Solvation molar enthalpies and heat capacities of n-alkanes and n-alkylbenzenes on stationary phases of wide-ranging polarity

A comparison of the most usual gas chromatographic methods for the calculation of partial molar enthalpies of solvation (ΔsolHo) has been carried out. Those methods based on the fitting of lnVg or ln(k/T) vs. 1/T and ln(k/T) vs. (1/T and the temperature arrangement, Ta) are the most adequate ones for obtaining ΔsolHo values. However, the latter is the only reliable option for ΔsolHo estimation when commercial WCOT capillary columns are used, since in this case the estimation of some variables involved in the Vg determination is less accurate or even impossible. Consequently, in this paper, ΔsolHo obtained from ln(k/T) vs. (1/T + Ta) fitting at 373.15 and 298.15 K for n-alkanes and n  -alkylbenzenes on 12 commercial capillary columns coated with stationary phases covering the 203–3608 McReynolds polarity range are reported. Moreover, molar heat capacities of solvation at constant pressure (ΔsolCpo) have also been calculated using this method. A clear influence on ΔsolHo of the type and content of the substitution group in the stationary phase was observed. In addition, a linear relationship of ΔsolCpo with the van der Waals volume of the n-alkanes and the temperature gradient of density of the stationary phase was found. The effect of the size of the hydrocarbon on both thermodynamic variables was also investigated.