COMBINED EFFECTS OF NONLINEAR ELECTROPHORESIS AND NONLINEAR CHROMATOGRAPHY ON CONCENTRATION PROFILES IN CAPILLARY ELECTROPHORESIS

A theory of peak evolution in a column under the combined action of el ectromigration dispersion and equilibrium adsorption-desorption is pre sented. The basic equations for mass transport in zone electrophoresis are combined with those for non-linear chromatography. Langmuir's iso therm is assumed for describing the analyte interaction with the colum n wall (capillary electrophoresis in thin capillaries) or a sorbent (e lectrokinetic chromatography). The transport equation thus obtained is analysed and three specific cases determining the peak evolution are found: (A) the concentration velocity as a function of concentration i s non-monotonous; (B) the velocity increases with analyte concentratio n; and (C) the velocity decreases with increments of concentration. So lutions to the transport equation for all three cases, describing the evolution of disperse boundary and discontinuities are derived. By ass uming a ''rectangular pulse'' initial profile, a variety of peak shape s are generated. In the case of a non-monotonous velocity dependence o n concentration, the initial concentration is shown to be an important parameter determining the peak shape and its transformations while mo ving along the column axis. A possibility of a counterbalance of the e lectromigration and adsorption mechanisms of the peak broadening, lead ing to a decay of the peak evolution into a ''triangle'' is found.