ELECTROPHORESIS IN SYNTHETIC ORGANIC POLYMER CAPILLARIES - VARIATION OF ELECTROOSMOTIC VELOCITY AND ZETA POTENTIAL WITH PH AND SOLVENT COMPOSITION

The electroosmotic velocity occurring in capillaries made from polyfluorocarbon (PFC), polyethylene (PE) or poly(vinyl chloride) (PVC) was determined by the use of electrically neutral marker substances in dependence on the pH in a solutions. The corresponding zeta-potentials were calculated from the von Smoluchowsky equation. All curves, describing the variation of the electroosmotic velocity and the zeta-potential, respectively, with pH exhibit the same shape, similar to a titration curve, with inflection points at pH 4.8 (PFC and PE) or 5.4 (PVC). With all materials the same value of the zeta-potential of about -60 mV is reached al high pH (at an ion strength of 0.01 mol/L). It can be assumed that the surface charge is originating from the dissociation of carboxylic groups on tho capillary surface. In contrast to fused silica, the adsorption of OH- at high pH seems to play a neglectible role. The addition of organic solvents (ethanol, acetonitrile, or DMSO) to the aqueous buffer drastically reduces the electroosmotic velocity. The zeta-potential, however, changes only to a minor extent in the concentration range of the organic solvent investigated (0-80 % v/v). This result can be explained by the surface properties of the synthetic organic polymers.