1、Designation: D 6259 98 (Reapproved 2004)An American National StandardStandard Practice forDetermination of a Pooled Limit of Quantitation1This standard is issued under the fixed designation D 6259; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、an 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:2E 456 Terminology Rela
4、ting to Quality and StatisticsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ASTM Adjuncts:ADJ6300 D2PP, Version 4.43, Determination of Precisionand Bias Data for Use in Test Methods for PetroleumProducts33. Terminology3.1 Definitions:3.1.1 poole
5、d limit of quantitation, nlevel 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 sa
6、melaboratory by the same operator 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 PracticeE 691.)NOTE 1The same operator, same equipment requirem
7、ent means thatfor a particular 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 i
8、n the shortest practical period 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 E 456.3.2 Acronyms:3.2.1 PLOQ, np
9、ooled limit of quantitation.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
10、.1 In a single laboratory, the limit of quantitation, LOQ,equal to ten standard deviations has been recommended.4A testresult 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-m
11、ended. A test result at this 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
12、 more sensitive proce-dures, 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 on
13、eof the procedures described 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 to1This practice is under the jurisdiction of Committee D02 on Petroleum
14、Productsand Lubricants and is the direct responsibility of Subcommittee D02.94 on QualityAssurance and Statistics.Current edition approved May 1, 2004. Published June 2004. Originallyapproved in 1998. Last previous edition approved in 1998 as D 525998.2For referenced ASTM standards, visit the ASTM w
15、ebsite, 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 ASTM International Headquarters. Order Adjunct No.ADJ6300.4Keith, L. H., et al, “Principles o
16、f Environmental Analysis,” Analytical Chem-istry, American Chemical Society, Vol 55, 1983, p. 227.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.bracket the PLOQ. In some cases, the PLOQ will be wellbelow the useful range. Then, it
17、is only necessary to determinea less than value.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 laboratory.6.2.2 Select
18、 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 otherpractical considera
19、tions.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 experi-ence.NOT
20、E 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 calculate the measur
21、ed 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 freedom here eq
22、uals 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, since the PLOQ de
23、pendson 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 interlaboratory study to
24、determine 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 broadly.6.3.2.2 R
25、un 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 on the LOQ. Excep
26、tional 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,instrumentation, or the s
27、ample 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.7.3 The level at
28、 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 example,chlorine
29、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 1 are generated
30、by the ADJ6300computer software program.9.2 Study in One LaboratoryThe abbreviated example inTable 2 illustrates one possible way to tabulate the data.TABLE 1 Interlaboratory Study ExamplesSample MeanWithin LaboratoriesRatio Mean/StandardDeviationStandardDeviationDegrees ofFreedomS8A110.0 44.72 10 2
31、.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 136.0 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-
32、Blank B Blank B-Blank1 800 10 790 1050 20 10302 900 5 895 1250 20 12303 900 10 890 1250 5 12454 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
33、A to its standard deviation is less than ten and is,therefore, lower than the LOQ.D 6259 98 (2004)29.2.1 It would seem that the LOQ is at or above the level ofSample A. Nevertheless, it is recommended that at leastanother sample at a lower level be run to make sure this is notan outlier.10. Keywords
34、10.1 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 any such patent
35、 rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either
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37、ring 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) of 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).D 6259 98 (2004)3
