Resolution of enantiomeric amides on a cellulose tribenzoate chiral stationary phase. Mobile phase modifier effects on retention and stereo-selectivity.

The effect of the steric structure and concentration of the mobile phase modifier on the retention (kappa') and stereoselectivity (alpha) of a series of enantiomeric amides has been investigated. The amides were chromatographed on a commercially available cellulose tribenzoate chiral stationary phase (CSP) using mobile phases composed of hexane and two homologous series of alcohols: methanol, ethanol, 1-propanol and 2-propanol, 2-butanol, 2-pentanol, 2-hexanol. The results of the study indicate that the alcoholic mobile phase modifiers compete with the solutes for achiral and chiral binding sites and that the steric bulk around the hydroxyl moiety of the modifier plays a role in this competition. Increased steric bulk tends to result in increased kappa' and alpha. However, the results also suggest that the effect of the alcoholic mobile phase modifiers on stereoselectivity may also be due to binding to achiral sites near or at the chiral cavities of the CSP which alters the steric environment of these cavities.