1、Designation: E275 08 (Reapproved 2013)Standard Practice forDescribing and Measuring Performance of Ultraviolet andVisible Spectrophotometers1This standard is issued under the fixed designation E275; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se of revision, 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.INTRODUCTIONIn developing a spectrophotometric method, it is the responsibility of the originator to d
3、escribe 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 measurements described in this practice are for the purpose of dete
4、rmining 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 capability of an instrument to perform a particular analysis. To
5、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 ananalysis are readily measured and easily specified for the various types
6、 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 characteristicsof absorption cells as the parameters of spectrophotometry that
7、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 requirements ofspectrophotometric performance, especially for test met
8、hods,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 spectrophotometricmethods, but it is specifically not to be conclude
9、d 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 instruments designed for diffuse transmission and diffusereflecti
10、on.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 is theresponsibility of the user of this standard to establish a
11、ppro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE169 Practices for Gen
12、eral Techniques of Ultraviolet-VisibleQuantitative 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 Ultra-Violet, Visible, and Luminescence Spectroscopy.Current edition a
13、pproved Jan. 1, 2013. Published January 2013. Originallyapproved in 1965. Last previous edition approved in 2008 as E275 08. DOI:10.1520/E0275-08R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStanda
14、rds volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E387 Test Method for Estimating Stray Radiant Power Ratioof Dispersive Spectrophotometers by the O
15、paque FilterMethodE958 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 E131.4. Significance and Use4.1 This practice permits an analyst to compare the g
16、eneralperformance 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 spectrophotometric testmethod (preferably in the section
17、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 can be operatedin a manner to give test results equ
18、ivalent 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 in establishing the method. This descriptionshould g
19、ive a numerical value showing the wavelengthaccuracy, wavelength repeatability, photometric accuracy, andphotometric repeatability found to give acceptable results. Arecommended spectral bandwidth maximum should be givenalong with typical spectra of the components to be determinedto indicate the res
20、olution 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 nonlinearity is encountered, the use of specialcalculation meth
21、ods 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 spectrophotometer may be described as a source ofradiant ene
22、rgy, 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 through a sample and the sensitivity andlinearity with wh
23、ich 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 measurement of these factors is beyond thescope of this p
24、ractice. The measurement of stray radiant energyis described in Test Method E387 and resolution in PracticeE958.6.2 Modern spectrophotometers are capable of more accu-racy than most analysts obtain. The problem lies in theselection and proper use of instrumentation. In order to ensureproper instrume
25、ntation 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 precision, spectral bandwidth, and absorption-cell consta
26、nts. 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 manufacturers recommendations. Tests shallthen be made to
27、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 obtaining spectrophotometric data, the analyst mustselect t
28、he 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. A record should be kept to document the operatingcondit
29、ions 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 factors in instrument operation, or theirequivalent:7.2.1 A
30、mbient 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 the measurement of analytical wavelength and photometric
31、data. 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 corrections) can affect wavelength measurement for digitalinst
32、ruments. 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 beselected to make sure that the detecting system can follow
33、 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-timeE275 08 (2013)2may produce apparent wavelength shifts. Mechan
34、ical repeat-ability of the various parts of the monochromator and recordingsystem are important in wavelength measurement. Instructionson obtaining proper mechanical repeatability are usually givenin the manufacturers literature.7.4 Digital spectrophotometers and diode array spectropho-tometers may
35、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 employ pure com-pounds or known mixtures for the purpo
36、se 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 is to aprimary source, either a national reference
37、 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, itis necessary for the analyst to evaluate and stat
38、e 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(nanometres, measured in air). Ref (1)3tabulates addition
39、alreference 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 aspectrophotometer to return to the same spectral po
40、sition 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 Region10.1 The most convenient spectra for wavelen
41、gth 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 parameters detailedbelow these spectra are those used to obt
42、ain these referencespectra and may not be appropriate for the system 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-n
43、ating the entrance slit of the monochromator with a quartzmercury 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
44、 far from the entrance slit in order to minimizethe scatter from 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 lampcompa
45、rtment for systems with the dispersing element (poly-chomator) located 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, i
46、n thenumber of lines observed and in the relative intensities of 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
47、 obtained by measuring the transmittance or absorbance ofa piece 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 ce
48、ll, with air as reference. For this material, thetransmittance minima of 18 absorption bands have beencertified by a multi-laboratory inter-comparison, at the highestlevel, allowing the peak value assignments as an intrinsicwavelength standard (3).10.5 The absorption spectrum of benzene is obtained
49、bymeasuring the absorbance of a 1-cm cell filled with vapor (Fig.4). The sample is prepared by placing 1 or 2 drops of liquidbenzene in the cell, pouring out the excess liquid, andstoppering the cell. Some care must be exercised to ensure thatthe concentration of benzene vapor is low enough to permitresolution of the strongest absorption bands.NOTE 2When using complex spectra for wavelength calibration, suchas is exhibited by benzene vapor in the ultraviolet, always use the smallestavailable spectral bandwidth. At bandwidths greater than 0.5 nm, all finedetail, other than t
