Influence of mobile phase composition on surface diffusion in reversed-phase liquid chromatography

Influence of column temperature and mobile phase composition (φ) on surface diffusion was studied in reversed-phase liquid chromatography using a C18-silica gel column and methanol–water mixtures. The temperature dependence of surface diffusion coefficient (Ds) was explained by considering that of the molecular diffusivity, suggesting the presence of a kind of correlation between surface and molecular diffusions. The influence of φ on Ds was accounted for by considering the restriction energy (Er) for surface diffusion. Physical meanings of the linear correlation between Er and the enthalpy change due to sample retention are discussed in connection with the mechanism of surface diffusion.