ASTM D6552-06(2016)
(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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D6552 − 06 (Reapproved 2016)
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 D4096Test Method for Determination of Total Suspended
ParticulateMatterintheAtmosphere(High–VolumeSam-
1.1 Assessment of airborne aerosol hazards in the occupa-
pler Method)
tional setting entails sampling onto a collection medium
D4532Test Method for Respirable Dust in Workplace At-
followed by analysis of the collected material. The result is
mospheres Using Cyclone Samplers
generally an estimated concentration of a possibly hazardous
D6062GuideforPersonalSamplersofHealth-RelatedAero-
material in the air. The uncertainty in such estimates depends
sol Fractions
on several factors, one of which relates to the specific type of
2.2 International Standards:
analysis employed. The most commonly applied method for
EN 481WorkplaceAtmospheres—Size Fraction Definitions
analysis of aerosols is the weighing of the sampled material.
for Measurement of Airborne Particles in the Workplace
Gravimetric analysis, though apparently simple, is subject to
EN 13205Workplace Atmospheres—Assessment of Perfor-
errorsfrominstabilityinthemassofthesamplingmediumand
mance of Instruments for Measurement of Airborne Par-
other elements that must be weighed. An example is provided
ticle Concentrations
by aerosol samplers designed to collect particles so as to agree
with the inhalable aerosol sampling convention (see ISO 7708,
2.3 ISO Standards:
Guide D6062, and EN 481). For some sampler types, filter and
ISO7708AirQuality—ParticleSizeFractionDefinitionsfor
cassette are weighed together to make estimates. Therefore, if
Health-related Sampling
the cassette, for example, absorbs or loses water between the
ISO 20581 Workplace Atmospheres—General Require-
weighings required for a concentration estimation, then errors
ments for Performance of Procedures for the Measure-
may arise. This practice covers such potential errors and
ment of Chemical Agents
provides solutions for their minimization.
ISO 20988Air Quality—Guidelines for Estimating Mea-
surement Uncertainty
1.2 The values stated in SI units are to be regarded as
ISO GUMGuide to the Expression of Uncertainty in Mea-
standard. No other units of measurement are included in this
surement (1998)
standard.
1.3 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
3.1.1 For definitions of terms used in this practice, refer to
priate safety and health practices and determine the applica-
Terminology D1356.
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents
3.2.1 blank substrate—a collection medium or substrate
2.1 ASTM Standards:
coming from the same batch as the sampling medium, but
D1356Terminology Relating to Sampling and Analysis of
unexposed.
Atmospheres
3.2.2 equilibrationtime—Forthepurposesofthispractice,a
time constant (seconds) characterizing an approximate expo-
1 nentiallydampedapproachofthemassofanaerosolcollection
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality
and is the direct responsibility of Subcommittee D22.04 on WorkplaceAir Quality. mediumtoaconstantvalue.Theconstantcanbedefinedasthe
Current edition approved Nov. 1, 2016. Published November 2016. Originally
approved in 2000. Last previous edition approved in 2011 as D6552–06 (2011).
DOI: 10.1520/D6552-06R16.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from European Committee for Standardization (CEN), Avenue
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Marnix 17, B-1000, Brussels, Belgium, http://www.cen.eu.
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 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 (2016)
mean difference of the mass from equilibrium per mean mass
N = number of blanks per substrate set
b
loss or gain rate as measured over a finite time interval.
ν = number of degrees of freedom in method
3.2.2.1 Discussion—There may be important instances in
evaluation
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)—2×estimatedstan-
that exceeds the random variable χ at prob-
dard deviation of estimated mass, in the case of negligible
ability γ)
uncorrectable bias (see ISO 20581).
RH = relative humidity
3.2.4 field blank—a blank substrate that undergoes the same u (µg) = uncertainty component in two balance
handling as the sample substrate, generally including condi-
readings, an estimate of σ
u (µg) = weighing uncertainty, estimate of σ
tioningandloadingintothesamplersortransportcontainers,as
w w
σ (µg) = uncorrectable (for example, by way of blank
well as transportation to the sampling site, but without being
correction) standard deviation in (single)
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—a blank substrate that undergoes the same
nation
handling as the sample substrate in the laboratory, including
U = overall uncertainty
conditioning and loading into the samplers or transport con-
tainers when this is done in the laboratory.
