An effective and sensitive method for the determination of isopyrazam (IZM) isomers (syn-IZM and anti-IZM) and their metabolites (syn545364 and syn545449) in tomato and soil by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed in the present study. The method showed excellent linearities (R2 = 0.999) at 0.005-5 mg/L. The recoveries were 92.0-107%, and the relative standard deviation (RSD) values were lower than 9.40% in tomato and soil matrices at 0.01, 0.1, and 10 mg/kg. The limits of detection (LODs) of the four compounds ranged from 6.88 × 10-5 to 2.70 × 10-4 mg/kg, while the limits of quantification (LOQs) ranged from 2.20 × 10-4 to 9.20 × 10-4 mg/kg. The storage stability test results showed that syn-IZM, anti-IZM, syn545449, and syn545364 were stable in tomato at -20 °C within 36 weeks, and the maximum degradation rates were 16.0, 12.0, 7.10, and 12.0%, respectively. The field dissipation test results showed that the half-lives of syn-IZM in tomato and soil were 2.60-10.2 and 13.6-33.0 days, respectively, while the half-lives of anti-IZM in soil were 21.7-46.2 days, and no residues of anti-IZM were detected in tomato. The terminal residue test results showed that the residue of syn-IZM and anti-IZM in tomato ranged from <0.0100-0.490 to <0.0100-0.0850 mg/kg. The present results showed that anti-IZM degraded faster than syn-IZM in tomato and soil, and had a lower residue level in tomato.
Keywords: UPLC-MS/MS; isomers; isopyrazam; metabolites; residues; tomato.