1、Designation: D6259 98 (Reapproved 2010)An American National StandardStandard Practice forDetermination of a Pooled Limit of Quantitation1This standard is issued under the fixed designation D6259; 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 the determination of a lowerquantitative limit for a test method for an
3、analyte. Thedetermined lower limit is hereinafter referred to as the pooledlimit of quantitation.1.2 Applicable test methods will produce test results greaterthan zero. Examples are those test methods that measuresample composition.2. Referenced Documents2.1 ASTM Standards:2E456 Terminology Relating
4、 to Quality and StatisticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ASTM Adjuncts:D2PP, Determination of Precision and Bias Data for Use inTest Methods for Petroleum Products33. Terminology3.1 Definitions:3.1.1 pooled limit of quantitation, n
5、level of property orconcentration of analyte above which quantitative test resultscan be obtained with a specified degree of confidence. See3.2.1 for acronym.3.1.2 repeatability conditions, nconditions under whichtest results are obtained with the same test method in the samelaboratory by the same o
6、perator with the same equipment in theshortest practical period of time using test units or testspecimens taken at random from a single quantity of materialthat is as nearly homogeneous as possible (see 10.3 of PracticeE691.)NOTE 1The same operator, same equipment requirement means thatfor a particu
7、lar step in the measurement process the same combination ofoperator and equipment is used for every test result. Thus, one operatormay prepare the test specimens, a second measure the dimensions, and athird measure the mass in a test method for measuring density.NOTE 2By in the shortest practical pe
8、riod of time is meant that thetest results, at least for one material, are obtained in a time period not lessthan in normal testing and not so long as to permit significant change intest material, equipment, or environment. See Terminology E456.3.2 Acronyms:3.2.1 PLOQ, npooled limit of quantitation.
9、4. Summary of Practice4.1 Determine the standard deviation of a test result, underrepeatability conditions, at progressively higher levels of theanalyte until the ratio of measured level to standard deviationbecomes greater than ten and remains so.5. Significance and Use5.1 In a single laboratory, t
10、he limit of quantitation, LOQ,equal to ten standard deviations has been recommended.4Atestresult at this LOQ has an uncertainty of 630 % at the 99 %confidence level. Similarly here, as a general estimate, thePLOQ, equal to ten repeatability standard deviations is recom-mended. A test result at this
11、PLOQ has an uncertainty of630 % at the 99 % confidence level.5.2 Values below the PLOQ are deemed to be too uncertainfor meaningful use in commerce, or in regulatory activities.5.3 Many test methods never find application outside theirPLOQ. However, in the quest for ever more sensitive proce-dures,
12、it can become difficult to distinguish an analyticalresponse from background noise with the technology at hand.Test methods defective in design or poorly executed may alsofunction outside their PLOQ.6. Procedure6.1 Make the preparations outlined in 6.2, then carry out oneof the procedures described
13、in 6.3.6.2 Preparations:6.2.1 Select Test LevelsDecide the objective of the testmethod, the range of typical samples it is expected to cover.Name a set of test levels covering this range and spaced tobracket the PLOQ. In some cases, the PLOQ will be wellbelow the useful range. Then, it is only neces
14、sary to determinea less than value.1This practice is under the jurisdiction of Committee D02 on Petroleum Productsand Lubricants and is the direct responsibility of Subcommittee D02.94 onCoordinating Subcommittee on Quality Assurance and Statistics.Current edition approved July 1, 2010. Published Ju
15、ly 2010. Originally approvedin 1998. Last previous edition approved in 2004 as D625998(2004). DOI:10.1520/D6259-98R10.2For 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 t
16、o the standards Document Summary page onthe ASTM website.3Withdrawn and no longer available from ASTM International.4Keith, L. H., et al, “Principles of Environmental Analysis,” Analytical Chem-istry, American Chemical Society, Vol 55, 1983, p. 227.1Copyright ASTM International, 100 Barr Harbor Driv
17、e, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 3Mean and standard deviation data from experienced labora-tories, archived research reports, and known limitations of the test methodor equipment can give a preliminary notion of the PLOQ. An LOQ can beestimated in a single laborat
18、ory.6.2.2 Select Sample MaterialsNormally, use sample ma-terials that are typical of those to which the test method isapplied. In special cases, the method of standard additions(spiking) can be necessary to achieve the selected test levels.Synthetic blends may be required because of cost or otherpra
