AQUEOUS 2-PHASE SYSTEMS FOR PROTEIN SEPARATION STUDIES ON PHASE INVERSION

Phase equilibrium studies were done with the PEG 400-phosphate system, obtaining equilibrium binodal lines, tie lines and phase inversion po ints. A method of calculation of the critical point on the binodal cur ve is described. The influence of the presence of NaCl in solution was studied, and the comparative results are presented. It was found that in some range of concentration the shift produced in the binodal line can be important. The rate of phase separation can be used as an indi cation of which of the phases is continuous. Using this method the pha se inversion point can be determined in the system for each tie line. A range of ambiguity was found, where the continuity of the phases is affected not only by the composition of the mixture, but also by the f luid dynamics. Within this range, gentle agitation produces a bottom-c ontinuous suspension, while strong agitation produces a top-continuous suspension. Two inversion points exist therefore on each tie line, de limiting on the phase equilibrium plane a region where the phase conti nuity depends on fluid dynamics. The convergence of this region toward s the critical point can be used to control of the consistency of the experimental data. (C) 1998 Elsevier Science B.V. All rights reserved.