Microwave-assisted solvent extraction and reversed-phase liquid chromatography UV detection for screening soils for sulfonylurea herbicides

A multi-residue method for the rapid assay of cinosulfuron, thifensulfuron-methyl, metsulfuron-methyl, sulfometuron-methyl and chlorsulfuron in soil samples has been developed. The method involves microwave-assisted solvent extraction (MASE) prior to analysis by reversed-phase liquid chromatography (RPLC) and UV detection at 226 nm. MASE conditions were established providing efficient extraction without degradation of the analytes, furthermore selectivity can be enhanced by limiting the coextraction of interferences. Selected MASE conditions, including dichloromethane-methanol (90:10,v/v) as the extraction solvent, provided, in 10 min, a complete extraction of the analytes from soil samples. The extracts obtained with the developed MASE procedure are analysed by RPLC-UV in less than 15 min without additional cleanup; the overall procedure allows the determination of the analytes in soils to a level of at least 5 mu g/kg. Method validation was performed by analysing freshly spiked sail samples and samples with aged residues at levels between 20 and 1000 mu g/kg. Depending on the spiked level and the type of spiked sample recoveries were obtained between 70-100% with R.S.D.s between 1-10%. (C) 1998 Elsevier Science B.V.