Multi-residue method for trace pesticide analysis in soils by LC-QQQ-MS/MS and its application to real samples

ABSTRACT

A method for the simultaneous determination of 30 pesticides residues in soil was developed and validated. Among the studied agrochemicals, there are herbicides (auxines, sulfonylureas, fops, imidazolinones), fungicides (azoles) and insecticides (organophosphorus) widely used in extensive agricultural activities in Uruguay. Five methods with different extraction times, type and amount of solvent, as well as the possibility of a clean-up step were compared in terms of percentage of recovery and repeatability. The final method was based on the extraction of the pesticides’ residues from soil using two successive solvent extraction steps. First, the soil was extracted with methanol in an orbital shaker for 4 h. Secondly, the solid residue was re-extracted overnight with ultrapure water. The methanolic extract was concentrated under vacuum, whereas the aqueous solution was passed through an OASIS HLB® cartridge, eluted with an appropriate solvent and concentrated under nitrogen stream. Both extracts were finally combined and analysed by LC-QQQ-MS/MS using the Document SANTE/11,945/2015 criteria. Recovery percentages at 1 and 10 μg kg^?1 for the studied compounds were in the range 70106% with relative standard deviations below 19 %. The quantification was performed using matrix-matched calibration curves as some compounds presented very strong signal suppression. Residuals of the matrix-matched calibration curves were below 20% for all the validated analytes. The quantification limit was1 μg kg^?1. The method also allows the screening of 11 pesticides in soil. Sixty-five real samples collected from regions where the use of pesticides is intensive were analysed. Quinclorac, tebuconazole, penoxsulam and clomazone were the most frequently pesticides detected.