Multi-residue pesticide analysis in soil by solid-phase disk extraction and gas chromatography ion-trap mass spectrometry

A rapid and reproducible multi-residue analysis was developed for the simultaneous determination of 46 pesticides belonging to triazines, organophosphorus and organochlorine compounds, carbamates, anilides, anilines, and amides in various soil samples. Soil samples including its natural water contents were extracted with a mixture of methanol/water (3/1, v/v). The aqueous methanol extracts were directly transferred to an extraction reservoir containing 1 L of reagent water and subjected to clean-up and enrichment by an SPE membrane workstation on Empore C-18 disks. The analytes were eluated, concentrated and analyzed without additional treatment by gas chromatography/ion-trap mass spectrometry (GC-ITDMS). Recoveries of the analytes using this procedure ranged from 65 to 102% measured at 20-200 mu g/kg spiked levels for 41 pesticides tested. With 10 g of soil sample, the detection limits were between 0.5 and 25 mu g/kg. The disk SPE procedure was compared to the soxhlet extraction, and comparable recoveries and precisions were demonstrated for most of the pesticides studied.