Analytical Chemistry Commons^™

Investigations Into Ambient Ionization Mechanisms: Electrospray Ionization And Direct Analysis In Real Time Mass Spectrometry, Stephen Colin Gibson

Doctoral Dissertations

Mass spectrometry (MS) is an important tool for chemical analyses. Despite the MS requirement for generation of analyte gas-phase ions, many ion source designs afford little-to-no fragmentation, allowing characterization of intact molecules. However, this does not assure that detected ions are representative of the analytes’ natural state. Ionization mechanisms are generally complex and rarely fully understood. Fundamental research into these mechanisms provides greater insight into the relationship between solution chemistry and mass spectra. Work herein addresses aspects of two ambient ionization mechanisms: electrospray ionization (ESI) and Direct Analysis in Real Time (DART).

Ions produced by ESI are dispersed into a …

Understanding The Plasmonic Properties Of Metallic Nanostructures With Correlated Photon- And Electron-Driven Excitations, Vighter Ozezinimize Iberi

Doctoral Dissertations

The collective oscillation of the conduction band electrons in metal nanostructures, known as plasmons, can be used to manipulate light on length scales that are smaller than the diffraction limit of visible light. In this dissertation, a correlated approach is used to probe localized surface plasmon resonances (LSPRs) in metallic nanostructures, and their application to surface-enhanced spectroscopy. This correlated approach involves the measurement of LSPRs with dark-field optical microscopy (resonance-Rayleigh scattering), and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Structural parameters of the exact same nanostructures obtained from the STEM are subsequently used in performing fully …

Development Of Optical Sensors For Chemical Detection, Jonathan Kelly Fong

Doctoral Dissertations

Detection of biodiesel at low and high concentrations in diesel is highly desired in the aviation and fuel industries. Cross contamination of jet fuel with biodiesel may impact the thermal stability and freezing point which can cause deposits in the fuel system or cause the fuel to gel, leading to jet engine operability problems and possible engine flameout. A dye doped optical sensor utilizing the dye Nile Blue Chloride has been developed for quick and direct detection of biodiesel which mainly contains fatty acid methyl esters (FAME). The sensing mechanism relies on the solvatochromatic properties of the dye which undergoes …

The Development Of Apci Mass Spectrometry Based Systems For Quantitative Real-Time Monitoring Of Process-Scale Homogenous And Heterogeneous Reactions, Zhenqian Zhu

Doctoral Dissertations

The dissertation presents solutions to monitor industrial chemical processes quantitatively in real time by mass spectrometry. Chapter 1 presents the background of atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Chapters 2-6 present methods developed based on flow injection analysis coupled to atmospheric pressure chemical ionization mass spectrometry (FIA/APCI-MS) for quantitative real-time monitoring of homogeneous and heterogeneous reactions conducted at molar concentrations.

Chapter 2 introduces auto-sampling FIA/APCI-MS with the ability to overcome potential sample overloading when molar concentration samples were analyzed without sample pretreatment procedures. A homogenous Michael-addition reaction between phenethylamine and acrylonitrile was conducted at room temperature and monitored quantitatively …

Using Ultra Performance Liquid Chromatography-Mass Spectrometric Based Metabolomics To Determine The Metabolic Differences Due To Low Temperature Or Genetic Mutation In Salmonella Enterica, Nicole Rhonda Mooney

Masters Theses

Metabolomics aims to identify and quantify all of the small molecules within a cell. The relative concentrations of metabolites within cells grown under different experimental conditions, or different species, can be compared using pool size data. Exposing cellular cultures to isotopically labeled compounds allows the progress of metabolites through metabolic pathways to be tracked, known as flux. In the first experiment, the metabolic effects of exposure to lower than optimal temperatures in wild type Salmonella enterica, i.e. cold shock, were determined. The metabolites involved in glycolysis, the citric acid cycle, and the pentose phosphate pathway had less efficient labeling …