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07 Chapter2.Pdf
22 METHODOLOGY 2.1 INTRODUCTION TO ELECTROCHEMICAL TECHNIQUES Electrochemical techniques of analysis involve the measurement of voltage or current. Such methods are concerned with the interplay between solution/electrode interfaces. The methods involve the changes of current, potential and charge as a function of chemical reactions. One or more of the four parameters i.e. potential, current, charge and time can be measured in these techniques and by plotting the graphs of these different parameters in various ways, one can get the desired information. Sensitivity, short analysis time, wide range of temperature, simplicity, use of many solvents are some of the advantages of these methods over the others which makes them useful in kinetic and thermodynamic studies1-3. In general, three electrodes viz., working electrode, the reference electrode, and the counter or auxiliary electrode are used for the measurement in electrochemical techniques. Depending on the combinations of parameters and types of electrodes there are various electrochemical techniques. These include potentiometry, polarography, voltammetry, cyclic voltammetry, chronopotentiometry, linear sweep techniques, amperometry, pulsed techniques etc. These techniques are mainly classified into static and dynamic methods. Static methods are those in which no current passes through the electrode-solution interface and the concentration of analyte species remains constant as in potentiometry. In dynamic methods, a current flows across the electrode-solution interface and the concentration of species changes such as in voltammetry and coulometry4. 2.2 VOLTAMMETRY The field of voltammetry was developed from polarography, which was invented by the Czechoslovakian Chemist Jaroslav Heyrovsky in the early 1920s5. Voltammetry is an electrochemical technique of analysis which includes the measurement of current as a function of applied potential under the conditions that promote polarization of working electrode6. -
Hydrodynamic Voltammetry As a Rapid and Simple Method for Evaluating Soil Enzyme Activities
Sensors 2015, 15, 5331-5343; doi:10.3390/s150305331 OPEN ACCESS sensors ISSN 1424-8220 www.mdpi.com/journal/sensors Article Hydrodynamic Voltammetry as a Rapid and Simple Method for Evaluating Soil Enzyme Activities Kazuto Sazawa 1,* and Hideki Kuramitz 2 1 Center for Far Eastern Studies, University of Toyama, Gofuku 3190, 930-8555 Toyama, Japan 2 Department of Environmental Biology and Chemistry, Graduate School of Science and Engineering for Research, University of Toyama, Gofuku 3190, 930-8555 Toyama, Japan; E-Mail: [email protected] * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel./Fax: +81-76-445-66-69. Academic Editor: Ki-Hyun Kim Received: 26 December 2014 / Accepted: 28 February 2015 / Published: 4 March 2015 Abstract: Soil enzymes play essential roles in catalyzing reactions necessary for nutrient cycling in the biosphere. They are also sensitive indicators of ecosystem stress, therefore their evaluation is very important in assessing soil health and quality. The standard soil enzyme assay method based on spectroscopic detection is a complicated operation that requires the removal of soil particles. The purpose of this study was to develop a new soil enzyme assay based on hydrodynamic electrochemical detection using a rotating disk electrode in a microliter droplet. The activities of enzymes were determined by measuring the electrochemical oxidation of p-aminophenol (PAP), following the enzymatic conversion of substrate-conjugated PAP. The calibration curves of β-galactosidase (β-gal), β-glucosidase (β-glu) and acid phosphatase (AcP) showed good linear correlation after being spiked in soils using chronoamperometry. -
Hydrodynamic Electrodes and Microelectrodes
CHEM465/865, 2004-3, Lecture 20, 27 th Sep., 2004 Hydrodynamic Electrodes and Microelectrodes So far we have been considering processes at planar electrodes. We have focused on the interplay of diffusion and kinetics (i.e. charge transfer as described for instance by the different formulations of the Butler-Volmer equation). In most cases, diffusion is the most significant transport limitation. Diffusion limitations arise inevitably, since any reaction consumes reactant molecules. This consumption depletes reactant (the so-called electroactive species) in the vicinity of the electrode, which leads to a non-uniform distribution (see the previous notes). ______________________________________________________________________ Note: In principle, we would have to consider the accumulation of product species in the vicinity of the electrode as well. This would not change the basic phenomenology, i.e. the interplay between