Study On The Analysis Method And Residue Digestion Of Difenoconazole And Pyraclostrobin On Citrus

A liquid chromatography-tandem mass spectrometry?LC-MS/MS?method was developed for the analysis of difenoconazole and pyraclostrobin in citrus whole fruit,peel,pulp and soil matrix,and the analytical method was verified.In 2017 and 2018,field experiment of 30%difenoconazole·pyraclostrobin SC on citrus were carried out in nine experimental sites in China.The dissipation dynamics and final residues of difenoconazole and pyraclostrobin on citrus and soil were tested and analyzed,in order to providing data reference for the fair use of difenoconazole and pyraclostrobin on citrus.The research results are as follows:1.In this paper,acetonitrile was used as an extractant for citrus and soil samples,and the extracting solution was sodium chloride salting out,purified by C₁₈,filtered and detected by LC-MS/MS.The results showed that:difenoconazole and pyraclostrobin have a good linear relationship in the pure methanol,whole fruit,peel,pulp and soil matrix?R² were 0.9978?1?.The limit of quantification of 2 kinds of fungicides in whole citru fruit,peel,pulp and soil are0.02 mg/kg;the recoveries ratio of 2 kinds of fungicides were good.The average recoveries in whole citru fruit,peel,pulp and soil matrix were between 73.74%and 100.00%,and the relative standard deviation?RSD?were between 0.23%and 9.59%.In 2017,the dissipation half-lives of difenoconazole in Hunan,Guizhou and Guangxi were10.67,9.24 and 9.63 days respectively;the dissipation half-lives of pyraclostrobin were 9.37,8.45 and 8.56 days.The results of the whole fruit dissipation experiment in 2017 showed that:The initial residual contents o f difenoconazole and pyraclostrobin were relatively low in.The datas were irregular and could not fit the first-order kinetic equation.In 2018,the initial contents of pyrazoxystrobin were too low in whole citru fruit in Yunnan to fit the first-order kinetic equation.The dissipation equation for difenoconazole in whole citru fruit was y=0.1581e^-0.15x,The dissipation half-live were 4.62 days.2.In 2017,the maximum residues of difenoconazole in in citrus pulp,peel,whole fruit and soil were 0.07 mg/kg,1.05 mg/kg,0.23 mg/kg and 2.31mg/kg.The maximum residues of pyraclostrobin in citrus pulp,peel,whole fruit and soil were 0.024 mg/kg,1.45 mg/kg,0.31mg/kg and 1.27 mg/kg.The results of field tests in Hunan,Guangxi,Guizhou,Hubei,Zhejiang,Yunnan,Anhui,Jiangsu,and Guangdong in 2018 showed that the maximum residues of pyraclostrobin and difenoconazole in citrus pulp were 0.02 mg/kg and 0.05 mg/kg.The maximum residues of pyraclostrobin and difenoconazole on whole fruit in nine experiment sites in 2018 were 0.29 mg/kgand and 0.38 mg/kg,respectively.After 31 days,the residual amounts of the two compounds are less than the MRL value specified on the citrus.