Selectivity enhancement for free zone capillary electrophoresis using conventional ion-pairing agents as complexing additives

Analyte selectivity in capillary zone electrophoresis may be limited due to similarities in the charge/size ration for related compounds. Conventional cationic and anionic ion-pair agents including alkylsulfonic acids and tetraalkylammonium salts have been investigated as additives to the electrophoretic run buffer to improve both the selectivity and resolution for organosolutes, peptides and proteins. Several different factors are responsible for changes in selectivity and resolution, including ionic interaction and hydrophobic association between solutes and additives as well as the modulation of electroosmotic flow. Selectivity improvements due to ionic interaction can be systematically optimized by varying size and concentration of the ion-pairing agent(s) in the buffer system. Butanesulfonic acid in particular appears to very useful for a diversity of applications including improved neurotransmitter separations, peptide mapping and separations of protein mixtures