Chiral separation of ephedrines by liquid chromatography using beta-cyclodextrins

beta-cyclodextrins (beta-CDs) have been evaluated as chiral recognition agents for the enantioseparation of ephedrines by liquid chromatography (LC). The compounds tested were norephedrine, ephedrine, pseudoephedrine, N-methylephedrine and Nmethylpseuoephedrine. Two possibilities have been investigated, the employment of a chiral stationary phase consisting of immobilized beta-cyclodextrin, and the addition of the chiral selector to the mobile phase. In the latter approach the following chiral agents have been assayed, native beta-cyclodextrin (beta-CD), methyl-beta-cyclodextrin (M-beta-CD), carboxyethyl-beta-cyclodextrin (CE-beta-CD), carboxymethyl-beta-cyclodextrin (CM-betaCD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD). The experimental factors affecting the chiral separations have been examined, including the percentage of organic solvent, the ionic strength and pH of the buffer, the type and concentration of chiral selector, and the mobile-phase flow rate. Differences in enantioselectivity displayed by the different methods are discussed.