Extraction of valid metal ion complexation parameters for heterogeneous ligands from voltammetric data is fraught with difficulties. We apply a straightforward calculation method to pulse polarograms, which overcomes some of the limitations. Our method takes into account the heterogeneity of complexants such as fulvic acids through the use of two parameters which are inherent properties of the substance under study and which allow complexation parameters to be calculated for other metal-loading conditions. The results obtained are used to generate theoretical polarograms, by using a numerical simulation model that allows kinetic effects to be taken into account. Application of this methodology to Cu(II)- and Pb(II)-complexation by Suwannee River fulvic acid showed that RPP polarographic waves for both of these metals are affected to some extent by adsorption of the ligand on the working electrode surface. For Cu(II), the complexation parameters were strongly dependent on the experimental conditions, implying that the overall impact of adsorption is far more significant than for Pb(II).