DOCSLIB.ORG

Potentiometric Ion-Selective Electrodes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Potentiometric Ion-Selective Electrodes Potentiometric Ion-Selective Electrodes An ion-selective electrode (ISE), is a type of electrochemical sensor that converts the activity of a specific ion dissolved in a solution into an electrical potential. The voltage of such electrode is dependent on the logarithm of the ionic activity, according to the Nernst equation. 푅푇 퐸 = 퐸 + 2.3 log 푎 (1) 표 푛퐹 Where Eo = a constant for a given cell (It is unique for the analyte, and also includes the sum of the potential differences at all the interfaces other than the membrane/sample solution interface.) R = the gas constant T = the Temperature in Kelvin n = the ionic charge F = the Faraday constant a = the activity of the ion in the sample solution and the expression 2.3RT/nF is termed the Slope Factor For example, the slope at 298K (25°C) has a value of 59.16 mV, when measuring Potassium ions, (i.e. n = +1). This is termed as the Ideal Slope Factor, and means that for each tenfold change in potassium concentration, an ideal measuring system will sense a change of 59.16 mV. The measurement of slope factor gives an indication of the performance of the electrode system. If the slope value is lower than the ideal slope factor, it signifies a loss in electrode’s performance. A number of factors such as interference from other ions, use of incorrect calibration, loss of electrolyte in the electrode or blockage of the reference junction, can be responsible for it and should be checked in such a case. The ion-selective membrane situated between the two aqueous phases, i.e., between the sample and inner solution that contain an analyte ion forms an essential part of the ISEs. It can be made of glass, a crystalline solid, or a liquid. The potential difference across the membrane is measured between the two reference electrodes positioned in the respective aqueous phases. reference electrode 2 || sample solution | membrane | inner solution || reference electrode 1 Figure 1: Schematic of a measurement setup using an Ion-Selective Electrode 1. Selectivity and interferences Ion-selective electrodes are selective but not specific. They can respond to other ions in solution although it is not designed to do so. The ion to be determined is referred as the primary ion (determinant) and other ions to which the electrode responds are known as interfering ions (interferent). The preference of an electrode for the determinant over the interferent is called the selectivity of the electrode. This preference, is expressed as a ratio called the selectivity coefficient, or ratio. Each electrode has its own set of selectivity coefficients. For example: -3 KK+/Na+ = 2.6 x 10 primary ion interfering ion Meaning that the preference for K+ (potassium) over Na+ (Sodium) for this electrode is 1 to 2.6 x 10-3 or 385:1. This means that the electrode is 385 times more selective to K+ than Na+. To take into account, the response of the electrode to an interfering ion an additional term is added to equation 1 푅푇 푛 퐸 = 퐸표 + 2.3 log(푎 + 푘 푎 푧 ) (2) 푛퐹 푖푗 푖푗 푗 Where aj is the activity of the interfering ion with charge z and kij is the selectivity coefficient, which is the response of the electrode to the interfering ion relative to its response to the primary ion. 2. Activity vs Concentration Ion-selective electrodes respond directly to the activity of an ion, rather than to its concentration. The concentration is the number of ions in a specific volume, this definition assumes that all of those ions have a similar behavior. However, ions do not always behave similar to one another: some are active i.e. exhibit properties associated with that ion, and some are not active. The number of active ions is called the activity of the solution. This means it is a relative term describing how “active” an ion is compared to when it is under standard state conditions. This characteristic is often a decided advantage, since the metabolic behavior of an ion is often more directly related to its activity. For example, the physiological effects of calcium in serum are related to the ionized Ca2+ activity rather than the total calcium concentration, which also includes protein-bound and complexed calcium species. In dilute solutions though, the ionic activity and the concentration are practically identical but in solutions containing many ions, activity and concentration may differ. This is why dilute samples are preferred for measurement with ISE's. However, it is possible to 'fix' the solution so that activity and concentration are equal. This can be done by adding a constant concentration of an inert electrolyte to the analyte solution. This is called an Ionic Strength Adjustment Buffer (I.S.A.B.). Thus in dilute solutions, the ion selective electrode will measure concentration directly. 