Speciation of copper

Meylan S, Odzak N, Behra R, Sigg L (2004) Speciation of copper and zinc in natural freshwater comparison of voltammetric measurements, diffusive gradients in thin Aims (DGT) and chemical equilibrium models. An Chim Acta 510 91... 

Zirino, A. and Yamamoto, S., A pH-dependent model for the chemical speciation of copper, zinc, cadmium, and lead in seawater, Limnol Oceanogr, 17 (5), 661-671, 1972. 

Sunda and Hanson [247] have used ligand competition techniques for the analysis of free copper (II) in seawater. This work demonstrated that only 0.02 -2% of dissolved copper (II) is accounted for by inorganic species. (i.e., Cu2+, CuC03, Cu(OH)+, CuCl+, etc.) the remainder is associated with organic complexes. Clearly, the speciation of copper (II) in seawater is markedly different from that in fresh water. 

Prior to the introduction of ion-selective electrode techniques, in situ monitoring of free copper (II) in seawater was not possible due to the practical limitations of existing techniques (e.g., ligand competition and bacterial reactions). Ex situ analysis of free copper (II) is prone to experimental error, as the removal of seawater from the ocean can lead to speciation of copper (II). Potentially, a copper (II) ion electrode is capable of rapid in situ monitoring of environmental free copper (II). Unfortunately, copper (II) has not been used widely for the analysis of seawater due to chloride interference that is alleged to render the copper nonfunctional in this matrix [288]. 

The speciation of copper is different at high and low pH. At pH 1.0 most of the copper will be labile and a total copper concentration will be measured. At pH 7.7 there should be a smaller proportion of labile copper, as much will be complexed in various forms, depending on the constituents of the seawater. 

Donat and Bruland [804] studied the speciation of copper and nickel in seawater by competitive ligand equilibration-cathodic stripping voltammetry, differential pulse ASV, and graphite furnace AAS. 

Numerous and disparate copper criteria are proposed for protecting the health of agricultural crops, aquatic life, terrestrial invertebrates, poultry, laboratory white rats, and humans (Table 3.8) however, no copper criteria are now available for protection of avian and mammalian wildlife, and this needs to be rectified. Several of the proposed criteria do not adequately protect sensitive species of plants and animals and need to be reexamined. Other research areas that merit additional effort include biomarkers of early copper stress copper interactions with interrelated trace elements in cases of deficiency and excess copper status effects on disease resistance, cancer, mutagenicity, and birth defects mechanisms of copper tolerance or acclimatization and chemical speciation of copper, including measurement of flux rates of ionic copper from metallic copper. 

Martinotti, W., Queirazza, G., Guarinoni, A. and Mori, G. (1995) In-flow speciation of copper, zinc, lead and cadmium in fresh waters by square wave anodic stripping voltammetry Part II. Optimization of measurement step. Anal. Chim. Acta, 305, 183-191. 

Procopio, J.R., Viana, M.D.M.O. and Hernandez, L.H. (1997) Microcolumn ion-exchange method for kinetic speciation of copper and lead in natural waters. Environ. Sci. Technol., 31,3081—3085. 

Rodriguez-Procopio, J. Ortiz-Viana, M. del M. Heman-dez-Hemandez, L. Microcolumn Ion-Exchange Method for Kinetic Speciation of Copper and Lead in Natural Waters, Environ. Sci. Technol. 1997, 31, 3081-3085. 

Finally, models were calculated which predict the variations in chemical speciation of copper resulting from changes in the chemical parameters pH, carbonate alkalinity, concentration of dissolved organic matter, and concentration of total dissolved copper. 

The chemical speciation of copper in river water and model solutions was investigated by a titration technique in which cupric ion activities were measured at constant pH as the total copper concentration ([Cujoj]) was varied by incremental additions of CUSO4. pCu(-log cupric ion activity) was measured with a cupric ion-selective electrode (Orion 94-29) and pH with a glass electrode (Beckman 39301) both coupled to a single junction Ag/AgCl reference electrode (Orion 90-01) in a temperature controlled (25 + 0.5°C) water bath. Total copper concentrations in the titrated solutions were determined directly by atomic absorption spectrophotometry (Perkin Elmer 603) using a graphite furnace (Perkin Elmer 2200). Measurement of total copper concentrations is necessary because of adsorptive loss of copper from solution onto container and/or electrode surfaces. 

Copper was selected as the first metal for which to attempt to optimize the shipboard analyses because considerable information is available about the marine chemistry of copper, and because this new analytical capability would greatly enhance our ability to study copper in the ocean. The concentration of copper in the ocean varies from 0.5 to 5 nmol/kg in response to biological and geochemical processes (Table I). The chemical speciation of copper has received considerable attention because the biological effects of copper depend on its chemical form (i-3). The principal forms of copper include inorganic complexes such as CUCO3, CuHCO , CuOH, and organically bound copper (4, 5). 

We will illustrate some of the processes involved in a eutrophic lake. Points of interest are the factors that determine the speciation of copper and zinc, the role of biologically produced ligands, how copper and zinc are bound in the settling particles, and whether the settling particles reflect the composition of algae with respect to trace elements. 

To better understand the mechanisms Involved In the release studies, computer equilibrium calculations were performed using Mineql. The equilibrium speciation of copper with hydroxide as a function of pH was first examined. As can be seen In Figure 7 for a 10 Cut solution the solid phase takes over from the free copper ion as the dominant phase at a pH 6.0. For the much lower copper concentrations typically found In water the transition pH is shifted higher. 

Sunda, W. G., and P. J. Hanson (1979), Chemical Speciation of Copper in River Water, in Chemical Modeling in Aqueous Systems, E. A. Jenne, Ed. (ACS Symposium Series No. 93), American Chemical Society, Washington, DC, Chapter 8. 

Mosselmans JFW, Patrick RAD, Chamock JM, Sole VA (1999) EXAFS of copper in hydrosulfide solutions at very low concentrations implications for the speciation of copper in natural waters. Mineral Mag 63 769-772... 

Fig. 6. The equilibrium speciation of copper(II) as a function of salinity along a model estuary. For other details, see Mantoura et al. (1978).

A quantitative impression of multiple interactive systems can be gained from Figs. 6 and 7 which depict the effect of variation in salinity on the speciation of copper in the presence of humic compounds (Mantoura et al., 1978). It is clear from Fig. 5 that the decomplexation mechanism of humic bound copper originating from acidic river systems is associated with the gradual increase in the concentration of hydroxy and carbonate ligands cor-... 

Berggren, D., 1992a. Speciation of copper in soil solution from podzols and cambisols of S. Sweden. Water Air Soil Pollut. 62, 111-123. 

Soares, H.M.V.M., Vasconcelos, M.T.S.D., 1995. Application of potentiometric stripping analysis for speciation of copper complexes with adsorbable ligands on the mercury electrode. Anal. Chim. Acta 314, 241-249. 

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