1、Designation: E 932 89 (Reapproved 2007)Standard Practice forDescribing and Measuring Performance of DispersiveInfrared Spectrometers1This standard is issued under the fixed designation E 932; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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.1. Scope1.1 This practice covers the necessary information toqualify dispersive infrared instruments for spe
3、cific analyticalapplications, and especially for methods developed by ASTMInternational.1.2 This practice is not to be used as a rigorous test ofperformance of instrumentation.1.3 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsib
4、ility 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 Techniques of In
5、frared Quanti-tative AnalysisE 387 Test Method for Estimating Stray Radiant PowerRatio of Dispersive Spectrophotometers by the OpaqueFilter MethodE 1252 Practice for General Techniques for Obtaining In-frared Spectra for Qualitative Analysis3. Terminology3.1 Definitions and SymbolsFor definitions of
6、 terms andsymbols, refer to Terminology E 131 and Compilation ofASTM Standard Definitions.34. Significance and Use4.1 This practice is intended for all infrared spectroscopistswho are using dispersive instruments for qualitative or quan-titative areas of analysis.4.2 The purpose of this practice is
7、to set forth performanceguidelines for testing instruments used in developing ananalytical method. These guidelines can be used to compare aninstrument in a specific application with the instrument(s) usedin developing the method.4.3 An infrared procedure must include a description of theinstrumenta
8、tion and of the performance needed to duplicate theprecision and accuracy of the method.5. Apparatus5.1 For the purposes of this practice, dispersive instrumentsinclude those employing prisms, gratings, or filters to separateinfrared radiation into its component wavelengths.5.2 For each new method,
9、describe the apparatus andinstrumentation both physically and mechanically, and also interms of performance as taught in this practice. That is, thedescription should give numerical values showing the fre-quency accuracy and the frequency and the photometricprecision. State the spectral slit width m
10、aximum or slit widthprogram if one is used.Where possible, state the maximum andminimum resolution if those data are a part of the instrumentdisplay. Show typical component spectra as produced by theinstrument to establish the needed resolution.5.3 If a computer program is used, describe the program
11、.Include the programming language and availability, or whetherthe program is proprietary to a manufacturer.6. Reference to this Practice in Standards6.1 Reference to this practice should be included in allASTM infrared methods. The reference should appear in thesection on apparatus where the particu
12、lar spectrometer isdescribed.7. Parameters in Spectroscopy7.1 Dispersive infrared spectrometers have a source ofquasi-monochromatic radiation together with a photometer formeasuring relative radiant power. Accurate spectrometry in-volves a large number of interrelated factors that determine thequali
13、ty of the radiant power passing through a sample and thesensitivity and linearity with which this radiant power can bemeasured. Assuming proper instrumentation and its use, theinstrumental factors responsible for inaccuracies in spectrom-etry are resolution, linearity (Practices E 168), stray radian
14、t1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.03 on Infrared and Near Infrared Spectroscopy.Current edition approved Dec. 1, 2007. Published December 2007. Originallyapproved in 19
15、89. Last previous edition approved in 2002 as E 932 - 89 (2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM websi
16、te.3Available from ASTM International Headquarters, 100 Barr Harbor Drive,West Conshohocken, PA 19428.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.power (Test Method E 387), and cell constants (PracticeE 1252). Rigorous measuremen
17、t of these factors is beyond thescope of this practice, and a more practical approach isdescribed for the accessible factors.8. Instrument Operation8.1 The analyst selects the proper instrumental operatingconditions in order to get satisfactory performance (1-3).4Because instrument design varies, th
18、e manufacturers recom-mendations are usually best. A record of operating conditionsshould be kept so that data can be duplicated by future users.8.2 In addition to operating conditions, the following shouldbe checked and recorded:8.2.1 Ambient temperature,8.2.2 Pen response time,8.2.3 Scanning speed
19、,NOTE 1In some instruments these functions are integrated in the scanmodes.8.2.4 Noise level, and8.2.5 Mechanical repeatability.8.3 Each of the above factors is important in the measure-ment of analytical wavenumber and photometric data. There isusually some lag between the recorded reading and the
20、correctreading. Proper selection of operating conditions and good,reproducible, sample handling techniques minimize these ef-fects or make the effects repeatable. For example:8.3.1 Variation in temperature of the monochromator orsample may cause changes in wavenumber precision andaccuracy.8.3.2 Scan
21、ning too fast will displace the apparent wavenum-ber towards the direction scanned and will decrease the peakabsorbance reading for each band.NOTE 2Some instruments provide for automatic monitoring andcorrection of this effect.8.4 Mechanical repeatability of the monochromator andrecording system as
22、well as positioning of chart paper areimportant in wavenumber measurement.8.4.1 Chart paper should be checked for uniformity of theprinted scale length as received and rechecked at time of use,particularly if the paper has been subjected to pronouncedhumidity changes. Instructions on obtaining prope
23、r mechanicalrepeatability may be given in the manufacturers literature.8.5 In the case of computerized dispersive instruments, anyspectrum printed from a computer file must be obtained asprescribed by the manufacturer and should be identical to theoriginal data.PRECISION AND ACCURACY9. Definitions9.
