1、Designation: E1601 10Standard Practice forConducting an Interlaboratory Study to Evaluate thePerformance of an Analytical Method1This standard is issued under the fixed designation E1601; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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 procedures and statistics for aninterlaboratory study (ILS) of the performance o
3、f an analyticalmethod. The study provides statistical values which are usefulin determining if a method is satisfactory for the purposes forwhich it was developed. These statistical values may beincorporated in the methods precision and bias section. Thispractice discusses the meaning of the statist
4、ics and what usersof analytical methods may learn from them.1.2 This standard does not purport to address all of thesafety 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-b
5、ility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Stu
6、dy toDetermine the Precision of a Test MethodE1169 Practice for Conducting Ruggedness TestsE1763 Guide for Interpretation and Use of Results fromInterlaboratory Testing of Chemical Analysis Methods3. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice, refer to Terminology E135
7、.3.2 Definitions of Terms Specific to This Standard:3.2.1 interlaboratory testmeasures the variability of re-sults when a test method is applied many times in a number oflaboratories.3.2.2 replicate resultsresults obtained by applying a testmethod a specified number of times to a material.3.2.3 test
8、 protocolgives instructions to each participatinglaboratory, detailing the way it is to conduct its part of theinterlaboratory test program.4. Summary of Practice4.1 Instructions are provided for planning and conducting acooperative evaluation of a proposed analytical method.4.2 The following list d
9、escribes the organization of thispractice:4.2.1 Sections 1-5 define the scope, significance and use,referenced documents, and terms used in this practice.4.2.2 Section 6 helps users of analytical methods understandand use the statistics found in the Precision and Bias section ofmethods.4.2.3 Section
10、s 7 and 8 instruct the ILS coordinator andmembers of the task group on how to plan and conduct theexperimental phase of the study.4.2.4 Section 9 discusses the procedures for collecting,evaluating, and disseminating the data from the interlaboratorytest.4.2.5 Section 10 presents the statistical calc
11、ulations.4.2.6 Sections 11 and 12 discuss the use of statistics toevaluate a test method and the means of incorporating the ILSstatistics into Precision and Bias statements.4.2.7 The Annex A1 gives the rationale for the calculationsin Section 10.5. Significance and Use5.1 Ideally, interlaboratory te
12、sting of a method is conductedby a randomly chosen group of laboratories that typifies thekind of laboratory that is likely to use the method. In actuality,this ideal is only approximated by the laboratories that areavailable and willing to undertake the test work. The coordi-nator of the program mu
13、st ensure that every participatinglaboratory has appropriate facilities and personnel and per-forms the method exactly as written. If this goal is achieved,the statistics developed during the ILS will be adequate fordetermining if the method is capable of producing satisfactoryprecision in actual us
14、e. If the program includes certifiedreference materials, the test data also provide information1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.22 on Laboratory Quality.Cu
15、rrent edition approved May 15, 2010. Published January 2011. Originallyapproved in 1994. Last previous edition approved in 2003 as E1601 98 (2003)1.DOI: 10.1520/E1601-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annu
16、al Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.concerning the accuracy of the method. The statistics providea general guide
17、 to the expected performance of the method.6. Statistical Guide for the Users of Analytical MethodsEvaluated in Accordance With This Practice6.1 Standard Deviations (for formal definitions, refer toTerminology E135):6.1.1 Minimum Standard Deviation of Method, sMThisstatistic measures the precision o
18、f test results under conditionsof minimum variability. Because it is improbable that a methodin ordinary use will exhibit precision this good, no predictiveindex is calculated for sM. Users adept in statistics may wish tocompare sMand the short-term standard deviation of themethod measured in their
19、laboratory. For most methods,short-term variability refers to results obtained within severalminutes by the same operator using the same equipment.(WarningThe standard deviation of results obtained ondifferent occasions, even in the same laboratory, probably willexceed sM.)6.1.2 Between-Laboratory S
