ASTM E932-89(1997)
(Practice)Standard Practice for Describing and Measuring Performance of Dispersive Infrared Spectrometers
Standard Practice for Describing and Measuring Performance of Dispersive Infrared Spectrometers
SCOPE
1.1 This practice covers the necessary information to qualify dispersive infrared instruments for specific analytical applications, and especially for methods developed by ASTM International.
1.2 This practice is not to be used as a rigorous test of performance of instrumentation.
1.3 This standard does not purport to address all of the safety problems, 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.
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Designation: E 932 – 89 (Reapproved 1997)
Standard Practice for
Describing and Measuring Performance of Dispersive
Infrared Spectrometers
This standard is issued under the fixed designation E 932; 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 instrumentation and of the performnace needed to duplicate the
precision and accuracy of the method.
1.1 This practice covers the necessary information to
qualify dispersive infrared instruments for specific analytical
5. Apparatus
applications, and especially for methods developed by ASTM.
5.1 For the purposes of this practice, dispersive instruments
1.2 This practice is not to be used as a rigorous test of
include those employing prisms, gratings, or filters to separate
performance of instrumentation.
infrared radiation into its component wavelengths.
1.3 This standard does not purport to address all of the
5.2 For each new method, describe the apparatus and
safety problems, if any, associated with its use. It is the
instrumentation both physically and mechanically, and also in
responsibility of the user of this standard to establish appro-
terms of performance as taught in this practice. That is, the
priate safety and health practices and determine the applica-
description should give numerical values showing the fre-
bility of regulatory limitations prior to use.
quency accuracy and the frequency and the photometric
2. Referenced Documents precision. State the spectral slit width maximum or slit width
program if one is used. Where possible, state the maximum and
2.1 ASTM Standards:
minimum resolution if those data are a part of the instrument
E 131 Terminology Relating to Molecular Spectroscopy
display. Show typical component spectra as produced by the
E 168 Practices for General Techniques of Infrared Quanti-
instrument to establish the needed resolution.
tative Analysis
5.3 If a computer program is used, describe the program.
E 387 Test Method for Estimating Stray Radiant Power
Include the programming language and availability, or whether
Ratio of Spectrophotometers by the Opaque Filter Method
the program is proprietary to a manufacturer.
E 1252 Practice for General Techniques for Qualitative
Infrared Analysis
6. Reference to this Practice in Standards
3. Terminology 6.1 Reference to this practice should be included in all
ASTM infrared methods. The reference should appear in the
3.1 Definitions and Symbols—For definitions of terms and
section on apparatus where the particular spectrometer is
symbols, refer to Terminology E 131 and Compilation of
3 described.
ASTM Standard Definitions.
7. Parameters in Spectroscopy
4. Significance and Use
7.1 Dispersive infrared spectrometers have a source of
4.1 This practice is intended for all infrared spectroscopists
quasi-monochromatic radiation together with a photometer for
who are using dispersive instruments for qualitative or quan-
measuring relative radiant power. Accurate spectrometry in-
titative areas of analysis.
volves a large number of interrelated factors that determine the
4.2 The purpose of this practice is to set forth performance
quality of the radiant power passing through a sample and the
guidelines for testing instruments used in developing an
sensitivity and linearity with which this radiant power can be
analytical method. These guidelines can be used to compare an
measured. Assuming proper instrumentation and its use, the
instrument in a specific application with the instrument(s) used
instrumental factors responsible for inaccuracies in spectrom-
in developing the method.
etry are resolution, linearity (Practices E 168), stray radiant
4.3 An infrared procedure must include a description of the
power (Test Method E 387), and cell constants (Practice
E 1252). Rigorous measurement of these factors is beyond the
This practice is under the jurisdiction of ASTM Committee E-13 on Molecular
scope of this practice, and a more practical approach is
Spectroscopy and is the direct responsibility of Subcommittee E13.03 on Infrared
described for the accessible factors.
Spectroscopy.
Current edition approved Aug. 25, 1989. Published October 1989.
Annual Book of ASTM Standards, Vol 03.06. 8. Instrument Operation
Available from ASTM Headquarters, 100 Barr Harbor Drive, West Consho-
8.1 The analyst selects the proper instrumental operating
hocken, PA 19428.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 932
conditions in order to get satisfactory performance (1-3). wavenumbers. The wavenumbers are either read from a dial,
Because instrument design varies, the manufacturer’s recom- optical display, chart paper, or a computer file.
mendations are usually best. A record of operating conditions
11. Reference Wavenumbers in the Infrared Region (2)
should be kept so that data can be duplicated by future users.
