1、Designation: E1601 10 E1601 12Standard 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
2、 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 procedures and statistics for an interlaboratory study (ILS) of the per
3、formance of an analytical method.The study provides statistical values which are useful in determining if a method is satisfactory for the purposes for which it wasdeveloped. These statistical values may be incorporated in the methods precision and bias section. This practice discusses themeaning of
4、 the statistics and what users of analytical methods may learn from them.1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine
5、the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related MaterialsE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Practice for Conducting an Interl
6、aboratory Study to Determine the Precision of a Test MethodE1169 Practice for Conducting Ruggedness TestsE1763 Guide for Interpretation and Use of Results from Interlaboratory Testing of Chemical Analysis Methods3. Terminology3.1 DefinitionsFor definitions of terms used in this practice, refer to Te
7、rminology E135.3.2 Definitions of Terms Specific to This Standard:3.2.1 interlaboratory testmeasures the variability of results when a test method is applied many times in a number oflaboratories.3.2.2 replicate resultsresults obtained by applying a test method a specified number of times to a mater
8、ial.3.2.3 test protocolgives instructions to each participating laboratory, 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 a cooperative evaluation of a proposed analytical method.4.2 The
9、following list describes the organization of this practice: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 understand and use the statistics found in the Precision and Bias section ofme
10、thods.4.2.3 Sections 7 and 8 instruct the ILS coordinator and members of the task group on how to plan and conduct the experimentalphase of the study.4.2.4 Section 9 discusses the procedures for collecting, evaluating, and disseminating the data from the interlaboratory test.4.2.5 Section 10 present
11、s the statistical calculations.1 This practice is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.22 on Laboratory Quality.Current edition approved May 15, 2010Dec. 15, 2012. Published Ja
12、nuary 2011January 2013. Originally approved in 1994. Last previous edition approved in 20032010as E1601 98 (2003)E1601 10. 1. DOI: 10.1520/E1601-10.10.1520/E1601-12.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual
13、Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.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. Becauseit may not be tec
14、hnically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO
15、 Box C700, West Conshohocken, PA 19428-2959. United States14.2.6 Sections 11 and 12 discuss the use of statistics to evaluate a test method and the means of incorporating the ILS statisticsinto Precision and Bias statements.4.2.7 The Annex A1 gives the rationale for the calculations in Section 10.5.
16、 Significance and Use5.1 Ideally, interlaboratory testing of a method is conducted by a randomly chosen group of laboratories that typifies the kindof laboratory that is likely to use the method. In actuality, this ideal is only approximated by the laboratories that are available andwilling to under
17、take the test work. The coordinator of the program must ensure that every participating laboratory has appropriatefacilities and personnel and performs the method exactly as written. If this goal is achieved, the statistics developed during the ILSwill be adequate for determining if the method is ca
18、pable of producing satisfactory precision in actual use. If the program includescertified reference materials, the test data also provide information concerning the accuracy of the method. The statistics providea general guide to the expected performance of the method.6. Statistical Guide for the Us
19、ers of Analytical Methods Evaluated in Accordance With This Practice6.1 Standard Deviations (for formal definitions, refer to Terminology E135):6.1.1 Minimum Standard Deviation of Method, sMThis statistic measures the precision of test results under conditions ofminimum variability. Because it is im
20、probable that a method in ordinary use will exhibit precision this good, no predictive indexis calculated for sM. Users adept in statistics may wish to compare sM and the short-term standard deviation of the method measuredin their laboratory. For most methods, short-term variability refers to resul
21、ts obtained within several minutes by the same operatorusing the same equipment. (WarningThe standard deviation of results obtained on different occasions, even in the samelaboratory, probably will exceed sM.)6.1.2 Between-Laboratory Standard Deviation, sRThis statistic is a measure of the precision
22、 expected for results obtained indifferent laboratories. It reflects all sources of variability that operate during the interlaboratory test (except test materialinhomogeneity in tests designed to eliminate that effect). It is used to calculate the reproducibility index, R. Use sR for evaluatingthe
23、precision of methods. It represents the expected variability of results when a method is used in different laboratories.6.1.3 Within-Laboratory Standard Deviation, srThis statistic cannot be calculated in a normal interlaboratory test. It isdetermined only in tests designed to measure variability wi
24、thin laboratories. When this statistic is given in a method, it reflects allvariability that may occur from day-to-day within a laboratory (for example, from calibration, standardization, or environmentalchanges). It is used to calculate the repeatability index, r. The user is cautioned that additio
25、nal sources of variation may affectresults 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 diligent; (3) analytical instruments and equipment must be i
26、n good condition;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 the expected range of differences in results reported from twolaboratories, a range that is not exceeded in more than 5
27、% of such comparisons. Use R to predict how well your results shouldagree with those from another laboratory: First, obtain a result under the conditions stated in 6.2, then add R to, and subtract Rfrom, this result to form a concentration confidence interval. Such an interval has a 95 % probability
28、 of including a result obtainableby the method should another laboratory analyze the same sample. For example, a result of 46.57 % was obtained. If R for themethod at about 45 % is 0.543, the 95 % confidence interval for the result (that is, one expected to include the result obtained inanother labo
29、ratory 19 times out of 20) extends from 46.03 % to 47.11 %.NOTE 1For those not conversant with statistical concepts, it is important to realize that in most such comparisons, the differences will be much smallerthan the confidence interval implies. The 50 % confidence interval is only about one thir
30、d (34.6 %) as wide. Thus, the “average” interval for the aboveresult (one expected to include the result obtained by another laboratory half the time) extends from 46.4 % to 46.8 %. The obvious implication is that,although half the differences will be more than 0.2 %, half will be less than 0.2 %.6.
