COMPETITIVE EQUILIBRATION TECHNIQUES FOR DETERMINING TRANSITION-METALSPECIATION IN NATURAL-WATERS - EVALUATION USING MODEL DATA

Competitive ligand equilibration with metal titrations is one of the m ost important approaches currently available for determining the chemi cal speciation of trace metals in seawater. However, ambiguities in da ta interpretation still complicate the application of these methods. H ere, we have used model data to explore and graphically demonstrate th e effects of analytical limitations and protocols on the results obtai ned using competitive equilibration techniques. We have confirmed that such methods are best suited for identifying low concentrations of li gands forming strong metal complexes. Nevertheless, with care, the inf ormation obtained for weaker metal complexes and speciation in complic ated ligand mixtures can give reasonable estimates of the in situ foe metal ion concentration. In general, speciation results from competiti ve equilibration analyses cannot necessarily be extrapolated to high t otal metal concentrations at which complexes with unidentified weak li gands could become important.