1、Designation: D2913 96 (Reapproved 2007)D2913 14Standard 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
2、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 covers is for the measurement of the concentration of mercaptans (organic thiols) in the atmosphere atconc
3、entrations below 100 parts per billion (ppb(v) = 195 g/m3). For concentrations above 100 ppb(v) level, ppb(v), the samplingperiod can be reduced or the trapping liquid volume increased either before or after aspirating. (See Practice D1357 for samplingguidance.) The minimum detectable amount of meth
4、yl mercaptan is 0.04 g/mL (1)2 in a final liquid volume of 25 mL. Whensampling air at the maximum recommended rate of 2 L/min for 2 h, the minimum detectable mercaptan concentration is 1.0 ppb(v)(1.95 g methyl mercaptan/m3 at 101.3 kPa (760 mm Hg) and 25C). This test method determines total mercapta
5、ns and does notdifferentiate among individual mercaptans, although it is most sensitive to the lower molecular weight alkanethiols.1.2 The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.1.3 This standard does not purport to a
6、ddress all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use. Specific precautionary statements are given in 8.7, 8.8
7、, and Section 9.2. Referenced Documents2.1 ASTM Standards:3D1193 Specification for Reagent WaterD1356 Terminology Relating to Sampling and Analysis of AtmospheresD1357 Practice for Planning the Sampling of the Ambient AtmosphereD1914 Practice for Conversion Units and Factors Relating to Sampling and
8、 Analysis of AtmospheresD2914 Test Methods for Sulfur Dioxide Content of the Atmosphere (West-Gaeke Method)D3195 Practice for Rotameter CalibrationD3249 Practice for General Ambient Air Analyzer ProceduresD3609 Practice for Calibration Techniques Using Permeation TubesD3631 Test Methods for Measurin
9、g Surface Atmospheric PressureE1E2251 Specification for ASTM Liquid-in-Glass ThermometersLiquid-in-Glass ASTM Thermometers with Low-HazardPrecision Liquids3. Terminology3.1 DefinitionsFor definitions of terms used in this test method, refer to Terminology D1356.4. Summary of Test Method4.1 This test
10、 method is intended for obtaining an integrated sample over a selected time span (such as 2 h) either manually orin an automatic sequential sampler using 10 mL of absorption liquid in a bubbler.4.2 The absorption liquid is delivered to the laboratory for colorimetric analysis by reaction between the
11、 collected mercaptanand N,N-dimethyl-p-phenylenediamine.1 This test method is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.03 on Ambient Atmospheresand Source Emissions.Current edition approved April 1, 2007Sept. 1, 2014. Published
12、May 2007October 2014. Originally approved in 1970. Last previous edition approved in 20012007 asD2913 - 96D2913 96 (2007).(2001)1. DOI: 10.1520/D2913-96R07.10.1520/D2913-14.2 The boldface numbers in parentheses refer to thea list of references at the end of this test method.standard.3 For referenced
13、ASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the use
14、r of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as
15、 published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 Mercaptans are odorous substances offensive at low concentrations and toxic at higher levels. They
16、 are emitted fromgeothermal sources, industrial processes, and food processing facilities. Mercaptans at low concentrations are commonly added tonatural gas and LP gases for safety purposes as well.6. Interferences6.1 The N,N-dimethyl-p-phenylenediamine reaction is also suitable forused in the deter
17、mination of other sulfur-containingcompounds including hydrogen sulfide and dimethyl disulfide (2). The potential for interference from these latter compounds isespecially important, since all of these compounds commonly coexist in certain industrial emissions. Appropriate selection of thecolor form
18、ation conditions and measurements of absorbance at the specified wavelength will eliminate the potential interferencefrom hydrogen sulfide.6.2 Hydrogen sulfide, if present in the sampled air, may cause a turbidity in the sample absorbing solution. This precipitate mustbe filtered before proceeding w
19、ith the analysis. One study showed that 100 g of H2S gave a mercaptan color equivalent to 1.5to 2.0 g of mercaptan (3). Another study reported no absorption at 500 nm in the presence of 150 g of hydrogen sulfide (4, 5).6.3 Approximately equimolar response is obtained from the hydrolysis products of
