Capillaries Modified by Polyelectrolyte Multilayers for Electrophoretic Separations

Abstract

Fused silica capillaries coated with thin films of physically adsorbed charged polymers are employed for capillary zone electrophoretic separations. The coating is a polyelectrolyte multilayer, constructed in situ by alternating rinses with positively and negatively charged polymers. The thickness of the multilayer and amount of surface charge is controlled by the concentration of salt in the deposition solutions. The direction of the electroosmotic flow oscillates as the multilayer surface charge alternates in polarity during buildup. The apparent surface charge, deduced from the electroosmotic mobility, is considerably less than the nominal surface charge of the film. Mechanisms limiting this apparent surface charge for a buffer-permeable layer are discussed. The multilayer-coated columns exhibit many desirable features in addition to ease of construction and reproducible control of electroosmotic flow: stable flow rates are achieved immediately on exposure of the column to running buffer, and reversed flow is possible. Columns are also found to be stable to extremes of pH and ionic strength, and to dehydration/rehydration. A series of basic proteins are separated with good efficiency, demonstrating column resistance to irreversible protein adsorption. Partitioning and separation of neutral solutes using thicker films is demonstrated.