3. Types of electrode There are four types of ion selective electrode whose construction and mode of operation differ considerably. These are: 1. Glass body electrode 2. Solid state (crystalline membrane) 3. Liquid ion exchange (polymer membrane) 4. Gas sensing type 1. Glass body electrodes The most common ISE is the glass-bodied pH electrode. Glass membranes are made from an ion- exchange type of glass (silicate or chalcogenide). This type of ISE has good selectivity, but only for several single-charged cations; mainly H+, Na+, and Ag+. 2. Solid state ion selective electrode In these type of electrode, the electrode potential of the standard and the sample solutions is measured across a solid, polished crystalline membrane. The crystalline material is prepared from a single compound or a homogeneous mixture of compounds (for example, the fluoride ISE has a Lanthanum Fluoride crystal) 3. Polymer membrane ion selective electrode These electrodes contain a polymeric membrane containing a selective ion exchanger, the liquid membranes are hydrophobic and immiscible with water. They are most commonly made of plasticized poly (vinyl chloride). By doping the membranes with a hydrophobic ion (ionic site) and a hydrophobic ligand (ionophore or carrier) that selectively and reversibly forms complexes with the analyte, these membranes are made selective. The electrode potential of solutions is measured by their effect on the ion exchange material. This type of ion-selective electrode is subject to more interferences than other ISEs due to complex properties of ion exchangers. Figure 2: Schematic view of the equilibrium between sample, ion-selective membrane, and inner filling solution (cell 1). The cation-selective membranes are based on (A) cation exchanger (R-), (B) electrically neutral ionophore (L) and anionic sites (R-), and (C) charged ionophore (L-) and cationic sites (R+). The aqueous solutions contain an analyte cation (I+) and its counter anion (X-). 4. Gas sensing type The gas sensing type of ISE use a membrane separating a sample and a filling solution. The gas from the sample solution (for e.g., liberation of ammonia by adding a caustic solution to it) permeates through the membrane and changes the pH of the filling solution. The change in pH is proportional to the concentration. This gives a quantitative measurement of the analyte gas in the sample solution. Figure 3: Schematic of the sensing portion on the 4 main types of Ion-selective/gas sensing electrodes 4. Reference Electrodes The potential of an Ion Selective Electrode can only be measured against an appropriate reference electrode in contact with the same test solution. Reference electrodes are electrodes with a stable and well-known electrode potential. By employing a redox system with constant (buffered or saturated) concentrations of each participant, a chemical equilibrium can be maintained inside them which is responsible for a constant value of the electrode potential. A silver chloride electrode is among the most commonly used reference electrodes, it is usually the internal reference electrode in pH meters. The electrode functions as a redox electrode by maintaining the equilibrium between the silver metal (Ag) and its salt—silver chloride (AgCl). The corresponding half-reactions inside electrode are as follows: - Ag+ + e- ⇋ Ag (s) AgCl (s) + e- ⇋ Ag (s) + Cl- This reaction is characterized by fast electrode kinetics, meaning that a sufficiently high current can be passed through the electrode with the 100% efficiency of the redox reaction (i.e., dissolution of the metal or cathodic deposition of the silver-ions). The reaction obeys these equations in solutions ranging from pH 0 to 13.5. The standard electrode potential E0 against standard hydrogen electrode (SHE) is 0.230 V ± 10 mV. 5. Methods of analysis 5.1 Potentiometry In potentiometry, the potential of a solution between two electrodes is passively measured, affecting the solution very little in the process. One of the electrode which has constant potential is called the reference electrode, while the other electrode whose potential changes with the composition of the sample is called indicator electrode. Therefore, the potential difference between the two electrodes is indicative of the composition of the sample. Potentiometry is a non-destructive technique, assuming that the electrode is in equilibrium with the solution we are measuring the potential of the solution. Potentiometry usually uses an ion-selective electrode, so that the potential solely depends on the activity of this ion of interest. The time taken by the electrode to establish equilibrium with the solution will affect the sensitivity or accuracy of the measurement. 5.2 Calibration Curve Method This is the simplest and most widely used method of obtaining quantitative results using Ion Selective Electrodes. Standard solutions are prepared by serial dilution of a concentrated standard. The recommended Ionic Strength Adjustment Buffer (ISAB), is added to each standard as well as to the unknown samples.
