1、Designation: E1421 99 (Reapproved 2015)1Standard Practice forDescribing and Measuring Performance of FourierTransform Mid-Infrared (FT-MIR) Spectrometers: Level Zeroand Level One Tests1This standard is issued under the fixed designation E1421; the number immediately following the designation indicat
2、es the year oforiginal 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.1NOTEUnits statement was inserted in 1.3 editorially in J
3、uly 2015.1. Scope1.1 This practice describes two levels of tests to measure theperformance of laboratory Fourier transform mid-infrared(FT-MIR) spectrometers equipped with a standard sampleholder used for transmission measurements.1.2 This practice is not directly applicable to Fourier trans-form in
4、frared (FT-IR) spectrometers equipped with variousspecialized sampling accessories such as flow cells or reflec-tance optics, nor to Fourier transform near-infrared (FT-NIR)spectrometers, nor to FT-IR spectrometers run in step scanmode.1.2.1 If the specialized sampling accessory can be removedand re
5、placed with a standard transmission sample holder, thenthis practice can be used. However, the user should recognizethat the performance measured may not reflect that which isachieved when the specialized accessory is in use.1.2.2 If the specialized sampling accessory cannot beremoved, then it may b
6、e possible to employ a modified versionof this practice to measure spectrometer performance. The useris referred to Guide E1866 for a discussion of how these testsmay be modified.1.2.3 Spectrometer performance tests for FT-NIR spectrom-eters are described in Practice E1944.1.2.4 Performance tests fo
7、r dispersive MIR instruments aredescribed in Practice E932.1.2.5 For FT-IR spectrometers run in a step scan mode,variations on this practice and information provided by theinstrument vendor should be used.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement
8、are included in thisstandard.1.3.1 ExceptionInformational inch-pound units are pro-vided in 5.4.1.4 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 appro-priate safety and health p
9、ractices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E131 Terminology Relating to Molecular SpectroscopyE932 Practice for Describing and Measuring Performance ofDispersive Infrared SpectrometersE1866 Guide for Establishing Spectr
10、ophotometer Perfor-mance TestsE1944 Practice for Describing and Measuring Performanceof Laboratory Fourier Transform Near-Infrared (FT-NIR)Spectrometers: Level Zero and Level One Tests3. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology E131. All identific
11、ations ofspectral regions and absorption band positions are given inwavenumbers (cm1), and spectral energy, transmittance, andabsorbance are signified in equations by the letters E, T, and Arespectively. The ratio of two transmittance or absorbancevalues, and the ratio of energy levels at two differ
12、ent wave-numbers are signified by the letter R. A subscripted numbersignifies a spectral position in wavenumbers (for example,A3082, the absorbance at 3082 cm1).3.1.1 level one (1) test, na simple series of measurementsdesigned to provide quantitative data on various aspects ofinstrument performance
13、 and information on which to base thediagnosis of problems.1This 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 May 1
14、, 2015. Published July 2015. Originally approvedin 1991. Last previous edition approved in 2009 as E1421 99 (2009). DOI:10.1520/E1421-99R15E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vo
15、lume 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 States13.1.2 level zero (0) test, na routine check of instrumentperformance, that can be done in a few minutes,
16、 designed tovisually detect significant changes in instrument performanceand provide a database to determine instrument function overtime.4. Significance and Use4.1 This practice permits an analyst to compare the generalperformance of an instrument on any given day with the priorperformance of an in
17、strument. This practice is not necessarilymeant for comparison of different instruments with each othereven if the instruments are of the same type and model. Thispractice is not meant for comparison of the performance of oneinstrument operated under differing conditions.5. Test Conditions5.1 Operat
18、ing ConditionsA record should be kept todocument the operating conditions selected so that they can beduplicated. In obtaining spectrophotometric data, the analystmust select proper instrumental operating conditions such aswarm-up time, purge rate, and beam splitter alignment in orderto realize sati
