Optimization of an Analytical Method for Indoxacarb Residues in Fourteen Medicinal Herbs Using GC-μECD, GC-MS/MS and LC-MS/MS

Pesticide residue analysis in medicinal herbs is a challenging task because of the matrix effect and its influence on quantitative analysis despite the continuous development of several new analytical methods and instrumentations. In this study, a modified QuEChERS method was developed for the analysis of indoxacarb residue in medicinal herbs by using the conventional instrument, gas chromatography micro-electron-capture-detector (GC-mu ECD), and comparing it with gas chromatography-tandem mass spectrometry (GC-MS/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Samples were extracted with acetonitrile and purified using an NH2 cartridge. The optimized method efficiently removes the co-extractives and offered a limit of quantification of 0.01 mg kg(-1). The GC-p.ECD analysis results of indoxacarb in seven medicinal herbs out of fourteen species at a fortification level of 0.01 mg kg(-1) showed a recovery range of 79.7-117.6%, while the rest showed recovery > 120%. Similarly, the recovery of indoxacarb by GC and LC-MS/SM were 74.1-105.9 and 73.0-99.0%, respectively, with a relative standard deviation of <20%. Matrix effects for the majority of medicinal herbs analyzed by GC-MS/MS were >+/- 20%. Whereas the results for LC-MS/MS were <20%, which was within the acceptable range according to the SANTE/11312/2021 guidelines. Considering the performance of the method and alignment with the regulatory guidelines, LC-MS/MS is recommended for the analysis of indoxacarb in selected medicinal herbs.