Equilibrium Phase Behavior of Poly(propylene glycol) + Potassium Phosphate + Water Two-Phase Systems at Various pH

The phase diagrams and compositions of coexisting phases have been determined for aqueous two-phase systems containing poly (propylene glycol) with average molecular weight of 425 and potassium phosphate at various pH of 5.32, 6.13, 6.79, 7.36 and 7.91. The effect of pH on the salting-out effect of poly (propylene glycol) by phosphate has been studied. It was found that, an increasing in pH caused the expansion of two-phase area; while, for the salt-rich region, expansion of the two-phase area was observed with increase in the pH. It was also observed that the slope of all equilibrium tie -lines increased with increasing pH. Furthermore, it was found that, Increasing pH also increases the concentration of PPG in the polymer rich phase, resulting in a higher difference in PPG and phosphate concentrations between the top and bottom phases.

Keywords:

Aqueous two-phase system , Phase equilibrium , poly (propylene glycol) , potassium phosphate.