Abstract: The degradation dynamics and residues of prothioconazole and its metabolite prothioconazole-desthio from 40% prothioconazole + tebuconazole suspension concentrate (SC) in wheat and soil were investigated by QuEChERS-high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The limit of detection (LOD) for both prothioconazole and prothioconazole-desthio was 2 × 10-3 ng, and the limit of quantitation (LOQ) was 0.02 mg/kg. The recoveries of prothioconazole from spiked wheat grains and straw and soil were 87.3%–103.0%, 93.6%–100.3% and 85.0%–100.5%, respectively, and the recoveries of prothioconazole-desthio were 93.2%–109.9%, 92.7%–101.9% and 81.7%–95.6%, respectively. The degradation of prothioconazole and its metabolite in wheat straws was fitted to a first-order reaction kinetic model. The half-lives of degradation of prothioconazole in wheat straw from Jiangsu, Henan and Beijing were 4.4, 1.8 and 3.3 d, respectively. The half-lives of degradation of prothioconazole-desthio in wheat straw from Jiangsu, Henan and Beijing were 6.2, 2.9 and 6.0 d, respectively. The final residues of prothioconazole in wheat grains and straw and soil were < 0.02, < 0.02–0.225 and < 0.02–0.033 mg/kg, respectively. The final residues of prothioconazole-desthio were < 0.02, < 0.02–0.282 and < 0.02–0.049 mg/kg, respectively. The spray application of 40% prothioconazole + tebuconazole SC twice at a dose of 300 g a.i./hm2 gave a final residual prothioconazole concentration in wheat grains consistent with the national standard (GB 2763-2016); thus, it can be safely used.

Key words: prothioconazole, prothioconazole-desthio, QuEChERS, HPLC-MS/MS, degradation, residue