Voltammetric measurement of copper(II)/organic interactions in estuarine waters

The voltammetry of copper in organic ligand/chloride media is dominated by the formation of CuCl^?₂ species and by induced adsorption of Cu(I) in organic coatings on the electrodes. These phenomena are utilised in a novel method for evaluating Cu(II)/organic ligand interactions, based on the principle of ligand exchange. The Cu(II)/organic species competes with glycine which forms copper glycinate. These two complexes can be distinguished voltammetrically: copper glycinate gives a higher surface excess of copper at a gelatin-coated hanging mercury drop electrode, partly because of the increased production of CuCl^?₂ from copper glycinate at the electrode surface. The method proved satisfactory for pure ligand/surfactant/chloride media and for estuarine waters. It is shown that there are two type of Cu(II)-binding ligand in estuarine waters: humic material (> 10^?6 mol l^?1, assuming 1:1 site binding) with polyelectrolyte-type binding, and discrete ligands (? 10^?6 M) with stability constants around 10⁹. The extent of Cu(II) binding by the humic material decreases down the estuary because of dilution and increased salinity.