ELECTROCHEMICAL REDUCTION OF NITRATE ION AT MERCURY-ELECTRODES IN THE PRESENCE OF ALKALINE-EARTH METAL-IONS

Electrochemical reduction of nitrate ion at mercury electrodes in the presence of akaline-earth metal ions ( Mg(II), Ca(II), Sr(II) and Ba(II) ) was investigated using dc polarography and cyclic voltammetry. The positive slope ( dE/dpH ) indicated that the greater the concentration of proton, the less the nitrate was reducible in the presence of these metal ions, where E was the reduction potential of the polarogram. We interpreted this result as indicating that the hydrolysis of these metal ions near the electrode supplied the proton to the nitrate ion during the electrode reduction. The result of cyclic voltammetry for the Mg(II)-NO3- system showed that the Mg(I) species was formed in the anodic sweep process after the potential of the working electrode was kept at the reduction potential of Mg(II); the existence of a univalent species was never confirmed with other alkaline-earth metal ions.