ASTM E1252-98(2007)
(Practice)Standard Practice for General Techniques for Obtaining Infrared Spectra for Qualitative Analysis
Standard Practice for General Techniques for Obtaining Infrared Spectra for Qualitative Analysis
SIGNIFICANCE AND USE
Infrared spectroscopy is the most widely used technique for identifying organic and inorganic materials. This practice describes methods for the proper application of infrared spectroscopy.
SCOPE
1.1 This practice covers the spectral range from 4000 to 50 cm−1 and includes techniques that are useful for qualitative analysis of liquid-, solid-, and vapor-phase samples by infrared spectrometric techniques for which the amount of sample available for analysis is not a limiting factor. These techniques are often also useful for recording spectra at frequencies higher than 4000 cm–1, in the near-infrared region.
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. Specific precautions are given in 6.5.1.
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Designation: E1252 − 98 (Reapproved2007)
Standard Practice for
General Techniques for Obtaining Infrared Spectra for
Qualitative Analysis
This standard is issued under the fixed designation E1252; 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 3. Terminology
3.1 Definitions—Fordefinitionsoftermsandsymbols,refer
1.1 This practice covers the spectral range from 4000 to 50
−1
to Terminology E131.
cm and includes techniques that are useful for qualitative
analysisofliquid-,solid-,andvapor-phasesamplesbyinfrared
4. Significance and Use
spectrometric techniques for which the amount of sample
4.1 Infraredspectroscopyisthemostwidelyusedtechnique
available for analysis is not a limiting factor.These techniques
for identifying organic and inorganic materials. This practice
areoftenalsousefulforrecordingspectraatfrequencieshigher
–1 describes methods for the proper application of infrared
than 4000 cm , in the near-infrared region.
spectroscopy.
1.2 This standard does not purport to address all of the
5. General
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5.1 Infrared (IR) qualitative analysis is carried out by
priate safety and health practices and determine the applica-
functional group identification (1-3) or by the comparison of
bility of regulatory limitations prior to use. Specific precau- IR absorption spectra of unknown materials with those of
tions are given in 6.5.1.
known reference materials, or both.These spectra are obtained
(4-8) through transmission, reflection, and other techniques,
2. Referenced Documents such as photoacoustic spectroscopy (PAS). Spectra that are to
be compared should be obtained by the same technique and
2.1 ASTM Standards:
under the same conditions. Users of published reference
E131Terminology Relating to Molecular Spectroscopy
spectra (9-16) should be aware that not all of these spectra are
E168Practices for General Techniques of Infrared Quanti-
fully validated.
tative Analysis
5.1.1 Instrumentation and accessories for infrared qualita-
E334Practice for General Techniques of Infrared Micro-
tive analysis are commercially available. The manufacturer’s
analysis
manual should be followed to ensure optimum performance
E573Practices for Internal Reflection Spectroscopy
and safety.
E932PracticeforDescribingandMeasuringPerformanceof
5.2 Transmission spectra are obtained by placing a thin
Dispersive Infrared Spectrometers
uniform layer of the sample perpendicular to the infrared
E1421Practice for Describing and Measuring Performance
radiation path (see 9.5.1 for exception in order to eliminate
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
interference fringes for thin films). The sample thickness must
eters: Level Zero and Level One Tests
be adequate to cause a decrease in the radiant power reaching
E1642Practice for General Techniques of Gas Chromatog-
the detector at the absorption frequencies used in the analysis.
raphy Infrared (GC/IR) Analysis
For best results, the absorbance of the strongest bands should
be in the range from 1 to 2, and several bands should have
absorbances of 0.6 units or more. There are exceptions to this
generalization based on the polarity of the molecules being
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
measured. For example, saturated hydrocarbons are nonpolar,
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
and their identifying bands are not strong enough unless the
Current edition approved Dec. 1, 2007. Published December 2007. Originally
−1
C-Hstretchat2920cm isopaqueandthedeformationbands
approved in 1988. Last previous edition approved in 2002 as E1252–98(2002).
