Systems containing metal ions which bind to macromolecular ligands usually contain a large number of chemical species with different numbers of metal ions bound to each macromolecule. Nevertheless, the formulation of macromolecular complexation in the voltammetric studies of such systems usually starts by considering the presence of only three formal species M, ML and L. The conditions under which the mathematical formulation of complexation, transport and adsorption processes for the real species reduces to the formulation of the same processes in a system with only the formal species are analyzed.