A Contribution to the Determination of Polychlorobenzenes in Sediments

A full analytical procedure involving extraction and clean-up is presented for the determination of the tri-, tetra-, penta- and hexa-chlorobenzenes in sediments. For this study, the gas chromatography coupled to electronic capture detection was used.

The samples were dried with sodium sulphate and Soxhlet extracted for 16 hours with dichloromethane. Then this solvent was replaced by hexane and the resulting solution was concentrated in a rotary evaporator. The clean-up process consisted of elution through a mixed silica column followed by a treatment with activated copper turnings to remove the sulphur. The sample was then concentrated down to 2 mL by nitrogen stream. The internal standard, 1,4-dibromobenzene, was added to the sample prior to the extraction, whereas the injection standard, 1,3,5-tribromobenzene, was added right before the sample was injected through the chromatographic system.

The limits of quantification ranged from 71 to 500 pg g^?1 (dry weight). The reproducibility in the peak areas within a day was better for the compounds with increasing number of chlorines, whereas the reproducibility over time studies provided no significant differences in the peak areas in consecutive days.

The method was successfully applied to the determination of polychlorobenzenes in a certified sediment and, finally, it was applied to the determination of these compounds in several sections of a sediment core from Esthwaite Water Lake (United Kingdom).