General Audience Oral Presentations Abstracts

TOPIC #8

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LC/MS/MS Analysis of Ambient Air Samples: Determination of PAH-Quinones and Algae-Derived Toxins in Ambient Air

Jake D. McDonald, Dean Kracko, and Yung-Sung Cheng
Lovelace Respiratory Research Institute, Albuquerque, NM

High performance liquid chromatography coupled to a triple quadrupole mass spectrometer (LC/MS/MS) was employed for the determination of two unique classes of organic compounds; polycyclic aromatic hydrocarbon (PAH)-quinones and brevotoxin (toxins in marine algae that are found in ambient air in coastal areas) compounds. Both of these organic compound classes have been implicated for an association between exposure (by inhalation) and acute respiratory health, and both of these classes pose unique analytical challenges that are alleviated from the utilization of LC/MS/MS. Simultaneous description of these methods allows an illustration of the range of the instrument application, and the challenges/considerations taken during method development of different compounds. PAH-Quinones, especially the higher molecular weight benzo(a)pyrene-quinone isomers, are typically present in ambient air at extremely low concentrations (e.g. pg/m3). Their analysis by gas chromatography is possible, but their low concentrations (relative to background) and poor chromatography (without targeted derivitization) decrease the selectivity and sensitivity of that technique. Analogous to selected ion monitoring in GC/MS analysis, LC/MS/MS analysis of select parent:daughter ion pairs offers superior selectivity by screening most of the ions in the between the first and third quadrupole. The result is a “clean” chromatogram of the target analytes without prior “clean-up” of the sample matrix. Enhanced sensitivity is provided by implementation of a recently developed atmospheric pressure photoionization source. In contrast, a heated nebulizer ionization source was required for the analysis of brevotoxins. These compounds are too large to analyze by GC (m.w. > 800 amu), and their concentrations are too low to analyze by LC with non selective detectors. Immuno-sorbent assays (ELISA) have been developed for these compounds, but their lack of specificity has left the results difficult to interpret. The LC/MS/MS was configured to produce a sensitive (e.g. pg/µl) assay that removed matrix interferences (by parent:daughter ion discrimination. The approaches for LC/MS/MS method development, and the range/limitations of the technique for ambient air analysis, will be placed in context in these method descriptions.

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Measurement of monosaccharide anhydrides in ambient aerosols for estimation of the wood smoke component

Roy W. Dixon and Jennifer R. Cruz
Chemistry Department, California State University, Sacramento

In cities in the central valley of California, high aerosol mass concentrations occur during periods of stagnant air in winter. Smoke from residential wood combustion may contribute significantly to aerosol mass during such time periods. Past studies have shown that wood smoke contains high concentrations of levoglucosan (1,6-anhydro-ßD-glucopyranose) as well as the presence other monosaccharide anhydrides. We are investigating using monosaccharide anhydride concentrations to estimate the fraction and concentration of aerosol mass originating from wood smoke. Twenty-three air filter samples of 24 hour duration were collected using California Air Resource Board PM2.5 (particulate matter under 2.5 mm in diameter) samplers located in Fresno and Chico, CA in January, 2001. Whole filters were extracted with methanol and water and analyzed using a novel method employing high performance liquid chromatography (HPLC) with aerosol charge detection. The HPLC system used a heated ligand-exchange column with a 100% aqueous eluent. In aerosol charge detection, the effluent from the HPLC column is converted to an aerosol and detected using an electrical aerosol size analyzer. Levoglucosan, mannosan, and an unidentified peak were well resolved while other sugars and galactosan were affected by some peak overlap or contaminant peaks. Levoglucosan was easily detected in all samples, while several other compounds were observed in samples more heavily affected by wood smoke. Concentrations of levoglucosan ranged up to 9.5 mg m-3, among the highest reported ambient concentrations, and some of the aerosol mass concentrations were above national standards. Major ions concentrations also were measured on some concurrently collected air samples. We are investigating simple mass apportionment models using one or two composite sources of wood smoke and levoglucosan, mannosan and potassium concentrations. The biggest challenges appear to be the variability in source levoglucosan fractions between hardwood and softwood smoke sources, collection of appropriate source data, and low signal to noise ratios in mannosan measurements. Levoglucosan was observed to correlate with both mannosan and potassium at each site. Higher mannosan to levoglucosan ratios observed in the Fresno samples are attributed to a greater fraction of smoke from softwood combustion. Wood smoke appeared to be a significant component of the aerosol mass in Fresno and a dominant component in Chico.

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Identification and quantification of biogenic marker compounds for secondary organic aerosol formation

Thorsten Hoffmann
Johannes Gutenberg University of Mainz
Institute of Inorganic and Analytical Chemistry
55128 Mainz Germany

Organic contributions to the atmospheric particle phase are known to derive from primary and secondary sources. Together these sources can account for 20 to 60% of the total PM2.5, depending on the site and time of the measurements. A significant fraction is believed to derive from natural sources. However, despite the high mass contribution of organic compounds, quantitative information about their origin and formation pathways are still rare (e.g. anthropogenic vs. natural, primary vs. secondary). The analytical challenge is always connected with the fact that the organic aerosol fraction is comprised of hundreds of individual compounds. This is also true for secondary organic aerosol components from natural sources.

In the past few years, several analytical techniques have been developed to identify and quantify specific marker compounds for biogenic SOA formation. Typically, these compounds represent low molecular weight, highly polar organics, such as multifunctional carboxylic acids. For the investigation of organic aerosol formation in chamber studies, mass spectrometric on-line techniques have successfully been utilized. The high time resolution of these
techniques often enable a direct insight into the chemical mechanisms leading to condensable products, especially when MS/MS capabilities are applied. Nevertheless, due to the complex composition of ambient tropospheric aerosols, the low concentration of individual marker compounds and the undesired fragmentation using classical ionization techniques of existing real-time aerosol measurement instruments, typically offline methods have to be employed for field measurements of organic tracer compounds.

Focused on biogenic SOA marker, this presentation tries to summarize the current state-of-the-art of on-line and off-line methods for the analysis of polar secondary organic aerosol components. As a part of that, recent results of our group using an on-line aerosol measurement techniques based laser desorption in combination with a soft ionization techniques will be presented at the workshop.

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