ASTM D6196-23

Standard Practice for Choosing Sorbents, Sampling Parameters and Thermal Desorption Analytical Conditions for Monitoring Volatile Organic Chemicals in Air

SIGNIFICANCE AND USE
5.1 This practice is recommended for use in measuring the concentration of VOCs in ambient, indoor, and workplace atmospheres. It may also be used for measuring emissions from materials in small or full scale environmental chambers for material emission testing or human exposure assessment.  
5.2 Such measurements in ambient air are of importance because of the known role of VOCs as ozone precursors, and in some cases (for example, benzene), as toxic pollutants in their own right.  
5.3 Such measurements in indoor air are of importance because of the association of VOCs with air quality problems in indoor environments, particularly in relation to sick building syndrome and emissions from building materials. Many volatile organic compounds have the potential to contribute to air quality problems in indoor environments and in some cases toxic VOCs may be present at such elevated concentrations in home or workplace atmospheres as to prompt serious concerns over human exposure and adverse health effects (5).  
5.4 Such measurements in workplace air are of importance because of the known toxic effects of many such compounds.
Note 1: While workplace air monitoring has traditionally been carried out using disposable sorbent tubes, typically packed with charcoal and extracted using chemical desorption (solvent extraction) prior to GC analysis – for example following NIOSH and OSHA reference methods – routine thermal desorption (TD) technology was originally developed specifically for this application area. TD overcomes the inherent analyte dilution limitation of solvent extraction improving method detection limits by 2 or 3 orders of magnitude and making methods easier to automate. Relevant international standard methods include ISO 16017-1 and ISO 16017-2. For a detailed history of the development of analytical thermal desorption and a comparison with solvent extraction methods see Ref (6).  
5.5 In order to protect the environment as a whole and human health in part...
SCOPE
1.1 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 used for measuring emissions from materials in small or full scale environmental chambers or for human exposure assessment.  
1.2 This practice is based on the sorption of VOCs from air onto selected sorbents or combinations of sorbents. Sampled air is either drawn through a tube containing one or a series of sorbents (pumped sampling) or allowed to diffuse, under controlled conditions, onto the sorbent surface at the sampling end of the tube (diffusive or passive sampling). The sorbed VOCs are subsequently recovered by thermal desorption 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 tubes containing one or more sorbents; (2) axial passive (diffusive) samplers (typically of the same physical dimensions as standard pumped sorbent tubes and containing only one sorbent); and (3) radial passive (diffusive) samplers.  
1.4 This practice recommends a number of sorbents that can be packed in sorbent tubes for use in the sampling of vapor-phase organic chemicals; including volatile and semi-volatile organic compounds which, generally speaking, boil in the range 0 °C to 400 °C (v.p. 15 kPa to 0.01 kPa at 25 °C).  
1.5 This practice can be used for the measurement of airborne vapors of these organic compounds over a wide concentration range.  
1.5.1 With pumped sampling, this practice can be used for the speciated measurement of airborne vapors of VOCs in a concentration range of approximately 0.1 μg/m3 to 1 g/m3, for individual organic compounds in 1 L to 10 L air samples. Quantitative measurements are possible when using validated procedures with appropri...

General Information

• Status: Published
• Publication Date: 31-Dec-2022
• ICS: 13.040.20 - Ambient atmospheres
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.05 - Indoor Air

Relations

• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D3686-20 - Standard Practice for Sampling Atmospheres to Collect Organic Compound Vapors (Activated Charcoal Tube Adsorption Method)
• Effective Date: 01-Mar-2020
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM D3686-13 - Standard Practice for Sampling Atmospheres to Collect Organic Compound Vapors (Activated Charcoal Tube Adsorption Method)
• Effective Date: 01-Apr-2013
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010
• Refers: ASTM D3686-08 - Standard Practice for Sampling Atmospheres to Collect Organic Compound Vapors (Activated Charcoal Tube Adsorption Method)
• Effective Date: 15-Dec-2008
• Refers: ASTM D5466-01(2007) - Standard Test Method for Determination of Volatile Organic Chemicals in Atmospheres (Canister Sampling Methodology)
• Effective Date: 01-Apr-2007
• Refers: ASTM D3670-91(2007) - Standard Guide for Determination of Precision and Bias of Methods of Committee D22
• Effective Date: 01-Mar-2007
• Refers: ASTM E355-96(2007) - Standard Practice for Gas Chromatography Terms and Relationships
• Effective Date: 01-Mar-2007
• Refers: ASTM D1356-05 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2005

Overview

ASTM D6196-23 is the internationally recognized standard practice for selecting sorbents, setting sampling parameters, and specifying thermal desorption analytical conditions when monitoring volatile organic compounds (VOCs) in air. Published by ASTM International, this standard provides comprehensive guidance for accurate air sampling across ambient, indoor, and workplace environments, as well as for emissions testing using environmental chambers or for human exposure assessments.

Monitoring VOCs is critical due to their environmental and health impacts, including their role as ozone precursors and potential toxic effects, such as those associated with benzene. This standard addresses selecting appropriate sorbents, sample collection methodologies, and analysis by thermal desorption followed by capillary gas chromatography.

Key Topics

• Sorbent Selection: Guidance on choosing sorbents or combinations of sorbents suitable for sampling target VOCs, determined by analyte volatility and required retention and desorption properties.
• Sampling Methods: Procedures for both active (pumped) and passive (diffusive) sampling using sorbent tubes or cores, including:
  • Pumped sampling
  • Axial passive (diffusive) sampling
  • Radial passive (diffusive) sampling
• Thermal Desorption: Best practices for recovering VOCs from sorbents using heat, followed by introduction into a gas chromatograph for analysis.
• Analytical Procedures: Recommendations for capillary gas chromatography, including suggesting suitable gases, sample volumes, and instrumental configurations for optimal detection and quantification.
• Interferences and Quality Control: Techniques for minimizing sampling and analytical interferences, including system conditioning, blank handling, and quality assurance measures.

Applications

ASTM D6196-23 is essential for:

• Ambient Air Monitoring: Quantification of VOCs in outdoor environments to support air quality regulations and track ozone precursor levels.
• Indoor Air Quality Assessment: Investigation and control of VOC exposures in homes, offices, schools, or other buildings, especially regarding sick building syndrome or emissions from materials.
• Workplace Exposure Monitoring: Occupational safety and health evaluations, ensuring workplace air complies with regulatory exposure limits for toxic VOCs.
• Material Emission Testing: Measurement of VOC emissions from building products, furnishings, or consumer goods in controlled chambers for compliance and certification.
• Personal and Fixed Location Sampling: Deployment of both active and passive sampling for short- and long-term monitoring at individual or stationary points.

Related Standards

Practitioners utilizing ASTM D6196-23 may also reference:

• ISO 16017-1: Indoor, Ambient and Workplace Air - Sampling and Analysis of Volatile Organic Compounds by Sorbent Tube/Thermal Desorption/Capillary Gas Chromatography - Part 1: Pumped Sampling
• ISO 16017-2: Similar methods for diffusive sampling.
• EN 482: General performance requirements for workplace chemical measurement.
• EN 838, EN 1076, EN 13528-3: Requirements and test methods for diffusive and pumped samplers.
• EPA Method TO-17: Determination of VOCs in ambient air using active sampling onto sorbent tubes.
• ASTM D5466, D3686: Complementary ASTM methods for VOC sampling and analysis.

