1、Designation: E2120 10Standard Practice forPerformance Evaluation of the Portable X-Ray FluorescenceSpectrometer for the Measurement of Lead in Paint Films1This standard is issued under the fixed designation E2120; the number immediately following the designation indicates the year oforiginal adoptio
2、n or, in the case of revision, 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 This practice covers portable X-ray fluorescence (XRF)instruments intended
3、for the measurement of lead in paint. It isintended that manufacturers apply this practice to one unit of aparticular model of an instrument when that model is initiallyavailable. Replicate tests on additional units of the same modelof an instrument are to be performed at the discretion of themanufa
4、cturer. This practice also is intended for use by thirdparties performing independent evaluation of portable X-rayfluorescence instruments.1.2 All performance evaluation data are to be in SI units.1.3 Tests of performance are based on replicate measure-ments of certified reference paint films on a v
5、ariety of substratematerials. Tests are performed to determine: bias, precision,linearity, limit of detection, interferences, substrate affects, andstability.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user
6、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:2D3332 Test Methods for Mechanical-Shock Fragility ofProducts, Using Shock MachinesE344 Terminology Relating to The
7、rmometry and Hydrom-etryE456 Terminology Relating to Quality and StatisticsE1605 Terminology Relating to Lead in Buildings2.2 ANSI Standards:3ANSI N5381979 Classification of Industrial Ionizing Ra-diation Gauging DevicesANSI N3231978 Radiation Protection InstrumentationTest and Calibration2.3 ISO St
8、andards:3ISO 2919 Radiation Protection Sealed RadioactiveSources General Requirements and Classification2.4 UL Standards:4UL 544 Safety for Medical andDental EquipmentUL 31011 Chemical Analyzers3. Terminology3.1 Definitions:3.1.1 accuracy, nthe theoretical maximum error of ameasurement, expressed as
9、 the proportion of the amount beingmeasured without regard for the direction of the error, that isachieved with a given probability (typically 0.95) by themethod.53.1.2 bias, nthe discrepancy between the mean of thedistribution of measurements from a method and the trueconcentration being measured.3
10、.1.3 limit of detection, nthe smallest (true) signal thatwill be detected with a probability 1 b (b is the probabilityof an error of the second kind, failing to decide that a substanceis present when it is), where the a posteriori decision mecha-nism has a built-in protection level, a (a is the prob
11、ability ofan error of the first kind, deciding that the substance is presentwhen it is not), against falsely concluding that a blankobservation represents a “real” signal. The b and a termstypically are 5 % or 1 %, depending on the requirements of thetesting program.63.1.4 precision, nthe closeness
12、of agreement betweenrepetitive test results obtained under prescribed conditions (seeTerminology E456). The precision of a single instrument is therandom component of its accuracy and is usually indicated bythe value of the standard deviation.1This practice is under the jurisdiction of ASTM Committe
13、e E06 on Perfor-mance of Buildings and is the direct responsibility of Subcommittee E06.23 on LeadHazards Associated with Buildings.Current edition approved Oct. 1, 2010. Published November 2010. Originallyapproved in 1999 as PS 116 99. Last previous edition approved in 2000 asE2120 00 which was wit
14、hdrawn January 2009 and reinstated in October 2010.2For referenced 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
15、 from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from Underwriters Laboratories (UL), 333 Pfingsten Rd., North-brook, IL 60062-2096, http:/.5Kennedy, E.R., T.J. Fischbach, R. Song, P.M. Miller, and S.A. Shulman,Guidelines
16、 for Air Sampling and Analytical Method Development and Evaluation,DHHS (NIOSH) Publication No. 95117. National Institute for Occupational Safetyand Health, Cincinnati, OH 45226, May 1995.6Currie, L.A., “Limits for Qualitative Detection and Quantitative Determina-tion,” Analytical Chemistry, Vol 40,
17、 No. 3, 1968, pp. 586593.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2 The definitions given in Terminologies E344 and E1605shall apply to this practice.3.3 Definitions of Terms Specific to This Standard:3.3.1 battery charger,
18、na means for recharging a portableinstruments self-contained battery pack, usually converting110 V AC to low level DC power.3.3.2 cycle or reading time, na period of X-ray datacollection (counting) performed automatically by some instru-ments. Such time may be established by a standardizationprocedu
