DETERMINATION OF COPPER COMPLEXATION IN SEA-WATER BY A LIGAND COMPETITION TECHNIQUE WITH VOLTAMMETRIC MEASUREMENT OF THE LABILE METAL FRACTION

A ligand competition-anodic stripping voltammetric (ASV) technique is proposed for investigating copper complexation in sea water. Increasing amounts of ethylenediamine were used to convert the non-reducible copper fraction into a labile copper complex and the change in the stripping peak current was followed. Ligand titration of sea water using this technique indicated that the naturally occurring non-labile copper fraction is bound to ligands having concentrations less than 5 X 10(-9) M and a conditional stability constant (log K(CuL)') of 13.1 +/- 0.3. An advantage of ligand exchange voltammetry is that when applied to raw sea water, it allows the investigation of copper "already" bound by inert ligands. On the other hand, when applied to copper-spiked sea-water samples, this method permits the investigation of the "newly formed" inert complexes. It was found that when copper was added to give [Cu] > 1 X 10(-8) M, the added copper assumed a different inert form than that of the already bound copper in the sample. The combined use of ligand competition-ASV with stripping polarography as a diagnostic method of speciation analysis is discussed.