Stoichiometric displacement of solvent by non-polar solutes in reversed-phase liquid chromatography.

This paper proposes a retention model which predicts that the displacement of non-polar solutes from a reversed-phase chromatographic column is accompanied by the adsorption of a stoichiometric number (Z) of solvent molecules. The number of solvent molecules involved in this process is a function of both solute and solvent contact surface areas. Increasing solute contact surface area would increase Z whereas increasing solvent contact surface area would decrease the Z value for a specific solute. The experimental observations presented are consistent with this model. Further predictions of the model are that (1) plots of log k' versus the inverse log of solvent concentration will be non-linear at solvent concentrations where the surface of a reversed-phase support is not fully solvated, and (2) only a portion of the total non-polar surface area of a molecule actually contacts the surface of a reversed-phase support. Non-linearity in plots of log k' versus the inverse log of solvent concentration was in fact observed at solvent concentrations where solvation of the reversed-phase support is incomplete.