General Audience Oral Presentations Abstracts

TOPIC #2

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1. Challenges Quantifying Hydroxylated Polyaromatic Hydrocarbons in Aerosols

Thomas M. Cahill1,2, Gehui Wang2, Chris Jakober1,
Peter B. Kelly2 and M. Judith Charles1

1Department of Environmental Toxicology, University of California, Davis 95616
2 Department of Chemistry, University of California, Davis, Davis, CA. 95616

Interest in acquiring quantitative data for hydroxylated-polycyclic aromatic compounds (OH-PAHs) is growing due to the potential of these compounds to adversely affect human health. The hydroxylated species can be emitted directly from combustion sources, or formed from photooxidation of the parent compounds during transport from the source region to the receptor area. Existing analytical methods either are not applicable to the analysis heavier OH-PAHs, or have not yielded quantitative data.

Our work establishes that although OH-PAHs can be analyzed directly by gas chromatography/mass spectrometry (GC/MS), the analytical sensitivity and the potential to detect a broad range of compounds can be improved by derivatizing the –OH moieties. Of the five derivatization reagents tested, N,O-bis (trimethylsilyl) trifluoracetamide (BSTFA) exhibited the greatest potential to derivatize a broad range of compounds with good sensitivity and reproducibility. The nature of the compound, substrate and extraction method influenced the extraction efficiency, which varied from about 3-100%. Higher recoveries were obtained by using shaking vs. sonication from quartz filters (26-92% vs. 3-99%) and aluminum strips (13-95% vs. 2.9-90%, respectively), whereas sonication provided higher recoveries from teflon coated glass filters (13-99% vs. 2.5-84%). The analyst must thus consider the substrate when choosing an extraction method. The most notable “problem children” were 1-hydroxypyrene, 12-hydroxybnezo[a]pyrene and 3-hydroxybenzo[e]pyrene. Additionally, the recoveries of OH-PAH comprised of 2-3 rings were higher than the parent PAH, presumably due to the lower vapor pressure of the OH-PAH. While volatile losses during sampling are expected for the lighter PAH, this is not true for the OH-PAH. Such differences are minimized for the heavier compounds, indicating that the ratio between parent and product species can be accurately obtained.

Diesel emissions were sampled onto teflon coated glass filters, and size-resolved ambient aerosols were collected on using aluminum strips in a Lundgren impactor. Sonication was used to extract OH-PAHs from onto teflon coated glass filters, and shaking was employed to extract the analytes from aluminum strips. We confirmed the identity and quantified 1-napthol, 2-napthol, 3-hydroxyphenantherene, and we tentatively identified three OH-PAH isomers in the diesel emission extracts. OH-PAHs were present in the smallest aerodynamic particles (2.0 and 0.50 mm) in the aerosol extracts with size-resolved data (e.g., 1-napthol, 2-napthol, 9-hydroxyphenanthrene, 3- hydroxyphenanthrene). The limit of detection of the compounds identified ranged from 0.11-1.3 mg/g of diesel soot extracts and 0.068-0.67 pg/m3 in the ambient aerosol. These results establish the ability of the method to measure OH-PAHs comprised of 2-5 rings, and provide the first report of quantitative data in size-resolved aerosols.

2. Thermal desorption-GCMS with silylation derivatization for analysis of PM2.5 samples from the St. Louis Supersite

Rebecca J Sheesley1, Mark Mieritz2, Min Suk Bae1, and James J Schauer1,2

1Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 660 N. Park St, Madison, WI 53706
2Wisconsin State Lab of Hygiene, University of Wisconsin-Madison, 2601 Agriculture Drive, Madison, WI 53718

The interest in adding detailed organic analysis to aerosol characterization studies is increasing due to efforts to apportion ambient particulate matter and more completely understand the nature of the organic carbon component of aerosol. Several factors inhibit the inclusion of organic analysis by extraction based GCMS methods in studies with large sample numbers. These include organic mass requirements, cost of analysis, and speed of analysis. Another factor is solubility, which limits the ability to quantify a higher percentage of compounds, including more polar compounds, with extraction based GCMS methods.

A new method using thermal desorption gas chromatography mass spectroscopy (TD-GCMS) has recently been employed to analyze the non-polar fraction of aerosol collected on quartz fiber filters. This method addresses the issues of organic mass, cost and speed because analysis is performed directly on a filter punch. However, without the inclusion of key polar compounds including alkanoic and aromatic acids, pyrolyzed sugars including levoglucosan, and sterols including cholesterol, source apportionment using organic tracers is not possible. To allow quantification of semi-polar and polar organics with acid and alcohol functional groups, this technique has been expanded by adding a silylation step before analysis. By elimating the solvent extraction step and adding derivatization, polarity limitations can be minimized thereby broadening the spectrum of compounds that can be identified and quantified. For example, carbohydrates present in soils such as glucose and sucrose can be quantified using this silylation-TD-GCMS method. Data will be shown of 24 hour samples from the St. Louis Supersite to illustrate the range of the method. With further experimentation with this technique and analysis of a variety of ambient samples, there is sure to be an expansion of the number of compound classes that can be regularly quantified in atmospheric particulate matter.

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