Online Characterization of Isomeric/Isobaric Components
in the Gas Phase of Mainstream Cigarette Smoke by Tunable Synchrotron
Radiation Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry
and Photoionization Efficiency Curve Simulation
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Abstract
A newly developed, qualitative and
quantitative method based on
tunable synchrotron radiation vacuum ultraviolet photoionization time-of-flight
mass spectrometry (SR-VUV-PI-TOFMS) and photoionization efficiency
(PIE) curve simulation was applied for the online analysis of isomers
and isobaric compounds in the gas phase of mainstream cigarette smoke.
After blocking the particulate phase components by the Cambridge filter
pad, a puff of fresh gas-phase cigarette smoke was immediately introduced
into a vacuum ionization chamber through a heated capillary, then
was photoionized, and analyzed by a TOF mass spectrometer. The PIE
curves for the mass peaks up to <i>m</i>/<i>z</i> = 106 were measured between 8.0 and 10.7 eV. Some components could
be directly identified by their discriminated ionization energies
(IEs) on the PIE curve. By simulating the PIE curve with the sum of
scaled absolute photoionization cross sections (PICSs), complex isomeric/isobaric
compounds along with their mole fractions could be obtained when the
best-fitting was realized between experimental and simulated PIE curves.
A series of reported toxic compounds for quantification, such as 1,3-butadiene
(<i>m</i>/<i>z</i> = 54), 1,3-cyclopentadiene
(<i>m</i>/<i>z</i> = 66), benzene (<i>m</i>/<i>z</i> = 78), xylene (<i>m</i>/<i>z</i> = 106), 2-propenal (<i>m</i>/<i>z</i> = 56),
acetone and propanal (<i>m</i>/<i>z</i> = 58),
crotonaldehyde (<i>m</i>/<i>z</i> = 70), furan
and isoprene (<i>m</i>/<i>z</i> = 68), were all
found to have other isomers and/or isobaric compounds with considerable
abundances. Some isomers have never been reported previously in cigarette
smoke, like C<sub>5</sub>H<sub>6</sub> isomers 1-penten-3-yne, 3-penten-1-yne,
and 1-penten-4-yne at <i>m</i>/<i>z</i> = 66.
Isomeric/isobaric compounds characterization for the mass peaks and
mole fraction calculations were discussed in detail below 10.7 eV,
an energy value covering several conventional used VUV light sources