Conclusion

ASTM D6196-23 delivers essential direction for reliable VOC monitoring, supporting compliance, research, and environmental stewardship. By following this standard practice, organizations can ensure accurate air sampling, proper sorbent selection, and efficient VOC analysis, enhancing occupational, indoor, and environmental air quality assessments worldwide. Using ASTM D6196-23 in conjunction with related international standards facilitates method harmonization, regulatory acceptance, and high-quality analytical results.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6196 − 23
Standard Practice for
Choosing Sorbents, Sampling Parameters and Thermal
Desorption Analytical Conditions for Monitoring Volatile
Organic Chemicals in Air
This standard is issued under the fixed designation D6196; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.5.1 With pumped sampling, this practice can be used for
the speciated measurement of airborne vapors of VOCs in a
1.1 This practice is intended to assist in the selection of
3 3
concentration range of approximately 0.1 μg/m to 1 g/m , for
sorbents and procedures for the sampling and analysis of
2 individual organic compounds in 1 L to 10 L air samples.
ambient (1), indoor (2), and workplace (3, 4) atmospheres for
Quantitative measurements are possible when using validated
a variety of common volatile organic compounds (VOCs). It
procedures with appropriate quality control measures.
may also be used for measuring emissions from materials in
1.5.2 With axial diffusive sampling, this practice is valid for
small or full scale environmental chambers or for human
the speciated measurement of airborne vapors of volatile
exposure assessment.
organic compounds in a concentration range of approximately
3 3
1.2 This practice is based on the sorption of VOCs from air
100 μg/m to 100 mg/m for individual organic compounds for
3 3
onto selected sorbents or combinations of sorbents. Sampled
an exposure time of 8 h or 1 μg/m to 1 mg/m for individual
air is either drawn through a tube containing one or a series of
organic compounds for an exposure time of four weeks.
sorbents (pumped sampling) or allowed to diffuse, under
1.5.3 With radial diffusive sampling, this practice is valid
controlled conditions, onto the sorbent surface at the sampling
for the measurement of airborne vapors of volatile organic
end of the tube (diffusive or passive sampling). The sorbed
compounds in a concentration range of approximately 5 μg/m
VOCs are subsequently recovered by thermal desorption and
to 5 mg/m for individual organic compounds for exposure
analyzed by capillary gas chromatography.
times of one to six hours.
1.5.4 The upper limit of the useful range is almost always
1.3 This practice applies to three basic types of samplers
set by the linear dynamic range of the gas chromatograph
that are compatible with thermal desorption: (1) pumped
sorbent tubes containing one or more sorbents; (2) axial column and detector, or by the sample splitting capability of
the analytical instrumentation used.
passive (diffusive) samplers (typically of the same physical
dimensions as standard pumped sorbent tubes and containing 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
only one sorbent); and (3) radial passive (diffusive) samplers.
interfering artifacts (or both) on the sorbent tubes.
1.4 This practice recommends a number of sorbents that can
1.6 This procedure can be used for personal and fixed
be packed in sorbent tubes for use in the sampling of
location sampling. It cannot be used to measure instantaneous
vapor-phase organic chemicals; including volatile and semi-
or short-term fluctuations in concentration. Alternative ‘grab
volatile organic compounds which, generally speaking, boil in
sampling’ procedures using canister air samplers (for example,
the range 0 °C to 400 °C (v.p. 15 kPa to 0.01 kPa at 25 °C).
Test Method D5466) may be suitable for monitoring instanta-
1.5 This practice can be used for the measurement of
neous or short term fluctuations in air concentration. Alterna-
airborne vapors of these organic compounds over a wide
tives for on-site measurement include, but are not limited to,
concentration range.
gas chromatography, real-time mass spectrometry detectors
and infrared spectrometry.
This practice is under the jurisdiction of ASTM Committee D22 on Air Quality
1.7 The sampling method gives a time-weighted average
and is the direct responsibility of Subcommittee D22.05 on Indoor Air.
result.
Current edition approved Jan. 1, 2023. Published March 2023. Originally
ɛ1
approved in 1997. Last previous edition approved in 2015 as D6196 – 15 . DOI:
1.8 The values stated in SI units are to be regarded as
10.1520/D6196-23.
standard. No other units of measurement are included in this
The bold face numbers in parentheses refer to the list of references at the end
of this practice. standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6196 − 23
1.9 This standard does not purport to address all of the EN 838 Workplace Atmospheres: Requirements and Test
safety concerns, if any, associated with its use. It is the Methods for Diffusive Samplers for the Determination of
responsibility of the user of this standard to establish appro- Gases and Vapours
priate safety, health, and environmental practices and deter- EN 1076 Workplace Atmospheres: Pumped Sorbent Tubes
mine the applicability of regulatory limitations prior to use. for the Determination of Gases and Vapours. Require-
1.10 This international standard was developed in accor- ments and Test Methods
dance with internationally recognized principles on standard- EN 13528-3 Ambient Air Quality—Diffusive Samplers for
ization established in the Decision on Principles for the the Determination of Concentrations of Gases and Va-
Development of International Standards, Guides and Recom- pours – Part 3: Guide to Selection, Use, and Maintenance
mendations issued by the World Trade Organization Technical EN 14662-1 Ambient Air Quality – Standard Method for
Barriers to Trade (TBT) Committee. Measurement of Benzene Concentrations – Part 1:
Pumped Sampling Followed by Thermal Desorption and
2. Referenced Documents
Gas Chromatography
EN 14662-4 Ambient Air Quality – Standard Method for
2.1 ASTM Standards:
Measurement of Benzene Concentrations – Part 4: Diffu-
D1356 Terminology Relating to Sampling and Analysis of
sive Sampling Followed by Thermal Desorption and Gas
Atmospheres
Chromatography
D3670 Guide for Determination of Precision and Bias of
Methods of Committee D22
2.4 EPA Method:
D3686 Practice for Sampling Atmospheres to Collect Or-
EPA Method TO-17 Determination of Volatile Organic Com-
ganic Compound Vapors (Activated Charcoal Tube Ad-
pounds in Ambient Air Using Active Sampling Onto
sorption Method)
Sorbent Tubes
D5466 Test Method for Determination of Volatile Organic
Compounds in Atmospheres (Canister Sampling, Mass
3. Terminology
Spectrometry Analysis Methodology)
3.1 Definitions—Refer to Terminology D1356 and Practice
E355 Practice for Gas Chromatography Terms and Relation-
E355 for definitions of terms used in this practice.
ships
3.2 Definitions of Terms Specific to This Standard:
2.2 ISO Standards:
3.2.1 breakthrough volume—the volume of a known atmo-
ISO 5725 Accuracy (Trueness and Precision) of Measure-
sphere that can be passed through the tube before the concen-
ment Methods and Results
tration of the vapor eluting from non-sampling end of the tube
ISO 6145-10 Gas Analysis. Preparation of Calibration Gas
reaches 5 % of the applied test concentration.
Mixtures. Permeation Method
ISO 13137 Workplace Atmospheres: Pumps for Personal
3.2.2 desorption effıciency—the ratio of the mass of analyte
Sampling of Chemical and Biological Agents. Require-
desorbed from a sampling device to that applied.
ments and Test Methods
3.2.3 diffusive (passive) sampler—a device that is capable of
ISO 16017-1 Indoor, Ambient, and Workplace Air – Sam-
collecting gases and vapors from an atmosphere at rates
pling and Analysis of Volatile Organic Compounds by
controlled by gaseous diffusion through a static air layer
Sorbent Tube/Thermal Desorption/Capillary Gas Chroma-
(diffusion gap), permeation through a membrane or some other
tography – Part 1: Pumped Sampling
diffusion-barrier, but which does not involve the active move-
ISO 16017-2 Indoor, Ambient, and Workplace Air – Sam-
ment of air through the sampler.
pling and Analysis of Volatile Organic Compounds by
3.2.4 axial diffusive sampler—a tube-form device with pre-
Sorbent Tube/Thermal Desorption/Capillary Gas Chroma-
cisely controlled dimensions that samples gaseous organic
tography – Part 2: Diffusive Sampling
chemicals in air diffusively through one end of the tube onto
ISO 16107 Workplace Atmospheres—Protocol for Evaluat-
the sorbent surface held inside the tube at a fixed distance from
ing the Performance of Diffusive Samplers
the sampling end.
ISO GUM Guide to the Expression of Uncertainty in Mea-
surement
3.2.5 radial diffusive sampler—a tube form device which
2.3 CEN Standards: allows controlled diffusive sampling around the walls of the
EN 482 Workplace Atmospheres: General Requirements for sampler; that is, parallel to the radius. The ends of a radial
the Performance of Procedures for the Measurement of sampler are sealed.
Chemical Agents
3.2.6 diffusive uptake rate or diffusive sampling rate (U)—
the rate at which the diffusive sampler collects a particular gas
or vapor from the atmosphere, expressed in nanograms per
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
-1
parts per million (volume/volume) per minute (ng.ppm (V/V)
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. Available from United States Environmental Protection Agency (EPA), William
Available from European Committee for Standardization (CEN), 36 rue de Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,
Stassart, B-1050, Brussels, Belgium, http://www.cenorm.be. http://www.epa.gov.
D6196 − 23
-1
min ), picograms per parts per billion (volume/volume) per 4.2 For axial diffusive sampling, a suitable sorbent is
-1 -1
minute (pg.ppb (V/V) min ), or cubic centimetres per minute selected for the compound or mixture to be sampled. If more
(cm /min). than one sorbent is required, two or more diffusive sampling
tubes, packed with different sorbents, are used in parallel. The
3.2.7 loading—the mass of analyte collected or introduced
diffusive sampler or samplers are exposed to the atmosphere
on the sampler.
for a measured time period. Provided the sorbents chosen are
3.2.8 pumped sampler—a device which is capable of taking
strong enough to maintain a zero (or negligible) analyte
samples of gases and vapors from the atmosphere and consist-
concentration at the sampling surface (that is, to minimize back
ing of a sampling medium, such as a sorbent tube, and an air
diffusion), Fick’s law of diffusion will apply. The uptake rate of
sampling pump. Air is passed through the sorbent tube at a rate
each volatile organic component, in terms of mass retained per
