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Comparison of several extraction procedures for the determination of biopesticides in soil samples by ultrahigh pressure LC-MS/MS.

A new procedure has been proposed for the determination of biopesticides (nicotine, sabadine, veratridine, rotenone, azadirachtin, cevadine, deguelin, spynosad D, and pyrethrins) and piperonyl butoxide in agricultural soils. Several extraction procedures such as solid-liquid extraction using mechanical shaking, sonication, pressurized liquid extraction, and modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) have been tested, obtaining better results when QuEChERS procedure without further cleanup steps was applied. The determination of the compounds was carried out by ultra high pressure liquid chromatography coupled to tandem mass spectrometry, using methanol and aqueous solution of ammonium formate 5 mM as mobile phase. The method was validated for all compounds at concentrations ranging from 10 to 100 μg/kg and recoveries ranged from 68 to 116%, except for nicotine and sabadine, with recoveries lower than 50%. Precision was estimated through intra- and inter-day studies, obtaining intra-day precision lower than 20% for most of the compounds, and inter-day precision was lower than 25%. Limits of detection and quantification were also estimated, obtaining limits of quantification equal or lower than 10 μg/kg. Finally, the method was applied to the analysis of 20 real agricultural soil samples and no biopesticide residues were found over the limit of quantification.