Load more

Recommended publications
  • Validation of Rapid Enzymatic Quantification of Acetic Acid In
    foods Article Validation of Rapid Enzymatic Quantification of Acetic Acid in Vinegar on Automated Spectrophotometric System Irene Dini 1,* , Ritamaria Di Lorenzo 1, Antonello Senatore 2, Daniele Coppola 2 and Sonia Laneri 1 1 Department of Pharmacy, University of Naples Federico II, Via Domenico Montesano 49, 80131 Napoli, Italy; [email protected] (R.D.L.); [email protected] (S.L.) 2 Lcm Laboratory for Product Analysis of Chamber of Commerce, Corso Meridionale, 80143 Napoli, Italy; [email protected] (A.S.); [email protected] (D.C.) * Correspondence: [email protected] Received: 9 May 2020; Accepted: 4 June 2020; Published: 9 June 2020 Abstract: Vinegar is produced from the fermentation of agricultural materials and diluted acetic acid (diluted with water to 4–30% by volume) via sequential ethanol and acetic acid fermentation. The concentration of acetic acid must be measured during vinegar production. A Community method for analyzing acetic acid in vinegar is a non-specific method based on the assumption that the total acid concentration of the vinegar is attributable to the acetic acid. It consists of titration with a strong base in the presence of an indicator. This test is laborious and has a time-consuming character. In this work, a highly specific automated enzymatic method was validated, for the first time, to quantify the acetic acid in the wine vinegar, in terms of linearity, precision, repeatability, and uncertainty measurement. The results were compared to the Community method of analysis. Regression coefficient 1 and the normal distribution of residuals in the ANOVA test confirmed the method’s linearity.
    [Show full text]
  • Elements of Electrochemistry
    Page 1 of 8 Chem 201 Winter 2006 ELEM ENTS OF ELEC TROCHEMIS TRY I. Introduction A. A number of analytical techniques are based upon oxidation-reduction reactions. B. Examples of these techniques would include: 1. Determinations of Keq and oxidation-reduction midpoint potentials. 2. Determination of analytes by oxidation-reductions titrations. 3. Ion-specific electrodes (e.g., pH electrodes, etc.) 4. Gas-sensing probes. 5. Electrogravimetric analysis: oxidizing or reducing analytes to a known product and weighing the amount produced 6. Coulometric analysis: measuring the quantity of electrons required to reduce/oxidize an analyte II. Terminology A. Reduction: the gaining of electrons B. Oxidation: the loss of electrons C. Reducing agent (reductant): species that donates electrons to reduce another reagent. (The reducing agent get oxidized.) D. Oxidizing agent (oxidant): species that accepts electrons to oxidize another species. (The oxidizing agent gets reduced.) E. Oxidation-reduction reaction (redox reaction): a reaction in which electrons are transferred from one reactant to another. 1. For example, the reduction of cerium(IV) by iron(II): Ce4+ + Fe2+ ! Ce3+ + Fe3+ a. The reduction half-reaction is given by: Ce4+ + e- ! Ce3+ b. The oxidation half-reaction is given by: Fe2+ ! e- + Fe3+ 2. The half-reactions are the overall reaction broken down into oxidation and reduction steps. 3. Half-reactions cannot occur independently, but are used conceptually to simplify understanding and balancing the equations. III. Rules for Balancing Oxidation-Reduction Reactions A. Write out half-reaction "skeletons." Page 2 of 8 Chem 201 Winter 2006 + - B. Balance the half-reactions by adding H , OH or H2O as needed, maintaining electrical neutrality.
    [Show full text]
  • Reaction Engineering of Polymer Electrolyte Membrane Fuel Cells
    Reaction Engineering of Polymer Electrolyte Membrane Fuel Cells A new approach to elucidate the operation and control of Polymer Electrolyte Membrane (PEM) fuel cells is being developed. A global reactor engineering approach is applied to PEM fuel cells to identify the essential physics that govern the dynamics in PEM fuel cells. Reaction engineering principles are employed to develop a one-dimensional differential PEM fuel cell suitable for elucidating the dynamic performance of PEM cells under well-defined conditions. Polymer Electrolyte Fuel Cells Polymer electrolyte membrane (PEM) fuel cells employ a polymer membrane with acid side groups to conduct protons from the anode to cathode. Water management in the fuel cell is critical for PEM fuel cell operation. Sufficient water must be absorbed into the membrane to ionize the acid groups; excess water can flood the cathode of the fuel cell diminishing fuel cell performance limiting the power output. A schematic of a polymer electrolyte membrane hydrogen-oxygen fuel cell is shown in Figure 1. load e- Figure 1. Hydrogen-oxygen PEM fuel cell. Hydrogen molecules hydrogen in oxygen in dissociatively adsorb at the anode and are oxidized to protons. Electrons travel through an external load resistance. Protons diffuse H+ through the PEM under an e t electrochemical gradient to the y l ro t c cathode. Oxygen molecules adsorb e l at the cathode, are reduced and react hydrogen r E oxygen e m y + water out with the protons to produce water. + water out l Po The product water is absorbed into the PEM, or evaporates into the gas anode cathode streams at the anode and cathode.