20、dimethyl disulfide, the molar extinctioncoefficient for the amine-mercaptan reaction product being 4.4 103, and the amine-dimethyl disulfide reaction product being5.16 103 (5). The interference due to dimethyl disulfide has been experimentally determined. Dimethyl disulfide concentrationsof 0.6 ppm(
21、v) and 1.0 ppm(v) given an equivalent response as 0.4 ppm(v) and 0.8 ppm(v), respectively, of methyl mercaptan.46.4 Sulfur dioxide up to 250 g does not influence the color development even when sampling a test atmosphere containing 300ppm(v) of SO2.6.5 Nitrogen dioxide does not interfere up to 700 g
22、 of NO2 when sampling a test atmosphere containing 6 ppm. ppmmercaptans. Higher concentrations of NO2 caused a positive interference when mercaptans were present, but no interference in theabsence of mercaptans. Such elevated NO2 concentrations are unrealistic and would not benot commonly encountere
23、d in theambient air except in the vicinity of an accidental spillage.6.6 The supply of mercuric acetate must be free of mercurous ion. If mercurous ion is present, turbidity will result when thechloride ion-containing reagents are added in the last step of the analytical procedure.7. Apparatus7.1 Sa
24、mpling Apparatus:7.1.1 AbsorberMidget bubbler with coarse porosity frit.7.1.2 Air Sample ProbeTFE-fluorocarbon, polypropylene, or glass tube with a polypropylene or glass funnel at the end.7.1.3 Moisture Trap-Glass, or polypropylene tube with a two port closure. The entrance port of the closure is f
25、itted with tubingthat extends to the bottom of the trap. The unit is loosely packed with 16-mesh activated charcoal to prevent moisture entrainment.The charcoal should be changed weekly.at least weekly and more frequently when sampling high humidity air.7.1.4 FilterMembrane, of 0.8 to 2.0 m porosity
26、.7.1.5 PumpCapable of maintaining a vacuum greater than 70 kPA (0.7 atm) at the specified flowrate.7.1.6 Flow Control DeviceA needle valve capable of maintaining a constant flow rate (62 %). Protect the needle valve fromparticulate matter and moisture entrainment.7.1.7 Flow meter, having a range of
27、0 to 2.5 L/min.7.1.8 ThermometersASTM Thermometer 33C, Precision digital thermometers based on resistance temperature detectors(RTDs), thermistors, thermocouples, or organic liquid-in-glass thermometers (such as Thermometer S18C in Specifications E2251)meeting the requirements of Specificationspecif
28、ic E1, will be suitable for most applications of this test method.applications in thismethod may be used.7.1.9 Barograph or BarometerCapable of measuring atmospheric pressure to 60.5 kPa (4 Torr), meeting the requirements ofTest Methods D3631.7.1.10 Stopwatch or timer, accurate to 61 s/24 h.7.1.11 T
29、he arrangements of the component parts of sampling is shown in Fig. 1a, Test Methods D2914.7.2 Calibration ApparatusA means of generating dynamic standard atmospheres using a permeation device. Dilution air andexcess dilution flow must be filtered through activated charcoal to prevent recirculating
30、small quantities of mercaptans. SeePractice D3609 for details.7.3 Colorimeter or Spectrophotometer, (at 500 nm)Use 2.5- or 5.0-cm path length to obtain adequate sensitivity.4 Supporting data giving the results of a laboratory examination of this method by the National Council of the Paper Industry f
31、or Air and Stream Improvement (NCASI)are available in special report No. 80-07, “ALaboratory Examination of the Use of theASTM/APHA. Spectrophotometric Method for the Measurement of Methyl Mercaptanin Kraft Mill Workspace Atmospheres,” May 1980, NCASI, 260 Madison Ave., New York, NY 10016.D2913 1428
32、. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. All reagents shall conform to the specifications ofthe Committee on Analytical Reagents of the American Chemical Society, where such specifications are available.5 Other gradesmay be used, provided it i
33、s first ascertained that the reagent is of sufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to water shall mean referee reagent water conforming toSpecification D1193.8.3 Solutions should be refrig
34、erated when not in use.8.4 Amine-Hydrochloric Acid Solution, StockDissolve 5.0 g of N,N-dimethyl- p-phenylenediamine hydrochloride (p-aminodimethylaniline hydrochloride) in 1 L of concentrated hydrochloric acid (HCL). Refrigerate (HCl). Refrigerate atapproximately 10C and protect from light. This so
