ASTM D5953M-1996(2001) Standard Test Method for Determination of Non-Methane Organic Compounds (NMOC) in Ambient Air Using Cryogenic Preconcentration and Direct Flame Ionization De.pdf

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1、Designation: D 5953M 96 (Reapproved 2001)METRICStandard Test Method forDetermination of Non-Methane Organic Compounds (NMOC)in Ambient Air Using Cryogenic Preconcentration and DirectFlame Ionization Detection Method Metric1This standard is issued under the fixed designation D 5953M; the number immed

2、iately 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

3、 test method2covers a procedure for sampling anddetermining concentrations of non-methane organic com-pounds (NMOC) in ambient, indoor, or workplace atmo-spheres.1.2 The test method describes the collection of cumulativesamples in passivated stainless steel canisters and subsequentlaboratory analysi

4、s.1.2.1 This test method describes a procedure for sampling incanisters at final pressures above atmospheric pressure (re-ferred to as pressurized sampling).1.3 This test method employs a cryogenic trapping proce-dure for concentration of the NMOC prior to analysis.1.4 This test method describes the

5、 determination of theNMOC by the simple flame ionization detector (FID), withoutthe gas chromatographic columns and complex proceduresnecessary for species separation.1.5 The range of this test method is from 20 to 10 000 ppbC(1, 2).3See 13.4 for procedures for lowering the range.1.6 The test method

6、 may yield less accurate results for somehalogenated or oxygenated hydrocarbons emitted from nearbysources of industrial air pollutants. This is especially true ifthere are high concentrations of chlorocarbons or chlorofluo-rocarbons present.1.7 The values stated in SI units are regarded as thestand

7、ard.1.8 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.2. Referenc

8、ed Documents2.1 ASTM Standards:4D 1193 Specification for Reagent WaterD 1356 Terminology Relating to Sampling and Analysis ofAtmospheresD 1357 Practice for Planning the Sampling of the AmbientAtmosphereD 5466 Test Method for the Determination of VolatileOrganic Chemicals in Atmospheres (Canister Sam

9、plingMethodology)3. Terminology3.1 Definitions For definitions of terms used in this testmethod, refer to Terminology D 1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 cryogena refrigerant used to obtain very low tem-peratures in the cryogenic traps of the analytical system.3.2.1.1 Dis

10、cussionLiquid argon (bp 185.7C at stan-dard pressure) is recommended for this test method. Cryogenswith lower boiling points, such as liquid nitrogen, should notbe used because of possible trapping of oxygen from thesample air, which might lead to the possibility of an explosionor fire. In addition,

11、 methane would be trapped.3.2.2 dynamic calibrationcalibration of an analytical sys-tem with pollutant concentrations that are generated in adynamic, flowing system, such as by quantitative, flow-ratedilution of a high-concentration gas standard with zero gas.3.2.3 NMOCnon-methane organic compounds.

12、3.2.3.1 DiscussionTotal non-methane organic compoundsare those compounds measured by a flame ionization detector,1This test method is under the jurisdiction of ASTM Committee D22 onSampling and Analysis of Atmospheres and is the direct responsibility of Subcom-mittee D22.03 on Ambient Atmospheres an

13、d Source Emissions.Current edition approved May 10, 1996. Published July 1996.2This test method is based on EPA Method TO-12: “Determination of Non-Methane Organic Compounds (NMOC) in Ambient Air Using Cryogenic Pre-Concentration and Direct Flame Ionization Detection (PDFID)”, Compendium ofMethods f

14、or the Determination of Toxic Organic Compounds in Ambient Air ,EPA600 4-89-017, U.S. Environmental Protection Agency, Research Triangle Park, NC,March 1990.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.4For referenced ASTM standards, visit the ASTM

15、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United

16、States.excluding methane and compounds with vapor pressure above102kPa, recovered from the canister.3.2.4 ppm C and ppb Cconcentration units of parts permillion and parts per billion of organic carbon as detected bythe FID.3.2.4.1 DiscussionDuring calibration with propane, forexample, they are equiv

17、alent to parts per million by volume(ppm (v) or parts per billion by volume (ppb (v), respectively,multiplied by the number of carbon atoms in propane.4. Summary of Test Method (2-6)4.1 An air sample is extracted directly from the ambient air,collected in a precleaned sample canister and transported

18、 to alaboratory.4.2 A fixed-volume portion of the sample air is drawn fromthe canister at a low flow rate through a glass-bead filled trapthat is cooled to approximately 186C with liquid argon. Thecryogenic trap simultaneously collects and concentrates theNMOC using condensation, while allowing the

