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

It is shown here that the interaction of sample and background electro lyte, in addition to undergoing excessive dispersion resulting in the characteristic triangular form, may lead to a sample peak splitting in to two separate, distant peaks connected by a valley of sample substan ce. The first peak, in which the sample is charged, moves electrophore tically, while the second peak represents the same substance, uncharge d, 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) i n the sample, while the shift of the base level between two peaks may be interpreted as a consequence of wall adsorption. The second peak ma y go unnoticed if the electroosmosis is weak and the experiment is ter minated before it appears at the detector. Two mathematical models, a simplified, diffusionless one and a more sophisticated one, were devel oped in order to explain this phenomenon. The first model allows an an alytical solution, while the second needs computers for solving the eq uations. Both gave good coincidence between experimental data and theo retical prediction. Qualitatively, this phenomenon may be explained us ing the Kohlrausch regulating functions, which claim that the electrol yte solution ''remembers'' its initial state and keeps it constant in time. The presence of a strong electrolyte co-ion in the buffer soluti on is a necessary condition for the existence of this effect, since it s penetration in the starting zone after the electric current is appli ed suppresses the sample's ionization and thus its ability to escape.