ASTM D6246-08(2018)
(Practice)Standard Practice for Evaluating the Performance of Diffusive Samplers
Standard Practice for Evaluating the Performance of Diffusive Samplers
SIGNIFICANCE AND USE
5.1 Gas or vapor sampling is often accomplished by actively pumping air through a collection medium such as activated charcoal. Problems associated with a pump – inconvenience, inaccuracy, and expense – are inextricable from this type of sampling. The alternative covered by this practice is to use diffusion for moving the compound of interest onto the collection medium. This approach to sampling is attractive because of the convenience of use and low total monitoring cost.
5.2 However, previous studies have found significant problems with the accuracy of some samplers. Therefore, although diffusive samplers may provide a plethora of data, inaccuracies and misuse of diffusive samplers may yet affect research studies. Furthermore, worker protections may be based on faulty assumptions. The aim of this practice is to counter the uncertainties in diffusive sampling through achieving a broadly accepted set of performance tests and acceptance criteria for proving the efficacy of any given diffusive sampler intended for use.
SCOPE
1.1 This practice covers the evaluation of the performance of diffusive samplers of gases and vapors for use over sampling periods from 4 to 12 h and for wind speeds less than 0.5 m/s. Such sampling periods and wind speeds are the most common in the indoor workplace setting. This practice does not apply to static or area sampling in wind speeds less than 0.1 m/s, when diffusion outside the sampler may dominate needed convection from the ambient air to the vicinity of the sampler. Given a suitable exposure chamber, the practice can be extended to cover sampler use for other sampling periods and conditions. The aim is to provide a concise set of experiments for classifying samplers primarily in accordance with a single sampler accuracy figure. Accuracy is defined (3.2.2) in this standard so as to take into account both imprecision and uncorrected bias. Accuracy estimates refer to conditions of sampler use which are normally expected in a workplace setting. These conditions may be characterized by the temperature, atmospheric pressure, humidity, and ambient wind speed, none of which may be constant or accurately known when the sampler is used in the field. Furthermore, the accuracy accounts for the effects of diffusive loss of analyte on the estimation of time-weighted averages of concentrations which may not be constant in time. Aside from accuracy, the samplers are tested for compliance with the manufacturer’s stated limits on capacity, possibly in the presence of interfering compounds.
1.2 This practice is an extension of previous research on diffusive samplers (1-14)2 as well as Practices D4597, D4598, D4599, and MDHS 27. An essential advance here is the estimation of sampler accuracy under actual conditions of use. Furthermore, the costs of sampler evaluation are reduced.
1.3 Knowledge gained from similar analytes expedites sampler evaluation. For example, interpolation of data characterizing the sampling of analytes at separated points of a homologous series of compounds is recommended. At present the procedure of (9) is suggested. Following evaluation of a sampler in use at a single homologous series member according to the present practice, higher molecular weight members would receive partial validations considering sampling rate, capacity, analytical recovery, and interferences. The test for diffusive analyte loss can be omitted if the effect is found negligible for a given sampler or analyte series.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
1.6 This international stan...
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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: D6246 − 08 (Reapproved 2018)
Standard Practice for
Evaluating the Performance of Diffusive Samplers
This standard is issued under the fixed designation D6246; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope the procedure of (9) is suggested. Following evaluation of a
sampler in use at a single homologous series member accord-
1.1 This practice covers the evaluation of the performance
ing to the present practice, higher molecular weight members
ofdiffusivesamplersofgasesandvaporsforuseoversampling
would receive partial validations considering sampling rate,
periods from 4 to 12 h and for wind speeds less than 0.5 m/s.
capacity, analytical recovery, and interferences. The test for
Such sampling periods and wind speeds are the most common
diffusive analyte loss can be omitted if the effect is found
intheindoorworkplacesetting.Thispracticedoesnotapplyto
negligible for a given sampler or analyte series.
static or area sampling in wind speeds less than 0.1 m/s, when
diffusion outsidethesamplermaydominateneededconvection 1.4 The values stated in SI units are to be regarded as
from the ambient air to the vicinity of the sampler. Given a standard. No other units of measurement are included in this
suitable exposure chamber, the practice can be extended to standard.
cover sampler use for other sampling periods and conditions.
