Correlation between Surface Diffusion and Molecular Diffusion in Reversed-Phase Liquid Chromatography

Abstract

Surface diffusion data previously measured for different compounds, mobile phase solvents, stationary phases, and temperatures in reversed-phase liquid chromatography (RPLC) were reevaluated to derive information related to the mechanism and characteristic features of surface diffusion. First, a comparison of the surface diffusion coefficient (Ds) and the corresponding molecular diffusivity (Dm) suggests that the dependence of Ds on the RPLC conditions is a consequence of that of Dm. There is a correlation between surface diffusion coefficients and molecular diffusivity. Second, we showed that Ds correlates with the adsorption equilibrium constant (K) and the isosteric heat of adsorption (Qst). These two parameters represent the intensity of the adsorptive interactions between the sample molecules and the surface of the stationary phase. Finally, the ratio Ds/Dm increases with decreasing K and −Qst and Ds becomes of the same order of magnitude as Dm when the adsorptive interactions become small. These res...