Residue Analysis And Stereoselective Degradation Of Chiral Fungicide Penthiopyrad In Soil

In this paper,the combination of experimental and calculated electronic circular dichroism(ECD)was used to confirm the absolute configuration of penthiopyrad stereoisomers.A chiral analytical method for the determination of penthiopyrad in soil and water by liquid chromatography with tandem mass spectrometry(LC-MS/MS)was developed and validated.In laboratory simulation trials,the stereoselective degradation of racemic and enantiopure penthiopyrad in soil and water was investigated.Finally,the potential metabolites of penthiopyrad in soil were identified by ultra-high performance liquid chromatography with high resolution mass spectrometry(UHPLC-HRMS).Comparing the experimental and calculated ECD spectra,the elution order of penthiopyrad stereoisomers was R-(-)-penthiopyrad,then S-(+)-penthiopyrad.The chiral separation of penthiopyrad ennatiomers was performed on a Superchiral S-OD column(4.6×150 mm,5?m).The separation conditions were:mobile phases,acetonitrile(0.1%formic acid)and 0.1%formic acid aqueous solution(50/50,v/v,isocratic elution);flow rate,1.0 m L/min;column temperature,30?;injection volume,3?L.The soil samples were extracted with acetonitrile and purified by PSA.The water samples(0.5 m L)were collected and mixed with an equal volume of acetonitrile.The linearity of the established method was good(R~2?0.996).The limits of quantitation and detection were 0.005?0.01 mg/kg and 0.0015?0.003 mg/kg,respectively.The average recoveries of penthiopyrad stereoisomers were 74.93%?111.34%,and the relative standard deviations were less than 11.5%.In soil,the degradation rate orders of penthiopyrad stereoisomers were HLJ>AH>GZ>HN.The degradation of penthiopyrad was mainly affected by soil organic matter content and microbial activity.Under different conditions,the stereoselective degradation of rac-penthiopyrad was observed in all four types of Chinese soil,that a preferential degradation of S-(+)-stereoisomer.Organic matter could inhibit the stereoselectivity of penthiopyrad degradation in soil.At the same time,the degradation of penthiopyrad was affected by incubation temperature and soil moisture.The configuration of penthiopyrad stereoisomer was stable during the degradation process.The degradation of enantiopure R-(-)-penthiopyrad was faster than its antipode,which was opposite to the degradation of stereoisomers in racemic penthiopyrad.A potential chiral metabolite of penthiopyrad,753-A-OH,was identified in soil.In natural water matrix,the degradation rate orders of penthiopyrad stereoisomers were lake water<rain water<tap water.The degradation rate was negatively correlated with the pH value of natural water samples.In different pH buffer solutions,the degradation rate orders of penthiopyrad stereoisomers were pH 5>pH 7>pH 9,which demonstrated that penthiopyrad was easy to hydrolyze in acidic solution.The preferential degradation of S-(+)-stereoisomer was observed in natural water matrices and buffer solutions.During the incubation process,two stereoisomers did not undergo configuration transformation.This paper confirmed the absolute configurations of penthiopyrad stereoisomers for the first time,established the chiral analytical method for determining penthiopyrad residues in soil and water which was successfully applied on the investigation of stereoselective degradation of penthiopyrad in soil and water.The results could provide some more accurate information to understand the environmental behavior and risk of penthiopyrad in soil and water at the stereoisomer level.