ASTM E1252-98(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1252 − 98 (Reapproved 2021)
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 E932PracticeforDescribingandMeasuringPerformanceof
−1 Dispersive Infrared Spectrometers
1.1 This practice covers the spectral range from 4000cm
−1 E1421Practice for Describing and Measuring Performance
to 50 cm and includes techniques that are useful for quali-
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
tative analysis of liquid-, solid-, and vapor-phase samples by
eters: Level Zero and Level One Tests
infrared spectrometric techniques for which the amount of
E1642Practice for General Techniques of Gas Chromatog-
sample available for analysis is not a limiting factor. These
raphy Infrared (GC/IR) Analysis
techniques are often also useful for recording spectra at
–1
frequencieshigherthan4000cm ,inthenear-infraredregion.
3. Terminology
1.2 The values stated in SI units are to be regarded as
3.1 Definitions—Fordefinitionsoftermsandsymbols,refer
standard. No other units of measurement are included in this
to Terminology E131.
standard.
4. Significance and Use
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4.1 Infraredspectroscopyisthemostwidelyusedtechnique
responsibility of the user of this standard to establish appro-
for identifying organic and inorganic materials. This practice
priate safety, health, and environmental practices and deter-
describes methods for the proper application of infrared
mine the applicability of regulatory limitations prior to use.
spectroscopy.
Specific precautions are given in 6.5.1.
1.4 This international standard was developed in accor- 5. General
dance with internationally recognized principles on standard-
5.1 Infrared (IR) qualitative analysis is carried out by
ization established in the Decision on Principles for the 3
functional group identification (1-3) or by the comparison of
Development of International Standards, Guides and Recom-
IR absorption spectra of unknown materials with those of
mendations issued by the World Trade Organization Technical
known reference materials, or both.These spectra are obtained
Barriers to Trade (TBT) Committee.
(4-8) through transmission, reflection, and other techniques,
such as photoacoustic spectroscopy (PAS). Spectra that are to
2. Referenced Documents
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.
5.2 Transmission spectra are obtained by placing a thin
uniform layer of the sample perpendicular to the infrared
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom- radiation path (see 9.5.1 for exception in order to eliminate
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
interference fringes for thin films). The sample thickness must
Current edition approved April 1, 2021. Published April 2021. Originally
be adequate to cause a decrease in the radiant power reaching
ɛ1
approved in 1988. Last previous edition approved in 2013 as E1252–98(2013) .
the detector at the absorption frequencies used in the analysis.
DOI: 10.1520/E1252-98R21.
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 (2021)
For best results, the absorbance of the strongest bands should materialsandpathlengths.Typicalpathlengthsare0.01mmto
be in the range from 1 to 2, and several bands should have 0.2mm.See5.2forconsiderationsinselectionofcellmaterials
absorbances of 0.6 units or more. There are exceptions to this and path lengths.
generalization based on the polarity of the molecules being
6.2 Capillary Films—Some liquids are too viscous to force
measured. For example, saturated hydrocarbons are nonpolar,
into or out of a sealed cell. Examination of viscous liquids is
and their identifying bands are not strong enough unless the
accomplished by placing one or more drops in the center of a
−1
C-Hstretchat2920cm isopaqueandthedeformationbands
flat window.Another flat window is then placed on top of the
are in the range from 1.5 to 2.0 absorbance units (A) at
liquid. Pressure is applied in order to form a bubble-free
−1 −1
1440cm to 1460cm . Spectra with different amounts of
capillary film covering an area large enough that the entire
sample in the radiation path may be required to permit reliable
radiation beam passes through the film. The film thickness is
analysis. If spectra are to be identified by computerized curve
regulated by the amount of pressure applied and the viscosity
matching, the absorbance of the strongest band should be less
of the liquid. A capillary film prepared in this manner has a
than 1; otherwise, the effect of the instrument line shape
path length of about 0.01 mm. Volatile and highly fluid
function will cause errors in the relative intensities of bands in
materials may be lost from films prepared in this manner.
spectra measured by dispersive spectrometers and by FT-IR
Demountable spacers can be used when a longer path length is
spectrometers with certain apodization functions (specially
required to obtain a useful spectrum.
