丙溴磷对映异构体在柑橘中的残留分析及选择性降解

基于手性固定相/高效液相色谱- 串联质谱结合QuEChERS前处理技术建立了柑橘中丙溴磷对映体残留的分析方法，并通过田间试验研究了丙溴磷对映异构体在柑橘中的选择性降解行为。柑橘样品经乙腈快速提取，多壁碳纳米管净化。丙溴磷对映体采用ND(2)-RH手性色谱柱分离，正离子多反应监测模式 (MRM) 检测，基质匹配标准曲线法定量。方法验证结果表明，丙溴磷对映体在2.5~250 μg/L质量浓度范围内线性关系良好 (r ≥ 0.999 6)，方法定量限 (LOQ) 为5 μg/kg。在3个添加水平(5、100、500 μg/kg)下，丙溴磷对映体的平均回收率为76%~83%，相对标准偏差 (RSD) 为2.6%~6.0%。田间试验结果表明，丙溴磷对映体在柑橘中的降解规律符合一级反应动力学方程，(+)-丙溴磷和 (?)-丙溴磷的降解半衰期分别为12.53 d和14.14 d；在施药后30 d，丙溴磷2个对映体的对映体分数值达到0.43，表明其在柑橘中的降解存在明显的对映体选择性差异。

Residual analysis and selective degradation of profenofos enantiomers in citrus

An analytical method of the chiral stationary phase/high performance liquid chromatography-tandem mass spectrometry technique coupled with QuEChERS for determination of the enantiomers of profenofos in citrus was developed, and the selective degradation behavior of profenofos enantiomers in citrus was studied through field experiments. The sample preparation involved quick extraction with acetonitrile and cleaning-up with multi-walled carbon nanotube sorbent. The enantiomers of profenofos were separated by a ND (2)-RH chiral column, detected by tandem mass spectrometry in multi-reaction monitoring (MRM) mode, and quantified using matrix-matched calibration curves. The results showed good linear relationships for the analytes in the concentration range of 2.5-250 μg/L with their correlation coefficients (r) >0.999 6. The limits of quantitation (LOQs) were 5 μg/kg. The average recoveries of the two enantiomers of profenofos in citrus ranged from 76% to 83% at three spiked levels(5, 100, 500 μg/kg) and the relative standard deviations (RSD) were between 2.6% and 6.0%. Field experiments were conducted to study the differences in the degradation of profenofos enantiomers in citrus. The results of dynamic experiments showed that degradation of the enantiomers of profenofos in citrus conformed to the first-order reaction kinetic equation, and the half-lives of (+)-profenofos and (?)-profenofos were 12.53 d and 14.14 d, respectively. The enantiomer fraction (EF) value of the profenofos enantiomers in the field experiments reached 0.43 after 30 d of application, indicating that there were significant enantio-selectivity in the degradation of profenofos enantiomers in citrus.