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Design and Testing of a Computer-Controlled Square Wave Voltammetry Instrument

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Design and Testing of a Computer-Controlled Square Wave Voltammetry Instrument Rochester Institute of Technology RIT Scholar Works Theses 6-1-1987 Design and testing of a computer-controlled square wave voltammetry instrument Nancy L. Wengenack Follow this and additional works at: https://scholarworks.rit.edu/theses Recommended Citation Wengenack, Nancy L., "Design and testing of a computer-controlled square wave voltammetry instrument" (1987). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. DESIGN AND TESTING OF A COMPUTER-CONTROLLED SQUARE WAVE VOLTAMMETRY INSTRUMENT by Nancy L. Wengenack J une , 1987 THESI S SUBM ITTED IN PARTIA L FULFI LLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE APPROVED: Paul Rosenberg Project Advisor G. A. Jakson Department Head Gate A. Gate Library Rochester Institute of Te chnology Rochester, New York 14623 Department of Chemistry Title of Thesis Design and Testing of a Computer- Controlled Square Wave Voltammetry Instrument I Nancy L. Wengenack hereby grant permission to the Wallace Memorial Library, of R.I.T., to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. Date %/H/n To Tom ACKNOWLEDGEMENTS I would like to express my thanks to my research advisor, Dr. L. Paul Rosenberg, for his assistance with this work. I would also like to thank my graduate committee: Dr. B. Edward Cain; Dr. Christian Reinhardt; and especially Dr. Joseph Hornak; for their help and guidance. Special thanks to Peter J. Michelsen for many helpful discussions. Financial assistance from the Department of Chemistry and Rochester Institute of Technology in the forms of a teaching assistantship and graduate fellowship is gratefully acknowledged. II List of Figures Figure 1 - DC Polarography a) Potential Waveform b) Current Response Curve 10 Figure 2 - Important Features of a Typical Polarogram 11 Figure 3 - Current Reaction to Mercury Drop Growth and Fall at the Working Electrode 15 Figure 4 - Potential Waveform and Current Response Curve For TAST Polarography 16 Figure 5 - Current Sampling Scheme For TAST Polarography 17 Figure 6 - Potential Waveform and Current Response Curve For NPP 20 Figure 7 - Capacitive and Faradaic Current Behavior During a Potential Pulse 22 Figure 8 - Potential Waveform and Current Response Curve For DPP 24 Figure 9 - Applied Potential Waveform For SWV 26 Figure 10 - a) Square Wave Voltammetry Timing Relationships b) Current response curve for Square Wave Voltammetry 28 Figure 11 - Effects of Square Wave Amplitude on Difference Current Magnitude a) Esw= 5 mV b) Esw= 15 mV c) ESw= 30 mV Solid line is the difference current 31 Figure 12 - Peak Width at half height versus Square Wave Ampl itude 32 Figure 13 - Traditional versus Postfix Notation 45 Figure 14 - Front and Rear Panel Configurations of the Model 264A Polarographic Analyzer/ Stripping Voltammeter 53 Figure 15 - Model 303A Static Mercury Drop Electrode Configuration 55 - Figure 16 LabMaster Daughter Board Conf iguration . .. .57 Figure 17 - A/D Linearity Plot 59 III LIST OF FIGURES (continued) Figure 18 - Current Measurement Scheme for SWV 72 Figure 19 - Computer-Controlled Square Wave Voltammetry - Block Diagram 74 Figure 20 - Potential versus Time Collected For SWV Using ASYST 76 Figure 21 - Voltammogram For Model System Collected Using SQUARE 78 Figure 22 - Square Wave Voltammetry Run on Internal Cell 83 Figure 23 - Collecting a Function Generator Created Square Wave 85 Figure 24 - Potential Data Collection with SQUARE While Sitting at One Potential 86 Figure 25 - Current Data Collection with SQUARE While Sitting at One Potential 88 Figure 26 - DPP Run on Internal Cell 89 Figure 27 - SWV of ZnCl2 - Plotting every 10th Point - Trial #1 91 Figure 28 - SWV of ZnCl2 - Plotting every 10th Point - Trial #2 92 Figure 29 - SWV of ZnCl2 - Plotting every 10th Point - Trial #3 93 Figure 30 - SWV of ZnCl2 - Signal Averaging 94 Figure 31 - Front and Rear Panel Configurations of the IBM EC/225 96 Figure 32 - Block Diagram of Analyzer with IBM EC/2252A 98 IV List of Tables Table I - Comparison of DPP and SWV Current Magnitude 36 Table II - ASYST Features 40 Table III - Comparison of Compilation and Run Times for FORTH and Several Other Languages ... .43 Table IV - Data Acquisition Boards Supported By ASYST 47 Table V - Comparison of Run Times for FORTH and BASIC Control Programs 102 List of Programs Program I - WAVE: ASYST Control Program 63 Program II - SQUARE: ASYST Control Program 67 Program III - Plotting Programs : ASYST Control Programs 70 Program IV - WAVE: BASIC Control Program 100 Program V - SQUARE: BASIC Control Program 101 List of Abbreviations