36 / 71
1432
Pang et al.:
J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
5, 2015
A. Principle
Test samples are extracted with acetonitrile using a
homogenizer, and the extracts are cleaned up with Cleanert
TPT (Agela Technologies, Tianjin, China), EnviCarb/PSA
or ECPSACB506 (UCT, Bristol, PA), BE Carbon 500 g/PSA
(Agilent Technologies, Santa Clara, CA), or InerSep GC/PSA
(GL Sciences, Tokyo, Japan), or equivalent cartridges. The
pesticides are eluted with acetonitrile–toluene (3 + 1, v/v),
concentrated, dried, dissolved in the recommended solution,
and analyzed by GC/MS, GC/MS/MS, or LC/MS/MS.
Quantifications is with a matrix-matched standard calibration
curve.
B. Reagents
(a)
Solvents
.—Acetonitrile, toluene, and
n
-hexane (HPLC
grade).
(b)
Acetonitrile–toluene.—
3 + 1 (v/v).
(c)
Ultrapure water
.—Obtained from a Milli-RO plus
system together with a Milli-Q system (EMD Millipore Corp.,
Billerica, MA).
(d)
Anhydrous sodium sulfate
.—Analytically pure. Baked
at 650°C for 4 h and stored in a desiccator.
C. Materials
(a)
SPE cartridges
.—Cleanert TPT (2000 mg, 12 mL; Agela
Technologies), or EnviCarb/PSA (500 mg/500 mg, 6 mL;
Supelco, Bellefonte, PA), or equivalent.
(b)
SPE tube adapter
.—For 12 mL SPE tubes (57267), for
6 mL SPE tubes (57020-U; Sigma-Aldrich Shanghai Trading
Co., Ltd, Shanghai, China), or equivalent.
(c)
Disposable flow control valve liners
.—For Visiprep
TM-DL (57059; Sigma-Aldrich Shanghai Trading Co., Ltd).
(d)
Pear-shaped flask
.—80 mL (Z680346-1EA; Sigma-
Aldrich Shanghai Trading Co., Ltd), or equivalent.
See
Figure
2014.09A
.
(e)
Reservoir
.—30 mL (A82030; Agela), or equivalent.
See
Figure
2014.09A
.
(f)
Centrifuge tube
.—80 mL.
(g)
Millipore filter membrane (nylon)
.—13 mm × 0.2 μm.
D. Preparation of Standard Solutions
(a)
Prep
aration
of stock solutions.—
Accurately weigh
5–10 mg individual pesticide and chemical pollutant standards
(accurate to 0.1 mg) into a 10 mL volumetric flask. Dissolve and
dilute to volume with methanol, toluene, acetone, acetonitrile,
isooctane, etc., depending on each individual compound’s
solubility. All standard stock solutions are stored in the dark at
0–4°C and can be used for 1 year.
(b)
Preparation of mixed standard solution.—
Depending on
properties and retention times of compounds, all compounds
are divided into a series of groups. The concentration of each
compound is determined by its sensitivity on the instrument
for analysis. Mixed standard solutions are stored in the dark
below 4°C.
(c)
Working standard mixed solution in matrix.—
Prepare
working standard mixture solution in matrix of pesticide and
chemical pollutants by diluting an appropriate amount of mixed
standard solution with blank extract, which has been taken
through the method with the rest of the samples. Mix thoroughly.
Used for plotting the standard curve. Working standard mixture
solution in matrix must be freshly prepared.
E. Apparatus and Conditions
(a)
GC/MS analysis.—
(
1
)
System
.—Model 7890A gas
chromatograph connected to a Model 5975C mass selective
detector with electron ionization (EI) source and equipped with
a Model 7683 autosampler and Chemstation data processing
software system (Agilent Technologies), or equivalent.
(
2
)
Column
.—DB-1701 capillary column (30 m × 0.25 mm ×
0.25 μm; J&W Scientific, Folsom, CA), or equivalent.
(
3
)
Column temperature
.—40°C hold 1 min, 30°C/min to
130°C, 5°C/min to 250°C, 10°C/min to 300°C, hold 5 min.
(
4
)
Carrier gas
.—Helium, purity ≥99.999%, flow rate
1.2 mL/min.
(
5
)
Injection port temperature
.—290°C.
Figure 2014.09A. SPE equipment.