Abstract In gas sensing, materials the key part is played by the surface. Therefore, in nanosized powders for which the surface can compete with the bulk, the chemical composition of the surface has to be systematically controlled. To this end Fourier transform infrared (FT-IR) spectrometry is a powerful technique provided a specific vaccum cell is attached to the spectrometer. The effect of the temperature and surrounding atmosphere on the adsorbed species is clearly demonstrated for Al 2O 3 and TiO 2 nanosized powders. Special attention is paid to water molecules and carbonate groups which are by far the most probable surface contaminants. Then the response of the titania surface to oxygen, carbon dioxide and carbon monoxide is investigated under various conditions. Based on these FT-IR spectroscopic results which clearly demonstrated the relevance of the method for gas-surface interaction analysis, a preliminary reaction mechanism for CO adsorption on titania is proposed.