19、ctical considerations.6.2.2.1 Plan to determine the PLOQ of each important testresult of a multicomponent test. The PLOQs are not additive.6.2.3 Select Number of LaboratoriesDetermine thePLOQ with the precision during an interlaboratory study sothat it will tend to be representative of industry wide
20、 experi-ence.NOTE 4Just as it is possible to obtain a preliminary estimate of testmethod repeatability by performing a study in one laboratory, so it ispossible to estimate the LOQ of the test method in one laboratory.6.2.4 Determine Number of Runs Per SampleIf a blankmeasurement is required to calc
21、ulate the measured level ofanalyte, the analyst must obtain a separate blank measurementfor each sample aliquot analyzed.NOTE 5At least six degrees of freedom are required. When aprecision study is done, the relevant standard deviation is the repeatabilitystandard deviation. The number of degrees of
22、 freedom here equals thenumber of participating laboratories times the number of repetitions lessone by each laboratory. When one laboratory is used, the relevant standarddeviation is that obtained by repeating the test seven or more times onportions of one sample.6.3 Continue with 6.3.1. However, s
23、ince the PLOQ dependson the attainable precision, there can be cases where alaboratory-specific precision and LOQ are needed by anindividual laboratory for a special purpose. If the decision ismade to determine the LOQ in a single laboratory, proceed to6.3.2.6.3.1 InterlaboratoryConduct the interlab
24、oratory study todetermine precision in a normal fashion making sure thatappropriate samples are included. Proceed to the calculationsteps (Section 7).6.3.2 One Laboratory:6.3.2.1 Select an initial sample. This initial sample and asecond sample (6.2.3) should be selected to bracket an ex-pected LOQ b
25、roadly.6.3.2.2 Run the entire test method on seven aliquots andcalculate mean, standard deviation, and the ratio mean/standarddeviation.6.3.2.3 Select a second sample and repeat the determina-tions and calculations.6.3.2.4 Repeat 6.3.2.1-6.3.2.3 and, for example by a binarysearch process, converge o
26、n the LOQ. Exceptional situationsinclude those where cases of practical interest are either allabove or all below the LOQ as evidenced by the mean tostandard deviation ratios.6.4 An LOQ should be redetermined when there are sub-stantive changes in the operator experience level, test method,instrumen
27、tation, or the sample types to which it is deemedapplicable, and another interlaboratory study becomes neces-sary.7. Calculation7.1 Arrange the means and corresponding standard devia-tions in ascending order of the mean.7.2 Divide each mean by the corresponding standard devia-tion to obtain a ratio.
28、7.3 The level at which these ratios becomes greater than tenand remains so is the PLOQ. A more precise value may beobtained by regression but not by extrapolation.8. Reporting Low-level Data8.1 Should a test result be reported that is below the PLOQ,give the PLOQ in parentheses after the data, for e
29、xample,chlorine content = 110 mg/kg (PLOQ=1000 mg/kg).8.2 A statement about the PLOQ should appear in the testmethod as a footnote to the Scope.9. Examples9.1 Examples from an interlaboratory study are provided inTable 1.9.1.1 The PLOQ itself might be estimated at 1000 mg/kg.Tables similar to Table
30、1 are generated by the ADJ6300computer software program.9.2 Study in One LaboratoryThe abbreviated example inTable 2 illustrates one possible way to tabulate the data.9.2.1 It would seem that the LOQ is at or above the level ofSample A. Nevertheless, it is recommended that at leastanother sample at
31、a lower level be run to make sure this is notan outlier.TABLE 1 Interlaboratory Study ExamplesSample MeanWithin LaboratoriesRatio Mean/StandardDeviationStandardDeviationDegrees ofFreedomS8A110.0 44.72 10 2.5S1A640.0 100.0 10 6.4S3A870.0 89.44 10 9.7S6 1180 94.87 10 12.4S2 1272 78.17 9 16.3S7 2505 13
32、6.0 10 18.4S4 3165 125.0 8 25.3S5 3338 112.4 10 29.6ARatio of mean to standard deviation is less than ten and is, therefore, lowerthan the PLOQ.TABLE 2 Abbreviated ExampleOne LaboratoryRunSample A Blank A-Blank B Blank B-Blank1 800 10 790 1050 20 10302 900 5 895 1250 20 12303 900 10 890 1250 5 12454
33、 800 0 800 1300 0 13005 750 0 750 1200 5 11956 950 20 930 1100 10 10907 1000 5 995 1150 5 1145Mean 864.3 1176.4StandardDeviation-87.29-94.06Ratio Mean/StandardDeviation9.9A12.5ARatio of the mean of sample A to its standard deviation is less than ten and is,therefore, lower than the LOQ.D6259 98 (201
34、0)210. Keywords10.1 limit of quantitation; pooled limit of quantitationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of
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37、ived a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) o
38、f this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D6259 98 (2010)3