DOI: 10.1520/E1252-98R07. are in the range from 1.5 to 2.0 absorbance units (A) at 1440
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
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1252 − 98 (2007)
−1
to 1460 cm . Spectra with different amounts of sample in the radiation beam passes through the film. The film thickness is
radiation path may be required to permit reliable analysis. If regulated by the amount of pressure applied and the viscosity
spectra are to be identified by computerized curve matching, of the liquid. A capillary film prepared in this manner has a
the absorbance of the strongest band should be less than 1; path length of about 0.01 mm. Volatile and highly fluid
otherwise, the effect of the instrument line shape function will materials may be lost from films prepared in this manner.
cause errors in the relative intensities of bands in spectra Demountable spacers can be used when a longer path length is
measured by dispersive spectrometers and by FT-IR spectrom- required to obtain a useful spectrum.
eters with certain apodization functions (specially triangular).
6.3 Internal Reflection Spectroscopy (IRS)—Viscous mate-
5.2.1 Techniques for obtaining transmission spectra vary
rials can be smeared on one or both sides of an internal
with the sample state. Most samples, except free-standing thin
reflection element (IRE). See Practices E573 for detailed
films, require IR transparent windows or matrices containing
information on this technique.
the sample. Table 1 gives the properties of IR window
6.4 Disposable IR Cards —These can be used to obtain
materials commonly employed. Selection of the window ma-
spectra of non-volatile liquids.Avery small drop, usually less
terial depends on the region of the IR spectrum to be used for
than 10 µLof the liquid, is applied near the edge of the sample
analysis, on the absence of interference with the sample, and
application area. If the sample does not easily flow across the
adequate durability for the sample type.
substrate surface, it may be spread using an appropriate tool.
5.3 Spectraobtainedbyreflectionconfigurationscommonly
The sample needs to be applied in a thin layer, completely
exhibit both reflection and absorption characteristics and are
covering an area large enough that the entire radiation beam
affected by the refractive indices of the media and the inter-
passes through the sample. Note that any volatile components
faces.Spectralinterpretationshouldbebasedonreferencesrun
of a mixture will be lost in this process, which may make the
underthesameexperimentalconditions.Inparticular,itshould
use of a disposable card a poor choice for such systems.
be realized that the spectrum of the surface of a sample
6.5 Solution Techniques:
recordedbyreflectionwilloftendifferfromthespectrumofthe
6.5.1 Analysis of Materials Soluble in Infrared (IR) Trans-
bulkmaterialasrecordedbytransmissionspectroscopy.Thisis
parent Solvent: The Split Solvent Technique—Many solid and
because the chemistry of the surface often differs from that of
liquid samples are soluble in solvents that are transparent in
the bulk, due to factors such as surface oxidation, migration of
parts of the infrared spectral region. A list of solvents com-
species from the bulk to the surface, and possible surface
monly used in obtaining solution spectra is given in Table 2.
contaminants. Some surface measurements are extremely sen-
The selection of solvents depends on several factors. The
sitive to small amounts of materials present on a surface,
sample under examination must have adequate solubility, it
whereas transmission spectroscopy is relatively insensitive to
must not react with the solvent, and the solvent must have
these minor components.
appropriate transmission regions that enable a useful spectrum
5.3.1 Reflection spectra are obtained in four configurations:
to be obtained. Combinations of solvents and window materi-
5.3.1.1 Specular reflectance (7.5),
als can often be selected that will allow a set of qualitative
5.3.1.2 Diffuse reflectance (7.6),
solution-phasespectratobeobtainedovertheentireIRregion.
5.3.1.3 Reflection-absorption (7.7),
One example of this “split solvent” technique utilizes carbon
5.3.1.4 Internal reflection (7.9). Refer to Practices E573.
tetrachloride (CCl ) and carbon disulfide (CS ) as solvents.
4 2
This technique is also called Attenuated Total Reflection
NOTE 1—Warning: Both CCl and CS are toxic; keep in a well
(ATR), and
4 2
ventilated hood. Use of these solvents is prohibited in many laboratories.
