1、Designation: E 275 08Standard Practice forDescribing and Measuring Performance of Ultraviolet andVisible Spectrophotometers1This standard is issued under the fixed designation E 275; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONIn developing a spectroph
3、otometric method, it is the responsibility of the originator to describe theinstrumentation 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 themethod.The tests and me
4、asurements described in this practice are for the purpose of determining theexperimental conditions required for a particular analytical method. In using this practice, an analysthas either a particular analysis for which he describes requirements for instrument performance or heexpects to test the
5、capability of an instrument to perform a particular analysis. To accomplish eitherof these objectives, it is necessary that instrument performance be obtained in terms of the factors thatcontrol the analysis. Unfortunately, it is true that not all the factors that can affect the results of ananalysi
6、s are readily measured and easily specified for the various types of spectrophotometricequipment.Of the many factors that control analytical results, this practice covers verification of the essentialparameters of wavelength accuracy, photometric accuracy, stray light, resolution, and characteristic
7、sof absorption cells as the parameters of spectrophotometry that are likely to be affected by the analystin obtaining data. Other important factors, particularly those primarily dependent on instrumentdesign, are also covered in this practice.1. Scope1.1 This practice covers the description of requi
8、rements ofspectrophotometric performance, especially for test methods,and the testing of the adequacy of available equipment for aspecific method (for example, qualification for a given appli-cation). The tests give a measurement of some of the importantparameters controlling results obtained in spe
9、ctrophotometricmethods, but it is specifically not to be concluded that all thefactors in instrument performance are measured, or in fact maybe required for a given application.1.1.1 This practice is primarily directed to dispersive spec-trophotometers used for transmittance measurements ratherthan
10、instruments designed for diffuse transmission and diffusereflection.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It
11、 is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 131 Terminology Relating to Molecular SpectroscopyE 168 Practices for General
12、Techniques of Infrared Quanti-tative AnalysisE 169 Practices for General Techniques of Ultraviolet-Visible Quantitative Analysis1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.01 on U
13、ltra-Violet, Visible, and Luminescence Spectroscopy.Current edition approved Oct. 15, 2008. Published November 2008. Originallyapproved in 1965. Last previous edition approved in 2001 as E 275 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
14、 serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E 387 Test Method for Estimating Stray Radiant Pow
15、erRatio of Dispersive Spectrophotometers by the OpaqueFilter MethodE 958 Practice for Measuring Practical Spectral Bandwidthof Ultraviolet-Visible Spectrophotometers3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology E 131.4. Significance and Use4.
16、1 This practice permits an analyst to compare the generalperformance of an instrument, as it is being used in a specificspectrophotometric method, with the performance of instru-ments used in developing the method.5. Reference to This Practice in Standards5.1 Reference to this practice in any spectr
17、ophotometric testmethod (preferably in the section on apparatus where thespectrophotometer is described) shall constitute due notifica-tion that the adequacy of the spectrophotometer performance isto be evaluated by means of this practice. Performance isconsidered to be adequate when the instrument
18、can be operatedin a manner to give test results equivalent to those obtained oninstruments used in establishing the method or in cooperativetesting of the method.5.2 It is recommended that the apparatus be described interms of the results obtained on application of this practice toinstruments used i
19、n establishing the method. This descriptionshould give a numerical value showing the wavelength accu-racy, wavelength repeatability, photometric accuracy, and pho-tometric repeatability found to give acceptable results. Arecommended spectral bandwidth maximum should be givenalong with typical spectr
