<p>High resolution tandem mass
spectrometry (MS<sup>n</sup>) coupled with various separation techniques, such
as high-performance liquid chromatography (HPLC) and gas chromatography (GC),
is widely used to analyze mixtures of unknown organic compounds. In a mass
spectrometric analysis, analytes of interest are at first transferred into the
gas phase, ionized (protonated or deprotonated) and introduced into the
instrument. Tandem mass spectrometric experiments may then be used to gain
insights into structure and reactivity of the analyte ions in the gas phase.
The tandem mass spectral data are often compared to those reported in external
databases. However, the tandem mass spectra obtained for protonated analytes
may be markedly different from those in external databases because protonation
site manifested during a mass spectrometric experiment can be affected by the
ionization technique, ionization solvents and condition of the ion source. This
thesis focuses on investigating the effects of instrumental conditions and
analyte concentrations on the protonation sites of 4-aminobenzoic acid.
Reactivities of radical species were also investigated. A modified bracketing
method was developed and proton affinities of a series of mono- and biradicals
of pyridine were measured. In another study, a <i>para</i>-benzyne analog was
generated in both solution and the gas phase and its reactivities towards
various neutral reagents in the gas phase were compared to those in solution.</p>
<p> Chapter 2 discusses the fundamental aspects of
the instruments used in this research. In chapter 3, the effects of residual
moisture in linear quadrupole ion trap on the protonation sites of
4-aminobenzoic acid are considered. Chapter 4 focuses on the use of gas-phase
ion-molecule reactions with trimethoxymethylsilane (TMMS) for the
identification of the protonation sites of 4-aminobenzoic acid. Further, the
effects of analyte concentration on the protonation sites of 4-aminobenzoic
acid are considered. Chapter 5 introduces a modified bracketing method for the
experimental determination of proton affinities of a series of pyridine-based
mono- and biradicals. In chapter 6, successful generation of <i>para</i>-benzynes
in solution is discussed. The reactivity of a <i>para</i>-benzyne analog, 1,4-didehydrophenazine, is compared to its
reactivity in the gas phase.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12480443 |
| Date | 17 June 2020 |
| Creators | Rashmi Kumar (8972660) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/INVESTIGATION_OF_THE_PROTONATION_SITES_IN_POLYFUNCTIONAL_ANALYTES_UPON_ATMOSPHERIC_PRESSURE_IONIZATION_IN_MASS_SPECTROMETRY_AND_STUDIES_OF_THE_REACTIVITIES_OF_RADICALS_IN_THE_GAS_PHASE_AND_SOLUTION/12480443 |
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