Enantiomeric separation of basic compounds using heptakis(2,3-di-O-methyl-6-O-sulfo)-β-cyclodextrin in combination with potassium camphorsulfonate in nonaqueous capillary electrophoresis: Optimization by means of an experimental design

The enantiomeric separation of a series of basic pharmaceuticals (β-blockers, local anesthetics, sympathomimetics) has been investigated in nonaqueous capillary electrophoresis (NACE) systems using heptakis(2,3-di-O-methyl-6-O-sulfo)-β-cyclodextrin (HDMS-β-CD) in combination with potassium camphorsulfonate (camphorSO3−). For this purpose, a face-centered central composite design with 11 experimental points was applied. The effect of the concentrations of HDMS-β-CD and camphorSO3− on enantioresolution was statistically evaluated and depended largely on the considered analyte. The presence of camphorSO3− was found to be particularly useful for the enantioseparation of compounds with high affinity for the anionic CD. CamphorSO3− seems to act as a competitor, reducing the affinity for the CD, probably by ion-pair formation with these analytes. For compounds with lower affinity for HDMS-β-CD, the combination of camphorSO3− and the CD appeared to have a favorable effect on enantioresolution only if the optimal CD concentration could be reached. On the other hand, for compounds characterized by a very low affinity for the anionic CD, the association of camphorSO3− and HDMS-β-CD is always unfavorable. Finally, experimental conditions were selected by means of the multivariate approach in order to obtain the highest resolution (Rs) value for each studied compound.