Interpretation of the influence of temperature on the solvation properties of gas chromatographic stationary phases using Abraham's solvation parameter model

Abstract

Abraham's solvation parameter model is used to interpret the influence of temperature on the contribution of cavity formation and solute—solvent intermolecular interactions to the solvation of a varied group of 62 solutes on ten representative stationary phases used in gas chromatography. It was observed that the magnitude of polar interactions increased at lower temperatures and that the change in the characteristic phase constants deduced from Abraham's model as a function of temperature could be described by a second-order polynomial function. Since the susceptibility of a solvent for a particular intermolecular interaction changes in a phase-specific manner as a function of temperature the observed ranking of phases for a particular intermolecular interaction at one temperature cannot be used to predict phase rankings at another temperature for the same interaction. A comparison of Abraham's model with an alternative cavity model proposed by Poole for the sum of the cavity and dispersion contributions to solvation shows similar trends as a function of temperature but differences in the magnitude of the contribution of the cavity—dispersion term to the overall free energy change for the solvation process. Agreement for the contribution of polar interactions to the solvation process is only qualitative for the two models unless a correction is made for the difference in magnitude for the cavity—dispersion contribution. A correction can be made by dividing the c term in Abraham's model into two contributions; a constant term independent of temperature which is assigned to the cavity-dispersion contribution to solvation and a temperature dependent term which is assigned to the polar interaction contribution to solvation. With this construct the two solvation models agree within experimental error for the relative contribution made by the cavity—dispersion term and solute—solvent polar interaction forces to the solvation process.