1、Designation: D6196 03 (Reapproved 2009)D6196 15Standard Practice forSelection of Sorbents, Sampling, Choosing Sorbents,Sampling Parameters and Thermal Desorption AnalysisProceduresAnalytical Conditions for Monitoring VolatileOrganic CompoundsChemicals in Air1This standard is issued under the fixed d
2、esignation D6196; 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 revisi
3、on or reapproval.1. Scope1.1 This practice is intended to assist in the selection of sorbents and procedures for the sampling and analysis of ambient (1)2,indoor (2),) and workplace (3, 4) atmospheres for a variety of common volatile organic compounds (VOCs). It may also be usedfor measuring emissio
4、ns from materials in small or full scale environmental chambers or for human exposure assessment.1.2 A complete listing of VOCs for which this practice has been tested, at least over part of the measurement range (1.6), isshown in Tables 1-9. For other compounds this practice shall be tested accordi
5、ng to EN 1076 (pumped); Practice D6246,ISO 16107, ANSI/ISEA 104, EN 838 or EN 13528-1EN 13528-2 (diffusive); or other appropriate validation protocols (Sections13 and 14). (5,1)1.2 This practice is based on the sorption of VOCs from air onto selected sorbents or combinations of sorbents. Sampled air
6、is either drawn through a tube containing one or a series of sorbents (pumped sampling) or allowed to diffuse, under controlledconditions, onto the sorbent tube or tubes surface at the sampling end of the tube (diffusive or passive sampling). The sorbed VOCsare subsequently recovered by thermal deso
7、rption and analyzed by capillary gas chromatography.1.3 This practice applies to three basic types of samplers that are compatible with thermal desorption: (1) pumped sorbent tubescontaining one or more sorbents; (2) axial diffusive passive (diffusive) samplers (typically of the same physical dimens
8、ions asstandard pumped sorbent tubes and containing only one sorbent); and (3) radial diffusive passive (diffusive) samplers.1.4 This practice recommends a number of sorbents that can be packed in sorbent tubes,tubes for use in the sampling of a widerange of different volatile organic compounds boil
9、ing vapor-phase organic chemicals; including volatile and semi-volatile organiccompounds which, generally speaking, boil in the range 0 to 400C (v.p. 15 to 0.01 kPa at 25C).1.5.1 For pumped sampling, sorbent selection is based on breakthrough capacity. Single-bed tubes containing for examplesorbent
10、Type A3,4 are appropriate for normal alkanes from n-C6 (hexane) to n-C10 (decane) and substances with similar volatility(v.p. 15 to 0.3 kPa at 25C). More volatile materials should be sampled on stronger sorbents, such as sorbent Type B3,5. Othersorbent types than those specified may be used, if thei
11、r breakthrough capacities are adequate and their thermal desorption blanksare sufficiently small. Examples are given in Appendix X2. A broader range of VOCs may be sampled using multi-bed tubes.1.5.2 Guidance given for the selection of sorbents for pumped monitoring tubes can be applied equally well
12、 to axial diffusivesampling tubes. The restriction to a single sampling surface (hence single sorbent), limits the target analyte range that can bemonitored by a single tube. However, the unobtrusive nature and low cost of diffusive samplers usually means that two or moresamplers containing differen
13、t sorbents can be used in parallel without impacting study objectives.1.5.3 The high sampling rate and associated risk of back diffusion associated with radial diffusive samplers typically restrictsthe use of these samplers to compounds of equal or lower volatility than benzene. It also means that s
14、tronger sorbents are generallyrequired for these samplers when compared with either axial diffusive or pumped sorbent tubes.1.5 This practice can be used for the measurement of airborne vapors of these volatile organic compounds over a wideconcentration range.1.5.1 With pumped sampling, this practic
15、e can be used for the speciated measurement of airborne vapors of VOCs in aconcentration range of approximately 0.1 g/m3 to 1 g/m3, for individual organic compounds in 110 L air samples. The method1 This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct respon
16、sibility of Subcommittee D22.05 on Indoor Air.Current edition approved March 1, 2009Nov. 1, 2015. Published March 2009February 2016. Originally approved in 1997. Last previous edition approved in 20032009as D6196 - 03.D6196 03 (2009). DOI: 10.1520/D6196-03R09.10.1520/D6196-15.2 The bold face numbers
