Development of a modified QuEChERS extraction for the determination of organochlorine pesticide residues in Chinese herbal medicines using gas chromatography – tandem mass spectrometry (GC-MS/MS): method validation and measurement uncertainty evaluation

Abstract This study presents the development and validation of a robust, high-throughput method for the determination of 26 organochlorine pesticide (OCPs) residues in Chinese herbal medicines (Chms). Given the complexity of Chm matrices, a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) protocol was employed, incorporating both dispersive solid-phase extraction (dSPE) and solid-phase extraction (SPE), coupled with gas chromatography–tandem mass spectrometry (GC-MS/MS). A custom dSPE sorbent blend − comprising magnesium sulfate (MgSO 4 ), graphitised carbon black (GCB), primary-secondary amine (PSA), C 18 and silica were specifically formulated for effective clean-up of plant-based Chm matrices. Matrix-matched calibration using isotopically labelled internal standards was adopted to mitigate matrix effects. Two representative Chm matrix blends (comprising different medicinal parts of Chm) were identified as suitable matrix blanks for calibration across diverse medicinal parts. The calibration curves exhibited excellent linearity up to 350 μg/L, with square of correlation coefficient (R 2 ) exceeding 0.990 for all analytes. Spike recovery experiments across eight representative medicinal parts, each at 3 concentration levels (n = 128 per pesticide) yielded recoveries ranging from 73.7 % to 127.2 %, with relative standard deviations (RSDs) between 0.1 % and 11.6 %. Measurement uncertainties were evaluated, with relative expanded measurement uncertainties ranging from ±21 % to ±33 %. The validated method has been successfully implemented in routine surveillance program monitoring pesticide residues in Chms available in Hong Kong.