controlled by the sampling pump.
unit of ambient air concentration per unit exposure time, will
3.2.9 safe sampling volume—70 % of breakthrough volume be a constant U – see 3.2.4. This means that, while Fick’s law
applies and back-diffusion remains negligible, the analyte mass
(3.2.1) or 50 % of the chromatographically-determined reten-
tion volume. collected by the sampler is directly proportional to the time
weighted average atmospheric concentration over a given
3.2.10 sorbent strength—term to describe the affinity of
exposure period.
sorbents for VOCs; a stronger sorbent is one which offers
4.3 For radial diffusive sampling, a suitable sorbent is
greater safe sampling volumes for VOCs relative to another,
selected for the compound or mixture to be sampled. If more
weaker, sorbent.
than one sorbent is required, two or more samplers, packed
3.2.11 sorbent tube—a tube, usually made of metal or glass,
with different sorbents, are used in parallel. The diffusive
containing one or more sorbents or a reagent-impregnated
sampler or samplers are exposed to the atmosphere for a
support which may be used to collect vapor-phase organic
measured time period. Provided the sorbents chosen are strong
chemicals either by passing air through the tube at a rate
enough to maintain a zero (or negligible) analyte concentration
controlled by an air sampling pump (pumped sampling) or by
at the sampling surface (that is, to minimize back diffusion),
allowing controlled diffusion of gases or vapors onto the
Fick’s law of diffusion will apply and the uptake rate of each
sorbent sampling surface (diffusive or passive sampling).
volatile organic component, in terms of mass retained per unit
3.3 Definitions of Acronyms Used in This Standard to
exposure time, is directly proportional to the atmospheric
Denote Specific Types or Classes of Sorbent (See Also for
concentration.
Details and Examples):
4.4 The collected vapor (on each tube or cartridge) is
3.3.1 PDMS—Polydimethyl siloxane-based sorbent (GC
desorbed by heat and is transferred under carrier gas into a gas
column packing material), typically comprising polydimethyl
chromatograph (GC) equipped with a capillary column and
siloxane gum coated on particles of inert support at a specified
either a conventional detector (such as the flame ionization or
loading levels: for example, 3 % or 10 %.
electron capture detector (ECD)) or a mass spectrometric
detector, where it is analyzed. A sample focusing trap between
3.3.2 VW-GCB—Very weak graphitized carbon black sor-
bent. the sampling tube and the gas chromatograph is commonly
employed to ensure injection of the analytes in as small a
3.3.3 W-PP—Weak porous polymer sorbent.
volume of carrier gas as possible, providing better peak
3.3.4 WM-GCB—Weak to medium strength graphitized car-
resolution and sensitivity than is normally achievable with
bon black sorbent.
single stage desorption. Where the sample to be analyzed
contains unknown components (indoor/ambient air
3.3.5 M-PP—Medium strength porous polymer sorbent.
applications), preliminary analysis of typical samples by GC-
3.3.6 MS-GCB—Medium to strong graphitized carbon black
mass spectrometry should be undertaken.
sorbent.
5. Significance and Use
3.3.7 CMS—Carbonized molecular sieve sorbent.
5.1 This practice is recommended for use in measuring the
4. Summary of Practice concentration of VOCs in ambient, indoor, and workplace
atmospheres. It may also be used for measuring emissions from
4.1 For active (pumped) sampling, a suitable sorbent or
materials in small or full scale environmental chambers for
series of sorbents is selected for the compound or mixture to be
material emission testing or human exposure assessment.
sampled. The sorbents selected are arranged in series, in order
5.2 Such measurements in ambient air are of importance
of increasing sorbent strength from the sampling end. This can
because of the known role of VOCs as ozone precursors, and
be done by linking together tubes containing the individual
in some cases (for example, benzene), as toxic pollutants in
sorbents or by packing a single tube with two or more sorbents.
their own right.
Provided suitable sorbents are chosen, volatile organic compo-
nents are retained by the sorbent tube(s) and thus are removed 5.3 Such measurements in indoor air are of importance
from the flowing air stream. The use of weaker sorbents in because of the association of VOCs with air quality problems
front of stronger sorbents during sampling prevents irreversible in indoor environments, particularly in relation to sick building
adsorption of higher boiling compounds on the stronger syndrome and emissions from building materials. Many vola-
sorbents. tile organic compounds have the potential to contribute to air
D6196 − 23
quality problems in indoor environments and in some cases (for example, >100 ppm) and shall be taken into consideration
toxic VOCs may be present at such elevated concentrations in if necessary during method development.
home or workplace atmospheres as to prompt serious concerns
6.4 The method is suitable for use in atmospheres of up to
over human exposure and adverse health effects (5).
95 % relative humidity for all hydrophobic sorbents such as
5.4 Such measurements in workplace air are of importance
porous polymers and graphitized carbon blacks – see Appendix
because of the known toxic effects of many such compounds. X1. When less hydrophobic, strong sorbents such as carbon-
ized molecular sieves are used in atmospheres with humidity in
NOTE 1—While workplace air monitoring has traditionally been carried
excess of 65 % RH, exercise care to prevent water interfering
out using disposable sorbent tubes, typically packed with charcoal and
extracted using chemical desorption (solvent extraction) prior to GC with the analytical process. Suitable water elimination or
analysis – for example following NIOSH and OSHA reference methods –
reduction procedures include sample splitting and selectively
routine thermal desorption (TD) technology was originally developed
dry purging moisture from the sorbent tube or focusing trap, or
specifically for this application area. TD overcomes the inherent analyte
both, prior to analysis. Other useful approaches to minimizing
dilution limitation of solvent extraction improving method detection limits
water interference include reducing the air volume sampled,
by 2 or 3 orders of magnitude and making methods easier to automate.
Relevant international standard methods include ISO 16017-1 and ISO for example, to 0.5 L (pumped sampling), and reducing the
16017-2. For a detailed history of the development of analytical thermal
time of sampling (diffusive sampling).
desorption and a comparison with solvent extraction methods see Ref (6).
5.5 In order to protect the environment as a whole and
7. Apparatus
human health in particular, it is often necessary to take
7.1 Use ordinary laboratory apparatus in addition to the
measurements of air quality and assess them in relation to
following.
mandatory requirements.
7.2 Sorbent tubes for pumped sampling, compatible with the
5.6 The choices of sorbents, sampling method, and analyti-
thermal desorption apparatus to be used (7.5). Typically, but
cal methodology affect the efficiency of sorption, recovery, and
not exclusively, they are constructed of glass or stainless steel
quantification of individual VOCs. This practice is potentially
tubing, 6.4 mm OD, 5 mm ID and 89 mm long and contain up
effective for any GC-compatible vapor-phase organic com-
to 60 mm total length of sorbent or sorbents, held in place with
pound found in air, over a wide range of volatilities and
stainless steel gauzes or glass wool, or both. Tubes of other
concentration levels. However, it is the responsibility of the
dimensions may be used but the safe sampling volumes (SSV)
user to ensure that the sampling, recovery, analysis, and overall
given in Appendix X2 are based on these tube dimensions. For
quality control of each measurement are within acceptable
labile analytes, such as sulfur-containing compounds, fused-
limits for each specific VOC of interest. Guidance for this
silica-coated steel (typically 5 mm ID) or glass tubes (typically
evaluation is part of the scope of this practice.
4 mm ID) should be used. (See Note 2.) One end of the tube is
marked, for example by a scored ring about 10 mm from the
6. Interferences
sampling inlet end to represent the end open to the atmosphere
6.1 Organic components, that have the same or nearly the
during sampling, otherwise the direction of sampling flow may
same retention time as the analyte of interest, will interfere
be marked with an arrow. The tubes are packed with one or
during the gas chromatographic analysis. Analytes and artifacts
more preconditioned sorbents (8.3), taking care to ensure that
can be generated during sampling and analysis (7, 8). Interfer-
the entire sorbent bed will be within the desorber heated zone
ences can be minimized by proper selection of gas chromato-
during thermal desorption, and that an air gap of at least 14 mm
graphic columns and conditions, and by stringent conditioning
is retained at each end of the tube to minimize errors due to
of both the sorbent tubes or radial sorbent cores and the
diffusive ingress at a very low pump flow rates. The tubes
analytical system before use. The use of capillary or microbore
described above typically contain between 100 mg and 1000
columns with superior resolution or columns of different
mg sorbent, depending on sorbent density, and the number of
polarity will frequently eliminate these problems. Artifacts
adsorbent beds. If more than one sorbent is used in a single
may be formed during storage of blank sorbent tubes/cores.
tube, the sorbents should be arranged in discrete beds in order
This is minimized by correctly sealing and storing blank and
of increasing sorbent strength with the weakest sorbent nearest
sampled tubes (see 9.1, 11.1.8, 11.1.9, and 16.3). Such artifact
to the sampling (inlet) end of the tube. Tubes should be labelled
formation is generally at low nanogram levels on well condi-
uniquely prior to conditioning. Do not use solvent-containing
tioned tubes desorbed at moderate temperatures – see 8.3 and
paints and markers or adhesive labels to label the tubes as high
Refs (9, 10).
levels of solvent might contaminate the tubes and adhesive
labels might jam the thermal desorption mechanism. Tubes
6.2 Selectivity may be further enhanced by the use of
may be obtained commercially which are already permanently
selective GC detectors such as the ECD for certain compounds
marked (for example, etched) with suitable identifiers such as
or by using a mass spectrometer in extracted- or selected ion
unique serial numbers in alphanumeric or barcode format, or
monitoring (SIM) mode as a GC detector. In this mode,
both.
co-eluting compounds can usually be determined. Spectral
deconvolution is also useful for distinguishing and identifying
