Residue Analysis And Digestion Dynamics Study Of 40% Thiophanate-pyrazole Ester Suspension On Citrus

This paper established a liquid chromatography triple-quadrupole mass spectrometry(LC-MS/MS)detection method for the determination of thiophanate-methyl and its metabolite carbendazim and pyraclostrobin residue in citrus and soil.The residual degradation and final residue test of 40% thiophanate-methyl·pyraclostrobin SC in citrus and soil were carried out in Guizhou,Guangxi and Hunan in 2015 and 2016 to provided a theoretical basis for the safe use of thiophanate-methyl and pyraclostrobin.Citrus,citrus peel,and citrus pulp were extracted with acetonitrile,sodium chloride salting out,purified by primary secondary amine(PSA),detected by LC-MS/MS.Soil samples were extracted with methanol,anhydrous magnesium sulfate in addition to water,purified by PSA,detected by LC-MS/MS.Carbendazim standard solution in citrus,citrus peel and citrus pulp of the linear range of was 0.00125~0.25 μg/m L,and carbendazim standard solution in soil of the linear range of was 0.00125~0.5 μg/mL.thiophanate-methyl standard solution in citrus,citrus peel and citrus pulp of the linear range of was 0.0125~2.5 μg/mL,and thiophanate-methyl standard solution in soil of the linear range of was 0.0125~5 μg/m L μg/m L.pyraclostrobin standard solution in citrus,citrus peel and citrus pulp of the linear range of was0.005~1 μg/mL,and pyraclostrobin standard solution in citrus,citrus peel and citrus pulp of the linear range of was0.005~2 μg/mL.Correlation coefficient were all >0.99.Spiked recoveries of carbendazim,thiophanate-methyl and pyraclostrobin in four matrices were 76.21%~105.08%,75.89%~114.48% and 70.34%~106.67%,respectively.And RSDs were 1.09%~5.11%、0.66%~3.21% and 0.60%~4.97%,respectively.The lowest detectable concentrations were 0.005 mg/kg,0.05 mg/kg and 0.02 mg / kg,respectively.The accuracy,sensitivity and precision of this method can satisfy the requirements of pesticide residue analysis.The dynamic patterns of digestion of thiophanate-methyl and pyraclostrobin in citrus and soil were studied.The dosage was 533 times(1.5 times of the high dose of the recommended dose).The half-life of thiophanate-methyl in citrus and soil was 4.56~6.60 d and 7.70~8.35 d,the half-life of pyraclostrobin in citrus and soil was 5.77~14.44 d and 5.46 d,which indicated thiophanate-methyl and pyraclostrobin belonged to the easily degraded of pesticides.The final residue of thiophanate-methyl and pyraclostrobin in citrus,citrus peel,citrus pulp and soil was examined by the terminal residue test.The dosage was 533 ~ 800 times,and the spraying time was 10 days,and the samples were collected at intervals of 14,21 and 28 days from the last application interval.The residues of thiophanate-methyl and pyraclostrobin were <0.005~0.477 mg/kg and <0.02~0.08 mg/kg,respectively.In this paper,the frozen storage stability of carbendazim,thiophanate-methyl and pyraclostrobin in 360 days at-20℃ was studied for the first time.The results showed that the degradation rate of carbendazim,thiophanate-methyl and pyraclostrobin in citrus pulp under the condition of-20 ℃ in 360 days was less than 10%,3.52% and 5%,respectively.