A multi-residue method for simultaneous determination of 74 pesticides in Chinese material medica using modified QuEChERS sample preparation procedure and gas chromatography tandem mass spectrometry

The present study is focused on the development of an analytical method for the simultaneous analysis of seventy-four pesticides belonging to different chemical classes (organochlorines, organophosphates, pyrethroids, dinitroanilines, dicarboximides, triazoles, etc.) in Chinese material medica. The samples were extracted according to the acetate QuEChERS protocol. To reduce the amount of co-extracted compounds, n-hexane instead of acetonitrile was employed as the extraction solvent. To improve the overall recoveries of problematic basic and base-sensitive compounds, sodium acetate was used to adjust the pH to a neutral condition, and florisil combined with octadecyl-modified silica (C18) were utilized in the cleanup step. The samples were analysed by GC-MS/MS, and quantified by matrix-matched calibration. The validation study was carried out on two representative herbs, Chuanxiong Rhizoma and Angelica Sinensis Radix. In two matrices, the linearity of the calibration was good between 5 and 250 ng/mL concentration ranges, and the limits of quantification (LOQs) less than 0.01 mg/kg for most pesticides. At the LOQs and ten times the LOQs, the mean recoveries of almost all pesticides were within 70-120%, with relative standard deviations (RSDs) lower than 10%. The method was applied on twenty real samples. Seven batches of Chuanxiong and five batches of Danggui were found to contain the residues. The combination of modified QuEChERS and GC-MS/MS offers low cost of analysis as well as excellent accuracy and sensitivity. This method could be especially useful for trace analysis of pesticide residues in complex matrices.