Solubility Parameter of Ionic Liquids: A Comparative Study of Inverse Gas Chromatography and Hansen Solubility Sphere

The solubility parameters of four ionic liquids (ILs), 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MeSO4]), 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]), 1-hexyl-3-methylimidazolium methyl sulfate ([HMIM][MeSO4]), and 1-octyl-3-methylimidazolium methyl sulfate ([OMIM][MeSO4]), were estimated using two complementary methods. The first is an inverse gas chromatography (IGC) method, which determined the Hildebrand solubility parameters of four ILs based on a series of formulaic calculations. The second is the Hansen solubility sphere method, which determined the Hansen solubility parameters (HSPs) of the four ILs based on solubility testing of four ILs in 30 pure solvents. The results showed that the Hansen solubility sphere method provides higher values of the solubility parameters, while the IGC method presents lower values. In addition, the miscibilities of ILs in various solvents were evaluated by the method of IGC, and the results exhibit good agreement with those derived from the Hansen solubility sphere method. It is confirmed that the IGC and Hansen solubility sphere methods can be used to determine the solubility parameters of the ILs and were useful for solvent selection.