Use of heptakis-(2,3-O-dimethyl-6-sulfato)-β-cyclodextrin, a new single-isomer chiral resolving agent for the separation of the enantiomers of neutral compounds by capillary electrophoresis

The single isomer, fully and permanently charged heptakis-(2,3-dimethyl-6-sulfato)-β-cyclodextrin was used to study the complexation behavior of the enantiomers of noncharged analytes in capillary electrophoresis. Separation selectivities were calculated from the measured effective mobilities and were used to determine the individual complexation constants by fitting the experimentally obtained selectivity values to the theoretically derived selectivity expression according to the charged resolving agent migration model of capillary electrophoresis. Though heptakis-(2,3-dimethyl-6-sulfato)-β-cyclodextrin complexed very weakly with the neutral analytes studied, good separation selectivities were observed. For all neutral analytes, separation selectivity decreased with increasing concentration of the charged cyclodextrin as long as the analytical concentration of the charged cyclodextrin was much greater than that of the analyte. In addition to adequate separation selectivity, good peak resolution required the simultaneous control of the magnitude of both the effective charge of the analyte and the dimensionless electroosmotic flow rate.