ASTM E275-08(2013)
(Practice)Standard Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
Standard Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
SIGNIFICANCE AND USE
4.1 This practice permits an analyst to compare the general performance of an instrument, as it is being used in a specific spectrophotometric method, with the performance of instruments used in developing the method.
SCOPE
1.1 This practice covers the description of requirements of spectrophotometric performance, especially for test methods, and the testing of the adequacy of available equipment for a specific method (for example, qualification for a given application). The tests give a measurement of some of the important parameters controlling results obtained in spectrophotometric methods, but it is specifically not to be concluded that all the factors in instrument performance are measured, or in fact may be required for a given application.
1.1.1 This practice is primarily directed to dispersive spectrophotometers used for transmittance measurements rather than instruments designed for diffuse transmission and diffuse reflection.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: E275 − 08 (Reapproved 2013)
Standard Practice for
Describing and Measuring Performance of Ultraviolet and
Visible Spectrophotometers
This standard is issued under the fixed designation E275; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
In developing a spectrophotometric method, it is the responsibility of the originator to describe the
instrumentation and the performance required to duplicate the precision and accuracy of the method.
It is necessary to specify this performance in terms that may be used by others in applications of the
method.
The tests and measurements described in this practice are for the purpose of determining the
experimental conditions required for a particular analytical method. In using this practice, an analyst
has either a particular analysis for which he describes requirements for instrument performance or he
expects to test the capability of an instrument to perform a particular analysis. To accomplish either
of these objectives, it is necessary that instrument performance be obtained in terms of the factors that
control the analysis. Unfortunately, it is true that not all the factors that can affect the results of an
analysis are readily measured and easily specified for the various types of spectrophotometric
equipment.
Of the many factors that control analytical results, this practice covers verification of the essential
parameters of wavelength accuracy, photometric accuracy, stray light, resolution, and characteristics
of absorption cells as the parameters of spectrophotometry that are likely to be affected by the analyst
in obtaining data. Other important factors, particularly those primarily dependent on instrument
design, are also covered in this practice.
1. Scope 1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This practice covers the description of requirements of
standard.
spectrophotometric performance, especially for test methods,
1.3 This standard does not purport to address all of the
and the testing of the adequacy of available equipment for a
safety concerns, if any, associated with its use. It is the
specific method (for example, qualification for a given appli-
responsibility of the user of this standard to establish appro-
cation).The tests give a measurement of some of the important
priate safety and health practices and determine the applica-
parameters controlling results obtained in spectrophotometric
bility of regulatory limitations prior to use.
methods, but it is specifically not to be concluded that all the
factors in instrument performance are measured, or in fact may
2. Referenced Documents
be required for a given application.
1.1.1 This practice is primarily directed to dispersive spec- 2.1 ASTM Standards:
E131 Terminology Relating to Molecular Spectroscopy
trophotometers used for transmittance measurements rather
than instruments designed for diffuse transmission and diffuse E168 Practices for General Techniques of Infrared Quanti-
tative Analysis (Withdrawn 2015)
reflection.
1 2
This practice is under the jurisdiction of ASTM Committee E13 on Molecular For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Spectroscopy and Separation Science and is the direct responsibility of Subcom- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
mittee E13.01 on Ultra-Violet, Visible, and Luminescence Spectroscopy. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Jan. 1, 2013. Published January 2013. Originally the ASTM website.
The last approved version of this historical standard is referenced on
approved in 1965. Last previous edition approved in 2008 as E275 – 08. DOI:
www.astm.org.
10.1520/E0275-08R13.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E275 − 08 (2013)
E169 PracticesforGeneralTechniquesofUltraviolet-Visible stants. Rigorous measurement of these factors is beyond the
Quantitative Analysis scopeofthispractice.Themeasurementofstrayradiantenergy
E387 TestMethodforEstimatingStrayRadiantPowerRatio is described in Test Method E387 and resolution in Practice
of Dispersive Spectrophotometers by the Opaque Filter E958.
