Model for the partition of metal ions in aqueous two-phase systems

A model for the partition of metal ions in aqueous two-phase systems (ATPS) has been developed. The partition coefficient of a metal ion D-M, is a fun ction of several variables of the ion (size, charge and electronegativity), characteristics of the ATPS such as type of salt, salt concentration and P EG concentration and additional inorganic salt present in the ATPS. The mod el has been tested for complex anions of BiX4- (BiCl4- BiBr4- and BiI4-) an d cations from groups I and II (Na+, Cs+, Ca2+, Sr2+ and Ba2+) giving a goo d correlation in both systems. It was found that for these systems partitio n coefficient increases with ion size and the variables Y which is a charac teristic of the ATPS and Z which is a characteristic of the additional salt present in the system. The partition coefficient of BiX4-, increases with the variable X which is a characteristic of the electrical interactions of the metal ion. The cations from groups II and I exhibit the opposite behavi or, which is attributable to the ion charge. (C) 2000 Elsevier Science B.V. All rights reserved.