ASTM_D_7375_-_08.pdf

Designation:D737508Standard Test Method forTrace Quantities of Water in Aromatic Hydrocarbons andTheir Mixtures by Coulometric Karl Fischer Titration1This standard is issued under the fixed designation D7375;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 describes the use of the CoulometricKarl Fischer(KF)titration for the determination of water inaromatic hydrocarbons and their mixtures,derivatives andrelated chemicals.1.2 This test method is applicable to samples with waterconcentrations from 10 to 400 mg/kg.1.3 In determining the conformance of the test results usingthis method to applicable specifications,results shall berounded off in accordance with the rounding-off method ofPractice E29.1.4 Values stated in SI units are to be regarded as thestandard.The preferred units are milligrams per kilogram(mg/kg).1.5 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.For a specifichazard statement see Section 8.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD3437 Practice for Sampling and Handling Liquid CyclicProductsD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE203 Test Method for Water Using Volumetric Karl FischerTitration2.2 Other Standard:OSHARegulations,29 CFR paragraphs 1910 and 1910.120033.Summary of Test Method3.1 In the Karl Fischer reaction,water will react with iodinein the presence of sulfur dioxide,alcohol and an organic baseaccording to the following equation:H2O1I21SO21CH3OH13RNRNH!SO4CH312RNH!I(1)where:RN=organic base.3.2 In the coulometric titration test method,the sample isinjected into an electrolytic cell where the iodine required forthe reaction with water is produced by an anodic oxidation ofiodide.With this technique,no standardization of reagents isrequired.4.Significance and Use4.1 High water concentrations can have a detrimental effecton many uses of aromatic hydrocarbons,their mixtures andrelated compounds.4.2 Water can inhibit desired reactions when aromatichydrocarbons,their mixtures and related compounds are usedin formulations and chemical processes.4.3 Water can cause corrosion problems and detrimentaleffects during the manufacture and processing of aromatichydrocarbons,their mixtures and related compounds.5.Interferences5.1 Certain compounds or classes of compounds interferewith the accurate determination of water by the Karl Fischertest method.They include aldehydes,ketones,free halogens,ferric salts and strong oxidizing and reducing agents.5.2 Free halogens can oxidize the iodate in the KF reagentsto form iodine:this causes erroneously low water values.1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.04 on Instrumental Analysis.Current edition approved Jan.1,2008.Published February 2008.DOI:10.1520/D7375-08.2For 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.3Available from U.S.Government Printing Office Superintendent of Documents,732 N.Capitol St.,NW,Mail Stop:SDE,Washington,DC 20401,http:/www.access.gpo.gov.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.3 A more detailed discussion of KF interferences can befound in Test Method E203 and other sources.46.Apparatus6.1 Coulometric TitratorConsisting of a single or dualbath electrolytic cell,dual platinum electrode,magnetic stirrerand control unit.6.1.1 Dual Bath Electrolytic CellThe dual bath coulom-etic titration cell consists of a sealed vessel containing both ananode and cathode compartment(a Fritted Cathode Cell).Theanodic compartment usually contains a solution consisting ofsulfur dioxide,iodide and an amine in an alcoholic basedsolvent.The cathodic compartment contains similar reagentsoptimized for the cathodic reduction.When a sample contain-ing water is injected into the anode compartment,the electro-lytic cell generates its own supply of iodine from the iodidepresent.The iodine reacts stoichiometrically with the water andthe completion of the reaction is detected with a dual platinum-sensing electrode.The coulombs of electricity required togenerate the necessary amount of iod