4. Significance and Use
3.2.6 limit of detection (LOD)—a value for which ex-
4.1 The weighing of collected aerosol is one of the most
ceedence by measured mass indicates the presence of a
common and purportedly simple analytical procedures in both
substance at given false-positive rate: 3 × estimated standard
occupational and environmental atmospheric monitoring (for
deviation of the measured blank substrate mass (see Annex
example, Test Method D4532 or D4096). Problems with
A2).
measurement accuracy occur when the amount of material
collected is small, owing both to balance inaccuracy and
3.2.7 limit of quantitation (LOQ)—a value for which ex-
variationintheweightofthatpartofthesamplingmediumthat
ceedence 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—sampling filter, foam, and so forth together
founded decisions in identifying, characterizing, and control-
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.
α = detection error rate 4.3 Recommendations are also provided for the reporting of
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-
tion experiment 5. Weight Instability, Causes, and Minimization
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
2 weight instability. Water may be directly collected by the filter
variable with variance σ
or foam or other substrate material that is weighed. Water
f = substrate index (1, ., F)
sorption by any part of the sampling system that is weighed
F = number of substrates (for example, filters) in
must be suspected as well. For example, the sampling cassette
each batch tested in method evaluation
itself,ifweighed,maybethecauseofsignificanterror (1) (see
γ = method evaluation error rate
also 8.2.2).
LOD (µg) = limit of detection:3×s
w
LOD (µg) = LOD confidence limit
1-γ
LOQ (µg) = limit of quantitation: 10 × s
w
The boldface numbers in parentheses refer to the list of references at the end of
LOQ (µg) = LOQ confidence limit
1-γ
this standard.
D6552 − 06 (2016)
5.1.1.2 The effects of water sorption can be reduced by 5.1.4.1 The air sampling equipment should be designed so
using nonsorptive materials. However, there may exist specific that the substrate is not damaged during assembly and disas-
sampling needs for which a hydrophobic material is not sembly.
feasible. Table 1 presents a list of common aerosol sampling 5.1.4.2 Flat tipped forceps are recommended for handling
substrates with different water adsorption features. filters. Nonoxidizing metal tins may be used to weigh delicate
substrates without direct handling.
NOTE 1—Gonzalez-Fernandez, Kauffer et al, and Lippmann (2-4)
5.1.4.3 Parts to be weighed shall not be touched with the
provide further details. Also, Vaughan et al (5) report that filters of
hands, unless gloved.
evidently the same material, but originating from different manufacturers,
may have widely differing variabilities.
5.1.4.4 Handling shall take place in a clean environment to
NOTE 2—There is generally a trade-off between hydrophobicity and
avoid contamination.
conductivity in many materials (6). Therefore, one must be aware of the
5.1.4.5 Gloves, if used, shall leave no residue on what is
possibility of creating sampling problems while reducing hygroscopicity.
weighed.
NOTE 3—Pretreatments of substrates, such as greasing, may also affect
5.1.5 Buoyancy Changes—Corrections (9) for air buoyancy,
water sorption.
equal to the density of air multiplied by the air volume
5.1.2 Electrostatic Effects—Electrostatic effects are a com-
displaced,arenotnecessaryforsmallobjects,suchasa37-mm
monsourceofweighingproblems.Theseeffectscanusuallybe
diameter membrane filter. However, there may exist circum-
minimized by discharging the substrate through the use of a
stances (for example, if an entire sampling cassette were
plasma ion source or a radioactive source. Using conductive
weighed without the use of correcting blanks) in which the
materials may reduce such problems. Lawless and Rodes (7)
object to be weighed is so large that buoyancy must be
present details on electrostatic effects and their minimization
corrected. For example, if the volume weighed exceeds 0.1
(see also Engelbrecht et al (8)).
cm , then correction would be required to weigh down to 0.1
5.1.3 Effects of Volatile Compounds (other than water)—
mgifpressurechangesoftheorderof10%betweenweighings
Volatilecompoundsmaybepresentinunusedcollectionmedia
are expected. If such a correction is necessary, the atmospheric
(3) or may be adsorbed onto media during sampling.
pressure and temperature at the time of weighing should be
5.1.3.1 Desorption of volatiles from unused media may be
recorded.
controlled,forexample,byheatingoroxygenplasmatreatment
prior to conditioning and weighing. Alternatively, losses may
6. Correcting for Weight Instability
be compensated by the use of blanks (see Section 6).
