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(4) Concentrate the extract to about 3 ml on a rotary evaporator.<br />
C. Clean-up<br />
(5) Activate high-qualify Florisil for 2 h at 130°C and store in a vacuum desiccator overnight.<br />
(6) Slurry the activated Florisil (21 g) with hexane into a chromatographic column (id-2cm) and<br />
place a plug of anhydrous sod ium sulphate (8 g) on top of the adsorbent to remove the last traces of water<br />
from the sample.<br />
(7) Introduce the hexane extract into the top of the column and elute with increasingly polar solvents<br />
as indicated below:<br />
Eluant ratio Quantity Flow rate<br />
Fraction ether/hexane (vol/vol) (mt) (ml/min)<br />
In 6/94 100 2<br />
2 6/94 100 2<br />
15/85 100 2<br />
3 15/85 100 2<br />
4 SO/50 200 2<br />
a Contents of these fractions will vary depending on a large number<br />
of circumstances. Compounds listed for each fraction are only a guide<br />
and should not be taken as an absolute.<br />
Note: The contents of these fractions will vary depending on a large number of circumstances. The<br />
compounds listed for each fraction are only a guide and should not be taken as absolute.<br />
(8) Evaporate the fractions to dryness on a rotary evaporator a nd make up to known volume with<br />
hexane ( 1- 10m I) for GC ana lysis.<br />
A large volume of elemental sulphur may be extracted in Frac tion I . Since this constitutes a major<br />
source of interference, it must be removed by using the following procedure (based on Goerlitz and Law<br />
1971). Concentrate the eluate (Fraction I) to about I ml and transfer to a centrifuge tube. Add mercury<br />
(0.2 ml) and agitate on a vortex mixer for I min. The sulphur precipitates as mercuric sulphide and is<br />
collected at the bottom together with unreacted mercury by centrifugation. Decant the hexane layer and<br />
repeat the process until the sample is free of mercury - usually this is accomplished by three treatments but<br />
more may be necessary for heavily contaminated <strong>samples</strong>. Analyze the sulphur-free hexane layer by Gc.<br />
Samples which remain "dirty" after the removal of the sulphur should be passed through the Florisil<br />
column at least two more times using the same eluant until a clear solution is obtained.<br />
1st Fraction - Lindane(y- BHC), Heptachlor, Heptachlor Epoxide, Aldrin, p,p'-DDD, p,p'-DDT,<br />
p,p '-DOE, Methoxychlor, cis-Chlordane. trans-Chlordane, PCB 's<br />
2nd Fraction - Dieldrin, Endrin, a-Endosulfan<br />
3rd Fraction - Unidentified components<br />
4th Fraction - [l-Endosulfan<br />
D. Detection and Quantification<br />
The following gas chromatographic method has been found to be satisfactory.<br />
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