Surface properties of silica-based adsorbents measured by inverse gas-solid chromatography at finite concentration

The adsorption energy distributions (AEDs) of methanol and dichloromethane on samples of the same silica unmodified and modified with octadecyldimethylsilyl (C-18) were estimated from isotherm data obtained by inverse gas chromatography at finite concentration. Wall-coated open tubular columns were used as they provide a high efficiency and a low pressure drop, allowing the acquisition of accurate isotherm data. The adsorption isotherms were obtained from nonlinear elution profiles using the characteristic points method of chromatography. The numerical estimation of AEDs was made by applying the expectation-maximization method to the experimental, unfitted adsorption isotherm data. The adsorption energy distributions obtained exhibit two peaks of adsorption energy. The height of the higher energy peak is reduced after chemical modification of the silica surface.