ASTM D6259-98

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An American National Standard
Designation: D 6259 – 98
Standard Practice for
Determination of a Pooled Limit of Quantitation
This standard is issued under the fixed designation D 6259; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Summary of Practice
1.1 This practice covers the determination of a lower 4.1 Determine the standard deviation of a test result, under
quantitative limit for a test method for an analyte. The repeatability conditions, at progressively higher levels of the
determined lower limit is herinafter referred to as the pooled analyte until the ratio of measured level to standard deviation
limit of quantitation. becomes greater than ten and remains so.
1.2 Applicable test methods will produce test results greater
5. Significance and Use
than zero. Examples are those test methods that measure
sample composition. 5.1 In a single laboratory, the limit of quantitation, LOQ,
equal to ten standard deviations has been recommended. A test
2. Referenced Documents
result at this LOQ has an uncertainty of 630 % at the 99 %
2.1 ASTM Standards: confidence level. Similarly here, as a general estimate, the
E 456 Terminology Relating to Quality and Statistics PLOQ, equal to ten repeatability standard deviations is recom-
E 691 Practice for Conducting an Interlaboratory Study to mended. A test result at this PLOQ has an uncertainty of
Determine the Precision of a Test Method 630 % at the 99 % confidence level.
5.2 Values below the PLOQ are deemed to be too uncertain
3. Terminology
for meaningful use in commerce, or in regulatory activities.
3.1 Definitions: 5.3 Many test methods never find application outside their
3.1.1 pooled limit of quantitation, n—level of property or
PLOQ. However, in the quest for ever more sensitive proce-
concentration of analyte above which quantitative test results dures, it can become difficult to distinguish an analytical
can be obtained with a specified degree of confidence. See
response from background noise with the technology at hand.
3.2.1 for acronym. Test methods defective in design or poorly executed may also
3.1.2 repeatability conditions, n—conditions under which
function outside their PLOQ.
test results are obtained with the same test method in the same
6. Procedure
laboratory by the same operator with the same equipment in the
shortest practical period of time using test units or test 6.1 Make the preparations outlined in 6.2, then carry out one
specimens taken at random from a single quantity of material of the procedures described in 6.3.
that is as nearly homogeneous as possible (see 10.3 of Practice 6.2 Preparations:
E 691.) 6.2.1 Select Test Levels—Decide the objective of the test
method, the range of typical samples it is expected to cover.
NOTE 1—The same operator, same equipment requirement means that
Name a set of test levels covering this range and spaced to
for a particular step in the measurement process the same combination of
bracket the PLOQ. In some cases, the PLOQ will be well
operator and equipment is used for every test result. Thus, one operator
may prepare the test specimens, a second measure the dimensions, and a below the useful range. Then, it is only necessary to determine
third measure the mass in a test method for measuring density.
a less than value.
NOTE 2—By in the shortest practical period of time is meant that the
NOTE 3—Mean and standard deviation data from experienced labora-
test results, at least for one material, are obtained in a time period not less
tories, archived research reports, and known limitations of the test method
than in normal testing and not so long as to permit significant change in
or equipment can give a preliminary notion of the PLOQ. An LOQ can be
test material, equipment, or environment. See Terminology E 456.
estimated in a single laboratory.
3.2 Acronyms:Acronym:
6.2.2 Select Sample Materials—Normally, use sample ma-
3.2.1 PLOQ, n—pooled limit of quantitation.
terials that are typical of those to which the test method is
applied. In special cases, the method of standard additions
This practice is under the jurisdiction of Committee D02 on Petroleum Products
and Lubricants and is the direct responsibility of Subcommittee D02.94 on Quality
Assurance and Statistics.
Current edition approved April 10, 1998. Published July 1998. Keith, L. H., et al, “Principles of Environmental Analysis,” Analytical Chem-
Annual Book of ASTM Standards, Vol 14.02. istry, American Chemical Society, Vol 55, 1983, p. 227.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6259–98
TABLE 1 Interlaboratory Study Examples
6.3.1 Interlaboratory—Conduct the interlaboratory study to
Within Laboratories determine precision in a normal fashion making sure that
Ratio Mean/Standard
Sample Mean appropriate samples are included. Proceed to the calculation
Standard Degrees of
Deviation
Deviation Freedom
steps (Section 7).
A
S8 110.0 44.72 10 2.5 6.3.2 One Laboratory:
A
S1 640.0 100.0 10 6.4
6.3.2.1 Select an initial sample. This initial sample and a
A
S3 870.0 89.44 10 9.7
second sample (6.2.3) should be selected to bracket an ex-
S6 1180 94.87 10 12.4
S2 1272 78.17 9 16.3 pected LOQ broadly.
S7 2505 136.0 10 18.4
6.3.2.2 Run the entire
...