1、Designation: E2529 06 (Reapproved 2014)Standard Guide forTesting the Resolution of a Raman Spectrometer1This standard is issued under the fixed designation E2529; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. 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 guide is designed for routine testing and assess-ment of the spectral resolution of Raman spectrometers usingeither a low
3、-pressure arc lamp emission lines or a calibratedRaman band of calcite.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 Because of the significant dangers associated with theuse of lasers, ANSI Z136.1 shall be followed in
4、 conjunctionwith this practice.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 practices and determine the applica-bility of regulatory limitatio
5、ns prior to use.2. Referenced Documents2.1 ASTM Standards:2E131 Terminology Relating to Molecular SpectroscopyE1683 Practice for Testing the Performance of ScanningRaman SpectrometersE1840 Guide for Raman Shift Standards for SpectrometerCalibration2.2 ANSI Standard:3ANSI Z136.1 Safe Use of Lasers3.
6、Terminology3.1 DefinitionsTerminology used in this guide conformsto the definitions in Terminology E131.4. 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 amongw
7、idely varying spectrometer systems, if spectra are to betransferred 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 l
8、ow-cost means to provideboth resolution and wave number calibration 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 po
9、sition leading to distortion of the line,especially if the entrance 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
10、 systems.4.3.3 Third, a significant contributor to line broadening ofRaman 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
11、emission source. This compound should bechemically inert, stable, and 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
12、been identified;however carbon tetrachloride (see Practice E1683) and naph-thalene (see Guide E1840) 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 naturallyoccurr
13、ing mineral that possesses many of the desired opticalproperties for 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 the1This guide is under the jurisdiction of AST
14、M Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.08 on Raman Spectroscopy.Current edition approved May 1, 2014. Published June 2014. Originallyapproved in 2006. Last previous edition approved in 2006 as E2529061. DOI:10.1520/E2529-
15、06R14.2For 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 website.3Available from American National Standards Institute (
16、ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1spectrometer, the dispersion of the grating, and the slit width.Field portable systems typically operate with fixe
17、d 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 theoptical path difference of the interferometer and furt
18、hermore iscapable of obtaining much lower spectral bandwidth than mostpractical dispersive systems. Therefore, data obtained of anarrow Raman band on a FT-Raman system can be used todetermine the resolution of a dispersive Raman system. Acalibration curve of the full width at half height (FWHH) fort
19、he 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 enables anestimation of the spectrometer resolution.4.7 This guide will describe the use of calcite and pen lampsfor the evaluation of R
20、aman spectrometer resolution fordispersive (grating based) Raman systems operating with a785-nm laser wavelength.5. Reagents5.1 Calcite and calcium carbonate (CaCO3) come in manyforms. Iceland spar, from Iceland and, more commonly,Mexico, is easily cleavable into a rhombohedron and is theclear cryst
21、al 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 discharge emission (pen) lamps arewidely available from optical supply companies. They aretypically made with noble gases or a metal v
22、apor. Argon,krypton, and xenon pen lamps are applicable as resolutioncalibration sources for Raman spectrometers operating with785-nm excitation. These pen lamps cover a wide wavenumber range but have reasonably sparse spectra.6. Procedure6.1 Calcite Calibration:6.1.1 Measure the Raman spectrum of c
23、alcite 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. Because the Ramanscattering of the 1085-cm-1band is polarized, the peak heightwill depend upon the polarization of the laser and the loc
24、ationof the sample with respect to the excitation laser. Rotate thesample under excitation laser beam to obtain the maximumsignal from the 1085-cm-1band. The calibration relationdetermined in 4.6 is:Bw1085cm21! 5 1.0209*Sresolution10.684 (1)Where:Bw1085= the measured bandwidth of the 1085-cm-1CaCO3R
25、aman 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 calcitesample, determine the FWHH of the 1085-cm-1band, Bw1085,by using the spectral analysis feature commonly found in thecontrol software provid
26、ed with the spectrometer. These pro-grams typically use a Levenburg-Marquardt nonlinear leastsquares to determine the line shape of the Raman band.5Thecalibration equation (Eq 1) was determined using a fit to amixed Gaussian and Lorentzian function. Solve for the nomi-nal resolution of the spectrome
27、ter under test by rearranging Eq1 to:Sresolution5 Bw10852 0.684!/1.0209 (2)6.1.3 This fit is reported to be good to approximately 20 %accuracy, which is adequate for validation purposes. The1085-cm-1band is a good approximation for system resolutionestimation as it is centered in the Raman spectra f
28、or fixedgrating systems that typically operate from 200 to approx. 20004Bowie, B. T. and Griffiths, P. R., “Determination of the Resolution of aMultichannel Raman Spectrometer Using Fourier Transform Raman Spectra,”Applied Spectroscopy, Vol 57, No 2, 2003, pp 190-196.5Marquardt, D. W., J. Soc. Ind.
