QUANTITATIVE DESCRIPTION OF ANALYTE MIGRATION BEHAVIOR-BASED ON DYNAMIC COMPLEXATION IN CAPILLARY ELECTROPHORESIS WITH ONE OR MORE ADDITIVES

A comprehensive theory is proposed to describe the migration behavior of analytes in capillary electrophoresis (CE) when one or more additiv es are present in the buffer solution. This theory amalgamates and ext ends the previous work done by others. The capacity factor (k') in thi s theory is defined as the product of the equilibrium constant and the additive concentration, thus, k' changes linearly with additive conce ntration, The net electrophoretic mobility of an analyte is a function of k', therefore, it can be changed by varying the additive concentra tion. Three parameters are needed to predict the mobility of an analyt e in a one-additive CE system: the mobility of the free analyte, the m obility of the complex, and the equilibrium constant for the analyte-a dditive interaction (which determines the fraction of the free analyte at different additive concentrations). When additives are used, the c hange in viscosity obscures this relationship, therefore, a viscosity correction factor is required to convert all mobilities to an ideal st ate where the viscosity remains constant. The migration behavior of an analyte in a solution with multiple additives can be predicted and co ntrolled, once the equilibrium constants of the interactions between t he analyte and each of the additives are obtained separately. beta-Cyc lodextrin and hydroxypropyl-beta-cyclodextrin are used as additives an d the migration behavior of phenol, p-nitrophenol, and benzoic acid ar e studied as a model system to verify this theory. When the necessary viscosity correction factor is included, the net electrophoretic mobil ities of the analytes obtained from experimental results agree with th e values predicted by the theory based on dynamic complexation. Althou gh only experiments with one and two additives were carried out to ver ify the theory, the equations apply to situations when more than two a dditives are used. The relationship between the theories of electropho resis and chromatography is clarified.