The Investigation Of Concentration Polarization And Water Splitting Effects In Micro Free Flow Electrophoresis System

Micro-free flow electrophoresis (μFFE) is a unique separation method which is well studied for the pretreatment of proteins and other biological samples, as the separation conditions are mild, and separation can be performed continuously. Usually in μFFE system the electrode reservoir and the separation chamber are isolated by something conductive, such as microchannel, neutral conductive membrane and gel. Ion exchange membrane (IEM) has nano pores with fixed charge on which ion concentration polarization (ICP) and water splitting takes place when an electric filed is applied. ICP effect has been used as a high efficient concentration mechanism in microfluidic system. Water splitting is a common phenomenon in electro-membrane system, and plays a great role in a bipolar membrane system for making acid and alkali.In this thesis IEM was introduced in a homemade μFFE system, and both ICP and water splitting in the separation chamber were studied by means of fluorescence imaging, conductivity and pH measurements of the collected fractions from the system. We observed the depletion zone and the second concentration directly with the fluorescence imaging. The conductivity and pH changes were studied, and it was found that a pH gradient formed. The concentration of H+ under 35 V was increased about five thousand of times in anion exchange membrane system, and the distribution of ions was in agreement with ICP theory.Among the four systems assembled by electrodes and different types of IEM, the pH of solution in separation chamber changed moderately in C system (anode-cation exchange membrane- anion exchange membrane-cathode). Separation of fluorescent probes and proteins were demonstrated with the system, and the effect of voltage, ionic strength and flow rate were investigated. A model mixture of bovine serum albumin, pepsin and cytochrome C were fractionated and characterized by SDS-PAGE. The proteins tended to migrate to the fraction position where the pH was close to their isoelectric points, indicating a typical isoelectric focusing character. It is anticipated that the IEM-FFE system find applications in the pretreatment of charged components and large biological molecules.