Determination of linuron and related compounds in soil by microwave-assisted solvent extraction and reversed-phase liquid chromatography with UV detection

The combination of microwave-assisted solvent extraction (MASE) and reverse d-phase liquid chromatography (RPLC) with UV detection has been investigate d for the efficient determination of phenylurea herbicides in soils involvi ng the single-residue method (SRM) approach (linuron) and the multi-residue method (MRM) approach (monuron, monolinuron, isoproturon, metobromuron, di uron and linuron). Critical parameters of MASE, viz. extraction temperature , water content and extraction solvent were varied in order to optimise rec overies of the analytes while simultaneously minimising co-extraction of so il interferences. The optimised extraction procedure was applied to differe nt types of soil with an organic carbon content of 0.4-16.7%. Besides fresh ly spiked soil samples, method validation included the analysis of samples with aged residues. A comparative study between the applicability of RPLC-U V without and with the use of column switching for the processing of unclea ned extracts, was carried out. For some of the tested analyte/matrix combin ations the one-column approach (LC mode) is feasible. In comparison to LC, coupled-column LC (LC-LC mode) provides high selectivity in single-residue analysis (linuron) and, although less pronounced in multi-residue analysis (all six phenylurea herbicides), the clean-up performance of LC-LC improves both time of analysis and sample throughput. In the MRM approach the devel oped procedure involving MASE and LC-LC-UV provided acceptable recoveries ( range, 80-120%) and RSDs (<12%) at levels of 10 mu g/kg (n=9) and 50 mu g/k g (n=7), respectively, for most analyte/matrix combinations. Recoveries fro m aged residue samples spiked at a level of 100 mu g/kg (n=7) ranged, depen ding of the analyte/soil type combination, from 41-113% with RSDs ranging f rom 1-35%. In the SRM approach the developed LC-LC procedure was applied fo r the determination of linuron in 28 sandy soil samples collected in a held study. Linuron could be determined in soil with a limit of quantitation of 10 mu g/kg. (C) 2000 Elsevier Science B.V. All rights reserved.