Adsorption of various organics, including n-alkanes, cyclohexane, benzene and halomethanes, on the solid surface obtained from colloidal silica was studied by gas-solid chromatography (GSC). Adsorption experiments, ranging from zero surface coverage and to finite concentration, were performed in the temperature region from 333 to 443 K. In order to reduce surface inhomogeneity, a modified material was prepared by controlled surface silanol proton-Co'+ ion exchange and its adsorption properties were also investigated by GSC. Comparing the values for the standard free energy change for adsorption at zero coverage for all absorbates used, it can be deduced that the modification procedure diminished the intensity of adsorption and so enhanced the homogeneity of the solid surface. Adsorption isotherms were obtained using the elution by characteristic point technique and the data were fitted to the BET equation. Thermodynamic parameters for adsorption in the finite concentration region were determined and are discussed in terms of the surface coverage.