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UBC Theses and Dissertations
Systematic study of dopants for use in atmospheric pressure photoionization mass spectrometry Smith, Derek Robert
Abstract
Atmospheric pressure photoionization (APPI) is an effective ionization technique for the analysis of low polarity and nonpolar compounds using liquid chromatography/mass spectrometry. Ions are produced through a mechanism which begins with initial photoionization of a primary reagent, termed a "dopant", followed by either proton transfer or charge exchange with the analyte(s). This thesis regards improving the ionization efficiency of APPI by identifying new dopant candidates that can increase the breadth of compounds amenable to APPI, and/or improve the ionization efficiency for compounds that are already amenable to APPI. The desired properties for a dopant candidate include high ionization energy (IE) and low reactivity of its photoions with solvent and dopant neutrals. Reactivity tests for 25 substituted-benzene compounds with substituents ranging from strongly electron withdrawing (EW) to strongly electron donating (ED) were performed. Results showed that ED groups decreased reactivity and IE while EW groups increased reactivity and IE; an exception was if the ED group was itself acidic. Of the compounds tested, 2,4-difluoroanisole and 3-(trifluoromethyl)anisole showed the best potential as dopants for charge exchange. These dopants - along with two other novel dopants, bromo- and chlorobenzene - were compared with established dopants (toluene, anisole, and a toluene/anisole mixture) for charge exchange ionization of polycyclic aromatic hydrocarbons (PAHs). Bromo- and chlorobenzene both showed significant improvement in ionization efficiency compared with previously established dopants due to their relatively low reactivity with the solvent and high IE. It was also found that the improved performance for higher IE PAHs, when using anisole, diluted to 0.5% with toluene, was possibly due to the presence of an impurity in anisole. Of the dopants tested, bromobenzene/2,4-difluoroanisole (99.5:0.5 v/v) was determined to be the best overall for charge exchange ionization.
Item Metadata
Title |
Systematic study of dopants for use in atmospheric pressure photoionization mass spectrometry
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2008
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Description |
Atmospheric pressure photoionization (APPI) is an effective ionization technique for the
analysis of low polarity and nonpolar compounds using liquid chromatography/mass
spectrometry. Ions are produced through a mechanism which begins with initial
photoionization of a primary reagent, termed a "dopant", followed by either proton
transfer or charge exchange with the analyte(s). This thesis regards improving the
ionization efficiency of APPI by identifying new dopant candidates that can increase the
breadth of compounds amenable to APPI, and/or improve the ionization efficiency for
compounds that are already amenable to APPI. The desired properties for a dopant
candidate include high ionization energy (IE) and low reactivity of its photoions with
solvent and dopant neutrals. Reactivity tests for 25 substituted-benzene compounds with
substituents ranging from strongly electron withdrawing (EW) to strongly electron
donating (ED) were performed. Results showed that ED groups decreased reactivity and
IE while EW groups increased reactivity and IE; an exception was if the ED group was
itself acidic. Of the compounds tested, 2,4-difluoroanisole and 3-(trifluoromethyl)anisole
showed the best potential as dopants for charge exchange. These dopants - along with
two other novel dopants, bromo- and chlorobenzene - were compared with established
dopants (toluene, anisole, and a toluene/anisole mixture) for charge exchange ionization
of polycyclic aromatic hydrocarbons (PAHs). Bromo- and chlorobenzene both showed
significant improvement in ionization efficiency compared with previously established
dopants due to their relatively low reactivity with the solvent and high IE. It was also
found that the improved performance for higher IE PAHs, when using anisole, diluted to
0.5% with toluene, was possibly due to the presence of an impurity in anisole. Of the
dopants tested, bromobenzene/2,4-difluoroanisole (99.5:0.5 v/v) was determined to be the
best overall for charge exchange ionization.
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Extent |
2846494 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-03-06
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0061683
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2008-11
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International