Band broadening in a microcapillary with a stepwise change in the zeta-potential.

In capillary zone electrophoresis (CZE), adsorption of charged analytes to walls has been observed to cause significant band broadening. The effect is believed to be due to modification of the flow pattern and the consequent Taylor dispersion caused by the alteration of the wall charge by the adsorbed analytes. Experiments using neutral (nonadsorbing) analytes in capillaries in which the zeta-potential has been deliberately altered in a controlled way by chemically coating a segment of the capillary have been performed by Towns and Regnier (Anal. Chem. 1992, 64, 2473) in an effort to understand the mechanism of the band broadening. In this paper, the Taylor dispersion due to electroosmotic flow in such a partially coated capillary is calculated and compared to the experimental data. The theoretical predictions are found to be in excellent agreement with the data, thus supporting the hypothesis that the decreased resolution can be attributed to Taylor dispersion due to the induced pressure gradient brought about by the nonuniformity of the zeta-potential.