1、Designation: E 925 02Standard Practice forMonitoring the Calibration of Ultraviolet-VisibleSpectrophotometers whose Spectral Slit Width does notExceed 2 nm1This standard is issued under the fixed designation E 925; the number immediately following the designation indicates the year oforiginal adopti
2、on or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONIn the application of spectrophotometric methods of analysis it is the re
3、sponsibility of the analystto verify and validate that the instrument is functioning properly and is capable of providingacceptable analytical results. It is preferable that the verification of instrument performance beaccomplished through the use of reference materials whose properties have been ac
4、curatelydetermined. Such materials are readily available, and their use in the tests and measurements describedin this practice is satisfactory for evaluating the performance of spectrophotometers whose spectral slitwidth does not exceed the value for which the intrinsic or certified properties are
5、valid. A compromisemaximum permissible spectral slit width of 2 nm is recommended for the reference materials and errortolerances recommended here.This practice covers some of the essential instrumental parameters that should be evaluated toensure the acceptability of the analytical data routinely o
6、btained on the instrument. These parametersinclude the accuracy of the wavelength and absorbance scales and stray radiant power levels.The accuracy of the wavelength scale in both the UV and visible regions is determined using thesharp absorption bands of a holmium oxide glass or solution filter. Th
7、e absorbance scale accuracy inthe UV region (235350 nm) is determined using acidic solutions of potassium dichromate. In thevisible region (440635 nm) the absorbance accuracy is determined using individually certified neutraldensity glass filters. The use of these reference materials provides a vali
8、d and relatively simple meansto test the errors in the wavelength and absorbance scales of small spectral slit width spectrophotom-eters in the spectral ranges indicated. A simplified version of the opaque filter method is provided asa test for excessive stray radiant energy.1. Scope1.1 This practic
9、e covers the parameters of spectrophotomet-ric performance that are critical for testing the adequacy ofinstrumentation for most routine tests and methods2within thewavelength range of 200 to 700 nm and the absorbance rangeof 0 to 2. The recommended tests provide a measurement of theimportant parame
10、ters controlling results in spectrophotometricmethods, but it is specifically not to be inferred that all factorsin instrument performance are measured.1.2 This practice may be used as a significant test of theperformance of instruments for which the spectral slit widthdoes not exceed 2 nm and for w
11、hich the manufacturersspecifications for wavelength and absorbance accuracy do notexceed the performance tolerances employed here. This prac-tice employs an illustrative tolerance of 61 % relative for theerror of the absorbance scale over the range of 0.2 to 2.0, andof 61.0 nm for the error of the w
12、avelength scale. A suggestedmaximum stray radiant power ratio of 4 3 10-4yields 1 nm) existbetween the true and measured wavelengths, repeat the proce-dure at a slower scan speed and smaller spectral slit width, ifpossible, to verify the nonconformity.7.2.3 Report the wavelength calibration data in
13、the mannerof Table 1, given as an example for the holmium oxide glassreference material.8. Evaluation of Stray Radiant Power Ratio (SRPR)8.1 DiscussionA portion of the unwanted stray radiantpower detected by the photodetector can be measured using thefollowing sharp cut-off solution filters in 1-cm
14、cells:Solution WavelengthKI, 1.0 g/L in H2O 220 nmK2Cr2O7, 0.25 g/L in aqueous 370 nm0.05 M KOH8.1.1 Reagent grade materials should be used for thesesolutions. They are essentially opaque at the indicated wave-lengths; any observed transmittance is equivalent to the effec-tive SRPR.8.1.2 An acceptab
15、le level of SRPR depends on the spectralcharacter and absorbance level of the sample under investiga-tion. However, an upper limit of 4 3 10-4is consistent with aworst-case absorbance bias of 1 % at the upper limit of theabsorbance range (0 0.001A) blank values are observed,use these to blank-correc
16、t measured apparent absorbances bysubtraction. Measure the apparent absorbance of each filter ateach wavelength versus air. Each filter should be oriented inthe same manner in the sample holder. If a corrected absor-bance reading is outside the acceptable absorbance range,repeat the procedure with a
17、 longer integration time and smallerspectral slit width, if possible, to verify the nonconformity.9.2.3 Report the visible region validation data in the mannerof Table 2, constructed for a set of three filters of the nominalabsorbances of NIST SRM 930.9.3 Ultraviolet RegionThe absorbance scale in th
18、e ultra-violet region is tested using acidic solutions of potassiumdichromate (available from NIST as SRM 935a). The wave-lengths of interest are:235 nm257 nm313 nm350 nmNOTE 1Acidic potassium dichromate solutions specifically preparedfor spectrophotometric validation are also available commercially