NOTE 2—With glass tubes the sorbent is typically held in place using a
co-eluting GCMS peaks. glass frit, or plugs of quartz or unsilanized glass wool.
6.3 Competitive sorption between VOCs, although unlikely 7.2.1 Sorbents with widely different (>100 °C) maximum
at normal sampling levels, is possible at high concentrations desorption temperatures such as medium strength porous
D6196 − 23
polymers and graphitized carbon blacks, or carbon molecular In practice packed tube dimensions will vary slightly (11) and
sieve when packed in the same tube, or both, must be tubes should be rejected where the inner air gap is outside the
conditioned and desorbed at temperatures below the maximum
range 14.0 mm and 14.6 mm.
of the least stable adsorbent in the tube.
7.3.2 Diffusive End Caps, typically push-on, “O”-ring seal
7.3 Sorbent tubes for axial diffusive sampling, compatible caps fitted with a metal gauze allowing the diffusive ingress of
with the thermal desorption apparatus to be used (7.5) and with vapor. The size of the gauze covered opening in the sampling
the sampling surface of the sorbent retained by a metal
cap should being the same as the cross section of the tube (Fig.
(typically stainless steel) gauze to give a precisely defined air 1). The diffusive endcap maintains the diffusive air gap
gap (7.3.1). Typically, but not exclusively, they are constructed
between the inlet of the tube and the sorbent. The use of the
of stainless steel tubing, 6.4 mm OD, 5 mm ID and 89 mm long
diffusive endcap also minimizes air movement within the
and with the sorbent held in place 14.3 mm from the sampling
diffusive air gap if sampling in windy conditions.
end using a stainless steel gauze (Fig. 1) Tubes of other
7.4 Sorbent cores for radial diffusive sampling, compatible
dimensions may be used but the uptake rates given in Appen-
with the thermal desorption apparatus to be used (7.5).
dix X3 are based on these tube dimensions. For labile analytes,
Typically, but not exclusively, they are constructed of a fine
such as sulfur-containing compounds, fused silica-coated steel
(400 mesh), stainless steel gauze tube, 4.8 mm OD and 55 mm
should be used for both the tube and sorbent-retaining gauze.
long, such that they are a snug fit inside a 5.0 mm ID
One end of the tube is marked, for example by a scored ring
desorption tube. Sorbent cores of other dimensions may be
about 14 mm from the sampling inlet end. The tubes are packed
used but the uptake rates given in Appendix X4 are based on
with sorbents (8.3) such that the sorbent bed will be within the
these dimensions. For labile analytes, such as sulfur-containing
desorber heated zone. Glass tubes are not usually considered
compounds, fused silica-coated steel should be used for the
suitable for passive sampling because it is more difficult to
gauze tube. The cores are completely packed with sorbent. The
define the diffusive air gap sufficiently accurately and repro-
mass of sorbent required will vary depending on sorbent
ducibly.
density—typically about 200 mg of weak porous polymer
NOTE 3—Tubes packed with more than one sorbent may be used for
sorbent, or 400 mg of medium to strong graphitized carbon
diffusive monitoring, but only the first sorbent, nearest the sampling end,
black sorbent.
plays any role in the sampling process.
7.4.1 Sampler bodies for radial diffusive sampling, compat-
7.3.1 Uptake rates in Appendix X3 are given for stainless
ible with the sorbent cores to be used. Typically, but not
steel or fused silica-coated stainless steel tubes with a nominal
exclusively, they are constructed of high density, non-emitting/
total air gap (between the sampling surface of the sorbent bed
and sampling surface of the diffusive end cap (7.3.2)) of 15 mm absorbing porous polymer with one permanently sealed end
and the other end sealed with a screw thread fitting such that
(see Fig. 1) and an inner air gap of 14.3 mm (between the outer
surface of the sorbent retaining gauze and the end of the tube). the sorbent core can readily be inserted and removed. It should
FIG. 1 Schematic of a Typical Axial Diffusive Sampler
D6196 − 23
not be necessary to handle the sorbent core when transferring 7.10 Connecting Tubing (pumped sampling only), if tubing
to and from the sampler body. is required upstream (for example, for connecting between the
sampling point and the sample tube when sampling in a remote
7.4.2 Storage and desorption carrier tubes for radial diffu-
location), inert PTFE tubing should be used and should be
sive sampling, compatible with the sorbent cores and thermal
replaced regularly. Any tubing used downstream of the sampler
desorption apparatus to be used. Typically, but not exclusively,
(that is, for connecting the non-sampling end of the tube to the
these are constructed of stainless steel or fused silica-coated
pump) does not need to be inert and can be of any suitable
stainless steel tubing, 6.4 mm OD, 5 mm ID and 89 mm long,
material. For personal monitoring, the tube is typically worn as
capable of retaining the sorbent core approximately 14 mm
close as possible to the breathing zone (for example, on the
from the desorption end of the carrier tube. The sorbent core
lapel of clothing), and the pump carried on a belt. In this case,
should be a relatively snug fit inside the carrier tube such that
clips should be provided to hold the sample tube and connect-
it can be easily inserted and removed but that gas flow passes
ing tubing to the wearer’s lapel area. This connecting tubing
through the sorbent core (rather than around the outside) during
typically needs to be about 90-cm long. All connections should
thermal desorption. It should be possible to seal the carrier
be leak proof.
tubes with long-term sorbent tube storage caps (7.6). Carrier
tubes should be labelled uniquely prior to conditioning. Do not
7.11 Soap Bubble Flow Meter or Electronic Flow Meter, for
use solvent-containing paints and markers or adhesive labels to calibrating pump, desorb, and split flows.
label the tubes. Carrier tubes may be obtained commercially
7.12 Gas Chromatographic Apparatus:
which are already permanently marked (for example, etched)
7.12.1 Gas Chromatograph, fitted with a flame ionization,
with suitable identifiers such as unique serial numbers in
photo ionization, mass spectrometric, or other suitable detector.
alphanumeric or barcode format, or both.
The detector selected should be capable of detecting an
injection of 0.5 ng toluene with a signal-to-noise ratio of at
7.5 Thermal Desorption Apparatus, for two-stage thermal
least 5:1.
desorption of sorbent tubes (or carrier tubes for radial sorbent
7.12.2 Gas Chromatographic Column, capable of separating
cores) and transfer of the desorbed vapors by an inert gas flow
the analytes of interest from other components. Typical dimen-
into a gas chromatograph. A typical apparatus contains a
sions are 50 m or 60 m long fused silica capillary columns,
mechanism for holding the tubes to be desorbed while they are
0.25 mm ID or 0.32 mm ID with a 0.5 micron to 5 micron film
heated and purged simultaneously with carrier gas. The des-
of an appropriate stationary phase.
orption temperature and time is adjustable, as is the carrier gas
flow rate. Air must be purged from the sample tube and
7.13 Injection Facility for Preparing Standards, comprising
analytical system before heat is applied to prevent sorbent and
a conventional packed column GC injection port may be used
analyte oxidation. The apparatus shall also incorporate addi-
for preparing sample tube standards. Ready-made injection
tional features, such as leak-testing, and a focusing (cold) trap
systems for loading liquid or gas-phase standards onto the
(Section 12). The desorbed sample, contained in the purge gas,
sampling end of sorbent tubes are also available commercially.
is routed to the gas chromatograph and capillary column either
Essential components include a fitting for the sampling end of
directly to the column or by way of a heated transfer line.
the tube, a controllable flow of inert (carrier) gas through the
Contaminants from the outer surfaces of tubes should be
injector body and a septum cap such that the liquid or gas
excluded from the sample flow path.
standard can be injected into the stream of gas at or near the
sampling surface of the sorbent tube.
NOTE 4—Leak testing should be carried out. Tubes that fail the leak test
should not be analyzed but resealed to await user intervention.
8. Reagents and Materials
NOTE 5—Internal standard addition to the sampling end of every sample
tube can be used as an additional or alternative check on sample integrity,
8.1 Unless otherwise stated, all reagents shall conform to
however, without a pre-desorption leak test (Note 4) results from leaking
the specifications of the committee on Analytical Reagents of
samples will be lost.
the American Chemical Society, where such specifications are
7.6 Sorbent Tube End Caps, to combine two or more tubes
available. Other grades may be used, provided that it is
together in series during pumped sampling. They typically
ascertained that use of the reagent does not lessen the accuracy
comprise 6.4 mm OD stainless steel couplings fitted with
of the practice.
combined (one-piece) PTFE ferrule seals.
8.2 Reagents:
8.2.1 Volatile Organic Compounds, for calibration. These
7.7 Sorbent Tube Unions (pumped sampling only), to com-
should reflect the compounds of interest. Typical components
bine two or more tubes in series during pumped sampling
are: propane, pentane, hexane, benzene, dichloromethane,
constructed of stainless steel couplings with combined (one-
111-trichloroethane, methanol, ethanol, n-butanol, methyl
piece) PTFE ferrule seals.
7.8 Syringes, a precision 1 μL or 5 μL liquid syringe
readable to 0.01 μL or 0.05 μL, a precision 10-μL gas tight
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
syringe readable to 0.1 μL and a precision 10-mL gas tight
Standard-Grade Reference Materials, American Chemical Society, Washington,
syringe readable to 0.1 mL.
DC. For suggestions on the testing of reagents not listed by the American Chemical
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
7.9 Sampling Pump, conforming to the performance re-
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
quirements of 8.3.1. copeial Convention, Inc. (USPC), Rockville, MD.
D6196 − 23
acetate, 2-methoxyethanol, methyl ethyl ketone, acetonitrile, VOCs may be sampled using multi-bed tubes, that is, sampling
n-butyl acetate, }-pinene, decane, ethylene oxide, propylene tubes packed with two or more sorbents, arranged in discrete
oxide, and hexanal. layers in order of increasing sorbent strength from the sampling
end.
8.2.2 Solvent, of chromatographic quality, free from com-
8.3.1.2 Guidance given for the selection of sorbents for
pounds co-eluting with the compound or compounds of interest
pumped monitoring tubes can be applied equally well to axial
(8.2.1). Methanol is most commonly used because it can often
