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Abstract

With a fused silica capillary tube, a streaming potential can be created when an electrolyte solution is forced through the tube from one reservoir to another, carrying the excess surface charges of the capillary surface to the outlet reservoir. When the resistance from the excess charges in the outlet reservoir reached an equilibrium with the moving surface charges from the capillary surface, a steady streaming potential can be measured between the inlet and outlet vials while a constant pressure is applied across the capillary. Chapter 1 introduced the technology of capillary electrophoresis (CE), the apparatus used for CE for chemical separation, and principles and theory of streaming potential measurements. Chapter 2 shows that changes in streaming potential can be used to characterize the properties of the capillary inner surface to improve CE performance. We demonstrated that capillary surface conditions can significantly change the streaming potential, and we showed that analyte dependent adsorption can be monitored and mitigated to improve the peak symmetry and migration times reproducibility. Chapter 3 explores the use of streaming potential to study the physicochemical properties of surfactants. Unlike other reported methods of determining CMC, streaming potential can be used as the physical parameter to reflect the abrupt changes in the properties of surfactants in this new method. We demonstrated that this new method can be used to determine the CMC of both ionic and nonionic surfactants. In chapter 4, numerical modeling of Taylor dispersion analysis (TDA) was performed using COMSOL Multiphysics to facilitate better and faster optimization of the experimental conditions. Parameters such as effect of pressure, diameter and length of capillary on the TDA conditions was examined for particles of different sizes. Also, the effect of the electric field on the validity and the applicability of TDA was studied using CE. We found that TDA can be used with the combination of electrophoretic migration and electroosmotic flow, but appropriate conditions must be met. The last chapter combines the work from chapters 3 and 4, demonstrating that measured streaming potentials combined with TDA can be used to characterize the CMC and hydrodynamic radius of micelles.