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In order to fully understand atmospheric processes and thus climate changes, detailed information on major components is necessary. Air particulate matter is known for its adverse impact on heath, as well as on ever discussed climate changes. The building blocks of particulate matter are metals, salts, organic species, and elemental carbon. While inorganics are fairly well identified and quantified, only 20-50% of organics are usually characterized. The organics can be differentiated as polar and non-polar species. Non-polar and slightly polar compounds are directly related to primary emissions, and are quite well characterized using organic solvent extraction and GC/MS. Thus, the interest of our laboratory focuses on polar organics, which are formed from the atmospheric oxidation of volatile organics species (secondary aerosol formation). The importance of polar organics lies also in their reactivity, and therefore, impact on human health and climate changes.

Comprehensive Picture on Atmospheric Organic Particles

Products of PAH Heterogeneous Reactions

The aim of the study was to evaluate a potential of two extraction/fractionation methods from three particulate matter (PM) samples (e.g., wood smoke, diesel exhaust SRM 2975 and urban PM SRM 1648). Both extraction methods using hot pressurized water (25–250 °C) and a series of organic solvents (hexane, methylene chloride, methanol) on Soxhlet achieved similar recoveries of ~50% and ~70% of extractable OC based on TOT and TOR, respectively. Both extraction methods also provided similar distribution of OC in different polarity fractions. The distribution of organics in wood smoke PM extracts reflected the polar nature of wood smoke PM. For diesel exhaust PM (which is considered non-polar due to a high content of EC), a significant portion of organics was found in the polar fractions using both extraction methods. This corroborates the results of toxicological studies showing a significant toxicity for the methanol fraction of diesel exhaust OC. Further characterization of obtained fractions (prior and after trimethylsilylation) was performed using GC/MS. The GC/MS analysis revealed that composition of the obtained extracts is not only affected by the polarity of the solvent, but also by the matrix-analyte interactions. For example, dicarboxylic acids were found in different polarity fractions obtained from wood smoke, diesel exhaust PM, and urban PM representing primary, and combination of primary and secondary emissions, respectively. While majority of dicarboxylic acids in urban PM was extracted in water-soluble fraction, the same acids were recovered more efficiently with higher temperature water (less polar) from wood smoke and diesel exhaust PM. This may be due to stronger embedding of dicarboxylic acids into the matrix in primary emission PMs (i.e., wood smoke, diesel exhaust PM) than when formed during secondary atmospheric processes (i.e., urban PM). This finding was observed also for other species and suggests that fractionation of organic PM based on the polarity of extracting solvent depends on the analyte-matrix interactions, which may be useful when accounting for the availability of those analytes in atmospheric processes. (Presented at 9th International Conference on Carbonaceous Particles in the Atmosphere in 2008 and published by Kubatova et al. Aero. Sci. Technol. 2009, 43 (7), 714–729).

This work was funded by National Science Foundation (NSF) Grant No. 0552762, ND EPSCoR Grant No. EPS-0447679, and U.S. Department of Energy (DOE) National Energy Technology Laboratory Cooperative Agreement No. DE-FC26-98FT40320.

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Reaction of PAHs on particlesPolycyclic aromatic hydrocarbons (PAHs) are found in atmospheric aerosols which are emitted to the atmosphere through incomplete combustion of fossil fuel. PAHs and their by-products are known to have carcinogenic and mutagenic activities. Both the kinetics of these reactions and the pathways of the formation of products are important in environmental studies. However, only limited knowledge is available on the products of the heterogeneous reactions of PAHs adsorbed on particles. Currently we are studying, the PAH reactions of phenanthrene, anthracene, fluoranthene, and pyrene with reactive gas species with focus on the detailed identification of mainly oxygenated products. These PAHs were chosen based on their partitioning into the atmospheric particulate matter. A small scale flow reactor was built and quartz filters were used as the solid support for the heterogeneous reactions. Several oxidation products with multiple functional groups forming carboxaldehydes, carboxylic acids, and/or hydroxylated species were observed especially for reactions of pyrene and anthracene with ozone. 1-nitropyrene and 9-nitroanthracene were found for the reaction of these PAHs with nitrogen dioxide. The combination of ozone and nitrogen dioxide led to the observation of a broader distribution of nitration products, apparently due to the in-situ formation of NO3, a more powerful reactant. The identified reaction products help further evaluation of product accumulation kinetics and their significance in atmospheric processes. This work is being funded by NSF Career grant ATM-0747349 and additional REU support.

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In MS extracted ions enable identificationIn order to determine the efficient methods for biofuel production and identify valuable byproducts, the detailed chemical characterization of biofuels is needed. Our laboratory collaborates within SUNRISE initative lead by Dr. Seames (Chemical Engineering Department) on the project involving generation of biofuels. With few exceptions current methods applied for characterization of biofuels are based on the ASTM methods for petroleum product. However, the properties and compositions of biofuels and petroleum products differ thus approariate method has to be developed. Such developement first requires understanding what are the major species and thus characterization performed using gas chromatography (GC) with flame ionization (FID) and mass spectrometric (MS) detectors. The critical aspect of our work is proper quantification using the FID with appropriate standards. This is eliminates errors caused when methods originally developed for petroleum fuels are employed. Such methods although correct for petroleum fuels assume all species are volatile enough to elute through GC. However, this cannot be said about the biofuel samples especially NOT intermediate products of the process. Complementary to the FID is the MS detection providing a great tool for the idetification of individual or classes of compounds. Using MS even those chemicals which are negligible on FID signal can be found and may dramatically affect properties of resulting biofuel (see figure below). The overall aim of our work is to provide detailed methods comparable to ASTM methods in petroleum fuels. These projects are funded through U.S. Department of Energy, the North Dakota Agricultural Production Utilization Commission, the North Dakota State Board of Agricultural Research, the North Dakota Soybean Council, and the National Science Foundation.

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Various bioactive molecules are today isolated and/or synthesized to be used in products for food and drug industry. Our work involves development of selective isolation methods, preferentially using nontoxic solvents such as carbon dioxide and water, for antioxidants, vitamins, essential oils and other important plant components. Identification of those species is performed using chromatographic techniques with mass spectrometric detection.

LC-TOFMS chromatogram of flax lignansAt present, the methods such as LC/MS/MS and GC/MS in selected ion monitoring mode (SIM) employed for characterization of lignans are focused on the determination of known species. We have developed a new method using HPLC with high resolution time of flight MS (TOF MS) for the determination of flaxseed-derived lignans. The analytical method was optimized, and compared to two existing methods (HPLC/MS/MS and GC/MS). For the HPLC/TOF MS method, we have obtained comparable limits of detection (LODs) of 0.002–0.043 pg (injected) to the those acquired with optimized and improved HPLC/MS/MS (0.001–0.015 pg). As expected the LODs for the optimized GC/MS (SIM) were higher (0.02–3.0 pg), nevertheless lower than those reported previously. Besides the optimization of determination method, several key flaxseed sample preparation parameters (including extraction, hydrolysis, and sample purification) were evaluated resulting in the development of efficient protocol for lignan quantification from flaxseed hulls and embryos. The results confirmed the importance of simultaneous quantification of both aglycones and unhydrolyzed glucosides in order to obtain accurate total lignan concentrations. The high resolution TOF MS enabled a confirmation of identity of suspected but unknown species. This works was published by Popova et al. J. Chromatogr. A 2009, 1216 (2), 217–229.

 

Disclamer: Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF), Department of Energy (DOE) or any other funding agency mentioned above. Back to Top

 

Last updated February 2012 | Chemistry Department | University of North Dakota |