ASTM E2056-00
(Practice)Standard Practice for Qualifying Spectrometers and Spectrophotometers for Use in Multivariate Analyses, Calibrated Using Surrogate Mixtures
Standard Practice for Qualifying Spectrometers and Spectrophotometers for Use in Multivariate Analyses, Calibrated Using Surrogate Mixtures
SCOPE
1.1 This practice relates to the multivariate calibration of spectrometers and spectrophotometers used in determining the physical and chemical characteristics of materials. A detailed description of general multivariate analysis is given in Practice E1655. This standard refers only to those instances where surrogate mixtures can be used to establish a suitable calibration matrix. This practice specifies calibration and qualification data set requirements for interlaboratory studies (ILSs), that is, round robins, of standard test methods employing surrogate calibration techniques that do not conform exactly to Practices E1655.
Note 1--For some multivariate spectroscopic analyses, interferences and matrix effects are sufficiently small that it is possible to calibrate using mixtures that contain substantially fewer chemical components than the samples that will ultimately be analyzed. While these surrogate methods generally make use of the multivariate mathematics described in Practices E1655, they do not conform to procedures described therein, specifically with respect to the handling of outliers.
1.2 This practice specifies how the ILS data is treated to establish spectrometer/spectrophotometer performance qualification requirements to be incorporated into standard test methods.
Note 2--Spectrometer/spectrophotometer qualification procedures are intended to allow the user to determine if the performance of a specific spectrometer/spectrophotometer is adequate to conduct the analysis so as to obtain results consistent with the published test method precision.
1.2.1 The spectroscopies used in the surrogate test methods would include but not be limited to mid- and near-infrared, ultraviolet/visible, fluorescence and Raman spectroscopies.
1.2.2 The surrogate calibrations covered in this practice are: multilinear regression (MLR), principal components regression (PCR) or partial least squares (PLS) mathematics. These calibration procedures are described in detail in Practices E1655.
1.3 For surrogate test methods, this practice recommends limitations that should be placed on calibration options that are allowed in the test method. Specifically, this practice recommends that the test method developer demonstrate that all calibrations that are allowed in the test method produce statistically indistinguishable results.
1.4 For surrogate test methods that reference spectrometer/spectrophotometer performance practices, such as Practices E275, E387, E388, E579, E925, E932, E958, E1421, E1683, E1866 or E1944, this practice recommends that instrument performance data be collected as part of the ILS to establish the relationship between spectrometer/spectrophotometer performance and test method precision.
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Designation: E 2056 – 00
Standard Practice for
Qualifying Spectrometers and Spectrophotometers for Use
in Multivariate Analyses, Calibrated Using Surrogate
Mixtures
This standard is issued under the fixed designation E 2056; 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 1.3 For surrogate test methods, this practice recommends
limitations that should be placed on calibration options that are
1.1 This practice relates to the multivariate calibration of
allowed in the test method. Specifically, this practice recom-
spectrometers and spectrophotometers used in determining the
mends that the test method developer demonstrate that all
physical and chemical characteristics of materials. A detailed
calibrations that are allowed in the test method produce
description of general multivariate analysis is given in Practice
statistically indistinguishable results.
E 1655. This standard refers only to those instances where
1.4 For surrogate test methods that reference spectrometer/
surrogate mixtures can be used to establish a suitable calibra-
spectrophotometer performance practices, such as Practices
tion matrix.This practice specifies calibration and qualification
E 275, E 387, E 388, E 579, E 925, E 932, E 958, E 1421,
data set requirements for interlaboratory studies (ILSs), that is,
E 1683, E 1866 or E 1944, this practice recommends that
round robins, of standard test methods employing surrogate
instrument performance data be collected as part of the ILS to
calibration techniques that do not conform exactly to Practices
establish the relationship between spectrometer/
E 1655.
spectrophotometer performance and test method precision.
NOTE 1—For some multivariate spectroscopic analyses, interferences
andmatrixeffectsaresufficientlysmallthatitispossibletocalibrateusing
2. Referenced Documents
mixtures that contain substantially fewer chemical components than the
2.1 ASTM Standards:
samples that will ultimately be analyzed. While these surrogate methods
D 6277 Test Method for Determination of Benzene in
generally make use of the multivariate mathematics described in Practices
Spark-Ignition Engine Fuels by Mid Infrared Spectros-
E 1655, they do not conform to procedures described therein, specifically
with respect to the handling of outliers.
copy
D 6300 Practice for Determination of Precision and Bias
1.2 This practice specifies how the ILS data is treated to
Data for Use in Test Methods for Petroleum Products and
establish spectrometer/spectrophotometer performance qualifi-
Lubricants
cation requirements to be incorporated into standard test
E 131 Terminology Relating to Molecular Spectroscopy
methods.
E 275 Practice for Describing and Measuring Performance
NOTE 2—Spectrometer/spectrophotometer qualification procedures are
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
intended to allow the user to determine if the performance of a specific
eters
spectrometer/spectrophotometer is adequate to conduct the analysis so as
E 387 Test Method for Estimating Stray Radiant Power of
to obtain results consistent with the published test method precision.
