ASTM D6552-06(2021)
(Practice)Standard Practice for Controlling and Characterizing Errors in Weighing Collected Aerosols
Standard Practice for Controlling and Characterizing Errors in Weighing Collected Aerosols
SIGNIFICANCE AND USE
4.1 The weighing of collected aerosol is one of the most common and purportedly simple analytical procedures in both occupational and environmental atmospheric monitoring (for example, Test Method D4532 or D4096). Problems with measurement accuracy occur when the amount of material collected is small, owing both to balance inaccuracy and variation in the weight of that part of the sampling medium that is weighed along with the sample. The procedures presented here for controlling and documenting such analytical errors will help provide the accuracy required for making well-founded decisions in identifying, characterizing, and controlling hazardous conditions.
4.2 Recommendations are given as to materials to be used. Means of controlling or correcting errors arising from instability are provided. Recommendations as to the weighing procedure are given. Finally, a method evaluation procedure for estimating weighing errors is described.
4.3 Recommendations are also provided for the reporting of weights relative to LOD (see 3.2.6) and LOQ (see 3.2.7). The quantities, LOD and LOQ, are computed as a result of the method evaluation.
SCOPE
1.1 Assessment of airborne aerosol hazards in the occupational setting entails sampling onto a collection medium followed by analysis of the collected material. The result is generally an estimated concentration of a possibly hazardous material in the air. The uncertainty in such estimates depends on several factors, one of which relates to the specific type of analysis employed. The most commonly applied method for analysis of aerosols is the weighing of the sampled material. Gravimetric analysis, though apparently simple, is subject to errors from instability in the mass of the sampling medium and other elements that must be weighed. An example is provided by aerosol samplers designed to collect particles so as to agree with the inhalable aerosol sampling convention (see ISO 7708, Guide D6062, and EN 481). For some sampler types, filter and cassette are weighed together to make estimates. Therefore, if the cassette, for example, absorbs or loses water between the weighings required for a concentration estimation, then errors may arise. This practice covers such potential errors and provides solutions for their minimization.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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.
1.4 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.
General Information
Relations
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: D6552 − 06 (Reapproved 2021)
Standard Practice for
Controlling and Characterizing Errors in Weighing Collected
Aerosols
This standard is issued under the fixed designation D6552; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 Assessment of airborne aerosol hazards in the occupa-
D1356Terminology Relating to Sampling and Analysis of
tional setting entails sampling onto a collection medium
Atmospheres
followed by analysis of the collected material. The result is
D4096Test Method for Determination of Total Suspended
generally an estimated concentration of a possibly hazardous
ParticulateMatterintheAtmosphere(High–VolumeSam-
material in the air. The uncertainty in such estimates depends
pler Method)
on several factors, one of which relates to the specific type of
D4532Test Method for Respirable Dust in Workplace At-
analysis employed. The most commonly applied method for
mospheres Using Cyclone Samplers
analysis of aerosols is the weighing of the sampled material.
D6062GuideforPersonalSamplersofHealth-RelatedAero-
Gravimetric analysis, though apparently simple, is subject to
sol Fractions
errorsfrominstabilityinthemassofthesamplingmediumand
2.2 International Standards:
other elements that must be weighed. An example is provided
EN 481Workplace Atmospheres — Size Fraction Defini-
by aerosol samplers designed to collect particles so as to agree
tions for Measurement ofAirborne Particles in the Work-
with the inhalable aerosol sampling convention (see ISO 7708,
place
Guide D6062, and EN 481). For some sampler types, filter and
EN 13205Workplace Atmospheres — Assessment of Per-
cassette are weighed together to make estimates. Therefore, if
formance of Instruments for Measurement of Airborne
the cassette, for example, absorbs or loses water between the
Particle Concentrations
weighings required for a concentration estimation, then errors
2.3 ISO Standards:
may arise. This practice covers such potential errors and
ISO 7708Air quality — Particle size fraction definitions for
provides solutions for their minimization.
health-related sampling
ISO20581Workplaceatmospheres—Generalrequirements
1.2 The values stated in SI units are to be regarded as
for performance of procedures for the measurement of
standard. No other units of measurement are included in this
chemical agents
standard.
ISO 20988Air quality — Guidelines for estimating mea-
1.3 This standard does not purport to address all of the
surement uncertainty
safety concerns, if any, associated with its use. It is the
ISO GUMGuide to the Expression of Uncertainty in Mea-
responsibility of the user of this standard to establish appro-
surement (1998)
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3. Terminology
1.4 This international standard was developed in accor-
3.1 Definitions:
dance with internationally recognized principles on standard-
3.1.1 For definitions of terms used in this practice, refer to
ization established in the Decision on Principles for the
Terminology D1356.