35、lution is stable for at least 6 months.8.5 Reissner SolutionDissolve 67.6 g of ferric chloride hexahydrate (FeCl36H2O) in distilled water, dilute to 500 mL, andmix with 500 mL of nitric acid (HNO3) solution containing 72 mL of boiled concentrated nitric acid (sp gr 1.42). This solutionis stable.stab
36、le for at least 3 months.8.6 Color-Developing ReagentMix 3 volumes of amine solution and 1 volume of Reissner solution. Prepare this solutionfreshly for each set of determinations.8.7 Absorbing SolutionDissolve 50 g of mercuric acetate Hg (CH3COO)2 in 400 mL of distilled water and add 25 mL ofglacia
37、l acetic acid (CH3COOH). Dilute to 1 L. The mercuric acetate must be free of mercurous salts to prevent precipitation ofmercurous chloride during color development. Reagent grade mercuric acetate sometimes contains mercurous mercury. Determinethe acceptability of each new bottle of mercuric acetate
38、by adding 3 mL of concentrated hydrochloric acid to 3 mL of the 5 %mercuric acetate. If the solution becomes cloudy, the mercuric acetate is not acceptable. (WarningThe absorbing solution andmercury salts are very poisonous. toxic. Avoid contact with the skin and especially with the eyes. Avoid gene
39、rating or breathingdust. Wash hands after use. Keep away from food. Do not ingest.)8.8 Lead Methyl MercaptideBubble tank methyl mercaptan gas (CH3SH) into 10 % lead acetate solution Pb(CH3COO)2 inan adequate a fume hood (1). Collect the yellow crystals by vacuum filtration, wash with distilled water
40、, and dry overnight in avacuum oven at 45C. Store crystals in a vacuum-sealed container in the dark. One mole of this mercaptide is equivalent to twomoles of a mercaptan. Lead mercaptide may be purchased from commercial sources, if desired. (Warning Methyl mercaptangas is extremely toxic. At high le
41、vels of exposure, the human olfactory sense may become insensitive to its presence.)8.9 Concentrated, Standard Lead Mercaptide SolutionWeigh out 156.6 mg of the crystalline lead mercaptide and make up to100 mLwith the 5 % mercuric acetate absorbing solution.This solution contains the equivalent of 5
42、00 g of methyl mercaptan/mL.8.10 Diluted Mercaptan Solution, StandardDilute 2 mL of the concentrated standard solution to 100 mL with the 5 %mercuric acetate absorbing solution. This solution contains the equivalent of 10 g CH3SH/mL.8.11 Methyl Mercaptan Permeation Device, with a permeation rate app
43、ropriate to the dilution flow and concentrations expected.For example, see the 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 mercury salts. salts, which are toxic. Precautions f
44、or its use are described in 8.7.9.2 Disposal procedures are described in Annex A3, Test Methods D2914.9.3 Compressed Gas Cylinders. Cylinders and Permeation TubesPermeation tubes and compressed gas standards should onlybe handled in well ventilated locations. Improper handling of compressed gas cyli
45、nders can result in explosion. Rapid release ofinert gases can result in asphyxiation. Compressed air supports combustion.9.3.1 Compressed gas cylinders may be used in this test method for preparation of reagents or standard atmospheres.Precautions on methyl mercaptan cylinders are described in 8.8.
46、9.3.2 General safety precautions for handling and storing compressed gas cylinders are described in Practice D3249.5 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical S
47、ociety, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D2913 14310. Sampling10.1 Sampling procedures are described for 2h sampling periods. Different sam
48、pling rates and sampling times may be selectedto suit specific requirements, but sample volume and flow rates must be adjusted to maintain linearity between absorbance andconcentration over the dynamic range of the colorimetric procedure.10.2 Measure the temperature of the atmosphere being sampled b
49、efore and after sampling.10.3 Measure the atmospheric pressure during sampling, in accordance with Test Methods D3631.11. Calibration and Standardization11.1 Sampling EquipmentCalibrate the flow meter before and after use in accordance with Practice D3195.11.1.1 The pressure drop of the flow meter must be maintained the same during sampling as during calibration.11.2 Standard AtmospheresSee Practice D3609 for preparation of standard atmospheres using the calibration apparatus andthe permeation device.11.2.1 Calibrate the componen
