Modified QuEChERS for Organophosphorus Pesticide Analysis in Agricultural Soils by Gas Chromatography-Tandem Mass...

Accurate determination of organophosphorus pesticide (OPP) residues in agricultural soils by gas chromatography-tandem mass spectrometry (GC-MS/MS) is often hindered by matrix-induced signal effects caused by co-extracted organic matter, humic substances, and mineral-associated interferents. Conventional Quick-Easy-Cheap-Effective-Rugged-Safe (QuEChERS) cleanup strategies may not sufficiently remove matrix components from complex soil extracts, compromising analytical performance. This study presents a modified QuEChERS protocol that incorporates the adsorbent into mixed-sorbent dispersive solid-phase extraction (dSPE) cleanup for the simultaneous determination of 12 OPPs in agricultural soils by GC-MS/MS. Seven dSPE sorbent combinations were evaluated across six agricultural soils with varying soil properties. Co-extractive removal was quantified gravimetrically, and the combination of primary-secondary amine, octadecylsilane, and a magnesium silicate adsorbent (50 mg each, with 150 mg anhydrous magnesium sulfate) achieved the highest average co-extractive removal (88%). Analyte protectants consisting of ethylglycerol, L-gulonic acid γ-lactone, D-sorbitol, and shikimic acid were incorporated into final extracts to minimize matrix effects, while matrix-matched calibration compensated for soil-specific signal variation. Chlorpyrifos-methyl-d10 and triphenyl phosphate were employed as procedural and injection internal standards, respectively. Matrix-matched calibration curves (5-600 µg/kg) demonstrated excellent linearity, with coefficients of determination ≥0.9933 for most analyte-soil combinations. The limit of detection (5 µg/kg) was used for linearity assessment, whereas the method limit of quantification was established at 50 µg/kg as the lowest validated level. Accuracy and precision assessed at three recovery levels (50, 200, and 400 µg/kg, n = 5 per level) demonstrated recoveries between 70% and 120% with relative standard deviations ≤20% for most analyte-soil combinations, meeting SANTE/2020/12830 (Rev.2) performance criteria. Lower recoveries were observed only for fenamiphos, pirimiphos-ethyl, and ethion in selected soil matrices. The results demonstrate that the magnesium silicate adsorbent improves dSPE cleanup by reducing co-extractives and that its combination with analyte protectants and matrix-matched calibration provides reliable multiresidue determination of OPPs in complex soil matrices by GC-MS/MS.