Enantioseparation of tetramisole by capillary electrophoresis and high performance liquid chromatography and application of these techniques to enantiomeric purity determination of a veterinary drug formulation of L-levamisole

Abstract

The enantioseparation of the chiral anthelmintic drug tetramisole was studied by capillary electrophoresis using various cyclodextrins as chiral selectors. In particular, the following aspects have been addressed: (1) the enantiomer affinity pattern of tetramisole towards various cyclodextrins; (2) development of a capillary electrophoretic method for quantitative determination of the enantiomeric impurity, i.e. of the R-(+) enantiomer, in S-(–)-tetramisole (levamisole); (3) application of the capillary electrophoretic method for the determination of the enantiomeric impurity of R-(+)-tetramisole in commercial samples and in a veterinary drug formulation of S-(–)-tetramisole; and (4) comparison of capillary electrophoretic and traditional pharmacopoeial polarimetric methods for the enantiomeric impurity determination in S-(–)-tetramisole. Opposite affinity order of tetramisole enantiomers was observed towards different cyclodextrins, depending on the nature of the substituents and the substitution pattern. In addition, an enantioseparation of tetramisole was developed by high performance liquid chromatography on polysaccharide type chiral stationary phase. This method was compared to the aforementioned capillary electrophoretic method. Preliminary validation results indicated that capillary electrophoresis represents a flexible, fast, and inexpensive technique for determination of the enantiomeric impurity of R-(+)-tetramisole in the commercial samples and drug formulations of S-(–)-tetramisole (levamisole). Both of the commercial samples as well as the veterinary drug formulation of levamisole contained R-(+)-tetramisole as enantiomeric impurity. Capillary electrophoresis represents a superior method for enantiomeric impurity determinations compared to the traditional polarimetric method still used in the major pharmacopoeias. CE offers the advantages of miniaturised techniques, as well as higher peak efficiency, flexibility, and shorter method development time compared to HPLC.