Supplementary Information
Regulated in situ Generation of Molecular Ions or Protonated Molecules under
Atmospheric-Pressure Helium-Plasma-Ionization Mass Spectrometric Conditions
Rekha Gangam, Julius Pavlov, Athula B. Attygalle*
Center for Mass Spectrometry, Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens
Institute of Technology, Castle Point on the Hudson, Hoboken, NJ 07030, USA
Athula.attygalle @stevens.edu
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Supplementary Figure S1. Positive-ion HePI mass spectra (m/z 1-100) recorded from
toluene placed in an enclosed HePI source successively flushed with
ambient air (top panel) or dry O2 (bottom panel).
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Supplementary Figure S2. Reconstructed ion chronograms for m/z 78 (red trace),
and 79 (blue trace) derived from positive-ion mass spectrometric data
(m/z 20-120) recorded from a sample of benzene in a glass vial placed
in an enclosed HePI source (a). Initially, the source was under dry
oxygen, and at 1.0 min the chamber was flushed with ambient air for a
period of one minute. The flushing sequence was repeated several
times. Panels (b) and (c) show typical spectra corresponding to each
flushing period.
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Supplementary Figure S3. A total-ion chronogram (m/z 20-120) recorded from a sample
of toluene placed in an enclosed HePI source. Initially, the source was exposed
to ambient air. At 1.0 min the source was flushed with helium. The process was
repeated several times at different helium flows as indicated in panel (a).
Panels (b)-(e) show the range m/z 88-98 of positive-ion spectra recorded in the
four regions of the chronogram.
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Supplementary Figure S4. Reconstructed ion chronograms for m/z 96 (red trace), and
97 (blue trace) derived from positive-ion mass spectrometric data (m/z 20120) obtained from a sample of fluorobenzene in an enclosed HePI source
(a). Initially, the source was under dry oxygen, and at 1.0 min the chamber
was flushed with ambient air for a period of one minute. The flushing
sequence was repeated several times. Panels (b) and (c) show typical spectra
corresponding to each flushing period.
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Supplementary Figure S5. A total-ion chronogram (m/z 60-160) obtained from a sample
of chlorobenzene in an enclosed HePI source (a). Initially, the source was
under dry oxygen and at 1.0 min the chamber was flushed with ambient air
for a period of one minute. The flushing sequence was repeated several
times. Panels (b) and (c) show typical spectra corresponding to each
flushing period.
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Supplementary Figure S6. A total-ion chronogram (m/z 80-180) obtained from a sample
of bromobenzene in an enclosed HePI source (a). Initially, the source was
under dry oxygen and at 1.0 min the chamber was flushed with ambient air
for a period of one minute. The flushing sequence was repeated several
times. Panels (b) and (c) show typical spectra corresponding to each
flushing period.
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Supplementary Figure S7. A total-ion chronogram (m/z 150-250) obtained from a sample
of iodobenzene in an enclosed HePI source (a). Initially, the source was
under dry oxygen and at 1.0 min the chamber was flushed with ambient air
for a period of one minute. The flushing sequence was repeated several
times. Panels (b) and (c) show typical spectra corresponding to each
flushing period.
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Supplementary Figure S8. A total-ion chronogram (m/z 60-200) obtained from an
equimolar mixture of fluorobenzene and bromobenzene. The source was
flushed with dry oxygen for 1.5 min starting at 1.0 min (a). The switching
procedure was repeated two more times. Panel (b) shows a chronogram
recorded in a similar manner but with a cotton swab soaked in water
placed in the source. Mass spectra corresponding to various regions of the
two chronograms are presented in panels a1, a2, b1 and b2.
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Supplementary Figure S9. A total-ion chronogram (m/z 100-250) obtained from an
equimolar mixture of bromobenzene and iodobenzene placed in an enclosed HePI
source exposed to ambient air. The source was flushed with dry oxygen for 1.5
min starting at at 1.0 min (a). The switching procedure was repeated two more
times. Panel (b) shows a chronogram recorded in a similar manner but with a
cotton swab soaked in water placed in the source. Mass spectra corresponding to
various regions of the two chronograms are presented in panels a1, a2, b1 and b2.
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Supplementary Figure S10. A total-ion chronogram (m/z 60-260) obtained from a mixture
of chlorobenzene and iodobenzene placed in an enclosed HePI source exposed to
ambient air. The source was flushed with dry oxygen for 1.5 min starting at 1.0
min (a). The switching procedure was repeated two more times. Panel (b) shows
a chronogram recorded in a similar manner but with a cotton swab soaked in
water placed in the source. Mass spectra corresponding to various regions of the
two chronograms are presented in panels a1, a2, b1 and b2.
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Supplementary Figure S11. Mass spectra recorded from an equimolar mixture of
fluorobenzene and chlorobenzene placed in an enclosed HePI source exposed to
ambient air, or dry oxygen. Spectra in panels a1 and b1 were recorded with the
sample exposed to ambient air, whereas those in panels a2 and b2 were recorded
with dry oxygen. The spectra in panels b1 and b2 were recorded with a cotton
swab soaked in water placed in the source.
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Supplementary Figure S12. Mass spectra recorded from an equimolar mixture of
chlorobenzene and bromobenzene placed in an enclosed HePI source exposed to
ambient air, or dry oxygen. Spectra in panels a1 and b1 were recorded with the
sample exposed to ambient air, whereas those in panels a2 and b2 were recorded
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with dry oxygen. In addition, spectra in panels b1 and b2 were recorded with a
cotton swab soaked in water placed in the source.
Supplementary Figure S13. Mass spectra recorded from an equimolar mixture of
fluorobenzene and iodobenzene placed in an enclosed HePI source exposed to
ambient air, or dry oxygen. The spectra in panels a1 and b1 were recorded with
the sample exposed to ambient air, whereas those in panels a2 and b2 were
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recorded with dry oxygen. In addition, the spectra in panels b1 and b2 were
recorded with a cotton swab soaked in water placed in the source.
Supplementary Table 1. Gas-phase ion energetics data of some aromatic compounds and water.
Compound
Ionization Energy, Ionizatio
Proton Affinity,
Gas-phase
eV*
n Energy,
kJ/mol*
basicity kJ/mol
kJ/mol*
Benzene
9.24378 ± 0.00007 891.89
750.4
725.4
Toluene
8.828 ± 0.001
851.77
784.0
756.3
Fluorobenzene (PhF)
9.20 ± 0.01
887.67
755.9
726.26
Chlorobenzene (PhCl) 9.07 ± 0.02
875.12
753.1
724.6
Bromobenzene (PhBr) 9.00 ± 0.03
868.37
754.1
725.8
Iodobenzene (PhI)
8.72 ± 0.04
841.35
Data not available Data not available
aniline
7.720± 0.002
744.87
882.5
850.6
water
12.621± 0.002
1217.74
691
660
* Data from NIST Chemistry WebBook, NIST Standard Reference Database Number 69
(http://webbook.nist.gov/chemistry/)
The Gibbs energy change associated with the protonation reaction is called the gas phase
basicity, GB, of molecule M.
Stable cations formed in the gas phase also include protonated neutral molecules, generated in
proton transfer reactions. Formally, the relationship between the enthalpy of formation of
MH+ and its neutral counterpart, M, is defined in terms of a quantity called the proton affinity,
PA. This the negative of the enthalpy change of the hypothetical protonation reaction:
M + H+ → MH+
Δ Hrxn = −PA
ΔfH;(MH+) = ΔfH°(M) + ΔfH;(H+) − PA
The ionization energy is the energy required to remove an electron from a molecule or atom:
M → M+ + e−
ΔHrxn = IEa
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