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ASTM D 6196 Document Information:
Title
Standard Practice for Selection of Sorbents, Sampling, and Thermal Desorption Analysis Procedures for Volatile Organic Compounds in Air
ASTM International
Publication Date:
May 10, 2003
Scope:
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.
A complete listing of VOCs for which this practice has been tested, at
least over part of the
measurement range (1.6), is shown in Tables 1-9. For other compounds
this practice shall be tested
according to EN 1076 (pumped); Practice D 6246, ISO 16107, ANSI/ISEA
104, EN 838 or EN 13528-1/EN
13528-2 (diffusive); or other appropriate validation protocols
(Sections 13 and 14). (5,1)
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 tube or tubes
(diffusive or passive sampling). The sorbed VOCs are subsequently
recovered by thermal desorption
and analyzed by capillary gas chromatography.
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
diffusive samplers (typically
of the same physical dimensions as standard pumped sorbent tubes and
containing only one sorbent);
and (3) radial diffusive samplers.
This practice recommends a number of sorbents that can be packed in
sorbent tubes, for use in the
sampling of a wide range of different volatile organic compounds
boiling in the range 0 to
400°C (v.p. 15 to 0.01 kPa at 25°C).
For pumped sampling, sorbent selection is based on breakthrough
capacity. Single-bed tubes
containing for example sorbent Type A are appropriate for normal
alkanes from n-C6(hexane) to
n-C10(decane) and substances with similar volatility (v.p. 15 to 0.3
kPa at 25°C). More
volatile materials should be sampled on stronger sorbents, such as
sorbent Type B. Other sorbent
types than those specified may be used, if their breakthrough
capacities are adequate and their
thermal desorption blanks are sufficiently small. Examples are given
in Appendix X2. A broader
range of VOCs may be sampled using multi-bed tubes.
Guidance given for the selection of sorbents for pumped monitoring
tubes can be applied equally
well to axial diffusive sampling tubes. The restriction to a single
sampling surface (hence single
sorbent), limits the target analyte range that can be monitored by a
single tube. However, the
unobtrusive nature and low cost of diffusive samplers usually means
that two or more samplers
containing different sorbents can be used in parallel without
impacting study objectives.
The high sampling rate and associated risk of back diffusion
associated with radial diffusive
samplers typically restricts the use of these samplers to compounds of
equal or lower volatility
than benzene. It also means that stronger sorbents are generally
required for these samplers when
compared with either axial diffusive or pumped sorbent tubes.
This practice can be used for the measurement of airborne vapors of
these volatile organic
compounds over a wide concentration range.
With pumped sampling, this practice can be used for the 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 1-10 L air samples. The method is also suitable for the
measurement of the airborne
concentrations of individual components of volatile organic mixtures,
provided that the total
loading of the mixture does not exceed the capacity of the tube.
Quantitative measurements are
possible when using validated procedures with appropriate quality
assurance measures.
With axial diffusive sampling, this practice is valid for the
measurement of airborne vapors of
volatile organic compounds in a concentration range of approximately 2
mg/m³ to 10 mg/m³
for individual organic compounds for an exposure time of 8 h or 0.3
mg/m³ to 300 mg/m³
for individual organic compounds for an exposure time of four weeks.
The method is also suitable
for the measurement of the airborne concentrations of individual
components of volatile organic
mixtures provided that the total loading of the mixture does not
exceed the capacity of the tube.
With radial diffusive sampling, this practice is valid for the
measurement of airborne vapors of
volatile organic compounds in a concentration range of approximately
0.3 mg/m³ to 300
mg/m³ for individual organic compounds for exposure times of one
to six hours. The method is
also suitable for the measurement of the airborne concentrations of
individual components of
volatile organic mixtures provided that the total loading of the
mixture does not exceed the
capacity of the tube.
The upper limit of the useful range is set by the sorptive capacity of
the sorbent used, and by the
linear dynamic range of the gas chromatograph, column and detector, or
by the sample splitting
capability of the analytical instrumentation used. The sorptive
capacity is measured as a
breakthrough volume of air, which determines the maximum air volume
that must not be exceeded when
sampling with a pump.
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.
Artifacts are typically <1ng for typical sampling tubes (7.2)
containing well-conditioned
sorbent Type C and carbonaceous sorbents such as graphitized carbon,
carbon molecular sieves and
pure charcoals; at 1 to 5 ng levels for sorbent Type D and at 5 to 50
ng levels for other porous
polymers such as sorbent Type A and sorbent Type E. Method sensitivity
is typically limited to 0.5
µg/m³ for 10 L air samples with this latter group of
sorbent types because of their
inherent high background.
This procedure can be used for personal and fixed location sampling.
It cannot be used to measure
instantaneous or short-term fluctuations in concentration.
Alternatives for on-site measurement
include, but are not limited to gas chromatography and infrared
spectrometry.
The sampling method gives a time-weighted average result.
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 and
health practices and determine the applicability of regulatory
limitations prior to use.
Keywords:
- air
- ambient air
- diffusive sampling
- indoor air
- gas chromatographic analysis
- passive sampling
- pumped sampling
- volatile organic compounds
- workplace air
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