Liquid chromatographic/mass spectrometric investigations of bio-oil and advances in laser-induced acoustic desorption fundamentals and instrumentation
Abstract
Tandem mass spectrometry has become a widely-used tool in the analytical sciences. Notable characteristics of tandem mass spectrometry include high sensitivity and speed, low detection limit, and high specificity. Tandem mass spectrometric experiments are performed by isolation of a desired ion followed by collision-induced dissociation (CID) or ion-molecule reactions. Coupling liquid chromatography (LC) with tandem MS allows researchers to tackle analytical problems of even greater complexity and difficulty. Some of the problems solved with high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) include separation and identification of isomers and complex mixtures. Bio-oil produced by fast pyrolysis of lignocellulosic biomass contains hundreds of compounds, yet with HPLC-MS, the mixture can be separated and analyzed by using the mass spectrometer. In addition, biooil can be catalytically upgraded to produce multiple isomers, which can be separated and analyzed using HPLC-MS/MS. Tandem mass spectrometry, as with any analytical tool, is not without weaknesses. Complex mixtures of nonvolatile compounds, such as asphaltenes, are difficult to analyze. No methods exist for the introduction of asphaltenes into the gas phase without aggregation and also feature unbiased, soft ionization. To aid in the analysis of samples such as asphaltenes, laser-induced acoustic desorption (LIAD) can be employed. LIAD enables desorption of low-energy, neutral compounds allowing the ionization method to be chosen based on the sample. Since the development of LIAD, significant research has been conducted concerning the fundamentals and analytical applications of LIAD. However, the current understanding of LIAD is still limited. Development of LIAD instrumentation has also continued over the years, leading to the development of fiber, fiberless, high vacuum, and atmospheric pressure LIAD. Much like the fundamentals, instrumentation research still continues to improve LIAD. This dissertation has a dual focus. One focus is on the development of LCMS/ MS methods for the separation, identification, and quantification of the major products of biomass fast pyrolysis. A method utilizing HPLC separation and MS based on ionization via ammonium attachment was developed to determine the products of pure dihydroeugenol after catalysis. Bio-oil, obtained from the Riberio group, was separated using a novel LC method, yielding three fractions, which were analyzed and quantified using HPLC-MS/MS. The other focus of this dissertation is the further investigation of LIAD fundamentals and improvement of instrumentation. The fundamental parameter controlling LIAD desorption efficiency were explored using multiple petroleum-related model compounds in addition to crude oil, deasphaltened oil, and asphaltene samples. Imaging of the sample desorption was performed using a scanning electron microscope (SEM). Design and construction of an automated rastering stage for atmospheric pressure LIAD was completed and validated. Optimal rastering speed and temperature change while rastering were investigated.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry
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