ASTM E1866-97(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1866 − 97 (Reapproved 2021)
Standard Guide for
Establishing Spectrophotometer Performance Tests
This standard is issued under the fixed designation E1866; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This guide covers basic procedures that can be used to
E131Terminology Relating to Molecular Spectroscopy
develop spectrophotometer performance tests. The guide is
E275PracticeforDescribingandMeasuringPerformanceof
intended to be applicable to spectrophotometers operating in
Ultraviolet and Visible Spectrophotometers
the ultraviolet, visible, near-infrared and mid-infrared regions.
E925Practice for Monitoring the Calibration of Ultraviolet-
1.2 This guide is not intended as a replacement for specific
Visible Spectrophotometers whose Spectral Bandwidth
practicessuchasPracticesE275,E925,E932,E958,E1421,or
does not Exceed 2 nm
E1683thatexistformeasuringperformanceofspecifictypesof
E932PracticeforDescribingandMeasuringPerformanceof
spectrophotometers. Instead, this guide is intended to provide
Dispersive Infrared Spectrometers
guidelines in how similar practices should be developed when
E958Practice for Estimation of the Spectral Bandwidth of
specific practices do not exist for a particular spectrophotom- Ultraviolet-Visible Spectrophotometers
eter type, or when specific practices are not applicable due to
E1421Practice for Describing and Measuring Performance
samplingorsafetyconcerns.Thisguidecanbeusedtodevelop of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
performance tests for on-line process spectrophotometers. eters: Level Zero and Level One Tests
E1655 Practices for Infrared Multivariate Quantitative
1.3 This guide describes univariate level zero and level one
Analysis
tests, and multivariate level A and level B tests which can be
E1683Practice for Testing the Performance of Scanning
implemented to measure spectrophotometer performance.
Raman Spectrometers
These tests are designed to be used as rapid, routine checks of
spectrophotometer performance.They are designed to uncover
3. Terminology
malfunctions or other changes in instrument operation, but do
3.1 Definitions—For terminology relating to molecular
not specifically diagnose or quantitatively assess the malfunc-
spectroscopic methods, refer to Terminology E131.
tionorchange.Thetestsarenotintendedforthecomparisonof
3.2 Definitions of Terms Specific to This Standard:
spectrophotometers of different manufacture.
3.2.1 action limit, n—the limiting value from an instrument
1.4 This standard does not purport to address all of the
performance test, beyond which the spectrophotometer is
safety concerns, if any, associated with its use. It is the
expected to produce potentially invalid results.
responsibility of the user of this standard to establish appro-
3.2.2 check sample, n—a single pure compound, or a
priate safety, health, and environmental practices and deter-
known,reproduciblemixtureofcompoundswhosespectrumis
mine the applicability of regulatory limitations prior to use.
constant over time such that it can be used in a performance
1.5 This international standard was developed in accor-
test.
dance with internationally recognized principles on standard-
3.2.3 level A test, n—a pass/fail spectrophotometer perfor-
ization established in the Decision on Principles for the
mance test in which the spectrum of a check or test sample is
Development of International Standards, Guides and Recom-
compared against historical spectra of the same sample via a
mendations issued by the World Trade Organization Technical
multivariate analysis.
Barriers to Trade (TBT) Committee.
3.2.4 level B test, n—a pass/fail spectrophotometer perfor-
mance test in which the spectrum of a check or test sample is
This guide is under the jurisdiction of ASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.03 on Infrared and Near Infrared Spectroscopy. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2021. Published April 2021. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1997. Last previous edition approved in 2013 as E1866–97(2013). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E1866-97R21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1866 − 97 (2021)
analyzed using a multivariate model, and the results of the be in effect during its intended use. Sufficient warm-up time
analysisarecomparedtohistoricalresultsforprioranalysesof should be allowed before the commencement of any measure-
the same sample. ments.
