Development and Validation for Simultaneous Determination of Disulfoton and Its Five Metabolites in Seven Agro-Products Using Liquid Chromatography-Tandem Mass Spectrometry Combined with QuEChERS Extraction Method

Disulfoton is highly toxic insecticide and acaricide. Food safety requires analysis of disulfoton and its five metabolites (disulfoton-sulfoxide, disulfoton-sulfone, demeton-S, demeton-S-sulfoxide, and demeton-S-sulfone). However, simultaneous determination of disulfoton and its metabolites in agro-products was not established, and the limits of quantification (LOQs) of reported methods could hardly meet the requirement of maximum residue limits (MRLs) set by some countries or organizations. In the present study, disulfoton and its five metabolites in seven agro-products (maize, oat, rice, pea, asparagus, milk and chicken) were extracted according to a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure and simultaneously determined with a liquid chromatograph tandem-mass spectrometer. The method was accurate and reliable after optimization of several key parameters (chromatographic columns, mobile phase, and clean-up sorbents). The sensitivity of the proposed method was greatly improved through the concentration process. Matrix effects for six analytes in different matrices were evaluated, and matrix-matched calibration standards were used to compensate these matrix enhancement or suppression effects. Under optimal conditions, the developed method showed satisfactory linearity with coefficients of determination (R²) > 0.9919. The limits of detection (LODs) for all target analytes in different agro-products ranged from 0.01 to 1.68 µg/kg, while the LOQs were 5 µg/kg for disulfoton, and 1 µg/kg for its each metabolite. At three fortification levels, the mean recoveries were in the range of 71.3–114.4% with relative standard deviations (RSDs) < 16%. Analysis of 70 market samples showed a trace amount of disulfoton and/or its metabolites in 10% samples. In conclusion, the developed method exhibited both high sensitivity and accuracy, and is suitable and practical for the simultaneous determination of trace levels of disulfoton and its five metabolites in agro-products of plant and animal origin.