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40.
Characterization of Organic Components in Aerosol Particles Using
Two-Step laser Desorption/Ionization Mass Spectormetry
T.
FERGE(1), F.MUEHLBERGER(1) and R. ZIMMERMANN(1,2,3)
(1)GSF
Forschungszentrum, Institut für Ökologische Chemie,
Ingolstädter Landstr. 1, 85764 Neuherberg, Germany
(2)BIfA-Bayerisches Institut für Angewandte Umweltforschung
und -technik GmbH, Abteilung Umweltchemie und Prozessanalytik,
Am Mittleren Moos 46, D-86167 Augsburg, Germany
(3)Analytische Chemie, Institut für Physik, Universität
Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
Keywords:
Desorption, Organics, Ambient Aerosols
INTRODUCTION
The organic fraction of ambient aerosols constitutes a complex
mixture of compounds both of inorganic as well as organic nature.
Especially the organic fraction is of interest due to possible
health related effects. Major compound classes in the ambient
and urban aerosol include aliphatic hydrocarbons, organic acids
and polycyclic aromatic hydrocarbons. For the characterization
of aerosol samples on filters, two-step laser desorption/ionization
has been extensively studied as a valuable analytical technique
(1,2).
The Vacuum-UV single photon ionization (VUV-SPI) suitable for
both aliphatic and aromatic compounds and in addition exhibits
only low fragmentation rates due to its energy being just above
the ionization threshold of most organic compounds (3).
METHODS
Aerosols are sampled on quartz fibre filters and introduced on
the tip of a sampling probe into the ion source of the mass spectrometer
via an air lock. For laser desorption, IR laser pulses (CO2-laser,
10,6 µm, 1mJ, spot size Æ = 1 mm) are focused on the
fibre filter disk surface for soft desorption of chemical compounds
from the particulate matter. Desorbed compounds are subsequently
ionized with VUV-radiation (118 nm), which is generated in a rare
gas cell for frequency tripling (3). In the new instrument a combination
of VUV-SPI and resonance enhance multiphoton ionization (REMPI)
is possible (4).
RESULTS
In the LD-VUV-SPI spectra, typical fragment ions of type CxHy+
as well as low mass hydrocarbons can be observed. Obviously, the
CO2-laser energy causes fragmentation of organic compounds. The
observed fragmentation rate is due to the high temperature in
the desorption plume effected by the CO2-laser pulse. With VUV-SPI,
a sum value of aliphatic hydrocarbons is accessible, whereas the
LD-REMPI (4) gives information about aromatic compounds.
The LD-VUV-SPI technique is a promising tool for fast analysis
of aerosol samples without the need for extensive sample preparation.
ACKNOWLEDGEMENTS
This study was carried out in the scope of the GSF-Focus-Network
“Aerosols and Health” which co-ordinates aerosol-related
research within the GSF Research Centre. T.F. thanks the Deutsche
Bundesstiftung Umwelt for a PhD scholarship.
REFERENCES
((1) Haefliger et al., Environ. Sci. Technol. (2000), 34, 2178-2183.
(2) Haefliger et al., Environ, Sci. Technol. (2000), 34, 2184-2189.
(3) Mühlberger et al., Anal. Chem. (2001), 73, 3590-3604.
(4) Hauler et al., Abstr. Of the EAC Madrid (2003), S943-S944.
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