1、Designation: E 2529 06Standard Guide forTesting the Resolution of a Raman Spectrometer1This standard is issued under the fixed designation E 2529; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、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 guide is designed for routine testing and assess-ment of the spectral resolution of Raman spectrometers usingeither a low-pressure arc l
3、amp emission lines or a calibratedRaman band of calcite.1.2 The values given in SI units are to be regarded as thestandard.1.3 Because of the significant dangers associated with theuse of lasers, ANSI Z136.1 shall be followed in conjunctionwith this practice.1.4 This standard does not purport to add
4、ress 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 practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 131 Termino
5、logy Relating to Molecular SpectroscopyE 1683 Practice for Testing the Performance of ScanningRaman SpectrometersE 1840 Guide for Raman Shift Standards for SpectrometerCalibration2.2 ANSI Standard:3ANSI Z136.1 Safe Use of Lasers3. Terminology3.1 DefinitionsTerminology used in this guide conformsto t
6、he definitions in Terminology E 131.4. Significance and Use4.1 Assessment of the spectrometer resolution and instru-ment line shape (ILS) function of a Raman spectrometer isimportant for intercomparability of spectra obtained amongwidely varying spectrometer systems, if spectra are to betransferred
7、among systems, if various sampling accessories areto be used, or if the spectrometer can be operated at more thanone laser excitation wavelength.4.2 Low-pressure discharge lamps (pen lamps such asmercury, argon, or neon) provide a low-cost means to provideboth resolution and wave number calibration
8、for a variety ofRaman systems over an extended wavelength range.4.3 There are several disadvantages in the use of emissionlines for this purpose, however.4.3.1 First, it may be difficult to align the lamps properlywith the sample position leading to distortion of the line,especially if the entrance
9、slit of the spectrometer is underfilledor not symmetrically illuminated.4.3.2 Second, many of the emission sources have highlydense spectra that may complicate both resolution and wavenumber calibration, especially on low-resolution systems.4.3.3 Third, a significant contributor to line broadening o
10、fRaman spectral features may be the excitation laser line widthitself, a component that is not assessed when evaluating thespectrometer resolution with pen lamps.4.3.4 An alternative would use a Raman active compound inplace of the emission source. This compound should bechemically inert, stable, an
11、d safe and ideally should provideRaman bands that are evenly distributed from 0 cm-1(Ramanshift) to the C-H stretching region 3000 cm-1and above. TheseRaman bands should be of varying bandwidth.4.4 To date, no such ideal sample has been identified;however carbon tetrachloride (see Practice E 1683) a
12、nd naph-thalene (see Guide E 1840) have been used previously for bothresolution and Raman shift calibration.4.5 The use of calcite to assess the resolution of a Ramansystem will be addressed in this guide. Calcite is a naturallyoccurring mineral that possesses many of the desired opticalproperties f
13、or a Raman resolution standard and is inexpensive,safe, and readily available.4.6 The spectral bandwidth of dispersive Raman spectrom-eters is determined primarily by the focal length of thespectrometer, the dispersion of the grating, and the slit width.Field portable systems typically operate with
14、fixed slits andgratings and thus operate with a fixed spectral bandwidth,while in many laboratory systems the slit widths and gratingsare variable. The spectral bandwidth of Fourier-Transform(FT)-Raman systems is continuously variable by altering the1This guide is under the jurisdiction of ASTM Comm
15、ittee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.08 on Raman Spectroscopy.Current edition approved Dec. 1, 2006. Published December 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
16、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100
17、 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.optical path difference of the interferometer and furthermore iscapable of obtaining much lower spectral bandwidth than mostpractical dispersive systems. Therefore, data obtained of anarrow Raman band on a FT-Raman syst
18、em can be used todetermine the resolution of a dispersive Raman system. Acalibration curve of the full width at half height (FWHH) forthe 1085-cm-1band of calcite as a function of spectralresolution has been reported for this purpose.4Measurement ofthis calcite band on a test dispersive instrument e
19、nables anestimation of the spectrometer resolution.4.7 This guide will describe the use of calcite and pen lampsfor the evaluation of Raman spectrometer resolution fordispersive (grating based) Raman systems operating with a785-nm laser wavelength.5. Reagents5.1 Calcite and calcium carbonate (CaCO3)
20、 come in manyforms. Iceland spar, from Iceland and, more commonly,Mexico, is easily cleavable into a rhombohedron and is theclear crystal commonly found in retail stores. It is readilyavailable and inexpensive but may fluoresce under blue exci-tation. In addition, it is birefringent.5.2 Low-pressure
21、 discharge emission (pen) lamps arewidely available from optical supply companies. They aretypically made with noble gases or a metal vapor. Argon,krypton, and xenon pen lamps are applicable as resolutioncalibration sources for Raman spectrometers operating with785-nm excitation. These pen lamps cov
22、er a wide wavenumber range but have reasonably sparse spectra.6. Procedure6.1 Calcite Calibration:6.1.1 Measure the Raman spectrum of calcite using thevendors recommended procedure for producing a Ramanspectrum of a sample with good signal to noise. The Ramanspectrum of calcite is shown in Fig. 1. B
