ASTM E1655-05(2012)
(Practice)Standard Practices for Infrared Multivariate Quantitative Analysis
Standard Practices for Infrared Multivariate Quantitative Analysis
SIGNIFICANCE AND USE
5.1 These practices can be used to establish the validity of the results obtained by an infrared (IR) spectrometer at the time the calibration is developed. The ongoing validation of estimates produced by analysis of unknown samples using the calibration model should be covered separately (see for example, Practice D6122).
5.2 These practices are intended for all users of infrared spectroscopy. Near-infrared spectroscopy is widely used for quantitative analysis. Many of the general principles described in these practices relate to the common modern practices of near-infrared spectroscopic analysis. While sampling methods and instrumentation may differ, the general calibration methodologies are equally applicable to mid-infrared spectroscopy. New techniques are under study that may enhance those discussed within these practices. Users will find these practices to be applicable to basic aspects of the technique, to include sample selection and preparation, instrument operation, and data interpretation.
5.3 The calibration procedures define the range over which measurements are valid and demonstrate whether or not the sensitivity and linearity of the analysis outputs are adequate for providing meaningful estimates of the specific physical or chemical characteristics of the types of materials for which the calibration is developed.
SCOPE
1.1 These practices cover a guide for the multivariate calibration of infrared spectrometers used in determining the physical or chemical characteristics of materials. These practices are applicable to analyses conducted in the near infrared (NIR) spectral region (roughly 780 to 2500 nm) through the mid infrared (MIR) spectral region (roughly 4000 to 400 cm−1).Note 1—While the practices described herein deal specifically with mid- and near-infrared analysis, much of the mathematical and procedural detail contained herein is also applicable for multivariate quantitative analysis done using other forms of spectroscopy. The user is cautioned that typical and best practices for multivariate quantitative analysis using other forms of spectroscopy may differ from practices described herein for mid- and near-infrared spectroscopies.
1.2 Procedures for collecting and treating data for developing IR calibrations are outlined. Definitions, terms, and calibration techniques are described. Criteria for validating the performance of the calibration model are described.
1.3 The implementation of these practices require that the IR spectrometer has been installed in compliance with the manufacturer's specifications. In addition, it assumes that, at the times of calibration and of validation, the analyzer is operating at the conditions specified by the manufacturer.
1.4 These practices cover techniques that are routinely applied in the near and mid infrared spectral regions for quantitative analysis. The practices outlined cover the general cases for coarse solids, fine ground solids, and liquids. All techniques covered require the use of a computer for data collection and analysis.
1.5 These practices provide a questionnaire against which multivariate calibrations can be examined to determine if they conform to the requirements defined herein.
1.6 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 herein, they do not conform to procedures described herein, specifically with respect to the handling of outliers. Surrogate methods may indicate that they make use of the mathematics described herein, but they should not claim to follow the procedures described herein.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are inc...
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E1655 − 05 (Reapproved 2012)
Standard Practices for
Infrared Multivariate Quantitative Analysis
This standard is issued under the fixed designation E1655; 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.
1. Scope analyzed. While these surrogate methods generally make use
of the multivariate mathematics described herein, they do not
1.1 These practices cover a guide for the multivariate
conform to procedures described herein, specifically with
calibration of infrared spectrometers used in determining the
respect to the handling of outliers. Surrogate methods may
physical or chemical characteristics of materials. These prac-
indicate that they make use of the mathematics described
tices are applicable to analyses conducted in the near infrared
herein, but they should not claim to follow the procedures
(NIR) spectral region (roughly 780 to 2500 nm) through the
described herein.
mid infrared (MIR) spectral region (roughly 4000 to 400
−1
cm ). 1.7 The values stated in SI units are to be regarded as
NOTE 1—While the practices described herein deal specifically with
standard. No other units of measurement are included in this
mid-andnear-infraredanalysis,muchofthemathematicalandprocedural
standard.
detail contained herein is also applicable for multivariate quantitative
1.8 This standard does not purport to address all of the
analysisdoneusingotherformsofspectroscopy.Theuseriscautionedthat
typicalandbestpracticesformultivariatequantitativeanalysisusingother safety concerns, if any, associated with its use. It is the
formsofspectroscopymaydifferfrompracticesdescribedhereinformid-
responsibility of the user of this standard to establish appro-
and near-infrared spectroscopies.
priate safety and health practices and determine the applica-
1.2 Procedures for collecting and treating data for develop-
bility of regulatory limitations prior to use.
ing IR calibrations are outlined. Definitions, terms, and cali-
bration techniques are described. Criteria for validating the
2. Referenced Documents
performance of the calibration model are described.
2.1 ASTM Standards:
1.3 The implementation of these practices require that the
D1265Practice for Sampling Liquefied Petroleum (LP)
IR spectrometer has been installed in compliance with the
Gases, Manual Method
manufacturer’s specifications. In addition, it assumes that, at
D4057Practice for Manual Sampling of Petroleum and
the times of calibration and of validation, the analyzer is
Petroleum Products
operating at the conditions specified by the manufacturer.