6.1 Recommended Method for Correction by Use of
5.1.3.2 When volatile materials collected during sampling
Blanks—The use of blanks is the most important practical tool
form part of the intended sample, standardized written proce-
for reducing errors due to weight instability. Correction for
duresarerequiredtoensurethatanylossesareminimizedorat
weight instability depends on the specific application and
least controlled, for example, by conditioning under tightly
should follow a written procedure. The general principles are
specified conditions.
as follows. Blank sampling media are exposed, as closely as
NOTE4—Whenvolatilematerialscollectedduringsamplingarenotpart possible, to the same conditions as the active sampling media,
of the intended sample, it may be difficult to eliminate them if weighing
without actually drawing air through. Correction is effected by
istheonlyformofanalysis.Preferablynonsorptivemediashouldbeused.
subtractingtheaverageblankweightgainfromtheweightgain
5.1.4 Handling Damage—Lawless and Rodes (7) give rec- of the active samples. Of course, if the atmosphere to be
ommendations on minimizing balance-operator effects. If fri-
sampledcontainswater(orothervolatile)droplets,thentheuse
able substrates are used, procedures are needed to avoid of blanks alone cannot correct. Kauffer et al (3) note that
mechanical damage during gravimetric analysis.
blanks may also offer correction for filter material losses.
Blanks shall be matched to samples, that is, if the sample
consists of a filter within a cassette that is weighed, the blank
shallbethesametypeoffilterwithinthesametypeofcassette.
6.1.1 An alternative procedure employs matched weight
TABLE 1 Water Sorption Characteristics of Some Aerosol
Sampling Media
filters consisting of two nearly equal-weight filters, one placed
in front of the other, with the sampler following employed as
Substrate or Cassette Type Very Low Low High Very High
Cellulose fiber filter *
blank. The collected mass is estimated simply by subtracting
Glass fiber filter *
thefiltermassesfollowingsampling.Analysisofuncertaintyis
Quartz fiber filter *
Cellulose ester membrane filter * similartothepresentationhere,butalsoinvolvesestimationof
Polytetrafluoroethylene filter *
the uncertainty of the filter matching.
P
...
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.
Designation: D6552 − 06 (Reapproved 2011) D6552 − 06 (Reapproved 2016)
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. 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
1.1 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 TR 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 givenstated 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D4096 Test Method for Determination of Total Suspended Particulate Matter in the Atmosphere (High–Volume Sampler
Method)
D4532 Test Method for Respirable Dust in Workplace Atmospheres Using Cyclone Samplers
D6062 Guide for Personal Samplers of Health-Related Aerosol Fractions
2.2 International Standards:
EN 481 Workplace Atmospheres—Size Fraction Definitions for Measurement of Airborne Particles in the Workplace
EN 482 Workplace Atmospheres—General Requirements for Performance of Procedures for the Measurement of Chemical
Agents
prENEN 13205 Workplace Atmospheres—Assessment of Performance of Instruments for Measurement of Airborne Particle
Concentrations
2.3 ISO Standards:
ISO TR 7708 Air Quality—Particle Size Fraction Definitions for Health-related Sampling
ISO GUM20581 Guide to the Expression of Uncertainty in Measurement (1993)Workplace Atmospheres—General Require-
ments for Performance of Procedures for the Measurement of Chemical Agents
ISO 20988 Air Quality—Guidelines for Estimating Measurement Uncertainty
This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.04 on Workplace Air Quality.
Current edition approved Oct. 1, 2011Nov. 1, 2016. Published October 2011November 2016. Originally approved in 2000. Last previous edition approved in 20062011
as D6552 - 06.D6552 – 06 (2011). DOI: 10.1520/D6552-06R11.10.1520/D6552-06R16.
