Evaluation of a Supercritical Fluid Extraction Method for Hexachlorobenzene from Artificially Spiked and Naturally Contaminated Oil Seeds and Soil Samples

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Abstract
Great differences in the supercritical fluid extraction (SFE) yield of hexachlorobenzene (HCB) in artificially spiked and naturally contaminated soil samples have been found. Extraction methods optimized for organochlorine pesticides (OCP's) in spiked samples yielding 98% recovery for HCB, failed in terms of sufficient recovery from real samples. The extraction yield dropped to 50% for HCB and, consequently, resulted in an unacceptable high variance of the results obtained (R.S.D. > 10%). Therefore, a procedure for the optimization of SFE parameters including carbon dioxide (CO2) density, extraction temperature and addition of organic modifiers for reliable HCB determination in real samples is reported. A nearly complete recovery of HCB (98%) was obtained for 0.80 g/ml CO2, 80[ddot]C, 15 min and the addition of 5% methanol. Direct injection of SFE-extracts from soil into GC-ECD could be achieved after selectively trapping the analytes on minicolumns filled with C18 coated silica material and elution with petroleum ether. For reliable GC-ECD determination of OCP's in oil seeds an additional cleanup step via solid phase extraction (SPE) and matrix degradation with sulfuric acid using newly developed “sandwich”-type adsorption columns was performed off-line or in-line to the SFE procedure.

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