19、 inE 9254sealed ampoules and cuvettes. Portions of the procedure below, for thepowder form, will not be required for these forms. Certified values andexpiration dates that accompany such preparations should be observed.9.3.1 The precautionary notes stated in the certificate andthe material safety da
20、ta sheet (MSDS) for SRM 935a should beobserved. These documents are available from the NISTinternet site at www.nist.gov under the Standard ReferenceMaterials Program online catalog.9.3.2 Procedure:9.3.2.1 Prepare the absorbance standard solutions of potas-sium dichromate by transferring 200.0 6 0.3
21、, 300.0 6 0.3,400.0 6 0.3, and 500.0 6 0.3 mg of the powder to fourseparate 100 mL volumetric flasks and dilute to volume withdistilled water (Absorbance Standard Stock Solutions). Stopperthe solutions and mix well. Dilute these solutions by pipetting20.0 mL of each solution separately to four 1-L v
22、olumetricflasks, adding 1 mL of 1M HClO4(8.6 mL of 70 % HClO4/100mL H2O) and diluting to volume with distilled water (Absor-bance Standard Sample Calibration Solutions). These finalcalibration solutions contain 40, 60, 80, and 100 mg ofpotassium dichromate per litre of solution, respectively. Pre-pa
23、re a blank solution by diluting 1 mL of 1 M HClO4to one Lwith the same distilled water. Stopper the solutions and mixwell.9.3.2.2 Clean and match the 1-cm solution cells (cuvettes).Measure the temperature of the sample compartment as de-scribed in Section 7.9.3.2.3 Determine the apparent absorbance
24、blank at theindicated wavelengths using solvent in each cuvette. Recordthese measurements. If large (0.01A) blank values are ob-served, re-cleaning the cuvettes may be necessary. Measure theapparent absorbance of each Absorbance Standard SampleCalibration Solution of potassium dichromate in the samp
25、lecuvette at each wavelength and record. Rinse the cuvettesseveral times with the solutions to be measured before they areplaced in the sample compartment and maintain the sameorientation of a cuvette throughout the procedure. If a correctedapparent absorbance value (Acorr) of an Absorbance Standard
26、Sample Calibration is outside the acceptable range, repeat thereading with a longer integration time and smaller spectral slitwidth, if possible. If the absorbance readings at all wavelengthsfor a solution are unacceptable, prepare a fresh solution at theconcentration of interest and repeat the abso
27、rbance measure-ments. If non-conformities are verified, corrective service mustbe performed by a qualified service person. If the user performsthis service, the manufacturers recommended procedureshould be followed carefully.9.3.3 Report the ultraviolet region calibration data in themanner of Table
28、3.TABLE 2 UV-VIS Spectrophotometers Absorbance CalibrationVisible RegionInstrumentDateTemperatureAnalystWavelength(nm)Filter No. AnomAAcertAAcorrABiasBToleranceCConformanceDDoes Does Not440.0 0.50.71.00.0050.0070.010465.0 0.50.71.00.0050.0070.010546.1 0.50.71.00.0050.0070.010590.0 0.50.71.00.0050.00
29、70.010635.0 0.50.71.00.0050.0070.010AAnom= nominal absorbance; Acert= certified absorbance; Acorr= measured absorbance, blank corrected as necessary.BBias = Acorr Acert.CTolerance taken for example as 1 % of the nominal. User to assign as appropriate for each application.DMeasurement conforms for |B
30、ias| # Tolerance; measurement does not conform for |Bias| Tolerance.E 925510. Documentation of Data10.1 Spectral charts and tables should be retained forreference.11. Keywords11.1 absorbance; molecular spectroscopy; reference materi-als; spectrophotometers; UV/visible; wavelengthREFERENCES(1) McNeir
31、ney, J., and Slavin, W., Applied Optics, Vol 1, 1962, p. 365. (2) Keegan, H. J, Schleter, J. C., and Weidner, V. R., J. Opt. Soc. Am.,Vol51, 1961, p. 1470.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard.
32、 Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed e
33、very five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible tec
34、hnical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoho
35、cken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).TABLE 3 UV-VIS Spectrophot
36、ometer Absorbance CalibrationUltraviolet Region (Potassium Dichromate)InstrumentDateTemperatureAnalystWavelength(nm)Solution(mg/L)AcertAAmeasBAblankBAcorrBBiasCToleranceDConformanceEDoes Does Not235.0 4060801000.4920.7410.9911.2430.0050.0070.0100.012257.0 4060801000.5730.8621.1541.4490.0060.0090.012
37、0.014313.0 4060801000.1920.2890.3860.4830.0020.0030.0040.005350.0 4060801000.4270.6450.8601.0710.0040.0060.0090.011AAcert= certified absorbance, computed from SRM 935a certified specific absorbance values for the given solution and a 10-mm pathlength.BAmeas= measured solution absorbance; Ablank= measured blank absorbance; Acorr= Ameas Ablank.CBias = Acorr Acert.DTolerance computed for illustrative purposes as 1 % of the certified absorbance. User may substitute appropriate tolerances.ECorrected absorbance conforms when |Bias| # Tolerance.E 9256
