Comparison of native, alkylated and charged cyclodextrins for the chiral separation of labetalol stereoisomers by capillary electrophoresis

A capillary electrophoresis method for the enantioresolution of labetalol was developed using CDs as chiral selectors and uncoated capillaries. Various native (α-, β- and γ-CD), alkylated (hydroxy propyl-β- and γ-CD, methyl-β-CD) and anionic (sulfated-β-CD and sulfobutylether-γ-CD) cyclodextrins were tested and operational parameters such as buffer pH, concentration of CD were investigated. Propranolol was also studied as a model compound. Uncharged γ-CDs were more effective than β-CDs to separate the enantiomers of labetalol but no complete resolution of the four isomers was obtained. The use of charged cyclodextrins led to a combination of hydrophobic inclusion and ion-pairing interaction in the chiral recognition mechanism. Thus, a complete resolution of the four enantiomers of the labetalol was attained using 7.7 g/l sulfated-β-CD in a 30 mM phosphate buffer, pH 6.5.