1.5 This standard does not purport to address all of the
The aim is to provide a concise set of experiments for
safety concerns, if any, associated with its use. It is the
classifying samplers primarily in accordance with a single
responsibility of the user of this standard to establish appro-
sampler accuracy figure. Accuracy is defined (3.2.2) in this
priate safety, health, and environmental practices and deter-
standard so as to take into account both imprecision and
mine the applicability of regulatory limitations prior to use.
uncorrected bias. Accuracy estimates refer to conditions of
1.6 This international standard was developed in accor-
sampler use which are normally expected in a workplace
dance with internationally recognized principles on standard-
setting. These conditions may be characterized by the
ization established in the Decision on Principles for the
temperature, atmospheric pressure, humidity, and ambient
Development of International Standards, Guides and Recom-
wind speed, none of which may be constant or accurately
mendations issued by the World Trade Organization Technical
known when the sampler is used in the field. Furthermore, the
Barriers to Trade (TBT) Committee.
accuracyaccountsfortheeffectsofdiffusivelossofanalyteon
the estimation of time-weighted averages of concentrations
2. Referenced Documents
which may not be constant in time. Aside from accuracy, the 3
2.1 ASTM Standards:
samplers are tested for compliance with the manufacturer’s
D1356Terminology Relating to Sampling and Analysis of
statedlimitsoncapacity,possiblyinthepresenceofinterfering
Atmospheres
compounds.
D4597Practice for Sampling Workplace Atmospheres to
1.2 This practice is an extension of previous research on Collect Gases or Vapors with Solid Sorbent Diffusive
diffusive samplers (1-14) as well as Practices D4597, D4598,
Samplers
D4599, and MDHS 27. An essential advance here is the D4598Practice for Sampling Workplace Atmospheres to
estimation of sampler accuracy under actual conditions of use.
Collect Gases or Vapors with Liquid Sorbent Diffusional
Furthermore, the costs of sampler evaluation are reduced. Samplers (Withdrawn 1995)
D4599Practice for Measuring the Concentration of Toxic
1.3 Knowledgegainedfromsimilaranalytesexpeditessam-
Gases or Vapors Using Length-of-Stain Dosimeters
pler evaluation. For example, interpolation of data character-
2.2 International Standards:
izing the sampling of analytes at separated points of a
CENEN838EuropeanStandard,WorkplaceAtmospheres–
homologous series of compounds is recommended.At present
Diffusive Samplers for the Determination of Gases or
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality
and is the direct responsibility of Subcommittee D22.04 on WorkplaceAir Quality. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2018. Published October 2018. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ɛ1
approved in 1998. Last previous edition approved in 2013 as D6246–08 (2013) . Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D6246-08R18. the ASTM website.
2 4
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof The last approved version of this historical standard is referenced on
this standard. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6246 − 08 (2018)
Vapours – Requirements and Test Methods
h = humidity (expressed as partial pressure)
MDHS 27Protocol for Assessing the Performance of a
n = number of diffusive samplers tested for measur-
Diffusive Sampler, Health and Safety Laboratory, United
ing sampler capacity
Kingdom p = atmospheric pressure
MDHS 80Volatile Organic Compounds in Air, Health and RSD = overall (true) relative standard deviation of con-
centration estimates (dependent on assumed en-
Safety Laboratory, United Kingdom
vironmental variability) expressed relative to a
3. Terminology
“true” concentration
RSD = relative standard deviation characterizing inter-
run
3.1 Definitions:
run chamber variability
3.1.1 For definitions of terms used in this practice, refer to
RSD = inter-sampler imprecision (relative to the refer-
s
Terminology D1356.
