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This paper extends the theory of gas-chromatographic elution of a highly dilute solute to the second order in gas-phase imperfection terms, yielding a precise expression for the ideal retention volume in terms of the thermodynamic parameters of the system. The effect of carrier gas dissolution in the solvent is included explicitly ; the cross-term second virial coefficient Bl for the system solute+ carrier gas cannot be evaluated unambiguously for an appreciably soluble carrier gas. The use in such cases of polar solvents in which non-polar carrier gases are effectively insoluble is discussed with reference to surface adsorption and chromatographic non-ideality, which are important in polar solvents. Extrapolation of observed retention volume to zero flowrate for each of a series of columns covering a range of solvent loadings should give, corresponding to the limit of infinite loading, unambiguous values of bulk-phase solutein-solvent activity coefficient and of B1 2. The theory has been applied to measurements on the systems benzene+nitrogen+glycerol, and benzene+ carbon dioxide+glycerol, using four columns loaded at 15-7,25.3,33*6 and 23-3 % by weight glycerol on Celite, and the system benzene+hydrogen+glycerol using a column loaded at 44.0 %. The flowrate-dependence of the net retention volume is approximately linear on all columns, the gradient correlating well with empirical plate height and with solvent loading, in accordance with theory and with the known facts about the distribution of a polar solvent on Celite. The zero-flowrate Biz values are effectively the same with all columns. These values of Blz at 50°C are, for benzene+ nitrogen, -98f9 cm3 mole-l, and for benzene+carbon dioxide, -2503~15 cm3 mole-l, both being in fair agreement with theoretical predictions for systems of non-spherical molecules of different sizes. The activity coefficient for benzene at infinite dilution in glycerol at 50°C is logy: = 2.0841 0 0 0 5 .

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Ionic liquids, with their very low vapor pressures and unique solvent properties, are potentially useful solvents for separating organic liquid mixtures by solvent extraction or by extractive distillation. In this work, the activity coefficients at infinite dilution, , for both polar and nonpolar solutes in the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate have been determined by gas−liquid chromatography at the temperatures (298.15, 313.15, 323.15) K. The partial molar excess enthalpies at infinite dilution and the selectivity values were calculated from the values obtained over the temperature range. The selectivity values have been determined and are used to predict the solvent potential of the ionic liquid for the separation of liquid mixtures by extractive distillation.

The activity coefficients at infinite dilution, γ 13 ∞ , for both polar and nonpolar solutes in an ionic liquid, 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM + ][BF 4 -]), have been determined by gas-liquid chromatography at T ) (298.15 K and 323.15 K). This work is part of our research focus on ionic liquids. The selectivity values have been calculated at T ) 298.15 K, and the results indicate that the ionic liquid, [HMIM + ][BF 4 -], should be a good solvent for separation of benzene and alkanes. The partial molar excess enthalpy values at infinite dilution have also been determined at T ) 298.15 K and have been discussed in terms of intermolecular interactions. The results have been discussed in terms of measurements of γ 13 ∞ , using other ionic liquids, taken from the recent literature.

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The activity coefficients at infinite dilution, , for both polar and nonpolar solutes in the ionic liquid 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) imidate have been determined by gas−liquid chromatography at the temperatures T = 303.15 K and T = 318.15 K. The results have been used to predict the solvent potential for the hexane−benzene separation using the calculated selectivity values. The results are compared to the for similar systems found in the literature in an attempt to understand the effect that the nature of the cation has on the solute−solvent interactions. The partial molar excess enthalpies at infinite dilution values, Δ , were calculated from the experimental values obtained at the two temperatures.