Effect of Electrical Double-Layer Overlap on the Electroosmotic Flow in Packed-Capillary Columns

A plug electroosmotic velocity profile is generally assumed to be characteristic of capillary electrochromatography. However, this ideal plug flow may be illusive in some experiments with packed-capillary columns due to overlap of electrical double layers in flow channels. We report here a theoretical analysis of the double-layer overlap effects in packed-capillary columns, which is based on Rice and Whitehead's theory of electroosmotic flow combined with a capillary tube model for porous packing. The results show that the electroosmotic velocity under the influence of double-layer overlap depends strongly on the operating parameters, which increases with the column porosity, the particle diameter, and the electrolyte concentration.