Citation:

BETOWSKI, L. D., M. ENLOW, AND D. H. AUE. ELECTRON AFFINITIES OF POLYNUCLEAR AROMATIC HYDROCARBONS AND NEGATIVE ION CHEMICAL IONIZATION SENSITIVITIES. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY AND ION PROCESSES. Elsevier Science Ltd, New York, NY, 255-256:123-129, (2006).

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:

Negative-ion chemical-ionization mass spectrometry (NICI MS) has the potential to be a very useful technique in identifying various polycyclic aromatic hydrocarbons (PAHs) in soil and sediment samples. Some PAHs give much stronger signals under NICI MS conditions than others. On the other hand, positive ion signals are largely comparable under the same source conditions. An extensive set of newly reevaluated experimental electron affinities (EAs), or free energies of electron attachment, are now available, as well as reliable predicted electron affinities from quantum theoretical calculations or from solution reduction potentials and theoretically predicted solvation energies. In order to show a high negative-ion sensitivity, a PAH must have an EA that exceeds a Threshold of approximately of 0.5 eV. Comparisons between the negativeion to positive-ion sensitivities (N/P ratios) and these new electron affinities shows a rough correlation between the two, but naphthacene and perylene are exceptions to this relationship with much lower sensitivities than expected from their high EA values. By calculating the EA for a PAH, one can predict whether a sensitivity enhancement under NICI MS conditions is to be

expected. Since aliphatic hydrocarbons and many other substances have negative or very low EAs, NICI MS is expected to be a good technique for detecting PAHs in samples contaminated with other hydrocarbons or compounds with low EAs.

Record Details: