Analysis of polymer molecular weight distributions in aqueous two-phase systems.

The partitioning of proteins and other biomaterials between two aqueous phases containing polyethyleneglycol and dextran is a strong function of the molecular weight of the two polymers. Although both polymers are polydispersed (especially Dx) most theoretical treatments refer only to the average molecular weight (number or mass) and assume that the molecular weight distribution of each polymer is the same in both phases. In this work the molecular weight distribution of each polymer is the same in both phases. In this work the molecular weight distributions of four stock solutions of PEG (4000, 6000, 10,000 and 20,000) and four stock solutions of Dx (10,000, 40,000, 110,000 and 500,000) were measured using High Performance Gel Chromatography. The measurements were repeated on the phases formed by the polymer solutions after they were mixed and allowed to equilibrate. The molecular weight distribution of the Dx differed in the top and bottom phase; both differed from that of the stock solution. Although we believe that the molecular weight distribution for PEG also differs in the top and bottom phases, we were unable to determine this within the resolution of our instruments.