passive sampling tubes because, in this case, sufficient sorbent
be selectively purged from tubes packed with weaker sorbents
strength (breakthrough volume) equates to low back diffusion
prior to standard analysis. However, alternative dilution
and stable uptake rates. The restriction to a single sampling
solvents, for example, ethyl acetate or cyclohexane can be
surface (hence single sorbent) limits the target analyte range
used, particularly if there is a possibility of reaction or
that can be monitored by any one passive sampling tube.
chromatographic co-elution.
However, the unobtrusive nature and low cost of passive
8.3 Sorbents, particle size, in the range 20 to 80 mesh,
samplers usually means that two or more samplers containing
typically 35 to 60 mesh. Medium strength porous polymer
different sorbents can be used in parallel without impacting
sorbents (Appendix X1) which are prone to shrinkage should
study objectives.
be preconditioned under a flow of inert gas by heating, at a
8.3.1.3 The high sampling rate and associated increased risk
temperature at least 25 °C below the published maximum for
of back diffusion associated with radial diffusion typically
that sorbent, for 16 h, before packing the tubes. If tubes are
limits these samplers to compounds of equal or lower volatility
packed with unconditioned sorbent, they should be stringently
than benzene. It also means that stronger sorbents are generally
conditioned at a temperature just below (10 °C to 25 °C) the
required when compared with sampling the same compounds
maximum recommended temperature of the least stable sorbent
using either axial passive or pumped sorbent tubes.
in the tube for not less than 2 h, with a flow of at least 100
8.3.1.4 A guide for selection of sorbents for pumped and
mL/min pure, carrier gas. The flow direction shall be opposite
axial diffusive sampling is given in Appendix X1. Equivalent
to that used during sampling. The lowest effective analytical
sorbents may be used. Information on sorbent conditioning and
desorption temperature shall be used (13.4) to minimize
analytical desorption parameters is given in Appendix X1 and
artifact levels. Temperatures shall be kept below those used for
is also available from manufacturers.
conditioning. Sorbent tubes prepacked by the manufacturer are
8.3.2 Apparent sorbent strength (breakthrough volumes)
also available with or without pre-conditioning.
may be reduced when air concentrations exceed 100 ppm (in
8.3.1 Sorbent selection is determined by sorbent strength,
the same way that retention times may fall slightly when a
typically assessed in terms of retention of the compound of
packed GC column is overloaded), but pumped sampling
interest (see Annex A2) – or breakthrough volume (that is, the
volumes or diffusive sampling times are invariably minimized
volume of air that can be sampled before the concentration of
when sampling under such extreme conditions so this effect is
analyte breaking through the sorbent and exiting from the far
rarely a significant limiting factor.
end of the tube becomes significant – typically >5 %) – see
8.3.3 Sorbent tube artifacts are <1ng for typical sampling
Annex A1. In essence, the sorbent or sorbents selected must be
tubes (7.2) containing well-conditioned carbonaceous sorbents
strong enough for complete retention of all the compounds of
such as graphitized carbon blacks (GCBs) and carbon molecu-
interest during sampling and weak enough for effective release
lar sieves (CMSs); at 1 ng to 5 ng levels for thermally stable
of all the compounds of interest (under reasonable analytical
weak porous polymer (W-PP) sorbents and at 5 ng to 50 ng
conditions) during subsequent thermal desorption.
levels for the range of medium strength porous polymer
(M-PP) sorbents.
NOTE 6—Analyte breakthrough (loss) from the far end of a sorbent tube
during pumped sampling is not a function of sampler ‘capacity’ in the
NOTE 7—Use of M-PP sorbents is in decline due to their inherent high
normal sense of the word – that is, it does not indicate that the sorbent tube
and variable background levels. Data relating to M-PP sorbents is
is ‘full’ or ‘saturated’ with that analyte under the given conditions. It is,
designated using gray font in this standard to indicate these sorbents
more accurately, a chromatographic function, relating to the affinity of the
should be used with caution.
analyte (sorbate) for the sorbent. Breakthrough, to a large extent, will be
NOTE 8—Inherent artifact levels will increase significantly with des-
unaffected by analyte concentration or loading in the same way that
orption temperature. The lowest effective desorption temperature should
chromatographic retention times are constant for a given analyte however
always be used.
big or small the peak. Studies have shown that the breakthrough volume
of a given analyte on a given sorbent tube remains constant for air
8.4 Calibration Standards:
concentrations up to 100 ppm (12).
8.4.1 Gas standards suitable for introducing target com-
8.3.1.1 In the case of pumped sampling, single-bed tubes pounds to the sampling end of conditioned sorbent tubes at the
containing a weak porous polymer (W-PP) sorbent are appro- levels of interest provide an optimum calibration option for air
priate for normal alkanes ranging in volatility from n-C monitoring methods because they allow analytes to be intro-
(hexane) or n-C (depending on required air sample volume) duced to the sorbent in a way which is closely analogous to air
up to n-C or n-C (depending on analytical thermal desorp- sampling and which introduces no potential interferences – for
22 30
tion capabilities and conditions). More volatile materials example, solvent. However, certified gas standards are difficult
should be sampled on stronger sorbents, such as medium to and expensive to obtain at trace (ppb) levels and stable gas
strong graphitized carbon blacks (MS-GCB) or carbon molecu- standards are not available for all compounds – for example;
lar sieves (CMS). Example sorbents and their respective higher boiling VOCs, polar compounds, reactive species and
applications are given in Appendix X1. A broader range of semi-volatile organics.
D6196 − 23
8.4.2 Calibration Solutions for Ambient and Indoor Air: 8.4.4 Loading Sorbent Tubes with Calibration Standards—
Prepare fresh liquid standard solutions weekly, or more fre-
8.4.2.1 Solution Containing Approximately 100 μg/mL of
quently if evidence is noted of deterioration, for example,
Each Liquid Component—Accurately weigh approximately 10
condensation reactions between alcohols and ketones.
mg of substance or substances of interest into a 100 mL
volumetric flask, starting with the least volatile substance.
8.5 Loaded Sorbent Tubes—Loaded sorbent tubes may be
Make up to 100 mL with solvent (8.2.2), stopper and shake to
prepared and used for the calibration of all 3 sorbent-based
mix.
monitoring methods described in this standard; axial and radial
8.4.2.2 Solutions Containing Approximately 1 mg/mL of
passive samplers and pumped sorbent tubes. Prepare loaded
Liquid Components—Introduce 50 mL of methanol into a 100
sorbent tubes by connecting the sampling end of blank,
mL volumetric flask. Add 10 mL of solution (8.4.2.1) Make up
conditioned sorbent tubes to a metered source of gas-phase
to 100 mL with methanol, stopper and shake to mix.
standard (8.4.1) using inert tubing and connections. A fixed and
8.4.2.3 Solution Containing Approximately 10 μg/mL of measured volume of standard gas at known pressure, for
Liquid Components—Introduce 50 mL of methanol into a 100 example, in a gas sample loop, can be introduced onto the
mL volumetric flask. Add 10 mL of solution (8.4.2.1). Make up sampling end of the tube in a stream of pure carrier gas.
to 100 mL with solvent, stopper and shake to mix. Alternatively, a controlled flow of standard gas can be passed
through a blank sorbent tube for a specific length of time.
8.4.2.4 Solution Containing Approximately 10 μg/mL of Gas
Aliquots of liquid standard solutions can be injected onto clean
Components—For gases, for example, ethylene oxide, prepare
sorbent tubes as follows: Fit the sampling end of the clean
a low level calibration solution as follows. Obtain pure gas at
sorbent tube into the injection unit (7.13) through which inert
atmospheric pressure by filling a small plastic gas bag from a
purge gas is passing at 100 mL/min and introduce a 1 μL to
gas cylinder. Fill a 10-μL gas-tight syringe with 10 μL of the
2 μL aliquot of an appropriate standard solution injected
pure gas and close the valve of the syringe. Using a 2-mL
through the septum. After 5 min, disconnect the tube and seal
septum vial, add 2-mL methanol and close with the septum
it. If calibration tubes are to be prepared using multiple
cap. Insert the tip of the syringe needle through the septum cap
standards (gas-phase or liquid solutions, or both), introduce
into the methanol. Open the valve and withdraw the plunger
those containing the least volatile compounds of interest first
slightly to allow the solvent to enter the syringe. The action of
and the most volatile compounds of interest (typically the gas
the gas dissolving creates a vacuum, and the syringe fills with
phase standards) last. Load fresh blank tubes with appropriate
solvent. Return the solution to the flask. Flush the syringe twice
calibration standards for each batch of samples. When using
with the solution and return the washings to the flask. Calculate
liquid standards to calibrate typical ambient and indoor air
the mass of gas added using the gas laws; that is, 1 mol of gas
monitoring methods, load sorbent tubes with 1 μL to 2 μL (at
at STP occupies 22.4 L.
least 3 levels) of solutions 8.4.2.1, 8.4.2.2, or 8.4.2.3. When
8.4.3 Calibration Solutions for Workplace Air:
using liquid standards to calibrate typical workplace air moni-
8.4.3.1 Solution Containing Approximately 10 mg/mL of
toring methods, load sorbent tubes with 1 μL to 2 μL (at least
Each Liquid Component—Accurately weigh approximately 1 g
3 levels) of solutions 8.4.3.1, 8.4.3.2, or 8.4.3.3.
of substance or substances of interest into a 100 mL volumetric
8.5.1 If it is not possible to selectively purge the solvent
flask, starting with the least volatile substance. Make up to 100
from the tubes during the standard loading process, for
mL with solvent (8.2.2), stopper and shake to mix.
example when using tubes packed with stronger sorbents, the
8.4.3.2 Solutions Containing Approximately 1 mg/mL of
liquid standard volume should be limited to 1 μL. High levels
Liquid Components—Introduce 50 mL of solvent into a 100
of unpurged solvent can cause chromatographic interferences,
mL volumetric flask. Add 10 mL of solution (8.4.3.1) Make up
split discrimination, detector quenching and column overload
to 100 mL with solvent, stopper and shake to mix.
and make standards behave significantly differently to than real
8.4.3.3 Solution Containing Approximately 1 mg/mL of Gas
samples. Use a syringe with sufficient precision to deliver the
...

