Abstract
Background: Chiral selectors play a vital role in the separation efficiency for chiral separation techniques. Recently much attention has been devoted to chiral ionic liquids (CILs) derived from natural sources, which could be used as chiral selectors in chiral discrimination.
Objective: In this study, chiral ionic liquids with L-phenylalanine ester as cations (L-phenylalanine ethyl ester bis (trifluoromethanesulphonyl) imide) were synthesized and applied as novel chiral ligand for chiral separation.
Method: Ligand exchange chromatography with L-phenylalanine ethyl ester bis (trifluoromethanesulphonyl) imide as chiral selector was used to separate ofloxacin enantiomers. The effects of copper ion concentration, Lphenylalanine ethyl ester bis(trifluoromethanesulphonyl)imide concentration, organic modifier ratio, pH of the mobile phase as well as temperature on efficiency of chiral separation were investigated and evaluated.
Results: Optimal separation conditions were obtained, where 8 mmol/L this chiral ionic liquids and 4 mmol/L Cu2+ were dissolved in methanol/water (12:88, v/v) with pH 4.8. Under the optimum conditions, well enantioseparation of ofloxacin enantiomers could be observed with the resolution of 1.84.
Conclusion: The results demonstrated the good applicability of the chiral ionic liquids with amino acid ester as cations to separate ofloxacin enantiomers in ligand exchange chromatography. It also exhibited the potential for the separation and determination of other chiral medicines by an ionic liquid-assisted ligand-exchange method, and would extend the application of chiral ionic liquids in separation science.
Keywords: Chiral ionic liquids, chiral separation, ligand exchange chromatography, novel chiral ligand, ofloxacin enantiomers.
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