1、Designation: D 2913 96 (Reapproved 2007)Standard Test Method forMercaptan Content of the Atmosphere1This standard is issued under the fixed designation D 2913; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 covers measurement of the concentra-tion of mercaptans (organic thiols) in the atmosphere atconcentrations belo
3、w 100 parts per billion (ppb(v) = 195g/m3). For concentrations above 100 ppb(v) level, the sam-pling period can be reduced or the liquid volume increasedeither before or after aspirating. The minimum detectableamount of methyl mercaptan is 0.04 g/mL(1)2in a final liquidvolume of 25 mL. When sampling
4、 air at the maximumrecommended rate of 2 L/min for 2 h, the minimum detectablemercaptan concentration is 1.0 ppb(v) (1.95 g methylmercaptan/m3at 101.3 kPa (760 mm Hg) and 25C). This testmethod determines total mercaptans and does not differentiateamong individual mercaptans, although it is most sens
5、itive tothe lower molecular weight alkanethiols.1.2 The values stated in SI units are to be regarded as thestandard.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
6、 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:3D 1193 Specification for Reagent WaterD 1356 Terminology Relating to Sampling and A
7、nalysis ofAtmospheresD 1357 Practice for Planning the Sampling of the AmbientAtmosphereD 1914 Practice for Conversion Units and Factors Relatingto Sampling and Analysis of AtmospheresD 2914 Test Methods for Sulfur Dioxide Content of theAtmosphere (West-Gaeke Method)D 3195 Practice for Rotameter Cali
8、brationD 3249 Practice for General Ambient Air Analyzer Proce-duresD 3609 Practice for Calibration Techniques Using Perme-ation TubesD 3631 Test Methods for Measuring Surface AtmosphericPressureE1 Specification for ASTM Liquid-in-Glass Thermometers3. Terminology3.1 DefinitionsFor definitions of term
9、s used in this testmethod, refer to Terminology D 1356.4. 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 absor
10、ption 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 geotherma
11、l sources, industrial processes, and food pro-cessing facilities.6. Interferences6.1 The N,N-dimethyl-p-phenylenediamine reaction is alsosuitable for the determination of other sulfur-containing com-pounds including hydrogen sulfide and dimethyl disulfide (2).The potential for interference from thes
12、e latter compounds isespecially important, since all of these compounds commonlycoexist in certain industrial emissions. Appropriate selection ofthe color formation conditions and measurements of absor-bance at the specified wavelength will eliminate the potentialinterference from hydrogen sulfide.6
13、.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 color1This test method is under the jurisdiction of ASTM Committee D22 o
14、n AirQuality and is the direct responsibility of Subcommittee D22.03 on AmbientAtmospheres and Source Emissions.Current edition approved April 1, 2007. Published May 2007. Originallyapproved in 1970. Last previous edition approved in 2001 as D 2913 - 96(2001)e1.2The boldface numbers in parentheses r
15、efer to the list of references at the end ofthis test method.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.
16、1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.equivalent 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 obt
17、ained from thehydrolysis products of dimethyl disulfide, the molar extinctioncoefficient for the amine-mercaptan reaction product being4.4 3 103, and the amine-dimethyl disulfide reaction productbeing 5.16 3 103(5). The interference due to dimethyl disul-fide has been experimentally determined. Dime
18、thyl disulfideconcentrations of 0.6 ppm(v) and 1.0 ppm(v) given an equiva-lent response as 0.4 ppm(v) and 0.8 ppm(v), respectively, ofmethyl mercaptan.46.4 Sulfur dioxide up to 250 g does not influence the colordevelopment even when sampling a test atmosphere containing300 ppm(v) of SO2.6.5 Nitrogen
19、 dioxide does not interfere up to 700 g of NO2when sampling a test atmosphere containing 6 ppm. Higherconcentrations of NO2caused a positive interference whenmercaptans were present, but no interference in the absence ofmercaptans. Such elevated NO2concentrations are unrealisticand would not be enco
20、untered in the ambient air except in thevicinity of an accidental spillage.6.6 The supply of mercuric acetate must be free of mercu-rous ion. If mercurous ion is present, turbidity will result whenthe chloride ion-containing reagents are added in the last stepof the analytical procedure.7. Apparatus
