A capillary electrophoresis method for the determination of the linagliptin enantiomeric impurity

Abstract

Linagliptin is a highly specific, long-acting inhibitor that is used as an orally administrable agent for type-2 diabetes treatment. Because only the R-enantiomer is of clinical use, we developed a capillary electrophoresis method for the determination of the enantiomeric impurity of this compound. Carboxymethyl-β-cyclodextrin was selected as the chiral selector for the separation of linagliptin enantiomers. Design of experiments and desirability functions were used for the analytical optimization, which was focused on understanding and improving the electrophoretic process. The effects of significant parameters (background electrolyte concentration and pH, cyclodextrin concentration, temperature, and voltage) were thoroughly investigated. The complete separation of linagliptin and its enantiomeric impurity with baseline resolution was achieved within 10min on an uncoated fused-silica capillary (50μm inner diameter, 365μm outer diameter, 64.5/56cm in total/ effective length) maintained at 25°C, under an applied voltage of 28.0kV. The background electrolyte contained 70mM sodium acetate and 4.7mM carboxymethyl-β-cyclodextrin, and the pH was adjusted to 6.10. The method was validated, and a limit of quantitation of 0.05% for the impurity was estimated.