Electroosmotic control of chiral separation in capillary zone electrophoresis.

The resolution in capillary zone electrophoresis (CZE), with the assumption of diffusion control only, is strongly dependent on the direction and magnitude of electroosmotic flow. In fact, excellent separation resolution will be obtained if the electroosmotic flow is in the opposite direction of the electrophoretic migration. By applying various radial electric potential gradients across the capillary wall, the direct control of the zeta potential and the electroosmotic flow results in a great enhancement of chiral resolution in cyclodextrin-modified CZE. All 12 basic chiral drugs, including (+/-)-ephedrine, (+/-)-pseudoephedrine, (+/-)-norephedrine, (+/-)-epinephrine, (+/-)-norepinephrine, and (+/-)-isoproterenol, are separated and resolved within 22 min of the analysis time. There is no additional band broadening and dispersion introduced by the direct control of electroosmosis with the application of various radial electric potential gradients.