Chiral Separation and Thermodynamic Investigation of Ezetimibe Optical Isomers on a Chiralpak IC Column

A liquid chromatographic separation method of ezetimibe optical isomers on the immobilised-type Chiralpak IC chiral stationary phase, onto which cellulose tris-(3,5-dichlorophenylcarbamate) was covalently grafted as a chiral selector, was developed under normal-phase conditions. The optimized chromatographic conditions were as follows: n-hexane-isopropanol-diethylamine (90:10:0.1, v/v) as mobile phase, 1.0 mL min^-1 as flow rate, 256 nm as UV detection wavelength and 25°C as column temperature. Several factors concerning the enantioseparation were studied, including quality and quantity of different polar organic modifiers, additives, and flow rate and column temperature. Separation and resolution in the temperature range of 15-35°C was investigated. Apparent thermodynamic parameters were calculated from the Van't Hoff plots and used to explain the strength of interactions between the optical isomers and chiral selector. The validated method is simple, rapid and robust. Four ezetimibe optical isomers can be effectively separated from each other and the resolutions are 3.5, 2.7 and 2.5 successively. The method has been demonstrated to be applicable in routine quality control of Ezetimibe.