Micellar electrokinetic capillary chromatography with in-situ charged micelles VI. Evaluation of novel chiral micelles consisting of steroidal-glycoside surfactant-borate complexes

Abstract

Novel in-situ charged micelles having chiral selectivity, namely N,N-bis-(- d-gluconamidopropyl)-cholamide and -dexycholamide (denoted by Big CHAP and Deoxy Big CHAP, respectively), were evaluated in micellar electrokinetic capillary chromatography (MECC) of enantiomers. The two neutral steroidal glycoside surfactants (i.e., Big CHAP and Deoxy Big CHAP) could be charged readily via borate complexation, and consequently the surface charge density of their corresponding micelles could be conveniently adjusted by varying the borate concentration and the pH of the running electrolyte. This allowed manipulation of the migration time window of the Big CHAP- and Deoxy Big CHAP-borate micellar systems over a certain range. As a result the enantiomeric resolution of a given racemic mixture could be optimized by varying the pH and borate concentration of the running electroyle. In addition, the stereoselectivity of the chiral steroidal micelles could be further tuned by changing the concentration and nature of the organic modifier and surfactant as well as by adjusting the temperature of the capillary column. In general, resolution increased with (i) increasing pH and borate concentration of the running electrolyte and (ii) decreasing capillary temperature. On the other hand, there was an optimum organic modifier and surfactant concentration for which maximum resolution was obtained. Big CHAP-borate micelles were less stereoselective than Deoxy Big CHAP-borate micellar systems under otherwise identical conditions. The novel micellar phases were useful for the separation of binaphthyl enantiomers, troger's base, dansl amino acid enantiomers and silvex herbicide optical isomers.