The theoretical description of the in situ thin gap radiotracer method has been given recently for the quantitative determination of sorption properties of metal surfaces covered by porous layers. In the present work, the theoretical approach elaborated was validated with experimental data obtained for Pt electrodes of roughness factor larger than 10. The deposition conditions of the uniform and adherent platinum layer were elaborated in such a thickness that the infinitely thin porous layer conditions could be applied. The system of rough polycrystalline platinum/chloride ion (labelled with Cl-36) in dilute aqueous solution (c<10(-3) mol dm(-3)) was studied. It was shown that the sensitivity of the measurements of the chloride ion adsorption can be increased by about two orders of magnitude by using rough Pt surfaces, while the uncertainty of the surface excess of the adsorbed ions could be reduced significantly. The mobility study of the adsorbed chloride ions showed that the adsorbed labelled ions could be partly replaced with inactive ions at constant electrode potential. The saturation time of the adsorption process increased with the thickness of the porous layer. (C) 2013 Elsevier Ltd. All rights reserved.