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Development and Evaluation of a Calibration Free Exhaustive Coulometric Detection System for Remote Sensing

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Development and Evaluation of a Calibration Free Exhaustive Coulometric Detection System for Remote Sensing University of Louisville ThinkIR: The University of Louisville's Institutional Repository Electronic Theses and Dissertations 5-2014 Development and evaluation of a calibration free exhaustive coulometric detection system for remote sensing. Thomas James Roussel University of Louisville Follow this and additional works at: https://ir.library.louisville.edu/etd Part of the Mechanical Engineering Commons Recommended Citation Roussel, Thomas James, "Development and evaluation of a calibration free exhaustive coulometric detection system for remote sensing." (2014). Electronic Theses and Dissertations. Paper 1238. https://doi.org/10.18297/etd/1238 This Doctoral Dissertation is brought to you for free and open access by ThinkIR: The University of Louisville's Institutional Repository. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of ThinkIR: The University of Louisville's Institutional Repository. This title appears here courtesy of the author, who has retained all other copyrights. For more information, please contact [email protected]. DEVELOPMENT AND EVALUATION OF A CALIBRATION FREE EXHAUSTIVE COULOMETRIC DETECTION SYSTEM FOR REMOTE SENSING by Thomas James Roussel, Jr. B.A., University of New Orleans, 1993 B.S., Louisiana Tech University, 1997 M.S., Louisiana Tech University, 2001 A Dissertation Submitted to the Faculty of the J. B. Speed School of Engineering of the University of Louisville in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Department of Mechanical Engineering University of Louisville Louisville, Kentucky May 2014 Copyright 2014 by Thomas James Roussel, Jr. All rights reserved DEVELOPMENT AND EVALUATION OF A CALIBRATION FREE EXHAUSTIVE COULOMETRIC DETECTION SYSTEM FOR REMOTE SENSING By Thomas James Roussel, Jr. B.A., University of New Orleans, 1993 B.S., Louisiana Tech University, 1997 M.S., Louisiana Tech University, 2001 A Dissertation Approved on April 21, 2014 by the following Dissertation Committee: _______________________________________ Dissertation Director Robert Keynton, Ph.D. _______________________________________ Richard Baldwin, Ph.D. _______________________________________ John Naber, Ph.D. _______________________________________ Balaji Panchapakesan, Ph.D. _______________________________________ Stuart Williams, Ph.D. ii DEDICATION This dissertation is dedicated to the memory of my mother Cherry Hall Roussel who always believed in me. Promised you I’d finish, mom. And I did. Toxey’s Favorite Mama Z’s Azaleas and Deep Purple Falls iii ACKNOWLEDGMENTS I would like to thank my mentor and friend, Dr. Robert Keynton, for his guidance over the many years we have collaborated. Who knows where I would be and what I would be doing had he not knocked on my door and sat me down for a chat in the spring of 1997. Not that I ever contemplate those possibilities; pursuing research as a career was a great decision, and next to marrying my wife, probably the best one I’ve ever made. Many thanks to Dr. Richard Baldwin for getting this all started by introducing me to the field of electrochemistry. Additionally, I want to thank my other committee members, Dr. John Naber, Dr. Balaji Panchapakesan, and Dr. Stuart J. Williams for their support and words of encouragement. Special thanks to Doug Jackson and Scott Cambron, two of the most talented engineers I know. Those guys might not know it, but both have the patience and hearts of teachers. To my lab mates, Dr. Susan Carroll and Mohamed Marei, thanks for their hard work and dedication to the project, and also for tolerating my odd schedule. Finally, to my wife, Melissa Ann Becker: Thank you for rewarding me with Emily Claire and for keeping everything together through all the late nights and long weekends while I worked towards this goal. iv ABSTRACT DEVELOPMENT AND EVALUATION OF A CALIBRATION FREE EXHAUSTIVE COULOMETRIC DETECTION SYSTEM FOR REMOTE SENSING Thomas J. Roussel, Jr. April 21, 2014 Most quantitative analytical measurement techniques require calibration to correlate signal with the quantity of analyte. The purpose of this study was to employ exhaustive coulometry, an implementation of coulometric analysis in a stopped-flow, fixed-volume, thin-layer cell, to attain calibration-free measurements that would directly benefit intervention-free analysis systems designed for remote deployment. This technique capitalizes on the short diffusion lengths (<100 µm) to dramatically reduce the time for analysis (< 30 sec). For this work, a thin-layer fluidic cell was designed in software, fabricated via CNC machining, and evaluated using Ferri/Ferrocyanide 3-/4- {Fe(CN)6 } as a model