Electrochemical behavior of the Eu(III/II)-EDTA system on a mercury electrode in water + dimethylsulphoxide (DMSO), water + acetonitrile (AN) and water + hexamethylphosphortriamide (HMPT) mixtures

The electrode reaction of the Eu(III)−EDTA/Eu(II)−EDTA system at mercury electrodes in mixed solvents, H2O + DMSO, H2O + AN and H2O + HMPT, was studied by using mostly chronocoulometry and other supplementary techniques. It was found that, in each case, addition of small quantities of non-aqueous solvents to water produces a pure inhibitive effect on the electrode process. At higher concentrations of both AN and DMSO, the non-aqueous solvent generates an increase of the standard rate constant. The mechanism of the electrode reaction of the Eu(III)−EDTA/Eu(II)−EDTA system in the mixed solvents used was compared with that of non-complexed solvated europium ions in these media.