5.3.1.5 Grazing angle reflectance.
Inaddition,CS is extremelyflammable;keepawayfromignitionsources,
5.4 Photoacoustic IR spectra (11.2). even a steam bath. Moreover, CS is reactive (sometimes violently) with
primaryandsecondaryaliphaticaminesandmustnotbeusedasasolvent
5.5 Emission spectroscopy (11.4).
for these compounds. Similarly, CCl reacts with aluminum metal.
Depending on conditions such as temperature and particle size, the
TEST METHODS AND TECHNIQUES
reaction has been lethally violent.
6.5.1.1 Absorption by CCl is negligible in the region 4000
6. Analysis of Liquids −1 −1
to 1330 cm and by CS in the region 1330 to 400 cm in
6.1 Fixed Cells—A wide range of liquid samples of low to
cells of about 0.1 mm thickness. (Other solvents can be used.)
moderate viscosity may be introduced into a sealed fixed-path
Solutionsareprepared,usuallyinthe5to10%weight/volume
length cell. These are commercially available in a variety of
range, and are shaken to ensure uniformity. The solutions are
materials and path lengths.Typical path lengths are 0.01 to 0.2
transferred by clean pipettes or by syringes that have been
mm. See 5.2 for considerations in selection of cell materials
cleaned with solvent and dried to avoid cross-contamination
and path lengths.
with a previous sample. If the spectrum of a 10% solution
contains many bands that are too deep and broad for accurate
6.2 Capillary Films—Some liquids are too viscous to force
frequency measurement, thinner cells or a more dilute solution
into or out of a sealed cell. Examination of viscous liquids is
must be used.
accomplished by placing one or more drops in the center of a
flat window.Another flat window is then placed on top of the
liquid. Pressure is applied in order to form a bubble-free
The 3M disposable IR Card is manufactured by 3M Co., Disposable Products
capillary film covering an area large enough that the entire Division.
E1252 − 98 (2007)
TABLE 1 Properties of Window Materials (in order of long-wavelength limit)
A
Cutoff Range Useful Transmission Range
Chemical Water Refractive at
Window Material Remarks
−1 −1
Composition Solubility Index (;µm)
(µm) (cm ) (µm) (cm )
B
Glass SiO + ;2.5 ;4000 0.35–2 28 570–5000 insoluble 1.5–1.9 HF, alkali
B
Quartz (fused) SiO ;3.5 ;2857 0.2–4 50 000–2500 insoluble 1.43 4.5 HF
SIlicon Nitrate Si N 0.3–4.5 33 000–2200
3 4
Silicon Carbide SiC 0.6–5 16 600–2000
C
Calcite CaCO 0.2–5 50 000–2000 1.65, 1.5 0.589 Reacts with acids
Sapphire Al O ;5.5 ;1818 0.2–5.5 50 000–1818 insoluble 1.77 0.55 Good strength, no cleavage
2 3
ALON 9AI O .5AIN 0.2–5.5 50 000–1700 1.8 0.6
2 3
Spinel MgAI O 0.2–6 50 000–1600 1.68 0.6
2 4
B
Strontium Titanate SrTiO 0.39–6 25 000–1700 insoluble 2.4 HF
B
Titanium Dioxide TiO 0.42–6 24 000–1700 insoluble 2.6–2.9 H SO and Alkali
2 2 4
B
Lithium Fluoride LiF ;6.0 ;1667 0.2–7 50 000–1429 slightly 1.39 1.39 Acid
B
Zirconia ZrO 0.36–7 27 000–1500 insoluable 2.15 HF and H SO