19、sfactory instrument performance. Operating con-ditions for individual instruments are best obtained from themanufacturers literature because of variations with instrumentdesign. It should be noted that many FT-IR instruments aredesigned to work best when left on or in the standby mode.Also note that
20、 spectrometers are to be tested only within theirrespective wavenumber ranges.NOTE 1This practice is designed to be used in situations where thedetector is not saturated. In some instruments, with some combinations ofoptics and detectors, the detector electronics are saturated with an emptybeam. The
21、se instruments are designed to have the infrared beam attenu-ated in the spectrometer or sample compartment to eliminate detectorsaturation. Consult your instrument manual or discuss appropriate attenu-ation techniques with the instrument vendor.5.2 The environment in which a spectrometer is operate
22、dcan affects its performance. Spectrometers should only beoperated in environments consistent with manufacturers rec-ommendations. Changes in the instrument environment includ-ing variations in temperature, vibration or sound levels, elec-trical power or magnetic fields should be recorded.5.3 Instru
23、mental characteristics can influence these mea-surements in several ways.5.3.1 Vignetting of the beam reduces the transmittancevalue measured in nonabsorbing regions, and on most instru-ments can change the apparent wavenumber scale by a smallamount, usually less than 0.1 cm1. Make sure that the fil
24、mholder does not vignet the beam.5.3.2 Focus changes can also change transmittance values,so the sample should be positioned in approximately the samelocation in the sample compartment each time.5.3.3 The angle of acceptance (established by the f number)of the optics between the sample and detector
25、significantlyaffects apparent transmittance. Changes to the optical pathincluding the introduction of samples can alter the acceptanceangle.5.3.4 Heating of the sample by the beam or by the highertemperatures which exist inside most spectrometers changesabsorbances somewhat, and even changes band ra
26、tios andlocations slightly. Allow the sample to come to thermalequilibrium before measurement.5.4 The recommended sample of matte-finish polystyreneused for these tests is approximately 38-m (1.5-mil) thick filmmounted on a card. The sample is mounted in a 2.5-cm (1-in.)circular aperture centered wi
27、thin the 5-cm (2.5-in.) width of thecard, and centered 3.8 cm (1.5 in.) from the bottom of the card.The card should be approximately 0.25-cm (0.1-in.) thick andindividually and unambiguously identified. A polystyrene filmmeeting these requirements is available from the NationalInstitute of Standards
28、 and Technology (NIST) as SRM 1921.3NOTE 2Very small beam diameters can defeat the interference fringesuppression provided by the matte finish on the sample.6. Level Zero Tests6.1 Nature of TestsRoutine checks of instrumentperformance, these tests can be performed in a few minutes.They are designed
29、to uncover malfunctions or other changes ininstrument operation but not to specifically diagnose or quan-titatively assess any malfunction. It is recommended that thelevel zero tests be conducted at the highest (smallest numericalvalue) resolution at which the instrument is typically used innormal o
30、peration. A nominal measurement time of 30 s shouldbe used. The exact measurement time, along with the date,time, sample identification, number of scans, exact data col-lection and computation parameters, and operators name,should always be recorded.6.2 PhilosphyThe philosophy of the tests is to use
31、 previ-ously stored test results as bases for comparison and the visualdisplay screen or plotter to overlay the current test results withthe known, good results. If the old and new results agree, theyare simply reported as no change. Level zero consists of threetests. The tests are run under the sam
32、e conditions that arenormally used to run a sample (that is, purge time, warm-uptime, detector, etc.).6.3 Variations in Operating Procedure for DifferentInstrumentsMost of the existing FT-IR instruments should beable to use the tests in this practice without modification.However, a few instruments m
33、ay not be able to perform thetests exactly as they are written. In these cases, it should bepossible to obtain the same final data using a slightly differentprocedure. Guide E1866 and the FT-IR manufacturer should beconsulted for appropriate alternative procedures.6.4 SampleThe recommended sample is
34、 described in 5.3.It is a matte-finish polystyrene film (approximately 38-mthick, in a 2.5-cm aperture). The same sample should be usedfor all comparisons (note serial number).6.5 Reference SpectraTwo spectra acquired and storedfollowing the last major instrument maintenance are used asreferences. M
