Determination of Residues of 5 Organophosphorus Pesticides in Crop Soil by Gas Chromatography-Tandem Mass Spectrometry with Accelerated Solvent Extraction and Gel Permeation Chromatography Purification

A method for the determination of residues of 5 organophosphorus pesticides (including of demeton methyl, phoxim, coumaphos, ethoprophos and naled) in crop soil by gas chromatography-tandem mass spectrometry (GC-MS/MS) with accelerated solvent extraction (ASE) and gel permeation chromatography (GPC) purification was proposed. Crop soil sample was randomly collected and passed through 0.3 mm screen mesh after removing large particle impurities and crushing. Screened soil sample (10 g) was placed in the accelerated solvent extraction tank, and 12 g of diatomite was added. The above solution was repeatedly extracted 3 times by ASE with a mixture of acetone and hexane at volume ratio of 1∶1. The collected extracted solution was transferred to GPC purification bottle, and then concentrated and purified by GPC. The purified solution was blown to near dry by nitrogen, and then dissolved with 1 mL of methanol and filtered by 0.45 μm filter membrane. The filtrate was analyzed by GC-MS/MS, and external standard method was used for quantification. As shown by the results, linear relationships between values of mass concentrations of 5 pesticides and their peak areas were kept in the same ranges of 0.02-10.00 mg·L^-1, with detection limits (3S/N) in the range of 1.6-3.2 μg·kg^-1. Test for recovery was made on negative sample at 3 concentration levels by standard addition method, giving results of 5 pesticides in the range of 90.0%-101%. 6 spiked solutions of negative sample were determined, and RSDs of the determined values of 5 pesticides were in the range of 2.8%-4.2%. This method has been applied to the analysis of actual crop soil samples, and demeton methyl, phoxim, ethoprophos were detected in varying degrees.