17、 in parentheses refer to the list of references at the end of this practice.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately
18、 depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, P
19、A 19428-2959. United States1is also suitable for the measurement of the airborne concentrations of individual components of volatile organic mixtures, providedthat the total loading of the mixture does not exceed the capacity of the tube. Quantitative measurements are possible when usingvalidated pr
20、ocedures with appropriate quality assurancecontrol measures.1.5.2 With axial diffusive sampling, this practice is valid for the speciated measurement of airborne vapors of volatile organiccompounds in a concentration range of approximately 2 mg/m100 g/m3 to 10100 mg/m3 for individual organic compoun
21、ds foran exposure time of 8 h or 0.3 mg/m1 g/m3 to 3001 mg/m3 for individual organic compounds for an exposure time of four weeks.The method is also suitable for the measurement of the airborne concentrations of individual components of volatile organicmixtures provided that the total loading of the
22、 mixture does not exceed the capacity of the tube.1.5.3 With radial diffusive sampling, this practice is valid for the measurement of airborne vapors of volatile organic compoundsin a concentration range of approximately 0.3 mg/m5 g/m3 to 3005 mg/m3 for individual organic compounds for exposure time
23、sof one to six hours. The method is also suitable for the measurement of the airborne concentrations of individual components ofvolatile organic mixtures provided that the total loading of the mixture does not exceed the capacity of the tube.1.5.4 The upper limit of the useful range is almost always
24、 set by the sorptive capacity of the sorbent used, and by the lineardynamic range of the gas chromatograph,chromatograph column and detector, or by the sample splitting capability of the analyticalinstrumentation used. The sorptive capacity is measured as a breakthrough volume of air, which determin
25、es the maximum airvolume that must not be exceeded when sampling with a pump.1.5.5 The lower limit of the useful range depends on the noise level of the detector and on blank levels of analyte or interferingartifacts, or both,artifacts (or both) on the sorbent tubes.1.6.6 Artifacts are typically 100
26、 ppm) and shall be taken into consideration if necessary during method development.6.4 The method is suitable for use in atmospheres of up to 95 % relative humidity for all hydrophobic sorbents such as porouspolymers and graphitized carbon. carbon blacks See Appendix X1. When less hydrophobic, stron
27、g sorbents such as purecharcoals or carbonized molecular sieves are used in atmospheres with humidity in excess of 65 % RH, exercise care to preventwater interfering with the analytical process. Suitable water elimination or reduction procedures include sample splitting;splittingand selectively dry
28、purging moisture from the sorbent tube or secondary focusing trap prior to analysis, trap, or both, prior toanalysis. Other useful approaches to minimizing water interference include reducing the air volume sampled sampled, for example,to 0.5 L (pumped sampling), use of a membrane that excludes wate
29、r in the diffusion barrier (diffusive sampling), and reducing thetime of sampling (diffusive sampling).7. Apparatus7.1 Use ordinary laboratory apparatus in addition to the following.7.2 Sorbent tubes for pumped sampling, compatible with the thermal desorption apparatus to be used (7.5). Typically, b
30、ut notexclusively, they are constructed of glass or stainless steel tubing, 6.4 mm 14 in. OD, 5 mm ID and 89 mm long and contain upto 60 mm total length of sorbent or sorbents, held in place with stainless steel gauzes. gauzes or glass wool, or both. Tubes of otherdimensions may be used but the safe
31、 sampling volumes (SSV) given in Tables 1-6Appendix X2 are based on these tubedimensions. For labile analytes, such as sulfur-containing compounds, fused-silica-coated steel (typically 5 mm ID) or glass tubes(typically 4 mm ID) should be used (inused. (See Note 2glass-lined or glass tubes the sorben
32、t is typically held in place using plugsof unsilanized glass wool). .) One end of the tube is marked, for example by a scored ring about 10 mm from the sampling inletend to represent the end open to the atmosphere during sampling, otherwise the direction of sampling flow may be marked withan arrow.