Development of International Standards, Guides and Recom-
3.2 Definitions of Terms Specific to This Standard:
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality the ASTM website.
and is the direct responsibility of Subcommittee D22.04 on WorkplaceAir Quality. Available from European Committee for Standardization (CEN), Avenue
Current edition approved Sept. 1, 2021. Published October 2021. Originally Marnix 17, B-1000, Brussels, Belgium, http://www.cen.eu.
approved in 2000. Last previous edition approved in 2016 as D6552–06 (2016). Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
DOI: 10.1520/D6552-06R21. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6552 − 06 (2021)
3.2.1 blank substrate, n—a collection medium or substrate
f = substrate index (1, ., F)
coming from the same batch as the sampling medium, but
F = number of substrates (for example, filters) in
unexposed.
each batch tested in method evaluation
γ = method evaluation error rate
3.2.2 equilibration time, n—For the purposes of this
LOD (µg) = limit of detection:3×s
w
practice, a time constant (seconds) characterizing an approxi-
LOD (µg) = LOD confidence limit
1-γ
mateexponentiallydampedapproachofthemassofanaerosol
LOQ (µg) = limit of quantitation: 10 × s
w
collection medium to a constant value. The constant can be
LOQ (µg) = LOQ confidence limit
1-γ
defined as the mean difference of the mass from equilibrium
N = number of blanks per substrate set
b
per mean mass loss or gain rate as measured over a finite time
ν = number of degrees of freedom in method
interval.
evaluation
3.2.2.1 Discussion—There may be important instances in
Φ = cumulative normal function
which several time constants are required to describe the
χ = chi-square random variable
approach to equilibrium.
χ = chi-square quantile (that is, a fixed number
γ,ν
3.2.3 estimated overall uncertainty (U), n—2 × estimated that exceeds the random variable χ at prob-
ability γ)
standard deviation of estimated mass, in the case of negligible
RH = relative humidity
uncorrectable bias (see ISO 20581).
u (µg) = uncertainty component in two balance
3.2.4 field blank, n—a blank substrate that undergoes the
readings, an estimate of σ
same handling as the sample substrate, generally including
u (µg) = weighing uncertainty, estimate of σ
w w
conditioning and loading into the samplers or transport
σ (µg) = uncorrectable (for example, by way of blank
containers, as well as transportation to the sampling site, but
correction) standard deviation in (single)
without being exposed.
mass-change measurement
3.2.4.1 Discussion—If blanks are not actually loaded into
σ (µg) = confidence limit on σ
1-γ
samplers, losses due to handling could be underestimated.
σ (µg) = standard deviation in collected mass determi-
w
3.2.5 lab blank, n—a blank substrate that undergoes the nation
U = overall uncertainty
same handling as the sample substrate in the laboratory,
including conditioning and loading into the samplers or trans-
4. Significance and Use
port containers when this is done in the laboratory.
4.1 The weighing of collected aerosol is one of the most
3.2.6 limit of detection (LOD), n—a value for which ex-
common and purportedly simple analytical procedures in both
ceedence by measured mass indicates the presence of a
occupational and environmental atmospheric monitoring (for
substance at given false-positive rate: 3 × estimated standard
example, Test Method D4532 or D4096). Problems with
deviation of the measured blank substrate mass (see Annex
measurement accuracy occur when the amount of material
A2).
collected is small, owing both to balance inaccuracy and
3.2.7 limit of quantitation (LOQ), n—a value for which
variationintheweightofthatpartofthesamplingmediumthat
exceedence by measured mass indicates the quantitation of a
is weighed along with the sample. The procedures presented
substanceatgivenaccuracy:10×estimatedstandarddeviation
here for controlling and documenting such analytical errors
of the measured blank substrate mass (see Annex A2).
will help provide the accuracy required for making well-
3.2.8 substrate, n—sampling filter, foam, and so forth to-
founded decisions in identifying, characterizing, and control-
gether with whatever mounting is weighed as a single item.
ling hazardous conditions.
3.2.8.1 Discussion—The 25 or 37-mm plastic filter cassette
4.2 Recommendations are given as to materials to be used.
often used for total dust sampling in either its closed-face or
Means of controlling or correcting errors arising from insta-
open-face version is NOTpart of the substrate in the definition
bility are provided. Recommendations as to the weighing
above, since it is not weighed.
procedure are given. Finally, a method evaluation procedure
3.3 Symbols:
for estimating weighing errors is described.
4.3 Recommendations are also provided for the reporting of
α = detection error rate
B = numberofsubstratebatchesinmethodevalu- weights relative to LOD (see 3.2.6) and LOQ (see 3.2.7). The
ation quantities, LOD and LOQ, are computed as a result of the
b = batch index (1, ., B) method evaluation.
β = mean substrate mass change during evalua-
5. Weight Instability, Causes, and Minimization
tion experiment
CV = maximum relative error acceptable in quan-
max 5.1 Weight instability of sampling substrates may be attrib-
tifying collected mass
uted to several causes. The following subclauses address the
∆m (µg) = substrate mass change
fb
more important of these.
