Electrokinetic Demixing of Two-Phase Aqueous Polymer Systems. II. Separation Rates of Polyethylene Glycol–Maltodextrin Mixtures

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Abstract
Aqueous two-phase extraction techniques have been successfully applied to the purification of enzymes and cells. However, due to their similar physical properties, immiscible aqueous phases do not separate rapidly. A method for enhanced demixing of aqueous two-phase systems in a thermostated vertical electrophoresis column was therefore studied. The effects of the electric field strength, field polarity, temperature, phase composition, and buffer concentration on demixing rates of a polyethylene glycol-maltodextrin (PEG-MDX) system were quantitatively measured. At normal electrical polarity (anode at the top of the column), using a maximum practicable field strength of 26.4 V/cm, the demixing rate was twice that in zero electric field at 25 ± 2°C. With poiarity reversed (anode at the bottom, electric field opposing gravitational settling) at a field of 26.4 V/cm, demixing was 5.5 times as fast as in zero field. Reduction of the temperature from 25 to 14°C caused an increase in demixing rate in the absence of an applied field, while reduced temperature did not change the rate when using electric fields of either normal or reverse polarity. Increased phosphate buffer concentration substantially increased the demixing rate for PEG-MDX mixtures.