Abstract:
Considering the complexity of the pre-processing process for standard methods of GB 23200.50—2016, the title method was used to determine the residue of 7 pyridine pesticides, including dithiopyr, imidacloprid, fluridone, thiazopyr, imazethapyr, acetamiprid and boscalid, in rice and wheat. An appropriate amount of rice or wheat samples was taken, crushed, and sieved. An aliquot (2.00 g) was taken, and 5 mL of water was added. The mixture was mixed well by vortex and settled for 30 min, and 10 mL of acetonitrile and 2 g of sodium chloride were added. The mixture was vortexed for 5 min, and centrifuged for 5 min. The supernatant was collected, and transferred to a 15 mL-centrifuge tube containing 300 mg of C
18 and 2.0 g of anhydrous sodium sulfate. The mixture was vortexed for 1 min, centrifuged for 5 min, and passed through a 0.22 μm hydrophilic PTFE syringe filter. The filtrate was determined by ultra-high performance liquid chromatography-tandem mass spectrometry. In chromatographic analysis, Shimadzu shim-pack GIST C
18 chromatographic column was used as the stationary phase, and a mixture of acetonitrile and 0.05% (volume fraction) formic acid solution at different volume ratios was used as the mobile phase for gradient elution. In the mass spectrometry analysis, the ESI
+ mode was used for ionization, the MRM mode was used for detection, and the matrix matching method was used for quantification. It was shown that linear relationships between values of the mass concentration and corresponding peak area were kept in the ranges of 2.0-50.0 μg·L
−1 for boscalid and 1.0-50.0 μg·L
−1 for the other 6 pesticides, with lower limits of determination (10S/N) of 0.010 mg·kg
−1 for boscalid and 0.005 mg·kg
−1 for the other 6 pesticides. At the spiked concentration levels of 0.01, 0.05, 0.2 mg·kg
−1, the recoveries of 7 pyridine pesticides were found in the range of 74.6%-103%, and RSDs (
n=6) of the determined values ranged from 0.84% to 6.9%, which were basically consistent with those (the recoveries were 72.1%-99.7%, and RSDs (
n=6) of the determined values were 1.1%-6.8%) given from GB 23200.50—2016, indicating that converting the solid phase extraction method in GB 23200.50—2016 to QuEChERS was feasible, and the pre-processing process of QuEChERS was simple, fast, and more suitable for detection of batch samples.