ASTM E573-01
(Practice)Standard Practices for Internal Reflection Spectroscopy
Standard Practices for Internal Reflection Spectroscopy
SCOPE
1.1 These practices provide general recommendations covering the various techniques commonly used in obtaining internal reflection spectra. Discussion is limited to the infrared region of the electromagnetic spectrum and includes a summary of fundamental theory, a description of parameters that determine the results obtained, instrumentation most widely used, practical guidelines for sampling and obtaining useful spectra, and interpretation features specific for internal reflection.
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Designation: E 573 – 01
Standard Practices for
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Internal Reflection Spectroscopy
This standard is issued under the fixed designation E573; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 5. Theory
1.1 These practices provide general recommendations cov- 5.1 In his studies of total reflection at the interface between
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ering the various techniques commonly used in obtaining two media of different refractive indices, Newton (1) discov-
,
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internal reflection spectra. Discussion is limited to the ered that light extends into the rarer medium beyond the
infrared region of the electromagnetic spectrum and includes a reflecting surface (see Fig. 1). In internal reflection spectros-
summary of fundamental theory, a description of parameters copy, IRS, this phenomenon is applied to obtain absorption
that determine the results obtained, instrumentation most spectra by measuring the interaction of the penetrating radia-
widely used, practical guidelines for sampling and obtaining tion with an external medium, which will be called the sample
useful spectra, and interpretation features specific for internal (2,3). Theoretical explanation for the interaction mechanisms
reflection. for both absorbing and nonabsorbing samples is provided by
Snell’s law, the Fresnel equations (4), and the Maxwell
2. Referenced Documents
relationships (5).
2.1 ASTM Standards:
NOTE 1—To provide a basic understanding of internal reflection phe-
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E131 Terminology Relating to Molecular Spectroscopy
nomena applied to spectroscopy, a brief description of the theory appears
E168 Practices for General Techniques of Infrared Quanti-
in Appendix X2. For a detailed theoretical discussion of the subject, see
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tative Analysis
(4).
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E284 Terminology of Appearance
6. Parameters of Reflectance Measurements
3. Terminology
6.1 Practical application of IRS depends on many precisely
3.1 Definitions of Terms and Symbols—For definitions of
controlled variables. Since an understanding of these variables
terms and symbols, refer to Terminologies E131 and E284, isnecessaryforproperutilizationofthetechnique,descriptions
and to Appendix X1. of essential parameters are presented.
6.2 Angle of Incidence, u—When u is greater than the
4. Significance and Use
criticalangle, u ,totalinternalreflectionoccursattheinterface
c
4.1 These practices provide general guidelines for the good
between the sample and the internal reflection element, IRE.
practice of internal reflection infrared spectroscopy.
When u is appreciably greater than u , the reflection spectra
c
most closely resemble transmission spectra. When u is less
than u , radiation is both refracted and internally reflected,
c
generally leading to spectral distortions. u should be selected
far enough away from the average critical angle of the
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sample—IRE combination that the change of u through the
These practices are under the jurisdiction of ASTM Committee E13 on c
Molecular Spectroscopy and are the direct responsibility of Subcommittee E13.03 region of changing index (which is related to the presence of
on Infrared Spectroscopy.
the absorption band of the sample) has a minimal effect on the
Current edition approved September 10, 2001. Published September 2001.
shapeoftheinternalreflectionband.Increasing udecreasesthe
Originally published as E573–76. Last previous edition E573–96.
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number of reflections, and reduces penetration. In practice,
Internal Reflection Spectroscopy, IRS, is the accepted nomenclature for the
technique described in these practices. Other terms are sometimes used which
there is some angular spread in a focused beam. For instru-
include: Attenuated Total Reflection, ATR; Frustrated Total Reflection, FTR;
ments that utilize f4.5 optics in the sample compartment, there
Multiple Internal Reflection, MIR; and other less commonly used terms. In older
is a beam spread of 6 5°, but the beam spread in the IRE is
literature, one may find references to Frustrated Total Internal Reflection, FTIR.
This should not be confused with Fourier Transform Infrared Spectroscopy FT-IR.
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Other terms sometimes used for referring to the internal reflection element are:
ATR crystal, MIR plate, or sample plate.
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Annual Book of ASTM Standards, Vol 03.06. Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
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Annual Book of ASTM Standards, Vol 06.01. these practices.
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E 573
6.4.1 The refractive index of a material undergoes abrupt
chan
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