19、re that would adjust for variation in the strength of theradioactive source. Also, it might be adjustable on someinstruments to achieve different levels of measurement preci-sion. Depending on the instrument model, one “cycle time”may be equivalent to one “measurement time” or several“cycles” may be
20、 automatically or manually averaged to equalone “measurement time.” The time begins with the opening ofthe XRF instrument shutter to expose the paint film surface tothe source radiation and is concluded when the source shutteris closed.3.3.3 display unit, nan electronic device that presents theresul
21、ts of the measurement to the user. Other parameters suchas total measurement time also may be presented.3.3.4 measurement time, nthe duration of a single mea-surement observed in real time. A measurement may compriseseveral individual readings or cycles.3.3.5 measurement value, nthe readout of a lea
22、d concen-tration in mg/cm2obtained at the end of one cycle time (orseveral cycle times if multiple readings are averaged) or at theend of one measurement time.3.3.6 probe, na hand-held device containing the radioac-tive source, X-ray detector, and associated mechanical andelectrical components that
23、is placed against the test sample toperform the measurement. The probe may constitute a part orall of the XRF instrument.3.3.7 radioactive source, na radioactive material (forexample,57Co,109Cd, and241Am) that emits X-rays or gammarays that serve to cause ionization of the lead atoms in thesample, a
24、nd subsequently a cascade of higher energy electronsinto the vacated lower energy shells.As these electrons fall intothe lower energy orbitals, they emit energy in the form ofX-rays that are characteristic of lead.3.3.8 standard paint films, nfree-standing, certified refer-ence paint films, that is,
25、 certified reference materials (CRMs),that are acquired from the National Institute of Standards andTechnology (NIST) or a commercial vendor. The lead levels inthe standard paint films (CRMs) shall be based on “x” level forlead where “x” is equal to the appropriate local, state, or federalaction lev
26、el for lead in coatings (in mg/cm2of lead coating).The paint films shall be as follows:(Film 1) 2x3.3.8.1 DiscussionAn example CRM in use is the NISTStandard Reference Material (SRM) 2579, which consists offive films at 2x). Next,perform ten 1-min measurements with each of these five CRMpaint films
27、(2x) on five different, additional substrates. Representativesubstrates and their order of testing are as follows:(1) 0.76-mm (0.030-in.) T6, 6061 aluminum sheet, or45-mm (1.75-in.) hollow core door, or 3.2-mm (0.125-in.)thick veneer paneling (cut to fit in the test box).(2) 13-mm (0.5-in.) thick gy
28、psum board, plasterboard, or15- to 20-mm (0.625- to 0.75-in.) thick birch, fir, or oak boardscut to fit in the test box.(3) 6-mm (0.25-in.) thick “836” steel plate cut to fit in thetest box.(4) Uncolored cinderblock slab or poured concrete slab50-mm (2-in.) thick cut to fit in the test box.(5) 40-mm
29、 (1.5-in.) thick red brick (place three-four bricksside by side in the test box).7.1.2.2 Calculate and report the mean and standard devia-tion for each of these thirty measurement conditions. Reportthe differences between each mean value and expected CRMvalue as the bias of the measurement for each
30、substrate andconcentration. Include in the report a description of eachsubstrate material and the method of substrate correction.NOTE 6Correction for substrate bias is to be performed according tothe manufacturers standard procedure.NOTE 7Some instruments may display a default value, for example, 1m
31、g/cm2, if the measurement value is within some predetermined range ofan action level or other level of concern. The default value cannot be usedin this evaluation; the actual measurement value must be used. If theactual measurement value cannot be determined (displayed), perform thisevaluation with
32、a CRM that is removed from the action level or other levelof concern such that it does not result in the display of a default value.7.1.2.3 PrecisionUsing the data from the measurementsperformed under 7.1.2.1 and 7.1.2.2, calculate the slope,standard deviation of the slope, intercept, and standard d
33、evia-tion of the intercept of the measured versus expected valuesusing a linear regression analysis.7Also calculate and reportthe correlation coefficient. Prepare a plot of standard deviationsof the average of each of the ten measurement values versus theconcentrations of the standard films. Include
34、 these results in thereport of this evaluation.NOTE 8These results are not to be used as an indication of theinstruments accuracy. They are solely to characterize the repeatability ofthe readings.NOTE 9Bias and precision, as determined by this practice, provideonly estimates of the bias and precisio
