1、Designation: E925 09 (Reapproved 2014)Standard 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 of
2、original adoption 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 analysi
3、s it is the responsibility 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 propertie
4、s have been accuratelydetermined. 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 pr
5、operties are valid. 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
6、 routinely obtained 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 gl
7、ass or solution filter. The absorbance scaleaccuracy in the UV region (235 to 350 nm) is determined using acidic solutions of potassiumdichromate. In the visible region (440 to 635 nm) the absorbance accuracy is determined usingindividually certified neutral density glass filters. The use of these r
8、eference materials provides 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
9、energy.1. Scope1.1 This practice 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 meas
10、urement of theimportant parameters 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 bandwidthd
11、oes not exceed 2 nm and for 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 6
12、1.0 nm for the error of the wavelength scale. A suggestedmaximum stray radiant power ratio of410-4yields 99.99 %), where value assignment is by self assertion (Note 1).3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual
13、 Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from National Technical Information Service (NTIS), 5301 ShawneeRd., Alexandria, VA 22312, http:/www.ntis.gov.5Available from International Organization for Standardization (ISO), 1,
14、 ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.6The boldface numbers in parentheses refer to a list of references at the end ofthis standard.E925 09 (2014)2Apurchaser should require certification by the supplier that thewavelengths of the absorption bands are within
15、0.2-nm of thevalues given in Ref. (2), and 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
16、 a multi-laboratory inter-comparison, at the 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
17、 nm279.3 nm 278.1 nm287.6 nm 287.2 nm333.8 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
18、Works Code 3131 glass and Kopp Glass Code 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 ban
19、dwidth valuesless than 1 nm.NOTE 1Self assertion may take the form of value assignment andcertification in many forms. Some specific examples are:(1) By a national metrology institute (NMI),(2) By an ISO 17025 and ISO Guide 34 accredited Reference Mate-rial producer, and(3) By a laboratory claiming
20、traceability to an NMI.In all cases, the user 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
21、 by performed on theinstrument by qualified personnel. 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 fr
22、om the manufacturers speci-fications.7.1.3 Computer 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 widt
23、hs should be smaller than the full-width-half-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 loca
24、tion algorithm.7.2 Procedure:7.2.1 Examine the 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 repl
25、acing the compart-ment cover securely. Place 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 (
26、airversus air) spectrum at the desired resolution 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 oxiderefe
27、rence material with respect to air and baseline 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-d
28、ure at a slower scan speed and smaller spectral 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
29、portion of the unwanted stray radiantpower detected 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 nmTABLE 1 UV-VIS Spectrophotometer Wavelength and StrayRadiant Power
30、 Ratio CalibrationInstrumentDateTemperatureAnalystWavelength Calibration: Holmium Oxide FilterTrueWavelength(nm)ObservedWavelength(nm)Difference(nm)ConformanceDoes Does Not241.5 1279.3 1287.6 1333.8 1360.8 1385.8 1418.5 1453.4 1459.9 1536.4 1637.5 1Stray Radiant Power RatioWavelength(nm)Transmittanc
31、eor AbsorbanceConformsDoes NotConform220340E925 09 (2014)38.1.1 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 acceptable level of SRPR depends on the spect
32、ralcharacter and absorbance level of the sample under investiga-tion. However, an upper limit of410-4is 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-correct measured apparent absorbances bysubtrac
33、tion. 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 longer integration time and smallerspect
34、ral 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 filters of the nominalabsorbances of NIST SRM 930.9.3 Ultraviolet RegionThe absorbance scale in the ultra-violet region is tested using acid
35、ic solutions of potassiumdichromate (available from NIST as SRM 935a). The wave-lengths of interest are:235 nm257 nm313 nm350 nmNOTE 2Acidic potassium dichromate solutions specifically preparedfor spectrophotometric validation are also available commercially insolution, sealed ampoules, and sealed c
36、uvette formats. Portions of theprocedure below, for the powder form, will not be required for theseforms. Certified values and expiration dates that accompany such prepa-rations should be observed.9.3.1 The precautionary notes stated in the certificate andthe material safety data sheet (MSDS) for SR
37、M 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, 300.0 6 0.3,400.0 6
38、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 volumetricflasks, addin
39、g 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-pare a blank solution by
40、 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.TABLE 2 UV-VIS Spectrophotometers Absorbance CalibrationVisible
41、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 0.50.71.00.0050.0070.010635.0 0.50.71.00.0050.0070.010AAnom= nominal absorbance; Ace
42、rt= 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 |Bias| # Tolerance; measurement does not conform for |Bias| Toleranc
43、e.E925 09 (2014)59.3.2.3 Determine the apparent absorbance blank at theindicated wavelengths using solvent in each cuvette. Recordthese measurements. If large (0.01A) blank values areobserved, re-cleaning the cuvettes may be necessary. Measurethe apparent absorbance of each Absorbance Standard Sampl
44、eCalibration Solution of potassium dichromate in the samplecuvette 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 correctedap
45、parent absorbance value (Acorr) of an Absorbance StandardSample Calibration is outside the acceptable range, repeat thereading with a longer integration time and smaller spectralbandwidth, if possible. If the absorbance readings at allwavelengths for a solution are unacceptable, prepare a freshsolut
46、ion at the concentration of interest and repeat the absor-bance measurements. If non-conformities are verified, correc-tive service must be performed by qualified personnel. If theuser performs this service, the manufacturers recommendedprocedure should be followed carefully.9.3.3 Report the ultravi
47、olet 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; molecular spectroscopy; reference materi-als; spectrophotometers; UV/visible; wavelengthTABLE 3 UV-VIS Spectrophotometer Absorban
48、ce CalibrationUltraviolet Region (Potassium Dichromate)InstrumentDateTemperatureAnalystWavelength(nm)Solution(mg/L)AcertAAmeasBAblankBAcorrBBiasCToleranceDConformanceEDoes Does Not235.0 4060801000.4920.7410.9911.2430.0050.0070.0100.012257.0 4060801000.5730.8621.1541.4490.0060.0090.0120.014313.0 4060
49、801000.1920.2890.3860.4830.0020.0030.0040.005350.0 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.E925 09 (2014)