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. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D6196 − 15 D6196 − 23
Standard Practice for
Choosing Sorbents, Sampling Parameters and Thermal
Desorption Analytical Conditions for Monitoring Volatile
Organic Chemicals in Air
This standard is issued under the fixed designation D6196; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made throughout in July 2018.
1. Scope
1.1 This practice is intended to assist in the selection of sorbents and procedures for the sampling and analysis of ambient (1),
indoor (2), and workplace (3, 4) atmospheres for a variety of common volatile organic compounds (VOCs). It may also be used
for measuring emissions from materials in small or full scale environmental chambers or for human exposure assessment.
1.2 This practice is based on the sorption of VOCs from air onto selected sorbents or combinations of sorbents. Sampled air is
either drawn through a tube containing one or a series of sorbents (pumped sampling) or allowed to diffuse, under controlled
conditions, onto the sorbent surface at the sampling end of the tube (diffusive or passive sampling). The sorbed VOCs are
subsequently recovered by thermal desorption 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 tubes
containing one or more sorbents; (2) axial passive (diffusive) samplers (typically of the same physical dimensions as standard
pumped sorbent tubes and containing only one sorbent); and (3) radial passive (diffusive) samplers.
1.4 This practice recommends a number of sorbents that can be packed in sorbent tubes for use in the sampling of vapor-phase
organic chemicals; including volatile and semi-volatile organic compounds which, generally speaking, boil in the range 0 to 400°C
(v.p. 15 to 0.01 kPa at 25°C).0 °C to 400 °C (v.p. 15 kPa to 0.01 kPa at 25 °C).
1.5 This practice can be used for the measurement of airborne vapors of these organic compounds over a wide concentration range.
1.5.1 With pumped sampling, this practice can be used for the speciated measurement of airborne vapors of VOCs in a
3 3
concentration range of approximately 0.1 μg/m to 1 g/m , for individual organic compounds in 1–10 L 1 L to 10 L air samples.
Quantitative measurements are possible when using validated procedures with appropriate quality control measures.
1.5.2 With axial diffusive sampling, this practice is valid for the speciated measurement of airborne vapors of volatile organic
3 3
compounds in a concentration range of approximately 100 μg/m to 100 mg/m for individual organic compounds for an exposure
3 3
time of 8 h or 1 μg/m to 1 mg/m for individual organic compounds for an exposure time of four weeks.
This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.05 on Indoor Air.
Current edition approved Nov. 1, 2015Jan. 1, 2023. Published February 2016March 2023. Originally approved in 1997. Last previous edition approved in 20092015 as
ɛ1
D6196 – 03 (2009).D6196 – 15 . DOI: 10.1520/D6196-15E01.10.1520/D6196-23.
The bold face numbers in parentheses refer to the list of references at the end of this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6196 − 23
1.5.3 With radial diffusive sampling, this practice is valid for the measurement of airborne vapors of volatile organic compounds
3 3
in a concentration range of approximately 5 μg/m to 5 mg/m for individual organic compounds for exposure times of one to six
hours.
1.5.4 The upper limit of the useful range is almost always set by the linear dynamic range of the gas chromatograph column and
detector, or by the sample splitting capability of the analytical instrumentation used.
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 interfering
artifacts (or both) on the sorbent tubes.
1.6 This procedure can be used for personal and fixed location sampling. It cannot be used to measure instantaneous or short-term
fluctuations in concentration. Alternative ‘grab sampling’ procedures using canister air samplers (for example, Test Method D5466)
may be suitable for monitoring instantaneous or short term fluctuations in air concentration. Alternatives for on-site measurement
include, but are not limited to, gas chromatography, real-time mass spectrometry detectors and infrared spectrometry.
1.7 The sampling method gives a time-weighted average result.
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D3670 Guide for Determination of Precision and Bias of Methods of Committee D22
D3686 Practice for Sampling Atmospheres to Collect Organic Compound Vapors (Activated Charcoal Tube Adsorption Method)
D5466 Test Method for Determination of Volatile Organic Compounds in Atmospheres (Canister Sampling, Mass Spectrometry
Analysis Methodology)
E355 Practice for Gas Chromatography Terms and Relationships
2.2 ISO Standards:
ISO 5725 Accuracy (Trueness and Precision) of Measurement Methods and Results
ISO 6145-10 Gas Analysis. Preparation of Calibration Gas Mixtures. Permeation Method
ISO 13137 Workplace Atmospheres: Pumps for Personal Sampling of Chemical and Biological Agents. Requirements and Test
Methods
ISO 16017-1 Indoor, Ambient, and Workplace Air – Sampling and Analysis of Volatile Organic Compounds by Sorbent
Tube/Thermal Desorption/Capillary Gas Chromatography – Part 1: Pumped Sampling
ISO 16017-2 Indoor, Ambient, and Workplace Air – Sampling and Analysis of Volatile Organic Compounds by Sorbent
Tube/Thermal Desorption/Capillary Gas Chromatography – Part 2: Diffusive Sampling
ISO 16107 Workplace Atmospheres—Protocol for Evaluating the Performance of Diffusive Samplers
ISO GUM Guide to the Expression of Uncertainty in Measurement
2.3 CEN Standards:
EN 482 Workplace Atmospheres: General Requirements for the Performance of Procedures for the Measurement of Chemical
Agents
EN 838 Workplace Atmospheres: Requirements and Test Methods for Diffusive Samplers for the Determination of Gases and
Vapours
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from European Committee for Standardization (CEN), 36 rue de Stassart, B-1050, Brussels, Belgium, http://www.cenorm.be.
D6196 − 23
EN 1076 Workplace Atmospheres: Pumped Sorbent Tubes for the Determination of Gases and Vapours. Requirements and Test
Methods
EN 13528-3 Ambient Air Quality—Diffusive Samplers for the Determination of Concentrations of Gases and Vapours – Part 3:
Guide to Selection, Use, and Maintenance
EN 14662-1 Ambient Air Quality – Standard Method for Measurement of Benzene Concentrations – Part 1: Pumped Sampling
Followed by Thermal Desorption and Gas Chromatography
EN 14662-4 Ambient Air WualityQuality – Standard Method for Measurement of Benzene Concentrations – Part 4: Diffusive
Sampling Followed by Thermal Desorption and Gas Chromatography
2.4 EPA Method:
EPA Method TO-17 Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling Onto Sorbent Tubes
3. Terminology
3.1 Definitions—Refer to Terminology D1356 and Practice E355 for definitions of terms used in this practice.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 breakthrough volume—the volume of a known atmosphere that can be passed through the tube before the concentration of
the vapor eluting from non-sampling end of the tube reaches 5 % of the applied test concentration.
3.2.2 desorption effıciency—the ratio of the mass of analyte desorbed from a sampling device to that applied.
3.2.3 diffusive (passive) sampler—a device that is capable of collecting gases and vapors from an atmosphere at rates controlled
by gaseous diffusion through a static air layer (diffusion gap), permeation through a membrane or some other diffusion-barrier, but
which does not involve the active movement of air through the sampler.
3.2.4 axial diffusive sampler—a tube-form device with precisely controlled dimensions that samples gaseous organic chemicals in
air diffusively through one end of the tube onto the sorbent surface held inside the tube at a fixed distance from the sampling end.
3.2.5 radial diffusive sampler—a tube form device which allows controlled diffusive sampling around the walls of the sampler;
that is, parallel to the radius. The ends of a radial sampler are sealed.
3.2.6 diffusive uptake rate or diffusive sampling rate (U)—the rate at which the diffusive sampler collects a particular gas or vapor
-1 -1
from the atmosphere, expressed in nanograms per parts per million (volume/volume) per minute (ng.ppm (V/V) min ),
-1 -1 3
picograms per parts per billion (volume/volume) per minute (pg.ppb (V/V) min ), or cubic centimetres per minute (cm /min).
3.2.7 loading—the mass of analyte collected or introduced on the sampler.
3.2.8 pumped sampler—a device which is capable of taking samples of gases and vapors from the atmosphere and consisting of
a sampling medium, such as a sorbent tube, and an air sampling pump. Air is passed through the sorbent tube at a rate controlled
by the sampling pump.
3.2.9 safe sampling volume—70 % of breakthrough volume (3.2.1) or 50 % of the chromatographically-determined retention
volume.
3.2.10 sorbent strength—term to describe the affinity of sorbents for VOCs; a stronger sorbent is one which offers greater safe
sampling volumes for VOCs relative to another, weaker, sorbent.
3.2.11 sorbent tube—a tube, usually made of metal or glass, containing one or more sorbents or a reagent-impregnated support
which may be used to collect vapor-phase organic chemicals either by passing air through the tube at a rate controlled by an air
sampling pump (pumped sampling) or by allowing controlled diffusion of gases or vapors onto the sorbent sampling surface
(diffusive or passive sampling).
Available from United States Environmental Protection Agency (EPA), William Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,
http://www.epa.gov.
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3.3 Definitions of Acronyms Used in This Standard to Denote Specific Types or Classes of Sorbent (See Also for Details and
Examples):
3.3.1 PDMS—Polydimethyl siloxane-based sorbent (GC column packing material), typically comprising polydimethyl siloxane
gum coated on particles of inert support at a specified loading levels: for example, 3 % or 10 %.
3.3.2 VW-GCB—Very weak graphitized carbon black sorbent.
3.3.3 W-PP—Weak porous polymer sorbent.
3.3.4 WM-GCB—Weak to medium strength graphitized carbon black sorbent.
3.3.5 M-PP—Medium strength porous polymer sorbent.
3.3.6 MS-GCB—Medium to strong graphitized carbon black sorbent.
3.3.7 CMS—Carbonized molecular sieve sorbent.
4. Summary of Practice
4.1 For active (pumped) sampling, a suitable sorbent or series of sorbents is selected for the compound or mixture to be sampled.
The sorbents selected are arranged in series, in order of increasing sorbent strength from the sampling end. This can be done by
linking together tubes containing the individual sorbents or by packing a single tube with two or more sorbents. Provided suitable
sorbents are chosen, volatile organic components are retained by the sorbent tube(s) and thus are removed from the flowing air
stream. The use of weaker sorbents in front of stronger sorbents during sampling prevents irreversible adsorption of higher boiling
compounds on the stronger sorbents.
4.2 For axial diffusive sampling, a suitable sorbent is selected for the compound or mixture to be sampled. If more than one sorbent
is required, two or more diffusive sampling tubes, packed with different sorbents, are used in parallel. The diffusive sampler or
samplers are exposed to the atmosphere for a measured time period. Provided the sorbents chosen are strong enough to maintain
a zero (or negligible) analyte concentration at the sampling surface (that is, to minimize back diffusion), Fick’s law of diffusion
will apply. The uptake rate of each volatile organic component, in terms of mass retained per unit of ambient air concentration per
unit exposure time, will be a constant U – see 3.2.4. This means that, while Fick’s law applies and back-diffusion remains
negligible, the analyte mass collected by the sampler is directly proportional to the time weighted average atmospheric
concentration over a given exposure period.
4.3 For radial diffusive sampling, a suitable sorbent is selected for the compound or mixture to be sampled. If more than one
sorbent is required, two or more samplers, packed with different sorbents, are used in parallel. The diffusive sampler or samplers
are exposed to the atmosphere for a measured time period. Provided the sorbents chosen are strong enough to maintain a zero (or
negligible) analyte concentration at the sampling surface (that is, to minimize back diffusion), Fick’s law of diffusion will apply
and the uptake rate of each volatile organic component, in terms of mass retained per unit exposure time, is directly proportional
to the atmospheric concentration.
4.4 The collected vapor (on each tube or cartridge) is desorbed by heat and is transferred under inert carrier gas into a gas
chromatograph (GC) equipped with a capillary column and either a conventional detector (such as the flame ionization or electron
capture detector (ECD)) or a mass spectrometric detector, where it is analyzed. A sample focusing trap between the sampling tube
and the gas chromatograph is commonly employed to ensure injection of the analytes in as small a volume of carrier gas as
possible, providing better peak resolution and sensitivity than is normally achievable with single stage desorption. Where the
sample to be analyzed contains unknown components (indoor/ambient air applications), preliminary analysis of typical samples
by GC-mass spectrometry should be undertaken.
5. Significance and Use
5.1 This practice is recommended for use in measuring the concentration of VOCs in ambient, indoor, and workplace atmospheres.
