A rapid and sensitive analytical method for determination of pyraclostrobin and thifluzamide in cowpea was established based on QuEChERS sample preparation and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Average recoveries of pyraclostrobin and thifluzamide on cowpea were 100%-105% and 99%-105% with RSDs of 1%-5% and 2%-6%, respectively. The storage stability tests showed degradation rates of < 20% for samples stored at - 18℃ within 12 weeks. The field trials at eight locations in China showed that the residues of pyraclostrobin in cowpea at 3 and 5 days after spraying were 0.081-0.49 mg/kg and 0.029-0.48 mg/kg, and the residues of thifluzamide were 0.12-0.46 mg/kg and 0.047-0.50 mg/kg, respectively, which were all lower than the corresponding maximum residue limits in China. The dissipation of both pyraclostrobin and thifluzamide in cowpea were fast with half-lives (T1/2) of 1.5-2.3 days and 1.7-2.4 days. This study provided risk assessment data for establishment of good agricultural practice in cowpea plant.
Keywords: Cowpea; Pyraclostrobin; QuEChERS; Residues; Thifluzamide.
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