Affinity capillary electrophoresis using a low-concentration additive with the consideration of relative mobilities

Most affinity studies in capillary electrophoresis assume that the analyte concentration is much smaller than the additive concentration so that the migration of the analyte has no effect on the concentration of the additive in the capillary. However, in most medium- to high-affinity interactions, the additive concentration has to be kept rather low to observe the changes in analyte mobility before saturation is reached. In this paper, a mathematical model is developed to describe the migration behavior of the analyte in a system where the complex formed becomes concentrated to levels much greater than the original concentration of the additive due to the differences in the mobilities of the analyte, additive, and complex. The analyte is flurbiprofen, the additive is transthyretin, and the stoichiometry of the reaction between the two is 1:2. This study also provides a new algorithm to determine medium- to high-affinity binding interaction constants by CE.