    [Show full text]
  • Galvanic Cell Notation • Half-Cell Notation • Types of Electrodes • Cell
    Galvanic Cell Notation ¾Inactive (inert) electrodes – not involved in the electrode half-reaction (inert solid conductors; • Half-cell notation serve as a contact between the – Different phases are separated by vertical lines solution and the external el. circuit) 3+ 2+ – Species in the same phase are separated by Example: Pt electrode in Fe /Fe soln. commas Fe3+ + e- → Fe2+ (as reduction) • Types of electrodes Notation: Fe3+, Fe2+Pt(s) ¾Active electrodes – involved in the electrode ¾Electrodes involving metals and their half-reaction (most metal electrodes) slightly soluble salts Example: Zn2+/Zn metal electrode Example: Ag/AgCl electrode Zn(s) → Zn2+ + 2e- (as oxidation) AgCl(s) + e- → Ag(s) + Cl- (as reduction) Notation: Zn(s)Zn2+ Notation: Cl-AgCl(s)Ag(s) ¾Electrodes involving gases – a gas is bubbled Example: A combination of the Zn(s)Zn2+ and over an inert electrode Fe3+, Fe2+Pt(s) half-cells leads to: Example: H2 gas over Pt electrode + - H2(g) → 2H + 2e (as oxidation) + Notation: Pt(s)H2(g)H • Cell notation – The anode half-cell is written on the left of the cathode half-cell Zn(s) → Zn2+ + 2e- (anode, oxidation) + – The electrodes appear on the far left (anode) and Fe3+ + e- → Fe2+ (×2) (cathode, reduction) far right (cathode) of the notation Zn(s) + 2Fe3+ → Zn2+ + 2Fe2+ – Salt bridges are represented by double vertical lines ⇒ Zn(s)Zn2+ || Fe3+, Fe2+Pt(s) 1 + Example: A combination of the Pt(s)H2(g)H Example: Write the cell reaction and the cell and Cl-AgCl(s)Ag(s) half-cells leads to: notation for a cell consisting of a graphite cathode - 2+ Note: The immersed in an acidic solution of MnO4 and Mn 4+ reactants in the and a graphite anode immersed in a solution of Sn 2+ overall reaction are and Sn .
    [Show full text]
  • Advances in Materials Design for All-Solid-State Batteries: from Bulk to Thin Films
    applied sciences Review Advances in Materials Design for All-Solid-state Batteries: From Bulk to Thin Films Gene Yang 1, Corey Abraham 2, Yuxi Ma 1, Myoungseok Lee 1, Evan Helfrick 1, Dahyun Oh 2,* and Dongkyu Lee 1,* 1 Department of Mechanical Engineering, College of Engineering and Computing, University of South Carolina, Columbia, SC 29208, USA; [email protected] (G.Y.); [email protected] (Y.M.); [email protected] (M.L.); [email protected] (E.H.) 2 Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, San José, CA 95192-0080, USA; [email protected] * Correspondence: [email protected] (D.O.); [email protected] (D.L.) Received: 15 June 2020; Accepted: 7 July 2020; Published: 9 July 2020 Featured Application: All solid-state lithium batteries, all solid-state thin-film lithium batteries. Abstract: All-solid-state batteries (SSBs) are one of the most fascinating next-generation energy storage systems that can provide improved energy density and safety for a wide range of applications from portable electronics to electric vehicles. The development of SSBs was accelerated by the discovery of new materials and the design of nanostructures. In particular, advances in the growth of thin-film battery materials facilitated the development of all solid-state thin-film batteries (SSTFBs)—expanding their applications to microelectronics such as flexible devices and implantable medical devices. However, critical challenges still remain, such as low ionic conductivity of solid electrolytes, interfacial instability and difficulty in controlling thin-film growth. In this review, we discuss the evolution of electrode and electrolyte materials for lithium-based batteries and their adoption in SSBs and SSTFBs.