20、tandard Deviation, sRThisstatistic is a measure of the precision expected for resultsobtained in different laboratories. It reflects all sources ofvariability that operate during the interlaboratory test (excepttest material inhomogeneity in tests designed to eliminate thateffect). It is used to cal
21、culate the reproducibility index, R. UsesRfor evaluating the precision of methods. It represents theexpected variability of results when a method is used indifferent laboratories.6.1.3 Within-Laboratory Standard Deviation, srThis sta-tistic cannot be calculated in a normal interlaboratory test. It i
22、sdetermined only in tests designed to measure variability withinlaboratories. When this statistic is given in a method, it reflectsall variability that may occur from day-to-day within a labo-ratory (for example, from calibration, standardization, or envi-ronmental changes). It is used to calculate
23、the repeatabilityindex, r. The user is cautioned that additional sources ofvariation may affect results obtained in other laboratories.6.2 Predictive IndexesFor the following indexes to apply,these conditions must be met: (1) the test materials must behomogeneous; (2) analysts must be competent and
24、diligent; (3)analytical instruments and equipment must be in good condi-tion; and (4) the method must be performed exactly as written(for formal definitions, refer to Terminology E135).6.2.1 Reproducibility Index, RThis statistic estimates theexpected range of differences in results reported from tw
25、olaboratories, a range that is not exceeded in more than 5 % ofsuch comparisons. Use R to predict how well your resultsshould agree with those from another laboratory: First, obtaina result under the conditions stated in 6.2, then add R to, andsubtract R from, this result to form a concentration con
26、fidenceinterval. Such an interval has a 95 % probability of including aresult obtainable by the method should another laboratoryanalyze the same sample. For example, a result of 46.57 % wasobtained. If R for the method at about 45 % is 0.543, the 95 %confidence interval for the result (that is, one
27、expected toinclude the result obtained in another laboratory 19 times out of20) extends from 46.03 % to 47.11 %.NOTE 1For those not conversant with statistical concepts, it isimportant to realize that in most such comparisons, the differences will bemuch smaller than the confidence interval implies.
28、 The 50 % confidenceinterval is only about one third (34.6 %) as wide. Thus, the “average”interval for the above result (one expected to include the result obtainedby another laboratory half the time) extends from 46.4 % to 46.8 %. Theobvious implication is that, although half the differences will b
29、e more than0.2 %, half will be less than 0.2 %.6.2.2 Repeatability Index, rThis statistic is given in themethod only if the interlaboratory test was designed to measuresr. It estimates the expected range of results reported in thesame laboratory on different days, a range that is not exceededin more
30、 than 5 % of such comparisons.7. Interlaboratory Test Planning7.1 Analytical test methods start from a perceived need tosupport one or more material specifications.7.1.1 Develop a performance requirement for a methodfrom the material specification(s). Include the following fac-tors: expected ranges
31、of chemical compositions of the materialsto be covered (methods general scope); specified elements andtheir concentrations (determination concentration ranges); andthe precision required.7.1.2 Prepare a table of the elements and concentrationranges to cover the critical values in the material specif
32、ications.Use this information together with knowledge of the charac-teristics of the candidate analytical method to select testmaterials for the interlaboratory program.7.2 Draft MethodThe process of developing methods andtesting them in a preliminary way is beyond the scope of thispractice. All ana
33、lytical skill and experience available to thetask group must be exerted to ensure that the method will meetthe project requirements in 7.1 and that it is free of technicalfaults.Apreliminary, informal test of a method must be carriedout in several laboratories before the final draft is prepared.Indi
34、viduals responsible for selecting the method may findhelpful information in Practice E691 and Practice E1169. Theformal interlaboratory test must not start until the task groupreaches consensus on a clearly written, explicitly stated, andunambiguously worded draft of the method in ASTM format,which