kinetics and transport would remain the same. But it would make the mathematical formalism considerably more complicated. In order to simplify things, we, thus, focus entirely on the reactant distribution, as the species being consumed. ______________________________________________________________________ In this part, we are considering a semiinfinite system: The planar electrode is assumed to have a huge surface area and the solution is considered to be an infinite reservoir of reactant. This simple system has only one characteristic length scale: the thickness of the diffusion layer (or mean free path) δδδ. Sometimes the diffusion layer is referred to as the “Nernst layer” . Now: let’s consider again the interplay of kinetics and diffusion limitations. Kinetic limitations are represented by the rate constant k 0 (or equivalently by the 0=== 0bα b 1 −−− α exchange current density j nFkcred c ox ). -
Linear Sweep Voltammetric Determination of Free Chlorine in Waters Using Graphite Working Electrodes
J.Natn.Sci.FoundationLinear sweep voltammetric Sri Lanka determination 2008 36 (1):of free 25-31 chlorine 25 RESEARCH ARTICLE Linear sweep voltammetric determination of free chlorine in waters using graphite working electrodes K.A.S. Pathiratne*, S.S. Skandaraja and E.M.C.M. Jayasena Department of Chemistry, Faculty of Science, University of Kelaniya, Kelaniya. Revised: 16 June 2007 ; Accepted: 23 July 2007 Abstract: Applicability of linear sweep voltammetry using and stored. During disinfecting processes, it is added graphite working electrodes for determination of free chlorine in to potable waters and it undergoes hydrolysis in water waters was demonstrated. Influence of the nature of supporting forming hypochlorous acid and hypochlorous ions. electrolyte, its concentrations, pH and rate of potential variation of working electrode on voltammetric responses corresponding - NaOCl + H O HOCl + NaOH (1) to the oxidation of ClO were examined. It was found that, any 2 of the salt solutions KNO , K SO or Na SO at the optimum 3 2 4 2 4 Kd concentration of 0.1 mol dm-3 could be used as a supporting HOCl ClO- + H+ (2) electrolyte for the above determination. The study also revealed (Dissociation Constant, K = 2.9 x 10-8 mol dm-3) that, any pH in the range of 8.5 to 11 could yield satisfactory d results. The anodic peak current at the working electrode potential of +1.030 V vs Ag/AgCl reference electrode was found As shown by equation (2), hypochlorous acid to linearly increase with concentration of free chlorine up to undergoes further dissociation and depending on the pH, 300 mg dm-3 (R2 = 0.9996). -
Linear Sweep Anodic Stripping Voltammetry: Determination of Chromium (VI) Using Synthesized Gold Nanoparticles Modified Screen-Printed Electrode
J. Chem. Sci. Vol. 127, No. 6, June 2015, pp. 1075–1081. c Indian Academy of Sciences. DOI 10.1007/s12039-015-0864-4 Linear sweep anodic stripping voltammetry: Determination of Chromium (VI) using synthesized gold nanoparticles modified screen-printed electrode SALAMATU ALIYU TUKURa,b, NOR AZAH YUSOFa,c,∗ and REZA HAJIANc,∗ aDepartment of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia bDepartment of Chemistry, Faculty of Science, Kaduna State University, Kaduna, Nigeria cInstitute of Advanced Technology, Universiti Putra Malaysia, Serdang, Selangor 43400, Malaysia e-mail: [email protected]; [email protected] MS received 16 October 2014; revised 17 February 2015; accepted 19 February 2015 Abstract. A highly sensitive electrochemical sensor has been constructed for determination of Cr(VI) with the lowest limit of detection (LOD) reported to date using gold nanoparticles (AuNPs) modified screen-printed electrode (SPE). The modification of SPE by casting pure AuNPs increases the sensitivity for detection of Cr(VI) ion using anodic stripping voltammetry. Cr(VI) ions are reduced to chromium metal on SPE-AuNPs by applying deposition potential of –1.1 V for 180 s. Afterwards, the oxidation peak current of chromium is obtained by linear sweep voltammetry in the range of −1.0 V to 0.2 V. Under the optimized conditions (HClO4, 0.06 mol L−1; deposition potential, –1.1 V; deposition time, 180s; scan rate, 0.1 V s−1), the limit of detection (LOD) was 1.6 pg mL−1. The fabricated electrode was successfully used for detection of Cr(VI) in tap and seawater. -
Μstat 4000P Multi Potentiostat
