ANODIC-STRIPPING VOLTAMMETRY OF COPPER IN NATURAL-WATERS - A QUALITATIVE APPROACH TO THE ADDITIONAL PEAK(S) OCCURRENCE

In the presence of natural organic species, the electrochemical behavior of metals can be modified Several authors have already noticed an extra peak or shoulder in the Cu peak during anodic stripping voltammetry (ASV) analysis, but the origin of this interference was generally not investigated and the experimental conditions were modified to make it disappear. in this article, this phenomenon alone was studied. The organic matter dissolved in interstitial waters of marine sediments was fractionated by ultrafiltration and gel permeation chromatography. The resulting fractions were qualitatively studied with respect to the complexity of the voltammograms they exhibit during an ASV analysis of Cu. Very similar electrochemical behaviors (multiple peaks) were found for interstitial waters and humic substances. The fractionation experiment suggests that particular families of molecules, which can be separated, are responsible for these extra peaks. Therefore, the ''multipeak'' phenomenon is related to the quality of the organic matter rather than to its quantity. This fact, supported by several experiments [DPASV, differential pulse polarography (DPP)], has led to a model which, although still somewhat speculative, describes well the usual observations: the extra peaks would originate from the oxidation of organic copper species [most likely as Cu(I)] adsorbed and stabilized on the mercury drop electrode.