ASTM E573-01(2007)
(Practice)Standard Practices for Internal Reflection Spectroscopy
Standard Practices for Internal Reflection Spectroscopy
SIGNIFICANCE AND USE
These practices provide general guidelines for the good practice of internal reflection infrared 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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Standards Content (Sample)
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Designation:E573 −01(Reapproved2007)
Standard Practices for
1
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 (´) 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
5
ering the various techniques commonly used in obtaining two media of different refractive indices, Newton (1) discov-
2,3
ered that light extends into the rarer medium beyond the
internal reflection spectra. Discussion is limited to the
infrared region of the electromagnetic spectrum and includes a reflecting surface (see Fig. 1). In internal reflection
spectroscopy, IRS, this phenomenon is applied to obtain
summary of fundamental theory, a description of parameters
that determine the results obtained, instrumentation most absorptionspectrabymeasuringtheinteractionofthepenetrat-
ingradiationwithanexternalmedium,whichwillbecalledthe
widely used, practical guidelines for sampling and obtaining
useful spectra, and interpretation features specific for internal sample (2,3). Theoretical explanation for the interaction
mechanisms for both absorbing and nonabsorbing samples is
reflection.
provided by Snell’s law, the Fresnel equations (4), and the
Maxwell relationships (5).
2. Referenced Documents
4
2.1 ASTM Standards: NOTE 1—To provide a basic understanding of internal reflection
phenomena applied to spectroscopy, a brief description of the theory
E131Terminology Relating to Molecular Spectroscopy
appears in Appendix X2. For a detailed theoretical discussion of the
E168Practices for General Techniques of Infrared Quanti-
subject, see (4).
tative Analysis
E284Terminology of Appearance
6. Parameters of Reflectance Measurements
6.1 Practical application of IRS depends on many precisely
3. Terminology
controlled variables. Since an understanding of these variables
3.1 Definitions of Terms and Symbols—For definitions of
isnecessaryforproperutilizationofthetechnique,descriptions
termsandsymbols,refertoTerminologiesE131andE284,and
of essential parameters are presented.
to Appendix X1.
6.2 Angle of Incidence, θ—When θ is greater than the
criticalangle, θ ,totalinternalreflectionoccursattheinterface
c
4. Significance and Use
between the sample and the internal reflection element, IRE.
4.1 These practices provide general guidelines for the good
When θ is appreciably greater than θ , the reflection spectra
c
practice of internal reflection infrared spectroscopy.
most closely resemble transmission spectra. When θ is less
than θ , radiation is both refracted and internally reflected,
c
generally leading to spectral distortions. θ should be selected
far enough away from the average critical angle of the
1
These practices are under the jurisdiction of ASTM Committee E13 on
sample—IRE combination that the change of θ through the
Molecular Spectroscopy and Separation Science and are the direct responsibility of
c
Subcommittee E13.03 on Infrared and Near Infrared Spectroscopy.
region of changing index (which is related to the presence of
Current edition approved March 1, 2007. Published March 2007. Originally
the absorption band of the sample) has a minimal effect on the
approved in 1976. Last previous edition approved in 2001 as E573–01. DOI:
shapeoftheinternalreflectionband.Increasing θdecreasesthe
10.1520/E0573-01R07.
2
Internal Reflection Spectroscopy, IRS, is the accepted nomenclature for the number of reflections, and reduces penetration. In practice,
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.
smaller because of its refractive index.The value will increase
3
Other terms sometimes used for referring to the internal reflection element are:
as lower f-number optics are utilized. This beam spread
ATR crystal, MIR plate, or sample plate.
4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5
Standards volume information, refer to the standard’s Document Summary page on Theboldfacenumbersinpa
...
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