Liquid-liquid equilibria of aqueous two-phase systems containing poly (ethylene glycols) of different molecular weight and sodium citrate

The phase diagrams corresponding to systems of sodium citrate and poly(ethylene glycol) of different molecular weights (600, 1000, 1450, 3350, and 8000) were determined at (22, 37 and 50) degrees C. Moreover, the medium pH (5.2, 8.2, and 9.2) effect was also studied. The binodal curves were described using a four-parameter sigmoidal equation, and the tie-lines were satisfactorily described using the Othmer-Tobias and Bancroft equations. An increase in temperature and 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.