Enantioselective Determination Of The Insecticide Indoxacarb In Cucumber And Tomato By Chiral Liquid Chromatography-tandem Mass Spectrometry

Usually, the activity and toxity of the chiral pesticides enantiomers are quite different, so it isvery important to carry out the separation of chiral pesticide enantiomers for assessingenvironmental risk accurately. For this study, this is the first time to establish analysis method fordetecting indoxacarb enantiomer in cucumber, tomato, grape and water by reversed-phase liquidchromatography-tandem mass spectrometry (LC-MS/MS), besides, the degradation rule ofindoxacarb enantiomer in cucumber and tomato was investigated under open conditions by theproposed method. Instead of the traditional UV detector, tandem mass spectrometry detector has ahigher sensitivity and selectivity. In cucumber and tomato, studing the degradation of indoxacarbcan provide technical support for evaluating its safety. The main content of the paper is dividedinto two parts:ⅰ) A reversed-phase chiral method for the determination of indoxacarb enantiomers wasestablished using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The targetanalytes were quantified by external standard method, and the difference in matrix effect betweenmatrix dispersed extraction and solid phase extraction was compared. The tomato and grapesamples were extracted by acetonitrile and then purified by NH2/Carb solid phase extraction (SPE),while water was preconcentrated and cleaned up by C18-H SPE cartridge. The chromatographicconditions were as follows: Chiralpak AD-RH column, acetonitrile/water=65/35, columntemperature was25℃, and flow rate was0.4mL/min. The results showed satisfied recoveries ofthe enantiomers in the range of65.5%-117.0%at levels from0.005mg/kg (or mg/L) to0.5mg/kg(or mg/L) with relative standard deviations of4.1%-18.1%(n=5). Limits of detection (LOD) of theenantiomers were in the range of1.4-4.3μg/kg (or μg/L), and limits of quantification (LOQ) were4.7-14.2μg/kg (or μg/L). The method is simple and suitable for the routine analysis of indoxacarbenantiomers in tomato, grape and water.ⅱ) The proposed method was successfully applied to investigate the possible enantioselectivedegradation of rac-indoxacarb in cucumber and tomato under open conditions. The results indicated that the degradation of indoxacarb enantiomers followed first-order kinetics in cucumberand tomato. The half-lives of (+)-S-indoxacarb in cucumber and tomato were3.0and5.9days,respectively; while the (-)-R-indoxacarb were7.3and12.2days, respectively. The data of thehalf-lives showed that (+)-S-indoxacarb was preferentially degraded in cucumber and tomato.Moreover, indoxacarb was degraded faster in cucumber than in tomato.At present, enantioselective behavior of chiral pesticides has become a focus of research inthe environment. It is very important to study the indoxacarb extensively in the other types ofplants, on the basis of studying enantioselective degradation of indoxacarb in cucumber andtomato. In the future, there need to enhance studying degradation mechanism of indoxacarb inplants on the molecular level. Besides, in ecosystem, whether there exist the enantiomericconversion and transport or not still need to do more research in future.