Investigation of analytical techniques for determination of metal speciation in natural waters

This thesis presents a critical appraisal of the following analytical techniques for quantitative determination of metal speciation: Diffusive Gradient in Thin Films (DGT) for in situ determination of DGT-labile metal species in aqueous systems; Ion Exchange Technique (IET) for quantitative determination of free metal ion concentrations in aqueous systems. Pseudopolarography employed for investigation of effect of heterogeneity and ligand loading in aqueous systems. It also presents a study of metal binding characteristics of a well-characterized Laurentian Fulvic Acid (LFA) as a function of the [metal]/[LFA] ratios and pH; Competing Ligand Exchange Method, coupled with Inductively-Coupled Plasma-Mass Spectrometry for determining dissociation rate constants of metal complexes in natural waters. Effects of various competing ligands: Chelex-100, Dowex MAC-3 and Dowex 50WX-8 in model solutions and in freshwater samples were also investigated.;Humic substances (HS) in natural waters are physically and chemically heterogeneous complexants. This work has investigated the efficacy of pseudopolarography for quantitative determination of effects of heterogeneity of humic substances on the release of metals from metal-HS complexes. The results clearly show that the heterogeneity parameter, &ceill0; , strongly affects the release of metals from metal complexes of HS. The general trend observed for the heterogeneity parameter was Gamma Zn ≥ GammaCd > Gamma Pb > GammaCu. It was found that the [metal]/[LFA] ratios and the heterogeneity of humic substances were main factors that affected the release of metals from their complexes. The environmental significance of this work is that it has thrown light into effects of heterogeneity of HS on the release of metals by metal-HS complexes in natural waters. An important contribution made by this work to the knowledge of metal speciation in the aquatic environment is that this is first time a clear-cut differentiation between the concept of lability (an intrinsic property) and the metal release by labile complexes (an extensive property) of metal-HS complexes has been made.