Enantioselective Determination of -Hexachlorocyclohexane in Food Samples by GC-MS

A method for the determination of individual α-hexachlorocyclohexane (α-HCH) enantiomers is described. The method consists of ultrasonic extraction, sulfuric acid-modified silica gel cleanup, fractionation on a polar silica solid-phase extraction (SPE) column, and final determination by gas chromatography/electron capture negative ion mass spectrometry (GC-MS/ECNI) on a Chirasil-Dex column. The MS is operated in selected ion monitoring mode. Racemic α-HCH is used as the calibration standard, and ε-HCH is used as the surrogate internal standard. Each α-HCH enantiomer is quantitated by the relative response factor method using the m/z 255 ion. The enantiomeric ratio (ER) is obtained as the area ratio of the (+)/(−) peaks eluting from the cyclodextrin column. ER determinations are important because enantiomers differ considerably in how they accumulate in organisms and decompose in the environment. This method provides a simple and useful tool to monitor the enantioselectivity of α-HCH in food samples.