Partition Coefficients of Low-Volatility Solutes in the Ionic Liquid 1- n -Butyl-3-methylimidazolium Hexafluorophosphate−Supercritical CO 2 System from Chromatographic Retention Measurements

Room temperature ionic liquid (RTIL) 1- n -butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) was employed as the stationary liquid in capillary column chromatography with supercritical carbon dioxide (scCO 2 ) as the mobile phase. Open tubular capillary columns were used to measure the retention factors of anisole, azulene, benzil, α-ionone, naphthalene, pyrene, and veratrole within 313−353 K and 8.1−23.2 MPa. The retention factors were converted to infinite-dilution solute partition coefficients in the [bmim][PF 6 ]−scCO 2 system. Analysis of the relative retention data by regular solution theory resulted in approximate values of the solubility parameter of CO 2 -expanded [bmim][PF 6 ]. Open tubular supercritical fluid chromatography appears to provide a viable method for rapid acquisition of partitioning data on low-volatility solutes in biphasic RTIL−scCO 2 systems.