Polarography of complex compounds in the absence of large excess of the complexing agent

A general expression for the current—voltage characteristic was derived which is valid for all degrees of reversibilities and ligand concentrations, taking into account quantitatively the effect of complex formation on the polarographic curves. When the reaction is reversible the current—voltage characteristic and half-wave potential are independent of the reaction mechanism. For quasi-reversible electron-transfer reactions both the reaction mechanism and the stability constants may be established. When the reaction is irreversible, quantitative investigation of the changes of (E_1/2^′)_irr with concentrations of complexing ligands leads to the composition of the activated complex. However, except in special cases independent information is necessary to determine stability constants. The theory of the polarographic reduction of metal ions in the absence of large excess of the complexing agent was tested experimentally. In the case of the Bi-NTA complex reduction, the electrode reaction was found to be quasi-reversible and the equations of the theoretical section to be applicable.