ence concentration)
3.2 Definitions of Terms Specific to This Standard:
RŜD = estimated inter-sampler imprecision RSD
s s
3.2.1 diffusive sampler, n—a device which is capable of
RSD = pulse-induced imprecision
t
takingsamplesofgasesorvaporsfromtheatmosphereatarate
RŜD = estimated overall relative standard deviation
controlled by a physical process such as gaseous diffusion
RSD
through a static air layer or permeation through a membrane,
RŜD = 95% confidence limit on the overall relative
95%
butwhichdoesnotinvolvetheactivemovementofairthrough
standard deviation RSD
the sampler. As such, direct-reading dosimeters, as well as
s = estimated standard deviation characterizing
samplers requiring lab analysis, are considered diffusive sam-
inter-sampler imprecision
plers within this practice.
t (υ) = value which, at probability 95%, exceeds ran-
0.95
dom variables distributed according to the stu-
3.2.2 symmetric accuracy range A, n—the fractional range,
symmetric about the true concentration c, within which 95% dentized t-distribution with υ degrees of free-
of sampler measurements are to be found (14-19). In terms of dom
T = temperature
the bias ∆ relative to true concentrations and the total (true)
v (m/s) = ambient wind speed
relative standard deviation RSD (sometimes designated as
α = concentration estimate dependence on environ-
x
TRSD), the accuracy rangeAis closely approximated (19) by:
mental variable x (T, h, v, or c).
2 2
1.960 3=∆ 1RSD,if ?∆?,RSD/1.645
∆ = bias relative to reference concentration c
A 5 (1)
H
ˆ
∆?11.645 3RSD, otherwise = estimated bias ∆
∆
?
ˆ
3.2.2.1 Discussion—In the case that bias is corrected, leav- = 95% confidence limit on the bias ∆
∆
95%
ingonlyanuncorrectableresidualbiasduetouncertaintyinthe
∆ = bias associated with concentration pulse
t
correction, 95%-confidence limits on A play the role of the υ = degrees of freedom in determining RSD
s
υ = effective number of degrees of freedom in de-
expanded uncertainty in (20). As described in (14), such an
eff
interpretation is an extension of (20) for measurement, as in termining RSD
σ = assumed concentration variability
occupational hygiene, of concentrations which are neither
c
σ = assumed humidity variability
spatially nor temporally constant. Rather than continually h
σ = assumed temperature variability
T
re-evaluating a method through estimate replicates, the accu-
σ = assumed ambient wind speed variability
v
racy provides confidence intervals bracketing (true) concentra-
tions at greater than a given probability (95%) for a fixed
4. Summary of Test Method
confidence (95%) in the initial sampler evaluation. Such
4.1 Bias, Inter-Sampler Imprecision and the Effects of
intervals with double confidence levels (in both measurement
Environmental Uncertainty:
and evaluation) are related to a branch of statistics known as
4.1.1 This practice gives a procedure for assessing the
the theory of tolerance or prediction intervals.
effects of variability in the following workplace variables:
3.3 Symbols:
temperature T, humidity h (expressed in terms of the water
vapor partial pressure to minimize interaction with the
A = symmetricaccuracyrangeasdefinedintermsof
temperature),theambientwindspeed vacrossthesamplerface
bias and imprecision
(see 4.7 regarding wind direction), and concentration c.An
 = estimated symmetric accuracy range A
experimentiscarriedoutwhichprovidesinformationaboutthe
A = 95% confidence limit on the symmetric accu-
95%
concentration estimates’ dependencies on these variables near
racy range A
conditions of intended sampler use (T , h , v , and c ). Testing
c(mg/m ) = true or reference analyte concentration
0 0 0 0
ĉ(mg/m ) = mean of (four) concentration estimates (includ- isrequiredattheconcentrationc ofintendeduse,aswellasat
concentrations reduced at least to c /2. Furthermore, the
ing (p, T)-corrections) obtained in accordance
with instructions of sampler manufacturer sampler bias and the inter-sampler standard deviation are
measured. Finally, the effect of diffusion of material out of the
sampler is measured. Pressure effects result in correctable bias
and are not evaluated in this practice (4.6).
Available from European Committee for Standardization (CEN), Avenue
4.1.2 Usingfoursamplersforeachoffiveexperimentalruns
Marnix 17, B-1000, Brussels, Belgium, http://www.cen.eu.