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 the ASTM website.
Available from CEN Central Secretariat: rue de Stassart 36, B-1050 Brussels, Belgium.European Committee for Standardization (CEN), Avenue Marnix 17, B-1000,
Brussels, Belgium, http://www.cen.eu.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 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 (2016)
ISO GUM Guide to the Expression of Uncertainty in Measurement (1998)
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this practice, refer to Terminology D1356.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 blank substrate—a collection medium or substrate coming from the same batch as the sampling medium, but unexposed.
3.2.2 equilibration time—For the purposes of this practice, a time constant (seconds) characterizing an approximate
exponentially damped approach of the mass of an aerosol collection medium to a constant value. The constant can be defined as
the mean difference of the mass from equilibrium per mean mass loss or gain rate as measured over a finite time interval.
3.2.2.1 Discussion—
There may be important instances in which several time constants are required to describe the approach to equilibrium.
3.2.3 estimated overall uncertainty (U)—2 × estimated standard deviation of estimated mass, in the case of negligible
uncorrectable bias (see EN 482).ISO 20581).
3.2.4 field blank—a blank substrate that undergoes the same handling as the sample substrate, generally including conditioning
and loading into the samplers or transport containers, as well as transportation to the sampling site, but without being exposed.
3.2.4.1 Discussion—
If blanks are not actually loaded into samplers, losses due to handling could be underestimated.
3.2.5 lab blank—a blank substrate that undergoes the same handling as the sample substrate in the laboratory, including
conditioning and loading into the samplers or transport containers when this is done in the laboratory.
3.2.6 limit of detection (LOD)—a value for which exceedence by measured mass indicates the presence of a substance at given
false-positive rate: 3 × estimated standard deviation of the measured blank substrate mass (see Annex A2).
3.2.7 limit of quantitation (LOQ)—a value for which exceedence by measured mass indicates the quantitation of a substance
at given accuracy: 10 × estimated standard deviation of the measured blank substrate mass (see Annex A2).
3.2.8 substrate—sampling filter, foam, and so forth together with whatever mounting is weighed as a single item.
3.2.8.1 Discussion—
The 25 or 37-mm plastic filter cassette often used for total dust sampling in either its closed-face or open-face version is NOT part
of the substrate in the definition above, since it is not weighed.
3.3 Symbols:
α = detection error rate
B = number of substrate batches in method evaluation
b = batch index (1, ., B)
β = mean substrate mass change during evaluation experiment
CV = maximum relative error acceptable in quantifying collected mass
max
Δm (μg) = substrate mass change
fb
ε (μg) = substrate weight-change random variable representing inter-batch variability
b
ε (μg) = substrate weight change residual random variable with variance σ
fb
f = substrate index (1, ., F)
F = number of substrates (for example, filters) in each batch tested in method evaluation
γ = method evaluation error rate
LOD (μg) = limit of detection: 3 × s
w
LOD (μg) = LOD confidence limit
1-γ
LOQ (μg) = limit of quantitation: 10 × s
w
LOQ (μg) = LOQ confidence limit
1-γ
N = number of blanks per substrate set
b
ν = number of degrees of freedom in method evaluation
Φ = cumulative normal function
χ = chi-square random variable
2 2
χ = chi-square quantile (that is, a fixed number that exceeds the random variable χ at probability γ)
γ,ν
D6552 − 06 (2016)
RH = relative humidity
u (μg) = uncertainty component in two balance readings, an estimate of σ
u (μg) = weighing uncertainty, estimate of σ
w w
σ (μg) = uncorrectable (for example, by way of blank correction) standard deviation in (single) mass-change measurement
σ (μg) = confidence limit on σ
1-γ
σ (μg) = standard deviation in collected mass determination
w
U = overall uncertainty
4. 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.
5. Weight Instability, Causes, and Minimization
5.1 Weight instability of sampling substrates may be attributed to several causes. The following subclauses address the more
important of these.
