Rapid chiral separation and impurity determination of levofloxacin by ligand-exchange chromatography

A sensitive, simple, and accurate method for determination of levofloxacin and its (R)-enantiomer was developed to determine the chiral impurity of levofloxacin in Cravit Tablets material by ligand-exchange high performance liquid chromatography. The effects of different kinds of ligands, concentration of ligands in mobile phase, organic modifier, pH of mobile phase, and temperature on enantioseparation were investigated and evaluated. Chiral separation was performed on a conventional C18 column, where the mobile phase consisted of a methanol–water solution (containing10 mmol L^-1 l-leucine and 5 mmol L^-1 copper sulfate) (88:12, v/v) and its flow-rate was set at 1.0 mL min^-1. The conventional C18 column offers baseline separation of two enantiomers with a resolution of 2.4 in less than 20 min. Thermodynamic data ((delta)(delta)H and (delta)(delta)S) obtained by Van’t Hoff plots revealed the chiral separation is an enthalpycontrolled process. The standard curves showed excellent linearity over the concentration range from 0.5 to 400 mg L^-1 for levofloxacin and its (R)-enantiomer. The linear correlation equations are: y = 1.33 × 10^5x + 6297 (r = 0.9991) and y = 1.34 × 10^5x + 3565 (r = 0.9997), respectively. The relative standard deviation (RSD) of the method was below 2.3% (n = 3).