24、1 wavenumber precisiona measure of the capability of aspectrometer to return to the same spectral position as mea-sured by a well-defined absorption or emission band when theinstrument is reset or rescanned. The index used in this practiceis the standard deviation.9.2 wavenumber accuracythe deviatio
25、n of the averagewavenumber reading of an absorption band or emission bandfrom the known wavenumber of that band.10. Nature of Test10.1 For the purpose of calibration, most methods employpure compounds and known mixtures at specified analyticalwavenumbers. The wavenumbers are either read from a dial,
26、optical display, chart paper, or a computer file.11. Reference Wavenumbers in the Infrared Region (2)11.1 The recommended wavenumber calibration points arethe absorption maxima of a standard (98.4/0.8/0.8 by weight)indene/camphor/cyclohexanone mixture listed in Table 1. Suit-able path lengths are 0.
27、2 mm for the range from 3800 to 1580cm1and 0.03 mm for the wavenumber range from 1600 to 600cm-1. A mixture containing equal parts by weight of indene,camphor, and cyclohexanone (1/1/1 by weight) at a path lengthof 0.1 mm may be used for the range from 600 to 300 cm1.See Table 2 and Fig. 1.11.2 Poly
28、styrene is also a convenient calibration standardfor the wavenumber range from 4000 to 400 cm1. Polystyrenefilms, approximately 0.03 to 0.05 mm thick, can be purchasedfrom instrument manufacturers. The recommended calibrationpeaks are listed in Fig. 2.NOTE 3The correction of frequency for the refrac
29、tive index of air issignificant in the wavenumber calculation only when wavelengths havebeen measured to better than 3 parts in 10 000. Reference (3) tabulatesadditional reference wavenumbers of interest.11.3 For low-resolution prism or filter instruments operatedin single-beam mode, the position of
30、 the atmospheric carbondioxide band near 2350 cm1can be useful. This band may beresolved into a doublet. The 2350-cm1value is for the4The boldface numbers refer to the list of references at the end of this practice.TABLE 1 Indene-Camphor-Cyclohexanone (98.4/0.8/0.8)MixtureRecommended Calibration Ban
31、ds5BandNo.Wavenumber,cm1BandNo.Wavenumber,cm11 3927.2 6 1.0 44a 1741.92 3901.6 44b 1713.43 3798.9 47 1661.85 3660.6 6 1.0 48 1609.88 3297.8 6 1.0 49 1587.59 3139.5 51 1553.210 3110.2 53 1457.3 6 1.012 3025.4 54 1393.515 2887.6 55 1361.117 2770.9 57 1312.419 2673.3 58 1288.020 2622.3 60 1226.221 2598
32、.4 6 1.0 61 1205.123 2525.5 62 1166.128 2305.1 64 1122.429 2271.4 66 1067.7 6 1.030 2258.7 67 1018.533 2172.8 69 947.234 2135.8 6 1.0 70 942.435 2113.2 71 914.736 2090.2 72 861.339 1943.1 73 830.540 1915.3 74 765.341 1885.1 76 718.142 1856.9 77 692.6 6 1.044 1797.7 6 1.0E 932 89 (2007)2approximate c
33、enter between the two branches. The atmo-spheric carbon dioxide band near 667 cm1is useful in thelow-wavenumber region.12. Dynamic Error Test12.1 For dispersively measured spectra, the following dy-namic error test is suitable for use with most grating and prismspectrometers. (4 and 5)12.2 The spect
34、rum of the (98.4/0.8/0.8) indene/camphor/cyclohexanone mixture is remeasured from 1350 to 850 cm1at one fourth of the scan rate used for the reference spectrumand with other operating conditions unchanged. The heightsfrom the baseline of the bands at 1288.0, 1226.2, 1205.1,1018.5 and 914.7 cm1are me
35、asured in absorbance units onboth the fast and slowly scanned charts. The absorbance ratiosA1226.2/A1288.0, A1205.1/A1226.2, and A914.7/A1018.5should not differ by more than 60.02 between the fast andslow runs.NOTE 4The indene/camphor/cyclohexanone should remain in sealed,refrigerated ampoules.13. S
36、election of Slit Width or Slit Program13.1 One of the most important parameters the analyst mustselect is the spectral slit width. The slit width affects resolutionand the signal-to-noise ratio (S/N). Generally, a narrower slitwidth gives higher resolution and lower S/N ratio. These mustbe optimized
37、 for any given analysis.13.2 The preferred manner of expressing resolution is interms of spectral band width, but methods of measuring thisquantity in all spectral regions are not available.13.2.1 Spectral band width is not constant throughout thespectrum and therefore must be determined in each reg
