ASTM D7783-13
(Practice)Standard Practice for Within-laboratory Quantitation Estimation (WQE)
Standard Practice for Within-laboratory Quantitation Estimation (WQE)
SIGNIFICANCE AND USE
5.1 Appropriate application of this practice should result in a WQE achievable by the laboratory in applying the tested method/matrix/analyte combination to routine sample analysis. That is, a laboratory should be capable of measuring concentrations greater than WQEZ %, with the associated RSD equal to Z % or less.
5.2 The WQE values may be used to compare the quantitation capability of different methods for analysis of the same analyte in the same matrix within the same laboratory.
5.3 The WQE procedure should be used to establish the within-laboratory quantitation capability for any application of a method in the laboratory where quantitation is important to data use. The intent of the WQE is not to impose reporting limits. The intent is to provide a reliable procedure for establishing the quantitative characteristics of the method (as implemented in the laboratory for the matrix and analyte) and thus to provide the laboratory with reliable information characterizing the uncertainty in any data produced. Then the laboratory may make informed decisions about censoring data and has the information necessary for providing reliable estimates of uncertainty with reported data.
SCOPE
1.1 This practice establishes a uniform standard for computing the within-laboratory quantitation estimate associated with Z % relative standard deviation (referred to herein as WQEZ %), and provides guidance concerning the appropriate use and application.
1.2 WQEZ % is computed to be the lowest concentration for which a single measurement from the laboratory will have an estimated Z % relative standard deviation (Z % RSD, based on within-laboratory standard deviation), where Z is typically an integer multiple of 10, such as 10, 20, or 30. Z can be less than 10 but not more than 30. The WQE10 % is consistent with the quantitation approaches of Currie (1)2 and Oppenheimer, et al (2).
1.3 The fundamental assumption of the WQE is that the media tested, the concentrations tested, and the protocol followed in the developing the study data provide a representative and fair evaluation of the scope and applicability of the test method, as written. Properly applied, the WQE procedure ensures that the WQE value has the following properties:
1.3.1 Routinely Achievable WQE Value—The laboratory should be able to attain the WQE in routine analyses, using the laboratory‘s standard measurement system(s), at reasonable cost. This property is needed for a quantitation limit to be feasible in practical situations. Representative data must be used in the calculation of the WQE.
1.3.2 Accounting for Routine Sources of Error—The WQE should realistically include sources of bias and variation that are common to the measurement process and the measured materials. These sources include, but are not limited to intrinsic instrument noise, some typical amount of carryover error, bottling, preservation, sample handling and storage, analysts, sample preparation, instruments, and matrix.
1.3.3 Avoidable Sources of Error Excluded—The WQE should realistically exclude avoidable sources of bias and variation (that is, those sources that can reasonably be avoided in routine sample measurements). Avoidable sources would include, but are not limited to, modifications to the sample, modifications to the measurement procedure, modifications to the measurement equipment of the validated method, and gross and easily discernible transcription errors (provided there was a way to detect and either correct or eliminate these errors in routine processing of samples).
1.4 The WQE applies to measurement methods for which instrument calibration error is minor relative to other sources, because this practice does not model or account for instrument calibration error, as is true of quantiation estimates in general. Therefore, the WQE procedure is appropriate when the dominant source of variation is not instrument calibration, but is perhaps one...
General Information
Standards Content (Sample)
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Designation: D7783 − 13
Standard Practice for
1
Within-laboratory Quantitation Estimation (WQE)
This standard is issued under the fixed designation D7783; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
Note—Balloted information was included and the year date changed on March 28, 2013.
1. Scope 1.3.3 Avoidable Sources of Error Excluded—The WQE
should realistically exclude avoidable sources of bias and
1.1 This practice establishes a uniform standard for com-
variation (that is, those sources that can reasonably be avoided
puting the within-laboratory quantitation estimate associated
in routine sample measurements). Avoidable sources would
with Z % relative standard deviation (referred to herein as
include, but are not limited to, modifications to the sample,
WQE ), and provides guidance concerning the appropriate
Z%
modifications to the measurement procedure, modifications to
use and application.
themeasurementequipmentofthevalidatedmethod,andgross
1.2 WQE is computed to be the lowest concentration for
Z%
and easily discernible transcription errors (provided there was
which a single measurement from the laboratory will have an
a way to detect and either correct or eliminate these errors in
estimatedZ%relativestandarddeviation(Z%RSD,basedon
routine processing of samples).
within-laboratory standard deviation), where Z is typically an
1.4 The WQE applies to measurement methods for which
integermultipleof10,suchas10,20,or30.Zcanbelessthan
instrument calibration error is minor relative to other sources,
10 but not more than 30. The WQE is consistent with the
10 %
2
because this practice does not model or account for instrument
quantitation approaches of Currie (1) and Oppenheimer, et a.l
calibration error, as is true of quantiation estimates in general.
(2).
Therefore, the WQE procedure is appropriate when the domi-
1.3 The fundamental assumption of the WQE is that the
nant source of variation is not instrument calibration, but is
media tested, the concentrations tested, and the protocol
perhaps one or more of the following:
followed in the developing the study data provide a represen-
1.4.1 Sample Preparation, and especially when calibration
tative and fair evaluation of the scope and applicability of the
standards do not go through sample preparation.
test method, as written. Properly applied, the WQE procedure
1.4.2 Differences in Analysts, and especially when analysts
ensures that the WQE value has the following properties:
have little opportunity to affect instrument calibration results
1.3.1 Routinely Achievable WQE Value—The laboratory
(as is the case with automated calibration).
shouldbeabletoattaintheWQEinroutineanalyses,usingthe
1.4.3 Differences in Instruments (measurement equipment),
laboratory‘s standard measurement system(s), at reasonable
such as differences in manufacturer, model, hardware,
cost. This property is needed for a quantitation limit to be
electronics, sampling rate, chemical-processing rate, integra-
feasible in practical situations. Representative data must be
tion time, software algorithms, internal signal processing and
used in the calculation of the WQE.
thresholds, effective sample volume, and contamination level.
1.3.2 Accounting for Routine Sources of Error—The WQE
should realistically include sources of bias and variation that
1.5 Data Quality Objectives—For a given method, one
are common to the measurement process and the measured
typically would compute the lowest % RSD possible for any
materials.Thesesourcesinclude,butarenotlimitedtointrinsic
givendataset.Thus,ifpossible,WQE wouldbecomputed.
10%
instrument noise, some typical amount of carryover error,
If the data indicated that the method was too noisy, one might
bottling, preservation, sample handling and storage, analysts,
have to compute instead WQE , or possibly WQE .In
20% 30%
sample preparation, instruments, and matrix.
any case, a WQE with a higher% RSD level (such as
WQE ) would not be considered, though a WQE with RSD
50%
<10%(suchasWQE )wouldbeacceptable.Theappropriate
1%
1
This practice is under the jurisdiction ofASTM Committee D19 on Water and
level of % RSD is based on the data-quality objective(s) for a
is the direct responsibility of Subcommittee D19.02 on Quality Systems,
particular use or uses. This practice allows for calculation of
Specification, and Statistics.
WQEs with user selected % RSDs less than 30%.
Current edition approved March 28, 2013. Published April 2013. Originally
approved in 2012. Last previous edition approved in 2012 as D7783–12. DOI:
1.6 This international standard was developed i
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