Abstract

QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) is widely applied as an effective sample preparation for determining pesticide residues. In this study, an analytical method based on QuEChERS followed by gas chromatography–tandem mass spectrometry (GC–MS/MS) was validated to determine 20 organochlorine pesticide residues in agricultural products. While the extraction step employed the acidified acetonitrile (ACN), this study focused on optimizing the subsequent steps, including clean-up dispersive solid phase extraction (d-SPE) and the additional liquid–liquid extraction (LLE) concentration step. The results indicated the most effective d-SPE mixture of MgSO4 and primary secondary amine (PSA). The introduced LLE switched the sample solvent from ACN to n-hexane, subjected to GC injection, and created a “salting-out” effect using NaCl, resulting in further removal of matrix components and enhancing recoveries by a factor of ~1.5. Negligible matrix effect (ME) was observed (|ME ratio| < 20%) for the spinach–a representative matrix with deep green color. The method showed quantification limits of 5–10 µg/kg, good linearity (R2 ≥ 0.995), and satisfactory precision for intra- (relative standard deviation of RSDr = 1.1–9.4% and inter-day (RSDR = 2.9–7.1%). The method was applied to tomatoes, cucumbers, Swiss chard, sweet potato leaves, and sweet potatoes, and detected no background pesticides. Recovery tests were conducted for these matrices at 10 µg/kg and for spinach at 10–30 µg/kg spiked levels, yielding 80–103% recoveries. Overall, the method demonstrated its reliability, sensitivity, and robustness for routine monitoring of organochlorine pesticide residues in agricultural commodities.