A modified QuEChERS method for simultaneous determination of 73 pesticides, 23 PCBs and 16 PAHs in wheat by GC-MS/MS

In this study, a modified QuEChERS method for the simultaneous determination of 73 pesticides, 23 PCBs and 16 PAHs in wheat was developed by gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS). The sample was first hydrated with 4 mL of ultrapure water, extracted with 10 mL of acetone-hexane (1 : 1, V:V), and then cleaned up with a mixture of 50 mg of PSA, 150 mg of C18, and 400 mg of anhydrous MgSO₄. Under the optimized conditions, the samples were analyzed by GC-MS/MS for quantitative analysis using the matrix-matched external standard method. As a result, 112 compounds showed good linearity in their linear ranges with correlation coefficients (R²) greater than 0.995, and the limits of detection (LODs) of the method were in the range of 0.15-3 μg kg^-1, and the limits of quantification (LOQs) were between 0.5 and 10 μg kg^-1. The recoveries ranged from 71.2% to 112.1%, with relative standard deviations (RSD, n = 6) below 20% at the three spiked levels (LOQ, 2× LOQ, and 10× LOQ). The intra-day precision and inter-day precision were within 0.5-11.6% and 2.4-18.9%, respectively. The proposed method was applied to 40 batches of wheat samples, and neither PCBs nor PAHs were detected. Five pesticides were detected: epoxiconazole, difenoconazole, flutriafol, bifenthrin, and simazine. Among them, simazine was detected in 10 batches of samples, with concentrations ranging from 10.01 to 48.31 μg kg^-1, which exceeded the MRL prescribed by the EU. The results demonstrate that the method is characterized by simple pretreatment, rapidity, and sensitivity, and is suitable for the simultaneous determination of pesticide residues and environmental pollutants in wheat.