ASTM_E_2529_-_06_2014.pdf

Designation:E252906(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 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 guide is designed for routine testing and assess-ment of the spectral resolution of Raman spectrometers usingeither a low-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 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 limitations 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.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 amongwidely 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 low-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 position 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 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 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 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 naturallyoccurring 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 ASTM 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/E2529-06R14.2For 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(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 States1 spectrometer,the dispersion of the grating,and the slit width.Field portable systems typically operate with 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 theoptical path difference