Comparison of gamma-cyclodextrin sulfobutyl ether and unmodified gamma-cyclodextrin as chiral selectors in capillary electrophoresis

gamma-Cyclodextrin sulfobutyl ether (gamma-CD-SBE) was synthesized and evaluated as a chiral selector for capillary electrophoresis. As expected, the new derivative combined the good enantioselectivity of gamma-cyclodextrin with the advantages of a negatively charged chiral selector, which have previously been reported also for the beta-cyclodextrin analogon. However, it became evident that the attachment of the sulfobutyl ether groups to the periphery of the gamma-cyclodextrin torus can markedly alter the enantioselectivity towards some racemic analytes. Thus, there was no general trend towards better separations with the use of gamma-CD-SBE rather than unmodified gamma-cyclodextrin or vice versa. Some racemates could only be resolved with one or the other system. For two racemates, even the elution order of the enantiomers with gamma-CD-SBE was opposite to that one expected from the experiments using unmodified gamma-cyclodextrin.