Adsorption of natural sulphated polysaccharides from algal sources, ι-, κ- and λ-carrageenans, on mercury surface was studied by out of phase a.c. voltammetry. Adsorption studies were performed in a wide concentration range (10 mg/L up to 15 g/L) and the influence of the adsorbed layer on the reduction of cadmium ions, used as a probe, was studied as well. The adsorption was measured at two potentials, -0.2 V and -0.6 V vs. Ag/AgCl reference electrode. The stronger, one step adsorption, was obtained at the potential of -0.2 V. At the potential of -0.6 V, the first adsorption plateau was established at the concentration of app. 100 mg/L of added polysaccharide while at the concentration of few g/L a second adsorption plateau was established. The oxido-reduction processes of Cd2+ ions were influenced by the presence of sulphopolysaccharides only in the concentration range of a few grams/L. At the potential of E = -0.6 V after the first adsorption plateau, adsorption is a slow process, determined by both the concentration of polymer in the solution and the time of adsorption. It is most probable that transformations of the adsorbed layer occur