5.1.1 Moisture Sorption:
5.1.1.1 Moisture sorption is the most common cause of weight instability. Water may be directly collected by the filter or foam
or other substrate material that is weighed. Water sorption by any part of the sampling system that is weighed must be suspected
as well. For example, the sampling cassette itself, if weighed, may be the cause of significant error (1) (see also 8.2.2).
5.1.1.2 The effects of water sorption can be reduced by using nonsorptive materials. However, there may exist specific sampling
needs for which a hydrophobic material is not feasible. Table 1 presents a list of common aerosol sampling substrates with different
water adsorption features.
NOTE 1—Gonzalez-Fernandez, Kauffer et al, and Lippmann (2-4) provide further details. Also, Vaughan et al (5) report that filters of evidently the same
material, but originating from different manufacturers, may have widely differing variabilities.
NOTE 2—There is generally a trade-off between hydrophobicity and conductivity in many materials (6). Therefore, one must be aware of the possibility
of creating sampling problems while reducing hygroscopicity.
NOTE 3—Pretreatments of substrates, such as greasing, may also affect water sorption.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
TABLE 1 Water Sorption Characteristics of Some Aerosol
Sampling Media
Substrate or Cassette Type Very Low Low High Very High
Cellulose fiber filter *
Glass fiber filter *
Quartz fiber filter *
Cellulose ester membrane filter *
Polytetrafluoroethylene filter *
PVC membrane filter *
Polycarbonate filter *
Silver membrane filter *
Polyurethane foam *
Greased polyester film impaction *
substrate
Greased aluminum foil impaction *
substrate
Carbon-filled resin *
Aluminum cassette *
Stainless steel cassette *
D6552 − 06 (2016)
5.1.2 Electrostatic Effects—Electrostatic effects are a common source of weighing problems. These effects can usually be
minimized by discharging the substrate through the use of a plasma ion source or a radioactive source. Using conductive materials
may reduce such problems. Lawless and Rodes (7) present details on electrostatic effects and their minimization (see also
Engelbrecht et al (8)).
5.1.3 Effects of Volatile Compounds (other than water)—Volatile compounds may be present in unused collection media (3) or
may be adsorbed onto media during sampling.
5.1.3.1 Desorption of volatiles from unused media may be controlled, for example, by heating or oxygen plasma treatment prior
to conditioning and weighing. Alternatively, losses may be compensated by the use of blanks (see Section 6).
5.1.3.2 When volatile materials collected during sampling form part of the intended sample, standardized written procedures are
required to ensure that any losses are minimized or at least controlled, for example, by conditioning under tightly specified
conditions.
NOTE 4—When volatile materials collected during sampling are not part of the intended sample, it may be difficult to eliminate them if weighing is
the only form of analysis. Preferably nonsorptive media should be used.
5.1.4 Handling Damage—Lawless and Rodes (7) give recommendations on minimizing balance-operator effects. If friable
substrates are used, procedures are needed to avoid mechanical damage during gravimetric analysis.
5.1.4.1 The air sampling equipment should be designed so that the substrate is not damaged during assembly and disassembly.
5.1.4.2 Flat tipped forceps are recommended for handling filters. Nonoxidizing metal tins may be used to weigh delicate
substrates without direct handling.
5.1.4.3 Parts to be weighed shall not be touched with the hands, unless gloved.
5.1.4.4 Handling shall take place in a clean environment to avoid contamination.
5.1.4.5 Gloves, if used, shall leave no residue on what is weighed.
5.1.5 Buoyancy Changes—Corrections (9) for air buoyancy, equal to the density of air multiplied by the air volume displaced,
are not necessary for small objects, such as a 37-mm diameter membrane filter. However, there may exist circumstances (for
example, if an entire sampling cassette were weighed without the use of correcting blanks) in which the object to be weighed is
so large that buoyancy must be corrected. For example, if the volume weighed exceeds 0.1 cm , then correction would be required
to weigh down to 0.1 mg if pressure changes of the order of 10 % between weighings are expected. If such a correction is
necessary, the atmospheric pressure and temperature at the time of weighing should be recorded.
6. Correcting for Weight Instability
6.1 Recommended Method for Correction by Use of Blanks—The use of blanks is the most important practical tool for reducing
errors due to weight instability. Correction for weight instability depends on the specific application
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