Diffuse reflection infrared Fourier transform (DRIFT) spectra have been quantitatively evaluated to determine unknown extinction coefficients as well as the number of active surface centers and the amount of adsorbed species. Sulfated zirconia withn-butane as probe gas was used as model system. For quantitative evaluation ofn-butane adsorption at 323 K, the sulfate band S=O at 1400 cm(-1)was chosen. During adsorption, this band is red-shifted to lower wavenumbers accompanied by a structural change of the band indicating isomerization reaction. By analyzing difference spectra and determining the areas of the selected band, the extinction coefficients as well as the number of active centers and the amount of chemisorbedn-butane were calculated. The quantitative evaluation results in a mean internal decadic extinction coefficient of 60 cm(-1)mu mol(-1), an average amount ofn-butane adsorbed to the sulfated zirconia of about 4 mu mol, and a number of active centers of around 21 mu mol/g. These results correspond very well with values from the literature obtained by microcalorimetry. Thus, this method is suggested to be transferred also to unknown systems of interest.