1、Designation: D6552 06 (Reapproved 2016)Standard Practice forControlling and Characterizing Errors in Weighing CollectedAerosols1This standard is issued under the fixed designation D6552; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 Assessment of airborne aerosol hazards in the occupa-tional setting entails sampling onto a collection
3、 mediumfollowed by analysis of the collected material. The result isgenerally an estimated concentration of a possibly hazardousmaterial in the air. The uncertainty in such estimates dependson several factors, one of which relates to the specific type ofanalysis employed. The most commonly applied m
4、ethod foranalysis of aerosols is the weighing of the sampled material.Gravimetric analysis, though apparently simple, is subject toerrors from instability in the mass of the sampling medium andother elements that must be weighed. An example is providedby aerosol samplers designed to collect particle
5、s so as to agreewith the inhalable aerosol sampling convention (see ISO 7708,Guide D6062, and EN 481). For some sampler types, filter andcassette are weighed together to make estimates. Therefore, ifthe cassette, for example, absorbs or loses water between theweighings required for a concentration e
6、stimation, then errorsmay arise. This practice covers such potential errors andprovides solutions for their minimization.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of th
7、esafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1356 Terminology Relating
8、to Sampling and Analysis ofAtmospheresD4096 Test Method for Determination of Total SuspendedParticulate Matter in theAtmosphere (HighVolume Sam-pler Method)D4532 Test Method for Respirable Dust in Workplace At-mospheres Using Cyclone SamplersD6062 Guide for Personal Samplers of Health-RelatedAero-so
9、l Fractions2.2 International Standards:3EN 481 Workplace AtmospheresSize Fraction Definitionsfor Measurement of Airborne Particles in the WorkplaceEN 13205 Workplace AtmospheresAssessment of Perfor-mance of Instruments for Measurement of Airborne Par-ticle Concentrations2.3 ISO Standards:4ISO 7708 A
10、ir QualityParticle Size Fraction Definitions forHealth-related SamplingISO 20581 Workplace AtmospheresGeneral Require-ments for Performance of Procedures for the Measure-ment of Chemical AgentsISO 20988 Air QualityGuidelines for Estimating Mea-surement UncertaintyISO GUM Guide to the Expression of U
11、ncertainty in Mea-surement (1998)3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology D1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 blank substratea collection medium or substratecoming from the same batch as the sampling medium, bu
12、tunexposed.3.2.2 equilibration timeFor the purposes of this practice, atime constant (seconds) characterizing an approximate expo-nentially damped approach of the mass of an aerosol collectionmedium to a constant value. The constant can be defined as the1This practice is under the jurisdiction ofAST
13、M Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.04 on Workplace Air Quality.Current edition approved Nov. 1, 2016. Published November 2016. Originallyapproved in 2000. Last previous edition approved in 2011 as D6552 06 (2011).DOI: 10.1520/D6552-06R16.2For reference
14、d ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from European Committee for Standardization (CEN), AvenueMarnix
15、17, B-1000, Brussels, Belgium, http:/www.cen.eu.4Available 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 States1mean differ
16、ence of the mass from equilibrium per mean massloss or gain rate as measured over a finite time interval.3.2.2.1 DiscussionThere may be important instances inwhich several time constants are required to describe theapproach to equilibrium.3.2.3 estimated overall uncertainty (U)2 estimated stan-dard
17、deviation of estimated mass, in the case of negligibleuncorrectable bias (see ISO 20581).3.2.4 field blanka blank substrate that undergoes the samehandling as the sample substrate, generally including condi-tioning and loading into the samplers or transport containers, aswell as transportation to th
