Milan Štědrý

Electroosmosis in capillary zone electrophoresis with non-uniform zeta potential

Abstract The influence of the longitudinally non-uniform zeta potential on processes in capillary zone electrophoresis was studied. The velocity field of the electroosmotic flow in capillary tubes is modelled by the Navier-Strokes equations. Their stationary solution represents connective transport of a solute which is taken into account in the continuity equation for the concentration distribution. All equations are studied numerically. The results represent the time evolution of initials forms of sample peaks. These are presented in graphical form for several cases of zeta potentials which are either instructive or closely related to situations encountered in practice. It is shown that plug-like flow in the capillary cannot be expected and that a non-uniform zeta potential generally leads to significant dispersion of peaks.

Contribution of the electroosmotic flow to peak broadening in capillary zone electrophoresis with uniform zeta potential

An expression is derived which gives the plate height contribution caused by an electroosmotic flow (EOF) in a cylindrical capillary with longitudinally uniform zeta potential. The derivation is made in terms of effective thickness of the electric double layer (an analogue to the Debye length). Typical values of the effective thickness calculated for common situations are given. The resulting expression for the plate height, H eo = β 2 υ eo /D, enables one to calculate the plate height simply as a function of the diffusion coefficient, D, of the solute, the electroosmotic velocity, v eo , and the thickness of the electric double layer, β. The impact of peak broadening by the EOF is compared with that from longitudinal diffusion and extra-column effects for solutes with widely varying diffusion coefficients.