The investigation of the biological reductive dechlorination of chlorobenzenes by methanogenic consortia in river sediments is dependent on reliable analytical procedures. Two different extraction methods for the determination of chlorobenzenes from sediment samples were developed. Lower chlorinated benzenes up to the trichloro isomers were extracted with satisfactory recoveries by thoroughly mixing the sediment with an equal volume of acetone. After centrifugation, the supernatant was subjected to solid phase extraction (SPE) using RP-C18 adsorbent. The tetra-, penta- and hexachlorobenzene isomers could only be satisfactorily recovered by liquid-liquid extraction with ethyl acetate. With both methods, 2,4-dichlorotoluene was added as surrogate standard. Determination was carried out by gas chromatography using a thick film megabore column coated with methyl silicone containing 35 phenyl groups and flame ionization detection. Applying a temperature program, all chlorobenzene isomers including benzene were found to be well separated and exhibiting good peak shape with the exception of 1,2,3,5 and 1,2,4,5-tetrachlorobenzene which formed a critical pair under all chromatographic conditions. Recovery values for most analytes at the 10 #x3BC;g/ml concentration level applying the internal standard method for quantitative analysis were found to be better than 75 for both extraction methods.
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