Influence of the degree of substitution of cyclodextrin sulfobutyl ether derivatives on enantioselective separations by electrokinetic chromatography

Several gamma-cyclodextrin sulfobutyl ether (gamma-CD-SBE) derivatives, differing in the degree of substitution (DS), were synthesized and characterized by matrix-assisted laser desorption/ionization time-on-flight MS. They were evaluated as chiral selectors for the separation of enantiomers by capillary electrophoresis. The results demonstrate that the number of sulfobutyl groups attached to the cyclodextrin moiety significantly influences the enantioseparation towards the racemic analytes. For the examined racemic solutes, a good resolution was generally obtained when using gamma-CD-SBE with an average DS ranging between 5 and 7, except for secobarbital which is only resolved when the average DS is higher than 7. For this compound the migration order of the enantiomers with gamma-CD-SBE (DS 7.6) was opposite to that one observed with unmodified gamma-cyclodextrin in the presence of sodium dodecyl sulfate micelles. For 1-(9-anthryl)-2,2,2-trifluoroethanol the resolution increases as DS is increasing. These different results clearly demonstrate that it is crucial to use well-characterized CD derivatives. (C) 1997 Elsevier Science B.V.