21、7.1 Sampling Apparatus:7.1.1 AbsorberMidget bubbler with coarse porosity frit.7.1.2 Air Sample ProbeTFE-fluorocarbon, polypropy-lene, or glass tube with a polypropylene or glass funnel at theend.7.1.3 Moisture Trap-Glass, or polypropylene tube with atwo port closure. The entrance port of the closure
22、 is fitted withtubing that extends to the bottom of the trap. The unit is looselypacked with 16-mesh activated charcoal to prevent moistureentrainment. The charcoal should be changed weekly.7.1.4 FilterMembrane, of 0.8 to 2.0 m porosity.7.1.5 PumpCapable of maintaining a vacuum greater than70 kPA (0
23、.7 atm) at the specified flowrate.7.1.6 Flow Control DeviceA needle valve capable ofmaintaining a constant flow rate (62 %). Protect the needlevalve from particulate matter and moisture entrainment.7.1.7 Flow meter, having a range of 0 to 2.5 L/min.7.1.8 ThermometersASTM Thermometer 33C, meetingthe
24、requirements of Specification E1, will be suitable for mostapplications of this test method.7.1.9 Barograph or BarometerCapable of measuring at-mospheric pressure to 60.5 kPa (4 Torr), meeting the require-ments of Test Methods D 3631.7.1.10 Stopwatch or timer, accurate to 61 s/24 h.7.1.11 The arrang
25、ements of the component parts of sam-pling is shown in Fig. 1a, Test Methods D 2914.7.2 Calibration ApparatusA means of generating dy-namic standard atmospheres using a permeation device. Dilu-tion air and excess dilution flow must be filtered throughactivated charcoal to prevent recirculating small
26、 quantities ofmercaptans. See Practice D 3609 for details.7.3 Colorimeter or Spectrophotometer, (at 500 nm)Use2.5- or 5.0-cm path length to obtain adequate sensitivity.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.All reagents shall conform to the s
27、pecificationsof the Committee on Analytical Reagents of the AmericanChemical Society, where such specifications are available.5Other grades may be used, provided it is first ascertained thatthe reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determinatio
28、n.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall mean referee reagent water conforming toSpecification D 1193.8.3 Solutions should be refrigerated when not in use.8.4 Amine-Hydrochloric Acid Solution, StockDissolve 5.0gofN,N-dimethyl-p-phenylenediamine hydrochloride (p-amino
29、dimethylaniline hydrochloride) in 1 L of concentratedhydrochloric acid (HCL). Refrigerate and protect from light.This solution is stable for at least 6 months.8.5 Reissner SolutionDissolve 67.6 g of ferric chloridehexahydrate (FeCl36H2O) in distilled water, dilute to 500 mL,and mix with 500 mL of ni
30、tric acid (HNO3) solution containing72 mL of boiled concentrated nitric acid (sp gr 1.42). Thissolution is stable.8.6 Color-Developing ReagentMix 3 volumes of aminesolution and 1 volume of Reissner solution. Prepare thissolution freshly for each set of determinations.8.7 Absorbing SolutionDissolve 5
31、0 g of mercuric acetateHg (CH3COO)2in 400 mL of distilled water and add 25 mL ofglacial acetic acid (CH3COOH). Dilute to 1 L. The mercuricacetate must be free of mercurous salts to prevent precipitationof mercurous chloride during color development. Reagentgrade mercuric acetate sometimes contains m
32、ercurous mer-cury. Determine the acceptability of each new bottle ofmercuric acetate by adding 3 mL of concentrated hydrochloricacid to 3 mL of the 5 % mercuric acetate. If the solutionbecomes cloudy, the mercuric acetate is not acceptable.(WarningThe absorbing solution and mercury salts are verypoi
33、sonous. Avoid contact with the skin and especially with theeyes.Avoid generating or breathing dust. Wash hands after use.Keep away from food. Do not ingest.)8.8 Lead Methyl MercaptideBubble tank methyl mercap-tan gas (CH3SH) into 10 % lead acetate solutionPb(CH3COO)2in an adequate fume hood (1). Col
34、lect the4Supporting data giving the results of a laboratory examination of this methodby the National Council of the Paper Industry for Air and Stream Improvement(NCASI) are available in special report No. 80-07, “A Laboratory Examination ofthe Use of the ASTM/APHA. Spectrophotometric Method for the
35、 Measurement ofMethyl Mercaptan in Kraft Mill Workspace Atmospheres,” May 1980, NCASI, 260Madison Ave., New York, NY 10016.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chem
