Introduction of migration indices for identification: chiral separation of some beta-blockers by using cyclodextrins in micellar electrokinetic capillary chromatography

Because of the different physiological impact that stereoisomers may have, it is often vital to separate these forms from one another. Because of their structural similarity, the separation is usually difficult to achieve and zones may elute very close to each other. This is a particular problem in capillary electrophoresis, where the repeatability of absolute migration times is fairly poor, mainly due to the irreproducibility of the electroosmotic flow. The separation is usually repeatable, however, and when the disturbing effects are eliminated by using a migration index system incorporating two marker compounds the identification of the enantiomers becomes extremely good. Relative standard deviation (RSD) values less than 0.1% for the migration index of each enantiomer were obtained in both intra-day and day-to-day (6 days) studies. The best separation was achieved with the electrolyte solution made of 40 mM borate, 32 mM sodium dodecyl sulfate (SDS), 12 mM beta-cyclodextrin (beta-CD), and 6 mM alpha-cyclodextrin (alpha-CD) at pH 9.3.