It may also be used for measuring emissions from materials in small or full scale environmental chambers for material emission
testing or human exposure assessment.
D6196 − 23
5.2 Such measurements in ambient air are of importance because of the known role of VOCs as ozone precursors, and in some
cases (for example, benzene), as toxic pollutants in their own right.
5.3 Such measurements in indoor air are of importance because of the association of VOCs with air quality problems in indoor
environments, particularly in relation to sick building syndrome and emissions from building materials. Many volatile organic
compounds have the potential to contribute to air quality problems in indoor environments and in some cases toxic VOCs may be
present at such elevated concentrations in home or workplace atmospheres as to prompt serious concerns over human exposure
and adverse health effects (5).
5.4 Such measurements in workplace air are of importance because of the known toxic effects of many such compounds.
NOTE 1—While workplace air monitoring has traditionally been carried out using disposable sorbent tubes, typically packed with charcoal and extracted
using chemical desorption (solvent extraction) prior to GC analysis – for example following NIOSH and OSHA reference methods – routine thermal
desorption (TD) technology was originally developed specifically for this application area. TD overcomes the inherent analyte dilution limitation of
solvent extraction improving method detection limits by 2 or 3 orders of magnitude and making methods easier to automate. Relevant international
standard methods include ISO 16017-1 and ISO 16017-2. For a detailed history of the development of analytical thermal desorption and a comparison
with solvent extraction methods see Ref (6).
5.5 In order to protect the environment as a whole and human health in particular, it is often necessary to take measurements of
air quality and assess them in relation to mandatory requirements.
5.6 The choices of sorbents, sampling method, and analytical methodology affect the efficiency of sorption, recovery, and
quantification of individual VOCs. This practice is potentially effective for any GC-compatible vapor-phase organic compound
found in air, over a wide range of volatilities and concentration levels. However, it is the responsibility of the user to ensure that
the sampling, recovery, analysis, and overall quality control of each measurement are within acceptable limits for each specific
VOC of interest. Guidance for this evaluation is part of the scope of this practice.
6. Interferences
6.1 Organic components, that have the same or nearly the same retention time as the analyte of interest, will interfere during the
gas chromatographic analysis. Analytes and artifacts can be generated during sampling and analysis (7, 8). Interferences can be
minimized by proper selection of gas chromatographic columns and conditions, and by stringent conditioning of both the sorbent
tubes or radial sorbent cores and the analytical system before use. The use of capillary or microbore columns with superior
resolution or columns of different polarity will frequently eliminate these problems. Artifacts may be formed during storage of
blank sorbent tubes/cores. This is minimized by correctly sealing and storing blank and sampled tubes (see 9.1, 11.1.8, 11.1.9, and
16.3). Such artifact formation is generally at low nanogram levels on well conditioned tubes desorbed at moderate temperatures
– see 8.3 and Refs (9, 10).
6.2 Selectivity may be further enhanced by the use of selective GC detectors such as the ECD for certain compounds or by using
a mass spectrometer in extracted- or selected ion monitoring (SIM) mode as a GC detector. In this mode, co-eluting compounds
can usually be determined. Spectral deconvolution is also useful for distinguishing and identifying co-eluting GCMS peaks.
6.3 Competitive sorption between VOCs, although unlikely at normal sampling levels, is possible at high concentrations (for
example, >100 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 porous
polymers and graphitized carbon blacks – see Appendix X1. When less hydrophobic, strong sorbents such as carbonized molecular
sieves are used in atmospheres with humidity in excess of 65 % RH, exercise care to prevent water interfering with the analytical
process. Suitable water elimination or reduction procedures include sample splitting and selectively dry purging moisture from the
sorbent tube or secondary focusing trap, or both, prior to analysis. Other useful approaches to minimizing water interference
include reducing the air volume sampled, for example, to 0.5 L (pumped sampling), and reducing the time of sampling (diffusive
sampling).
D6196 − 23
7. Apparatus
7.1 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, but not
exclusively, they are constructed of glass or stainless steel tubing, 6.4 mm OD, 5 mm ID and 89 mm long and contain up to 60
mm total length of sorbent or sorbents, held in place with stainless steel gauzes or glass wool, or both. Tubes of other dimensions
may be used but the safe sampling volumes (SSV) given in Appendix X2 are based on these tube dimensions. 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. (See Note 2.) One end of the tube is marked, for example by a scored ring about 10 mm from the sampling inlet end to
represent the end open to the atmosphere during sampling, otherwise the direction of sampling flow may be marked with an arrow.
The tubes are packed with one or more preconditioned sorbents (8.3), taking care to ensure that the entire sorbent bed will be within
the desorber heated zone during thermal desorption, and that an air gap of at least 14 mm is retained at each end of the tube to
minimize errors due to diffusive ingress at a very low pump flow rates. The tubes described above typically contain between
100100 mg and 1000 mg sorbent, depending on sorbent density, and the number of adsorbent beds. If more than one sorbent is
used in a single tube, the sorbents should be arranged in discrete beds in order of increasing sorbent strength with the weakest
sorbent nearest to the sampling (inlet) end of the tube. Tubes should be labelled uniquely prior to conditioning. Do not use
solvent-containing paints and markers or adhesive labels to label the tubes as high levels of solvent might contaminate the tubes
and adhesive labels might jam the thermal desorption mechanism. Tubes may be obtained commercially which are already
permanently marked (for example, etched) with suitable identifiers such as unique serial numbers in alphanumeric or barcode
format, or both.
NOTE 2—With glass tubes the sorbent is typically held in place using a glass frit, or plugs of quartz or unsilanized glass wool.
7.2.1 Sorbents with widely different (>100°C)(>100 °C) maximum desorption temperatures such as medium strength porous
polymers and graphitized carbon blacks, or carbon molecular sieve when packed in the same tube, or both, must be conditioned
and desorbed at temperatures below the maximum of the least stable adsorbent in the tube.
7.3 Sorbent tubes for axial diffusive sampling, compatible with the thermal desorption apparatus to be used (7.5) and with the
sampling 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 tubing, 6.4 mm OD, 5 mm ID and 89 mm long and with the
sorbent held in place 14.3 mm from the sampling end using a stainless steel gauze (Fig. 1) Tubes of other dimensions may be used
but the uptake rates given in Appendix X3 are based on these tube dimensions. For labile analytes, such as sulfur-containing
compounds, fused silica-coated steel should be used for both the tube and sorbent-retaining gauze. One end of the tube is marked,
for example by a scored ring about 14 mm from the sampling inlet end. The tubes are packed with sorbents (8.3) such that the
sorbent bed will be within the desorber heated zone. Glass tubes are not usually considered suitable for passive sampling because
it is more difficult to define the diffusive air gap sufficiently accurately and reproducibly.
NOTE 3—Tubes packed with more than one sorbent may be used for diffusive monitoring, but only the first sorbent, nearest the sampling end, plays any
role in the sampling process.
7.3.1 Uptake rates in Appendix X3 are given for stainless steel or fused silica-coated stainless steel tubes with a nominal total air
gap (between the sampling surface of the sorbent bed and sampling surface of the diffusive end cap (7.3.2)) of 15 mm (see Fig.
1) and an inner air gap of 14.3 mm (between the outer surface of the sorbent retaining gauze and the end of the tube). In practice
packed tube dimensions will vary slightly (11) and tubes should be rejected where the inner air gap is outside the range
14.014.0 mm and 14.6 mm.
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 cap should being the same as the cross section of the tube (Fig. 1). The
diffusive endcap maintains the diffusive air gap between the inlet of the tube and the sorbent. The use of the diffusive endcap also
minimizes air 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 constructed of a fine (400 mesh), stainless steel gauze tube, 4.8 mm OD and 55 mm long, such that they
are a snug fit inside a 5.0 mm ID desorption tube. Sorbent cores of other dimensions may be used but the uptake rates given in
Appendix X4 are based on these dimensions. For labile analytes, such as sulfur-containing compounds, fused silica-coated steel
D6196 − 23
FIG. 1 Schematic of a Typical Axial Diffusive Sampler
should be used for the gauze tube. The cores are completely packed with sorbent. The mass of sorbent required will vary depending
on sorbent density—typically about 200 mg of weak porous polymer sorbent, or 400 mg of medium to strong graphitized carbon
black sorbent.
7.4.1 Sampler bodies for radial diffusive sampling, compatible with the sorbent cores to be used. Typically, but not exclusively,
they are constructed of high density, non-emitting/absorbing porous polymer with one permanently sealed end and the other end
sealed with a screw thread fitting such that the sorbent core can readily be inserted and removed. It should not be necessary to
handle the sorbent core when transferring to and from the sampler body.
7.4.2 Storage and desorption carrier tubes for radial diffusive sampling, compatible with the sorbent cores and thermal desorption
apparatus to be used. Typically, but not exclusively, these are constructed of stainless steel or fused silica-coated stainless steel
tubing, 6.4 mm OD, 5 mm ID and 89 mm long, capable of retaining the sorbent core approximately 14 mm from the desorption
end of the carrier tube. The sorbent core should be a relatively snug fit inside the carrier tube such that it can be easily inserted
and removed but that gas flow passes through the sorbent core (rather than around the outside) during thermal desorption. It should
be possible to seal the carrier tubes with long-term sorbent tube storage caps (7.6). Carrier tubes should be labelled uniquely prior
to conditioning. Do not use solvent-containing paints and markers or adhesive labels to label the tubes. Carrier tubes may be
obtained commercially which are already permanently marked (for example, etched) with suitable identifiers such as unique serial
numbers in alphanumeric or barcode format, or both.
7.5 Thermal Desorption Apparatus, for two-stage thermal desorption of sorbent tubes (or carrier tubes for radial sorbent cores)
and transfer of the desorbed vapors by an inert gas flow into a gas chromatograph. A typical apparatus contains a mechanism for
holding the tubes to be desorbed while they are heated and purged simultaneously with inert carrier gas. The desorption
temperature and time is adjustable, as is the carrier gas flow rate. Air must be purged from the sample tube and analytical system
before heat is applied to prevent sorbent and analyte oxidation. The apparatus shouldshall also incorporate additional features, such
as leak-testing, and a focusing (cold) trap in the transfer line to concentrate the desorbed sample (Section 12). The desorbed sample,
contained in the purge gas, is routed to the gas chromatograph and capillary column either directly to the column or by way of
a heated transfer line. Contaminants from the outer surfaces of tubes should be excluded from the sample flow path. If the design
of the given TD means contaminants cannot be completely excluded, care should be taken to minimize contamination of the outer
surfaces of tubes (for example, from finger oils, grease, etc.) for example, by wearing clean white cotton gloves when handling
the tubes in the field and laboratory.
NOTE 4—Leak testing should be carried out under no-flow conditions, at low temperature, and at column head pressure such that it is suitably stringent,
but does not compromise sample integrity. out. Tubes that fail the leak test should not be analyzed but resealed to await user intervention.
D6196 − 23
NOTE 5—Internal standard addition to the sampling end of every sample tube can be used as an additional or alternative check on sample integrity,
however, without a pre-desorption leak test (Note 4) results from leaking samples will be lost.
7.6 Sorbent Tube End Caps, to combine two or more tubes together in series during pumped sampling. They typically comprise
6.4 mm OD stainless steel couplings fitted with combined (one-piece) PTFE ferrule seals.
7.7 Sorbent Tube Unions (pumped sampling only), to combine two or more tubes in series during pumped sampling constructed
of stainless steel couplings with combined (one-piece) PTFE ferrule seals.
7.8 Syringes, a precision 11 μL or 5 μL liquid syringe readable to 0.010.01 μL or 0.05 μL, a precision 10-μL gas tight syringe
