Development and application of a comprehensive thermal desorption/photoionisation mass spectrometry instrument for the determination of the nature of the carbonaceous fraction and the oligomeric/polymeric content of ambient participate matter
Final Report Abstract
The project dealt with the determination of the nature of the carbonaceous fraction and the oligomeric/polymeric content of ambient particulate matter. For this purpose a commercial carbon analyzer was coupled to a photo ionization-time-of-flight-mass spectrometer. The carbon analyzer enables the stepwise heating of the filter samples and the determination of the carbon content with distinction into organic (OC) and elemental carbon (EC). The photo ionization mass spectrometer allows the almost fragment free analysis of the aromatic (REMPI) and the aromatic and aliphatic (SPI) content of the samples. Standard substances (alkanes, PAH´s), standard polymers (cellulose, lignin, xylane and NOM), ambient samples from different sites and seasons and emission samples from different sources (diesel, biodiesel and wood combustion) were analyzed with this system. With multi-photon ionization homologue rows of polyaromatic hydrocarbons can be assigned in the obtained mass spectra of OC1 and OC2 of the urban aerosol sample and wood combustion emission samples as well as of the diesel and biodiesel emission sample. SPI measurements revealed smaller molecules, such as acetone or acetaldehyde, furan derivatives, alkanes, etc. In all ambient and emission samples, no matter which ionization technique was used, higher temperatures (starting with OC3) led to the formation of smaller molecules. This can be explained by the thermal decomposition of larger, low volatile substances. This decomposition is very interesting because the fragments can give information about the structure of these polymeric compounds, about whose composition little is known until now. By detecting breakdown products of the standard substances (e.g. lignin, NOM) in ambient or emission samples, the structure of therein contained larger molecules should be similar to those standards. The comparison of diesel and biodiesel emission samples revealed a complete different behavior. Whereas the OC1 step of the biodiesel sample displays the greatest fraction, only small amounts of carbon were released in OC1 of the diesel sample. The molecular pattern was also completely different. The OC4 step shows relatively high carbon contents which can be explained neither by REMPI nor by SPI data. This indicates either that the separation between OC and EC is not satisfactory, that means that a part of the EC already evolves in OC 4, or that the molecules are not ionized by SPI. EC fractions do not contain aromatic compounds anymore. This indicates that the separation between organic and elemental carbon in the carbon analyzer is sufficiently, except the possible release of EC in the OC4-step and that there are no organic compounds left, which could be assigned to EC.
Publications
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Hyphenation of a carbon analyzer to photo-ionzation mass spectrometry to unravel the organic composition of particulate matter on a molecular level. Anal Bioanal Chem (2011) 401: 3153-3164
J. Grabowsky, T. Streibel, M. Sklorz, J.C. Chow, J.G. Watson, A. Mamakos, R. Zimmermann
