ELECTROKINETIC DEMIXING OF 2-PHASE AQUEOUS POLYMER SYSTEMS .1. SEPARATION RATES OF POLYETHYLENE-GLYCOL DEXTRAN MIXTURES

The separation of biomolecules and cells using aqueous two-phase systems provides a mild, nontoxic extraction medium, in contrast with conventional organic-aqueous phase extraction. However, due to their similar physical properties, immiscible aqueous phases do not separate rapidly. Because a net surface potential occurs on phase droplets due to the unequal partitioning of certain dissolved ions, a study was undertaken in which the resulting motion in an electric field (electro-phoresis) was explored as a possible method for rapid demixing of aqueous two-phase systems in a vertical electrophoresis column. The effects of electric field strength, buffer concentration, and field polarity on the demixing rate of mixtures of polyethylene glycol and dextran in phosphate buffer were measured. It was found that an optimum field strength of around 29.2 V/cm exists at which demixing is most rapid and occurs at about twice the rate in zero field at 25 ± 2°C using normal polarity (anode at the top of the column). With reverse polarity (anode at the bottom; electric field opposing gravitational settling) at a field strength of 14.6 V/cm the rate was 3 times as fast as in zero field. Strong convection was observed at high field strengths. Increasing the phosphate concentration increased the demixing rate. © 1990, Taylor & Francis Group, LLC. All rights reserved.