Size-dependent electrophoretic migration and separation of liposomes by capillary zone electrophoresis in electrolyte solutions of various ionic strengths

The size-dependent electrophoretic migration and separation of liposomes wa s demonstrated and studied in capillary zone electrophoresis (CZE). The lip osomes were extruded and nonextruded preparations consisting of phosphatidy lcholine/phosphatidylglycerol in various ratios and ranging from 125 to 488 nm in mean diameter. When liposomes of identical surface charge density we re subjected to CZE in Tris-HCI (pH 8) buffers of various ionic strengths ( 0.001-0.027), they migrated in order of their size. Size-dependent electrop horetic migration and separation of liposomes in CZE can be enhanced or bro ught about by decreasing the ionic strength of the buffer. It was shown tha t size-dependent migration is primarily a function of KR, where K-1 is the thickness of the electric double layer (which can be derived from the ionic strength, I, of the buffer) and R, the liposome radius. Liposome mobility depends on KR and surface charge density in a manner consistent with that e xpected from the Overbeek-Booth electrokinetic theory. Thus, the relaxation effect appears to be the physical mechanism underlying the size-dependent electrophoretic separation of liposomes.