Elucidation of the chemical speciation of trace metals in the natural aquatic environment will lead to a better understanding of their distribution and ecological effects. One approach which can provide useful information about the chemical reactivity of metal ions is the measurement of their activity. Phase equilibrium methods are required and liquid-liquid partition equilibria are applicable. This study utilized model systems to demonstrate this applicability. The partitioning of copper(II) ions as a chelate of acetylacetone was used to determine the trace activity coefficients of the copper(II) electrolyte in the CU(N03)2-HN03-KN03, Cu(N03)2-HCl04-NaCl04 and CuC12-HCl-KCl systems over a wide range of ionic strengths (u). By careful control of pH and acetylacetone concentration only 1-3% of the metal ion was extracted. Under these conditions the amount extracted is proportional to the activity. The concentration of the bis(Acetylacetonato) Copper(II) was determined in the organic phase by spectrophotometric and atomic absorption methods but any convenient concentration technique could be used to measure the amount extracted. A comparison of activity measurements by liquid-liquid partitioning was made with electrochemical measurements by utilizing a copper ion selective electrode. The significantly lower activity coefficient values obtained by the electrochemical method were explained in terms of the liquid junction potential and the necessity for extrathermodynamic approaches to single ion activities. Potential application of the liquid-liquid partitioning method to the determination of trace activity coefficients in natural aquatic systems was demonstrated by extension of the method to measurements in copper(II) amino acid solutions at u = 0.001 and u = 0.723. The ionic strength adjustments in this case were made with NaCl. A significant difference in the free copper (II) ion activity was observed between solutions of copper(II) glycinate and copper(II) alaninate under identical conditions of metal and ligand concentrations, pH and ionic strength. The copper(II) activity measurements made in the presence of the amino acids at u = 0.723 are not possible with copper ion selective electrodes due to chloride interference.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-1845 |
| Date | 01 January 1978 |
| Creators | Kennish, John Michael |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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