39 / 71
Pang et al.:
J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
5, 2015
1435
(
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
identification
and
confirmation
.—(
1
) Measure the retention time of the monitored
peaks and match them with the same peaks in the pesticide
standard chromatograms.
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
14.76
306/264, 306/206
50
2
15.87
177/127, 177/101, 200/199, 183/102
50
3
18.06
173/145, 173/109, 238/166, 238/96
50
4
19.26
230/154, 230/111, 287/272, 287/242, 267/252, 267/93
25
5
20.07
290/233, 290/125
50
6
21.87
353/282, 353/263
50
7
22.60
359/331, 359/303, 318/248, 318/246
50
8
23.59
335/303, 335/173, 318/248, 318/246, 283/96, 283/255
50
9
26.71
148/105, 148/79, 408/363, 408/59, 237/208, 237/182
25
10
27.88
266/246, 266/218, 181/166, 181/165
50
11
28.96
341/185, 341/183
50
Table 2014.09E. Gradient elution conditions for LC/MS/MS analysis
Step
Time, min
Flow rate, μL/min
Mobile phase A
(0.1% formic acid in water, %)
Mobile phase B
(acetonitrile, %)
0
0.00
400
99.0
1.0
1
3.00
400
70.0
30.0
2
6.00
400
60.0
40.0
3
9.00
400
60.0
40.0
4
15.00
400
40.0
60.0
5
19.00
400
1.0
99.0
6
23.00
400
1.0
99.0
7
23.01
400
99.0
1.0