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Appl. Sci. 2018, 8(9), 1617; https://doi.org/10.3390/app8091617

Determination of Relative Ionization Cross Sections for Resonance Enhanced Multiphoton Ionization of Polycyclic Aromatic Hydrocarbons

1
Joint Mass Spectrometry Centre, Chair of Analytical Chemistry, Institute of Chemistry, University of Rostock, Dr. Lorenz—Weg 2, 18059 Rostock, Germany
2
Joint Mass Spectrometry Centre, Cooperation Group Comprehensive Molecular Analytics, Helmholtz Zentrum München-German Research Center of Environmental Health (GmbH), Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany
*
Author to whom correspondence should be addressed.
Received: 15 July 2018 / Revised: 4 September 2018 / Accepted: 6 September 2018 / Published: 11 September 2018
(This article belongs to the Special Issue Photoionization Mass Spectrometry)
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Abstract

Resonance enhanced multiphoton ionization (REMPI) is a powerful method for the sensitive determination of polycyclic aromatic hydrocarbons (PAHs) in gaseous mixtures via mass spectrometry (MS). In REMPI, ions are produced by the absorption of at least two photons including defined electronic intermediate states. As a result—unlike other laser-based ionization techniques—spectroscopic selectivity is involved into the ionization process. Nevertheless, these wavelength-dependent ionization rates impede the quantification using REMPI. For this purpose, relative photoionization cross sections (relPICS) give an easy-to-use approach to quantify REMPI-MS measurements. Hereby, the ionization behavior of a single compound was compared to that of a reference substance of a given concentration. In this study, relPICS of selected single-core aromatics and PAHs at wavelengths of 266 nm and 248 nm were determined using two different time-of-flight mass spectrometric systems (TOFMS). For PAHs, relPICS were obtained which showed a strong dependence on the applied laser intensity. In contrast, for single-core aromatics, constant values of relPICS were determined. Deviations of relPICS between both TOFMS systems were found for small aromatics (e.g., benzene), which can be assigned to the differences in UV generation in the particular system. However, the relPICS of this study were found to be in good agreement with previous results and can be used for system-independent quantification. View Full-Text
Keywords: REMPI-TOFMS; quantification; cross section; polycyclic aromatic hydrocarbons REMPI-TOFMS; quantification; cross section; polycyclic aromatic hydrocarbons
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Gehm, C.; Streibel, T.; Passig, J.; Zimmermann, R. Determination of Relative Ionization Cross Sections for Resonance Enhanced Multiphoton Ionization of Polycyclic Aromatic Hydrocarbons. Appl. Sci. 2018, 8, 1617.

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