The subject of salt effect is of both fundamental and applied interest in the viewpoint of . . thermodynamics, where its study provides considerable information about solute-solute and ·solute-solvent interactions. The salt effect can be defmed as the change in the solubility of solute 1 in solution caused by the addition of the solute 2, which is a more solvent familiar than the former solute. If by addition of solute 2 to solution containing solute 1, the activity coefficient of solute I in solution decreases, which results in increasing its solubility, it could be argued that salting-in phenomenon has been occurred. While decreasing the solubility (or increasing the activity ·coefficient) of solute 1 in solution by the addition of solute 2 can be named the salting-out effect. In the case of salting-out effect, by addition of solute 2 to a solute 1-water solution, solute I may be transferred from the solution to a gas phase (study of salt effect on the solubility of gases in· ·aqueous solution and the study of composition of vapor phase, which is in equilibrium with a liquid ·phase), solid phase (the effect of added salts on the solubility and stability of biological materials, especially proteins), pseudo-phase (salt effect on the micellization and surface behavior of surfactants in aqueous solutions) or another liquid phase (formation of aqueous biphasic systems, (ABSs)). Since ABSs have a widespread use in biochemistry and biotechnology for purification, extraction, and enrichment ofbiomolecules, cells, cell particles, anions and cations, etc., the study of salt effect on the formation of ABSs is a highly significant subject. ABS consists of two immiscible aqueous-rich phases in which each phase contains mainly one of the compounds and a small amount of the other, with water as solvent in both equilibrium phases. The aqueous nature of both phases as well as difference in their properties makes it possible to use them for the partitioning and separation of biolo
