Citation: CHENG JIUHUA (2009-09-24). Protein separation in ion-exchange membrane partitioned free -flow isoelectric focusing (IEM-FFIEF) system. ScholarBank@NUS Repository.
Abstract: Ion Exchange Membrane Partitioned Free-Flow Isoelectric Focusing (IEM-FFIEF) is an emerging separation process combining both membrane technologies and electrophoresis technologies in a series of separated chambers. Driven by electric field, IEM-FFIEF allows charged species freely migrate in bulk solutions, selectively cross the membranes and pre-determinedly be concentrated in a certain chamber. Hence, IEM-FFIEF is practically effective and economically feasible for the separation of protein mixtures as well as other bio-products from plasma or fermentation broth. The purpose of this work is to explore the feasibility of IEM-FFIEF, to fabricate high performance protein separation ion exchange membranes, and to investigate the effects of various factors on separation performance. Emphases are placed on the understanding of mass transfer across the separation membrane under an environment of isoelectric focusing. This study firstly investigated the feasibility of a combination of membrane technology and the Free-Flow Isoelectric Focusing (FFIEF) technology for a high-performance protein separation, in which ion exchange membranes are used as the separation media. A FFIEF device has been designed and extensive experiments have been conducted to prove its efficacy in enhancing the protein separation performance. This work clearly demonstrates the great potential of FFIEF for industrial applications. Moreover, experimental results in the consecutive semi-batch operations suggests that the membrane fouling phenomenon is not severe, and high reproducibility in separation fluxes can be realized in our designed IEM-FFIEF system. Secondly, this study was then extended to the investigation of protein mass transfer in IEMFFIEF system. A series polysulfone based cation-exchange membranes with strong mechanical strength have been developed and applied in free-flow isoelectric focusing (IEMFFIEF). A fundamental understanding of protein mass transfer in the IEM-FFIEF process has been revealed experimentally. Experimental results show that the real velocity and real mobility (of Mb in this study) are comparable with the mathematic model developed by Ennis et al. These results suggest that the equation proposed by Ennis et al. is sufficient to capture the mass transfer through membrane in the IEM-FFIEF system after considering the effects of pore size distribution and effects of disturbed electric field. Thirdly, a very unique phenomenon - self-sharpening arisen by ion-exchange membranes is studied in this research work. In order to reduce the overlapping components in a single chamber, aminated poly(2, 6-dimethyl-1, 4-phenylene oxide) (APPO) based anion-exchange membranes are applied in free-flow isoelectric focusing (FFIEF) instead of conventional immobiline membranes as the selective mass transfer media. The protein mixture comprising bovine serum albumin (BSA), myoglobin (Mb) and lysozyme (Lys) is used as feed solution. Experimental results show that membranes with a higher charge density not only can affect a higher mass transfer rate, but also strengthens the ¿self-sharpening¿ function greatly. Therefore, highly charged porous membranes are favorable in reducing the amount of overlapping components in individual chambers for multi-component protein separations. Fourthly, by means of amination with diamine and methylation with methyl iodide, we have modified P84 microporous polyimide membranes with characteristics of highly charged anion-exchange membranes. By using the newly developed membranes, a free-flow isoelectric focusing (IEM-FFIEF) has been set up for the separation of myoglobin (Mb) and lysozyme (Lys) mixtures. Experimental data show that (1) the Mb flux via the highly charged P84 anion-exchange membrane can be 10 times higher than that of the original P84 membrane and (2) the high surface charge is the predominant factor for the enhanced Mb flux.