Simultaneous Determination of Residues of 7 Common Herbicides in Planting Soil by Gas Chromatography-Tandem Mass Spectrometry with Accelerated Solvent Extraction

The planting soil samples about 20 cm below the surface were collected, removed from impurities, naturally dried by air, ground, and passed through a sieve with pore size of 0.18 mm. An aliquot (10 g) of the sample was taken and mixed with 10 g of Florisil and 5 g of diatomaceous earth. The mixture was pretreated by accelerated solvent extraction with ethyl acetate-acetone mixed solution at volume ratio of 1∶1 at 90 ℃. All the extract was collected and blown to about 2 mL in 70 ℃ water bath by nitrogen. The solution obtained was passed through Florisil solid phase extraction column activated beforehand, and elution was carried out by 10 mL of acetone-n-hexane mixed solution at volume ratio of 1∶1. The eluate was collected, blown to near dryness in 70 ℃ water bath by nitrogen, and diluted to 1.0 mL by acetone. The resulting solution was passed through a 0.22 μm filter membrane, and the filtrate was introduced into the gas chromatography-triple quadrupole mass spectrometer. Seven common herbicides, including bensulfuron methyl, cyclochlor, dimefop, pochlor, vochlor, flufop-p-ethyl, and bufloxacin, were separated by programmed temperature on the DB-5MS quartz capillary chromatographic column, ionized by the electron impact ion source, detected by the multiple reaction monitoring mode, and quantitatively analyzed by external standard method. As found by the results, linear relationships between values of the mass concentration and respective peak area of the 7 herbicides were kept in the range of 0.02-5.0 mg·L^-1, with detection limits (3s) of method in the range of 0.008-0.017 μg·kg^-1. Test for recovery was made by standard addition method, giving recoveries in the range of 87.3%-102%, and RSDs (n=6) of the determined values were less than 5.0%. The proposed method was applied to the analysis of the rice, wheat, corn, apple, and grape-planting soil samples, and vochlor, bensulfuron methyl, dimefop, and flufop-p-ethyl were detected in rice, wheat, apple, and grape-planting soil samples, with detection amounts of 32.15, 14.22, 11.62, 27.15 μg·kg^-1, respectively.