5.1.1 Ifpossible,theopticalconfigurationusedformeasure-
3.2.5 level one (1) test, n—a simple series of measurements
mentsoftestandchecksamplesshouldbeidenticaltothatused
designed to provide quantitative data on various aspects of
for normal operations. If identical optical configurations are
spectrophotometer performance and information on which to
not possible, the user should recognize that the performance
base the diagnosis of problems.
tests may not measure the performance of the entire instru-
3.2.6 level zero (0) test, n—a routine check of spectropho-
ment.
tometer performance, which can be done in a few minutes,
5.1.2 Data collection and computation conditions should
designed to visually detect significant changes in instrument
generally be identical to those used in normal operation.
performance and provide a database to determine instrument
Spectraldatausedinperformancetestsshouldbedateandtime
performance over time.
stamped, and the results of the tests should be stored in a
3.2.7 optical reference filter, n—an optical filter or other
historical database.
device which can be inserted into the optical path in the
spectrophotometer or probe producing an absorption spectrum
6. Samples Used for Performance Testing
which is known to be constant over time such that it can be
used in place of a check or test sample in a performance test. 6.1 Thesampleusedforperformancetestingischosentobe
compatible with the spectrophotometer configuration, and to
3.2.8 test sample, n—a process or product sample, or a
providespectralfeatureswhichareadequateforthetestsbeing
mixture of process or product samples which has a constant
performed.
spectrum for a finite time period and which can be used in a
6.1.1 The sample used for performance testing should
performance test. Test samples and their spectra are generally
generallybeinthesamephysicalstate(gas,liquid,orsolid)as
not reproducible in the long term.
the samples to be analyzed during normal operation of the
4. Significance and Use spectrophotometer.
6.1.2 The sample used for performance testing should be
4.1 IfASTM Committee E13 has not specified an appropri-
physically and chemically compatible with the samples ana-
ate test procedure for a specific type of spectrophotometer, or
lyzed during normal operation.
if the sample specified by a Committee E13 procedure is
incompatible with the intended spectrophotometer operation, 6.1.3 The sample used for performance is chosen such that
then this guide can be used to develop practical performance its spectrum is similar to the spectra which will be collected
tests. during normal operation.
4.1.1 For spectrophotometers which are equipped with per-
6.1.4 The sample used for performance testing should have
manent or semi-permanent sampling accessories, the test
severalsignificantabsorbances(0.3 sample specified in a Committee E13 practice may not be
thespectralrangeusedfornormaloperationofthespectropho-
compatible with the spectrophotometer configuration. For
tometer.
example, for FT-MIR instruments equipped with transmittance
6.1.5 In order to adequately determine the photometric
or IRS flow cells, tests based on polystyrene films are imprac-
linearityoftheinstrument,thepeakabsorbanceforatleastone
tical. In such cases, these guidelines suggest means by which
absorption band of the sample should be similar to and
the recommended test procedures can be modified so as to be
preferablyslightlygreaterthanthelargestabsorbanceexpected
performed on a compatible test material.
for samples measured during normal operation.
4.1.2 For spectrophotometers used in process
6.2 Check Samples—Check samples are generally used for
measurements, the choice of test materials may be limited due
conducting performance tests. Check samples are single pure
to process contamination and safety considerations. These
compoundsormixturesofcompoundsofdefinitecomposition.
guidelines suggest means of developing performance tests
6.2.1 Ifmixturesareutilizedaschecksamples,theymustbe
basedonmaterialswhicharecompatiblewiththeintendeduse
preparedinarepeatablemannerand,ifstored,storedsuchthat
of the spectrophotometer.
the mixture is stable over long periods of time. In preparing
4.2 Tests developed using these guidelines are intended to
mixtures, components should be accurately pipetted or
allow the user to compare the performance of a spectropho-
weighed at ambient temperature. It is recommended that
tometeronanygivendaywithpriorperformance.Thetestsare
mixtures be independently verified for composition prior to
intended to uncover malfunctions or other changes in instru-
use.
ment operation, but they are not designed to diagnose or
6.2.2 While mixtures can be used as check samples, their
quantitatively assess the malfunction or change. The tests are
spectra may be adversely affected by temperature sensitive
not intended for the comparison of spectrophotometers of
interactions that may manifest themselves by wavelength
different manufacture.
(frequency) and absorbance changes.
