Voltammetric investigation of formation of complexes in low ionic strength environments - Theoretical description and modeling

Digital simulation of steady-state voltammetry of diffusion-migration systems with the reactant involved in the complexation reaction has been carried out using a FIFD-related algorithm. It has been found, that in the case of neutral ligands, the shift of the halfwave potential caused by the formation of the complex has the same magnitude in solutions with and without supporting electrolyte. The measurement data can thus be interpreted using the standard methods for voltammetric analysis, like, e.g. De Ford-Hume scheme. For charged ligands it is possible to find a value for the ligand:reactant concentration ratio above which the migrational effects can be neglected. This allows one to use classic methods also to the systems with charged ligands. The simulation results show that the limiting ligand:reactant concentration ratio mentioned above differs for different charge numbers of species and for different complex formation constants, but for the majority of the considered systems this ratio should be not less than 5 in the total absence of supporting electrolyte. The proposed approach has been applied to the experimental results obtained for Tl+ with 18-crown-6 ligand in water without addition of supporting electrolyte. (C) 2004 Elsevier Ltd. All rights reserved.