35、n that may be achieved in the field.Bias and precision in the field will depend upon the instrument calibration,the form and composition of the substrate, and the structure of the paintfilm being analyzed.7.1.2.4 Linearity with Real-World SubstratesThe slope,standard deviation of the slope, and the
36、correlation coefficientfrom 7.1.2.3 are taken as a measure of the linearity of responseof the instrument.7.1.3 Estimate of Limit of Detection (LOD):7.1.3.1 The procedure presented here for estimating LODhas been developed especially for radiochemical applications.It has the advantage that it allows
37、precision to vary withconcentration, as predicted by counting statistics. This proce-dure is a simplification of the general method described byL.A. Currie.6The determination of the limit of detection isbased on Hypothesis Testing, which is subject to two kinds oferror: deciding that lead is present
38、 at or above a specified level,when it is not (error of the first kind), and conversely, decidingthat lead is not present at or above a specified level, when infact, it is (error of the second kind). In this approach, readingsthat fall above a particular threshold value, xt, are classified as“contai
39、ning lead,” while readings that fall below the thresholdare classified as “not containing lead.” The analyst selects thethreshold value, xt, such that if the true concentration of lead ona surface is zero (0 mg/cm2), 95 % of the readings on thatzero-lead surface will fall below the threshold value,
40、xt, andtherefore will be classified correctly as “not containing lead,”while only 5 % of the readings on that zero-lead surface will bemisclassified as “containing lead.” The limit of detection, xLOD,is the true concentration of a lead-bearing surface such that95 % of the readings on that surface wi
41、ll fall above thethreshold xtand therefore will be correctly classified as“containing lead,” while only 5 % of the readings on thatlead-bearing surface will be misclassified as “not containinglead.” Note that xLODis always higher than xt, and is almostalways at least twice xt.7.1.3.2 As noted, this
42、procedure has the advantage that itallows precision to vary with concentration, as predicted bycounting statistics, but it does not require intimate knowledgeof the instrument calibration. Simplifying assumptions are thatthe variance of the population, sx2, is linear with concentration(sx2= A + Bx),
43、 as is predicted by counting statistics, and thatthe distribution of readings is purely Gaussian, rather than themore exact Poisson (see Appendix X1 for additional informa-tion).7.1.3.3 The procedure is as follows:(1) Twenty replicate 1-min measurements are to be per-formed at a known concentration,
44、 x0, below the expecteddetection limit. If an instrument provides for the display ofnegative results, a nondetectable-lead sample is to be used. Ifan instrument does not provide for the display of negativeresults, a lead standard of sufficient level to produce onlypositive results must be used. If t
45、he instrument provides for thedisplay of negative results, use the same system and testconditions described in 7.1.2 and perform ten additionalmeasurements with the CRM at 2x CRM underneath the pine board,with painted surfaces toward the XRF unit. Calculate the meanand the standard deviation for the
46、 ten measurements and reportthe difference between the mean value and expected value as abias to the X-ray measurement due to read through.7.1.4.3 Effects of Paint ThicknessInstruments have thepotential for yielding a low response to lead within theinnermost layers of very thick coatings of paint. T
47、he followingis performed to test for this potential source of error (bias).Using the system and test conditions described in 7.1.2,perform ten 1-min measurements with the 1-in. white pineboard and CRMs arranged in the following configurations: (1)the 1.5x to 2x CRM covered by the 0.7x to 1.3x CRM co
48、veredby the 0.2x CRM and; (2) the 0.7x to 1.3x CRM covered bythe 0.2x to 0.5x CRM covered by the 0.2x CRM; all paintedsurfaces toward the XRF unit. Calculate the mean and thestandard deviation for the ten measurements for both setupsand report the difference between the mean values and theexpected s
49、um as bias to the instruments measurements due topaint thickness.NOTE 15Real paint films are not usually as thick as the procedureprescribes. The purpose of the test is to show the potential impact, if any,of this particular condition, and also the ability of the instrument tocompensate for this particular condition.7.1.4.4 Effects of Paint LayeringInstruments have thepotential for yielding a low response to lead within theinnermost layers of multi-layered coatings of paint. Thefollowing is performed to test for this potential source
