SURFACE-DIFFUSION OF ALKYLBENZENES ON OCTADECYLSILYL-SILICA GEL

Surface diffusion phenomena of alkylbenzenes in reversed-phase liquid chromatography (RP-LC) using an octadecylsilyl-silica gel and methanol /water (70/30, v/v) were analyzed on the basis of a restricted molecul ar diffusion model, in which surface diffusion coefficient, D-s, was c orrelated with molecular diffusivity, D-m, by introducing a restrictio n energy, E-r. The average ratio of E-r to isosteric heat of adsorptio n Q(st), gamma, in RP-LC was about 0.3. It was also indicated that gam ma at different temperatures could be represented as a linear function of the reciprocal of -Q(st) when a linear free-energy relation held a nd an enthalpy-entropy compensation for adsorption equilibrium was est ablished. An estimation procedure of D-s was proposed on the basis of the results. It was demonstrated that D-s at a given temperature could be calculated with an error of less than about 10% from only one datu m of the adsorption equilibrium constant.