Voltammetric investigation of the complexation equilibria in the presence of a low level of supporting electrolyte. Experiments with an inert complex Original Research Article

The experimental voltammetric studies of an inert complex has been carried out in the absence of intentionally added supporting electrolyte. The chosen system consisted of europium(III) nitrate and 1,4,8,11-tetraazacyclotetradecane (cyclam) in a 4:1 mixture (v/v) of methanol and dimethylsulfoxide. The complex formed is reduced at glassy carbon electrodes at −1.4 V vs. the reference electrode used. The complex stoichiometry is 1:1. The formation constant in the presence of supporting electrolyte (0.1 M tetrabutylammonium perchlorate), log β=3.3, has been determined in the usual manner using a glassy carbon electrode. Under the conditions of the absence of excess supporting electrolyte, reduction wave height of the Eu3+ ion depends on concentration of electroinactive ions in the way predicted by the Myland–Oldham theory. The complex stoichiometry (1:1) and the complex formation constant (log β=3.2), in the absence of supporting electrolyte, have been determined by nonlinear curve-fitting of the steady-state currents measured at a gold microelectrode for various concentrations of the ligand. A good agreement of these two values supports the theoretical model presented in the previous paper of this series.