The application of chiral ultra-high-performance liquid chromatography tandem mass spectrometry to the separation of the zoxamide enantiomers and the study of enantioselective degradation process in agricultural plants

In this study, an effective and sensitive chiral analytical method was developed to detect zoxamide enantiomers in vegetables, fruits and environmental matrices using ultra-high-performance liquid chromatography-tandem mass spectrometry. Optimal separation conditions were achieved with Lux Amylose-2 chiral column using acetonitrile/water (70:30 v/v) as mobile phase with a flow rate and column temperature of 0.5 mL/min and 25 °C. The absolute configuration, optical rotation and elution order were confirmed for the first time. The average recoveries in all matrices at four spiking levels (0.5, 5, 50, 250 μg/kg) ranged from 89.7 to 117.4%, with relative standard deviations being less than 10.9% for two enantiomers. The enantioselective dissipation of zoxamide in tomato showed that (−)-R-zoxamide was preferentially degraded leading to an enrichment of (+)-S-isomer, with half-lives of 3.80 d and 5.17 d, respectively. Inversely, (+)-S-zoxamide degraded faster than (−)-R-zoxamide in pepper (1.95 day and 2.28 day, respectively) and grape (2.03 day and 2.87 day). No significant enantioselectivity was observed in cucumber. The results of this study could help facilitate more accurate risk assessments of zoxamide in the future.