Understanding the reaction-diffusion processes of metal species is essential for an adequate description and control of metal availability. Electroanalytical techniques are well suited to probe dynamic speciation in aqueous systems, because transport and reaction influence the current. This short review hinges on the quantification of the contribution of complexes to the resulting flux via the lability degree, while highlighting extensions and other approaches. The reaction scheme is the Chemical Electrochemical (CE) mechanism, but special emphasis is focussed in mixtures of ligands given their relevance in natural waters. Despite the intensive theoretical work devoted to dynamic speciation, there is still a need of further progress, especially regarding heterogeneous ligands, nanoparticles, etc. Rigorous numerical solutions are progressively more accessible. Analytical contributions are usually restricted to limiting cases, but greatly facilitate the physicochemical interpretation of complex systems.