A comparative method based on thermogravimetry is applied in order to characterise chemically functionalised surfaces. The mass loss of silica modified with -aminopropyl-trimethoxysilane (-APS) adsorbed from a range of solvents is interpreted by considering the physically adsorbed water, the silanol groups and the organic solvent. DRIFT spectroscopy is used to analyse the binding structure and adsorption mechanism. The mass loss calculated from thermogravimetric analysis is found to be in agreement with the values obtained by classical elemental analysis. Thermogravimetric analysis is found to be a quick and reproducible method, which only requires a few milligram sample. The amount adsorbed seems to be primarily dependent on the solvation of the -aminopropyl-trimethoxysilane by the solvent. A good solvent prevents adsorption as shown when comparing the magnitude of the mass loss with the difference between the solubility parameters of the -APS and the solvents. Ethanol seems to influence the structure of the adsorbed -aminopropyl-trimethoxysilane film.