Study On The Stereoselective Behavior Of Chiral Pesticide Glufosinate-ammonium In Water And Soil Environment

A method for the determination of enantiomers of glufosinate and two metabolites in soil and water samples was established on ultra high performance liquid chromatography with high-resolution mass spectrometry(UHPLC–HRMS)using a crown ether chiral stationary phase.The enantioselective degradation and chiral stability of the chiral pesticide glufosinate in water and soil samples were studied using glufosinate racemate,pure D-glufosinate and pure L-glufosinate,respectively.The degradation characteristics of chiral pesticide glufosinate in water and soil samples were studied,and the formation trends of metabolites 3-(methylphosphino)propionic acid(MPP)and N-acetyl glufosinate(NAG)were elucidated.The glufosinate enantiomer was successfully separated on the crown ether chiral stationary phase.The resolution of the two enantiomers was 1.55.The separation conditions were as follows:The mobile phase was 1.5%aqueous formic acid;the column temperature was 6°C;the injection volume was 5?L;the flow rate was 0.3mL/min;the CROWNPAK CR(+)chiral column was used to detect and analyze the glufosinate enantiomers and their metabolites MPP and NAG in electrospray ionization(ESI)SIM scanning mode.The soil sample was extracted by shaking with distilled water and purified with dichloromethane.The water sample was directly filtered and the glufosinate and two metabolites were detected by UHPLC-HRMS.The linearities of the matrix-matched calibration curves in five water and four soil samples were good,with a correlation coefficient R~2>0.9985,and the mean recoveries were85.22%-100.36%,with relative standard deviations of 0.95%-7.11%.The degradation rate of the glufosinate enantiomer in the buffer solution was very slow,the degradation rate was basically equal to zero after 100 d of culture.The degradation rate of culture in unsterilized pond water for 100 d is less than 22%.Although the degradation is slow,L-glufosinate degrades slightly faster and preferentially degrades in two natural water samples(pond water and river water).The enantiomers of glufosinate were not tested for conversion between the two enantiomers in the five aqueous culture experiments,the glufosinate enantiomer remained stable in aqueous solution.Among the four unsterilized soil samples,L-glufosinate degraded faster than D-glufosinate.The enantiomers of glufosinate have enantioselective degradation in the soil,L-glufosinate is preferentially degraded.In the two sterilized soil samples,the degradation rates of the two enantiomers of glufosinate in the soil were the same,and the degradation of the glufosinate enantiomers in the sterilized soil was not selective,no enantioselective degradation occurred.The biological processes by microorganisms was crucial in the enantioselective degradation of glufosinate compared to unsterilized soil samples.In most cases of glufosinate degradation in soils,the concentration of metabolite MPP is greater than NAG.However,the amount of NAG was significantly greater at 0-14 d as optically pure L-glufosinate degraded in ac-4 soil.In the entire degradation test of the pure enantiomer of glufosinate in the soil,no conversion between the two enantiomers was detected,the glufosinate enantiomer remained structurally stable in the soil sample.This study provides a feasible manner of positively identifying the chirality of glufosinate and its metabolites in water and soil samples.The results may be helpful to systematically evaluate the environmental behaviours of glufosinate enantiomers and their metabolites,providing reference data for the rational use of the chiral pesticide glufosinate.