Electroosmotic Dispersion in Micro‐Channels and its Implications

Dispersion of a non‐electrolyte solute due to the electroosmotic flow through a long straight micro‐channel is analyzed theoretically. Two sources of dispersions are considered, namely, the departure from adsorption equilibrium for the solute under consideration and the non‐uniformity of the flow velocity within the channel cross‐section. Two types of electroosmotic velocity non‐uniformity, which result in dispersion, are taken into account: the non‐uniformity of electroosmotic flow within the double layer region and the non‐uniformities of parasite pressure driven flow which often accompanies electroosmosis. Analytical expressions are obtained to address dispersion in terms of plate height for arbitrary magnitude of electric surface potential, electrolyte composition and cross‐section geometry. It is discussed how the predicted plate height depends on the cross‐section geometry, electrokinetic potential, electrolyte content, adsorption isotherm and adsorption rate constant.