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

The experimental voltammetric studies of an inert complex has been carried out in the absence of intentionally added supporting electrolyte. The chose n system consisted of europium(III) nitrate and 1,4,8,11-tetraazacyclotetra decane (cyclam) in a 4:1 mixture (v/v) of methanol and dimethylsulfoxide. T he 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 c onstant in the presence of supporting electrolyte (0.1 M tetrabutylammonium perchlorate), log beta=3.3, has been determined in the usual manner using a glassy carbon electrode. Under the conditions of the absence of excess supporting electrolyte, reduc tion wave height of the Eu3+ ion depends on concentration of electroinactiv e ions in the way predicted by the Myland-Oldham theory. The complex stoichiometry (1:1) and the complex formation constant (log bet a=3.2), in the absence of supporting electrolyte, have been determined by n onlinear curve-fitting of the steady-state currents measured at a gold micr oelectrode for various concentrations of the ligand. A good agreement of th ese two values supports the theoretical model presented in the previous pap er of this series. (C) 1998 Elsevier Science B.V. All rights reserved.