TEMPERATURE-DEPENDENT PHASE INVERSION AND ITS EFFECT ON PARTITIONING IN THE POLY(ETHYLENE GLYCOL)-AMMONIUM SULFATE AQUEOUS 2-PHASE SYSTEM

As temperature is increased, the poly(ethylene glycol) (PEG)-ammonium sulfate aqueous two-phase system exhibits a phase inversion. Specifically, the PEG-enriched phase -which at low temperature is the less dense upper phase- becomes the lower phase at elevated temperatures. The effect depends on the concentrations of PEG and ammonium sulfate in the system, with lower concentrations of either phase-forming constituent causing the inversion to occur at a lower temperature. The partitioning of several solutes is examined in this phase system at temperatures of 20-70 degrees C. The results show that the logarithm of the partition coefficient of each solute is proportional to the PEG concentration difference between the phases (i.e., upper phase concentration minus lower phase concentration), whether this difference has a positive or negative value.