Metal speciation and characterization of copper complexing ligands in seawater using electrospray ionization mass spectrometry
| Autor: | Ross, Andrew R. S. |
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| Jazyk: | angličtina |
| Rok vydání: | 1998 |
| Druh dokumentu: | Text |
| Popis: | Electrospray ionization mass spectrometry (ESI-MS) provides information regarding the structure and distribution of dissolved polar and ionic metal species which cannot be obtained using electroanalytical or spectroscopic techniques. Such information is necessary if the role of metal complexes in biological and geochemical processes is to be fully understood. The utility of ESI-MS for metal speciation is evaluated using a range of well characterized organic ligands and biogeochemically important metal ions. The technique reveals the stoichiometry and metal oxidation state of organic and inorganic complexes and how speciation changes with solution pH. Results for Cu²⁺ and 8-hydroxyquinoline (HL) show for the first time that ESI-MS can determine the distribution of dissolved metal species at equilibrium. A detection limit of 13 nM for the complex Cu[sup II]L⁺ demonstrates the potential of this technique for studying metal species in natural waters. Ionization of uncharged complexes is achieved by protonation, deprotonation or electrochemical oxidation of the ligand. N,N-Diethyldithiocarbamate oxidation is confirmed by studies involving alkali and alkaline earth metals, which suggest that ESI-MS detection also depends on the polarity and thermodynamic stability of the complex. Metal complexation by large polyfunctional organic compounds is investigated using tannins as model natural ligands. Simultaneous detection of free and complexed tannins allows the effects of metal concentration, pH and ionic strength to be investigated. Determination of ligand structure and copper binding site by tandem mass spectrometry further illustrates the unique capabilities of this technique for metal speciation. ESI-MS is combined with immobilized metal-ion affinity chromatography (IMAC) to extract and characterize copper complexing ligands from British Columbia coastal waters. Initial UV analysis of IMAC extracts suggests that river and surface waters are significant sources of these ligands. Subsequent ESI-MS analysis requires matrix removal which is achieved on-line by flow injection analysis using a custom made XAD- 16 column. A copper ligand of molecular mass 259 is identified in the surface seawater extract with highest UV absorbance. The data are consistent with a dipeptide containing two primary amino groups, a result supported by studies in which IMAC is combined with other methods for characterizing copper ligands in seawater. Science, Faculty of Chemistry, Department of Graduate |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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