DEVELOPMENT OF TANDEM MASS SPECTROMETRIC METHODS FOR THE MOLECULAR-LEVEL CHARACTERIZATION OF ASPHALTENES AND IMPROVEMENT OF THE LASER-INDUCED ACOUSTIC DESORPTION TECHNOLOGY

Mass spectrometry (MS) is a powerful tool for the molecular-level characterization of complex mixtures. It is susceptible, selective, versatile, and fast. MS provides molecular weight information for the ionized analytes based on their mass-to-charge (m/z) ratios. Elemental compositions of the ionized analytes can be provided by MS operated at high resolution. In addition, MS provides invaluable information through tandem mass spectrometric approaches. Tandem mass spectrometry (MSn, n ≥ 2, where n is the number of ion-separation steps) utilizing collision-activated dissociation (CAD) has proven especially effective for elucidating the structures of individual compounds in complex mixtures. MS can be coupled with various external desorption/ionization methods. Laser-induced acoustic desorption (LIAD) is a technique that enables the evaporation of nonvolatile and thermally labile compounds into a mass spectrometer from the surface of the metal foil. LIAD is a soft evaporation technique that is a great companion for MS because it causes minimal fragmentation to the desorbed neutral molecules. LIAD can also be coupled with instruments other than mass spectrometers, such as molecular rotational resonance (MRR) spectrophotometer as a versatile evaporation technique.

This dissertation focuses on research using high-resolution tandem mass spectrometric methods for the structural characterization of isomeric cations of asphaltene model compounds. The fragmentation behaviors of seven isomeric n-pentylquinoline radical cations are studied. Mechanisms for the formation of several fragment ions are also discussed based on quantum chemical calculations. Additionally, a novel suspension spin coating method is reported to improve LIAD performance. Further discussed in the dissertation is the endeavor of expanding the field of LIAD applications to MRR spectroscopy.