D4177Practice for Automatic Sampling of Petroleum and
Petroleum Products
1.4 These practices cover techniques that are routinely
D4855Practice for Comparing Test Methods (Withdrawn
applied in the near and mid infrared spectral regions for
2008)
quantitative analysis. The practices outlined cover the general
D6122Practice for Validation of the Performance of Multi-
cases for coarse solids, fine ground solids, and liquids. All
variate Online,At-Line, and Laboratory Infrared Spectro-
techniques covered require the use of a computer for data
photometer Based Analyzer Systems
collection and analysis.
D6299Practice for Applying Statistical Quality Assurance
1.5 These practices provide a questionnaire against which
and Control Charting Techniques to Evaluate Analytical
multivariate calibrations can be examined to determine if they
Measurement System Performance
conform to the requirements defined herein.
D6300Practice for Determination of Precision and Bias
1.6 For some multivariate spectroscopic analyses, interfer-
Data for Use in Test Methods for Petroleum Products and
encesandmatrixeffectsaresufficientlysmallthatitispossible
Lubricants
to calibrate using mixtures that contain substantially fewer
E131Terminology Relating to Molecular Spectroscopy
chemical components than the samples that will ultimately be
1 2
These practices are under the jurisdiction of ASTM Committee E13 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Molecular Spectroscopy and Separation Science and are the direct responsibility of contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Subcommittee E13.11 on Multivariate Analysis. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2012. Published May 2012. Originally the ASTM website.
approved in 1997. Last previous edition approved in 2005 as E1655–05. DOI: The last approved version of this historical standard is referenced on
10.1520/E1655-05R12. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1655 − 05 (2012)
E168Practices for General Techniques of Infrared Quanti- 3.2.8 reference method, n—the analytical method that is
tative Analysis (Withdrawn 2015) used to estimate the reference component concentration or
E275PracticeforDescribingandMeasuringPerformanceof property value which is used in the calibration and validation
Ultraviolet and Visible Spectrophotometers procedures.
E334Practice for General Techniques of Infrared Micro-
3.2.9 reference values, n—the component concentrations or
analysis
property values for the calibration or validation samples which
E456Terminology Relating to Quality and Statistics
are measured by the reference analytical method.
E691Practice for Conducting an Interlaboratory Study to
3.2.10 spectrometer/spectrophotometer qualification,
Determine the Precision of a Test Method
n—the procedures by which a user demonstrates that the
E932PracticeforDescribingandMeasuringPerformanceof
performance of a specific spectrometer/spectrophotometer is
Dispersive Infrared Spectrometers
adequate to conduct a multivariate analysis so as to obtain
E1421Practice for Describing and Measuring Performance
precision consistent with that specified in the method.
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
eters: Level Zero and Level One Tests
3.2.11 surrogate calibration, n—a multivariate calibration
E1866Guide for Establishing Spectrophotometer Perfor-
that is developed using a calibration set which consists of
mance Tests
mixtures which contain substantially fewer chemical compo-
E1944Practice for Describing and Measuring Performance
nents than the samples which will ultimately be analyzed.
of Laboratory Fourier Transform Near-Infrared (FT-NIR)
3.2.12 surrogate method, n—a standard test method that is
Spectrometers: Level Zero and Level One Tests
based on a surrogate calibration.
3. Terminology
3.2.13 validation samples—asetofsamplesusedinvalidat-
3.1 Definitions—Forterminologyrelatedtomolecularspec- ing the model. Validation samples are not part of the set of
calibration samples. Reference component concentration or
troscopic methods, refer to Terminology E131. For terminol-
property values are known (measured by reference method),
ogy relating to quality and statistics, refer to Terminology
and are compared to those estimated using the model.
E456.
3.2 Definitions of Terms Specific to This Standard:
4. Summary of Practices
3.2.1 analysis, n—in the context of this practice,theprocess
of applying the calibration model to a spectrum, preprocessed
4.1 Multivariate mathematics is applied to correlate the
as required, so as to estimate a component concentration value
spectra measured for a set of calibration samples to reference
or property.
component concentrations or property values for the set of
3.2.2 calibration, n—a process used to create a model
samples. The resultant multivariate calibration model is ap-
relating two types of measured data. In the context of this
plied to the analysis of spectra of unknown samples to provide
practice, a process for creating a model that relates component
an estimate of the component concentration or property values
concentrations or properties to spectra for a set of known
for the unknown sample.
reference samples.
