Metolachlor stereoisomers: Enantioseparation, identification and chiral stability

November 2, 2018

Title

Metolachlor stereoisomers: Enantioseparation, identification and chiral stability

Author

Jingqian Xie, Lijuan Zhang, Lu Zhao, Qiaozhi Tang, Kai Liu, Weiping Liu

Year

2016

Journal

Journal of Chromatography A

Abstract

Metolachlor is a chiral herbicide consisting of four stereoisomers, which is typically used as a racemic mixture or is enriched with the herbicidally active 1 S-isomers. Because studies on the enantioselective behavior of phyto-biochemical processes and the environmental fate of metolachlor have become significant, a practical method for analyzing and separating metolachlor stereoisomers must be developed. In the present study, the enantiomeric separation of metolachlor was achieved using OD-H, AS-H, OJ-H and AY-H chiral columns. The effects of different organic modifiers in an n-hexane-based mobile phase were investigated, and various temperatures and flow rates, which may influence metolachlor separation, were also explored. The optimal resolution was obtained using an AY-H column with n-hexane/EtOH (96/4) as the mobile phase at a rate and temperature of 0.6 mL min−1 and 25 ◦C, respectively. The absolute configuration of the four stereoisomers was identified as SS, RS, ˛SR, ˛RR using computed and experimentally measured ECD and VCD spectra. Thermal interconversion and solvent stability experiments were also performed. Pure metolachlor stereoisomers in different organic solvents and water at 4 ◦C or 30 ◦C were stable. These results were used to establish a sound method for analyzing, preparing, characterizing, and preserving individual metolachlor stereoisomers in most natural environments.

Instrument

FVS-6000

Keywords

Vibrational circular dichroism, Metolachlor stereoisomers, Enantioseparation, Electronic circular dichroism, Chiral stability