5. Test Conditions
6.3 Test Samples—A test sample is a process or product
5.1 Whenconductingtheperformancetests,thespectropho- sample or a mixture of process or product samples whose
tometer should be operated under the same conditions as will spectrum is expected to be constant for the time period it is
E1866 − 97 (2021)
used in performance testing.The test sample must be stored in example, absorptions of water vapor and carbon dioxide) and
bulkquantitiesincontrolledconditionssuchthatthematerialis from interferences due to optical components (for example,
stable over time. OH absorptions in SiO cells and fibers). Preferably, regions
6.3.1 Since test samples are often complex mixtures which where the background spectrum is relatively flat and slowly
cannot be synthetically reproduced, they can only be used for varying should be used for this test.
performancetestingforlimitedtimeperiods.Iftestsamplesare 7.1.3 To minimize the effects of photometric noise on the
usedforthispurpose,collectionofhistoricaldataonanewtest
energy level measurement, it is preferable to average the
sample should be initiated before previous test samples are energy over a narrow frequency (wavelength) window.
depleted.Itisrecommendedthatnewtestsamplesbeanalyzed
Typically, the intensity at five points centered on the test
sequentially with old test samples at least 15 times before they frequency are averaged.
are used to replace the old test sample. The 15 analyses must
7.2 Photometric Noise Tests—Photometric noise is mea-
be performed over a time period that does not exceed one
sured at the same frequencies (wavelengths) used for the
month in duration.
energy level tests. Preferably, photometric noise tests are
6.4 Optical Filters—An optical reference filter is an optical
conducted on a 100% line spectrum.Alternatively, photomet-
filter or other optical device located in the spectrophotometer
ricnoisetestsmaybeconductedonthespectrumofacheckor
or in a fiber optic sample probe which produces an absorption
test sample at regions where the spectrum is relatively flat and
spectrum which is known to be constant over time. This filter
the sample absorbance is minimal (<0.1).
may be automatically inserted into the optical path to allow
7.2.1 For single beam spectrophotometers where back-
instrument performance tests to be performed.
groundandsamplespectraaremeasuredseparatelyatdifferent
6.4.1 Optical filters are used principally with on-line pro-
times, a 100% line spectrum is obtained by ratioing two
cessspectrophotometersequippedwithfiberopticprobeswhen
successivebackgroundmeasurementstoobtainatransmittance
removal of the probe is inconvenient, precluding the use of
spectrum. If, during normal operation of the
check or test samples for routine instrument performance
spectrophotometer, backgrounds are collected with a reference
testing.
materialintheopticalpath,thenthissameconfigurationshould
6.4.2 If an optical filter is used routinely to check or correct
be used for performance testing. Photometric noise calcula-
thespectraldatacollectionorcomputation,thenthesamefilter
tions are preferably done directly on the transmittance spec-
ispreferablynotusedforinstrumentperformancetesting.Ifthe
trum. Alternatively, the transmittance spectrum may be con-
same filter is used, then the part of the filter spectrum used in
verted to an absorption spectrum by taking the negative log
the performance testing should preferably differ from that part
before the photometric noise calculations.
used to check or correct the instrument. For example, polysty-
7.2.2 For double beam spectrophotometers, a 100% line
rene filters are used to standardize (continuously check and
spectrum is measured when the two beams are both empty,
correct) the wavelength scale of some dispersive NIR spectro-
both contain empty matched cells, or both contain reference
photometers. For such systems, polystyrene filters are prefer-
samples in matched cells.
ably not to be employed for wavelength stability performance
7.2.3 Photometric noise is measured by fitting a line to the
testing. If polystyrene filters are used, then the peaks used for
spectrum over a short spectral region centered on the test
wavelengthstabilitytestingshouldbedifferentfromthoseused
frequency (wavelength). The region should contain at least 11
for standardizing the wavelength scale.
datapoints,preferablycontains101datapoints,andshouldnot
exceed 2% of the spectral range. The line is subtracted from
7. Univariate Measures of Spectrophotometer
thespectraldata,andtheRMSnoiseiscalculatedasthesquare
Performance
root of the mean square residual.
