Residual Analysis And Digestion Dynamics Of Clethodim In 15% Sulfopyrimone·Clethodim Dispersible Oil Suspension Concentrate On Tobacc

This paper established a method for the simultaneous determination of clethodim and its metaboles the clethodim sulfoxide and clethodim sulfone in tobacco and soil.Field trials were conducted in 2016 and 2017 at Guizhou and Hunan province.Through the analysis of field samples in two years,we hope to provide reasonable suggestions for the safe use of clethodim in tobacco.Acetonitrile was used as the extractant for green tobacco leaf,cured tobacco leaf and soil samples.The sodium chloride was used for salting out,and C₁₈ was used for purification.Liquide chromatography with tandem mass spectrometry（LC-MS/MS）was used for detection.The linear ranges of matrix standard solutions of clethodim,clethodim,sulfoxide,and clethodim sulfone in three tobacco and soil were all 0.01-1μg/mL.Good linearity was obtained with the correlation coefficients>0.99.The average recoveries of clethodim,clethodim sulfoxide and clethodim sulfone in matrices were 78.3-97.1%,74.8-104.4%and 82.7-102.0%,respectively.The intra-day standard deviations（RSD,n=5）of clethodim,clethodim sulfoxide and clethodim sulfone were 2.1-7.0%,1.1-5.7%,and 1.9-12.1%,respectively,and the inter-day RSDs（n=15）were 2.2-12.0%.The lowest detectyion concentrations were 0.08,0.2and 0.08 mg/kg,respectively.The results showed that the developed method met the pesticide residual analysis requirements.The dissipation dynamics of clethodim in fidldgreen tobacco leavf and soil samples were investigated.The application dosage was 168.75 g a.i./ha.The initial concentrations of clethodim in green tobacco leaf and soil sample were relatively small and could not be calculated by first-order kinetic equation.Therefore,the two-year dissipation data only served as monitoring data.In the terminal residue experments,the application were 112.5 g a.i./ha（low dosages）and 168.75 g a.i./ha（high dosages）.The application was performed once,and tobacco and soil samples were collected at harves.The terminal residues levels of clethodim（the sum of clethodim and its metabolites clethodim sulfoxide and clethodim sulfone）in cured tobacco leaf and soil samples were 0.58 and 0.23 mg/kg,respectively,in 2016 and 2017.In addition,an indoor simulation dissipation experiment of clethodim in soil was conducted.The dissipation behaviors of clethodim in different soil,different temperature and different moisture content conditions were discussed.There might be many uncontrollable factors in the field experiment which could influence the dissipation of clethodim in soil,so our date could explain the phenomenon.