1、Designation: E 1421 99 (Reapproved 2009)Standard Practice forDescribing and Measuring Performance of FourierTransform Mid-Infrared (FT-MIR) Spectrometers: Level Zeroand Level One Tests1This standard is issued under the fixed designation E 1421; the number immediately following the designation indica
2、tes 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.1. Scope1.1 This practice describes two levels of tests
3、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 infrared (FT-IR) spectrometers equipped with variousspecialized sam
4、pling 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 replaced with a standard transmission sample holder, thenthis pract
5、ice 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 be re-moved, then it may be possible to employ a modified versionof this practice to meas
6、ure spectrometer performance. The useris referred to Guide E 1866 for a discussion of how these testsmay be modified.1.2.3 Spectrometer performance tests for FT-NIR spectrom-eters are described in Practice E 1944.1.2.4 Performance tests for dispersive MIR instruments aredescribed in Practice E 932.1
7、.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.2. Referenced Documents2.1 ASTM Standards:2E 131 Terminology Relating to Molecular SpectroscopyE 932 Practice for Describing and Measuring Performanceof Di
8、spersive Infrared SpectrometersE 1866 Guide for Establishing Spectrophotometer Perfor-mance TestsE 1944 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
9、terms used in this prac-tice, refer to Terminology E 131. All identifications of spectralregions and absorption band positions are given in wavenum-bers (cm1), and spectral energy, transmittance, and absorbanceare signified in equations by the letters E, T, and A respectively.The ratio of two transm
10、ittance or absorbance values, and theratio of energy levels at two different wavenumbers aresignified by the letter R. A subscripted number signifies aspectral position in wavenumbers (for example, A3082, theabsorbance at 3082 cm1).3.1.1 level one (1) test, na simple series of measurementsdesigned t
11、o provide quantitative data on various aspects ofinstrument performance and information on which to base thediagnosis of problems.3.1.2 level zero (0) test, na routine check of instrumentperformance, that can be done in a few minutes, designed tovisually detect significant changes in instrument perf
12、ormanceand 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 instrument. This practice is not necessarilymeant for comparison of
13、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 Operating ConditionsA record should be kept todocument the operating con
14、ditions selected so that they can beduplicated. In obtaining spectrophotometric data, the analyst1This 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 Spect
15、roscopy.Current edition approved March 1, 2009. Published March 2009. Originallyapproved in 1991. Last previous edition approved in 2004 as E 1421 99 (2004).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AS
16、TMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.must select proper instrumental operating conditions such aswarm-up time, purge rate, and
17、 beam splitter alignment in orderto realize satisfactory 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 wh
18、en left on or in the standby mode.Also note that 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
19、electronics are saturated with an emptybeam. These 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 Th
20、e environment in which a spectrometer is operatedcan 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
21、or magnetic fields should be recorded.5.3 Instrumental 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, u
22、sually less than 0.1 cm1. Make sure that the filmholder 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 numbe
23、r)of the optics between the sample and detector 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 chang
24、esabsorbances somewhat, and even changes band ratios 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
25、in a 2.5-cm (1-in.)circular aperture centered within 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 a
26、vailable from the NationalInstitute of Standards 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 instrument perfor-mance, these tests ca
27、n be performed in a few minutes. They aredesigned to uncover malfunctions or other changes in instru-ment operation but not to specifically diagnose or quantita-tively assess any malfunction. It is recommended that the levelzero tests be conducted at the highest (smallest numericalvalue) resolution
28、at which the instrument is typically used innormal operation. 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 recorde
29、d.6.2 PhilosphyThe philosophy of the tests is to use 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 con
30、sists of threetests. The tests are run under the same 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 shouldbe able to use the tests in this practi
31、ce without modification.However, a few instruments may 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. Practice E 1866 and the FT-IR manufacturer shouldbe consulted for appropriate al
32、ternative procedures.6.4 SampleThe recommended sample is 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 la
33、st major instrument maintenance are used asreferences. Major maintenance could include changes insource, laser, detector, or optical alignment. These spectra willbe identified as Reference 1 and Reference 2.6.5.1 Reference Spectrum 1 is a single-beam energy spec-trum of an empty beam. (In this and a
34、ll later usage, emptybeam means that nothing is in the sample path except air orthe purge gas normally present within the spectrometer samplecompartment). If possible, the interferogram corresponding toReference Spectrum 1 should also be saved.6.5.2 Reference Spectrum 2 is a transmittance spectrum o
35、fthe polystyrene sample. Optionally, an absorbance spectrummay also be stored.NOTE 3If the instrument software will not allow for subtraction oftransmittance spectra, Reference Spectrum 2 should be saved as anabsorbance spectrum.6.6 Reproducibility of ProceduresCare should be takenthat each of the s
36、pectral measurements is made in a consistentand reproducible manner, including sample orientation (al-though different spectral measurements do not necessarily usethe identical procedure). In particular, for those instrumentshaving more than one sample beam or path in the main sample3SRM 1921 is ava
37、ilable from the Standard Reference Materials Program,National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070,Gaithersburg, MD 20899-1070, http:/www.nist.gov.E 1421 99 (2009)2compartment, all of the test spectra always should be measuredusing the same path. It may be desirabl
38、e to repeat the tests oneach path.6.7 MeasurementsAcquire 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 Spectru
39、m 1 should also be stored. If Spectrum 1 isstored only as 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 againstSpe
40、ctrum 1.6.7.3 Spectrum 3Acquire and store a spectrum of 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 absorbancespectr
41、um. To reproducibly insert the sample, the serial number(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
42、Test Procedures7.1 Energy Spectrum TestOverlay Spectrum 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
43、-tion may limit the accuracy to which this test can be interpretedif 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 i
44、nter-preting this because minor changes in interferogram 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 significan
45、tnonphysical energy will be observed. If the centerburst 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 r
46、atioed against Reference 1 over therange of 95 to 105 % 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 th
47、e maximum-energy region ofthe spectrum, for example:Rnonphysical5 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 higherwavenumbe
48、rs 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.FIG. 1 Effect of Misalignme
49、nt on Single-Beam Energy SpectraE 1421 99 (2009)37.1.2.2 An overall drop in the energy level without wave-number dependence suggests beam obstruction or misalign-ment of noninterferometer optical components.7.1.2.3 The appearance of bands or other features indicatespurge gas contributions, beam obstruction by a partiallytransmitting object, oil, or smoke deposition on mirrors orwindows, or a forgotten sample in the beam.7.1.2.4 With cooled detectors, the appearance of a bandaround 3440 cm1indicates ice deposition on the detectorsurface.7.1.2.5 Non-z