35、has completed editorial review.7.3 Test MaterialsAppropriate test materials are essentialfor a successful ILS. The larger the number of test materialsincluded in the test program, the better the statistical informa-tion generated. Conversely, the burden of running a very largenumber of materials may
36、 reduce the number of laboratorieswilling to participate. A method must cover a concentrationrange extending both above and below the specified value(s). Ifpossible, provide test materials near each limit. Concentrationranges covering several orders of magnitude should be testedwith three or more ma
37、terials.7.3.1 Material composition and form must be within thegeneral scope of the method. If possible, include all materialtypes the scope is expected to cover. Often, only limitednumbers of certified reference materials are available. Usethose that best meet the criteria for the test. If they do n
38、ot coverall concentration levels, find or prepare other materials to fill inmissing values.E1601 1027.3.2 The quantity of the material must be sufficient todistribute to all laboratories participating in the test with about50 % held in reserve to cover unforeseen eventualities.7.3.3 Materials should
39、 be homogeneous on the scale of thetest portion consumed in each determination as well as amongthe portions sent to different laboratories. Usually certifiedreference materials have been tested for homogeneity, but testmaterials from other sources may have had only a minimalexamination. The use of l
40、aboratory-scale melting and castingto produce test materials can sometimes lead to segregation ofone or more components in an alloy. Unless specially gatheredor prepared materials have been subjected to a thoroughhomogeneity test, they require the use of Test Plan B. Itstatistically removes the effe
41、ct of moderate test materialinhomogeneity from the estimates of the ILS statistics.7.3.4 Test material sent to each laboratory must be perma-nently marked with its identity in such a manner that theidentification is not likely to be lost or obliterated.7.3.5 If the test program is to evaluate the ac
42、curacy of themethod, at least one test material must be certified for theconcentration of each element in the scope of the method.More certified materials provide more complete information onaccuracy.7.3.6 Prepare a list of the test materials, their identifyingnumbers, a brief description of materia
43、l type (for example,low-carbon steel), and approximate concentration of the ele-ments to be determined. This table becomes part of thedocumentation sent to participating laboratories and providesinformation needed for the research report and the precisionand bias statement.7.4 Number of Cooperating
44、LaboratoriesConventionalwisdom holds that the more laboratories participating in anILS, the better. Further, the laboratory types included in thestudy task group should consist of typical users laboratories.There is wide agreement that estimates of precision based uponfewer than six laboratories bec
45、ome increasingly unreliable asthe number decreases. A test program involving fewer than sixlaboratories does not comply with the requirements of thispractice (Note 2). An effort should be made to enlist at leastseven qualified laboratories before beginning a test program, toallow for attrition. To b
46、e qualified to participate, a laboratorymust have proper equipment and personnel with sufficienttraining and experience to enable them to perform the methodexactly as it is written.NOTE 2If all reasonable efforts fail to recruit at least six cooperatinglaboratories, up to two of the recruited labora
47、tories may each volunteer tosubmit two independent sets of test data as an expedient to provide a totalof at least six sets of data. Minimum requirements for independence arethat two typical analysts, who do not consult with each other about themethod, perform the test protocol on different days. Th
48、ey should useseparate equipment if possible and must not share calibration solutions orcalibration curves.8. Conducting the Interlaboratory Study (ILS)8.1 Program CoordinatorOne individual (presumably thetask group chairman) will coordinate the entire ILS, if practi-cal. A prospective ILS program co
49、ordinator will find helpfulinformation on conducting the program in Practice E691. Oneway to organize the work to provide close control whilemoving the program steadily to its conclusion is as follows:8.1.1 Prepare a draft of the method to be tested.8.1.2 Recruit a task group of participating laboratories.8.1.3 Select a set of test materials and assemble them intokits, one for each laboratory.8.1.4 Write the test protocol to instruct each laboratory howto run the test.8.1.5 Prepare a report form.8.1.6 Establish a realistic time schedule for each part of thetest
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