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Elucidating the Fundamentals of Laser ELUCIDATING THE FUNDAMENTALS OF LASER ELECTROSPRAY MASS SPECTROMETRY AND CHARACTERIZATION OF COMPOSITE EXPLOSIVES AND CLASSIFICATION OF SMOKELESS POWDER AND ITS RESIDUE USING MULTIVARIATE STATISTICAL ANALYSIS A Dissertation Submitted To the Temple University Graduate Board In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Johnny J. Perez December 2016 Examining Committee Members: Robert J. Levis, Associate Dean, Department of Chemistry, Temple University Daniel R. Strongin, Advisory Chair, Department of Chemistry, Temple University Michael J. Zdilla, Department of Chemistry, Temple University Anthony Lagalante, External Member, Department of Chemistry, Villanova University © Copyright 2016 by Johnny J. Perez All Rights Reserved ii ABSTRACT This dissertation expounds growing insight of the electrospray droplet ionization mechanism following ablation of dried hydrophobic and hydrophilic molecules using femtosecond laser pulses and mass analysis of the gas phase ions. Both hydrophobic and hydrophilic molecules were laser vaporized into an electrospray solvent opposite in polarity revealing appreciable ion intensity for all samples in contrast to ESI-MS and DESI measurements were solubility of the analyte in the spray solvent is a prerequisite. Quantitative analysis of equimolar protein solutions was established using LEMS reporting over three decades of quantitave response with little evidence of ion suppression. In contrast, ESI-MS measurements of similar equimolar protein solutions revealed severe ion suppression eliminating ion current from one of the protein analytes. Finally, the nature of an analyte following nonresonant laser vaporization has been the subject of debate. Aqueous trypsin was laser vaporized into an electrospray solvent containing either buffer or acid with substrate. LEMS measurements using buffer revealed enzyme-substrate intermediate charge states and continued enzymatic activity while the lack of enzyme-substrate intermediates and stymied enzymatic activity observed using acid suggests nonresonant laser vaporization preserves solution phase structure. This dissertation also extends considerably the use of LEMS for identification and characterization of energetic materials in their pre- and post-blast forms without sample preparation. The use of mulivarate analysis for the classification of large sample sets was also demonstrated showing high fidelity assignment of commercial formulations iii to their manufacturer. Five unburnt smokeless powders investigated using LEMS revealed unique combinations of organic molecules such as stabilizers and plasticizers using a simple electrospray solvent. Principal component analysis (PCA) provided exact classification of the mass spectra with respect to the manufacturer of the ordinance. LEMS measurments were then obtained from five commercial gunshot residue samples, or post-blast smokeless powder, revealing trace amounts of organics such as the stabilizers and large quantities of inorganic barium originating from the primer. Principal component analysis (PCA) again provided exact classification of the gunshot residue mass spectra with respect to the manufacturer of the ordinance.The use of a common transition metal complexation agent enabled full characterization of eight gunshot residue samples to include the heavy metals contained in the primer and the organics such as the stabilizers and plasticizers without any sample preparation or pre-concentration procedures. Principal component analysis (PCA) again provided high fidelity classification of the gunshot residue mass spectra with respect to the manufacturer of the ordinance after mass analysis with LEMS. Finally, highly energetic formulations such as composition 4 (C-4) and detonation cord subjected to nonresonant femtosecond laser vaporization enabled full characterization of these complex compositions identifying binders, stabilizers, the explosive ingredient and age-related decomposition derivative signature molecules with appreciable ion current detected using both positive and negative ion modes. iv To my family, friends, and colleagues for all their support, love and encouragement v ACKNOWLEDGMENTS First and foremost, I would like to thank my adviser, Professor Robert Levis, for his mentorship, guidance and unbridled support of my research plans and aspirations. I would like to thank Temple University’s support staff, Ed Kaczanowicz, Matthew McCormick and Richard Harris for their tireless support with our research projects. I would like to thank past and present group members for their mentorship and guidance. I especially thank John Brady, Santosh Karki and Erin McCole Dulogoz whom, under their own volition, took an enormous amount of their free time to educate me on standard operating procedures and complexities of the mass spectrometer and femtosecond laser system. I would also like to thank past and present members of the Levis group, to include Elizabeth Judge, Paul Flanigan, Timothy Bohinski, Johanan Odhner, Jieutonne Archer, Fengjian Shi and David Watson, for their invalueable input and discourse. I would also like to thank my family and especially my girlfriend, Michelle Virone, for their vigorous support and constant encouragement throughout my graduate school career. Finally, I would like to thank Temple University and the Chemistry Department for their consistent support while deployed to Support Operation's Iraqi Freedom and New Dawn and their immediate reception and rematriculation into the graduate program upon my return to the United States. vi TABLE OF CONTENTS Page ABSTRACT ....................................................................................................................... iii DEDICATION .....................................................................................................................v ACKNOWLEDGMENTS ................................................................................................. vi LIST OF TABLES ........................................................................................................... xiv LIST OF FIGURES ...........................................................................................................xv CHAPTER 1. INTRODUCTION .........................................................................................................1 1.1 The History Leading to the Development of Atmospheric Pressure Mass Spectrometry.............................................................................................1 1.2 The Development of Laser Desorption and Its Use as an Ionization Source ................................................................................................................5 1.3 Desorption Electrospray Ionization (DESI)- the Bellwether of Ambient Mass Spectrometry.............................................................................................7 1.4 Ambient Mass Spectral Analysis Using Laser Desorption and Electrospray Post-ionization ............................................................................10 1.4.1 Electrospray-assisted Laser Desorption/Ionization (ELDI) ....................10 1.4.2 Matrix-assisted Laser Desorption Electrospray Ionization (MALDESI) .....................................................................................................12 1.4.3 Laser Ablation Electrospray Ionization (LAESI) ...................................14 1.4.4 Infrared-laser assisted Desorption Electrospray Ionization (IR- LADESI) ..........................................................................................................16 1.5 Laser Electrospray Mass Spectrometry ...........................................................17 1.6 Scope of this Dissertation ................................................................................30 vii 1.7 References ........................................................................................................40 2. EFFECT OF ANALYTE SOLUBILITY INTO AN INSOLUBLE ELECTROSPRAY SOLUTION FOLLOWING NONRESONANT LASER VAPORIZATION ........................................................................................................48 2.1 Overview ..........................................................................................................49 2.2 Introduction ......................................................................................................47 2.3 Experimental ....................................................................................................51 2.3.1 Materials ...........................................................................................51 2.3.2 Sample Preparation ...........................................................................51 2.3.3 Laser Vaporization and Ionization ....................................................53 2.3.4 Mass Spectrometry............................................................................53 2.3.5 Safety Considerations .......................................................................54 2.4 Results and Discussion ....................................................................................54 2.4.1 Analysis of Class A Molecules in Non-Aqueous ESI Solvents using LEMS .........................................................................................54 2.4.2 Analysis of Class B Molecules in Aqueous ESI Solvent using LEMS ...................................................................................................55 2.5 Conclusion .......................................................................................................57
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