readable to 0.1 μL and a precision 10-mL gas tight syringe readable to 0.1 mL.
7.9 Sampling Pump, conforming to the performance requirements of 8.3.1.
7.10 Connecting Tubing (pumped sampling only), if tubing is required upstream (for example, for connecting between the
sampling point and the sample tube when sampling in a remote location), inert PTFE tubing should be used and should be replaced
regularly. Any tubing used downstream of the sampler (that is, for connecting the non-sampling end of the tube to the pump) does
not need to be inert and can be of any suitable material. For personal monitoring, the tube is typically worn as close as possible
to the breathing zone (for example, on the lapel of clothing), and the pump carried on a belt. In this case, clips should be provided
to hold the sample tube and connecting tubing to the wearer’s lapel area. This connecting tubing typically needs to be about 90-cm
long. All connections should be leak proof.
7.11 Soap Bubble Flow Meter or Electronic Flow Meter, for calibrating pump, desorb, and split flows.
7.12 Gas Chromatographic Apparatus:
7.12.1 Gas Chromatograph, fitted with a flame ionization, photo ionization, mass spectrometric, or other suitable detector. The
detector selected should be capable of detecting an injection of 0.5 ng toluene with a signal-to-noise ratio of at least 5:1.
7.12.2 Gas Chromatographic Column, capable of separating the analytes of interest from other components. Typical dimensions
are 5050 m or 60 m long fused silica capillary columns, 0.25 mm ID or 0.32 mm ID with a 0.5 to 5 micron 0.5 micron to 5 micron
film of an appropriate stationary phase.
7.13 Injection Facility for Preparing Standards, comprising a conventional packed column GC injection port may be used for
preparing sample tube standards. Ready-made injection systems for loading liquid or gas-phase standards onto the sampling end
of sorbent tubes are also available commercially. Essential components include a fitting for the sampling end of the tube, a
controllable flow of inert (carrier) gas through the injector body and a septum cap such that the liquid or gas standard can be
injected into the stream of gas at or near the sampling surface of the sorbent tube.
8. Reagents and Materials
8.1 Unless otherwise stated, all reagents shall conform to the specifications of the committee on Analytical Reagents of the
American Chemical Society, where such specifications are available. Other grades may be used, provided that it is ascertained
that use of the reagent does not lessen the accuracy of the practice.
8.2 Reagents:
8.2.1 Volatile Organic Compounds, for calibration. These should reflect the compounds of interest. Typical components are:
Reagent Chemicals, American Chemical Society Specifications, ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for
Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K.U.K., and the United States Pharmacopeia and National Formulary, U.S. PharmaceuticalPharmacopeial Convention,
Inc. (USPC), Rockville, MD.
D6196 − 23
propane, pentane, hexane, benzene, dichloromethane, 111-trichloroethane, methanol, ethanol, n-butanol, methyl acetate,
2-methoxyethanol, methyl ethyl ketone, acetonitrile, n-butyl acetate, }-pinene, decane, ethylene oxide, propylene oxide, and
hexanal.
8.2.2 Solvent, of chromatographic quality, free from compounds co-eluting with the compound or compounds of interest (8.2.1).
Methanol is most commonly used because it can often be selectively purged from tubes packed with weaker sorbents prior to
standard analysis. However, alternative dilution solvents, for example, ethyl acetate or cyclohexane can be used, particularly if
there is a possibility of reaction or chromatographic co-elution.
8.3 Sorbents, particle size, in the range 20 to 80 mesh, typically 35–60 35 to 60 mesh. Medium strength porous polymer sorbents
(Appendix X1) which are prone to shrinkage should be preconditioned under a flow of inert gas by heating, at a temperature at
least 25°C25 °C below the published maximum for that sorbent, for 16 h, before packing the tubes. If tubes are packed with
unconditioned sorbent, they should be stringently conditioned at a temperature just below (10 to 25°C)(10 °C to 25 °C) the
maximum recommended temperature of the least stable sorbent in the tube for not less than 2 h, with a flow of at least 100 mL/min
pure, inert carrier gas. The flow direction shall be opposite to that used during sampling. The lowest effective analytical desorption
temperature shall be used (13.4) to minimize artifact levels. Temperatures shall be kept below those used for conditioning. Sorbent
tubes prepacked by the manufacturer are also available with or without pre-conditioning.
8.3.1 Sorbent selection is determined by sorbent strength, typically assessed in terms of retention of the compound of interest (see
Annex A2) – or breakthrough volume (that is, the volume of air that can be sampled before the concentration of analyte breaking
through the sorbent and exiting from the far end of the tube becomes significant – typically >5 %) – see Annex A1. In essence,
the sorbent or sorbents selected must be strong enough for complete retention of all the compounds of interest during sampling
and weak enough for effective release of all the compounds of interest (under reasonable analytical conditions) during subsequent
thermal desorption.
NOTE 6—Analyte breakthrough (loss) from the far end of a sorbent tube during pumped sampling is not a function of sampler ‘capacity’ in the normal
sense of the word – that is, it does not indicate that the sorbent tube is ‘full’ or ‘saturated’ with that analyte under the given conditions. It is, more
accurately, a chromatographic function, relating to the affinity of the analyte (sorbate) for the sorbent. Breakthrough, to a large extent, will be unaffected
by analyte concentration or loading in the same way that chromatographic retention times are constant for a given analyte however big or small the peak.
Studies have shown that the breakthrough volume of a given analyte on a given sorbent tube remains constant for air concentrations up to 100 ppm (12).
8.3.1.1 In the case of pumped sampling, single-bed tubes containing a weak porous polymer (W-PP) sorbent are appropriate for
normal alkanes ranging in volatility from n-C (hexane) or n-C (depending on required air sample volume) up to n-C or n-C
6 7 22 30
(depending on analytical thermal desorption capabilities and conditions). More volatile materials should be sampled on stronger
sorbents, such as medium to strong graphitized carbon blacks (MS-GCB) or carbon molecular sieves (CMS). Example sorbents
and their respective applications are given in Appendix X1. A broader range of VOCs may be sampled using multi-bed tubes, that
is, sampling tubes packed with two or more sorbents, arranged in discrete layers in order of increasing sorbent strength from the
sampling end.
8.3.1.2 Guidance given for the selection of sorbents for pumped monitoring tubes can be applied equally well to axial passive
sampling tubes because, in this case, sufficient sorbent strength (breakthrough volume) equates to low back diffusion and stable
uptake rates. The restriction to a single sampling surface (hence single sorbent) limits the target analyte range that can be monitored
by any one passive sampling tube. However, the unobtrusive nature and low cost of passive samplers usually means that two or
more samplers containing different sorbents can be used in parallel without impacting study objectives.
8.3.1.3 The high sampling rate and associated increased risk of back diffusion associated with radial diffusion typically limits these
samplers to compounds of equal or lower volatility than benzene. It also means that stronger sorbents are generally required when
compared with sampling the same compounds using either axial passive or pumped sorbent tubes.
8.3.1.4 A guide for selection of sorbents for pumped and axial diffusive sampling is given in Appendix X1. Equivalent sorbents
may be used. Information on sorbent conditioning and analytical desorption parameters is given in Appendix X1 and is also
available from manufacturers.
8.3.2 Apparent sorbent strength (breakthrough volumes) may be reduced when air concentrations exceed 100 ppm (in the same
way that retention times may fall slightly when a packed GC column is overloaded), but pumped sampling volumes or diffusive
sampling times are invariably minimized when sampling under such extreme conditions so this effect is rarely a significant limiting
factor.
D6196 − 23
8.3.3 Sorbent tube artifacts are <1ng for typical sampling tubes (7.2) containing well-conditioned carbonaceous sorbents such as
graphitized carbon blacks (GCBs) and carbon molecular sieves (CMSs); at 11 ng to 5 ng levels for thermally stable weak porous
polymer (W-PP) sorbents and at 55 ng to 50 ng levels for the range of medium strength porous polymer (M-PP) sorbents.
NOTE 7—Use of M-PP sorbents is in decline due to their inherent high and variable background levels. Data relating to M-PP sorbents is designated using
gray font in this standard to indicate these sorbents should be used with caution.
NOTE 8—Inherent artifact levels will increase significantly with desorption temperature. The lowest effective desorption temperature should always be
used.
8.4 Calibration Standards:
8.4.1 Gas standards suitable for introducing target compounds to the sampling end of conditioned sorbent tubes at the levels of
interest provide an optimum calibration option for air monitoring methods because they allow analytes to be introduced to the
sorbent in a way which is closely analogous to air sampling and which introduces no potential interferences – for example, solvent.
However, certified gas standards are difficult and expensive to obtain at trace (ppb) levels and stable gas standards are not available
for all compounds – for example; higher boiling VOCs, polar compounds, reactive species and semi-volatile organics.
8.4.2 Calibration Solutions for Ambient and Indoor Air:
8.4.2.1 Solution Containing Approximately 100 μg/mL of Each Liquid Component—Accurately weigh approximately 10 mg of
substance or substances of interest into a 100 mL volumetric flask, starting with the least volatile substance. Make up to 100 mL
with solvent (8.2.2), stopper and shake to mix.
8.4.2.2 Solutions Containing Approximately 1 mg/mL of Liquid Components—Introduce 50 mL of methanol into a 100 mL
volumetric flask. Add 10 mL of solution (8.4.2.1) Make up to 100 mL with methanol, stopper and shake to mix.
8.4.2.3 Solution Containing Approximately 10 μg/mL of Liquid Components—Introduce 50 mL of methanol into a 100 mL
volumetric flask. Add 10 mL of solution (8.4.2.1). Make up to 100 mL with solvent, stopper and shake to mix.
8.4.2.4 Solution Containing Approximately 10 μg/mL of Gas Components—For gases, for example, ethylene oxide, prepare a low
level calibration solution as follows. Obtain pure gas at atmospheric pressure by filling a small plastic gas bag from a gas cylinder.
Fill a 10-μL gas-tight syringe with 10 μL of the pure gas and close the valve of the syringe. Using a 2-mL septum vial, add 2-mL
methanol and close with the septum cap. Insert the tip of the syringe needle through the septum cap into the methanol. Open the
valve and withdraw the plunger slightly to allow the solvent to enter the syringe. The action of the gas dissolving creates a vacuum,
and the syringe fills with solvent. Return the solution to the flask. Flush the syringe twice with the solution and return the washings
to the flask. Calculate the mass of gas added using the gas laws; that is, 1 mol of gas at STP occupies 22.4 L.
8.4.3 Calibration Solutions for Workplace Air:
8.4.3.1 Solution Containing Approximately 10 mg/mL of Each Liquid Component—Accurately weigh approximately 1 g of
substance or substances of interest into a 100 mL volumetric flask, starting with the least volatile substance. Make up to 100 mL
with solvent (8.2.2), stopper and shake to mix.
8.4.3.2 Solutions Containing Approximately 1 mg/mL of Liquid Components—Introduce 50 mL of solvent into a 100 mL
volumetric flask. Add 10 mL of solution (8.4.3.1) Make up to 100 mL with solvent, stopper and shake to mix.
8.4.3.3 Solution Containing Approximately 1 mg/mL of Gas Components—For gases, for example, ethylene oxide, prepare a low
level calibration solution as follows. Obtain pure gas at atmospheric pressure by filling a small plastic gas bag from a gas cylinder.
Fill a 1 mL gas-tight syringe with 1 mL of the pure gas and close the valve of the syringe. Using a 2 mL septum vial, add 2 mL
solvent and close with the septum cap. Insert the tip of the syringe needle through the septum cap into the solvent. Open the valve
and withdraw the plunger slightly to allow the solvent to enter the syringe. The action of the gas dissolving creates a vacuum, and
the syringe fills with solvent. Return the solution to the flask. Flush the syringe twice with the solution and return the washings
to the flask. Calculate the mass of gas added using the gas laws, that is, 1 mol of gas at STP occupies 22.4 litres.L.
8.4.4 Loading Sorbent Tubes with Calibration Standards—Prepare fresh liquid standard solutions weekly, or more frequently if
evidence is noted of deterioration, for example, condensation reactions between alcohols and ketones.
D6196 − 23
8.5 Loaded Sorbent Tubes—Loaded sorbent tubes may be prepared and used for the calibration of all 3 sorbent-based monitoring
methods described in this standard; axial and radial passive samplers and pumped sorbent tubes. Prepare loaded sorbent tubes by
connecting the sampling end of blank, conditioned sorbent tubes to a metered source of gas-phase stan
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