19、nitrogen,oxygen, methane, and other compounds with boiling pointsbelow 186C to pass through the trap without retention. Thesystem is dynamically calibrated so that the volume of samplepassing through the trap does not have to be quantitativelymeasured, but must be precisely repeatable between the ca

20、li-bration and the analytical phases.4.3 After the fixed-volume air sample has been drawnthrough the trap, a helium carrier gas flow is diverted to passthrough the trap, in the opposite direction to the sample flow,and into an FID. When the residual air and methane have beenflushed from the trap and

21、 the FID baseline restabilizes, thecryogen is removed and the temperature of the trap is raised to80 to 90C.4.4 The organic compounds previously collected in the traprevolatilize due to the increase in temperature and are carriedinto the FID, resulting in a response peak or peaks from theFID. The ar

22、ea of the peak or peaks is integrated, and theintegrated value is translated to concentration units using apreviously obtained calibration curve relating integrated peakareas with known concentrations of propane.4.5 The cryogenic trap simultaneously concentrates theNMOC while separating and removing

23、 the methane from airsamples. The technique is thus direct reading using FID forNMOC and, because of the concentration step, it is moresensitive than conventional continuous NMOC analyzers.4.6 The sample is injected into the hydrogen-rich flame ofthe FID, where the organic vapors burn, producing ion

24、izedmolecular fragments. The resulting ion fragments are thencollected and detected. Because this test method employs ahelium carrier gas, the detector response is nearly identical formany hydrocarbon compounds of interest. Thus, the historicalshort-coming of varying FID response to aromatic, olefin

25、ic,and paraffinic hydrocarbons is minimized. The FID is muchless sensitive to most organic compounds containing functionalgroups such as carbonyls, alcohols, halocarbons, etc.5. Significance and Use5.1 Many industrial processes require determination ofNMOC in the atmosphere.5.2 Accurate measurements

26、 of ambient concentrations ofNMOC are important for the control of photochemical smogbecause these organic compounds are primary precursors ofatmospheric ozone and other oxidants (7, 8).5.2.1 The NMOC concentrations typically found at urbansites may range up to 1 to 3 ppm C or higher. In order todet

27、ermine transport of precursors into an area, measurement ofNMOC upwind of the area may be necessary. Rural NMOCconcentrations originating from areas free from NMOCsources are likely to be less than a few tenths of 1 ppm C.5.3 Conventional test methods that depend on gas chroma-tography and qualitati

28、ve and quantitative species evaluation areexcessively difficult and expensive to operate and maintainwhen speciated measurements are not needed. The test methoddescribed here involves a simple, cryogenic preconcentrationprocedure with subsequent direct detection with the FID. Thetest method is sensi

29、tive and provides accurate measurements ofambient total NMOC concentrations where speciated data arenot required.5.4 An application of the test method is the monitoring ofthe cleanliness of canisters.5.5 Another use of the test method is the screening ofcanister samples prior to analysis.5.6 Collect

30、ion of ambient air samples in pressurized canis-ters provides the following advantages:5.6.1 Convenient integration of ambient samples over aspecific time period,5.6.2 Capability of remote sampling with subsequent centrallaboratory analysis,5.6.3 Ability to ship and store samples, if necessary,5.6.4

31、 Unattended sample collection,5.6.5 Analysis of samples from multiple sites with oneanalytical system,5.6.6 Collection of replicate samples for assessment ofmeasurement precision, and5.6.7 Specific hydrocarbon analysis can be performed withthe same sample system.6. Interferences6.1 In laboratory eva

32、luations, moisture in the sample hasbeen found to cause a positive shift in the FID baseline. Theeffect of this shift is minimized by carefully selecting theintegration termination point and adjusting the baseline usedfor calculating the area of the NMOC peaks.6.2 With helium as a carrier gas, FID r

33、esponse is quiteuniform for most hydrocarbon compounds, but the responsecan vary considerably for other types of organic compounds.7. Apparatus7.1 Sample Collection System,(Fig. 1).7.1.1 Sample Canister(s), stainless steel, Summa5-polishedvessel(s) of 4 to 6 L capacity, used for automatic collection

34、 ofintegrated field air samples.7.1.1.1 Mark each canister with a unique identificationnumber stamped on its frame.5The Summa process is a trademark of Molectrics, Inc., 4000 E. 89th St.,Cleveland, OH 44105.D 5953M 96 (2001)27.1.2 Sample Pump, stainless steel, metal bellows type.7.1.2.1 Ensure that

35、the pump is free of leaks, and uncon-taminated by oil or organic compounds.7.1.2.2 Shock mount the pump to minimize vibration.7.1.3 Pressure Gage, 0 to 210 kPa (0 to 30 psig).7.1.4 Solenoid Valve, controls the sample flow to the canis-ter with negligible temperature rise.7.1.5 Flow Control Device, m