Spectrophotometers by the Opaque Filter Method
1.2.1 The spectroscopies used in the surrogate test methods
E 388 Test Method for Spectral Bandwidth and Wavelength
would include but not be limited to mid- and near-infrared, 3
Accuracy of Fluorescence Spectrophotometers
ultraviolet/visible, fluorescence and Raman spectroscopies.
E 579 Test Method for Limit of Detection of Fluorescence
1.2.2 The surrogate calibrations covered in this practice are:
of Quinine Sulfate
multilinearregression(MLR),principalcomponentsregression
E 691 Practice for Conducting an Inter-Laboratory Study to
(PCR) or partial least squares (PLS) mathematics. These
Determine the Precision of a Test Method
calibration procedures are described in detail in Practices
E 925 PracticeforthePeriodicCalibrationofNarrowBand-
E 1655.
Pass Spectrophotometers
E 932 Practice for Describing and Measuring Performance
of Dispersive Infrared Spectrometers
This practice is under the jurisdiction of ASTM Committee E13 on Molecular
Spectroscopy and is the direct responsibility of Subcommittee E13.11 on Chemo-
metrics.
Annual Book of ASTM Standards, Vol 05.03.
Current edition approved Sept. 10, 2000. Published November 2000. Originally
Annual Book of ASTM Standards, Vol 03.06.
published as E 2056 – 99. Last previous edition E 2056 – 99.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 2056
E 958 Practice for Measuring Practical Spectral Bandwidth The specific mathematics (MLR, PCR or PLS) should be
of Ultraviolet-Visible Spectrophotometers specified,andtheacceptablerangeforthenumbersofvariables
E 1421 Practice for Describing and Measuring Performance should be given.
of Fourier Transform Infrared Spectrophotometers: Level 4.5 When the ILS is conducted to establish the precision of
Zero and Level One Tests
the surrogate test method, the calibration data for all of the
E 1655 Practices for Infrared, Multivariate, Quantitative participating laboratories should be collected and used to
Analysis
calculate a pooled standard error of calibration for the test
E 1683 Practice for Testing the Performance of Scanning method. The pooled standard error of calibration and its
Raman Spectrometers
associated degrees of freedom should be reported in the test
E 1866 Guide for Establishing Spectrophotometer Perfor- method.
mance Tests
4.5.1 When a user is calibrating a spectrometer/
E 1944 Practice for Describing and Measuring Performance
spectrophotometer, the standard error of calibration is calcu-
of Fourier Transform Near-Infrared Spectrometers: Level
lated and compared to the pooled standard error of calibration
Zero and Level One Tests
from the ILS to determine if the performance of the calibrated
spectrometer/spectrophotometer is adequate to produce analy-
3. Terminology
ses of the precision specified in the test method.
3.1 Definitions:
4.5.2 If a user is purchasing a precalibrated spectrometer/
3.1.1 For definitions of terms and symbols relating to
spectrophotometer, the instrument vendor should supply the
infrared, ultraviolet/visible and Raman spectroscopy, refer to
standard error of calibration and its statistical comparison to
Terminology E 131.
the pooled standard error of calibration.
3.1.2 For definitions of terms and symbols relating to
4.6 During the ILS, each participating laboratory analyzes a
multivariate analysis, refer to Practices E 1655.
set of qualification samples and reports both the compositions
3.2 Definitions of Terms Specific to This Standard:
of the qualification set and the estimates made using the
3.2.1 spectrometer/spectrophotometer qualification, n—the
multivariate analysis. A pooled error of qualification is calcu-
procedures by which a user demonstrates that the performance
lated and reported as part of the test method along with its
of a specific spectrometer/spectrophotometer is adequate to
corresponding degrees of freedom.
conduct a multivariate analysis so as to obtain precision
4.6.1 Before a user may use the spectrometer/
consistent with that specified in the test method.
spectrophotometer, it must be qualified to perform the surro-
3.2.2 surrogate calibration, n—a multivariate calibration
gate test method. The qualification set is analyzed, and a
that is developed using a calibration set which consists of
standard error of qualification is calculated. The standard error
mixtureswithpre-specifiedandreproduciblecompositionsthat
of qualification is statistically compared with the pooled
contain substantially fewer chemical components than the
standard error of qualification to determine if the performance
samples that will ultimately be analyzed.
ofthecalibratedspectrometer/spectrophotometerisadequateto
3.2.3 surrogate test method, n—a standard test method that
produce analyses of the precision specified in the test method.
is based on a surrogate calibration.
4.6.2 Spectrometer/spectrophotometer qualification is re-
quiredregardlessofwhetherthecalibrationisperformedbythe
4. Summary of Practice
vendor or the user.
