Systematic approach to treatment of enantiomeric separations in capillary electrophoresis and liquid chromatography.: I. Initial evaluation using propranolol and dansylated amino acids

Abstract

A systematic approach is outlined for treatment of enantiomeric separations in capillary electrophoresis (CE) and liquid chromatography (LC) using chiral mobile phase additives. General equations and data analysis methods are presented to relate mobilities or capacity factors to equilibrium constants in binding equilibria, and to maximise mobility or retention time differences as a function of selector concentration. The use of cyclohexanol as a competitor is shown to be beneficial in optimising chiral separations of species which bind strongly to β-cyclodextrins. This general treatment has been applied with the test systems 1: propranolol and β-cyclodextrin and 2: dansylated amino acids and β-cyclodextrin. Chiral separations and binding constants, determined using LC with β-cyclodextrin as a mobile phase additive or a chiral stationary phase, are compared with results using the same selector in CE for system 2. Mobile phase equilibria defined by CE reveal more complex stationary phase binding equilibria in LC. Our studies make a link between LC and CE which may allow rational separation strategies to be transferred between the two fields.