23、ecause the Ramanscattering of the 1085-cm-1band is polarized, the peak heightwill depend upon the polarization of the laser and the locationof the sample with respect to the excitation laser. Rotate thesample under excitation laser beam to obtain the maximumsignal from the 1085-cm-1band. The calibra
24、tion relationdetermined in 4.6 is:Bw1085cm21! 5 1.0209 * Sresolution1 0.684 (1)Where:Bw1085= the measured bandwidth of the 1085-cm-1CaCO3Raman band, andSresolution= the nominal resolution of the reference FT-Raman spectrometer described in 4.6.6.1.2 After acquiring the Raman spectrum of the calcites
25、ample, determine the FWHH of the 1085-cm-1band , Bw1085,by using the spectral analysis feature commonly found in thecontrol software provided with the spectrometer. These pro-grams typically use a Levenburg-Marquardt nonlinear leastsquares to determine the line shape of the Raman band.5Thecalibratio
26、n equation (Eq 1) was determined using a fit to amixed Gaussian and Lorentzian function. Solve for the nomi-nal resolution of the spectrometer under test by rearranging Eq1 to:Sresolution5 Bw1085 0.684!/1.0209 (2)6.1.3 This fit is reported to be good to approximately 20 %accuracy, which is adequate
27、for validation purposes. The1085-cm-1band is a good approximation for system resolutionestimation as it is centered in the Raman spectra for fixedgrating systems that typically operate from 200 to approx. 2000cm-1. This material is suitable for use with all laser wave-lengths; however, many samples
28、have been observed to fluo-resce with excitation wavelengths below 532-nm excitation.4B.T. Bowie and P.R. Griffiths, “Determination of the Resolution of a Multi-channel Raman Spectrometer Using Fourier Transform Raman Spectra,” AppliedSpectroscopy, Vol 57, No 2., 2003, pp 190-196.5D. W. Marquardt, J
29、. Soc. Ind. Appl. Math.,Vol 11, 1963, pp. 431-441.FIG. 1 Calcite Raman SpectrumE25290626.2 Pen Lamp CalibrationThe spectra of xenon, argon,and krypton in Raman shift from 12 739 cm-1(785-nm excita-tion) are shown in Figs. 2-4. The associated emission linesfrom each source is listed in Table 1 in air
30、 wavelength, absolutecm-1(air), and Raman shift from 12739 cm-1. If a fiber-probe-based Raman system is to be calibrated, a convenient source ofan argon spectra is the light emitted from older backlit laptopcomputer screens or overhead fluorescent lights. Place atranslucent target at the focal point
31、 of the fiber collectionsystem. An example would be several thicknesses of scotchtape placed on a glass slide. Otherwise, illuminate the slit asevenly as possible. Check for symmetric lines in the collectedspectrum and use integration times that prevent saturation ofthe detector. This is especially
32、true for the xenon source inwhich the 881.9-nm line is very intense. Determine the FWHHof bands in the low, middle, and long Raman shift region of thespectra. The resolution (FWHH) shall not be constant, but varyfrom the low to high Raman shift region. Gratings disperselight nearly linearly in wavel
33、ength and therefore the reciprocallinear dispersion in wavelength units (nm) will be nearlyconstant. The reciprocal linear dispersion in wave number(cm-1) units will increase at higher Raman (Stokes) shift due tothe inverse relation between wavelength and wave number. ForRaman systems based upon the
34、 commonly used spectrometerdesigns, the resolution will theoretically increase (FWHHdecreases) on the Stokes-shifted (longer wavelength) side ofthe excitation laser line. It is not unusual, however, to observethe center of the spectra of fixed grating systems to have thesmallest FWHH (highest resolu
35、tion) while the edges (low andhigh Raman shift region) exhibit lower resolution. This effectis due to error incurred by the curvature of the focal plane forlow fnumber spectrometers.7. Keywords7.1 calcite; low-pressure arc lamp calibration; Raman spec-troscopy; resolution calibrationFIG. 2 Emission
36、Spectra of Argon Plotted in Shift Units from 12 738.85 cm-1(785 nm)E2529063FIG. 3 Emission Spectra of Krypton Plotted in Shift Units from 12 738.85 cm-1(785 nm)FIG. 4 Emission Spectra of Xenon Plotted in Shift Units from 12 738.85 cm-1(785 nm)E2529064ASTM International takes no position respecting t
37、he 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
38、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 standardsand should be addressed to ASTM International H
39、eadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This
40、standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), o
41、r serviceastm.org (e-mail); or through the ASTM website(www.astm.org).Argon Krypton Xenonnm Abs cm-1(Air) ShiftAnm Abs cm-1(Air) ShiftAnm Abs cm-1(Air) ShiftA794.818 12 581.50 157.4 805.95 12 407.72 331.1 823.163 12 148.26 590.6800.616 12 490.38 248.5 810.436 12 339.04 399.8 828.012 12 077.12 661.78
42、01.479 12 476.93 261.9 819.005 12 209.94 528.9 834.7 11 980.35 758.5810.369 12 340.06 398.8 826.324 12 101.79 637.1 840.919 11 891.75 847.1811.531 12 322.39 416.5 828.105 12 075.76 663.1 881.941 11 338.63 1400.2826.453 12 099.90 639.0 829.811 12 050.94 687.9 895.2 11 170.69 1568.2840.821 11 893.14 8
43、45.7 850.887 11 752.44 986.4 904.54 11 055.34 1683.5842.145 11 869.93 868.9 877.675 11 393.74 1345.1 916.265 10 913.87 1825.0852.145 11 735.09 1003.8 892.869 11 199.85 1539.0912.297 10 961.34 1777.5 975.176 10 254.56 2484.3922.45 10 840.70 1898.2 985.624 10 145.86 2593.0AShift from 785 nm or 12 738.85 cm-1, Absolute cm-1number are invariant. Shift numbers will vary depending upon the actual wavelength of the excitation laser.E2529065
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