Dependence of the electroosmotic mobility on the applied electric field and its reproducibility in capillary electrophoresis.

Experimental results on the electroosmotic mobility in fused-silica capillaries are presented for different applied voltages and solutions of different pH. The electroosmotic mobility is shown to be dependent on the applied voltage and this dependence cannot be attributed to the temperature effects. Results of the electroosmotic mobility measurements are found to be dependent also on the electrophoresis unit they have been performed in. The explanation given and the relevant theory presented are based on the hypothesis that these effects are produced by a radial electric field inevitably existing in any electrophoresis unit. The concept of the limiting electrophoretic mobility, i.e. extrapolated to the zero applied voltage, is introduced in order to characterize the properties of the solution-wall interface. The slope of the electroosmotic mobility dependence on the applied voltage depends on the solution pH and the surroundings of the capillary. Theoretical estimations agree well with both experimentally found limiting mobilities and slopes. Long-term variations of the electroosmotic mobility are supposed to be related with the cation penetration into the capillary wall.