18、e sampling site, but without beingexposed.3.2.4.1 DiscussionIf blanks are not actually loaded intosamplers, losses due to handling could be underestimated.3.2.5 lab blanka blank substrate that undergoes the samehandling as the sample substrate in the laboratory, includingconditioning and loading int
19、o the samplers or transport con-tainers when this is done in the laboratory.3.2.6 limit of detection (LOD)a value for which ex-ceedence by measured mass indicates the presence of asubstance at given false-positive rate: 3 estimated standarddeviation of the measured blank substrate mass (see AnnexA2)
20、.3.2.7 limit of quantitation (LOQ)a value for which ex-ceedence by measured mass indicates the quantitation of asubstance at given accuracy: 10 estimated standard deviationof the measured blank substrate mass (see Annex A2).3.2.8 substratesampling filter, foam, and so forth togetherwith whatever mou
21、nting is weighed as a single item.3.2.8.1 DiscussionThe 25 or 37-mm plastic filter cassetteoften used for total dust sampling in either its closed-face oropen-face version is NOT part of the substrate in the definitionabove, since it is not weighed.3.3 Symbols: = detection error rateB = number of su
22、bstrate batches in method evalu-ationb = batch index (1, ., B) = mean substrate mass change during evalua-tion experimentCVmax= maximum relative error acceptable in quan-tifying collected massmfb(g) = substrate mass changeb(g) = substrate weight-change random variable rep-resenting inter-batch varia
23、bilityfb(g) = substrate weight change residual randomvariable with variance 2f = substrate index (1, ., F)F = number of substrates (for example, filters) ineach batch tested in method evaluation = method evaluation error rateLOD (g) = limit of detection:3swLOD1-(g) = LOD confidence limitLOQ (g) = li
24、mit of quantitation: 10 swLOQ1-(g) = LOQ confidence limitNb= number of blanks per substrate set = number of degrees of freedom in methodevaluation = cumulative normal function2= chi-square random variable,2= chi-square quantile (that is, a fixed numberthat exceeds the random variable 2at prob-abilit
25、y )RH = relative humidityu (g) = uncertainty component in two balancereadings, an estimate of uw(g) = weighing uncertainty, estimate of w (g) = uncorrectable (for example, by way of blankcorrection) standard deviation in (single)mass-change measurement1-(g) = confidence limit on w(g) = standard devi
26、ation in collected mass determi-nationU = overall uncertainty4. Significance and Use4.1 The weighing of collected aerosol is one of the mostcommon and purportedly simple analytical procedures in bothoccupational and environmental atmospheric monitoring (forexample, Test Method D4532 or D4096). Probl
27、ems withmeasurement accuracy occur when the amount of materialcollected is small, owing both to balance inaccuracy andvariation in the weight of that part of the sampling medium thatis weighed along with the sample. The procedures presentedhere for controlling and documenting such analytical errorsw
28、ill help provide the accuracy required for making well-founded decisions in identifying, characterizing, and control-ling hazardous conditions.4.2 Recommendations are given as to materials to be used.Means of controlling or correcting errors arising from insta-bility are provided. Recommendations as
29、 to the weighingprocedure are given. Finally, a method evaluation procedurefor estimating weighing errors is described.4.3 Recommendations are also provided for the reporting ofweights relative to LOD (see 3.2.6) and LOQ (see 3.2.7). Thequantities, LOD and LOQ, are computed as a result of themethod
30、evaluation.5. Weight Instability, Causes, and Minimization5.1 Weight instability of sampling substrates may be attrib-uted to several causes. The following subclauses address themore important of these.5.1.1 Moisture Sorption:5.1.1.1 Moisture sorption is the most common cause ofweight instability. W
31、ater may be directly collected by the filteror foam or other substrate material that is weighed. Watersorption by any part of the sampling system that is weighedmust be suspected as well. For example, the sampling cassetteitself, if weighed, may be the cause of significant error (1)5(seealso 8.2.2).
