| Bioavailability of metal ions to organisms, as well as their toxic effects strongly depends on the chemical speciation of the metal ions. Chemical species can be differentiated on the basis of their physical characteristics and chemical reactivity. A scheme for chemical speciation, which combines physical characterization by ultrafiltration of the dissolved metal species based on their molecular weights with chemical characterization of the dissolved metal species by their chemical reactivity, such as dissociation kinetics, has been developed and applied to samples of river surface waters, rain and snow. The kinetics of metal complex dissociation has been studied by ion exchange by Chelex-100 cation-exchange resin using the Chelex batch technique. Assuming that in aqueous samples all of the metal complexes dissociate independently simultaneously at their own rates and that all dissociation rates are slower than those uptake rates of metal aquo ions by the Chelex resin in Chelex batch technique, a model for the dissociation kinetics of metal complexes has been developed and tested using samples of river surface water, rain and snow. Two analytical techniques of great sensitivity, graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma mass spectrometry (ICP-MS), have been tested for quantitation of metals and compared in terms of their usefulness for providing the kinetic data required for this work. It is concluded that ICP-MS has a greater potential for the resolution of labile complexes than GFAAS. The iterative deconvolution method, which uses a non-linear regression algorithm, has been applied to the analysis of kinetic data. The assumptions made in the kinetic model have been verified and the experimental conditions optimized using model solutions containing metal ions and organic complexants. The Chelex batch technique, the kinetic model and the iterative deconvolution method have been validated using model systems, Cu-EDTA and Cu-NTA. Kinetic studies of chemical speciation have revealed that aluminum and copper are present in snow and rain waters, both as aquo ions and as simple inorganic complexes of organic ligands, and are bound to polyfunctional complexants or colloidal macromolecular materials in samples of Rideau River surface waters. |