analyte. The 2 µL fixed volume incorporated an oval, 8mm by 4 mm, thin-film gold electrode sensor with an integrated Ag|AgCl pseudo-reference electrode. The flow cell area matched the shape of the sensor, with a volume set by the thickness of a laser-cut silicone rubber gasket (~80 µm). A semi-permeable membrane isolated the working electrode and counter electrode chambers to prevent analyte diffusion. A miniaturized custom potentiostat was designed and built to measure reaction currents ranging from 10 mA to 0.1 nA. Software was developed to perform step v voltammetry as well as cyclic voltammetry analysis for verifying electrode condition and optimal redox potential levels. Experimentally determined oxidation/reduction potentials of -100 mV and 400 mV, respectively, were applied to the working electrode for sample concentrations ranging from 50 µM to 10,000 µM. The current generated during the reactions was recorded and the total charge captured at each concentration was obtained by integrating the amperograms. When compared to the expected charge for a 2 µL sample, the total charge vs. concentration plots displayed a near perfect linearity over the full concentration range, and the expected charge (100 % converted) was reached within 20 seconds. The reaction currents ideally should have decayed to background levels, but exhibited constant offset values slightly larger than the background signal, a phenomenon assumed to be lingering residual flow from sample injection. After adding rigid tubing and external valves, the thin-layer cell was shown to remain within 6% of the theoretical charge after 200 seconds. Continued development of this system will offer the possibility of remote, calibration-free determinations of real-world analytes such mercury and lead. vi TABLE OF CONTENTS PAGE ACKNOWLEDGMENTS ................................................................................................ iv ABSTRACT .......................................................................................................................v LIST OF TABLES .......................................................................................................... xii LIST OF FIGURES ........................................................................................................ xiii LIST OF EQUATIONS .................................................................................................. xix CHAPTER I. INTRODUCTION .......................................................................................1 1.1 Purpose of Study .................................................................................................5 1.2 Specific Aims.... ..................................................................................................5 1.3 Significance of the Study ....................................................................................7 CHAPTER II. BACKGROUND ........................................................................................8 2.1 Microtechnology and Microfluidics ...................................................................8 2.1.1 Microtechnology .....................................................................................9 2.1.2 Microfluidics .........................................................................................10 2.2 Modern Analytical Chemistry ...........................................................................11 2.3 Analytical Instrumental Methods of Detection .................................................13 2.4 Electrochemical Detection ................................................................................15 2.4.1 Principles of Electrochemistry ..............................................................16 2.4.1.1 Redox Reactions .....................................................................17 2.4.1.2 The Electrochemical Cell........................................................19 2.4.1.2.1 Electrochemical Electrodes.................................. 19 2.4.1.2.2 Electrode Materials .............................................. 23 2.4.1.2.3 The Reference Electrode ...................................... 25 vii 2.4.1.2.4 The Electrode-Electrolyte Interface ..................... 27 2.4.1.2.5 Electrode Fabrication ........................................... 30 2.4.2 ECD Electronics ....................................................................................31 2.4.2.1 The Potentiostat ......................................................................31 2.4.3 Volumetric Configurations and Flow Considerations ..........................33 2.4.3.1 Bulk Electrolysis .....................................................................35 2.4.3.2 Wall Jet Configuration ............................................................37 2.4.3.3 Flow Over/By Configuration ..................................................38
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