29、Appl. Math., Vol 11, 1963, pp. 431-441.FIG. 1 Calcite Raman SpectrumE2529 06 (2014)2cm-1. This material is suitable for use with all laser wave-lengths; however, many samples have been observed to fluo-resce with excitation wavelengths below 532-nm excitation.6.2 Pen Lamp CalibrationThe spectra of x
30、enon, argon,and krypton in Raman shift from 12 739 cm-1(785-nmexcitation) are shown in Figs. 2-4. The associated emissionlines from each source is listed in Table 1 in air wavelength,absolute cm-1(air), and Raman shift from 12739 cm-1.Ifafiber-probe-based Raman system is to be calibrated, a conve-ni
31、ent source of an argon spectra is the light emitted from olderbacklit laptop computer screens or overhead fluorescent lights.Place a translucent target at the focal point of the fibercollection system. An example would be several thicknesses ofscotch tape placed on a glass slide. Otherwise, illumina
32、te theslit as evenly as possible. Check for symmetric lines in thecollected spectrum and use integration times that preventsaturation of the detector. This is especially true for the xenonsource in which the 881.9-nm line is very intense. Determinethe FWHH of bands in the low, middle, and long Raman
33、 shiftregion of the spectra. The resolution (FWHH) shall not beconstant, but vary from the low to high Raman shift region.Gratings disperse light nearly linearly in wavelength andtherefore the reciprocal linear dispersion in wavelength units(nm) will be nearly constant. The reciprocal linear dispers
34、ionin wave number (cm-1) units will increase at higher Raman(Stokes) shift due to the inverse relation between wavelengthand wave number. For Raman systems based upon the com-monly used spectrometer designs, the resolution will theoreti-cally increase (FWHH decreases) on the Stokes-shifted (longerwa
35、velength) side of the excitation laser line. It is not unusual,however, to observe the center of the spectra of fixed gratingsystems to have the smallest FWHH (highest resolution) whilethe edges (low and high Raman shift region) exhibit lowerresolution. This effect is due to error incurred by the cu
36、rvatureof the focal plane for low fnumber spectrometers.7. Keywords7.1 calcite; low-pressure arc lamp calibration; Raman spec-troscopy; resolution calibrationFIG. 2 Emission Spectra of Argon Plotted in Shift Units from 12 738.85 cm-1(785 nm)E2529 06 (2014)3FIG. 3 Emission Spectra of Krypton Plotted
37、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)E2529 06 (2014)4ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this
38、 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 is subject to revision at any time by the responsible technical committee and must be reviewed every five year
39、s 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 Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committ
40、ee, 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 standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428
41、-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), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the stan
42、dard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).TABLE 1 Emission Lines of Argon, Krypton, and XenonArgon 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
43、248.5 810.436 12 339.04 399.8 828.012 12 077.12 661.7801.479 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
44、050.94 687.9 895.2 11 170.69 1568.2840.821 11 893.14 845.7 850.887 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.E2529 06 (2014)5