    [Show full text]
  • Chapter 13: Electrochemical Cells
    March 19, 2015 Chapter 13: Electrochemical Cells electrochemical cell: any device that converts chemical energy into electrical energy, or vice versa March 19, 2015 March 19, 2015 Voltaic Cell -any device that uses a redox reaction to transform chemical potential energy into electrical energy (moving electrons) -the oxidizing agent and reducing agent are separated -each is contained in a half cell There are two half cells in a voltaic cell Cathode Anode -contains the SOA -contains the SRA -reduction reaction -oxidation takes place takes place - (-) electrode -+ electrode -anions migrate -cations migrate towards the anode towards cathode March 19, 2015 Electrons move through an external circuit from the anode to cathode Electricity is produced by the cell until one of the reactants is used up Example: A simple voltaic cell March 19, 2015 When designing half cells it is important to note the following: -each half cell needs an electrolyte and a solid conductor -the electrode and electrolyte cannot react spontaneously with each other (sometimes carbon and platinum are used as inert electrodes) March 19, 2015 There are two kinds of porous boundaries 1. Salt Bridge 2. Porous Cup · an unglazed ceramic cup · tube filled with an inert · separates solutions but electrolyte such as NaNO allows ions to pass 3 through or Na2SO4 · the ends are plugged so the solutions are separated, but ions can pass through Porous boundaries allow for ions to move between two half cells so that charge can be equalized between two half cells 2+ 2– electrolyte: Cu (aq), SO4 (aq) 2+ 2– electrolyte: Zn (aq), SO4 (aq) electrode: zinc electrode: copper March 19, 2015 Example: Metal/Ion Voltaic Cell V Co(s) Zn(s) Co2+ SO 2- 4 2+ SO 2- Zn 4 Example: A voltaic cell with an inert electrode March 19, 2015 Example Label the cathode, anode, electron movement, ion movement, and write the half reactions taking place at each half cell.
    [Show full text]
  • Standardizing Analytical Methods
    Chapter 5 Standardizing Analytical Methods Chapter Overview 5A Analytical Standards 5B Calibrating the Signal (Stotal) 5C Determining the Sensitivity (kA) 5D Linear Regression and Calibration Curves 5E Compensating for the Reagent Blank (Sreag) 5F Using Excel and R for a Regression Analysis 5G Key Terms 5H Chapter Summary 5I Problems 5J Solutions to Practice Exercises The American Chemical Society’s Committee on Environmental Improvement defines standardization as the process of determining the relationship between the signal and the amount of analyte in a sample.1 In Chapter 3 we defined this relationship as SktotalA=+nSA reagtor Skotal = AAC where Stotal is the signal, nA is the moles of analyte, CA is the analyte’s concentration, kA is the method’s sensitivity for the analyte, and Sreag is the contribution to Stotal from sources other than the sample. To standardize a method we must determine values for kA and Sreag. Strategies for accomplishing this are the subject of this chapter. 1 ACS Committee on Environmental Improvement “Guidelines for Data Acquisition and Data Quality Evaluation in Environmental Chemistry,” Anal. Chem. 1980, 52, 2242–2249. 147 148 Analytical Chemistry 2.1 5A Analytical Standards To standardize an analytical method we use standards that contain known amounts of analyte. The accuracy of a standardization, therefore, depends on the quality of the reagents and the glassware we use to prepare these standards. For example, in an acid–base titration the stoichiometry of the acid–base reaction defines the relationship between the moles of analyte and the moles of titrant. In turn, the moles of titrant is the product of the See Chapter 9 for a thorough discussion of titrant’s concentration and the volume of titrant used to reach the equiva- titrimetric methods of analysis.