31、2.2 Repeatability Index, rThis statistic is given in the method only if the interlaboratory test was designed to measure sr.It estimates the expected range of results reported in the same laboratory on different days, a range that is not exceeded in morethan 5 % of such comparisons.7. Interlaborator
32、y Test Planning7.1 Analytical test methods start from a perceived need to support one or more material specifications.7.1.1 Develop a performance requirement for a method from the material specification(s). Include the following factors:expected ranges of chemical compositions of the materials to be
33、 covered (methods general scope); specified elements and theirconcentrations (determination concentration ranges); and the precision required.7.1.2 Prepare a table of the elements and concentration ranges to cover the critical values in the material specifications. Use thisinformation together with
34、knowledge of the characteristics of the candidate analytical method to select test materials for theinterlaboratory program.7.2 Draft MethodThe process of developing methods and testing them in a preliminary way is beyond the scope of thispractice. All analytical skill and experience available to th
35、e task group must be exerted to ensure that the method will meet theE1601 122project requirements in 7.1 and that it is free of technical faults. A preliminary, informal test of a method must be carried out inseveral laboratories before the final draft is prepared. Individuals responsible for select
36、ing the method may find helpful informationin Practice E691 and Practice E1169. The formal interlaboratory test must not start until the task group reaches consensus on aclearly written, explicitly stated, and unambiguously worded draft of the method in ASTM format, which has completed editorialrevi
37、ew.7.3 Test MaterialsAppropriate test materials are essential for a successful ILS. The larger the number of test materialsincluded in the test program, the better the statistical information generated. Conversely, the burden of running a very large numberof materials may reduce the number of labora
38、tories willing to participate. A method must cover a concentration range extendingboth above and below the specified value(s). If possible, provide test materials near each limit. Concentration ranges coveringseveral orders of magnitude should be tested with three or more materials.7.3.1 Material co
39、mposition and form must be within the general scope of the method. If possible, include all material types thescope is expected to cover. Often, only limited numbers of certified reference materials are available. Use those that best meet thecriteria for the test. If they do not cover all concentrat
40、ion levels, find or prepare other materials to fill in missing values.7.3.2 The quantity of the material must be sufficient to distribute to all laboratories participating in the test with about 50 % heldin reserve to cover unforeseen eventualities.7.3.3 Materials should be homogeneous on the scale
41、of the test portion consumed in each determination as well as among theportions sent to different laboratories. Usually certified reference materials have been tested for homogeneity, but test materialsfrom other sources may have had only a minimal examination. The use of laboratory-scale melting an
42、d casting to produce testmaterials can sometimes lead to segregation of one or more components in an alloy. Unless specially gathered or prepared materialshave been subjected to a thorough homogeneity test, they require the use of Test Plan B. It statistically removes the effect ofmoderate test mate
43、rial inhomogeneity from the estimates of the ILS statistics.7.3.4 Test material sent to each laboratory must be permanently marked with its identity in such a manner that the identificationis not likely to be lost or obliterated.7.3.5 If the test program is to evaluate the accuracy of the method, at
44、 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 on accuracy.7.3.6 Prepare a list of the test materials, their identifying numbers, a brief description of material type (for example,
45、 low-carbonsteel), and approximate concentration of the elements to be determined. This table becomes part of the documentation sent toparticipating laboratories and provides information needed for the research report and the precision and bias statement.7.4 Number of Cooperating LaboratoriesConvent
46、ional wisdom holds that the more laboratories participating in an ILS, thebetter. Further, the laboratory types included in the study task group should consist of typical users laboratories. There is wideagreement that estimates of precision based upon fewer than six laboratories become increasingly
47、 unreliable as the numberdecreases. A test program involving fewer than six laboratories does not comply with the requirements of this practice (Note 2).An effort should be made to enlist at least seven qualified laboratories before beginning a test program, to allow for attrition. Tobe qualified to
48、 participate, a laboratory must have proper equipment and personnel with sufficient training and experience to enablethem to perform the method exactly as it is written.NOTE 2If all reasonable efforts fail to recruit at least six cooperating laboratories, up to two of the recruited laboratories may
49、each volunteer to submittwo independent sets of test data as an expedient to provide a total of at least six sets of data. Minimum requirements for independence are that two typicalanalysts, who do not consult with each other about the method, perform the test protocol on different days. They should use separate equipment if possibleand must not share calibration solutions or calibration curves.8. Conducting the Interlaboratory Study (ILS)8.1 Program CoordinatorOne individual (presumably the task group chairman) will coordinate the entire ILS, if practical.