7.2.3.1 IfT isthetransmittanceatthefrequencyv,thenthe
7.1 Energy Level Tests—Energy level tests are intended to
i i
slope, m, and intercept, b, of a line through the n data points
detect changes in the radiant power in the spectrophotometer
centered at test frequency v are given by the following:
beam. Decreases in energy levels may be associated with
deterioration of the spectrophotometer source, with contami-
n iT 2 T i
i i
( ( (
nation or misalignment of optical surfaces in the light path, or m 5 (1)
n i 2 ~ i!
( (
with malfunctions of the detector.
i T 2 i iT
7.1.1 For single beam spectrophotometers where back-
( ( i ( ( i
b 5 (2)
groundandsamplespectraaremeasuredseparatelyatdifferent
n i 2 ~ i!
( (
times, energy level tests are generally conducted on a back-
The photometric noise is calculated as follows:
ground spectrum. For double beam spectrophotometers where
the ratio of background and sample beam intensities is mea-
T 2 mi1b
~ ~ !!
( i
sureddirectly,energylevelscanbemeasuredifitispossibleto Noise 5Π(3)
RMS
n 22
block the sample beam.
The index i in Eq 1-3 runs from−(n − 1)/2 to (n − 1)/2 (n
7.1.2 Energy levels should be measured at at least three
must be odd).The intercept represents the transmittance at test
fixed frequencies (wavelengths), one each in the upper, middle
frequency v .
and lower third of the spectral range. The frequencies (wave-
lengths)atwhichenergylevelsaremeasuredshouldbechosen 7.2.3.2 If photometric noise is calculated on absorbance
to avoid interferences due to atmospheric components (for spectra, the absorbance values, A, are used in place of the
i
E1866 − 97 (2021)
transmittance values, T,in Eq 1-3. If the abscissa for the outside this range, the wavelength stability measurement may
i
spectral data is wavelength, then wavelength values, λ, are show greater sensitivity to photometric noise.
i
used in place of the frequency values, v,in Eq 1-3. Calcula- 7.6.2 Peaks used for the frequency stability test are prefer-
i
tions should be consistently performed on the same data types. ably symmetric in shape and well resolved from neighboring
peaks. If such peaks are not available in the spectrum of the
7.2.4 Increases in the photometric noise can indicate a
misalignment of optical components, a source malfunction, or check/testsampleoropticalfilter,theusershouldbeawarethat
changes in spectrophotometer resolution will affect the mea-
a malfunction in the detector or electronics.
sured peak position.
7.3 ShortTermBaselineStabilityTest—Thetransmittanceis
7.6.3 It is recommended that the peak position be deter-
monitoredateachofthetestfrequencies(wavelengths)usedin
mined by the following steps:
the energy level and photometric noise tests. The intercept
7.6.3.1 Compute the first derivative of the spectrum by
calculated in Eq 2 represents the transmittance averaged over
applying the appropriate digital filter to the spectrum. A
the n points around test frequency v . Deviation from 100%
commonly used filter has been defined by Savitzki and Golay
transmittance is an indication of short term baseline instability
(1) with corrections by Steiner, Termonia, and Deltour (2),
and may indicate a malfunction of the spectrophotometer.
withapplicationcriteriadiscussedbyWillsonandPolo (3).The
7.3.1 If the tests are conducted on absorbance spectra,
latterreferencediscussesoptimumfilterparametersbasedupon
deviations from zero absorbance is used as an indication of
the relationship between spectral bandwidth and digitization
baseline instability.
interval.Acubic filter is recommended. The number of points
7.3.2 If photometric noise tests are conducted on the spec-
used in the filter should be the quotient of the full-width-at-
trum of a check or test sample, then variations in the absor-
half-maximum of the peak being measured divided by the
bance spectrum at the test frequencies are taken as an indica-
digital resolution, and rounded up to the nearest odd integer.
tion of short term baseline instability.
7.6.3.2 Identify the zero crossing associated with the peak
7.4 Optical Contamination Tests—The single beam back-
absorbance and compute its location by linear interpolation
ground scan which was used for the energy tests is examined
between the two adjacent points straddling the zero crossing.
for absorptions which might indicate contamination of optical
The zero crossing is taken as a measure of the peak position.
surfaces in the beam path.
