ASTM_D_7318_-_13.pdf

Designation:D731813Standard Test Method forExistent Inorganic Sulfate in Ethanol by PotentiometricTitration1This standard is issued under the fixed designation D7318;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.Scope*1.1 This test method covers a potentiometric titration pro-cedure for determining the existent inorganic sulfate content ofhydrous,anhydrous ethanol,and anhydrous denatured ethanol,which is added as a blending agent with spark ignition fuels.Itis intended for the analysis of denatured ethanol samplescontaining between 1.020 mg/kg existent inorganic sulfate.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.Material SafetyData Sheets are available for reagents and materials.Reviewthem for hazards prior to usage.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4052 Test Method for Density,Relative Density,and APIGravity of Liquids by Digital Density MeterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System Performance3.Terminology3.1 Definitions:3.1.1 existent inorganic sulfate,ninorganic sulfate speciesactually present in the sample at the time of analysis with nooxidation treatment.3.1.1.1 DiscussionSpecifically in this test method,inor-ganic sulfate is present as sulfate in ethanol.3.1.2 inorganic sulfate,nsulfate(SO4-2)species present assulfuric acid,ionic salts of this acid,or mixtures of these.4.Summary of Test Method4.1 An ethanol sample containing inorganic sulfate istitrated in ethanolic medium with a standard lead nitratesolution.Lead sulfate precipitate is formed during the titration.Perchloric acid is added to remove possible interference fromcarbonate.The endpoint is signaled by an increase in lead ionactivity,as measured by a leadselective electrode.5.Significance and Use5.1Ethanol is used as a blending agent added to gasoline.Sulfates are indicated in filter plugging deposits and fuelinjector deposits.When fuel ethanol is burned,sulfates maycontribute to sulfuric acid emissions.Ethanol acceptability foruse depends on the sulfate content.Sulfate content,as mea-sured by this test method,can be used as one measure ofdetermination of the acceptability of ethanol for automotivespark-ignition engine fuel use.6.Apparatus6.1 Potentiometric Titration AssemblyA titration assem-bly consisting of an automatic titrator fitted with a leadion-selective electrode,a double-junction reference electrode,buret,and stirring is used.Stirring may be accomplished bymeans of magnetic or propeller type stirrer mechanisms.Theburet size should ideally be 10 or 20 mL.6.2 Reference ElectrodeA double junction reference elec-trode with the inner electrode composed of silver/silver chlo-ride with a potassium chloride solution as internal electrolyte.The external solution is composed of 1 M lithium chloride inethanol.This configuration is used to prevent silver ion,a leadelectrode poison,from leaching into the analyte solution duringtitration.Preferred electrolytes for use in double junctionelectrodes may vary with the manufacturer;use the manufac-turers recommended electrolytes for the application.Other1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved June 15,2013.Published August 2013.Originallyapproved in 2007.Last previous edition approved in 2011 as D7318 11.DOI:10.1520/D7318-13.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 types of reference electrodes may be considered with somecaveats(for example,single junction,combination,or glassycarbon),but the data presented in this test method weregenerated using exclusively a double junction electrode,whichis the best choice for this determination.6.3 Lead ElectrodeAlead sulfidebased crystalline sensortype lead