ASTM E1683-95A

Standard Practice for Testing the Performance of Scanning Raman Spectrometers

SCOPE
1.1 This practice is designed for routine testing of scanning Raman spectrometer performance and to assist in locating problems when performance has degraded. It is also intended as a guide for obtaining and reporting Raman spectra.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific precautions, see 7.2.1.
1.3 Because of the significant dangers associated with the use of lasers, ANSI Z136.1 should be followed in conjunction with this practice.

General Information

• Status: Historical
• Publication Date: 09-Mar-2002
• ICS: 71.040.50 - Physicochemical methods of analysis
• Technical Committee: E13 - Molecular Spectroscopy and Separation Science
• Drafting Committee: E13.08 - Raman Spectroscopy

Relations

• Replaced By: ASTM E1683-02 - Standard Practice for Testing the Performance of Scanning Raman Spectrometers
• Effective Date: 10-Mar-2002
• Referred By: ASTM E2056-04(2016) - Standard Practice for Qualifying Spectrometers and Spectrophotometers for Use in Multivariate Analyses, Calibrated Using Surrogate Mixtures
• Effective Date: 10-Mar-2002
• Referred By: ASTM D8470-22 - Standard Practice for Development and Implementation of Instrument Performance Tests for Use on Multivariate Online, At-Line and Laboratory Spectroscopic Based Analyzer Systems
• Effective Date: 10-Mar-2002
• Referred By: ASTM E1866-97(2021) - Standard Guide for Establishing Spectrophotometer Performance Tests
• Effective Date: 10-Mar-2002
• Referred By: ASTM E2529-06(2022) - Standard Guide for Testing the Resolution of a Raman Spectrometer
• Effective Date: 10-Mar-2002
• Referred By: ASTM E1840-96(2022) - Standard Guide for Raman Shift Standards for Spectrometer Calibration
• Effective Date: 10-Mar-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 1683 – 95a
Standard Practice for
Testing the Performance of Scanning Raman
Spectrometers
This standard is issued under the fixed designation E 1683; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Use of this practice is intended only for trained optical
spectroscopists and should be used in conjunction with stan-
1.1 This practice is designed for routine testing of scanning
dard texts.
Raman spectrometer performance and to assist in locating
problems when performance has degraded. It is also intended
5. Apparatus
as a guide for obtaining and reporting Raman spectra.
5.1 Laser—A monochromatic, continuous laser source,
1.2 This standard does not purport to address all of the
such as an argon, krypton, or helium-neon laser, is normally
safety concerns, if any, associated with its use. It is the
used for Raman measurements. The laser intensity should be
responsibility of the user of this standard to establish appro-
measured at the sample with a power meter because optical
priate safety and health practices and determine the applica-
components between the laser and sample reduce laser inten-
bility of regulatory limitations prior to use. For specific
sity. A filtering device should also be used to remove non-
precautions, see 7.2.1.
lasting plasma emission lines from the laser beam before they
1.3 Because of the significant dangers associated with the
reach the sample. Plasma lines can seriously interfere with
use of lasers, ANSI Z136.1 should be followed in conjunction
Raman measurements. Filtering devices include dispersive
with this practice.
monochromators and interference filters.
2. Referenced Documents 5.2 Sampling Optics—Commercial instruments can be pur-
chased with sampling optics to focus the laser beam onto a
2.1 ASTM Standards:
sample and to image the Raman scattering onto the monochro-
E 131 Terminology Relating to Molecular Spectroscopy
mator entrance slit. Sample chamber adjustments are used to
2.2 ANSI Standard:
center the sample properly and align the Raman scattered light.
Z136.1 Safe Use of Lasers
A schematic view of a conventional 90° Raman scattering
3. Terminology
geometry is shown in Fig. 1. The laser beam propogates at a
right angle to the direction in which scattered light is collected.
3.1 Terminology used in this practice conforms to the
It is focused on the sample at the same position as the
definitions in Terminology E 131.
monochromator entrance slit image. Other geometries such as
4. Significance and Use
180° backscattering are also used. With single monochroma-
tors, a filter is normally placed in the optical collection path to
4.1 A scanning Raman spectrometer should be checked
block light at the laser frequency from entering the monochro-
regularly to determine if its condition is adequate for routine
mator.
measurements or if it has changed. This practice is designed to
5.3 Polarization—For routine measurements the polariza-
facilitate that determination and, if performance is unsatisfac-
tion of the laser at the sample is oriented normal to the plane
tory, to identify the part of the system that needs attention.
of the page in Fig. 1. However, measurements using different
These tests apply for single-, double-, or triplemonochromator
polarizations are sometimes used to determine vibrational
scanning Raman instruments commercially available. They do
symmetries as part of molecular structure determinations. A
not apply for multichannel or Fourier transform instruments, or
variety of optical configurations can be used to make polariza-
