1、Designation: E925 09Standard Practice forMonitoring the Calibration of Ultraviolet-VisibleSpectrophotometers whose Spectral Bandwidth does notExceed 2 nm1This standard is issued under the fixed designation E925; the number immediately following the designation indicates the year oforiginal adoption
2、or, in the case 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 the application of spectrophotometric methods of analysis it is the respon
3、sibility 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 accura
4、telydetermined. 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 spectralbandwidth does not exceed the value for which the intrinsic or certified properties are valid
5、. Acompromise maximum permissible spectral bandwidth of 2 nm is recommended for the referencematerials and error tolerances recommended here.This practice covers some of the essential instrumental parameters that should be evaluated toensure the acceptability of the analytical data routinely obtaine
6、d 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 ultraviolet (UV) and visible regions is determinedusing the sharp absorption bands of a holmium oxide glass or solution fi
7、lter. The absorbance scaleaccuracy in the UV region (235350 nm) is determined using acidic solutions of potassiumdichromate. In the visible region (440635 nm) the absorbance accuracy is determined usingindividually certified neutral density glass filters. The use of these reference materials provide
8、s a validand relatively simple means to test the errors in the wavelength and absorbance scales of small spectralbandwidth spectrophotometers in the spectral ranges indicated. A simplified version of the opaquefilter method is provided as a test for excessive stray radiant energy.1. Scope1.1 This pr
9、actice 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 p
10、arameters 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 bandwidthdoes not exceed 2 nm and f
11、or which 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 t
12、he wavelength scale. A suggestedmaximum stray radiant power ratio of 4 3 10-4yields 99.99 %), where value assignment is by self assertion (Note 1).Apurchaser should require certification by the supplier that thewavelengths of the absorption bands are within 0.2-nm of thevalues given in Ref. (2), and
13、 reported below. The appropriatesolution standard is 4 % (mass fraction) holmium oxide in10 % (volume fraction) perchloric acid, contained in a 10-mmpath length cuvette. For this material, the transmittance minimaof 18 absorption bands have been certified by a multi-laboratory inter-comparison, at t
14、he highest level, allowing thepeak value assignments as an intrinsic wavelength standard (3).Absorbance maxima or transmittance minima must be locatedwithin 61 nm of the wavelengths given below:Glass FilterADilute Acidic SolutionB241.5 nmC241.1 nm. . . 249.9 nm279.3 nm 278.1 nm287.6 nm 287.2 nm333.8
15、 nm 333.5 nm. . . 345.4 nm360.8 nm 361.3 nm385.8 nm 385.6 nm418.5 nm 416.3 nm453.4 nm . . .D459.9 nm 467.8 nm. . . 485.3 nm536.4 nm 536.6 nm637.5 nm 640.5 nmAWavelengths taken from Ref. (2) for Corning Glass Works Code 3130 glass,superceded by Corning Glass Works Code 3131 glass and Kopp Glass Code
16、3131glass, for which the wavelengths are also valid.BWavelengths rounded to 0.1 nm for a 1-nm spectral bandwidth taken from Ref.(3).CMay not be usable, depending on the base glass of the filter.DPeak omitted because it resolves into a doublet at spectral bandwidth valuesless than 1 nm.NOTE 1Self ass
17、ertion may take the form of value assignment andcertification in many forms. Some specific examples are:(1) By a national metrology institute (NMI),(2)ByanISO 17025 and ISO Guide 34 accredited Reference Mate-rial producer, and(3) By a laboratory claiming traceability to an NMI.In all cases, the user
18、 should be satisfied that the quality of the valueassignment data meets the laboratory requirements.7.1.1 If the observed absorption bands of the holmium oxideglass or solution deviate by more than 61 nm from the valuesstated, then corrective service must by performed on theinstrument by qualified p
19、ersonnel. If the user performs thisservice, the manufacturers recommended procedure should befollowed carefully.7.1.2 The wavelength accuracy is dependent on the spectralbandwidth and thus on the physical bandwidth. Spectralbandwidths may be determined from the manufacturers speci-fications.7.1.3 Co
20、mputer based peak location algorithms that may beused to assign absorbance maxima or transmittance minima arediscussed in 7.6 of Guide E1866. It should be noted that peakasymmetries in the holmium oxide reference materials are suchthat digital filter widths should be smaller than the full-width-half
21、-maximum recommendation of that guide.7.1.4 In the absence of drift or slippage in the wavelengthdrive train, repeatability of the band positions should be on theorder of 60.1 nm for a given instrument, especially with theuse of a computer based peak location algorithm.7.2 Procedure:7.2.1 Examine th
22、e holmium oxide reference material andremove any surface contamination using a soft brush orlint-free cloth. Measure the temperature of the sample com-partment by placing an appropriate sensor into the cell com-partment of a stabilized instrument and replacing the compart-ment cover securely. Place
23、the sensor as close as possible to theactual position that will be occupied by the standard. After asuitable period of time record the temperature reading, removethe sensor, and resume normal operations.7.2.2 Record the blank absorbance or transmittance (airversus air) spectrum at the desired resolu
