Measurement and correlation of water activity of aqueous solutions of sodium tungstate + poly(ethylene glycol) 6000 at 298.15 K

Aqueous two-phase systems (ATPS) are formed when two incompatible polymers or a polymer and a salt are dissolved in water,with the first polymer predominating in one phase and the second polymer or the salt predominating in the other phase. ATPS can be useful for the separation of various biological materials, [1-3]. It has been found that the polymer + salt aqueous two-phase systems have more advantages than the polymer + polymer aqueous two-phase systems such as low cost, low viscosity, and a short time for phase splitting. In an ATPS, water constitutes the bulk component of the two phases and therefore water is a special and key component and closely related with the other two phase-forming components. Thus,the thermodynamic properties of water in these systems should be paid great attention. Also, the activity is an important and key thermodynamic property, because, it is closely related with the other thermodynamic properties and in thermodynamic modeling for separation methods, it is the essential variable. In this study, water activities of the binary aqueous sodium tungstate (Na2WO4) solutions and ternary polyethylene glycol (PEG) + Na2WO4 + H2O system have been determined experimentally using an improved isopiestic method [4] at 298.15 that have not been previously published. The segment-based local composition Wilson and NRTL model [5, 6] has been used for the correlation of the experimental water activity data.