for gated integrator systems requiring a pulsed laser source.
tion measurements; a detailed discussion of these is beyond the
scope of this practice. Briefly, for polarization simple measure-
ments of randomly-oriented samples (most of the clear liq-
This practice is under the jurisdiction of ASTM Committee E-13 on Molecular
Spectroscopy and is the direct responsibility of Subcommittee E13.08 on Raman
uids), an analyzing element such as a polaroid filter or
Spectroscopy.
analyzing prism is added to the optical system and Raman
Current edition approved Sept. 10, 1995. Published November 1995. Originally
spectra are collected for light scattered in (1) the same direction
published as E 1683 – 95. Last previous edition E 1683 – 95.
Annual Book of ASTM Standards, Vol 03.06. as the source (parallel), (2) perpendicular to the source.
Available from American National Standards Institute, 11 W. 42nd Street, 13th
Floor, New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1683
FIG. 1 Typical Raman Scattering Measurement Geometry
Depolarization ratios are calculated using Raman band inten- turer for detailed sample chamber alignment instructions. Upon
sities from the two spectra as follows:
installation, each optical component should be aligned indi-
vidually. For optimal alignment the sample image should be
Intensity parallel
Depolarization ratio 5 (1)
centered on the entrance slit of the monochromator (often
Intensity perpendicular
viewed through a periscope accessory or with the aid of a
5.3.1 A polarization scrambler is shown in Fig. 1. This
highly scattering sample or a white card at the slit). To perform
element is used to avoid making corrections for polarization-
the alignment a test sample is mounted in the sample compart-
dependent grating effects. The scrambler is also frequently
ment, centered in the laser beam, and translated to the
used during routine measurements and should be placed
approximate center of the monochromator optic axis. The
between the sample and entrance slit, close to the collection
monochromator is set to monitor a strong Raman band and its
lens. A polaroid filter placed between the scrambler and
signal is maximized by adjusting the sample stage, lenses, or a
collection lens provides a simple polarization measurement
combination of the two. Normally three orthogonal lens
system.
adjustments are used: (1) the laser focusing lens is translated
5.4 Monochromator—A scanning monochromator used for
along the direction of the beam; (2) the Raman scattering
Raman spectroscopy will exhibit high performance require-
collection lens, positioned between the sample and the entrance
ments. Double and triple monochromators have particularly
slit, is translated along the direction of the propogating
stringent performance standards. During the original instru-
scattered light in order to provide focus; and (3) the collection
ment design, features are usually introduced to minimize
lens is translated perpendicular to the scattered light in order to
optical aberrations. However, proper maintenance of optical
scan the image of the laser-excited scattering volume across the
alignment is essential. A focused image on the entrance slit
width of the monochromator entrance slit. (Refer to Fig. 1.)
should be optically transferred to and matched with the other
This collection lens adjustment should be made during major
slits. If the monochromator is not functioning properly contact
instrument alignment (for example, during initial set-up), but
the manufacturer for assistance.
should not be necessary during routine sample-to-sample
5.5 Photomultiplier Tube—A photomultiplier tube is nor-
alignment. Sample and lens adjustments should be repeated as
mally used for detecting Raman scattered radiation. A tube
necessary while the slits are narrowed from a relatively large
with good response characteristics at and above the laser
initial width down to the size determined by the resolution
wavelength should be selected. Dark signal can be reduced
requirements of the measurement.
with thermoelectric cooling for improved detection of weak
6.2 Calibration:
signals. Current and voltage amplification or photon counting
6.2.1 Spectral Response—The spectral response of an opti-
are commercially available options with photomultiplier tubes.
cal spectrometric system will depend on the efficiency of the
6. Guidelines for Obtaining and Reporting Raman
gratings (which is both wavelength and polarization depen-
Spectra
dent) and the spectral response of the photomultiplier tube.
6.1 Alignment of Optical Elements—Refer to the manufac- This can be measured routinely by collecting light from a
E 1683
FIG. 2 Carbon Tetrachloride Raman Spectrum for Evaluating Resolution and Scanning Accuracy
tungsten halogen lamp or other NIST-traceable standard light wavenumbers, then 1-wavenumber increments would produce
source. A complete procedure for performing spectral response five data points within the FWHM in a scan of a line from a
corrections has been published by Scherer and Kint (1). It is plasma emission source. To better define peak shape decrease
strongly recommended that corrections for spectral response be the size of the increments. This is especially important for
incorporated directly into the software when a computer is used bands that deviate from Lorentzian shape.
to collect spectra. 6.4 Reporting Experimental Conditions—The spectral slit
