Simultaneous determination of speciation parameters of Cu, Pb, Cd and Zn in model solutions of Suwannee River fulvic acid by pseudopolarography

Abstract

There is a growing awareness of the importance of quantitative determinations of speciation parameters of the trace metals Cu, Zn, Cd and Pb in aqueous samples containing chemically heterogeneous humic substances, especially when they are present together, interacting with one another and competing for specific binding sites of the humic substances. Such determinations require fundamental knowledge and understanding of these complex interactions, gained through basic laboratory-based studies of well-characterized humic substances in model solutions. Since the chemical heterogeneity of humic substances plays an important role in the thermodynamics (stability) and kinetics (lability) of trace metal competition for humic substances, a metal speciation technique such as pseudopolarography that can reveal the special, distinctive nature of metal complexation is required, and it was therefore used in this study. A comparison of the heterogeneity parameters (Gamma) for Zn(II), Cd(II), Pb(II) and Cu(II) complexes in model solutions of Suwannee River fulvic acid (SRFA) shows that GammaCd>GammaZn>GammaPb>GammaCu, suggesting that SRFA behaves as a relatively homogeneous complexant for Zn(II) and Cd(II), whereas it behaves as a relatively heterogeneous complexant for Pb(II) and an even more heterogeneous complexant for Cu(II) under the experimental conditions used. The order of values of log K* (from the differential equilibrium function, DEF) for the trace metals at pH 5.0 follow the sequence: log K*Cu>log K*Pb>log K*Zn>log K*Cd. These results are in good agreement with the literature values. The results of this work suggest the possibility of simultaneously determining several metals in a sample in a single experiment, and hence in a shorter time than required for multiple experiments.

Competition from Cu(II), Zn(II) and Cd(II) in Pb(II) Binding to Suwannee River Fulvic Acid

“…Peak height and peak area were recorded in this work. The ratio of peak area-to-height for Pb(II)-SRFA was relatively constant across the range of the deposition potentials used in this experiments as was reported in our recent publication (Chakraborty et al 2007). In this work, peak heights were used in all calculations.…”

“…It was reported in our recent study (Chakraborty et al 2007) that a comparison of the heterogeneity parameters (Γ ) for Zn(II),Cd(II), Pb(II) and Cu(II) complexes in the model solutions of SRFA showed that Γ Cd > Γ Zn > Γ Pb > Γ Cu , suggesting that SRFA behaved as a relatively more homogeneous complexant for Zn(II) and Cd(II), whereas it behaved as a relatively more heterogeneous complexant for Pb(II). It was also found (Chakraborty et al 2007) that the order of stability of M-SRFA complex is typically K* Cu >K* Pb >K* Zn >K* Cd .…”

“…It was also found (Chakraborty et al 2007) that the order of stability of M-SRFA complex is typically K* Cu >K* Pb >K* Zn >K* Cd .…”

“…The reported Γ values for Cu binding by humic substances are in the range 0.3-0.5 (Town and van Leeuwen 2004;Filella and Town 2000;Vasconcelos and Gomes 1997;Chakraborty et al 2007), depending on the humic substances. These rather low values of Γ suggest that a relatively wide distribution range of binding sites are available for Cu in humic substances.…”

Estudo voltamétrico da adsorção de Cd(II) e Zn(II) na microalga marinha Tetraselmis gracilis

“…A interpretação dos dados de titulação de um sistema altamente heterogêneo levou à definição do parâmetro de equilíbrio diferencial (K DEF ) dado pela média aritmética ponderada das constantes de equilíbrio condicionais K j para todos os sítios do tipo j envolvidos na complexação (Buffle 1988;Pinheiro, Mota et al 1994;Chakraborty, Fasfous et al 2007). (Pinheiro, Mota et al 1994):…”