Determination of Residues of 4 Organophosphorus Pesticides in Fruits and Vegetables by High Performance Liquid Chromatography after Solid Phase Extraction with Molecularly Imprinted Polymers

Molecular imprinted polymers (MIPs) were prepared by hydrothermal polymerization method with mixed compounds of 4 targets (profenofos, chlorpyrifos, diazinon and phoxim) as template molecule, ethylene glycol dimethacrylate as crosslinking agent, and methacrylic acid as functional monomer. The MIPs were filled in a blank polypropylene column to prepare a MIPs solid phase extraction (MIPs-SPE) column. After washing, drying, and crushing, 5.00 g of the fruit and vegetable samples were taken, and 2 g of anhydrous sodium sulfate was added. The mixture was ground evenly, and 30 mL of acetonitrile was added for ultarsound for 1.5 h, and centrifugation for 10 min. An aliquot (1 mL) of the supernatant was taken and passed through the MIPs-SPE column activated, which was washed by 4 mL of n-hexane, and eluted by 6 mL of methanol-acetic acid mixed solution at volume ratio of 9∶1. The eluate was collected, and blown to dryness by nitrogen at 35 ℃. Then 1 mL of acetonitrile was used for constant volume, and the resulting solution was analyzed by high performance liquid chromatography. It was shown that MIPs could specifically recognize 4 targets, with an adsorption capacity of about 2.5 times than that of non molecularly imprinted polymers (NIPs). The adsorption capacity of parathion, malathion, methyl parathion, and methyl chlorpyrifos was significantly lower than that of targets. After purification by MIPs-SPE column, most of the matrix components in the sample were removed, and there was no interference in the determination of targets. Linear relationships of values of the concentration and respective peak area of 4 targets were kept in the range of 0.005-2.0 μmol · L⁻¹, with detection limits (3S/N) in the range of 0.001 5-0.004 0 μmol · L⁻¹. At the spiked concentration levels of 0.01, 0.5, 1.0, 2.0 mg · kg⁻¹, the recoveries of 4 targets were found in the range of 85.9%-102%, and RSDs (n=5) of the determined values ranged from 3.0% to 7.1%. The proposed method was used for the analysis of 4 samples of vegetables and fruits, profenofos was detected in the strawberry sample with detection amount of 0.07 mg · kg⁻¹, phoxim was detected in the cabbage sample with detection amount of 0.05 mg · kg⁻¹, and 4 targets were not detected in other samples.