Detection of small differences in the hydrophilicity of ions using the LCST-type phase transition of an ionic liquid-water mixture.

The phase separation temperature of the tetrabutylphosphonium trifluoroacetate-water mixture, which undergoes a lower critical solution temperature-type phase transition, is highly sensitive to the hydrophilicity of added salts; this system can be used to compare the hydrophilicity of the added ions.