THE EFFECTS OF A MIXTURE OF CHARGED AND NEUTRAL ADDITIVES ON ANALYTE MIGRATION BEHAVIOR IN CAPILLARY ELECTROPHORESIS

Multicomponent additives, such as derivatized cyclodextrins with vario us degrees of substitution, can be considered single-component additiv es as long as the fraction of each component remains constant. In this paper, equations are derived describing the effect of such additives on the migration behavior of analytes. These equations are used in the study of capillary electrophoresis (CE) systems with differentially c harged cyclodextrins as additives. For weakly acidic analytes, the bin ding with highly negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) increases their negative electrophoretic mobility, whil e the binding with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD ) decreases their negative mobility. By obtaining the equilibrium cons tants and mobilities for each additive with each analyte (in this case , phenol, 2-naphthol and 1-naphthol), the migration behavior of these analytes in CE systems is quantitatively predicted at various concentr ations of mixtures of the two additives. The properties of the contour lines in the binding isotherm surfaces of such CE systems are discuss ed.