Method
6.2 Modern spectrophotometers are capable of more accu-
E958 Practice for Estimation of the Spectral Bandwidth of
racy than most analysts obtain. The problem lies in the
Ultraviolet-Visible Spectrophotometers
selection and proper use of instrumentation. In order to ensure
proper instrumentation and its use in a specific spectrophoto-
3. Terminology
metric method, it is necessary for an analyst to evaluate certain
3.1 Definitions:
parameters that can control the results obtained. These param-
3.1.1 For definitions of terms used in this practice, refer to
eters are wavelength accuracy and precision, photometric
Terminology E131.
accuracy and precision, spectral bandwidth, and absorption-
cell constants. Unsatisfactory measurement of any of these
4. Significance and Use
parameters may be due to improper instrumentation or to
4.1 This practice permits an analyst to compare the general
improper use of available instrumentation. It is therefore first
performance of an instrument, as it is being used in a specific
necessary to determine that instrument operation is in accor-
spectrophotometric method, with the performance of instru-
dance with the manufacturer’s recommendations. Tests shall
ments used in developing the method.
then be made to determine the performance of an instrument in
terms of each of the parameters in 6.1 and 6.2. Lastly,
5. Reference to This Practice in Standards
variations in optical geometry and their effects in realizing
5.1 Reference to this practice in any spectrophotometric test satisfactory instrument performance are discussed.
method (preferably in the section on apparatus where the
spectrophotometer is described) shall constitute due notifica-
7. Instrument Operation
tionthattheadequacyofthespectrophotometerperformanceis
7.1 In obtaining spectrophotometric data, the analyst must
to be evaluated by means of this practice. Performance is
select the proper instrumental operating conditions in order to
consideredtobeadequatewhentheinstrumentcanbeoperated
realize satisfactory instrument performance. Operating condi-
in a manner to give test results equivalent to those obtained on
tions for individual instruments are best obtained from the
instruments used in establishing the method or in cooperative
manufacturer’s literature because of variations with instrument
testing of the method.
design. A record should be kept to document the operating
5.2 It is recommended that the apparatus be described in
conditions selected so that they may be duplicated.
terms of the results obtained on application of this practice to
7.2 Because tests for proper instrument operation vary with
instruments used in establishing the method. This description
instrument design, it is necessary to rely on the manufacturer’s
should give a numerical value showing the wavelength
recommendations. These tests should include documentation
accuracy, wavelength repeatability, photometric accuracy, and
of the following factors in instrument operation, or their
photometric repeatability found to give acceptable results. A
equivalent:
recommended spectral bandwidth maximum should be given
7.2.1 Ambient temperature,
along with typical spectra of the components to be determined
7.2.2 Response time,
to indicate the resolution found to be adequate to perform the
7.2.3 Signal-to-noise ratio,
analysis. If it is considered necessary in a particular analysis,
7.2.4 Mechanical repeatability,
the use of only the linear portion of an analytical curve
7.2.5 Scanning parameters for recording instruments, and
(absorbance per centimetre versus concentration) may be
7.2.6 Instrument stability.
specified, or if nonlinearity is encountered, the use of special
calculation methods may be specified. However, it is not
7.3 Each of the factors in instrument operation is important
permissible to specify the amount of curvature if a nonlinear
in the measurement of analytical wavelength and photometric
workingcurveisused,becausethismayvarysignificantlyboth
data. For example, changes in wavelength precision and
with time and the instrument used.
accuracy can occur because of variation of ambient tempera-
ture of various parts of a monochromator. The correspondence
6. Parameters in Spectrophotometry
of the absorbance to wavelength and any internal calculations
6.1 Any spectrophotometer may be described as a source of (or corrections) can affect wavelength measurement for digital
radiant energy, a dispersing optical element, and a detector instruments. In scanning spectrophotometers, there is always
together with a photometer for measuring relative radiant somelagbetweentherecordedreadingandthecorrectreading.
