Chemical Reactions in the Gas Phase, Solution Phase and at Interfaces to Facilitate Mass Spectrometric Analysis and Rapid Synthesis

Chemical derivatization is the act of taking an analyte and transforming it into something with more desirable properties, typically for analytical purposes. In the cases presented here, the desirable properties are those which increase the ionization efficiency of the species of interest or those which facilitate the discrimination of isomers. Nanoparticles are often utilized in biological assays, but unless they are made of metal such that they can be ionized directly by inductively coupled plasma (ICP) ionization, they are undetectable by mass spectrometry. Surface functionalization of silica nanoparticles (SiNPs) facilitates the reversible binding of highly ionizable molecules which can serve as reporters for the presence of the particle. This constitutes chemical derivatization. In this dissertation, the synthesis of imidazolium salts for use as chemical derivatization reagents (mass labels) is reported. They were designed to be synthesized quickly and cheaply and bind reversibly to amine and diol functionalized nanoparticles. The pre-charged (imidazolium) nature of the labels facilitates excellent limits of detection (1 nM). Binding and release of the mass labels from nanoparticles is demonstrated and analysis of the loading and release efficiency is conducted. Isobaric amino acids in the backbone of a peptide are difficult to determine. The prime example of a problematic isobaric pair of amino acids is the coding aspartic acid (Asp) and the product of its post-translational modification, isoaspartic acid (isoAsp). Reported here is the use of a common reagent which binds carboxylic acids, substituted carbodiimide, to determine the percentage of isoAsp in a sample of peptide. The carbodiimide is added to a solution of the peptide and it binds the carboxylate of the Asp or isoAsp residue. The resulting acylisourea (AiU) is ionzed and, in the gas phase, it rearranges via a 1–3 acyl shift to yield an N-acylurea (NAU). The AiU and NAU yield different fragment ions and so even though they are isobaric, they can be differentiated via collision induced dissociation (CID) product ion mass spectrometry. Importantly, the AiU derived from isoAsp rearranges more slowly to NAU than the AiU from derived from Asp. The rearrangement occurs on the timescale of the MS experiment (milliseconds) and so can be affected by the residence time of ions in the ion trap, the bandwidth of the isolation waveform, the potential offset applied to the transfer optics in the high-pressure region of the atmospheric pressure interface and the amplitude of the activation waveform. Saturated alkanes are a third example of analytes which pose a problem to mass spectrometry. They are completely inaccessible to spray-based ionization methods and often require specialized equipment or niche methods for ionization. Field ionization persists as the gold-standard in hydrocarbon ionization and atmospheric pressure chemical ionization (APCI) continues to develop in the field. Typical products of APCI of saturated hydrocarbons are hydride abstraction ([M-H]+), nitric oxide addition ([M+NO]+) or electron abstraction (M+.). This dissertation reports the chemical derivatization of saturated hydrocarbons by selective fixation of nitrogen (to generate ions of the formula [M+N]+) or oxygen (to generate ions of the formula [M+O-H]+). The standard Waters APCI-Gas Chromatography (APGC) ion source was used to affect this chemistry. The oxidation process was shown to be regioselective and energetic enough to induce C-C bond cleavage. The off-line collection of ketones and aldehyde fragments of those ketones is reported. Subsequent analysis of the collected species shows that even outside of the mass spectrometry experiment, the chemistry is regioselective. The ion chemistry leading to oxidation is elucidated as an ion/molecule reaction between charged hydrocarbons and neutral ozone. Spray-based mass spectrometry has yielded interesting insights into the acceleration of reaction rates at the interface between small charged droplets and air. Other developments have included accelerated reactions in thin films. The phase of the reaction at the point of acceleration is explored in this dissertation by utilizing the Fischer Indole Synthesis under conditions which produce different products depending on the phase in which the reaction takes place. Reaction acceleration has typically been conducted on the small-scale. Production of milligrams of material per hour has been demonstrated with spray-based ionization sources but this scale still does not represent synthetically useful quantities. Discussed herein is the scale-up of the accelerated Claisen-Schmidt and Katritzky reactions as well as the acceleration of ester hydrolysis and imine formation in a rotary evaporator. The Suziki reaction is also demonstrated to undergo reaction acceleration at the interface of chloroform and water; a biphasic system commonly encountered in a separating funnel during the normal workflow of the synthetic organic chemist

Mass spectra of halogenostyrylbenzoxazoles

NoSeveral series of styrylbenzoxazoles of general formula XC6H3(NCO)CH=CHC6H4Y [X= F, Cl or Br; Y = H, F, Cl, Br, CH3 or CH3O] have been investigated by positive ion electrospray and electron ionization mass spectrometry. These compounds, many of which are biologically active or have pharmaceutical potential, show in their electrospray spectra strong peaks for MH+ ions, which undergo relatively little fragmentation. The electron ionization spectra are extremely clean, being dominated by the loss of an atom or radical, Y*, from the ortho position of the pendant ring, by a rearrangement that may be interpreted as a proximity effect. The resultant [M-Y](+) ions are exceptionally stable and rarely undergo further fragmentation. The analytical value of this proximity effect, which is analogous to intramolecular aromatic substitution, in revealing the presence of a substituent in the pendant ring and determining its position, is emphasized. Elimination of a species (including H* or F*) derived from an ortho substituent in the pendant ring occurs even when apparently more favourable alternative fragmentation is possible by direct cleavage of the C-X bond (X = Cl or Br) in the benzoxazole ring

A Low-Cost, Simplified Platform of Interchangeable, Ambient Ionization Sources for Rapid, Forensic Evidence Screening on Portable Mass Spectrometric Instrumentation

Portable mass spectrometers (MS) are becoming more prevalent due to improved instrumentation, commercialization, and the robustness of new ionization methodologies. To increase utility towards diverse field-based applications, there is an inherent need for rugged ionization source platforms that are simple, yet robust towards analytical scenarios that may arise. Ambient ionization methodologies have evolved to target specific real-world problems and fulfill requirements of the analysis at hand. Ambient ionization techniques continue to advance towards higher performance, with specific sources showing variable proficiency depending on application area. To realize the full potential and applicability of ambient ionization methods, a selection of sources may be more prudent, showing a need for a low-cost, flexible ionization source platform. This manuscript describes a centralized system that was developed for portable MS systems that incorporates modular, rapidly-interchangeable ionization sources comprised of low-cost, commercially-available parts. Herein, design considerations are reported for a suite of ambient ionization sources that can be crafted with minimal machining or customization. Representative spectral data is included to demonstrate applicability towards field processing of forensic evidence. While this platform is demonstrated on portable instrumentation, retrofitting to lab-scale MS systems is anticipated

Simultaneous Online Monitoring of Multiple Reactions Using a Miniature Mass Spectrometer

Advances in chemical sampling using miniature mass spectrometer technology are used to monitor slow reactions at a frequency of ca. 180 h^–1 (on the Mini 12) with no sample carryover and with inline derivatization in the case of poorly ionizing compounds. Moreover, we demonstrate high reproducibility with a relative error of less than 10% for major components. Monitoring is enabled using a continuous-flow nanoelectrospray (CF-nESI) probe contained in a custom-built 3D-printed rotary holder. The holder position is automatically set using a stepper motor controlled by a microcontroller. Reaction progress of up to six reactions, including hydrazone formation and Katritzky transamination, can be monitored simultaneously without carryover for several hours