In previous work, a model was proposed for the voltammetric study of metal ions in mixtures of macromolecular and simple ligands, with the assumption that the complexes formed are totally labile or totally inert. In this paper, the general equations of that model are applied to the study by differential pulse polarography (DPP) of the system Zn(II) + lambda-carrageenan + nitrilotriacetic acid (NTA), which is taken as a model system with both labile and inert complexes. In general terms, there is good agreement between the experimental set of current data and the theoretical predictions. It should be pointed out that the results yielded by the measurement of the peak current data and those yielded by the peak potential data were in good correspondence due to the minimum influence of electrodic adsorption. Results also show that the DeFord-Hume method is applicable even in the presence of inert complexes and provides a good estimate of the free metal ion concentration.