4.1 Asurrogatetestmethodmustspecifythecompositionof
4.6.3 Spectrometer/spectrophotometer qualification should
two sets of samples. One set is used to calibrate the
berepeatedaftermajormaintenancehasbeenperformedonthe
spectrometers/spectrophotometers. The second set of samples
spectrometer/spectrophotometer so as to determine whether
is used to qualify the spectrometer/spectrophotometer to per-
recalibration is required.
form the analysis. The compositions of both sets are expressed
in terms of weight or volume fraction depending on whether
5. Significance and Use
thesamplesarepreparedgravimetricallyorvolumetrically.The
5.1 This practice should be used by the developer of
compositions of both sets should be specified in the surrogate
standard test methods that employ surrogate calibrations.
test method. If the surrogate test method is being used to
5.1.1 This practice assists the test method developer in
estimate a physical property, then the test method should
setting and documenting requirements for the spectrometer/
indicate what value of the property is to be assigned to each of
spectrophotometers that can perform the test method.
the calibration and qualification samples.
5.1.2 This practice assists the test method developer in
4.2 The surrogate test method should specify the minimum
spectrometer/spectrophotometer requirements for instruments setting and documenting spectral data collection and compu-
tation parameters for the test method.
that can be used to perform the test method.
4.3 The spectrometer/spectrophotometer test method should 5.1.3 This practice assists the test method developer in
specify the exact conditions that are to be used to collect and, selecting among possible multivariate analysis procedures that
where appropriate, to calculate the spectral data used in the could be used to establish the surrogate calibration. The
calibration and analysis. practice describes statistical tests that should be performed to
4.4 The test method should specify the exact mathematics ensurethatallmultivariateanalysisproceduresthatareallowed
that are to be used to develop the multivariate calibration. within the scope of the test method produce statistically
Allowable spectral preprocessing methods should be defined. indistinguishable results.
E 2056
5.1.4 This practice describes statistical calculations that the analysis of that component is to be conducted. Additional
test method developer should perform on the calibration and components that are present in the calibration set to simulate
qualification data that should be collected as part of the ILS interferences should be independently and uniformly varied
that establishes the test method precision. These calculations over a range at least as large as is likely to be encountered
establish the level of performance that spectrometers/ during actual application of the test method.
spectrophotometers must meet in order to perform the test 6.2.3 When calibrating for a property that depends on more
method.
than one chemical component, the calibration set should
5.2 This practice describes how the person who calibrates a uniformly span the range over which the property analysis is to
spectrometer/spectrophotometer can test the performance of
be conducted, and all components that contribute to the
said spectrometer/spectrophotometer to determine if the per- property should be varied independently.
formance is adequate to conduct the test method.
6.2.4 The test method should specify the compositions of
5.3 This practice describes how the user of a spectrometer/
the calibration samples, including components and target
spectrophotometer can qualify the spectrometer/
concentrations. The purity of materials to be used in preparing
spectrophotometer to conduct the test method.
the calibration samples should also be specified in the test
method.
6. Surrogate Calibrations
6.3 Qualification Sets:
6.1 Practices E 1655 assumes that the calibration set used to
6.3.1 The sets of surrogate samples that are used to qualify
develop a multivariate model contains samples of the same
the spectrometers/spectrophotometers should satisfy the vali-
type as those that are to eventually be analyzed using the
dation requirements of Practices E 1655. If k is the number of
model. Practices E 1655 requires use of outlier statistics to
variables (MLR wavelengths or frequencies, PCR principal
ensure that samples being analyzed are sufficiently similar to
components or PLS latent variables) used in the model, then
the calibration samples to produce meaningful results. For
the minimum number of qualification samples should be the
some spectroscopic analyses, however, it is possible to cali-
greater of 20 or 5k.
brate using gravimetrically or volumetrically prepared mix-
6.3.2 The compositions of the qualification samples should
tures that contain significantly fewer components than the
span the same ranges as did the calibration samples.
samples that will ultimately be analyzed. For these surrogate
6.3.3 The test method should specify the compositions of
testmethods,theoutlierstatisticsdescribedinPracticesE 1655
the qualification samples, including components and target
arenotappropriatesinceallsamplesareexpectedtobeoutliers
concentrations. The purity of materials to be used in preparing
relative to the simplified calibrations. Thus, surrogate test
the qualification samples should also be specified in the test
methods cannot fulfill the requirements of Practices E 1655.
method.
While surrogate test methods may make use of the mathemat-
6.4 Precision of Surrogate Calibration Test Methods:
ics described in Practices E 1655, they should not claim to
6.4.1 An ILS determines the precision of a surrogate test
follow the procedures described in that practice.
method.Theinterlaboratorystudymustconformtotherequire-
6.1.1 Indevelopingsurrogatetestmethods,itisnecessaryto
ments of Practice E 691, and to any other relevant practices.
thoroughly understand and account for potential spectral inter-
For example, a test method applicable to petroleum products
ferences. Typically, the spectral range used in surrogate cali-
should conform to Practice D 6300.
brations will be limited so as to minimize interferences. For
6.4.2 The standard error of calibra
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