power.Accurate spectrophotometry involves a large number of Itisnecessarytoselecttheconditionsofoperationtomakethis
interrelated factors that determine the quality of the radiant effect negligible or repeatable. Scanning speeds should be
energy passing through a sample and the sensitivity and selected to make sure that the detecting system can follow the
linearity with which this radiant energy may be measured. signal from narrow emission lines or absorption bands. Too
Assuming proper instrumentation and its use, the instrumental rapid scanning may displace the apparent wavelength toward
factors responsible for inaccuracies in spectrophotometry in- the direction scanned and peak absorbance readings may vary
clude resolution, linearity, stray radiant energy, and cell con- with speed of scanning. A change in instrument response-time
E275 − 08 (2013)
may produce apparent wavelength shifts. Mechanical repeat- 10.2 The mercury emission spectrum is obtained by illumi-
abilityofthevariouspartsofthemonochromatorandrecording nating the entrance slit of the monochromator with a quartz
system are important in wavelength measurement. Instructions mercury arc or by a mercury arc that has a transmitting
on obtaining proper mechanical repeatability are usually given envelope (Note 1). It is not necessary, when using an arc
in the manufacturer’s literature. source, that the arc be in focus on the entrance slit of the
monochromator. However, it is advantageous to mount the
7.4 Digital spectrophotometers and diode array spectropho-
lamp reasonably far from the entrance slit in order to minimize
tometers may require a calibration routine to be completed
the scatter from the edges of the slit. Reference wavelengths
prior to measurement of wavelength or absorbance accuracy.
for diode array spectrophotometers can be obtained by placing
Consult the manufacturer’s manual for any such procedures.
a low-pressure mercury discharge lamp in the sample compart-
ment.Itisnotnecessarytoputthereferencesourceinthelamp
WAVELENGTH ACCURACY AND PRECISION
compartment for systems with the dispersing element (poly-
8. Nature of Test
chomator) located after the sample compartment.
8.1 Most spectrophotometric methods employ pure com-
NOTE 1—Several commercially available mercury arcs are satisfactory,
pounds or known mixtures for the purpose of calibrating and these may be found already fitted, or available as an accessory from
several instrument manufacturers. They may differ, however, in the
instruments photometrically at specified analytical wave-
numberoflinesobservedandintherelativeintensitiesofthelinesbecause
lengths. These reference materials may simply be laboratory
of differences in operating conditions. Low-pressure arcs have a high-
prepared standards, or certified reference materials (CRMs),
intensity line at 253.65 nm, and other useful lines as seen in Fig. 1 are
where the traceability of the certified wavelength value is to a
satisfactory.
primary source, either a national reference laboratory or
10.3 The absorption spectrum of holmium oxide glass (Fig.
physical standard. The wavelength at which an analysis is
2) is obtained by measuring the transmittance or absorbance of
made is read from the dial of the monochromator, from the
a piece of holmium oxide glass about 2 to 4 mm thick.
digital readout, from an attached computer, or from a chart in
10.4 The absorption spectrum of holmium oxide solution
recording instruments. To reproduce measurements properly, it
(Fig. 3) is obtained similarly by measuring an approximately
isnecessaryfortheanalysttoevaluateandstatetheuncertainty
4 % solution of holmium oxide in 1.4 M perchloric acid (40
budget associated with the analytical wavelength chosen.
g/L) in a 1-cm cell, with air as reference. For this material, the
8.2 The accompanying spectra are given to show the loca-
transmittance minima of 18 absorption bands have been
tion of selected reference wavelengths which have been found
certified by a multi-laboratory inter-comparison, at the highest
useful. Numerical values are given in wavelength units
level, allowing the peak value assignments as an intrinsic
(nanometres, measured in air). Ref (1) tabulates additional
wavelength standard (6).
reference wavelengths of interest.
10.5 The absorption spectrum of benzene is obtained by
9. Definitions measuring the absorbance of a 1-cm cell filled with vapor (Fig.
4). The sample is prepared by placing 1 or 2 drops of liquid
9.1 wavelength accuracy—the deviation of the average
benzene in the cell, pouring out the excess liquid, and
wavelength reading at an absorption band or emission band
stoppering the cell. Some care must be exercised to ensure that
from the known wavelength of the band.
the concentration of benzene vapor is low enough to permit
9.2 wavelength precision—a measure of the ability of a
resolution of the strongest absorption bands.
spectrophotometer to return to the same spectral position as
NOTE 2—When using complex spectra for wavelength calibration, such
measured by an absorption band or emission band of known
asisexhibitedbybenzenevaporintheultraviolet,alwaysusethesmallest
wavelength when the instrument is reset or read at a given
available spectral bandwidth. At bandwidths greater than 0.5 nm, all fine
wavelength. The index of precision used in this practice is the
detail, other than the main peaks will be lost (that is, unresolved).
standard deviation. NOTE 3—This test is not recommended for routine use because of the
poss
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