On the Solute-Stationary Phase Interaction in Gas Liquid Chromatography. Relative Retention Values for Mono-substituted Benzene Derivatives and Their Energy Partition by Means of Regression Analysis.

Abstract

Thermodynamic parameters were determined by variable temperature experiments on the gas-liquid chromatography (GLC) relative retention values, log γ, of mono-substituted benzene derivatives. The free energy change ΔΔG°s which is estimated from the enthalpy ΔΔH°s and the entropy ΔΔS°s at 298 K is less than -15kJ·mol-1, corresponding to an interaction between the sample and the liquid stationary phase. With regards to the co-linearlity with the standard entropy S°(B··C) of the complex, between the sample and the liquid stationary phase, an excellent linear relationship of ΔΔS°s with the electron-donating and -withdrawing groups was obtained. The log γ can also be expressed by the linear combination of the descriptors σs°, μ2/α, and σR which are the dispersion and repulsion, the induction and orientation, and the charge transfer interaction energies respectively, and from the evaluation of the standard coefficient by the z-score of log γ, (Edis+Erep)>ECT>(Eind+Eori). Under non-polar conditions, (Edis+Erep) was dominant while under polar conditions, the ratio of [(Eind+Eori)+ECT] increased to the level of (Edis+Erep).