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And the Reference Electrode (Right) Development of an Electrochemical Sensor for Detection of 2,4-Dinitrotoluene A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Eric James Olson IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Philippe Bühlmann, Adviser July 2012 © Eric J. Olson 2012 Acknowledgements During the course of my doctoral work, I have received the assistance and support from the following people: First and foremost, I am truly indebted to my adviser, Philippe Bühlmann. His undying dedication to science and insatiable thirst for knowledge has been an inspiration to me over the last five years. More than that, the guidance, support, and, most importantly, friendship that Phil has provided has greatly benefitted my development both as a person and as a scientist. I must give special thanks to Dr. Paul Boswell and Dr. Scott Thorgaard for helping me get started in the lab and teaching me best practices for performing electrochemistry experiments. I would also like to thank the following people for their specific contributions to the work described in this thesis: Our collaborator, Professor Andreas Stein, for the many hours that he has spent discussing our collaborative research. His insight and unique point of view has been extremely useful. Dr. Bradley Givot at the 3M Corporate Research Laboratory for measuring the dielectric spectra presented in Chapter 2. Dr. Letitia Yao of the University of Minnesota Chemistry NMR Lab for her assistance with measuring the self-diffusion coefficient of perfluoro(methylcyclohexane) in Chapter 2. Peter Ness of the University of Minnesota Physics Machine Shop for his assistance in designing the microcell described in Chapter 3. Teng Xiong for performing the initial work that led us to question the traditional interpretation of the interaction of 2,4-dinitrotoluene with amines. Amanda Zeise and Jing-Lei Zhang for their preliminary contributions to the UV-Vis studies presented in Chapter 4. Professor Christopher Cramer for performing the DFT studies in Chapter 4. i Melissa Fierke for the synthesis, chemical modification, and characterization of the three-dimensionally ordered macroporous carbon electrodes used for the selective detection of 2,4-dinitrotoluene. I would also like to thank my colleagues in the Bühlmann research group for their friendship and support. The people that I have had the opportunity to work with over the last five years have made my graduate studies a truly enjoyable experience. Lastly, I owe a great deal to my family. Without their love, devotion, and support, I would not be where I am today. ii Dedication This dissertation is dedicated to Amber Rose Olson. iii Table of Contents Acknowledgements ............................................................................................................ i Dedication ......................................................................................................................... iii Table of Contents ............................................................................................................. iv List of Tables .................................................................................................................. viii List of Figures ................................................................................................................... ix List of Symbols and Abbreviations ............................................................................ xviii List of Publications ........................................................................................................ xxi 1 CHAPTER ONE ........................................................................................................1 Introduction ........................................................................................................................1 1.1 Chapter Overview .........................................................................................................2 1.2 2,4-Dinitrotoluene as an Analyte ..................................................................................3 1.3 An Introduction to Electrochemistry ............................................................................4 1.3.1 The Electrochemical Cell .............................................................................. 5 1.3.2 The Reference Electrode ............................................................................... 7 1.3.3 Application of an External Voltage .............................................................. 9 1.3.4 Cyclic Voltammetry .................................................................................... 11 1.3.5 Voltammetry with Weakly Supported Media ............................................. 21 1.4 Overview .....................................................................................................................25 2 CHAPTER TWO .....................................................................................................28 Electrochemistry in Media of Exceptionally Low Polarity: Voltammetry with a Fluorous Solvent...............................................................................................................28 2.1 Introduction .................................................................................................................30 2.2 Experimental ...............................................................................................................32 2.2.1 Chemicals .................................................................................................... 32 2.2.2 Resistance Measurements ........................................................................... 32 2.2.3 Voltammetry ............................................................................................... 33 19 2.2.4 DOSY F NMR .......................................................................................... 34 2.2.5 Dielectric Dispersion Spectroscopy ............................................................ 34 2.3 Results and Discussion ...............................................................................................35 2.3.1 Electrolyte Characteristics .......................................................................... 35 2.3.2 Electrochemical Window ............................................................................ 36 2.3.3 Voltammetric Measurements ...................................................................... 38 2.3.4 Heterogeneous Rate Constant ..................................................................... 42 2.3.5 Dielectric Spectroscopy .............................................................................. 45 2.4 Conclusions.................................................................................................................46 2.5 Supporting Information ..............................................................................................48 2.5.1 Differential Scanning Calorimetry (DSC) .................................................. 48 2.5.2 Correction of Solution Resistance Effects .................................................. 48 2.5.3 Determination of the Oxidation Limit of NBu4BArF104/perfluoro(methylcyclohexane) ........................................................... 50 iv 2.5.4 Cyclic Voltammetry of Ferrocene-Free Electrolyte Solution ..................... 50 3 CHAPTER THREE .................................................................................................52 Minimizing Hazardous Waste in the Undergraduate Analytical Laboratory: A Microcell for Electrochemistry .......................................................................................52 3.1 Introduction .................................................................................................................53 3.2 Cell Details .................................................................................................................53 3.3 Supplement .................................................................................................................55 3.3.1 Detailed Cell Construction .......................................................................... 55 3.3.2 Microelectrode Polishing Procedure ........................................................... 58 3.3.3 Cyclic Voltammetry (CV) of Ferrocyanide ................................................ 58 3.3.4 CV of Ferrocene in Acetonitrile ................................................................. 61 3.3.5 Concentration Profiles and Currents at Microelectrodes ............................ 61 4 CHAPTER FOUR ....................................................................................................64 Interaction of a Weakly Acidic Dinitroaromatic with Alkylamines: Avoiding the Meisenheimer Trap ..........................................................................................................64 4.1 Introduction .................................................................................................................66 4.2 Results and discussion ................................................................................................68 4.2.1 Effect of solvent polarity ............................................................................ 68 4.2.2 The Special Case of Hydroxide .................................................................. 69 4.2.3 Interaction of DNT with Alkylamines ........................................................ 70 4.2.4 Model for
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