33、The tubes are packed with one or more preconditioned sorbents (8.3), so taking care to ensure that the entire sorbent bedwill be within the desorber heated zone, and a zone during thermal desorption, and that an air gap of at least 14 mm is retainedat each end of the tube to minimize errors due to d
34、iffusive ingress at a very low pump flow rates. Tubes The tubes described abovetypically contain between 200100 and 1000 mg sorbent, depending on sorbent density typically about 250 mg sorbent Type D,300 mg sorbent Type A or 500 mg sorbent Type B. The sorbents are retained by stainless steel gauzes
35、or unsilanized glass woolplugs, or both. density, and the number of adsorbent beds. If more than one sorbent is used in a single tube, the sorbents shouldbe arranged in discrete beds in order of increasing sorbent strength and separated by unsilanized glass wool, with with the weakestsorbent nearest
36、 to the marked sampling inlet(inlet) end of the tube. Tubes should be labelled uniquely prior to conditioning. Donot use solvent-containing paints and markers or adhesive labels to label the tubes as high levels of solvent might contaminate thetubes and adhesive labels might jam the thermal desorpti
37、on mechanism. Tubes may be obtained commercially which are alreadypermanently marked (for example, etched) with suitable identifiers such as unique serial numbers in alphanumeric or barcodeformat, or both.NOTE 2With glass tubes the sorbent is typically held in place using a glass frit, or plugs of q
38、uartz or unsilanized glass wool.7.2.1 Sorbents with widely different ( 50C) (100C) maximum desorption temperatures such as sorbent Type A andgraphitized carbon, must NOT be packed into a single tube or it will be impossible to condition or desorb the more stable sorbent(s)sufficiently thoroughly wit
39、hout causing degradation medium strength porous polymers and graphitized carbon blacks, or carbonmolecular sieve when packed in the same tube, or both, must be conditioned and desorbed at temperatures below the maximumof the least stable sorbent(s).adsorbent in the tube.7.3 Sorbent tubes for axial d
40、iffusive sampling, compatible with the thermal desorption apparatus to be used (7.5) and with thesampling surface of the sorbent retained by a metal (typically stainless steel) gauze to give a precisely defined air gap (7.3.1).Typically, but not exclusively, they are constructed of stainless steel t
41、ubing, 6.4 mm 14 in. OD, 5 mm ID and 89 mm long andwith the sorbent held in place 14.3 mm from the sampling end using a stainless steel gauze.gauze (Fig. 1) Tubes of otherdimensions may be used but the uptake rates given in Tables 7 and 8Appendix X3 are based on these tube dimensions. For labileanal
42、ytes, such as sulfur-containing compounds, fused silica-coated steel should be used for both the tube and sorbent-retaininggauze. One end of the tube is marked, for example by a scored ring about 14 mm from the sampling inlet end. The tubes are packedwith sorbents (8.3) such that the sorbent bed wil
43、l be within the desorber heated zone and a consistent inner air gap of about 14.3D6196 156mm is retained between the end of the tube and the surface of the sorbent-retaining gauze zone. Glass tubes are not usuallyconsidered suitable for passive sampling because it is more difficult to define the dif
44、fusive air gap sufficiently accurately andreproducibly.NOTE 3Tubes packed with more than one sorbent may be used for diffusive monitoring, but only the first sorbent, nearest the sampling end, playsany role in the sampling process.at the sampling marked (diffusive) end of the tube. Tubes contain bet
45、ween 200 and 1000 mg sorbent,depending on sorbent density - typically about 250 mg sorbent Type D, 300 mg sorbent Type A or 500 mg sorbent Type B. Labelthe tubes uniquely prior to conditioning. Do not use solvent-containing paints and markers or adhesive labels to label the tubes.Tubes may be obtain
46、ed, pre-marked with suitable identifiers such as unique serial numbers.7.3.1 Uptake rates in Tables 7 and 8Appendix X3 are given for stainless steel or fused silica-coated stainless steel tubes witha nominal total air gap (between the sampling surface of the sorbent bed and sampling surface of the d
47、iffusive end cap (7.3.2)of 15 mm. mm (see Fig. 1) and an inner air gap of 14.3 mm (between the outer surface of the sorbent retaining gauze and the endof the tube). In practice packed tube dimensions will vary slightly (1311) and tubes should be rejected where the inner air gap(between stainless ste
48、el screen retaining the sorbent bed and the end of the tube) is outside the range 14.0 and 14.6 mm (Seemm.Fig. 1).7.3.2 Diffusive End Caps, typically push-on, “O”-ring seal caps fitted with a metal gauze allowing the diffusive ingress of vapor.The size of the gauze covered opening in the sampling ca
49、p should being the same as the cross section of the tube (Fig. 1). Someversions of the diffusive end cap incorporate a silicon membrane next to the gauze to minimize ingress of water.The diffusiveendcap maintains the diffusive air gap between the inlet of the tube and the sorbent. The use of the diffusive endcap also minimizesair movement within the diffusive air gap if sampling in windy conditions.7.4 Sorbent cores for radial diffusive sampling, compatible with the thermal desorption apparatus to be used (7.5). Typically,but not exclusively, they are
