ASTM E925-09(2014)
(Practice)Standard Practice for Monitoring the Calibration of Ultraviolet-Visible Spectrophotometers whose Spectral Bandwidth does not Exceed 2 nm
Standard Practice for Monitoring the Calibration of Ultraviolet-Visible Spectrophotometers whose Spectral Bandwidth does not Exceed 2 nm
SIGNIFICANCE AND USE
4.1 This practice permits an analyst to compare the performance of an instrument to the manufacturer's supplied performance specifications and to verify its suitability for continued routine use. It also provides generation of calibration monitoring data on a periodic basis, forming a base from which any changes in the performance of the instrument will be evident.
SCOPE
1.1 This practice covers the parameters of spectrophotometric performance that are critical for testing the adequacy of instrumentation for most routine tests and methods2 within the wavelength range of 200 to 700 nm and the absorbance range of 0 to 2. The recommended tests provide a measurement of the important parameters controlling results in spectrophotometric methods, but it is specifically not to be inferred that all factors in instrument performance are measured.
1.2 This practice may be used as a significant test of the performance of instruments for which the spectral bandwidth does not exceed 2 nm and for which the manufacturer's specifications for wavelength and absorbance accuracy do not exceed the performance tolerances employed here. This practice employs an illustrative tolerance of ±1 % relative for the error of the absorbance scale over the range of 0.2 to 2.0, and of ±1.0 nm for the error of the wavelength scale. A suggested maximum stray radiant power ratio of 4 × 10-4 yields
1.3 This practice should be performed on a periodic basis, the frequency of which depends on the physical environment within which the instrumentation is used. Thus, units handled roughly or used under adverse conditions (exposed to dust, chemical vapors, vibrations, or combinations thereof) should be tested more frequently than those not exposed to such conditions. This practice should also be performed after any significant repairs are made on a unit, such as those involving the optics, detector, or radiant energy source.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E925 − 09 (Reapproved 2014)
Standard Practice for
Monitoring the Calibration of Ultraviolet-Visible
Spectrophotometers whose Spectral Bandwidth does not
Exceed 2 nm
This standard is issued under the fixed designation E925; 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.
INTRODUCTION
In the application of spectrophotometric methods of analysis it is the responsibility of the analyst
to verify and validate that the instrument is functioning properly and is capable of providing
acceptable analytical results. It is preferable that the verification of instrument performance be
accomplished through the use of reference materials whose properties have been accurately
determined.Suchmaterialsarereadilyavailable,andtheiruseinthetestsandmeasurementsdescribed
in this practice is satisfactory for evaluating the performance of spectrophotometers whose spectral
bandwidth does not exceed the value for which the intrinsic or certified properties are valid. A
compromise maximum permissible spectral bandwidth of 2 nm is recommended for the reference
materials and error tolerances recommended here.
This practice covers some of the essential instrumental parameters that should be evaluated to
ensure the acceptability of the analytical data routinely obtained on the instrument. These parameters
include the accuracy of the wavelength and absorbance scales and stray radiant power levels.
Theaccuracyofthewavelengthscaleinboththeultraviolet(UV)andvisibleregionsisdetermined
using the sharp absorption bands of a holmium oxide glass or solution filter. The absorbance scale
accuracy in the UV region (235 to 350 nm) is determined using acidic solutions of potassium
dichromate. In the visible region (440 to 635 nm) the absorbance accuracy is determined using
individuallycertifiedneutraldensityglassfilters.Theuseofthesereferencematerialsprovidesavalid
andrelativelysimplemeanstotesttheerrorsinthewavelengthandabsorbancescalesofsmallspectral
bandwidth spectrophotometers in the spectral ranges indicated. A simplified version of the opaque
filter method is provided as a test for excessive stray radiant energy.
1. Scope 1.2 This practice may be used as a significant test of the
performance of instruments for which the spectral bandwidth
1.1 Thispracticecoverstheparametersofspectrophotomet-
does not exceed 2 nm and for which the manufacturer’s
ric performance that are critical for testing the adequacy of
specifications for wavelength and absorbance accuracy do not
instrumentation for most routine tests and methods within the
exceed the performance tolerances employed here. This prac-
wavelength range of 200 to 700 nm and the absorbance range
tice employs an illustrative tolerance of 61% relative for the
of0to2.Therecommendedtestsprovideameasurementofthe
error of the absorbance scale over the range of 0.2 to 2.0, and
important parameters controlling results in spectrophotometric
of 61.0 nm for the error of the wavelength scale.Asuggested
methods, but it is specifically not to be inferred that all factors
-4
maximum stray radiant power ratio of4×10 yields <1%
in instrument performance are measured.
absorbance bias at an absorbance of 2. These tolerances are
chosen to be compatible with many chemical applications
while comfortably exceeding the uncertainty of the certified
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
values for the reference materials and typical manufacturer’s
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
specifications for error in the wavelength and absorbance
mittee E13.01 on Ultra-Violet, Visible, and Luminescence Spectroscopy.
