Solubility of solids in near-critical conditions: effect of a third component.

The effect of cosolvents on the solubility equilibria near the critical end-point of binary mixtures is analyzed. The problem has received recent attention for the particular case of ionic cosolvents (Mazo, R. M. J. Phys. Chem. B 2007, 111, 7288-7290), where a pronounced salting-out effect was predicted. Here we make a thermodynamic analysis to view the problem from a different perspective. Our conclusions are that, at the critical end-point, the Setchenov constant, which reflects the effect of cosolvents on solubility equilibria, diverges following the behavior of the osmotic susceptibility and that the sign of this divergence is encoded in the critical end-line of the ternary system.