µStat 4000P Multi Potentiostat 01 Ref. STAT4000P Following the format of our multipotentiostats with a size of only 22x20x7 cm, includes 4 channels that can act at the same time as 4 independent potentiostats; it also includes one multichannel that can act as a poten- tiostat where up to 4 working electrodes share an auxiliary and a reference electrode. With µStat 4000P users can perform up to 4 different electrochemical techniques at the same time; or carry out the study of one technique’s parameter in just one step by applying the same electrochemical technique in several channels but selecting different values for the parameter under study. These are just exam- ples of the enormous capabilities that our new instrument offers. µStat 4000P can be applied for Voltammetric or Amperometric measurements, including 12 electroanalytical techniques. In addition, µStat 4000P owners can later upgrade their instrument to a µStat 4000P by just purchasing an extension. This self-upgrade does not require any hardware modification, but it is implemented by means of a Galvanostat software update kit. This Multi Potentiostat is Li-ion Battery powered (DC charger adaptor also compatible), and can be easily connected to a PC via USB or through Wireless connection. µStat 4000P is controlled by the powerful software “DropView 8400” which is included and that allows plotting of the measurements and performing the analysis of results. DropView software provides powerful functions such as experimental control, graphs or file handling, among others. Available -
Basics and Applications of a Quartz Crystal Microbalance Monitoring Surface Interactions Via Small-Scale Mass Changes
Basics and Applications of a Quartz Crystal Microbalance CORROSION BATTERY TESTING Monitoring Surface Interactions via Small-scale Mass Changes COATINGS PHOTOVOLTAICS gamry.com Contents Basics of QCM ........................................................................................................................3 Calibration of a QCM ................................................................................................... 13 Investigation of a Thin Polymer Film ..........................................................................21 The eQCM 10M System ..................................................................................................... 26 The QCM-I System .............................................................................................................. 27 References .......................................................................................................................29 Additional Resources .................................................................................................... 30 2 gamry.com Basics of a Quartz Crystal Microbalance This section provides an introduction to the quartz crystal microbalance (QCM) which is an instrument that allows a user to monitor small mass changes on an electrode. The reader is directed to the numerous reviews 1 and book chapters1 & 2 for a more in-depth description concerning the theory and application of the QCM. A basic understanding of electrical components and concepts is assumed. The two major points of this section are: -
A Practical Organic-Mediated Hybrid Electrolyser That Decouples
Electronic Supplementary Material (ESI) for Chemical Science. This journal is © The Royal Society of Chemistry 2018 Supplementary Information for: A Practical Organic-Mediated Hybrid Electrolyser that Decouples Hydrogen Production at High Current Densities Niall Kirkaldy,a Greig Chisholm,a Jia-Jia Chena and Leroy Cronin*a a WestCHEM, School of Chemistry, University of Glasgow, University Avenue, Glasgow, G12 8QQ, UK * Corresponding author, [email protected] 1 Contents SI-1. General Experimental Remarks .................................................................................................. 3 SI-2. Electrochemical Characterisation ............................................................................................... 4 SI-3. Gas Headspace Measurements................................................................................................... 6 SI-4. Hybrid PEME Construction and Operation ................................................................................. 7 SI-5. PEME Characterisation Methods ................................................................................................ 8 SI-6. PEME Efficiency Calculations .................................................................................................... 10 SI-7. Cost Calculations ....................................................................................................................... 11 2 SI-1. General Experimental Remarks 9,10-anthraquinone-2,7-disulfonic acid disodium salt was purchased from Santa Cruz Biotechnology -
Cyclic Voltammetry
