Separation of enantiomeric basic drugs by microemulsion electrokinetic chromatography with chiral 2-octanol as the oil core

Abstract

The effects of oil substitution on separation of the enantiomers of basic drugs by microemulsion electrokinetic chromatography (MEEKC) have been studied. The presence of the chiral oils (S)-(+)-2-octanol or (R)-(-)-2-octanol in the microemulsion droplets seemed to have a very important effect on the mechanism of chiral separation. The importance of hydrogen bonding between the β-amino proton of the test solutes [(±)-ephedrine, (±)-norephedrine, and dl-propranolol] and the hydroxyl oxygen of the chiral selector (chiral 2-octanol) is suggested. Addition of methanol to the chiral MEEKC system had a large effect on this hydrogen bonding and thus on chiral discrimination, probably because competition of between the solutes and the methanol for binding to the hydrogen-bonding site on the chiral selector in the microemulsion system. The order of elution of the (±)-norephedrine enantiomers can be reversed by switching from (S)-2-octanol to (R)-2-octanol in the microemulsion system. © 2007 Friedr. Vieweg & Sohn Verlag/GWV Fachverlage GmbH.