Investigation of the ionization mechanism of polycyclic aromatic hydrocarbons using an ethanol/bromobenzene/chlorobenzene/anisole mixture as a dopant in liquid chromatography/atmospheric pressure photoionization mass spectrometry

Handle URI:
http://hdl.handle.net/10754/562330
Title:
Investigation of the ionization mechanism of polycyclic aromatic hydrocarbons using an ethanol/bromobenzene/chlorobenzene/anisole mixture as a dopant in liquid chromatography/atmospheric pressure photoionization mass spectrometry
Authors:
Amad, Maan H.; Sioud, Salim
Abstract:
RATIONALE An ethanol-based multicomponent dopant consisting of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v/v/v) has been used as a dopant for atmospheric pressure photoionization (APPI) of polycyclic aromatic hydrocarbons (PAHs). In this study the mechanism of ionization of PAHs assisted by the ethanol-based multicomponent dopant is investigated. METHODS The reactant background cluster ions of the ethanol-based multicomponent dopant observed in the positive ion APPI were studied. These studies were performed to investigate the mechanism behind the generation of a molecular radical cation (M +•) for PAHs by APPI assisted by the ethanol-based multicomponent dopant. Full scan and MS/MS analyses were conducted using an LTQ Orbitrap mass spectrometer. The effect of acidification of the mobile phase on the dopant cluster ion formation was also investigated. RESULTS With the ethanol-based multicomponent dopant, a single type of molecular radical cation M +• was observed for the studied PAHs. The characteristic ion signal of the multicomponent dopant mixture consisted of mainly anisole photoions at m/z 108.05697 and its adduct ions at m/z 124.05188 and 164.07061. The anisole ion response at m/z 108.05697 was stable in the presence of acetonitrile, methanol, water and 0.1% formic acid mobile phase composition. CONCLUSIONS The abundance formation of anisole photoions shows the universality of this multicomponent dopant in ionizing compounds with ionization energy ranging from 7.1-8.2 eV. Since the ionization energy of anisole is 8.2 eV and is lower than those of chlorobenzene (9.07 eV) and bromobenzene (9.0 eV), the mechanism of formation of anisole photoions even with its very minute amounts was not only governed by its photoionization by the krypton lamp photon energy (10.0 eV and 10.6 eV), but also by charge transfer from bromobenzene and chlorobenzene radical cations. PAH molecules were mainly ionized by charge transfer reaction from photoionized anisole and oxidized anisole radical cations as well as by the krypton lamp. Copyright © 2012 John Wiley & Sons, Ltd.
KAUST Department:
Analytical Core Lab; Core Labs
Publisher:
Wiley-Blackwell
Journal:
Rapid Communications in Mass Spectrometry
Issue Date:
23-Sep-2012
DOI:
10.1002/rcm.6373
Type:
Article
ISSN:
09514198
Sponsors:
The authors gratefully acknowledge the research support from the Analytical Core Lab at the King Abdullah University of Science and Technology, Saudi Arabia.
Appears in Collections:
Articles; Analytical Core Lab

Full metadata record

DC FieldValue Language
dc.contributor.authorAmad, Maan H.en
dc.contributor.authorSioud, Salimen
dc.date.accessioned2015-08-03T10:01:10Zen
dc.date.available2015-08-03T10:01:10Zen
dc.date.issued2012-09-23en
dc.identifier.issn09514198en
dc.identifier.doi10.1002/rcm.6373en
dc.identifier.urihttp://hdl.handle.net/10754/562330en
dc.description.abstractRATIONALE An ethanol-based multicomponent dopant consisting of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v/v/v) has been used as a dopant for atmospheric pressure photoionization (APPI) of polycyclic aromatic hydrocarbons (PAHs). In this study the mechanism of ionization of PAHs assisted by the ethanol-based multicomponent dopant is investigated. METHODS The reactant background cluster ions of the ethanol-based multicomponent dopant observed in the positive ion APPI were studied. These studies were performed to investigate the mechanism behind the generation of a molecular radical cation (M +•) for PAHs by APPI assisted by the ethanol-based multicomponent dopant. Full scan and MS/MS analyses were conducted using an LTQ Orbitrap mass spectrometer. The effect of acidification of the mobile phase on the dopant cluster ion formation was also investigated. RESULTS With the ethanol-based multicomponent dopant, a single type of molecular radical cation M +• was observed for the studied PAHs. The characteristic ion signal of the multicomponent dopant mixture consisted of mainly anisole photoions at m/z 108.05697 and its adduct ions at m/z 124.05188 and 164.07061. The anisole ion response at m/z 108.05697 was stable in the presence of acetonitrile, methanol, water and 0.1% formic acid mobile phase composition. CONCLUSIONS The abundance formation of anisole photoions shows the universality of this multicomponent dopant in ionizing compounds with ionization energy ranging from 7.1-8.2 eV. Since the ionization energy of anisole is 8.2 eV and is lower than those of chlorobenzene (9.07 eV) and bromobenzene (9.0 eV), the mechanism of formation of anisole photoions even with its very minute amounts was not only governed by its photoionization by the krypton lamp photon energy (10.0 eV and 10.6 eV), but also by charge transfer from bromobenzene and chlorobenzene radical cations. PAH molecules were mainly ionized by charge transfer reaction from photoionized anisole and oxidized anisole radical cations as well as by the krypton lamp. Copyright © 2012 John Wiley & Sons, Ltd.en
dc.description.sponsorshipThe authors gratefully acknowledge the research support from the Analytical Core Lab at the King Abdullah University of Science and Technology, Saudi Arabia.en
dc.publisherWiley-Blackwellen
dc.titleInvestigation of the ionization mechanism of polycyclic aromatic hydrocarbons using an ethanol/bromobenzene/chlorobenzene/anisole mixture as a dopant in liquid chromatography/atmospheric pressure photoionization mass spectrometryen
dc.typeArticleen
dc.contributor.departmentAnalytical Core Laben
dc.contributor.departmentCore Labsen
dc.identifier.journalRapid Communications in Mass Spectrometryen
kaust.authorAmad, Maan H.en
kaust.authorSioud, Salimen
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