35、ajor maintenance could include changes insource, laser, detector, or optical alignment. These spectra willbe identified as Reference 1 and Reference 2.3SRM 1921 is available from the Standard Reference Materials Program,National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070
36、,Gaithersburg, MD 20899-1070, http:/www.nist.gov.E1421 99 (2015)126.5.1 Reference Spectrum 1 is a single-beam energy spec-trum of an empty beam. (In this and all later usage, emptybeam means that nothing is in the sample path except air orthe purge gas normally present within the spectrometer sample
37、compartment). If possible, the interferogram corresponding toReference Spectrum 1 should also be saved.6.5.2 Reference Spectrum 2 is a transmittance spectrum ofthe polystyrene sample. Optionally, an absorbance spectrummay also be stored.NOTE 3If the instrument software will not allow for subtraction
38、 oftransmittance spectra, Reference Spectrum 2 should be saved as anabsorbance spectrum.6.6 Reproducibility of ProceduresCare should be takenthat each of the spectral measurements is made in a consistentand reproducible manner, including sample orientation (al-though different spectral measurements
39、do not necessarily usethe identical procedure). In particular, for those instrumentshaving more than one sample beam or path in the main samplecompartment, all of the test spectra always should be measuredusing the same path. It may be desirable to repeat the tests oneach path.6.7 MeasurementsAcquir
40、e and store three test spectra.The test spectra will be identified hereafter as Spectrum 1,Spectrum 2, and Spectrum 3.6.7.1 Spectrum 1Acquire and store a single-beam energyspectrum of any empty beam. When possible, the interfero-gram of Spectrum 1 should also be stored. If Spectrum 1 isstored only a
41、s an interferogram, it must be transformed beforeuse in the ensuing tests.6.7.2 Spectrum 2Acquire and store an empty-beam spec-trum taken immediately after Spectrum 1. This spectrumshould be stored as a transmittance spectrum ratioed againstSpectrum 1.6.7.3 Spectrum 3Acquire and store a spectrum of
42、thepolystyrene sample reasonably soon after Spectrum 2. Thisspectrum should be stored as a transmittance spectrum calcu-lated using either Spectrum 1 or Spectrum 2 as a background.Optionally, Spectrum 3 may also be stored as an absorbancespectrum. To reproducibly insert the sample, the serial number
43、(or other identifying information) should be right side upfacing the instrument detector.NOTE 4If the instrument software will not allow for subtraction oftransmittance spectra, Spectrum 2 should be saved as an absorbancespectrum.7. Level Zero Test Procedures7.1 Energy Spectrum TestOverlay Spectrum
44、1 and Refer-ence 1. Note any change in energy level across the spectrum.Ratio Spectrum 1 to Reference Spectrum 1 to produce atransmittance spectrum, and look for significant changes from100 %, especially at high wavenumber. Video display resolu-tion may limit the accuracy to which this test can be i
45、nterpretedif the comparison is made on-screen. In addition, if theinterferogram for Spectrum 1 was saved, it may be displayed orplotted and the center burst height recorded and compared tothe allowable range for the instrument. Use caution in inter-preting this because minor changes in interferogram
46、 heightonly affect performance at high wavenumbers, and do notnecessarily affect photometric performance.NOTE 5If the centerburst height exceeds the dynamic range of theanalog-to-digital converter, the energy profile is distorted and significantnonphysical energy will be observed. If the centerburst
47、 is small relative tothe dynamic range, then the signal-to-noise of the measurement may beless than optimal.7.1.1 ReportageReport by (1) making an overlay plot ofSpectrum 1 and Reference 1, (2) plotting the transmittancespectrum of Spectrum 1 ratioed against Reference 1 over therange of 95 to 105 %
48、T, and by reporting the following energyratios:R4000/20005 E4000/E2000(1)R2000/10005 E2000/E1000If possible, from Spectrum 1, report the ratio between theapparent energy in the wavenumber region below the instru-ment cutoff and the energy in the maximum-energy region ofthe spectrum, for example:Rnon
49、physical5 E150/Emax(2)Report the date and time of both spectra used, and the actualnumbers of scans and measurement times.7.1.2 InterpretationAn overall drop in the energy level inwhich the largest percentage of change occurs at higherwavenumbers usually indicates interferometer misalignment ora reduction in source temperature. An example of the affect ofmisalignment is shown in Fig. 1.7.1.2.1 If the instrument has been exposed to high humidity,this drop in energy level may reflect beamsplitter or windowfogging.7.1.2.2 An overall drop in the energ
