338 / 471
(
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 stsandard; 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 on the pesticide standard chromatograms.
(
2
) Measure the ion abundances for the qualifier ions for the detected pesticides and verify that they are
within the expected limits; if the peaks match, the presence of the pesticide is confirmed.
See
Table
2014.09H
.
(
b
)
Quantitative calculations.—
(
1
) Use instrument data processing software for GC-MS (SIM), GC-
MS/MS, and/or LC-MS/MS to calculate a response ratio (measured adundance of pesticide/measured
abundance of heptachlor epoxide for GC and chlorpyrifos methyl for LC) and construct a 5-point matrix-
matched calibration curve of response ratio versus concentration of pesticide in standard solution.
(
2
) Using the regression data from the appropriate matrix-matched calibration curve, calculate the
concentration of each pesticide found in the samples.
(
3
) If a validated computer system is not being used for calculations, follow the steps below:
(
a
) Measure the peak area of each respective standard level for each pesticide and the peak area of
corresponding internal standard.
Candidates for 2016 Method of the Year
278