INTERPRETATION OF THE INFLUENCE OF TEMPERATURE ON THE SOLVATION PROPERTIES OF GAS-CHROMATOGRAPHIC STATIONARY PHASES USING ABRAHAM SOLVATIONPARAMETER MODEL

Abraham's solvation parameter model is used to interpret the influence of temperature on the contribution of cavity formation and solute-sol vent intermolecular interactions to the solvation Of a varied group of 62 solutes on ten representative stationary phases used in gas chroma tography. It was observed that the magnitude Of polar interactions inc reased at lower temperatures and that the change in the characteristic phase constants deduced from Abraham's model as a function of tempera ture could be described by a second-order polynomial function. Since t he susceptibility of a solvent for a particular intermolecular interac tion changes in a phase-specific manner as a function of temperature t he observed ranking of phases for a particular intermolecular interact ion at one temperature cannot be used to predict phase rankings at ano ther temperature for the same interaction. A comparison of Abraham's m odel with an alternative cavity model proposed by Poole for the sum of the cavity and dispersion contributions to solvation shows similar tr ends as a function of temperature but differences in the magnitude of the contribution of the cavity-dispersion term to the overall free ene rgy change for the solvation process. Agreement for the contribution o f polar interactions to the solvation process is only qualitative for the two models unless a correction is made for the difference in magni tude for the cavity-dispersion contribution. A correction can be made by dividing the c term in Abraham's model into two contributions; a co nstant 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 experimenta l error for the relative contribution made by the cavity-dispersion te rm and solute-solvent polar interaction forces to the solvation proces s.