CHARACTERIZATION AND SEPARATION OF INORGANIC FINE PARTICLES BY CAPILLARY ELECTROPHORESIS WITH AN INDIFFERENT ELECTROLYTE SYSTEM

The feasibility of using capillary electrophoresis to characterize and separate submicrometer- and micrometer-size metal bil oxide particles (e.g., TiO2, Al2O3, and Fe2O3) was investigated. The use of indiffere nt electrolyte solutions such as sodium nitrate solutions leads to an electrolyte system without specific surface adsorption of ions but wit h essentially only electrostatic interactions between electrolyte ions and the surface of metal oxide particles. This system permitted devel opment of a two-site dissociation model that was then applied to a des cription of the electrophoretic mobility of metal oxide particles as a function of the pH of the indifferent electrolyte solution. The use o f unbuffered solutions, along with the tendency of metal oxide particl es to form aggregates, prohibits the accurate determination of the ele ctrophoretic mobility. Therefore, only a general agreement between the predicted electrophoretic mobilities and the measured values was obta ined using the model. Also, general agreement was achieved between the estimated isoelectric points for the metal oxides and the values repo rted in the literature. Furthermore, the optimum conditions for separa ting mixtures of metal oxide particles in indifferent electrolyte solu tions were identified. Successful separations of different kinds of me tal oxide particles and of metal oxide particles with different polymo rphic forms were achieved.