Investigation of mass transfer in the ion‐exchange‐membrane‐partitioned free‐flow IEF system for protein separation

Abstract

In this study, novel polysulfone-based cation-exchange membranes with strong mechanical strength have been developed and applied in ion-exchange-membrane-partitioned free-flow IEF (IEM-FFIEF) to replace the conventional immobiline membranes. A fundamental understanding of protein mass transfer in the IEM-FFIEF process has been revealed experimentally with the aid of membrane-based boundary effect model contributed by Ennis et al. we have proven experimentally the existence of a pH gradient across the membrane cross-section when an IEM-FFIEF system is in operation. The boundary effects on particle velocities are calculated based on the IEF assumption and various characterizations, and are compared with the experimental results. In the IEM-FFIEF experiments, a protein mixture (BSA and myoglobin (Mb)) and sulfonated polysulfone membranes with different ion-exchange capacities are applied. 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. This suggests 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. The charge properties of the membrane surface play a dominant role on the separation performance of the membranes. The newly developed porous solid-phase ion-exchange membranes may potentially and effectively replace immobilines to perform the selective function for protein separation.

Synthesis of mosaic membranes and application for egg white protein fractionation by partitioned free-flow isoelectric focusing (FFIEF)

“…these titration results, the states of charging on membranes can be indirectly obtained. This is critical for the mass transfer in an ion-exchange membrane-based electrophoresis, because a membrane's surface -potential is an important factor influencing the mass transfer rate in IEM-FFIEF [16]. As can be seen in Fig.…”

“…For the convenience of discussion, the smallest pore size required for the smallest protein molecule to permeate through the membrane will be defined as the effective pore size. Previous methodologies adapted to calculate and determine effective pore sizes as well as their applications in IEM-FFIEF have been demonstrated in our previous study [16]. In this study, we only focus on the fact that the percentage of pores above the effective pore size is another important parameter constraining the mass transfer rate.…”

“…In our previous work, both the strong cation and the strong anion exchange membranes have been studied and good performances for protein separation have been obtained [15][16][17]. However, the FFIEF separation performance for mosaic membranes (a blend of positively and negatively charged polymers) has never been mentioned in literature previously.…”

“…This chemical modification was confirmed by FTIR spectra in the range of 400-1800 cm −1 . The detailed analysis of FTIR spectra and XPS spectra has been fully explored elsewhere [16,17].…”

“…After prudently comparing the chemical structures and functions of isoelectric membranes with commonly used ion-exchange membranes, Cheng and Chung [15] found that (1) the function of isoelectric membranes can be partially accomplished by an industrial type porous ion-exchange membrane; (2) a narrow range of pH gradients exists in a single membrane cross-section during the operation [16]; (3) a series of pH values (in chambers) queue up in an increasing order of pH values along the electric field direction [17]. Therefore, isoelectric membranes (immobilines) can be replaced by an industrial purpose ion-exchange membrane in MCE to achieve protein separation and concentration.…”