32、5The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D6552 06 (2016)25.1.1.2 The effects of water sorption can be reduced byusing nonsorptive materials. However, there may exist specificsampling needs for which a hydrophobic material is notfeasible. Table 1
33、 presents a list of common aerosol samplingsubstrates with different water adsorption features.NOTE 1Gonzalez-Fernandez, Kauffer et al, and Lippmann (2-4)provide further details. Also, Vaughan et al (5) report that filters ofevidently the same material, but originating from different manufacturers,m
34、ay have widely differing variabilities.NOTE 2There is generally a trade-off between hydrophobicity andconductivity in many materials (6). Therefore, one must be aware of thepossibility of creating sampling problems while reducing hygroscopicity.NOTE 3Pretreatments of substrates, such as greasing, ma
35、y also affectwater sorption.5.1.2 Electrostatic EffectsElectrostatic effects are a com-mon source of weighing problems. These effects can usually beminimized by discharging the substrate through the use of aplasma ion source or a radioactive source. Using conductivematerials may reduce such problems
36、. 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
37、 of volatiles from unused media may becontrolled, for example, by heating or oxygen plasma treatmentprior to conditioning and weighing. Alternatively, losses maybe compensated by the use of blanks (see Section 6).5.1.3.2 When volatile materials collected during samplingform part of the intended samp
38、le, standardized written proce-dures are required to ensure that any losses are minimized or atleast controlled, for example, by conditioning under tightlyspecified conditions.NOTE 4When volatile materials collected during sampling are not partof the intended sample, it may be difficult to eliminate
39、 them if weighingis the only form of analysis. Preferably nonsorptive media should be used.5.1.4 Handling DamageLawless and Rodes (7) give rec-ommendations on minimizing balance-operator effects. If fri-able substrates are used, procedures are needed to avoidmechanical damage during gravimetric anal
40、ysis.5.1.4.1 The air sampling equipment should be designed sothat the substrate is not damaged during assembly and disas-sembly.5.1.4.2 Flat tipped forceps are recommended for handlingfilters. Nonoxidizing metal tins may be used to weigh delicatesubstrates without direct handling.5.1.4.3 Parts to be
41、 weighed shall not be touched with thehands, unless gloved.5.1.4.4 Handling shall take place in a clean environment toavoid contamination.5.1.4.5 Gloves, if used, shall leave no residue on what isweighed.5.1.5 Buoyancy ChangesCorrections (9) for air buoyancy,equal to the density of air multiplied by
42、 the air volumedisplaced, are not necessary for small objects, such as a 37-mmdiameter membrane filter. However, there may exist circum-stances (for example, if an entire sampling cassette wereweighed without the use of correcting blanks) in which theobject to be weighed is so large that buoyancy mu
43、st becorrected. For example, if the volume weighed exceeds 0.1cm3, then correction would be required to weigh down to 0.1mg if pressure changes of the order of 10 % between weighingsare expected. If such a correction is necessary, the atmosphericpressure and temperature at the time of weighing shoul
44、d berecorded.6. Correcting for Weight Instability6.1 Recommended Method for Correction by Use ofBlanksThe use of blanks is the most important practical toolfor reducing errors due to weight instability. Correction forweight instability depends on the specific application andshould follow a written p
45、rocedure. The general principles areas follows. Blank sampling media are exposed, as closely aspossible, to the same conditions as the active sampling media,without actually drawing air through. Correction is effected bysubtracting the average blank weight gain from the weight gainof the active samp
46、les. Of course, if the atmosphere to besampled contains water (or other volatile) droplets, then the useof blanks alone cannot correct. Kauffer et al (3) note thatblanks may also offer correction for filter material losses.Blanks shall be matched to samples, that is, if the sampleconsists of a filte
47、r within a cassette that is weighed, the blankshall be the same type of filter within the same type of cassette.6.1.1 An alternative procedure employs matched weightfilters consisting of two nearly equal-weight filters, one placedin front of the other, with the sampler following employed asblank. Th
48、e collected mass is estimated simply by subtractingthe filter masses following sampling.Analysis of uncertainty issimilar to the presentation here, but also involves estimation ofthe uncertainty of the filter matching.6.2 Minimum Number of BlanksGenerally, at least oneblank is recommended for each t
49、en samples. Measurementschemes in current use require between one and four blanks perbatch. See A1.1 for advantages of multiple blanks.6.3 Weighing Times and SequenceBlanks shall be inter-spersed with samples, before and after use, so as to detectsystematic variations in mass (for example, due to sorption orevaporation of a contaminant during weighing).TABLE 1 Water Sorption Characteristics of Some AerosolSampling MediaSubstrate or Cassette Type Very Low Low High Very HighCellulose fiber filter *Glass fiber