36、ass flowmeter, critical orifice,or short capillary to maintain the sample flow over thesampling period.7.1.6 Particulate Matter Filter, inert in-line filter, 2 m orless, or other suitable filter, used to filter the air sample.7.1.7 Auxiliary Vacuum Pump or Blower, draws sample airthrough the sample

37、inlet line to reduce inlet residence time tono greater than 10 s.7.1.7.1 Shock mount the pump to minimize vibration.7.1.8 Timer, programmable, and electrically connected tothe solenoid valve (7.1.4) and pumps (7.1.2 and 7.1.7), capableof controlling the pumps and the solenoid valve.7.1.9 Sample Inle

38、t Line, transports the sample air into thesample system, consisting of stainless steel tubing components.7.2 Sample Canister Cleaning System,(Fig. 2).7.2.1 Vacuum Pump, capable of evacuating sample canis-ter(s) to an absolute pressure of # 2 Pa (15 m Hg).7.2.2 Manifold, stainless steel manifold with

39、 connectionsfor simultaneously cleaning several canisters.7.2.3 Shut-off Valve(s), nine required.7.2.4 Pressure Gage, 0 to 350 kPa (0 to 50 psig)monitorszero-air pressure.7.2.5 Cryogenic Trap (2 required), U-shaped open tubulartrap cooled with liquid argon used to prevent contaminationfrom back diff

40、usion of oil from vacuum pump, and providingclean, zero-air to the sample canister(s).7.2.6 Vacuum Gage, capable of measuring vacuum in themanifold to an absolute pressure of 15 Pa (0.1 mm Hg) or less,with scale divisions of 0.1 Pa (0.5 m Hg).7.2.7 Flow Control Valve, regulates flow of zero-air into

41、 thecanister(s).7.2.8 Humidifier, water bubbler or other system capable ofproviding moisture to the zero-air supply.7.2.9 Isothermal Oven, for heating canisters, not shown inFig. 2.7.3 Analytical System,(Fig. 3).7.3.1 FID System, includes flow controls for the FID fueland combustion air, temperature

42、 control for the FID, and signalprocessing electronics. Set the FID combustion air, hydrogen,and helium carrier flow rates as defined by the manufacturersinstructions to obtain an adequate FID response while main-taining a stable flame throughout all phases of the analyticalcycle.7.3.2 Data Reductio

43、n Device, such as a computer, equippedwith data acquisition hardware and software and a laser printer,or an electronic integrator, with chart recorder, capable ofintegrating the area of one or more FID response peaks andcalculating peak area corrected for baseline drift.7.3.2.1 If a separate integra

44、tor and chart recorder are used,exercise care to ensure that these components do not interferewith each other electrically or electronically.7.3.2.2 Range selector controls on both the integrator andthe FID analyzer may not provide accurate range ratios, soprepare individual calibration curves for e

45、ach range.7.3.2.3 The integrator must be capable of marking thebeginning and ending of peaks, constructing the appropriatebaseline between the start and end of the integration period,and calculating the peak area.7.3.3 Cryogenic Trap, constructed from a single piece ofchromatographic-grade stainless

46、 steel tubing (3 mm outsidediameter, 2 mm inside diameter), as shown in Fig. 4.7.3.3.1 Pack the central portion of the trap (70 to 100 mm)with silanized 180 to 250 m (60/80 mesh) glass beads, withsmall silanized glass wool plugs, to retain the beads.7.3.3.2 The arms of the trap must be of such lengt

47、h to permitthe beaded portion of the trap to be submerged below the levelof cryogen in the Dewar flask.7.3.3.3 Connect the trap directly to the six-port valve (7.3.4)to minimize the line length between the trap (7.3.3) and theFID (7.3.1).7.3.3.4 Mount the trap to allow clearance so the Dewar flaskma

48、y be applied and withdrawn to facilitate cooling and heatingthe trap (see 7.3.12).7.3.4 Six-Port Valve Locate the six-port valve and asmuch of the interconnecting tubing as practical inside an ovenor otherwise heat it to 80 to 90C to minimize wall losses oradsorption/desorption in the connecting tub

49、ing. All lines mustbe as short as practical.7.3.5 Multistage Pressure Regulators (3 required), standardtwo-stage, stainless steel diaphragm regulators with pressuregages, for helium, air, and hydrogen cylinders.7.3.6 Auxilliary Flow or Pressure Regulators (2 required),to maintain constant flow rates, within 1 mL/min for the heliumcarrier and the hydrogen.7.3.7 Fine Needle Valve (2 required)One adjusts thesample flow rate through the trap, and the other adjusts thesample flow rate from the canister.7.3.8 Dewar Flask, holds cryogen used to cool the trap,size