Gas-phase ion-molecule reactions and laser -induced acoustic desorption mass spectrometry for complex mixture analysis and structural elucidation

Abstract

Mass spectrometry (MS) has proven invaluable in the field of mixture analysis and structural elucidation of mixture components, due to its high sensitivity, selectivity and speed. Tandem mass spectrometry (MS/MS) utilizing collision-activated dissociation (CAD) has become the technique of choice for structural elucidation of unknown analytes. The coupling of MS with high performance liquid chromatography (HPLC) has allowed the trace level analysis of components in very complex mixtures. However, these experiments alone do not always allow for unambiguous identification of an unknown analyte in a mixture. The experiments described in this thesis were aimed at providing more detailed structural information of mixture components that is difficult to obtain by established methods. In the first section (chapters 3, 4 and 5), gas-phase ion-molecule reactions were developed and implemented on a commercially available linear quadrupole ion trap (LQIT) mass spectrometer (Finnigan LTQ) to make these methods more widely applicable to the pharmaceutical industry. First, the performance a reagent mixing manifold that allows ion-molecule reactions to be carried out in the LQIT was probed by examining an established ion-molecule reaction previously employed on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Next, a novel ion-molecule reaction was developed using the new setup that exploits the favored formation of sodium and ammonium ion adducts when oxygen-containing analytes are ionized via electrospray ionization (ESI). Finally, the modified instrument was coupled with an HPLC to demonstrate that LC-MS3 using ion-molecule reactions and collision-activated dissociation (CAD) provides a powerful technique for the analysis of low level drug metabolites and impurities in pharmaceutical mixtures. Further, these methods were automated using the data-dependent features of the instrument, allowing for detailed structural information of unknown analytes “on-the-fly.” The second section (chapters 6, 7 and 8) focus on the development of laser-induced acoustic desorption (LIAD) methodology for structural elucidation. First, the coupling of this technique with a LQIT is presented and LIAD experiments are compared to those performed in a FT-ICR. Next, the use of LIAD in studies on the gas-phase reactivity of phenyl radicals toward tetrapeptides is presented. Very interesting results were obtained on the susceptibility of the disulfide bond to radical attack, especially considering the important role these bonds play in defining proteins’ structures. Finally, the ability of LIAD-based methods to perform unparalleled characterization of petroleum fractions is presented. Also, the development of ClMn(H2O)+ chemical ionization (CI) on the LQIT is examined. The coupling of this CI method with LIAD on the LQIT is the initial step for future implementation of this methodology on a hydrid LQIT/FT-ICR instrument to provide one of the most powerful instruments for petroleum characterization in the industry