2 2 4
D
Silicon Si 1.5–7 and 6600–1430 insoluble 3.4 11.0 Reacts with HF, alkali
10–FIR
Yttria Y 0.25–8 40 000–1250 1.9 0.6
Yttria (La-doped) 0.09La O - 0.25–8 40 000–1250 1.8 0.6
2 3
0.91Y O
2 3
E B
IRTRAN I MgF 2–8 5 000–1 250 slightly 1.3 6.7 HNO
2 3
B
Magnesium Oxide MgO 0.4–8 25 000–1300 insoluble 1.6 5 Acid and NH salts
B
Fluorite CaF ;8.0 ;1250 0.2–10 50 000–1000 insoluble 1.40 8.0 Amine salt and NH salts
2 4
Strontium Fluoride SrF 0.13–11 77 000–909 slightly 1.4
E
IRTRAN III CaF 0.2–11 50 000–909 insoluble 1.34 5.0 Polycrystalline, no cleavage
Gallium Phosphide GaP 0.5–11 20 000–910
GaP
Lead Fluoride PbF 0.3–12 3450–833 1.7 1
F B
Servofrax As S 1–12 10 000–833 insoluble 2.59 0.67 Alkali , softens at 195°C
2 3
slightly (hot)
Barium Fluoride BaF ;11 ;909 0.2–13 50 000–769 insoluble 1.45 5.1
AMTIR GeAsSe Glass 0.9–14 11 000–725 insoluble 2.5 10 Hard, brittle, attacked by alkali, good
ATR material
E
IRTRAN II ZnS 1–14 10 000–714 insoluble 2.24 5.5 Insoluble in most solvents
Indium Phosphide InP 1–14 10 000–725
Potassium Floride KF 0.16–15 62 500–666 soluble 1.3 0.3 Extremely deliquescent: not
recommended for routine use
G
Rock salt NaCl ;16 ;625 0.2–16 50 000–625 soluble 1.52 4.7 Soluble in glycerine
Cadmium Sulfide CdS 0.5–16 20 000–625
Arsenic Triselenide As Se 0.8–17 12 500–600 slightly 2.8 Soluble in bases
2 3
Gallium Arsenide GaAs 1–17 10 000–600 insoluble 3.14 Slightly soluable in acids and bases
Germanium Ge 2–20 5 000–500 insoluble 4.0 13.0
G
Sylvite KCl 0.3–21 33 333–476 soluble 1.49 0.5 Soluble in glycerine
E
IRTRAN IV ZnSe 1–21 10 000–476 insoluble 2.5 1.0 Polycrystalline
Sodium Bromide NaBr 0.2–23 50 000–435 Soluble 1.7 0.35
Sodium Iodide NaI 0.25–25 40 000–400 Soluble 1.7 0.5
H
Silver Chloride AgCl ;22 ;455 0.6–25 16 6667–400 insoluble 2.0 3.8 Soft, darkens in light reacts with
metals
Potassium Bromide KBr ;25 ;400 0.2–27 50 000–370 soluble 1.53 8.6 Soluble in alcohol; fogs
B
Cadmium Telluride CdTe ;28 ;360 0.5–28 20 000–360 insoluble 2.67 10 Acids, HNO
Thallium Chloride 0.4–30 25 000–330 slightly 2.2 0.75 Toxic
TICI
KRS-6 Tl CIBr 0.4–32 25 000–310 slightly 2.0–2.3 0.6–24 Toxic
H
Silver Bromide AgBr ;35 ;286 2–35 5 000–286 insoluble Soft, darkens in light , reacts with
metals
B
KRS-5 Tl2Brl ;40 ;250 0.7–38 14 286–263 slightly 2.38 4.0 Toxic, soft, soluble in alcohol, HNO
Cesium Bromide CsBr ;35 ;286 0.3–40 33 333–250 soluble 1.66 8.0 Soft, fogs, soluble alcohols
Potassium Iodide Kl 0.15–45 66 600–220
Thallium Bromide TIBr 0.45–45 22 000–220 slightly 2.3 0.6–25 Toxic
Cesium Iodide CsI ;52 ;192 0.3–50 33 330–220 soluble 1.74 8.0
Low-density (CH CH )n 20–220 500–45 insoluble 1.52 Very soft, organic liquids penetrate
2 2
polyethylene into polymer at ambient
temperature
I
Type 61 (CH CH )n 2–220 5 000–45 insoluble 1.52 Softens at 90°C
2 2
I J
Type 62 (CF CF )n 2–220 5 00
...
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