NOTE 1—Other peak finding algorithms can be used provided that they
7.4.1 Failure to clean cell or probe windows, IRS surfaces,
accurately track peak position. The procedure described in Annex A1
etc., are the most common source of optical contamination.
should be used to test peak finding algorithms to determine if they are
Frequencies (wavelengths) at which typical samples exhibit appropriate for this application. It is the users responsibility to demon-
strate that the peak finding algorithm is appropriate for monitoring
maximum absorbance should generally be examined. For
spectrophotometer frequency (wavelength) stability.
example, for IR systems used in hydrocarbon analysis, the
7.7 Resolution Stability Tests—The resolution stability of
regions where the C-H stretching vibrations occur should be
the spectrophotometer is monitored by measuring the band-
examined. Significant increases above a nominal background
widths of several absorption peaks in the absorption spectrum
level may indicate contamination of windows and surfaces.
of the check/test sample or optical filter. At least three peaks
7.4.2 Spectrophotometer optical surfaces can be contami-
are used for the test. If possible, the peaks should be in the
nated by impurities in purge gases. For systems equipped with
upper, middle and lower third of the spectral range. Variations
flow cells or circulating liquid temperature control, leaks in
in the measured bandwidths are taken as an indication that the
connecting lines can expose an optical surface to contamina-
opticalresolutionofthespectrophotometerisvarying,suggest-
tion. Users should consider possible sources of contamination
ing a malfunction.
and determine appropriate frequencies at which absorptions
7.7.1 The absorption for peaks used in this test are prefer-
would result.
ably in the range from 0.37 to 0.75. For peak absorptions
7.5 Purge Contamination Tests—For spectrophotometers
outside this range, the resolution stability measurement may
which are purged to minimize absorptions due to atmospheric
show increased sensitivity to photometric noise.
components, the single beam spectrum used for energy tests
7.7.2 Peaks used for the resolution stability test are prefer-
should be checked for variations in purge quality. Frequencies
ably symmetric in shape and well resolved from neighboring
(wavelengths) at which potential contaminants absorb should
peaks. If such peaks are not available in the spectrum of the
be identified, as should baseline points where contaminant
check/test sample or optical filter, the results of the resolution
absorption would be minimal. The absorbance for contami-
stability test may be variable.
nantsiscalculatedasthenegativelog oftheratioofthepeak
7.7.3 It is recommended that the peak bandwidth be deter-
intensity to the baseline intensity.
mined by the following steps:
7.6 Frequency (Wavelength) Stability Tests—Frequency
7.7.3.1 Compute the second derivative of the spectrum by
(wavelength) stability tests are conducted by monitoring the applying the appropriate digital filter to the spectrum. A
peak positions of several peaks across the absorption spectrum
commonly used filter has been defined by Savitzki and Golay
ofthecheckortestsampleoropticalfilter.Atleastthreepeaks (1)withcorrectionsbySteiner,Termonia,andDeltour (2),with
are used for the test. If possible, the peaks should be in the
upper, middle and lower third of the spectral range.
7.6.1 The absorption for peaks used in this test are prefer-
The boldface numbers in parentheses refer to a list of references at the end of
ably in the range from 0.37 to 0.75. For peak absorptions this standard.
E1866 − 97 (2021)
application criteria discussed by Willson and Polo (3). The 8.1.2.1 In this LevelAtest, a least squares fit of the current
latterreferencediscussesoptimumfilterparametersbasedupon spectrum of the check sample, test sample or optical filter is
the relationship between spectral bandwidth and digitization
conducted against a historical spectrum of the same material.
interval.Acubic filter is recommended. The number of points Baseline terms may be included in the fit to compensate for
used in the filter should be the quotient of the full-width-at-
variations in baseline, and scaling may be applied to compen-
half-maximum of the peak being measured divided by the
sate for pathlength variations. The types of compensations
digital resolution, and rounded up to the nearest odd integer.
(baseline or pathlength) used in the fit should be similar to
7.7.3.2 Identify the zero crossing on each side of the peak
those e
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