Some problems of zeta potential determination in electrophoretic measurements on lipid membranes

Electrophoretic mobilities were measured for cardiolipin, phosphatidylinositol and phosphatidylserine liposomes in solutions of potassium chloride. The zeta potential as a function of ionic strength deviates significantly from the predictions of the double-layer theory in the 10(-3)-5.10(-2) M range. This might be due to changes in pH in the course of the experiment and/or to the inapplicability of the Smoluchowski equation at low ionic strengths. Taking into account the relaxation effects results in theoretical curves, calculated for various particle sizes at low ionic strength, which are in better agreement with the experiment. However, for quantitative comparison with experimental data, further investigations are necessary.