6.2.2 Wavenumber—The accuracy of the wavenumber cali- width (wavenumbers), scan rate, laser wavelength and power at
bration over a large region should be determined using a the sample, polarization conditions, integration time, correc-
standard low-pressure emission source with enough lines to tions for instrumental response, type of spectrometer and
make many measurements over the range of the instrument. detector, sample information (physical state, concentration,
Low-pressure mercury, argon, and neon lamps are frequently geometry, and so forth), and other important experimental
used. The non-lasing emission lines of the laser can also be conditions should always be recorded with the spectra and
used if the laser filtering device is removed. Accurate wave- reproduced for performance testing. A complete record of the
number values are available (2-9). For measurement at resolu- parameters to be specified is available in Table 1 of the IUPAC
tions <0.5 wavenumbers a more rigorous calibration method Recommendations for the Presentation of Raman Spectra in
should be employed. Data Collections (10).
6.3 Recording Raman Spectra—The following guidelines
7. Evaluation of Raman Instrument Parameters
are provided for recording spectra with a rare meter and strip
chart recorder or with a computer or digital signal averager. In 7.1 The performance of an instrument should be evaluated
both cases it is important to record a spectrum so that spectral
regularly to determine if it has degraded. This is most easily
features are not distorted by the mode of data acquisition. accomplished with a test sample such as carbon tetrachloride
6.3.1 Recording With a Rate-Meter and Strip Chart
measured under a set of standard conditions established for the
Recorder—The range on the rate-meter is set by monitoring particular instrument. Signal intensity and wavelength accu-
the strongest peak in the spectrum. The relationship between
racy are the two spectral features to check. If peak signal levels
the scan rate, spectral slit width, and time constant of the have diminished or are shifted from accepted wavenumber
rate-meter, as recommended by IUPAC (10), is:
values, the components of the system should be evaluated
independently to locate the source of performance degradation.
spectral slit width, cm21
Scan rate, cm21/s |La (2)
Guidelines for such an evaluation are as follows:
4 3 time constant, s
7.2 Test Samples—The following readily available materials
In addition, the time constant of the recorder should be
are commonly used for evaluating the performance of Raman
considerably faster than the rate-meter’s time constant, and the
spectrometers:
speed of the paper should be adequate to measure the spectral
features.
TABLE 1 Recommended Frequencies from the Spectrum of
6.3.2 Recording With a Computer or Signal Averager—In
Indene for Evaluating Scanning Accuracy
this case one needs to define the increments in wavenumbers
A 1
Band Frequency, cm
between data points. A minimum criterion is to collect five data
1 730.4 6 0.5
points in the full width at half the maximum intensity (FWHM)
2 1018.3 6 0.5
of the narrowest spectral band. For example, if the slits were
3 1205.6 6 0.5
set to provide a measured band width at half maximum of 4
4 1552.7 6 0.5
5 1610.2 6 0.5
6 2892.2 6 1
4 7 3054.7 6 1
The boldface numbers in parentheses refer to a list of references at the end of
A
the text. Bands from Fig. 3.
E 1683
7.2.1 Carbon Tetrachloride—The major Raman bands are does not reduce the bandwidth as expected, then there is a
218, 314, and 459 wavenumbers (see Fig. 2). problem and the manufacturer should be consulted.
7.3.2 Resolution—A test frequently used to check the reso-
NOTE 1—Warning: Carbon tetrachloride is toxic and a suspected
lution of Raman spectrometers is illustrated in Fig. 4. The four
carcinogen. It is recommended that carbon tetrachloride be used in closed
containers to avoid inhalation of harmful vapors. components of the mercury 579.1-nm emission line are dis-
tinctly visible. Alternately, the components of the carbon
7.2.2 Cyclohexane—The major Raman bands are at 385,
tetrachloride 459 wavenumber Raman scattering band can be
804, 1449, and 2855 wavenumbers.
used, as shown in Fig. 2. The spectral bandwidth described in
7.2.3 Indene—There are many bands at well-known wave-
7.3.1 is also commonly used as a convenient means to measure
numbers (2, 11, 12). Samples should be vacuum-distilled,
resolution.
sealed, and stored in the dark. A reference spectrum is shown
7.3.3 Coupling—If the stages of a Raman spectrometer are
in Fig. 3 (2).
improperly coupled it may possibly go undetected in a resolu-
7.3 Monochromator—There is a trade-off between spectral
tion test. Poor coupling results in a loss in Raman signal
resolution of a monochromator and the intensity throughput.
intensity, often as a function of wavelength. To check the
The following five characteristics of a monochromator can be
coupling of two monochromator stages, measure the Raman
evaluated independently:
scattering of a test liquid at a major band intensity maximum.
7.3.1 Spectral Bandwidth—The minimum spectral band-
Set the entrance slit of the first stage and the exit slit of the
width that can be measured with a Raman spectrometer is
second stage to narrow widths (for example, 50 μm). Set the
determined by the focal length of the mirror
...