24、tion and at theappropriate wavelength intervals and scan speeds, in order toperform any necessary baseline adjustments. The wavelengthintervals should be no greater than the spectral bandwidth used.Acquire the appropriate spectrum of the holmium oxidereference material with respect to air and baseli
25、ne correct ifnecessary using the blank spectrum. Record the wavelengths ofthe positions of the relevant bands, and compare these values tothe expected values. If large discrepancies (1 nm) existbetween the true and measured wavelengths, repeat the proce-dure at a slower scan speed and smaller spectr
26、al bandwidth, ifpossible, to verify the nonconformity.7.2.3 Report the wavelength calibration data in 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 de
27、tected by the photodetector can be measured using thefollowing sharp cut-off solution filters in 1-cm cells:Solution WavelengthKI or NaL, 10.0 g/L in H2O 220 nmNaNo2, 50.0 g/L in H2O 370 nm8.1.1 Reagent grade materials should be used for thesesolutions. They are essentially opaque at the indicated w
28、ave-lengths; any observed transmittance is equivalent to the effec-tive SRPR.8.1.2 An acceptable 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 upp
29、er limit of theabsorbance range (0 0.001A) blank values are observed,use these to blank-correct 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 correc
30、ted absor-bance reading is outside the acceptable absorbance range,repeat the procedure with a longer integration time and smallerspectral bandwidth, 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 filte
31、rs of the nominalabsorbances of NIST SRM 930.9.3 Ultraviolet RegionThe absorbance scale in the 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 2Acidic potassium dichromate sol
32、utions specifically preparedfor spectrophotometric validation are also available commercially insolution, sealed ampoules, and sealed cuvette formats. Portions of theprocedure below, for the powder form, will not be required for theseforms. Certified values and expiration dates that accompany such p
33、repa-rations should be observed.9.3.1 The precautionary notes stated in the certificate andthe material safety data 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
34、 Procedure:9.3.2.1 Prepare the absorbance standard solutions of potas-sium dichromate by transferring 200.0 6 0.3, 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). Stoppe
35、rthe solutions and mix well. Dilute these solutions by pipetting20.0 mL of each solution separately to four 1-L volumetricflasks, 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 finalcalibr
36、ation solutions contain 40, 60, 80, and 100 mg ofTABLE 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
37、.50.71.00.0050.0070.010590.0 0.50.71.00.0050.0070.010635.0 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 fo
38、r each application.DMeasurement conforms for |Bias| # Tolerance; measurement does not conform for |Bias| Tolerance.E925 095potassium dichromate per litre of solution, respectively. Pre-pare a blank solution by diluting 1 mL of 1 M HClO4to one Lwith the same distilled water. Stopper the solutions and
39、 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 blank at theindicated wavelengths using solvent in each cuvette. Recordthese measurements. If large (0.01A) blank
40、 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 samplecuvette at each wavelength and record. Rinse the cuvettesseveral times with the solutions to be measured before
41、 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 StandardSample Calibration is outside the acceptable range, repeat thereading with a longer integration time and smaller
42、spectralbandwidth, if possible. If the absorbance readings at allwavelengths for a solution are unacceptable, prepare a freshsolution at the concentration of interest and repeat the absor-bance measurements. If non-conformities are verified, correc-tive service must be performed by qualified personn
43、el. If theuser performs this service, the manufacturers recommendedprocedure should be followed carefully.9.3.3 Report the ultraviolet region calibration data in themanner of Table 3.10. Documentation of Data10.1 Spectral charts and tables should be retained forreference.11. Keywords11.1 absorbance;
44、 molecular spectroscopy; reference materi-als; spectrophotometers; UV/visible; wavelengthTABLE 3 UV-VIS Spectrophotometer Absorbance CalibrationUltraviolet Region (Potassium Dichromate)InstrumentDateTemperatureAnalystWavelength(nm)Solution(mg/L)AcertAAmeasBAblankBAcorrBBiasCToleranceDConformanceEDoe
45、s Does Not235.0 4060801000.4920.7410.9911.2430.0050.0070.0100.012257.0 4060801000.5730.8621.1541.4490.0060.0090.0120.014313.0 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 specifi
46、c 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 toleran
47、ces.ECorrected absorbance conforms when |Bias| # Tolerance.E925 096REFERENCES(1) McNeirney, J., and Slavin, W., Applied Optics, Vol 1, 1962, p. 365.(2) Keegan, H.J, Schleter, J.C., and Weidner, V.R., Journal of the OpticalSociety of America, Vol 51, 1961, p. 1470.(3) Travis, J.C., Acostab, J.C., And
48、orc, G., Bastied, J., Blattnere, P.,Chunnilall, C.J., Crossona, S.C., et al, “Intrinsic Wavelength StandardAbsorption Bands in Holmium Oxide Solution for UV/visible Mo-lecular Absorption Spectrophotometry,” Journal of Physical Chem-istry, Reference Data, Vol 34, No. 1, 2005.ASTM International takes
49、no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. 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 every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional stand