Used A/D - Analog-to-Digital Ag/AgCl - Silver/Silver Chloride Electrode BNC - British Navy Connector D/A - Digital-to-Analog DCP - DC Polarography DIP - Dual Inline Package DME - Dropping Mercury Electrode DOS - Disk Operating System DPP - Differential Pulse Polarography FFT - Fast Fourier Transform GPIB - General Purpose Interface Bus HMDE - Hanging Mercury Drop Electrode HPLC - High Performance Liquid Chromotography LIFO - Last-in, First-Out Stack NPP - Normal Pulse Polarography PARC - Princeton Applied Research Corporation RPN - Reverse Polish Notation SCE - Saturated Calomel Electrode SMDE - Static Mercury Drop Electrode SWV - Square Wave Voltammetry TAST - Current-Sampled Polarography VI TABLE OF CONTENTS Abstract 1 1 . 0 Introduction 3 1.1 Basic Cell Design 7 1 . 2 DC Polarography (DCP) 9 1.3 TAST or Current Sampled Polarography 14 1.4 Normal Pulse Polarography (NPP) 19 1.5 Differential Pulse Polarography (DPP) 23 1.6 Square Wave Voltammetry (SWV) 25 1.7 ASYST 38 1 . 8 FORTH 42 1.9 Data Acquisition Boards 47 2.0 Purpose 48 3.0 Experimental 49 3.1 EG&G PARC Model 264A Polarographic Analyzer/ Stripping Voltammeter 50 3.2 EG&G PARC Model 303A Static Mercury Drop Electrode 54 3.3 Tecmar LabMaster Data Acquisition Board 56 3.4 Hewlett-Packard HP7475A Plotter 60 3.5 IBM PC 61 4.0 Results and Discussion 62 4 . 1 Control Programs 62 4.2 Current Measurement Scheme 71 4.3 Instrument Design 73 VII TABLE OF CONTENTS (continued) 4.4 Model System Results 77 4.5 Instrument Operation 79 4.6 Elimination of Noise 81 EC/2252A 4.7 Interfacing the IBM Voltammetric Analyzer 95 4.8 Control Programs Written in BASIC 99 Suggestions for Future Work 104 Conclusion 105 References 107 VIII ABSTRACT Square Wave Voltammetry is rapidly becoming the most popular and versatile electrochemical technique used in research laboratories today. A discussion of electroanalytical techniques, which are the forerunners to square wave voltammetry, provides a basis for understanding the theoretical and experimental aspects of SWV which are presented. A computer-controlled square wave voltammetry system was designed and built using an IBM PC computer, a Tecmar data acquisition board, an EG&G PARC Model 264A Polarographic Analyzer/Stripping Voltammeter, an EG&G PARC Model 303A Static Mercury Drop Electrode, and the scientific software package, ASYST. The system was tested by performing computer-controlled square wave voltammetry on a Zn system, popular for standardization of square wave analysis systems. The major problem encountered with the system was a large amount of noise in the collected data. The noise was substantially reduced by various data smoothing techniques which included signal averaging. The universality of the system was successfully 2A tested by using an IBM EC/225 Voltammetric Analyzer and a homemade electrolytic cell for the analysis. Finally, the control programs were written in BASIC as well as FORTH, the language of ASYST. FORTH proved to be the superior language for the interfacing application in terms of speed and accuracy of data collection. 1.0 INTRODUCTION The roots of modern electroanalytical chemistry date back to the early 1920 's when Jaroslav Heyrovsky, a Czechoslovakian chemist, developed DC Polarography. Although his peers did not immediately recognize its significance, Heyrovsky eventually won the Nobel Prize in chemistry for the development of DC Polarography in 1959. By 1950, polarography had reached its peak of popularity and most scientists regarded it as an area in which there were few avenues left to explore. At the same time, other analytical techniques were experiencing surges in popularity. Atomic absorption spectroscopy had recently been developed and was being heavily promoted as the technique of greatest promise in analytical chemistry. Gas chromatography was a technique which had come to the forefront for the analysis of organic compounds. This combination of factors led many scientists to believe that polarography was essentially a "dead" technique and very few scientists continued work to improve voltammetric techniques (1). electrochemists Fortunately for , electrochemistry did not become a forgotten technique, but a popular, modern method for chemical analysis. Between 1955 and 1965, the limitations of atomic absorption spectroscopy and gas chromatography were realized. Atomic absorption was found to be a limiting method in that all the sample being analyzed must be ionized in a flame. Gas chromatography is limited to those substances which are able to be volatilized. Polarography 's great advantage over these two techniques is that the species of interest is examined in its original chemical environment and therefore a better representation of its behavior in
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