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 indifferent electrolyte solutions such as sodium nitrate solutions leads to an electrolyte system without specific surface adsorption of ions but with essentially only electrostatic interactions between electrolyte ions and the surface of metal oxide particles. This system permitted development of a two-site dissociation model that was then applied to a description of the electrophoretic mobility of metal oxide particles as a function of the pH of the indifferent electrolyte solution. The use of unbuffered solutions, along with the tendency of metal oxide particles to form aggregates, prohibits the accurate determination of the electrophoretic mobility. Therefore, only a general agreement between the predicted electrophoretic mobilities and the measured values was obtained using the model. Also, general agreement was achieved between the estimated isoelectric points for the metal oxides and the values reported in the literature. Furthermore, the optimum conditions for separating mixtures of metal oxide particles in indifferent electrolyte solutions were identified. Successful separations of different kinds of metal oxide particles and of metal oxide particles with different polymorphic forms were achieved.