The invention relates to a device to determine the adsorption/desorption isotherms and porosity in thin films, supported membranes, and directly supported nanostructured materials. For this purpose, the adsorption and desorption isotherms of the sample are determined and subsequently used to determine the type of porosity of the sample, as well as the pore volume and pore size distribution thereof, using solid surface thermodynamic and physicochemical concepts.