ASTM_D_3961_-_98.pdf

Designation:D 3961 98Standard Test Method forTrace Quantities of Sulfur in Liquid Aromatic Hydrocarbonsby Oxidative Microcoulometry1This standard is issued under the fixed designation D 3961;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(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method determines total sulfur content inaromatic hydrocarbons,their derivatives,and related chemi-cals.1.2 This test method is applicable to samples with sulfurconcentrations from 0.5 to 100 mg/kg.1.3 The following applies to all specified limits in this testmethod:for purposes of determining conformance with thistest method,an observed value or a calculated value shall berounded off“to the nearest unit”in the last right-hand digitused in expressing the specification limit,in accordance withthe rounding-off method of Practice E 29.1.4 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 specific hazardstatements,see Section 9.2.Referenced Documents2.1 ASTM Standards:D 1193 Specification for Reagent Water2D 3437 Practice for Sampling and Handling Liquid CyclicProducts3E 29 Practice for Using Significant Digits in Test Data toDetermine Conformance with Specifications42.2Other Document:OSHA Regulations-29 CFR paragraphs 1910.1000 and1910.120053.Terminology3.1 Definitions:3.1.1 dehydration tubea chamber containing phosphoricacid 85%that scrubs the effluent gases from combustion toremove water vapor.3.1.2 oxidative pyrolysisa process in which a sample iscombusted in an oxygen-rich atmosphere at high temperatureto break down the components of the sample into elementaloxides.3.1.3 recovery factoran indication of the efficiency of themeasurement computed by dividing the measured value of astandard by its theoretical value.3.1.4 reference sensor pairdetects changes in triiodide ionconcentrations.3.1.5 titration parametersvarious instrumental conditionsthat can be changed for different types of analysis.3.1.6 working electrode(generator electrode)an electrodeconsisting of an anode and a cathode separated by a salt bridgeor a liquid electrolyte bridge;maintains a constant triiodide ionconcentrations.4.Summary of Test Method4.1 Aliquid specimen is injected into a combustion tube thatcan be maintained between 900 to 1200 C and having aflowing stream of gas containing approximately 50 to 75%oxygen and 25 to 50%inert gas(for example helium,argon,etc.).Oxidative pyrolysis converts the sulfur to sulfur dioxide,which then flows into a titration cell where it reacts withtriiodide ion present in the electrolyte.The triiodide thusconsumed is coulometrically replaced and the total electricalwork required to replace it is a measure of the sulfur present inthe sample injected.4.2 The reaction is generated in the titration cell as sulfurdioxide as follows:I31 SO21 H2O SO31 3I1 2H1(1)This triiodide ion consumed in the above reaction in gener-ated coulometrically thus:3I I31 2e(2)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 May 10,1998.Published August 1998.Originallypublished as D 3961 80.Last previous edition D 3961 89(1993).e12Annual Book of ASTM Standards,Vol 11.01.3Annual Book of ASTM Standards,Vol 06.04.4Annual Book of ASTM Standards,Vol 14.02.5Available from Superintendent of Documents,U.S.Government PrintingOffice,Washington,DC 20402.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.5.Significance and Use5.1 Total sulfur concentrations are typically required forbenzene,toluene,and xylenes used as chemical intermediatesand in solvents.This test method may be used for both finalproduct inspections and process control.5.2 This test method is applicable in the presence of totalhalide concentrations of up to 10 times the sulfur level and totalnitrogen concentrations of up to 1000 times the sulfur level.6.Interferences6.1 This test method is not applicable in the presence oftotal metal concentrations(for example,nickel,vanadium,andlead)in excess of 500 mg/kg.NOTE1To ensure reliable results,all sources of sulfur contaminationmust be eliminated.7.Apparatus7.1 Pyrolysis Furnace,which can maintain a temperaturesufficient to pyrolyze the organic matrix and convert sulfurpresent in the specimen to sulfur dioxide.7.2 Pyrolysis Tube,made of quartz and constructed so thatwhen a sample is volatilized in the front of the furnace,it isswept into the pyrolysis zone by an inert gas,where itcombus