Current edition approved May 1, 2014. Published June 2014. Originally
scales of the instrument under test. The user is encouraged to
approved in 1983. Last previous edition approved in 2009 as E925–09. DOI:
develop and use tolerance values more appropriate to the
10.1520/E0925-09R14.
2 requirements of the end use application. This procedure is
Routine tests are defined as those in which absorbance data obtained on a
sample are compared to those of a standard sample preparation. designed to verify quantitative performance on an ongoing
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E925 − 09 (2014)
basis and to compare one instrument’s performance with that ISOGuide34General Requirements for the Competence of
of other similar units. Refer to Practice E275 to extensively Reference Material Producers
evaluate the performance of an instrument.
3. Terminology
1.3 This practice should be performed on a periodic basis,
3.1 Definitions:
the frequency of which depends on the physical environment
3.1.1 For the definitions of terms used in this practice, refer
within which the instrumentation is used. Thus, units handled
to Terminology E131.
roughly or used under adverse conditions (exposed to dust,
3.1.2 For a description of the instrumental parameters
chemical vapors, vibrations, or combinations thereof) should
evaluated in this practice, refer to Practice E275.
be tested more frequently than those not exposed to such
3.1.3 For a description of quantitative ultraviolet spectro-
conditions. This practice should also be performed after any
photometric techniques, refer to Practice E169.
significant repairs are made on a unit, such as those involving
the optics, detector, or radiant energy source.
4. Significance and Use
1.4 The values stated in SI units are to be regarded as
4.1 This practice permits an analyst to compare the perfor-
standard. No other units of measurement are included in this
mance of an instrument to the manufacturer’s supplied perfor-
standard.
mance specifications and to verify its suitability for continued
1.5 This standard does not purport to address all of the
routine use. It also provides generation of calibration monitor-
safety concerns, if any, associated with its use. It is the
ing data on a periodic basis, forming a base from which any
responsibility of the user of this standard to establish appro-
changes in the performance of the instrument will be evident.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Reference to this Calibration-Monitoring Procedure
5.1 Reference to this practice in any spectrophotometric
2. Referenced Documents
calibration-monitoring scheme shall constitute due notification
2.1 ASTM Standards:
that the adequacy of the spectrophotometer performance has
E131Terminology Relating to Molecular Spectroscopy
been evaluated by means of this practice. Performance is
E169PracticesforGeneralTechniquesofUltraviolet-Visible
considered to be adequate when the data obtained are within
Quantitative Analysis
the stated tolerances from the true values.
E275PracticeforDescribingandMeasuringPerformanceof
Ultraviolet and Visible Spectrophotometers 6. Instrument Operation
E387TestMethodforEstimatingStrayRadiantPowerRatio
6.1 In obtaining spectrophotometric calibration data the
of Dispersive Spectrophotometers by the Opaque Filter
analyst must select the proper instrumental operating condi-
Method
tions to realize satisfactory instrument performance. Operating
E1866Guide for Establishing Spectrophotometer Perfor-
conditions for individual instruments are best obtained from
mance Tests
the manufacturer’s literature because of variations in instru-
2.2 NIST Publications:
ment design.
NISTSpecialPublication260-54 Certification and Use of
6.2 When using reference materials, all the components of
AcidicPotassiumDichromateSolutionsAsAnUltraviolet
the spectrophotometer must be functioning properly. In
Absorbance Standard
addition, the temperature of the specimen compartment should
NISTSpecialPublication260-102 Holmium Oxide Solu-
be between 20 and 25°C. Matched solution cells should be
tion Wavelength Standard from 240 to 640 nm—SRM
used for calibration purposes.
6.3 Each of the above factors in instrument operation is
NISTSpecialPublication260-116Glass Filters as a Stan-
important in the determination of wavelength and absorbance
dard Reference Material for Spectrophotometry—
accuracy.
Selection,Preparation,Certification,andUseofSRM930
and SRM 1930
7. Determination of Wavelength Accuracy in the
NISTSpecialPublication260-140 Technical Specifications
Ultraviolet and Visible Spectral Regions
for Certification of Spectrophotometric NTRMs
7.1 Discussion—The holmium oxide glass filter (1, 2) or
2.3 ISO Publications:
solution standard (NISTSpecialPublication260-102) may be
ISO17025General Requirements for the Competence of
used for evaluating wavelength accuracy. The glass and solu-
Testing and Calibration Laboratories
tion standards are both available commercially from reference
material producers, in the sealed cuvette format (a cuvette-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
shaped metal holder is used for the glass) or as a bottled
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
solution, prepared from high purity Holmium Oxide (>
Standards volume information, refer to the standard’s Document Summary page on
99.99%),wherevalueassignmentisbyselfassertion(Note1).
the ASTM website.
Available from NationalTechnical Information Service (NTIS), 5301 Shawnee
Rd., Alexandria, VA 22312, http://www.ntis.gov.
5 6
Available from International Organization for Standardization (ISO), 1, ch. de The boldface numbers in parentheses refer to a list of references at the end of
la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org. this standard.
