Properties of multivariate binding isotherms in capillary electrophoresis

When more than one complexation additive is used in capillary electrophoresis (CE), the migration behavior of an analyte can be described using contour plots and profile plots of the multivariate binding isotherms, At a certain concentration of one additive, the net electrophoretic mobility of the analyte is not affected by the concentration of the second additive, even though the second additive does alter the mobility of the analyte when used alone. The concentration of the first additive, in this situation, is defined as the dengsu concentration (dengsu means "same speed" in Chinese), The presence of a dengsu concentration for one additive is a strong indication that the second additive interacts with the analyte in a 1:1 (analyte-additive) stoichiometry, The binding isotherms in a profile plot can be used to unambiguously determine the binding stoichiometry of the analytes, as well as to determine the effect of interactions between the additives. The apparent complex mobilities obtained from the profile plots can also be used to determine whether there are interactions between the additives or whether the analyte can bind both additives at the same time.