Agriculture Reference
In-Depth Information
isooctane, and so on to the volume based on the solubility of the standard. The
standard solutions are stored in the dark at 0
C.
Mixed standard solutions
: The concentration of mixed standard solutions depends
upon the sensitivity of the method for each compound. Pipette an adequate amount of
individual stock standard solution into a 50ml volumetric
-
4
°
flask and dilute to volume
with toluene or
n
-hexane. Mixed standard solutions should be stored in dark below
4
C and can be used for 1 month.
The internal standard solution was prepared by accurately weighing 3.5mg
heptachlor epoxide into a 10ml volumetric
°
flask and dissolving and diluting with
toluene.
Matrix mixed standard solutions were prepared by diluting 40
linternal
standard solution and an appropriate amount of mixed standard solution to
1.0ml with blank extract, which had been taken through the method with the
rest of the samples, and mixing thoroughly. These solutions were used to construct
calibration plots.
μ
5.2.4 Sample Preparation
Extraction
: Weigh 5 g fat sample (from pork or human body; accurate to 0.01 g) into
an 80ml centrifuge tube containing 15 g anhydrous sodium sulfate (to absorb the
moisture in fat) and add 35ml acetonitrile, then homogenize at 15,000 rpm for 1 min,
and centrifuge at 4200 rpm for 5 min.
The supernatants are made to pass through a glass funnel containing a glass wool
plug and
15 g anhydrous sodium sulfate and collected in a 100ml pear-shaped
∼
flask. Repeat extracting the dregs with 35ml acetonitrile one time, centrifuge,
consolidate the extractions of over two times, and rotary evaporate in water bath at
45
C until about 2ml remain. Then two separate additions of 7ml ethyl acetate
-
°
cyclohexane (1
+
1) are made for solvent exchange and the residue is evaporated to
1ml for cleanup.
Cleanup
:40
l internal standard solution is added to the 1ml concentrate and
mixed. The mixture is transferred to a 10ml colorimetric tube. The 100ml pear-
shaped
μ
1, v/v) (8ml
solvent is added in three separate times), and the solvent is transferred to the
colorimetric tube. The colorimetric tube is diluted with ethyl acetate to the
volume. After membrane
flask is rinsed with 8ml ethyl acetate
-
cyclohexane (1
+
filtration (0.45
μ
m) to a 10ml cuvette, the solution is
cleanedbyGPC,andthe23
60min elution fraction is collected. The eluate
is treated in two different ways for analyzing by different methods: (a) The eluate
is automatically concentrated to 1ml with acetate
-
-
cyclohexane (1
+
1) for
analyzing by GC
MS. (b) Two separate additions of 5ml
acetonitrile are made for solvent exchange of the eluate until nearly dry. Add
1ml acetonitrile
-
MS/MS and GC
-
+
μ
-
water (3
2) to the residue and
filter with 0.2
m membrane for
analyzing by LC
MS/MS.
Simultaneously, a blank fat sample is extracted by the extraction and cleanup
steps above to prepare blank extractionformatrixmixedstandardsolu ion
preparation.
-
