ASTM_D_2913_-_14.pdf

Designation:D291314Standard Test Method forMercaptan Content of the Atmosphere1This standard is issued under the fixed designation D2913;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 is for the measurement of mercaptans(organic thiols)in the atmosphere at concentrations below 100parts per billion(ppb(v)=195 g/m3).For concentrationsabove 100 ppb(v),the sampling period can be reduced or thetrapping liquid volume increased either before or after aspirat-ing.(See Practice D1357 for sampling guidance.)The mini-mum detectable amount of methyl mercaptan is 0.04 g/mL(1)2in a final liquid volume of 25 mL.When sampling air atthe maximum recommended rate of 2 L/min for 2 h,theminimum detectable mercaptan concentration is 1.0 ppb(v)(1.95 g methyl mercaptan/m3at 101.3 kPa(760 mm Hg)and25C).This test method determines total mercaptans and doesnot differentiate among individual mercaptans,although it ismost sensitive to the lower molecular weight alkanethiols.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.Specific precau-tionary statements are given in 8.7,8.8,and Section 9.2.Referenced Documents2.1 ASTM Standards:3D1193 Specification for Reagent WaterD1356 Terminology Relating to Sampling and Analysis ofAtmospheresD1357 Practice for Planning the Sampling of the AmbientAtmosphereD1914 Practice for Conversion Units and Factors Relating toSampling and Analysis of AtmospheresD2914 Test Methods for Sulfur Dioxide Content of theAtmosphere(West-Gaeke Method)D3195 Practice for Rotameter CalibrationD3249 Practice for General Ambient Air Analyzer Proce-duresD3609 Practice for Calibration Techniques Using Perme-ation TubesD3631 Test Methods for Measuring Surface AtmosphericPressureE2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision Liquids3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,refer to Terminology D1356.4.Summary of Test Method4.1 This test method is intended for obtaining an integratedsample over a selected time span(such as 2 h)either manuallyor in an automatic sequential sampler using 10 mL of absorp-tion liquid in a bubbler.4.2 The absorption liquid is delivered to the laboratory forcolorimetric analysis by reaction between the collected mer-captan and N,N-dimethyl-p-phenylenediamine.5.Significance and Use5.1 Mercaptans are odorous substances offensive at lowconcentrations and toxic at higher levels.They are emittedfrom geothermal sources,industrial processes,and food pro-cessing facilities.Mercaptans at low concentrations are com-monly added to natural gas and LP gases for safety purposes aswell.6.Interferences6.1 The N,N-dimethyl-p-phenylenediamine reaction is alsoused in the determination of other sulfur-containing com-pounds including hydrogen sulfide and dimethyl disulfide(2).The potential for interference from these latter compounds isespecially important,since all of these compounds commonlycoexist in certain industrial emissions.Appropriate selection of1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.03 on AmbientAtmospheres and Source Emissions.Current edition approved Sept.1,2014.Published October 2014.Originallyapproved in 1970.Last previous edition approved in 2007 as D2913 96(2007).DOI:10.1520/D2913-14.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For 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 the color formation conditions and measurements of absor-bance at the specified wavelength will eliminate the potentialinterference from hydrogen sulfide.6.2 Hydrogen sulfide,if present in the sampled air,maycause a turbidity in the sample absorbing solution.Thisprecipitate must be filtered before proceeding with the analysis.One study showed that 100 g of H2S gave a mercaptan colorequivalent to 1.5 to 2.0 g of mercaptan(3).Another studyreported no absorption at 500 nm in the presence of 150 g ofhydrogen sulfide(4,5).6.3 Approximately equimolar response is obtained from thehydrolysis products of dimethyl disulfide,