E925 − 09 (2014)
Apurchasershouldrequirecertificationbythesupplierthatthe 7.2.1 Examine the holmium oxide reference material and
wavelengths of the absorption bands are within 0.2-nm of the remove any surface contamination using a soft brush or
values given in Ref. (2), and reported below. The appropriate lint-free cloth. Measure the temperature of the sample com-
solution standard is 4% (mass fraction) holmium oxide in partment by placing an appropriate sensor into the cell com-
10% (volume fraction) perchloric acid, contained in a 10-mm partment of a stabilized instrument and replacing the compart-
pathlengthcuvette.Forthismaterial,thetransmittanceminima mentcoversecurely.Placethesensorascloseaspossibletothe
of 18 absorption bands have been certified by a multi- actual position that will be occupied by the standard. After a
laboratory inter-comparison, at the highest level, allowing the suitable period of time record the temperature reading, remove
peakvalueassignmentsasanintrinsicwavelengthstandard (3). the sensor, and resume normal operations.
Absorbance maxima or transmittance minima must be located 7.2.2 Record the blank absorbance or transmittance (air
within 61 nm of the wavelengths given below: versus air) spectrum at the desired resolution and at the
A B
appropriate wavelength intervals and scan speeds, in order to
Glass Filter Dilute Acidic Solution
C
241.5 nm 241.1 nm
perform any necessary baseline adjustments. The wavelength
. . . 249.9 nm
intervalsshouldbenogreaterthanthespectralbandwidthused.
279.3 nm 278.1 nm
Acquire the appropriate spectrum of the holmium oxide
287.6 nm 287.2 nm
333.8 nm 333.5 nm
reference material with respect to air and baseline correct if
. . . 345.4 nm
necessaryusingtheblankspectrum.Recordthewavelengthsof
360.8 nm 361.3 nm
thepositionsoftherelevantbands,andcomparethesevaluesto
385.8 nm 385.6 nm
418.5 nm 416.3 nm
the expected values. If large discrepancies (>1 nm) exist
D
453.4 nm . . .
between the true and measured wavelengths, repeat the proce-
459.9 nm 467.8 nm
dure at a slower scan speed and smaller spectral bandwidth, if
. . . 485.3 nm
536.4 nm 536.6 nm
possible, to verify the nonconformity.
637.5 nm 640.5 nm
7.2.3 Report the wavelength calibration data in the manner
of Table 1, given as an example for the holmium oxide glass
A
Wavelengths taken from Ref. (2) for Corning Glass Works Code 3130 glass,
reference material.
supercededbyCorningGlassWorksCode3131glassandKoppGlassCode3131
glass, for which the wavelengths are also valid.
B
Wavelengths rounded to 0.1 nm for a 1-nm spectral bandwidth taken from Ref.
8. Evaluation of Stray Radiant Power Ratio (SRPR)
(3).
C
May not be usable, depending on the base glass of the filter.
8.1 Discussion—A portion of the unwanted stray radiant
D
Peak omitted because it resolves into a doublet at spectral bandwidth values
powerdetectedbythephotodetectorcanbemeasuredusingthe
less than 1 nm.
following sharp cut-off solution filters in 1-cm cells:
NOTE 1—‘Self assertion’ may take the form of value assignment and
Solution Wavelength
certification in many forms. Some specific examples are:
KI or NaL, 10.0 g/L in H O 220 nm
(1) By a national metrology institute (NMI),
NaNo , 50.0 g/L in H O 370 nm
2 2
(2) By an ISO17025 and ISOGuide34 accredited Reference Mate-
rial producer, and
(3) By a laboratory claiming ‘traceability’to an NMI.
In all cases, the user should be satisfied that the quality of the value
assignment data meets the laboratory requirements. TABLE 1 UV-VIS Spectrophotometer Wavelength and Stray
Radiant Power Ratio Calibration
7.1.1 Iftheobservedabsorptionbandsoftheholmiumoxide
Instrument
glass or solution deviate by more than 61 nm from the values
Date
stated, then corrective service must by performed on the
Temperature
Analyst
instrument by qualified personnel. If the user performs this
Wavelength Calibration: Holmium Oxide Filter
service, the manufacturer’s recommended procedure should be
followed carefully.
True Observed
Conformance
Difference
7.1.2 The wavelength accuracy is dependent on the spectral
Wavelength Wavelength
(nm)
Does Does Not
(nm) (nm)
bandwidth and thus on the physical bandwidth. Spectral
241.5 ± 1
bandwidthsmaybedeterminedfromthemanufacturer’sspeci-
279.3 ± 1
fications. 287.6 ± 1
333.8 ± 1
7.1.3 Computer based peak location algorithms that may be
360.8 ± 1
usedtoassignabsorbancemaximaortransmittanceminimaare
385.8 ± 1
discussed in 7.6 of Guide E1866. It should be noted that peak 418.5 ± 1
453.4 ± 1
asymmetriesintheholmiumoxidereferencematerialsaresuch
459.9 ± 1
that digital filter widths should be smaller than the full-width-
536.4 ± 1
637.5 ± 1
half-maximum recommendation of that guide.
7.1.4 In the absence of drift or slippage in the wavelength
Stray Radiant Power Ratio
drive train, repeatability of the band positions should be on the
Wavelength Transmittance Does Not
Conf
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