4.2 Multilinear regression (MLR), principal components
3.2.3 calibration model, n—the mathematical expression or
regression(PCR),andpartialleastsquares(PLS)areexamples
the set of mathematical operations that relates component
of multivariate mathematical techniques that are commonly
concentrations or properties to spectra for a set of reference
used for the development of the calibration model. Other
samples.
mathematical techniques are also used, but may not detect
3.2.4 calibration samples, n—the set of reference samples
outliers, and may not be validated by the procedure described
used for creating a calibration model. Reference component
in these practices.
concentration or property values are known (measured by
4.3 Statistical tests are applied to detect outliers during the
reference method) for the calibration samples and a calibration
development of the calibration model. Outliers include high
modelisfoundwhichrelatesthesevaluestothespectraduring
leverage samples (samples whose spectra contribute a statisti-
the calibration.
cally significant fraction of one or more of the spectral
3.2.5 estimate, n—the value for a component concentration
variables used in the model), and samples whose reference
or property obtained by applying the calibration model for the
values are inconsistent with the model.
analysis of an absorption spectrum.
4.4 Validation of the calibration model is performed by
3.2.6 model validation, n—the process of testing a calibra-
using the model to analyze a set of validation samples and
tion model with validation samples to determine bias between
statisticallycomparingtheestimatesforthevalidationsamples
the estimates from the model and the reference method, and to
toreferencevaluesmeasuredforthesesamples,soastotestfor
testtheagreementbetweenestimatesmadewiththemodeland
bias in the model and for agreement of the model with the
the reference method.
reference method.
3.2.7 multivariate calibration, n—a process for creating a
model that relates component concentrations or properties to 4.5 Statistical tests are applied to detect when values esti-
the absorbances of a set of known reference samples at more mated using the model represent extrapolation of the calibra-
than one wavelength or frequency. tion.
E1655 − 05 (2012)
4.6 Statistical expressions for calculating the repeatability varietyofdatatreatmentsandcalibrationalgorithms.Themore
of the infrared analysis and the expected agreement between common linear techniques are discussed in Section 12.A
the infrared analysis and the reference method are given. variety of statistical techniques are used to evaluate and
optimize the model. These techniques are described in Section
5. Significance and Use
15. Statistics used to detect outliers in the calibration set are
covered in Section 16.
5.1 These practices can be used to establish the validity of
6.1.5 ValidationoftheCalibrationModel—Validationofthe
theresultsobtainedbyaninfrared(IR)spectrometeratthetime
the calibration is developed. The ongoing validation of esti- efficacy of a specific calibration model (equation) requires that
the model be applied for the analysis of a separate set of test
mates produced by analysis of unknown samples using the
calibration model should be covered separately (see for (validation)samples,andthatthevaluespredictedforthesetest
samples be statistically compared to values obtained by the
example, Practice D6122).
reference method. The statistical tests to be applied for
5.2 These practices are intended for all users of infrared
validation of the model are discussed in Section 18.
spectroscopy. Near-infrared spectroscopy is widely used for
6.1.6 Application of the Model for the Analysis of
quantitative analysis. Many of the general principles described
Unknowns—The mathematical model is applied to the spectra
in these practices relate to the common modern practices of
of unknown samples to estimate component concentrations or
near-infrared spectroscopic analysis. While sampling methods
property values, or both, (see Section 13). Outlier statistics are
and instrumentation may differ, the general calibration meth-
used to detect when the analysis involves extrapolation of the
odologies are equally applicable to mid-infrared spectroscopy.
model (see Section 16).
New techniques are under study that may enhance those
6.1.7 Routine Analysis and Monitoring—Once the efficacy
discussedwithinthesepractices.Userswillfindthesepractices
of one or more calibration equations is established, the equa-
to be applicable to basic aspects of the technique, to include
tions must be monitored for continued accuracy and precision.
sample selection and preparation, instrument operation, and
Simultaneously, the instrument performance must be moni-
data interpretation.
tored so as to trace any deterioration in performance to either
5.3 The calibration procedures define the range over which
thecalibrationmodelitselfortoafailureintheinstrumentation
measurements are valid and demonstrate whether or not the
performance. Procedures for verifying the performance of the
sensitivityandlinearityoftheanalysisoutputsareadequatefor
analysis are only outlined in Section 22. For petrochemicals,
providing meaningful estimates of the specific physical or
these procedures are covered in detail in Practice D6122. The
chemical characteristics of the types of materials for which the
useofPracticeD6122requiresthataqualitycontrolprocedure
calibration is developed.
be established at the time the model is developed. The QC
check sample is discussed in Section 22. For practices to
6. Overview of Multivariate Calibration
compare reference methods and analyzer methods, refer to
6.1 The practice of infrared multivariate quantitative analy-
Practices D4855.
sis involves the following steps:
6.1.8 Transfer of Calibrations—Transferable calibrations
6.1.1 Selecting the Calibration Set—This set is also termed
are equations that can be transferred from the original
thetrainingsetorspectrallibraryset.Thissetistorepresentall
instrument, where calibration data were collected, to other
of the chemical and physical variation normally encountered
instruments where the calibrations are to be used to predict
forroutineanalysisforthedesiredapplication.Selectionofthe
samples for routine analysis. In order for a calibration to be
calibration set is discussed in Section 17, after the statistical
transferable it must perform prediction after transfer without a
terms necessary to define the selection criteria have been
significantdecreaseinperformance,asind
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