38、ion ofinterest. In the neighborhood of 1200 cm1, the spectral bandwidth can be determined approximately from the ratioA1205.1/A1226.2 of the (98.4/0.8/0.8) indene/camphor/cyclohexanone mixture, computed in the dynamic error test, asgiven in Table 3.13.3 In each infrared method, typical spectra of th
39、e compo-nents, or a spectrum of a suitable mixture of components,should be included to illustrate the resolution found to beadequate to perform the analysis. These spectra should bedirect copies of the plotted spectra and not redrawn curves.PHOTOMETRY14. Linearity of Absorbance14.1 In a spectrometri
40、c method, photometric data are usedto determine concentrations. Linearity of absorbance is afunction of instrument response. The relationship must bedetermined in the concentration range of interest.14.2 Procedure for testing linearity and establishing work-ing curves are described in Practices E 16
41、8.14.3 Some methods for quantitative analysis do not requirelinear response. The ultimate criterion for these is whether amethod gives correct answers for known samples.15. Measurement Procedure for Frequency Accuracy andPrecision15.1 From Tables 1-3, select calibration wavenumbers,preferably bracke
42、ting each analytical wavenumber and readeach wavenumber ten times.15.2 Average the observed readings for each wavenumber.The wavenumber accuracy is the difference between the truewavenumber and the average observed wavenumber.NOTE 5To check the wavenumber accuracy of a non-scanning instru-ment, bala
43、nce the instrument at the true value of the absorbancemaximum. Adjust the wavenumber drive until maximum apparent absor-bance is found.Always approach the line or band from the same direction.Repeat ten times.15.3 Calculate the precision of each observed wavenumberusing the following equation:s 5(Xi
44、2 X!2n 2 1(1)where:s = estimated standard deviation of the series of results,Xi= individual observed value (wavenumber, absorbance,or transmittance)X= average (arithmetic mean) of the observed values, andn = number of observations.15.4 Results should be specified in the following order: truepeak pos
45、ition of reference material, average wavenumberdetermined, and wavenumber standard deviation.16. Measurement Procedure for Photometric Precision16.1 Photometric precision represents the capability of thephotometer system to reproduce the same value in successivedeterminations. The index of precision
46、 used in this practice isthe standard deviation.16.2 Photometric precision is determined on a calibrationsample by measuring the absorbance or transmittance of thesame sample ten times, following the same procedure used toobtain the data for the linearity test.16.3 Tabulate the individual readings o
47、f apparent absor-bance or transmittance. Calculate the standard deviation of theten readings using the equation in 15.3. Report the averagereading and the standard deviation.17. Stray Radiate Power17.1 Stray radiant power (SRP) causes an error in thespectrometer zero transmittance reading. If measur
48、ed at thedesignated path lengths, the indene/camphor/cyclohexanonereference spectrum should show essentially zero transmittanceat 3050.0, 1609.6 and 765.4 cm1. The test spectra at thesewavenumbers should therefore match the spectrometer trans-mittance zero within the manufacturers tolerances. A0.4-m
49、mTABLE 2 Indene-Camphor- Cyclohexanone (1/1/1) MixtureRecommended Calibration Bands5Band No.Wavenumber,cm11 592.12 551.73 521.44 490.2 6 1.05 420.56 393.17 381.68 301.4E 932 89 (2007)3layer of pure indene is almost totally absorbing at 392, 420, and551 cm1and this can be used to establish the stray radiantpower below 600 cm1. This should not exceed 2 % transmit-tance at wavenumbers greater than 600 cm1; the permissibleamount at lower wavenumbers is left to the discretion of theevaluator.18. Performance Evaluation18.1 Performance is adequate when test
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