CONSEQUENCES OF WALL ADSORPTION IN CAPILLARY ELECTROPHORESIS - THEORYAND SIMULATION

Simple theoretical models are utilized to assess the extent of zone br oadening and relative decrease in resolution that takes place when an adsorptive wall is included in a model of capillary electrophoresis. O ne 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 ag ree favorably with a stochastic computer simulation used to test the l ong-time assumptions implicitly present in these theories. The theorie s predict that small levels of retention drastically reduce resolution from that expected from broadening due solely to axial diffusion. Con siderations of capillary diameter demonstrate that, when adsorption is present, small capillaries are advantageous for small molecule solute s (large diffusion coefficients) to minimize the resolution loss. For larger molecules (small diffusion coefficients), small diameter capill aries offer little advantage in performance when adsorption is present as compared to larger capillaries; hence, in this case larger capilla ries are suggested for use because the larger path length gives greate r sensitivity for on-column detection.