Abstract:

Disulfoton, an organophosphorus pesticide, is used to control cotton, beet, potato, and other seedling period aphids, leaf moths, underground pests, etc., with internal absorption, killing, gastric poisoning, and fumigation. Disulfoton is a highly toxic organophosphate pesticide, which can inhibit cholinesterase activity, resulting in neurophysiological disorders by inhalation, feeding, and transdermal absorption. Disulfoton is difficult to degrade in the environment, which leads to enrichment in organisms and interference with endocrine. This compound is harmful to the ecological environment and human health. To ensure the quality and safety of food, it is important to develop a detection method for disulfoton and its metabolites in agricultural products. A reliable method based on dispersive solid phase extraction (d-SPE) with ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed for the determination of disulfoton and its metabolites (disulfoton sulfone, disulfoton sulfoxide, demeton-S, demeton-S sulfone, and demeton-S sulfoxide) in agricultural products (pea, asparagus, wheat, coffee bean, and peanut). The optimal extraction method was as follows: 5.0 g the samples were extracted with acetonitrile (wheat, coffee bean, and peanut presoaked in 5 mL water) in a 50 mL centrifuge tube, followed by 10 min vortex. Before 30 s vortex, 4 g NaCl was added. After 5 min centrifugation, 1.5 mL of the supernatant was cleaned up with 50 mg octadecylsilane bonded silica (C₁₈), 50 mg primary secondary amine (PSA), and 50 mg aminopropyl (NH₂) adsorbents. The analytes were separated on a Thermo Syncronis C₁₈ column (150 mm×2.1 mm, 5 μm) with gradient elution using water and acetonitrile at a column temperature of 40 ℃. The injection volume was 2 μL. Disulfoton and its metabolites were analyzed in multiple reaction monitoring (MRM) mode with positive electrospray ionization (ESI⁺) for the selective quantification. Qualitative and quantitative analyses were accorded to the retention times and characteristic ion pairs with one parent ion and two fragment ions. Quantitative analysis was performed by an external standard method using matrix-matched calibration curves. All the parameters that affected the extraction efficiencies were optimized. C₁₈, PSA, and NH₂ gave good recoveries of 87.9%-109.0%. Other adsorbents, multiwalled carbon nanotubes (MWCNTs), hydroxylated multiwalled carbon nanotubes (OH-MWCNTs), carboxylated multiwalled carbon nanotubes (COOH-MWCNTs), octylsilane bonded silica (C₈), strong cation exchange (SCX) and neutral alumina (N-Al₂O₃), led to recoveries below 56.2%. The combination of adsorbents was also considered. Seven different combinations of 50 mg C₁₈, 50 mg PSA, and 50 mg NH₂ were chosen for the optimization experiments. There were no obvious differences in these combinations, and the target analytes recoveries ranged from 81.0% to 109.3% with relative standard deviations (RSDs) between 0.6% and 12.5%. The matrix effect could affect the extraction efficiency. The adsorbents of 50 mg C₁₈, 50 mg PSA, and 50 mg NH₂ showed weaker matrix effects as compared with other combinations of adsorbents in the instrument. The results for the matrix effect showed that peanuts and asparagus exceeded 20%, requiring matrix-matched calibration curves. Under the optimized conditions, disulfoton and its metabolites showed good linearities (R²≥0.9981) in the range of 2.0-200.0 μg/L. The average spiked recoveries of disulfoton and its metabolites in peas, asparagus, wheat, peanuts, and coffee beans ranged from 75.0% to 110.0%, with RSDs of 0.7% to 14.9%. The limits of detection (LODs) were between 0.02 and 2.0 μg/kg, and the limits of quantification (LOQs) were 5.0 μg/kg. The method was applied for the detection of 80 commercial productions, and neither disulfoton nor its metabolites were found. The proposed method is rapid, accurate, highly selective, and sensitive, and it is suitable for the simultaneous determination of disulfoton and its metabolites in grain, oil crops, vegetables, and other matrices.

Key words: ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), dispersive solid phase extraction (d-SPE), disulfoton, metabolites, agricultural products