ε (µg) = substrateweight-changerandomvariablerep-
b
5.1.1 Moisture Sorption:
resenting inter-batch variability
5.1.1.1 Moisture sorption is the most common cause of
ε (µg) = substrate weight change residual random
fb
weight instability. Water may be directly collected by the filter
variable with variance σ
or foam or other substrate material that is weighed. Water
D6552 − 06 (2021)
istheonlyformofanalysis.Preferablynonsorptivemediashouldbeused.
sorption by any part of the sampling system that is weighed
must be suspected as well. For example, the sampling cassette
5.1.4 Handling Damage—Lawless and Rodes (7) give rec-
itself,ifweighed,maybethecauseofsignificanterror (1) (see
ommendations on minimizing balance-operator effects. If fri-
also 8.2.2).
able substrates are used, procedures are needed to avoid
5.1.1.2 The effects of water sorption can be reduced by
mechanical damage during gravimetric analysis.
using nonsorptive materials. However, there may exist specific
5.1.4.1 The air sampling equipment should be designed so
sampling needs for which a hydrophobic material is not
that the substrate is not damaged during assembly and disas-
feasible. Table 1 presents a list of common aerosol sampling
sembly.
substrates with different water adsorption features.
5.1.4.2 Flat tipped forceps are recommended for handling
filters. Nonoxidizing metal tins may be used to weigh delicate
NOTE 1—Gonzalez-Fernandez, Kauffer et al, and Lippmann (2-4)
provide further details. Also, Vaughan et al (5) report that filters of
substrates without direct handling.
evidently the same material, but originating from different manufacturers,
5.1.4.3 Parts to be weighed shall not be touched with the
may have widely differing variabilities.
hands, unless gloved.
NOTE 2—There is generally a trade-off between hydrophobicity and
conductivity in many materials (6). Therefore, one must be aware of the
5.1.4.4 Handling shall take place in a clean environment to
possibility of creating sampling problems while reducing hygroscopicity.
avoid contamination.
NOTE 3—Pretreatments of substrates, such as greasing, may also affect
5.1.4.5 Gloves, if used, shall leave no residue on what is
water sorption.
weighed.
5.1.2 Electrostatic Effects—Electrostatic effects are a com-
5.1.5 Buoyancy Changes—Corrections (9) for air buoyancy,
monsourceofweighingproblems.Theseeffectscanusuallybe
equal to the density of air multiplied by the air volume
minimized by discharging the substrate through the use of a
displaced,arenotnecessaryforsmallobjects,suchasa37-mm
plasma ion source or a radioactive source. Using conductive
diameter membrane filter. However, there may exist circum-
materials may reduce such problems. Lawless and Rodes (7)
stances (for example, if an entire sampling cassette were
present details on electrostatic effects and their minimization
weighed without the use of correcting blanks) in which the
(see also Engelbrecht et al (8)).
object to be weighed is so large that buoyancy must be
5.1.3 Effects of Volatile Compounds (other than water)—
corrected. For example, if the volume weighed exceeds 0.1
Volatilecompoundsmaybepresentinunusedcollectionmedia
cm , then correction would be required to weigh down to 0.1
(3) or may be adsorbed onto media during sampling.
mgifpressurechangesoftheorderof10%betweenweighings
5.1.3.1 Desorption of volatiles from unused media may be
are expected. If such a correction is necessary, the atmospheric
controlled,forexample,byheatingoroxygenplasmatreatment
pressure and temperature at the time of weighing should be
prior to conditioning and weighing. Alternatively, losses may
recorded.
be compensated by the use of blanks (see Section 6).
5.1.3.2 When volatile materials collected during sampling
6. Correcting for Weight Instability
form part of the intended sample, standardized written proce-
duresarerequiredtoensurethatanylossesareminimizedorat 6.1 Recommended Method for Correction by Use of
Blanks—The use of blanks is the most important practical tool
least controlled, for example, by conditioning under tightly
specified conditions. for reducing errors due to weight instability. Correction for
weight instability depends on the specific application and
NOTE4—Whenvolatilematerialscollectedduringsamplingarenotpart
should follow a written procedure. The general principles are
of the intended sample, it may be difficult to eliminate them if weighing
as follows. Blank sampling media are exposed, as closely as
possible, to the same conditions as the active sampling media,
without actually drawing air through. Correction is effected by
The boldface numbers in parentheses refer to the list of references at the end of
this standard.
subtractingtheaverageblankweightgainfromtheweightgain
of the active samples. Of course, if the atmosphere to be
TABLE 1 Water Sorption Characteristics of Some Aerosol
sampledcontainswater(orothervolatile)droplets,thentheuse
Sampling Media
of blanks alone cannot correct. Kauffer et al (3) note that
Substrate or Cassette Type Very Low Low High Very High
blanks may also offer correction for filter material losses.
Cellulose fiber filter *
Blanks shall be matched to samples, that is, if the sample
Glass fiber filter *
consists of a filter within a cassette
...
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