Optimization of a capillary electrophoresis method to determine the chiral purity of a drug

Capillary electrophoresis (CE) using hydroxypropyl-β-cyclodextrin (HP-β-CD) in the separation buffer was investigated to determine the overall chiral purity of a drug containing a single stereogenic center. The effects of primary factors —pH, buffer components, buffer concentration, cyclodextrin concentration and sample amount (concentration and injection volume) — on the resolution of the enantiomers were investigated. Secondary factors such as the HP-β -CD source, lot and degree of substitution that were expected to affect the robustness of the assay were investigated also. The linearity, quantitation limit for the trace enantiomer and the precision of the measurements were determined. This study shows that understanding and optimizing the assay conditions leads to a chiral CE separation that is comparable to that obtained by chiral HPLC. However, chiral CE separations achieved with buffer additives have the advantages of shorter run times, higher numbers of theoretical plates (greater resolution), smaller amounts of chiral additive (less cost) and greater ruggedness (separation virtually independent of column properties unlike HPLC).