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The natural alkaloid quinine (QN) was immobilized on porous silica particles, and part of the material was subsequently endcapped with n-hexyl hydrocarbon chains. Two synthetic strategies for silanization of the support were first compared. These columns were thoroughly evaluated in order to study the influence of endcapping in the enantiorecognition features. Enantioseparations of twenty N-derivatized 2,4-dinitrophenyl α-amino acids (DNP-amino acids) were studied by changing mobile phase pH, buffer concentration, type of organic solvent in the mobile phase, and column temperature. Maximum retention factors were observed at pH ≈6, at this intermediate pH the tertiary amine of the quinine is protonated to a high degree and therefore available for strong electrostatic interactions with unprotonated anionic DNP-amino acids. The enantioselectivity factors, however, increased as the pH did in the range between 5 and 7. The increase in ionic strength had influence on retention, but not on enantioselectivity, allowing the use of this variable for optimization of retention factors. Finally, the thermodynamic transfer parameters of the enantiomers from the mobile to both CSPs (with and without endcapping, QN-CSP(EC) and QN-CSP, respectively) were estimated from van't Hoff plots within the range of 10-40 °C. Thus, the differences in the transfer enthalpy, Δ(ΔH°), and transfer entropy, Δ(ΔS°), enabled an investigation of the origin of the differences in interaction energies., (Published by Elsevier B.V.)

The solvation behavior of n-alkanes on poly(oxyethylene) was studied employing capillary gas chromatography. Interfacial effects were discriminated and evaluated through the analysis of retention data from six commercial fused-silica capillary columns, having film thicknesses of 0.15-5 microm. Expressions for the mixed retention mechanism in capillary columns were deduced from assumptions of a general character. Partition coefficients were determined for the n-alkanes up to 28 carbon atoms, at temperatures ranging from 40 to 240 degrees C. In agreement with other authors, it was observed that interfacial phenomena contribute poorly to the chromatographic retention, being negligible over 140 degrees C for homologues with less than 16 carbons.

Retention volumes of 21 aliphatic alcohols were measured at five temperatures between 30 and 60 degrees C in columns packed with different percentages of squalane or with solutions of tri-n-octylphosphine oxide (TOPO) in squalane coated on previously deactivated Chromosorb W. Experimental data fit to a 1:1 alcohol-TOPO association model, with association constants ranging from 26 to 59 dm3 mol(-1) at 45 degrees C. Association constants follow the trend primary alcohols>secondary alcohols>tertiary alcohols, with minor differences between the members of each of these three groups. The association enthalpy for the 21 alcohols averages -21.8 kJ mol(-1), with a standard deviation of -1.3 kJ mol(-1).

In this communication, we revise some aspects of the [ideal gas/Van der Waals fluid] partition, derived in an earlier publication. The general character of the conclusions concerning the dependence of the partial molar free energy of solution, deltaGs(n), on the chain length, n, of linear solute molecules is shown through the relationship with more general partition formulations. Simultaneously, the correction of an error in the expression of the retention time dependence on the phase ratio of the chromatographic column, beta, is carried out. The misleading source of this error was redundant accounting in the solute translational contribution to deltaGs(n).

Thermodynamic properties of solution in 3-methylsydnone (3MS) and of adsorption at the nitrogen/3MS interface were gas chromatographically measured for a group of fifteen hydrocarbons at infinite dilution conditions. Retention volumes were measured at five temperatures within the range 37-52°C in six columns containing different loadings of 3MS on Chromosorb P AW. Partition and adsorption coefficients were calculated and from their temperature dependence the corresponding enthalpies were obtained, although with considerable error; infinite dilution activity coefficients of the hydrocarbons in the bulk and in the surface phases demonstrated a strong correlation. Bulk activity coefficients in 3MS were very much smaller than those previously measured for the same solutes in formamide (FA) and in ethyleneglycol (EG), and were also smaller than what could be predicted on account of 3MS cohesive energy density as estimated from the quotient sigma/v1/3 (sigma, surface tension; v, molar volume). There was not such a large difference between the surface activity coefficients in the three solvents; furthermore, the quotients (surface activity coefficient/bulk activity coefficient) for a given solute in 3MS were twice as large as in FA and about three times larger than in EG. These results make evident the difficulties inherent in the prediction of surface phase properties from those in the bulk and cast doubts on the pertinency of employing the surface tension to compare cohesive energy densities of polar solvents with important chemical differences.