CONSEQUENCES OF WALL ADSORPTION IN CAPILLARY ELECTROPHORESIS - THEORY AND SIMULATION

Simple theoretical models are utilized to assess the extent of zone broadening and relative decrease in resolution that takes place when an adsorptive wall is included in a model of capillary electrophoresis. One of the theoretical models is derived from plate height theory, and the other results from a modification of the kinetic zone shape theory of Lapidus and Amundson, used in chromatography. Both are shown to agree favorably with a stochastic computer simulation used to test the long-time assumptions implicitly present in these theories. The theories predict that small levels of retention drastically reduce resolution from that expected from broadening due solely to axial diffusion. Considerations of capillary diameter demonstrate that, when adsorption is present, small capillaries are advantageous for small molecule solutes (large diffusion coefficients) to minimize the resolution loss. For larger molecules (small diffusion coefficients), small diameter capillaries offer little advantage in performance when adsorption is present as compared to larger capillaries; hence, in this case larger capillaries are suggested for use because the larger path length gives greater sensitivity for on-column detection.