Electroosmotlc mobility was determined as a function of pH at constant Ionic strength by using a neutral marker. It was observed that the electroosmotlc mobility was dependent on the preconditioning of the fused silica column. The electroosmotlc mobility values that were obtained from a column previously exposed to acidic conditions for varying periods of time were consistently lower than the values from columns previously exposed to alkaline conditions, particularly in the pH 4-6 region. The equilibration of the surface charge on the fused silica surface appears to be a relatively slow phenomenon. Since the peak area In capillary zone electrophoresis varies Inversely with the solute mobility, attention should be paid to capillary preconditioning, particularly In the pH 4-6 range.

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