36、ical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D 2913 96 (2007)2yellow crystals by vacuum filtration, wash with distilled water,and dry overn
37、ight in a vacuum oven at 45C. Store crystals ina vacuum-sealed container in the dark. One mole of thismercaptide is equivalent to two moles of a mercaptan. Leadmercaptide may be purchased from commercial sources, ifdesired.6(WarningMethyl mercaptan gas is extremelytoxic. At high levels of exposure,
38、the human olfactory sensemay become insensitive to its presence.)8.9 Concentrated, Standard Lead Mercaptide SolutionWeigh out 156.6 mg of the crystalline lead mercaptide andmake up to 100 mL with the 5 % mercuric acetate absorbingsolution. This solution contains the equivalent of 500 g ofmethyl merc
39、aptan/mL.8.10 Diluted Mercaptan Solution, StandardDilute 2 mLof the concentrated standard solution to 100 mL with the 5 %mercuric acetate absorbing solution. This solution contains theequivalent of 10 g CH3SH/mL.8.11 Methyl Mercaptan Permeation Device, with a perme-ation rate appropriate to the dilu
40、tion flow and concentrationsexpected.7For example, see table below.Concentrations Permeation Rate Required10 ppb(v) 2 L/min100 ppm(v) 1 L/min40 ng/min200 ng/min9. Safety Precautions9.1 MercuryThe absorbing solution contains mercurysalts. Precautions for its use are described in 8.7.9.2 Disposal proc
41、edures are described in Annex A3, TestMethods D 2914.9.3 Compressed Gas Cylinders.9.3.1 Compressed gas cylinders may be used in this testmethod for preparation of reagents or standard atmospheres.Precautions on methyl mercaptan cylinders are described in8.8.9.3.2 General safety precautions for handl
42、ing and storingcompressed gas cylinders are described in Practice D 3249.10. Sampling10.1 Sampling procedures are described for 2h samplingperiods. Different sampling rates and sampling times may beselected to suit specific requirements, but sample volume andflow rates must be adjusted to maintain l
43、inearity betweenabsorbance and concentration over the dynamic range of thecolorimetric procedure.10.2 Measure the temperature of the atmosphere beingsampled before and after sampling.10.3 Measure the atmospheric pressure during sampling, inaccordance with Test Methods D 3631.11. Calibration and Stan
44、dardization11.1 Sampling EquipmentCalibrate the flow meter beforeand after use in accordance with Practice D 3195.11.1.1 The pressure drop of the flow meter must be main-tained the same during sampling as during calibration.11.2 Standard AtmospheresSee Practice D 3609 forpreparation of standard atmo
45、spheres using the calibrationapparatus and the permeation device.11.2.1 Calibrate the components of the calibration apparatusand the permeation device in accordance with Practice D 3609before and after use.11.3 Calibration Curve:11.3.1 Sample five standard atmospheres in accordance withSection 12.1.
46、 The mercaptan content of the standard atmo-spheres shall be such that the intensities of the color of theresultant analyzed solutions shall be evenly spaced over thedynamic range of the analytic procedure. One of the fivestandard atmospheres shall be a blank, generated by removingor bypassing the p
47、ermeation device.11.3.2 Analyze the solutions according to 12.2.11.3.3 Prepare a calibration curve of total mass of mercap-tan collected versus absorbance of developed color, using theleast squares method.11.4 Spot checks or audit samples are prepared by analyzingthe diluted standard Mercaptan solut
48、ions prepared in 8.10.Aminimum of two audit samples shall be analyzed for each tenatmospheric samples.11.4.1 Pipet appropriate aliquots of the diluted standard leadmercaptide into a series of 25-mL volumetric flasks, dilutingeach to 15 mL with 5 % mercuric acetate absorbing solutionand developing th
49、e color in the same manner as the samples. Areference blank is prepared in the same manner with theexception that no lead mercaptide is added. Determine theabsorbance at 500 nm against the mercaptan-free referenceblank.12. Procedure12.1 Collection of SampleCollect the sample by bubblingthe air through 10 mL of absorbing solution in a bubbler at ameasured rate between 0.6 to 2.0 L/min for a selected period upto 2-h duration.12.2 AnalysisQuantitatively transfer the sample from thebubbler to a 25-mL volumetric flask and dilute to approxi-mately