Available from HMSO Books, PO Box 276, London, England, SW8 5DT. (the minimum possible), the sensitivities α , α , α , and α
T h v c
D6246 − 08 (2018)
(relative to the chamber reference concentration and target 4.2.3 In some cases, the time-dependence of a workplace
environmental parameters) to changes in T, h, v, and c are concentrationcorrelatesstronglywiththesamplingperiod.For
measured, following the sampler manufacturer’s instructions example, a cleanup operation at the end of a workday could
regarding p- and T- corrections (if any). These experiments introducesolventonlythen.Thiscouldimplyapositivebiasin
alsogiveavaluefortheestimatedsamplerbias∆relativetothe the concentration estimates obtained from a day’s sampling.
chamber reference concentration (defined for the target condi- For simplicity, however, this practice is set up for assessing
tions). Two further runs describing time-effects (4.2.5) from performance of samplers for use in a concentration with
diffusive loss of analyte are also carried out. The chamber stationary fluctuations, so that time-dependent effects are
reference concentration must be traceable to primary standards treatedsimplyascomponentsofsamplervariance.Specifically,
of mass and volume. theeffectofanisolated0.5-hpulseoccurringatrandomwithin
the sampling period is estimated.
4.1.3 Errorintheestimatesofthesensitivities α , α , α ,and
T h v
α will exist on account of inter-sampler relative standard 4.2.4 Challengingsamplersto0.5-hpulsesissimilartotests
c
suggested by NIOSH (3) and CEN (EN 838).
deviation RSD and an inter-run chamber standard deviation
s
RSD . The latter results in part from uncertainty in the 4.2.5 Let ∆ (>0) represent one-half the bias between esti-
run t
matesfroma0.5-hpulseattheendversusthebeginningofthe
reference concentration. RSD is obtained by pooling the
s
samplingperiod,relativetothemeanoftheestimates.Assume,
variance estimates from each run and therefore is estimated
conservatively (see, for example, (6)), that the bias in the
with7×3=21 degrees of freedom (or 15 degrees of freedom
estimates of 0.5-h pulse occurring at random within (for
if the reverse diffusion experiment is omitted (1.3)). So as to
example,an8-hsamplingperiodrangesuniformlybetween–∆
avoid re-measurement at each sampler/analyte evaluation,
t
and +∆. Then the variance RSD associated with sampling a
RSD is obtained by a separate characterization of the
run t t
0.5-hpulseatrandomwithinthesamplingperiodisasfollows:
chamber with several runs at (for example) fixed environmen-
tal conditions. An example in which the sensitivities α and
2 2
RSD 5 ∆ (2)
RSD , are estimated is presented in the Annex A1.
t t
s
NOTE1—Itisuptotheuserastohowtraceabilityisestablished.Within
4.3 Capacity; Control of Effects from Interfering Com-
(12) the concentration estimate as calculated from the chamber’s analyte
pounds:
generation parameters is regarded as the benchmark, although an inde-
4.3.1 This practice provides a test for confirming a manu-
pendent estimate is required and must be within 5% of the calculated
facturer’s claimed sampler capacity under stated conditions of
estimate. If these estimates differ, then a third independent estimate is
required to establish the reference concentration through agreement with use. Such conditions would normally refer to a specific
one of the other independent estimates. One possibility for such an
sampling period and to environmental extremes, such as 80%
independent estimate is the mean of at least five independent, active
relative humidity at a temperature equal to 30°C.Additionally,
sampler estimates per run within the chamber. Experiment (12) on the
a manufacturer may claim a value of capacity for sampling in
accuracy of such reference measurements using sorbent tubes indicates
the presence of specific interferences at stated concentrations.
that a relative standard deviation of the order of 2% can be achieved for
the individual measurements. Alternatively, (3) requires averaging of at 4.3.2 Capacity is defined here as the sampled mass (or
least two independent methods (possibly including calculated estimates)
equivalentlyastheconcentrationataspecificsamplingperiod)
with at least four samples per method. EN 838 has adopted the looser
at which concentration estimate
...
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