The influence of different dissolved gases on the adsorption of cinchonidine from CCl4 Solutions onto polycrystalline platinum surfaces has been studied by in situ reflection-absorption infrared spectroscopy (RAIRS). It was observed that Ar, N-2, O-2, air, or CO2 neither enhances the adsorption of cinchonidine nor damages cinchonidine adlayers once they have formed on the surface. On the other hand, H-2 plays a unique role, initially facilitating the uptake of cinchonidine, but later removing some of the resulting adsorbed cinchonidine from the platinum surface. It was also found that CO is a strong inhibitor, significantly retarding the adsorption of cinchonidine. Adsorbed CO can be removed by H-2 dissolved in the cinchonidine solution, a process that also boosts the adsorption of cinchonidine. O-2 can remove the surface adsorbed CO as well, but without facilitating cinchonidine adsorption. The cleanliness of Pt surfaces at different stages of the experiment was probed by CO adsorption. Possible correlations between the RAIRS results from the present study and reported data from catalytic studies are discussed. (C) 2003 Elsevier Inc. All rights reserved.