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Research Summary | |
| Trace Metal Analysis/X-Ray Emission Spectroscopy (PIXE and Micro-PIXE)/Metal Complexes-Synthesis, Structure and Reactivity The determination of trace levels of elements in environmental and biological samples is an area of intense activity in analytical chemistry. In our work in this field we employ a high energy proton beam as an excitation source and record the energy spectrum of x-rays that are emitted from the sample target. We can determine, with this technique, elemental profiles, at parts per million levels, in thin or thick targets of biological materials, and environmental as well as forensic samples. This PIXE technique has proved to be a powerful tool for probing the interactive toxicity of metal ions and for understanding the role of metal ions in certain biological processes. The ability to focus the high energy proton beam and probe an area of 5µm2 has enhanced our analytical capabilities. With the aid of this proton microprobe, (i.e. the micro-PIXE system), we can determine the location of trace elements in tissue slices and even in single cells. The capability of mapping the elemental composition in microstructures will enable us to better define the manner in which metal ions are involved in biological processes. We have initiated a research program to investigate the feasibility of non-destructive microchemical analysis of environmental particulates, biological and forensic samples with the aid of a low intensity focused beam of heavy ions with energies of 0.5 to 1 MeV/amu. These heavy ions deposit a large fraction of their energy in a small impact area with the resulting generation of useful analytical signals, such as the desorption of atomic and molecular fragments. Our initial objective in this work is to demonstrate the capability of recognizing trace signatures with the particle-induced desorption and to develop the technology for the complete non-destructive analysis and imaging of environmental, biological and forensic samples. We are investigating a class of ligands with oxygen and nitrogen donor atoms that have macrocyclic structures. These macrocycles, with 12 to 34 membered rings, and an appropriate number of pendant carboxylic acid groups, form non-ionic complexes with divalent transition metal ions, e.g. Mn2+ and Pb2+, and trivalent lanthanide ions, e.g. Gd3+, Dy3+ and Y3+. The resulting metal complexes are highly water soluble and have potential applications as x-ray contrast media, diagnostic agents in magnetic resonance imaging, and as radiopharmaceuticals. The use of "zero-valence" iron for the removal of certain toxic organic contaminants from ground water and soils is an active area of investigation in many environmental laboratories. We have developed a simple and relatively inexpensive bimetallic system which can be used under ambient conditions for the rapid hydrodechlorination of all saturated and unsaturated aliphatic compounds (e.g. CCl4, CHCl3, CH2Cl2, trichlorethylene, the dichloroethylenes & vinyl chloride) and for the dechlorination of chlorinated aromatic compounds such as chlorinated phenols and polychorinated biphenyls. The mechanisms of these complex reductive dechlorinations are under investigation in our laboratory. Another aspect of our environmental studies involves the remediation of soil, from mine tailings, that is contaminated with toxic heavy metals such as mercury, lead, cadmium and arsenic species. Attempts that are being made to recover trace levels of gold and silver from these mine tailings result in further damage to the environment because water-soluble complexes of these toxic heavy metals that are formed, eventually contaminate the groundwater. The main objectives of our work is to understand the chemical reactions that occur during the recovery processes and to minimize the formation of water soluble toxic heavy metal species that contaminate groundwater plumes. |
