Determination of Residues of 4 Organophosphorus Pesticides in Vegetables by Gas Chromatography after Purification with Self-Made Co₃O₄ Porous Material

The residues of the 4 organophosphorus pesticides (phosphamidon, fenthion, quinalphos and profenofos) in vegetable samples were determined by the method mentioned by title. Porous material of Co₃O₄ was prepared by the combustion of Co(NO₃)₂ and glycine, and characterized by XRD, FESEM, BET and TG. As found by results, the purifier was spinel-type Co₃O₄ material with layered loose porous structure, its specific surface area was 22.054 m²·g^-1, and mass fraction of Co₃O₄ was 87.0%. After chopping and grinding, 2.5 g of vegetable samples were extracted with 5.0 mL of toluene by vortex. After centrifugation, 0.07 g of Co₃O₄ porous material was added into 4.0 mL of supernatant, and the mixture was vortexed for 5 min. After centrifugation, an aliquot (0.6 mL) of the supernatant was taken out and passed through a 0.22 μm filter membrane. The filtrate was introduced into the gas chromatography, the 4 pesticides were separated on the HP-5 capillary column with temperature program, and detected by flame photometric detector. It was shown that the amount of porous material of Co₃O₄ was only 1% of that of QuEChERS method. A baseline separation of the 4 organophosphorus pesticides was achieved within 15 min, and the cis-and trans-isomers of phosphamidon were also separated. The linear ranges of standard curves were 0.032-0.60 mg·L^-1 (for phosphamidon and profenofos) and 0.016-0.30 mg·L^-1 (for fenthion and quinalphos), with detection limits (3S/N) of 0.004-0.010 mg·L^-1. Test for the spiked recovery was made on the blank rapeseed samples at the 4 concentration levels, giving recoveries of the 4 organophosphorus pesticides in the range of 89.2%-95.8%, and RSDs (n=6) of the determined values were not more than 7.0%. The proposed method was applied to the analysis of 11 kinds of vegetable samples, and the residues of the 4 organophosphorus pesticides were not detected, which met the requirements of GB 2763-2021.