Cyclodextrins as selectivity enhancers in capillary zone electrophoresis of proteins

The selectivity in the capillary zone electrophoresis (CZE) of a variety of acidic and basic proteins including alpha-chymotrypsinogen A, cytochrome c, lysozyme, ribonuclease A, ovalbumin, and beta-lactoglobulins A and B, was altered by adding 6-monodeoxy-6-monoamino-beta-cyclodextrin or carboxymethylated beta-cyclodextrin to the electrophoretic medium of aqueous 50 mM sodium phosphate, pH 2.5. On the other hand, no significant improvement was obtained in the separation upon addition of heptakis (2,6-di-O-methyl)-beta-cyclodextrin. Whereas protein adsorption on the wall of raw silica capillaries was significant in the absence of cyclodextrin, by addition of beta-cyclodextrin or its derivatives to the background electrolyte, wall adsorption was reduced with concomitant enhancement of the recovery. The results confirm that in various separation techniques, particularly those which employ microcolumns, certain cyclodextrin additives can be useful selectivity enhancers not only in the separation of small sample molecules but also in that of proteins.