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| Titel |
Characterization of Proton Transfer Reaction Mass Spectrometry for the detection of sesquiterpenes |
| VerfasserIn |
M. Demarcke, C. Amelynck, N. Schoon, J. Dewulf, H. Van Langenhove |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022549
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| Zusammenfassung |
| It is well-known that terrestrial vegetation is an important source of non-methane volatile
organic compounds (NMVOC) of which terpenoid compounds, such as isoprene,
monoterpenes and sesquiterpenes, constitute an important fraction. Measurements of
sesquiterpenes (C15H24) are still sparse and hard to perform because of the low volatility of
these compounds and their high reactivity with the main atmospheric oxidants (OH, O3,
NO3). Nevertheless, they may well play an important role in atmospheric chemistry because
of their high reactivity and their high potential to contribute to secondary organic aerosol
(SOA) formation.
Important efforts have been made lately to develop and improve analytical techniques for
sesquiterpene detection and recently proton transfer reaction mass spectrometry (PTR-MS)
has also been applied for sesquiterpene detection by a limited number of research groups.
Further exploitation of the PTR-MS technique for this class of terpenoid compounds may
benefit from a better characterization of the ion chemistry inside the PTR-MS reactor at
varying instrumental and environmental parameters.
Therefore, product ion distributions of four important sesquiterpenes (beta-caryophyllene,
alpha-humulene, longifolene and alpha-cedrene) have been measured in a commercial high
sensitivity PTR-MS instrument (Ionicon Analytik GmbH) at different values of the ratio of
the electric field strength to the buffer gas number density in the reactor (E∕N) and at
different water vapour pressures in the inlet line. Although the nascent excited complex,
which is formed in the H3O+.(H2O)n/sesquiterpene reaction, partially decomposes into a
variety of fragment ions, the protonated sesquiterpene remains the major product ion for all
four species studied. The product ion distributions show a large dependence on
E∕N, but, interestingly, are not found to be much influenced by changing relative
humidities.
From the results it is expected that sesquiterpene detection sensitivity based on the
protonated sesquiterpene ion signal (at m∕z 205) can be enhanced by a factor of three when
decreasing the E∕N value from 140 to 80 Td.
Since some of the sesquiterpene fragment ions have the same m∕z value as the
common monoterpene PTR-MS fingerprint ions (C10H17+ at m∕z 137 and C6H9+ at
m∕z 81), care should be taken when quantifying monoterpenes in the presence of
sesquiterpenes.
The authors gratefully acknowledge the support from the Belgian Science Policy through
the Program “Science for a Sustainable Development: Terrestrial Ecology” (contract #
SD/TE/03A) and from the “Fonds Wetenschappelijk Onderzoek - Vlaanderen” (contract #
G.0031.007). |
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