Electrochemical speciation of trace metals in sea water

Abstract

Various approaches, such as bioassays, computer-assisted modelling and direct measurement following physical separation are currently being used to investigate the speciation of trace metals in sea water. The electrochemical techniques used successfully as a necessary prerequisite for the experiments involved include conventional polarography, anodic stripping voltammetry (ASV) and potentiometry. Differential pulse anodic stripping voltammetry (DPASV) using mercury film electrodes enables direct studies in ultratrace levels present in non-contaminated ocean waters. By varying the conditions of the sample chemistry and electroanalysis it is possible to characterize metal-organic interactions. This is demonstrated in the case of natural sea water samples subjected to ASV diagnosis. Differences in the Pb and Cu values yielded for Baltic waters by two methods based on DPASV and AAS are discussed with regard to speciation. An analysis of the existing literature is used to briefly summarize the needs of future research. Important problems requiring a more precise quantitative analysis include the adsorption of organics on electrodes and the kinetics and thermodynamic constants of chelates with special regard to the physico-chemical nature of metal-humic substances. The introduction of new and improved electroanalytical techniques and equipment for speciation studies is strongly recommended.