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A NEW NON-AMBIGUOUS ANALYTICAL TECHNIQUE FOR THE IDENTIFICATION OF AEROSOL OXYGENATED COMPOUNDS
Citation:
Jaoui, M., E. H. Daughtrey Jr., E. W. Corse, T E. Kleindienst, M Lewandowski, AND E O. Edney. A NEW NON-AMBIGUOUS ANALYTICAL TECHNIQUE FOR THE IDENTIFICATION OF AEROSOL OXYGENATED COMPOUNDS. Presented at American Association for Aerosol Research National Meeting, Anaheim, CA, October 20-24, 2003.
Impact/Purpose:
1. Using laboratory and field study data generated during FY99-FY04, develop a science version of a PM chemistry model for predicting ambient concentrations of water, inorganics, and organics in PM2.5 samples. The model will include the Aerosol Inorganic Model for predicting concentrations of inorganic compounds and a computational chemistry-based method for predicting concentrations of organic compounds.
2. Identify and evaluate methods for analyzing the polar fraction of PM2.5 samples.
3. Carry out short term field studies in Research Triangle Park, North Carolina in the summer and the winter to determine the composition of the organic fraction of ambient PM2.5 samples, with special emphasis placed on identifying and determining ambient concentrations of polar compounds.
4. Conduct laboratory studies to establish the chemical composition of secondary organic aerosol (SOA) and to determine source signatures for aromatic and biogenic SOA.
5. Conduct laboratory and theoretical investigations of thermodynamic properties of polar organic compounds.
6. Evaluate the science version of the PM chemistry model using laboratory and field data generated under this task as well as other available data in the literature.
7. Conduct PM chemistry-related special studies for OAQPS
Description:
The most important organic products identified in the particle phase from field samples and from smog chamber experiments are polar oxygenated compounds containing one, two, three or more oxygenated functional groups (e.g. hydroxyl, carboxylic acid, ketone). Current procedures used for analyzing oxygenated compounds are based on derivatizing carbonyls group using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) or methoxyamine along with a silylation agent (e.g. bis-(trimethylsilyl)trifluoroacetamide (BSTFA)) to trimethylsilylate carboxylic and hydroxyl groups simultaneously. When one or more hydroxyl group coexist in the same molecule with a carboxylic group, this popular method suffers from lack of resolution between these two different groups.
In this study, a new analytical technique was developed toward the identification of multi-functional compounds bearing at least one hydroxyl and one carboxylic group. This technique is based on derivatizing the carboxylic group(s) first of the multi-functional compound using an alcohol (e.g. methanol, n-butanol) in the presence of a relatively strong Lewis acid (BF3) as catalyst. This esterification reaction quickly and quantitatively converts carboxylic acids to their ester forms. The second step is based on silylation of the ester compounds using BSTFA as derivatizing agent. For compounds bearing in addition to carboxylic and hydroxyl groups, ketone groups, a third step was used based on PFBHA derivatization of the carbonyls. Different parameters including temperature, time of reaction and artifacts were optimized. A GC-MS in EI or in methane CI mode was used for the analysis of these compounds.
The technique was tested on a number of multi-functional compounds bearing at least one hydroxyl and one carboxylic group. The interpretation of their methane CI mass spectra shows two different clear fragmentation patterns. For example, when derivatized only with BF3/methanol their mass spectra comprises three primary ions at m/z M+1, M+29, and M-31 for compounds bearing only hydroxyl groups and M+1, M+29, M-31, and M-17 for those bearing hydroxyl and carboxylic groups. However, when a second derivatization (BSTFA) was used, compounds bearing hydroxyl and carboxylic groups show in addition to the ions observed before, ions at m/z 73, M-15, M+73, M-59, and M-75. To the best of our knowledge, this technique describes for the first time the power to identify multi-functional oxygenated compounds bearing simultaneously one or more hydroxyl and carboxylic groups. The knowledge gained regarding this technique was used to positively identify reaction products in an extract of three complex mixtures that was difficult if not impossible before the development of this technique. The first two mixtures were obtained from a smog chamber photo-oxidation of a-pinene and toluene in the presence of NOx respectively, and the third one was obtained from particle field sample.
This work has been funded fully, or in part, by the United States Environmental Protection Agency, under Contract Number 68-D-00-206 to ManTech Environmental Technology, Inc. It has been subjected to Agency review and approved for publication.