No abstract

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, R-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.

Monolithic capillary columns have been prepared in fused-silica capillaries by radical co-polymerization of ethylene dimethacrylate and butyl methacrylate in the presence of porogen solvent mixtures containing various concentration ratios of 1-propanol, 1,4-butanediol, and water with azobisisobutyronitrile as the initiator of the polymerization reaction. The through pores in organic polymer monolithic columns can be characterized by "equivalent permeability particle size", and the mesopores with stagnant mobile phase by "equivalent dispersion particle size". Increasing the concentration of propanol in the polymerization mixture diminishes the pore volume and size in the monolithic media and improves the column efficiency, at a cost of decreasing permeability. Organic polymer monolithic capillary columns show similar retention behaviour to packed alkyl silica columns for compounds with different polarities characterized by interaction indices, I x , but have different methylene selectivities. Higher concentrations of propanol in the polymerization mixture increase the lipophilic character of the monolithic stationary phases. Best efficiencies and separation selectivities were found for monolithic columns prepared using 62 -64% propanol in the porogen solvent mixture. To allow accurate characterization of the properties of capillary monolithic columns, the experimental data should be corrected for extra-column contributions.

Open-tubular capillary-column supercritical fluid chromatography (SFC) with the room-temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as the stationary liquid and supercritical carbon dioxide (scCO2) as the mobile phase was employed to measure solute retention factors within 313-353 K and 8.1-23.2 MPa. The selection of solutes included 18 compounds of diverse volatilities and chemical functionalities. The retention factors were converted to infinite-dilution solute partition coefficients in the biphasic [bmim][BF4]-scCO2 system. At a constant temperature, an increase in scCO2 density produced distinct shifts in relative retention (=separation factor), thus providing some pressure-tunable selectivity. At a particular temperature and density of CO2, solute partition coefficients can be correlated in terms of linear solvation energy relationships. This important finding indicates a future possibility to estimate the partitioning data in RTIL-scCO2 systems using limited experimental information and the molecular descriptors available for a large variety of prospective solutes. Analysis of the relative retention data by regular solution theory resulted in approximate values of the solubility parameter of CO2-expanded [bmim][BF4].

Limiting partition coefficients of a selection of low-to-medium volatility solutes between both phases in a biphasic trihexyltetradecylphosphonium chloride ([thtdp][Cl]) ionic liquid (IL)-supercritical carbon dioxide (scCO2) system were obtained by capillary column chromatography with [thtdp][Cl] as the stationary liquid and scCO2 as the carrier fluid. It is shown that supercritical fluid chromatography can be used to probe the partitioning behavior of solutes in biphasic IL-scCO2 systems even when the IL has nonzero solubility in scCO2. Relative partition coefficients of solutes at a particular temperature and density of CO2 can be correlated within Abraham's linear solvation energy relationships. Compared with our previous results in a [bmim][BF4]-scCO2 system, the solute partition coefficients in the [thtdp][Cl]-scCO2 system are more sensitive to the solute hydrogen bond acidity descriptor.