Aqueous Biphasic Systems. Properties and Applications in Bioseparation

Abstract

The first experiments on partition of cells and cell particles in aqueous polymer phase systems were carried out in 1955 and published in 1956.1 These experiments involved the use of one polymer, polyethylene glycol (PEG), together with water and potassium phosphate and the partitioned particles were bacteria, algae, chloroplast fragments, cell walls, and starch grains. It was shown that these particles partitioned either completely to one phase or the other, or they were adsorbed at the liquid-liquid interface. These results agreed with what one would expect from the theories by Bronsted2 and De Courdes.3 Later several phase systems with two incompatible polymers were characterized by phase diagrams4 and used for partition experiments with cell particles4 and proteins.5,6 Essentially, these studies showed that proteins could be dissolved and equilibrated between the phases with a reproducible partition coefficient. Separation could be achieved either by a batch procedure or by countercurrent distribution. In the case of particles, the selective adsorption at the interface could also be used for separation in a multistage process such as countercurrentdistribution.7 Thus, cells and cell organelles were analyzed for heterogeneity by countercurrent distribution, a procedure which is reminiscent of liquid-liquid chromatography for soluble small molecules.