1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF(6)) was synthesized and purified to be used as a ionic liquid solvent. Its physicochemical properties were studied. The ionic liquid/water (P(il/water)) and ionic liquid/heptane (P(il/heptane)) distribution coefficients of a set of 40 compounds with various functionalities, including organic acids, organic bases, amino acids, antioxidants, and neutral compounds, were measured using liquid chromatography. For ionizable compounds, the P(il/water) values measured at pH 2, 5.1, and 10 were very different. These allowed the determination of both the molecular P(o)il(/water) values and the ion P(-)il(/water) value for each compound. These coefficients were compared to the corresponding P(oct/water) coefficients. Marked differences in the partitioning behavior of basic, acidic, and neutral compounds were observed. The relationship between P(il/water) and P(oct/water) is different from that reported previously. By using the linear free energy solvation approach and the descriptors found for 12 solutes, the BMIM-PF(6) solvent parameters were calculated for the ionic liquid/water and ionic liquid/heptane biphasic systems. The regression parameters show a low basicity of the BMIM-PF(6) solvent compared to octanol. The high cohesion of the ions in the ionic liquid phase is also indicated by the regression equations obtained. Ionized phenols (phenoxide ions) associate more strongly with BMIM-PF(6) than most other ionized molecules. Amino acids were not soluble in ionic liquid; however, it is possible to extract them partially by adding a crown ether to the ionic liquid phase and working at pH 1. The positive form of amino acids is complexed by the crown ether and the complex is extracted in the ionic liquid phase.

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Countercurrent chromatography (CCC) is a liquid chromatography technique with a liquid stationary phase. Taking advantage of the liquid nature of the stationary phase, it is possible to perform unique operations not possible in classical liquid chromatography with a solid stationary phase. It is easy to avoid any solute-irreversible absorption in the CCC column. If the retention volumes of solutes become too high, the dual mode will be used. The roles of the phases are reversed. The stationary phase becomes the mobile phase, and the CCC column is started again. The solutes elute rapidly in what was previously the stationary phase. The theoretical basis of the dual-mode method is recalled. The dual-mode method is a discontinuous method. The separation should be stopped when the phase switch is performed. The elution-extrusion procedure is another way to avoid any irreversible adsorption of solutes in the column. The method uses the fact that the liquid volumes occupied by the solutes highly retained inside the column can be orders of magnitude lower than the mobile-phase volume that would be needed to elute them. The elution-extrusion method also has two steps: the first step is a regular CCC chromatogram. Next, the stationary phase containing the partially separated hydrophobic solutes is extruded out of the column in a continuous way using the liquid stationary phase. The theory of the process is developed and compared to the dual-mode theory. Alkylbenzene homologues are experimentally used as model compounds with the heptane/methanol/water biphasic liquid system to establish the theoretical treatment and compare the performance of two types, hydrodynamic and hydrostatic, of CCC columns. It is shown that the method can dramatically boost the separation power of the CCC technique. An apparent efficiency higher than 20 000 plates was obtained for extruded octylbenzene and a 160-mL hydrodynamic CCC column with less than 500 plates when conventionally used.