 g within ±0.01 g.

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

© 2018 AOAC INTERNATIONAL