Selectivity of the stationary phase in gas-liquid chromatography

The use of molar refractions is insufficient to describe the retention volumes and thermodynamic functions of solutions in nonpolar stationary phases. The heats of dissolution of monofunctional derivatives of the alkanes are proportional to the polarizability and inversely proportional to the sixth power of the van der Waals' radius of the interacting particles. The heat of dissolution of substances being analyzed, with the same number of carbon atoms, in aromatic solvents depends on the conditions of contact between the molecules of the substances being analyzed and the benzene rings of the solvent. The order of the heats of dissolution of substances being analyzed in different nonpolar solvents does not remain the same, indicating that the theory of regular solutions cannot be applied to these systems. To determine the order of the heats of dissolution of isomers in nonpolar stationary phases it is necessary to take account of the electron density distribution in the molecules of the reacting substances and the probability of molecular arrangement for the most favorable interaction.