    [Show full text]
  • Ch.14-16 Electrochemistry Redox Reaction
    Redox Reaction - the basics ox + red <=> red + ox Ch.14-16 1 2 1 2 Oxidizing Reducing Electrochemistry Agent Agent Redox reactions: involve transfer of electrons from one species to another. Oxidizing agent (oxidant): takes electrons Reducing agent (reductant): gives electrons Redox Reaction - the basics Balance Redox Reactions (Half Reactions) Reduced Oxidized 1. Write down the (two half) reactions. ox1 + red2 <=> red1 + ox2 2. Balance the (half) reactions (Mass and Charge): a. Start with elements other than H and O. Oxidizing Reducing Agent Agent b. Balance O by adding water. c. balance H by adding H+. Redox reactions: involve transfer of electrons from one d. Balancing charge by adding electrons. species to another. (3. Multiply each half reaction to make the number of Oxidizing agent (oxidant): takes electrons electrons equal. Reducing agent (reductant): gives electrons 4. Add the reactions and simplify.) Fe3+ + V2+ → Fe2+ + V3 + Example: Balance the two half reactions and redox Important Redox Titrants and the Reactions reaction equation of the titration of an acidic solution of Na2C2O4 (sodium oxalate, colorless) with KMnO4 (deep purple). Oxidizing Reagents (Oxidants) - 2- 2+ MnO4 (qa ) + C2O4 (qa ) → Mn (qa ) + CO2(g) (1)Potassium Permanganate +qa -qa 2-qa 16H ( ) + 2MnO4 ( ) + 5C2O4 ( ) → − + − 2+ 2+ MnO 4 +8H +5 e → Mn + 4 H2 O 2Mn (qa ) + 8H2O(l) + 10CO2( g) MnO − +4H+ + 3 e − → MnO( s )+ 2 H O Example: Balance 4 2 2 Sn2+ + Fe3+ <=> Sn4+ + Fe2+ − − 2− MnO4 + e→ MnO4 2+ - 3+ 2+ Fe + MnO4 <=> Fe + Mn 1 Important Redox Titrants
    [Show full text]
  • A Guide to Ion Selective Measurement
    Ion Selective Book Master 25/5/99 10:55 pm Page 1 A GUIDE TO ION SELECTIVE MEASUREMENT 1 Ion Selective Book Master 25/5/99 10:55 pm Page 2 INTRODUCTION The measurement of the concentration or activity of an ion in a solution by means of an Ion Selective Electrode is as simple as making a routine pH measurement. A pH electrode is only a rather special case of an almost perfectly selective Ion Selective Electrode but the principles and practice are the same in both cases. The chief difference between the pH electrode and other electrodes is that the latter, generally speaking, are not as selective as the pH electrode and some account must be taken of possible interferences in an analytical situation. Sophisticated, microprocessor-controlled Ion meters have operational modes which enable concentration results to be obtained directly from sample solutions. Calibration is automatic and the ability of the Ion meter to retain this data in memory dispenses with the drawing of calibration curves. The information contained in this booklet should enable the reader to understand the principles of operation and methods of analysis involving Ion Selective Electrodes. 2 Ion Selective Book Master 25/5/99 10:55 pm Page 3 CONTENTS Page Section 1 Ion selective measurement 4 ● Basic theory 4 ● Selectivity, interferences, activity 5 ● Types of electrode 6 Section 2 Methods of analysis 9 ● Direct potentiometry 9 ● One point calibration 10 ● Incremental techniques 11 ● Multiple sample additon 14 ● Titrimetric procedures 15 Section 3 Laboratory measurements 17
    [Show full text]
  • Vanadium Redox Flow Batteries: a Review Oriented to Fluid-Dynamic Optimization
    energies Review Vanadium Redox Flow Batteries: A Review Oriented to Fluid-Dynamic Optimization Iñigo Aramendia 1,* , Unai Fernandez-Gamiz 1 , Adrian Martinez-San-Vicente 1, Ekaitz Zulueta 2 and Jose Manuel Lopez-Guede 2 1 Nuclear Engineering and Fluid Mechanics Department, University of the Basque Country UPV/EHU, Nieves Cano 12, 01006 Vitoria-Gasteiz, Spain; [email protected] (U.F.-G.); [email protected] (A.M.-S.-V.) 2 Automatic Control and System Engineering Department, University of the Basque Country UPV/EHU, Nieves Cano 12, 01006 Vitoria-Gasteiz, Spain; [email protected] (E.Z.); [email protected] (J.M.L.-G.) * Correspondence: [email protected]; Tel.: +34-945-014-066 Abstract: Large-scale energy storage systems (ESS) are nowadays growing in popularity due to the increase in the energy production by renewable energy sources, which in general have a random intermittent nature. Currently, several redox flow batteries have been presented as an alternative of the classical ESS; the scalability, design flexibility and long life cycle of the vanadium redox flow battery (VRFB) have made it to stand out. In a VRFB cell, which consists of two electrodes and an ion exchange membrane, the electrolyte flows through the electrodes where the electrochemical reactions take place. Computational Fluid Dynamics (CFD) simulations are a very powerful tool to develop feasible numerical models to enhance the performance and lifetime of VRFBs. This review aims to present and discuss the numerical models developed in this field and, particularly, to analyze different types of flow fields and patterns that can be found in the literature.
