Self-sharpening phenomenon arisen by ion-exchange membranes in multi-compartment free-flow isoelectric focusing (IEM-FFIEF)

In this article, the self-sharpening phenomenon arisen by ion-exchange membranes is studied. In order to reduce the overlapped 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 APPO polymers with different amination rates are blended with polysulfone and cast on non-woven clothes by the phase inversion technology. Characterizations of XPS scanning, streaming potential and ion-exchange capacity (IEC) demonstrate that the self-prepared membranes posses different extent of amination and IEC values. The performances of the three prepared APPO membranes with different IEC values are compared. Nine pieces identical solid phase porous APPO membranes are employed in FFIEF instead of pH imbedded gel-like immobiline membrane with a protein mixture comprising bovine serum albumin, myoglobin and lysozyme as a separation model. Experimental results show that membranes with the higher charge density perform not only the higher mass transfer rate, but also the stronger "self-sharpening" function. Therefore, the highly charged porous membranes are favorable in reducing components' overlaps in individual chamber for multi-component protein separations.