Determination of 69 Pesticide Residues in Cowpea Products by Gas Chromatography-Tandem Mass Spectrometry and Liquid Chromatography-Tandem Mass Spectrometry Combined with QuEChERS

Cowpea is prone to pesticide residues due to its growth habits and unique planting environment, while pesticides are also introduced when producing and processing sour and dry bean products, further increasing the potential food safety risks of cowpea products. However, research on pesticide residue detection methods of cowpea products lacked, so the title method was proposed. After crushing the sour and dry bean samples, 10 g of sour bean sample was taken (5 g of dry bean sample was taken, and 5 mL of water was added), and 10 mL of acetonitrile was taken. The mixture was extracted by vortex for 2 min, and 1 ceramic average proton and a QuEChERS extraction salt package containing 4 g of magnesium sulfate, 1 g of sodium chloride, 1 g of sodium citrate, and 0.5 g of disodium hydrogen citrate were added. The mixture was extracted by vortex for 2 min, and centrifuged for 2 min. The supernatant was placed into a QuEChERS purification tube containing 900 mg of anhydrous magnesium sulfate, 150 mg of PSA, and 15 mg of GCB, and the tube was vortexed for 1 min, and centrifuged for 2 min. An aliquot (1 mL) of the supernatant was passed through a 0.22 μm organic filter membrane, and the filtrate was analyzed by LC-MS/MS. An aliquot (1 mL) of the supernatant was taken, and blown to near dryness by nitrogen at 40 ℃. After 1 mL of acetone was added, the mixture was vortexed for 30 s, and passed through a 0.22 μm organic filter membrane, and the filtrate was analyzed by GC-MS/MS. In GC-MS/MS analysis, the 41 pesticides were separated on Thermo TG-5SILMS chromatographic column under temperature programmed conditions, ionized by EI source, detected by MRM mode, and quantified by matrix matching method. In LC-MS/MS analysis, the 28 pesticides were separated by gradient elution on ACQUITY UPLC BEH C₁₈ column with mixed solutions composed of 5 mol · L⁻¹ ammonium acetate solution containing 0.01% (volume fraction, the same below) formic acid and methanol solution containing 0.01% formic acid at different volume ratios, ionized by ESI⁺ mode, detected by MRM mode, and quantified by matrix matching method. It was shown that linear relationships between values of the mass concentration and peak area of pesticides were kept in the ranges of 0.010-0.400 mg · L⁻¹ for GC-MS/MS and 0.005-0.150 mg · L⁻¹ for LC-MS/MS, with correlation coefficients greater than 0.998 0, and lower limits of determination (10S/N) of 0.01 mg · kg⁻¹. Test for recovery was made according to standard addition method, giving recoveries in the range of 70.6%-117%, and RSDs (n=6) of the determined values ranged from 0.45% to 7.0%. The proposed method was applied to the analysis of 26 batches of sour samples and 22 batches of dry bean samples, the detection rate of the positive samples was up to 81.2%, and the number of pesticides detected was up to 57 kinds.