    [Show full text]
  • Viewed, Most SPME Extractions Are Performed in Aqueous Matrices.11,16 the Organic Solvent Most Likely Acted As an Interference with the Analyte Extraction
    A COMPARISON OF COMMON LABORATORY TECHNIQUES FOR THE ANALYSIS OF THIOCARBAMATE PESTICIDES A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Tammy Schumacher Donohue August, 2012 A COMPARISON OF COMMON LABORATORY TECHNIQUES FOR THE ANALYSIS OF THIOCARBAMATE PESTICIDES Tammy Schumacher Donohue Thesis Approved: Accepted: ________________________________ ________________________________ Advisor Dean of the College Dr. Claire Tessier Dr. Chand Midha ________________________________ ________________________________ Faculty Reader Dean of the Graduate School Dr. Kim C. Calvo Dr. George R. Newkome ________________________________ ________________________________ Department Chair Date Dr. Kim C. Calvo ii ABSTRACT The United States Environmental Protection Agency has devised a set of regulations limiting the use of thiocarbamate pesticides for the health and safety of humans and the environment. These regulations dictate the maximum amount of thiocarbamate compounds that may be released or present in soil, waste, and groundwater. Therefore, it is important to be able to determine their concentration accurately and reproducibly. A study was conducted to determine the best way to identify and quantify six thiocarbamate herbicides using equipment commonly found in industrial laboratories. Three analytical methods were tested: gas chromatography-mass spectrometry, high performance liquid chromatography, and infrared spectroscopy. They were chosen for their common usage, broad application, and operative ability. A comparison of these methods was made to determine the most effective technique for thiocarbamate identification and quantification. iii DEDICATION To my husband, Chris, whose steadfast belief in me never wavered. Thank you for always letting me know you were behind me, no matter what. I love you.
    [Show full text]
  • Guidance for the Validation of Analytical Methodology and Calibration of Equipment Used for Testing of Illicit Drugs in Seized Materials and Biological Specimens
    Vienna International Centre, PO Box 500, 1400 Vienna, Austria Tel.: (+43-1) 26060-0, Fax: (+43-1) 26060-5866, www.unodc.org Guidance for the Validation of Analytical Methodology and Calibration of Equipment used for Testing of Illicit Drugs in Seized Materials and Biological Specimens FOR UNITED NATIONS USE ONLY United Nations publication ISBN 978-92-1-148243-0 Sales No. E.09.XI.16 *0984578*Printed in Austria ST/NAR/41 V.09-84578—October 2009—200 A commitment to quality and continuous improvement Photo credits: UNODC Photo Library Laboratory and Scientific Section UNITED NATIONS OFFICE ON DRUGS AND CRIME Vienna Guidance for the Validation of Analytical Methodology and Calibration of Equipment used for Testing of Illicit Drugs in Seized Materials and Biological Specimens A commitment to quality and continuous improvement UNITED NATIONS New York, 2009 Acknowledgements This manual was produced by the Laboratory and Scientific Section (LSS) of the United Nations Office on Drugs and Crime (UNODC) and its preparation was coor- dinated by Iphigenia Naidis and Satu Turpeinen, staff of UNODC LSS (headed by Justice Tettey). LSS wishes to express its appreciation and thanks to the members of the Standing Panel of the UNODC’s International Quality Assurance Programme, Dr. Robert Anderson, Dr. Robert Bramley, Dr. David Clarke, and Dr. Pirjo Lillsunde, for the conceptualization of this manual, their valuable contributions, the review and finali- zation of the document.* *Contact details of named individuals can be requested from the UNODC Laboratory and Scientific Section (P.O. Box 500, 1400 Vienna, Austria). ST/NAR/41 UNITED NATIONS PUBLICATION Sales No.
    [Show full text]