Aqueous two-phase systems of Poly (ethylene glycol) and a salt are considered as extraction media for large scale downstream processing of industrially important biomolecules. The present paper deals with such kind of systems with different molecular weights of Poly (ethylene glycol) and sodium citrate salt. The binodal curves corresponding to systems of sodium citrate and Poly (ethylene glycol) of different molecular weights (2000, 3000, 4000, 6000, 10000) g.mol , were determined at pH (5, 7, 9). Moreover, the effect of pH and different molecular weights of Poly (ethylene glycol) on binodal data is observed. An increase in pH caused the expansion of the two-phase area. The binodal curves became more asymmetric and close to the origin with an increase in Poly (ethylene glycol) molecular weight.

Key words: ATPS, Poly ethylene glycol, Sodium citrate, Binodal curve.