Comparison of two aqueous biphasic systems used for the partition of biological material.

Two biphasic systems, both consisting of water, dextran and poly(ethylene glycol) but differing in the molecular weight of the latter polymer, Mr = 35 000 (systems A) and 6000 (systems B), have been studied. The phase diagrams for the two systems at 20 degrees are compared. The partition of proteins influenced by salts and the viscosity of the phases are direct functions of the difference in composition between the upper and the lower phase as measured by the lengths of the tie-lines found for the systems in the phase diagram. The solubility of gamma-globulin is 1.5-2 times larger in an A system than in a B system with corresponding tie-line. In both systems, poly(ethylene glycol) palmitate has less effect on the partition of serum albumin than would be predicted from the distribution of poly(ethylene glycol) and reflects the non-ideality of simple equilibrium models.