Simultaneous Determination of Residues of Neonicotinoid Pesticides and Their Metabolites in Soil by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry with Disperse Solid Phase Extraction

Considering the low recovery of nitenpyram using existing methods and lack of methods for simultaneously detecting neonicotinoid pesticides and their metabolites in soil, this study was conducted mentioned by the title. Soil samples were collected within 20 cm of the soil surface, dried by air, removed from impurities and sieved. An aliquot (5 g) was taken, and mixed with 3.0 mL of water. The mixture was shaken, settled for 10 min, and mixed with 10 mL of acetonitrile solution containing 1.0% (volume fraction) acetic acid. After shaking for 30 min, 5.0 g of anhydrous magnesium sulfate and 1.0 g of sodium chloride were added, and the mixture was shaken vigorously for 1 min, and centrifuged at 4℃ for 5 min. Then 0.15 g of anhydrous magnesium sulfate and 0.05 g of PSA were placed into a 5 mL-centrifuge tube with a stopper, and 2.0 mL of the above sample extract was added. The mixed solution was shaken for 1 min by vortex, and centrifuged at 4℃ for 3 min. An aliquot (0.5 mL) of the supernatant was taken, and mixed with 0.5 mL of water. After mixing well, the resulting solution was passed through a 0.2 μm filter membrane. The filtrate was collected and detected by the ultra-high performance liquid chromatograph-tandem mass spectrometer. Fourteen targets (including 10 neonicotinoid pesticides and 4 metabolites) were separated on the Waters ACQUITY UPLC HSS T3 chromatographic column by gradient elution with mixed solutions composed of methanol solution containing 5 mmol·L^-1 ammonium formate and 0.1% (volume fraction) formic acid solution containing 5 mmol·L^-1 ammonium formate at different volume ratios, ionized by the ESI⁺ mode, detected by the MRM mode, and quantified by matrix matching method. It was shown that linear relationships between values of the mass concentration and the corresponding peak area of 14 targets were kept in the ranges of 2.0-200.0 μg·L^-1 (clothianidin) and 0.5-200.0 μg·L^-1 (other 13 targets), with detection limits (3S/N) in the range of 0.36-2.49 μg·kg^-1. Test for recovery was made according to the standard addition method, giving recoveries in the range of 75.4%-112%, and RSDs (n=6) of the determined values were less than 9.0%. The proposed method was applied to the analysis of 16 orchard soil samples, and imidacloprid (13 samples), thiamethoxam (8 samples), and clothianidin (1 sample) were detected, with detection amounts of 0.007-0.31 mg·kg^-1, 0.005-0.28 mg·kg^-1 and 0.009 mg·kg^-1, respectively.