Partitioning of organics between ionic liquids and supercritical CO2: Limiting K-factors in [bmim][N(CN)2]–scCO2 system and generalized correlation with cation- and anion-specific LSERs

• Solute–[bmim][N(CN)2]–CO2 systems were studied by supercritical fluid chromatography.
• Solute retention factors were converted to solute K-factors.
• Hiraga model including linear solvation energy relationships was used for K-factors.
• [bmim][N(CN)2]–CO2 system K-factors were modeled from those in other IL–CO2 systems.
• Ionic liquid cation- and anion-specific LSERs improved the fit.

Infinite dilution partition coefficients (K-factors) of a selection of organic solutes in biphasic 1-n-butyl-3-methylimidazolium dicyanamide ([bmim][dca])–supercritical carbon dioxide (scCO2) system were obtained from retention measurements by open tubular capillary column supercritical fluid chromatography (SFC) with [bmim][dca] serving as the stationary liquid and scCO2 as the carrier fluid. Therefore, the SFC-based route to solute K-factors in ionic liquid (IL)–scCO2 systems is feasible even with low viscosity ILs such as [bmim][dca].The experimental K-factors in [bmim][dca]–scCO2 system were used to test an earlier generalized correlation of solute K-factors in IL–scCO2 systems. Further, another version of the generalized correlation was introduced and tested. In the linear solvation energy (LSER) part of the former correlation the IL has been treated as a single species whereas, in the new version, the IL cation- and anion-specific LSER part has been employed. The introduction of the ion-specific LSERs resulted in some performance improvement of the correlation.

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