Comparison of the differential isosteric adsorption enthalpies and entropies calculated from chromatographic data

The differential isosteric enthalpies, −ΔHads, and entropies, −ΔSads, of adsorption were calculated taking the retention times of the peak maxima and the centres of gravity of peaks into account and compared with the results obtained from the adsorption second virial coefficients. A mathematical link between the −ΔHads and −ΔSads magnitudes and experimental data was derived through the Antoine-type equation which enables the −ΔHads and −ΔSads magnitudes to be found from adsorption second virial coefficients, B2S, calculated on the basis of chromatographically determined adsorption isotherm data. The virial coefficients were calculated employing the values of the Tóth and Unilan equation parameters. There are no significant differences to be found between the isosteric enthalpies obtained, whereas the values of the adsorption entropies were the highest for the centre of peak gravity data.