Mass Spectrometric Studies on the Primary Products of Fast Pyrolysis of Carbohydrates and the Molecular Structures of Asphaltenes, and the Development of a Rastering Probe for Laser-Induced Acoustic Desorption into an Atmospheric Pressure Chemical Ionization Source
Date of Award
Doctor of Philosophy (PhD)
Committee Member 1
Committee Member 2
Committee Member 3
Mass spectrometry (MS) has proven invaluable in the field of mixture analysis and structural elucidation. Tandem mass spectrometry (MS/MS) utilizing collision-activated dissociation (CAD) has become the technique of choice for structural elucidation of unknown analytes in mixtures. When coupled with gas chromatography (GC) or high performance liquid chromatography (HPLC), it allows for trace level analysis of mixture components. In spite of the utility of mass spectrometry in complex mixture analysis, it does have limitations. Traditional GC/MS methods used for the analysis of fast pyrolysis products cannot be used to analyze the primary products, thus limiting the knowledge that can be obtained regarding the true mechanisms of fast pyrolysis, ultimately restricting the level of control over what final products are formed. Analysis of mixtures of hydrocarbons, such as crude oil, is also still a problematic area for mass spectrometry due to the lack of suitable evaporation/ionization methods for the heavier components. Consequently, very little is known about the structures of molecules in asphaltenes, the heaviest fraction of crude oil and one of the most complex mixtures in nature. Elucidating the structures of the compounds present in these mixtures is important for the rational design of methods to prevent the problems the cause.
Experiments described in this thesis employed tandem mass spectrometry to achieve a better understanding of the primary products of fast pyrolysis of carbohydrates and structures of molecules in asphaltenes. Chapter 2 briefly describes the instrumentation used for the research presented in this dissertation. Chapter 3 discusses the development of on-line mass spectrometric methods for the determination of the primary products of fast pyrolysis of carbohydrates and their gas- phase reactivity, demonstrating that there are many primary products that cannot be analyzed using traditional methods. Chapter 4 examines the differences in the molecular structures of petroleum and coal asphaltenes. Chapter 5 focuses on changes to asphaltenes' molecular structures when they are subjected to the hydrocracking process, a common practice in crude oil refinement. Chapter 6 compares field deposit asphaltenes, removed from a pipeline, to heptane precipitated asphaltenes from crude oil in a laboratory. Chapter 7 contrasts the effects of using different solvents in atmospheric pressure chemical ionization (APCI) of asphaltenes.
Chapters 8 and 9 focus on advances for laser-induced acoustic desorption (LIAD). Chapter 8 discusses improvements LIAD/APCI, including the development of a high-power laser probe for more reproducible evaporation of high-mass compounds into the gas phase, and the development of a rastering assembly that greatly increases the surface area of the LIAD foil that can be sampled. Chapter 9 discusses a novel chamber for preparing sample foils for LIAD by using a drying gas to prepare foils. The new chamber that helps in the production of foils with a more uniform sample layer than previously possible for nonpolar analytes to improve the reproducibility of LIAD.
Hurt, Matthew Robert, "Mass Spectrometric Studies on the Primary Products of Fast Pyrolysis of Carbohydrates and the Molecular Structures of Asphaltenes, and the Development of a Rastering Probe for Laser-Induced Acoustic Desorption into an Atmospheric Pressure Chemical Ionization Source" (2013). Open Access Dissertations. 140.