Residue Analysis Of Difenoconazole Enantiomers On Citrus

In this paper,a method for residue determination of difenoconazole four enantiomers in citrus was established by liquid chromatography tandem mass spectrometry(HPLC-MS/MS)on a Superchiral S-OX column.Field experiments were carried out from May to July 2019 in Guizhou,Guangdong and Hunan,which investigate the stereoselectivity of difenoconazole four enantiomers degradation in citrus leaves,and detect the final residues of difenoconazole four enantiomers in whole fruits.The enantioselective behavior of four enantiomers of difenoconazole on citrus leaves was investigated by the amount residue and the values of EF.This paper examines that the baseline separation of difenoconazole four enantiomers in eight chiral columns,different mobile phases and different temperatures.Finally,the baseline separation of the enantiomers was achieved under the conditions of Superchiral S-OX,10 ?,100% ethanol and the wavelength of 220nm.The absolute configuration of difenoconazole enantiomers was determined by single crystal diffraction.The results showed that the peak sequence on the Superchiral S-OX column was(2S,4R)-difenoconazole,(2S,4R)-difenoconazole,(2R,4R)-difenoconazole and(2R,4S)-difenoconazole.The samples were extracted by acetonitrile,purified by Oasis PRIME HLB column and tested on HPLC-MS/MS.The limits of quantification(LOQ)and limits of detection(LOD)were 0.011 and 0.0044mg/kg,respectively,and 0.0004 and 0.0002mg/kg,respectively,in citrus leaves and fruits.The linear relationship between peak area and concentration was good when the enantiomer concentration was 0.025?5?g/m L for citrus leaves and 0.01?2.5 ?g/m L for citrus fruits,respectively,and the correlation coefficient was greater than 0.99.In citrus leaves,the average of difenoconazole enantiomers at three different level of 0.05,0.5 and 5mg/kg was83.82%?104.24%,and the relative standard deviation was 1.25%?5.47%,respectively.In whole citrus,the averae recovery of difenoconazole enantiomers at three different leaves of 0.02,0.2 and 2mg/kg was 82.45%?102.79%,and the relative standard deviation was 0.91%?3.57%.The analytical method was applied to 10 % difenoconazole water dispersible granules in field samples of citrus orchards in Guizhou,Hunan and Guangdong.The results showed that the application dose of 2000 times,the degradation of difenoconazole enantiomers in the citrus leaves samples all followed first-order kinetics.In Hunan,the degradation half-lives of difenoconazole enantiomers are2.56?2.85 days.In Guizhou,the degradation half-lives of difenoconazole enantiomers are 6.42?7.62 days.The degradation rates of difenoconazole enantiomers in Guizhou and Hunan are basically the same.In the Guangdong,The degradation half-life of difenoconazole enantiomers are 8.15?13.59 days.Obviously,the degradation of(2R,4R)-difenoconazole is slower than(2S,4S)-difenoconazole,and(2S,4R)-difenoconazole and(2R,4S)-difenoconazole.The teat results in the application dose of 2666 times,1333 times and 1000 times are consistent with the test results of the application dose of 2000 times.The whole fruit samples were collected on the 14 th day after the second applicati on with the application of the dose of 2000 times.The test results found that the total residue of difenoconazole enantiomers is 0.147mg/kg in Guizhou.the total residue of difenoconazole enantiomers is 0.068mg/kg in Hunan.the total residue of difenoconazole enantiomers is < 0.022mg/kg in Guangdong.In Guizhou,Hunan and Guangdong,the residual value of difenoconazole is slower than China's maximum residual value of 0.6mg/kg(GB 2763,2019).Therefore,whole citrus samples from the three places are safe.