20、a of the components to be determinedto indicate the resolution found to be adequate to perform theanalysis. If it is considered necessary in a particular analysis,the use of only the linear portion of an analytical curve(absorbance per centimetre versus concentration) may bespecified, or if nonlinea
21、rity is encountered, the use of specialcalculation methods may be specified. However, it is notpermissible to specify the amount of curvature if a nonlinearworking curve is used, because this may vary significantly bothwith time and the instrument used.6. Parameters in Spectrophotometry6.1 Any spect
22、rophotometer may be described as a source ofradiant energy, a dispersing optical element, and a detectortogether with a photometer for measuring relative radiantpower. Accurate spectrophotometry involves a large number ofinterrelated factors that determine the quality of the radiantenergy passing th
23、rough a sample and the sensitivity andlinearity with which this radiant energy may be measured.Assuming proper instrumentation and its use, the instrumentalfactors responsible for inaccuracies in spectrophotometry in-clude resolution, linearity, stray radiant energy, and cell con-stants. Rigorous me
24、asurement of these factors is beyond thescope of this practice. The measurement of stray radiant energyis described in Test Method E 387 and resolution in PracticeE 958.6.2 Modern spectrophotometers are capable of more accu-racy than most analysts obtain. The problem lies in theselection and proper
25、use of instrumentation. In order to ensureproper instrumentation and its use in a specific spectrophoto-metric method, it is necessary for an analyst to evaluate certainparameters that can control the results obtained. These param-eters are wavelength accuracy and precision, photometricaccuracy and
26、precision, spectral bandwidth, and absorption-cell constants. Unsatisfactory measurement of any of theseparameters may be due to improper instrumentation or toimproper use of available instrumentation. It is therefore firstnecessary to determine that instrument operation is in accor-dance with the m
27、anufacturers recommendations. Tests shallthen be made to determine the performance of an instrument interms of each of the parameters in 6.1 and 6.2. Lastly,variations in optical geometry and their effects in realizingsatisfactory instrument performance are discussed.7. Instrument Operation7.1 In ob
28、taining spectrophotometric data, the analyst mustselect the proper instrumental operating conditions in order torealize satisfactory instrument performance. Operating condi-tions for individual instruments are best obtained from themanufacturers literature because of variations with instrumentdesign
29、. A record should be kept to document the operatingconditions selected so that they may be duplicated.7.2 Because tests for proper instrument operation vary withinstrument design, it is necessary to rely on the manufacturersrecommendations. These tests should include documentationof the following fa
30、ctors in instrument operation, or theirequivalent:7.2.1 Ambient temperature,7.2.2 Response time,7.2.3 Signal-to-noise ratio,7.2.4 Mechanical repeatability,7.2.5 Scanning parameters for recording instruments, and7.2.6 Instrument stability.7.3 Each of the factors in instrument operation is importantin
31、 the measurement of analytical wavelength and photometricdata. For example, changes in wavelength precision andaccuracy can occur because of variation of ambient tempera-ture of various parts of a monochromator. The correspondenceof the absorbance to wavelength and any internal calculations(or corre
32、ctions) can affect wavelength measurement for digitalinstruments. In scanning spectrophotometers, there is alwayssome lag between the recorded reading and the correct reading.It is necessary to select the conditions of operation to make thiseffect negligible or repeatable. Scanning speeds should bes
33、elected to make sure that the detecting system can follow thesignal from narrow emission lines or absorption bands. Toorapid scanning may displace the apparent wavelength towardthe direction scanned and peak absorbance readings may varywith speed of scanning. A change in instrument response-timemay
34、produce apparent wavelength shifts. Mechanical repeat-ability of the various parts of the monochromator and recordingsystem are important in wavelength measurement. InstructionsE275082on obtaining proper mechanical repeatability are usually givenin the manufacturers literature.7.4 Digital spectropho
35、tometers and diode array spectropho-tometers may require a calibration routine to be completedprior to measurement of wavelength or absorbance accuracy.Consult the manufacturers manual for any such procedures.WAVELENGTH ACCURACY AND PRECISION8. Nature of Test8.1 Most spectrophotometric methods emplo