11.1 The recommended wavenumber calibration points are
8.2 In addition to operating conditions, the following should
the absorption maxima of a standard (98.4/0.8/0.8 by weight)
be checked and recorded:
indene/camphor/cyclohexanone mixture listed in Table 1. Suit-
8.2.1 Ambient temperature,
able path lengths are 0.2 mm for the range from 3800 to 1580
8.2.2 Pen response time,
−1
cm and 0.03 mm for the wavenumber range from 1600 to 600
8.2.3 Scanning speed,
-1
cm . A mixture containing equal parts by weight of indene,
NOTE 1—In some instruments these functions are integrated in the scan
camphor, and cyclohexanone (1/1/1 by weight) at a path length
modes.
−1
of 0.1 mm may be used for the range from 600 to 300 cm .
8.2.4 Noise level, and
See Table 2 and Fig. 1.
8.2.5 Mechanical repeatability.
11.2 Polystyrene is also a convenient calibration standard
−1
8.3 Each of the above factors is important in the measure-
for the wavenumber range from 4000 to 400 cm . Polystyrene
ment of analytical wavenumber and photometric data. There is
films, approximately 0.03 to 0.05 mm thick, can be purchased
usually some lag between the recorded reading and the correct
from instrument manufacturers. The recommended calibration
reading. Proper selection of operating conditions and good,
peaks are listed in Fig. 2.
reproducible, sample handling techniques minimize these ef-
NOTE 3—The correction of frequency for the refractive index of air is
fects or make the effects repeatable. For example:
significant in the wavenumber calculation only when wavelengths have
8.3.1 Variation in temperature of the monochromator or
been measured to better than 3 parts in 10 000. Reference (3) tabulates
sample may cause changes in wavenumber precision and
additional reference wavenumbers of interest.
accuracy.
11.3 For low-resolution prism or filter instruments operated
8.3.2 Scanning too fast will displace the apparent wavenum-
in single-beam mode, the position of the atmospheric carbon
ber towards the direction scanned and will decrease the peak
−1
dioxide band near 2350 cm can be useful. This band may be
absorbance reading for each band.
−1
resolved into a doublet. The 2350-cm value is for the
NOTE 2—Some instruments provide for automatic monitoring and
approximate center between the two branches. The atmo-
−1
correction of this effect.
spheric carbon dioxide band near 667 cm is useful in the
low-wavenumber region.
8.4 Mechanical repeatability of the monochromator and
recording system as well as positioning of chart paper are
12. Dynamic Error Test
important in wavenumber measurement.
12.1 For dispersively measured spectra, the following dy-
8.4.1 Chart paper should be checked for uniformity of the
namic error test is suitable for use with most grating and prism
printed scale length as received and rechecked at time of use,
spectrometers. (4 and 5)
particularly if the paper has been subjected to pronounced
humidity changes. Instructions on obtaining proper mechanical
TABLE 1 Indene-Camphor-Cyclohexanone (98.4/0.8/0.8)
repeatability may be given in the manufacturer’s literature.
Mixture—Recommended Calibration Bands
8.5 In the case of computerized dispersive instruments, any
Band Wavenumber, Band Wavenumber,
−1 −1
spectrum printed from a computer file must be obtained as No. cm No. cm
prescribed by the manufacturer and should be identical to the
1 3927.2 6 1.0 44a 1741.9
original data. 2 3901.6 44b 1713.4
3 3798.9 47 1661.8
5 3660.6 6 1.0 48 1609.8
PRECISION AND ACCURACY
8 3297.8 6 1.0 49 1587.5
9 3139.5 51 1553.2
9. Definitions
10 3110.2 53 1457.3 6 1.0
12 3025.4 54 1393.5
9.1 wavenumber precision—a measure of the capability of a
15 2887.6 55 1361.1
spectrometer to return to the same spectral position as mea-
17 2770.9 57 1312.4
19 2673.3 58 1288.0
sured by a well-defined absorption or emission band when the
20 2622.3 60 1226.2
instrument is reset or rescanned. The index used in this practice
21 2598.4 6 1.0 61 1205.1
is the standard deviation.
23 2525.5 62 1166.1
28 2305.1 64 1122.4
9.2 wavenumber accuracy—the deviation of the average
29 2271.4 66 1067.7 6 1.0
wavenumber reading of an absorption band or emission band
30 2258.7 67 1018.5
from the known wavenumbe
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