Cyclic Voltammetry Denis Andrienko January 22, 2008 2 Literature: 1. Allen J. Bard, Larry R. Faulkner “Electrochemical Methods: Fundamentals and Applications” 2. http://www.cheng.cam.ac.uk/research/groups/electrochem/teaching.html Chapter 1 Cyclic Voltammetry 1.1 Background Cyclic voltammetry is the most widely used technique for acquiring qualitative information about elec- trochemical reactions. it offers a rapid location of redox potentials of the electroactive species. A few concepts has to be introduced before talking about this method. 1.1.1 Electronegativity Electronegativity is the affinity for electrons. The atoms of the various elements differ in their affinity for electrons. The term was first proposed by Linus Pauling in 1932 as a development of valence bond theory. The table for all elements can be looked up on Wikipedia: http://en.wikipedia.org/wiki/Electronegativity. Some facts to remember: • Fluorine (F) is the most electronegative element. χF = 3.98. • The electronegativity of oxygen (O) χO = 3.44 is exploited by life, via shuttling of electrons between carbon (C, χF = 2.55) and oxygen (O): Moving electrons against the gradient (O to C) - as occurs in photosynthesis - requires energy (and stores it). Moving electrons down the gradient (C to O) - as occurs in cellular respiration - releases energy. • The relative electronegativity of two interacting atoms plays a major part in determining what kind of chemical bond forms between them. Examples: • Sodium (χNa = 0.93) and Chlorine (χCl = 3.16) = Ionic Bond: There is a large difference in electronegativity, so the chlorine atom takes an electron from the sodium atom converting the atoms into ions (Na+) and (Cl−). -
Pulse Voltammetry Software Brochure
Data Analysis density. This feature is particularly useful for comparing data from electrodes of different areas. The analysis of the software data is performed in the Echem Analyst. Specific analysis routines have been created to Baseline Add: Baselines can be added to the data graph by either drawing a Freehand Line or by extrapolating a handle this software data files. The general features of the Echem Analyst are described in a separate brochure entitled part of the baseline with the Linear Fit feature. Redefining Electrochemical Measurement “Overview of Gamry Software.” Integrate: Integration of the current in Differential Pulse These specific routines include: Voltammetry and Square Wave Voltammetry is possible by defining a baseline and then selecting the portion of the Pulse Voltammetry Software Peak Find: Use the Region Selector button to select a curve you want to integrate. Then select Integrate from the portion of the curve that includes the region where the drop-down menu and the result is reported on the curve The Pulse Voltammetry Software adds Differential Pulse peak is located. Click on the Peak Find button to find the and also on a new tab. This software incorporates the following pulse techniques: peak position and the peak height. A perpendicular line is Voltammetry, Square Wave Voltammetry, and other drawn on the chart from the peak to the baseline. Background Subtract: A background file can be recognized pulse voltammetry techniques to the Gamry ● Square Wave subtracted from the current active data file by selecting software product family. For qualitative and mechanistic ● Square Wave Stripping Subtract from the menu and choosing the file. -
Emstat-Go-Description.Pdf
z Rev. 1-2019 EmStat Go potentiostat ...............................................................................................................2 Sensor Extension module .........................................................................................................2 Sleeves in any color .................................................................................................................3 Modular design ........................................................................................................................3 Optional battery for connecting via Bluetooth ...........................................................................3 Reduce your time-to-market ....................................................................................................4 Supported techniques ..............................................................................................................4 Voltammetric techniques ......................................................................................................4 Techniques as a function of time ..........................................................................................4 Custom software options .............................................................................................................5 Specifications of general parameters ...........................................................................................6 General pretreatment............................................................................................................6 -
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.