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IDENTIFICATION OF COMPOUNDS IN SOUTH AFRICAN STREAM SAMPLES USING ION COMPOSITION ELUCIDATION (ICE)
Citation:
Grange, A H., P. Thomas, M. Solomon, AND G W. Sovocool. IDENTIFICATION OF COMPOUNDS IN SOUTH AFRICAN STREAM SAMPLES USING ION COMPOSITION ELUCIDATION (ICE). Presented at 51st American Society for Mass Spectrometry Meeting, Montreal, CA, June 8-12, 2003.
Impact/Purpose:
Provide state-of-the-science sampling, analysis, separation, and detection methods to allow rapid, accurate field and laboratory analyses of contaminated soils, sediments, biota, and groundwater to support Superfund clean-up decisions. Apply state-of-the-science methods in chemical analysis and data interpretation (e.g., mass spectral interpretation) to actual problems of OSWER, the Regions, and the States, in cooperation with the Las Vegas Technical Support Center as well as by direct contacts with Regional and State employees. Provide technical advice and guidance to OSWER using the environmental chemistry expertise (e.g., mass spectrometry, analytical methods development, clean-up methodology, inorganics, organometallics, volatile organics, non-volatile organics, semi-volatile organics, separation technologies, etc.) found within the branch.
Technical research support for various projects initiated either by Regions/Program Offices or ECB scientists. While these efforts will support the Regions and Program Offices, they cannot be predicted or planned in advance, and may serve multiple duty (e.g., solve real-world problems, serve to ground-truth analytical approaches that ECB is developing, transfer new technology). Many of the activities in this task support requests involving enforcement decisions and therefore are categorized as "environmental forensics".
Description:
Analytical methods for target compounds usually employ clean-up procedures to remove potential mass interferences and utilize selected ion recording (SIR) to provide low detection limits. Such an approach, however, could overlook non-target compounds that might be present and that could pose risks to ecosystems or to humans. In an ideal world, it would be preferred that all compounds present be identified, quantified, and evaluated for toxicity.
The US EPA's Environmental Chemistry Branch is identifying as many compounds as possible in several stream samples collected near Johannesburg, South Africa, using Ion Composition Elucidation (ICE), a high resolution mass spectrometric technique developed in-house. This SIR based technique measures the exact masses of an ion and its +1 and +2 mass peak profiles that arise from heavier isotopes such as 13C, 2H, 15N, 17(, 180, 33S, and 34S. The abundances of the +1 and +2 profiles relative to the monoisotopic ion's profile are also measured for compounds that provide gas chromatographic peaks. Comparison of measured and calculated values of these three exact masses and two relative abundances for the ion compositions that are possible based on the ion's exact mass and its error limits provides unique compositions for the ions in a mass spectrum. Mass spectral interpretation based on these ion compositions often provides tentative identifications when multiple library matches occur, when poor quality mass spectra are obtained, or when no library matches are found.