EXPERIMENTAL AND THEORETICAL-STUDY OF ARTIFACTUAL PEAK SPLITTING IN CAPILLARY ELECTROPHORESIS

It is shown here that the interaction of sample and background electrolyte, in addition to undergoing excessive dispersion resulting in the characteristic triangular form, may lead to a sample peak splitting into two separate, distant peaks connected by a valley of sample substance. The first peak, in which the sample is charged, moves electrophoretically, while the second peak represents the same substance, uncharged, sad moves under the impact of electroosmosis. This phenomenon, when occurring, may be misunderstood and treated wrongly, e.g., the second peak maybe ascribed to the presence of another substance (impurity) in the sample, while the shift of the base level between two peaks may be interpreted as a consequence of wall adsorption. The second peak may go unnoticed if the electroosmosis is weak and the experiment is terminated before it appears at the detector. Two mathematical models, a simplified, diffusionless one and a more sophisticated one, were developed in order to explain this phenomenon. The first model allows an analytical solution, while the second needs computers for solving the equations. Both gave good coincidence between experimental data and theoretical prediction. Qualitatively, this phenomenon may be explained using the Kohlrausch regulating functions, which claim that the electrolyte solution ''remembers'' its initial state and keeps it constant in time. The presence of a strong electrolyte co-ion in the buffer solution is a necessary condition for the existence of this effect, since its penetration in the starting zone after the electric current is applied suppresses the sample's ionization and thus its ability to escape.