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
materials commonly employed. Selection of the window ma- 6.4 Disposable IR Cards —These can be used to obtain
terial depends on the region of the IR spectrum to be used for spectra of non-volatile liquids.Avery small drop, usually less
analysis, on the absence of interference with the sample, and than 10 µLof the liquid, is applied near the edge of the sample
adequate durability for the sample type. application area. If the sample does not easily flow across the
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
recordedbyreflectionwilloftendifferfromthespectrumofthe 6.5 Solution Techniques:
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
(Warning—Both CCl and CS are toxic; keep in a well
4 2
(ATR), and
ventilated hood. Use of these solvents is prohibited in many
5.3.1.5 Grazing angle reflectance.
laboratories. In addition, CS is extremely flammable; keep
5.4 Photoacoustic IR spectra (11.2).
away from ignition sources, even a steam bath. Moreover, CS
is reactive (sometimes violently) with primary and secondary
5.5 Emission spectroscopy (11.4).
aliphatic amines and must not be used as a solvent for these
TEST METHODS AND TECHNIQUES
compounds. Similarly, CCl reacts with aluminum metal.
Dependingonconditionssuchastemperatureandparticlesize,
the reaction has been lethally violent.)
6. Analysis of Liquids
6.1 Fixed Cells—A wide range of liquid samples of low to
moderate viscosity may be introduced into a sealed fixed-path
The 3M disposable IR Card is manufactured by 3M Co., Disposable Products
length cell. These are commercially available in a variety of Division.
E1252 − 98 (2021)
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 5000–1250 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 5000–500 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 5000–286 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 5000–45 insoluble 1.52 Softens at 90 °C
2 2
I J
Type 62 (CF CF )n 2–220 5000–45 insoluble 1.52 Useful to 200 °C for short durations
2 2
J B
Diamond 2–4 and 4500–2500 insoluble 2.4 10 K Cr O7, H SO
2 2 2 4
6–300 and 1667–33
A
Cutoff range is defined as the frequency range within which the transmittance ofa2cmthick sample is greater than 0.5. FT-IR spectrometers may be able to work outside
this range.
B
Reacts with.
C
Ordinary and extraordinary rays.
D
Long wavelength limit depends on purity.
E
Trademark of Eastman Kodak Co.
F
Trademark of Servo Corp of America.
G
Window material will react with some inorganics (for example, SO , HNO , Pb(NO ) ).
2 3 3 2
H
These materials should be stored in the dark when not being used, and should not be placed in contact with metal frames.
I
Trademark of 3M.
J
Microporous polytetrafluoroethylene.
E1252 − 98 (2021)
TABLE 2 Commonly Employed IR Solvents
NOTE 1—Data obtained from IR spectra recorded in the Analytical Laboratories, Instrumental Group, Dow Chemical Company, Midland, MI. It is
recommendedthattheuserofthesetablesrecordthespectrumforanysolventusedinthisapplication,sinceminorimpuritiesmayexhibittotalabsorption
in the region of interest when using relatively long path length cells.