36、y pure com-pounds or known mixtures for the purpose of calibratinginstruments photometrically at specified analytical wave-lengths. These reference materials may simply be laboratoryprepared standards, or certified reference materials (CRMs),where the traceability of the certified wavelength value i
37、s to aprimary source, either a national reference laboratory orphysical standard. The wavelength at which an analysis ismade is read from the dial of the monochromator, from thedigital readout, from an attached computer, or from a chart inrecording instruments. To reproduce measurements properly, it
38、is necessary for the analyst to evaluate and state the uncertaintybudget associated with the analytical wavelength chosen.8.2 The accompanying spectra are given to show the loca-tion of selected reference wavelengths which have been founduseful. Numerical values are given in wavelength units (na-nom
39、etres, measured in air). Ref (1)3tabulates additionalreference wavelengths of interest.9. Definitions9.1 wavelength accuracythe deviation of the averagewavelength reading at an absorption band or emission bandfrom the known wavelength of the band.9.2 wavelength precisiona measure of the ability of a
40、spectrophotometer to return to the same spectral position asmeasured by an absorption band or emission band of knownwavelength when the instrument is reset or read at a givenwavelength. The index of precision used in this practice is thestandard deviation.10. Reference Wavelengths in the Ultraviolet
41、 Region10.1 The most convenient spectra for wavelength calibra-tion in the ultraviolet region are the emission spectrum of thelow-pressure mercury arc (Fig. 1), the absorption spectra ofholmium oxide glass (Fig. 2), holmium oxide solution (Fig. 3),and benzene vapor (Fig. 4). The instrument parameter
42、s detailed3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Line Number Wavelength, nm Line Number Wavelength, nm Line Number Wavelength, nm1 253.651 4 356.016 7 546.0752 296.725 5 404.657 8 576.9603 312.570 6 435.834 9 579.066Instrument: Cary 5000 Spectra
43、l Bandwidth: 0.05 nmScanning Speed: 1.2 nm/min Spectral Data Interval : 0.01 nmFIG. 1 Mercury Arc Emission Spectrum in the Ultraviolet and Visible Regions Showing Reference Wavelength (4)E275083below these spectra are those used to obtain these referencespectra and may not be appropriate for the sys
44、tem beingqualified. Guidance with respect to optimum parameter settingsfor a given spectrophotometer should be obtained from theinstrument vendor or other appropriate reference.10.2 The mercury emission spectrum is obtained by illumi-nating the entrance slit of the monochromator with a quartzmercury
45、 arc or by a mercury arc that has a transmittingenvelope (Note 1). It is not necessary, when using an arcsource, that the arc be in focus on the entrance slit of themonochromator. However, it is advantageous to mount thelamp reasonably far from the entrance slit in order to minimizethe scatter from
46、the edges of the slit. Reference wavelengthsfor diode array spectrophotometers can be obtained by placinga low-pressure mercury discharge lamp in the sample compart-ment. It is not necessary to put the reference source in the lampcompartment for systems with the dispersing element (poly-chomator) lo
47、cated after the sample compartment.NOTE 1Several commercially available mercury arcs are satisfactory,and these may be found already fitted, or available as an accessory fromseveral instrument manufacturers. They may differ, however, in thenumber of lines observed and in the relative intensities of
48、the lines becauseof differences in operating conditions. Low-pressure arcs have a high-intensity line at 253.65 nm, and other useful lines as seen in Fig. 1 aresatisfactory.10.3 The absorption spectrum of holmium oxide glass (Fig.2) is obtained by measuring the transmittance or absorbance ofa piece
49、of holmium oxide glass about 2 to 4 mm thick.410.4 The absorption spectrum of holmium oxide solution(Fig. 3) is obtained similarly by measuring an approximately4 % solution of holmium oxide5in 1.4 M perchloric acid (40g/L) in a 1-cm cell, with air as reference. For this material, thetransmittance minima of 18 absorption bands have been4Sealed cuvettes of Didymium oxide (1+1 Neodymium and Praesodymium) andDidymium oxide glass polished filters are available from commercial sources.5Sealed cuvettes of holmium oxide solution are available from commercialsources and as (the now w
