ASTM_D_1498_-_14.pdf

Designation:D149814Standard Test Method forOxidation-Reduction Potential of Water1This standard is issued under the fixed designation D1498;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the apparatus and procedure forthe electrometric measurement of oxidation-reduction potential(ORP)in water.It does not deal with the manner in which thesolutions are prepared,the theoretical interpretation of theoxidation-reduction potential,or the establishment of a stan-dard oxidation-reduction potential for any given system.Thetest method described has been designed for the routine andprocess measurement of oxidation-reduction potential.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed Conduits3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 oxidation-reduction potential,nthe electromotiveforce,Em,developed between a noble metal electrode and astandard reference electrode.3.2.1.1 DiscussionThis oxidation-reduction potential(ORP)is related to the solution composition by:Em5 Eo12.3RTnFlogAox/Ared#where:Em=ORP,Eo=constant that depends on the choice of refer-ence electrodes,F=Faraday constant,R=gas constant,T=absolute temperature,C+273.15,n=number of electrons involved in processreaction,andAoxand Ared=activities of the reactants in the process.4.Summary of Test Method4.1 This is a test method designed to measure the ORPwhich is defined as the electromotive force between a noblemetal electrode and a reference electrode when immersed in asolution.The test method describes the equipment available tomake the measurement,the standardization of the equipmentand the procedure to measure ORP.The ORP electrodes areinert and measure the ratio of the activities of the oxidized tothe reduced species present.5.Significance and Use5.1 Variousapplicationsincludemonitoringthechlorination/dechlorination process of water,recognition ofoxidants/reductants present in wastewater,monitoring thecycle chemistry in power plants,and controlling the processingof cyanide and chrome waste in metal plating baths.5.2 The measurement of ORP has been found to be useful inthe evaluation of soils,for evaluating treatment design data atsites contaminated with certain chemicals,and in evaluatingsolid wastes.6.Interferences6.1 The ORP electrodes reliably measure ORP in nearly allaqueous solutions and in general are not subject to solutioninterference from color,turbidity,colloidal matter,and sus-pended matter.6.2 The ORP of an aqueous solution is sensitive to changein temperature of the solution,but temperature correction is1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits,Analysis of Water for Power Generation and Process Use,On-Line Water Analysis,and Surveillance of Water.Current edition approved Feb.15,2014.Published March 2014.Originallyapproved in 1957.Last previous edition approved in 2008 as D1498 08.DOI:10.1520/D1498-14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 rarely done due to its minimal effect and complex reactions.Temperature corrections are usually applied only when it isdesired to relate the ORP to the activity of an ion in thesolutions.6.3 The ORP of an aqueous solution is almost alwayssensitive to pH variations even to reactions that do not appearto involve hydrogen or hydroxyl ions.The ORPgenerally tendsto increase with an increase in hydrogen ions and to decreasewith an increase in hydroxyl ions during such reactions.6.4 Reproducible oxidation-reduction potentials cannot beobtained for chemical systems that are not reversible.Mostnatural and ground waters do not contain reversible systems,ormay contain systems that are shifted b