A −1
Compound Structure Transmission Windows (cm ) Path Length (mm)
B
carbon tetrachloride CCl 5000-909, 666-36 0.1
5000-1316 (absorption; 1666-1429) 0.1
5000-1666, 1499-1299 1.0
250-36 2.0
B
perchloroethylene C Cl 5000-1042 0.1
2 4
B
5000-1408 1.0
C B
chloroform CHCl 5000-3125, 2941-1299, 1136-870 0.1
B
5000-3226, 2941-2532, 2222-1587 1.0
C −1B
chloroform-d CDCl 5000-1000 cm 0.1
1 3
B
5000-3225, 2778-2439, 2000-1538 1.0
C B
methylene chloride CH Cl 5000-1449, 1205-854, 625-200 0.1
2 2
B
5000-3225, 2000-1538, 1111-1000, 625-500 1.0
C B
methylene chloride-d CD Cl 5000-2500, 2000-1449, 1333-1177, 625-400 0.5
2 2 2
C
bromoform CHBr 5000-3125, 2941-1250, 1111-800, 500-200 0.1
5000-3125, 2941-1408, 1111-1000 1.0
D B
carbon disulfide CS 5000-2350, 2100-1600, 1400-410 0.1
5000-2439, 2000-1666, 1.0
1351-909, 800-704 2.0
333-278, 238-36
acetonitrile CH CN 5000-3225, 2778-2500, 2000-1587, 1299-1099, 1000-952, 0.1
B
909-787, 714-400
B
5000-3333, 2000-1666, 1298-1141, 704-400 1.0
B
acetonitrile-d CD CN 5000-2380, 2000-1250, 800-714, 645-400 0.1
3 3
B
5000-3448, 1852-1333, 645-400 1.0
B
acetone (CH ) CO 3448-3125, 2703-1852, 1053-952, 885-813, 746-588 0.1
3 2
B
3448-3225, 870-813, 746-606, 357-200 1.0
E B
dimethyl sulfoxide (CH ) SO 5000-3333, 2703-1539, 1266-1149, 870-769, 645-200 0.1
3 2
E
dimethyl-d sulfoxide 1,4-dioxane (CD ) SO O(CH - 5000-2381, 1961-1190, 606-400 0.1
6 3 2 2
CH ) O
2 2
5000-3125, 2632-2040, 1923-1539, 800-666, 588-385 0.2
water H O 5000-3846, 2857-1754, 1492-1000 0.025
heavy water D O 5000-2778, 2000-1299 0.07
A
Recommended handling and storage is in ventilated hood for these organic solvents.
B
Some bands may be present, but their absorption is readily compensated by placing solvent in a variable path length cell in the reference beam, or by spectral subtraction
using computer techniques for full-range utility in the ranges given.
C
These compounds decompose and are often stabilized with a small amount of a compound such as ethanol. These compounds will react with amines.
D
Carbon disulfide will react with primary and secondary amines, sometimes violently. It is highly flammable and toxic.
E
Picks up H O from the atmosphere if not well capped.
6.5.1.1 Absorption by CCl is negligible in the region manufacturer’s manual for each instrumental system to per-
−1 −1 −1
4000cm to 1330 cm and by CS in the region 1330cm form the computer-assisted manipulation of the spectral data
−1
to400cm incellsofabout0.1mmthickness.(Othersolvents necessary for hard copy presentation. Spectra from both CCl
can be used.) Solutions are prepared, usually in the 5% to andCS solutionscanbepresentedonthesamehardcopyover
−1 −1
10% weight/volume range, and are shaken to ensure unifor- the region 4000cm to 400 cm , or the presentation can be
−1 −1
mity. The solutions are transferred by clean pipettes or by over the 4000cm to 1330 cm region for the CCl solution
−1 −1
syringesthathavebeencleanedwithsolventanddriedtoavoid and over the 1330cm to 400 cm region for the CS
cross-contaminationwithaprevioussample.Ifthespectrumof solution. The former choice is preferable because both band
a 10% solution contains many bands that are too deep and frequencies and band intensities are affected differently by the
broad for accurate frequency measurement, thinner cells or a different solvents (due to solvent-solute interaction).
more dilute solution must be used.
6.5.1.3 Split solution spectra are acceptable without solvent
compensation, but recognition of the solvent bands that are
NOTE 1—New syringes should be cleaned before use. Glass is the
present is mandatory when such spectra are compared with
preferred material. If plastic is used as containers, lids, syringes, pipettes,
and so forth, analytical blanks are necessary as a check against contami-
those recorded, either with solvent compensation or with
nation.
computer-assisted solvent subtraction. The IR spectrum of a
−1 −1
6.5.1.2 A spectrum obtained by the split-solvent technique solution over the entire 4000cm to 400 cm region can be
incellsupto0.5mmto1.0mmthickness,canbecompensated useful, but it is not recommended for solutions of unknown
for all solvent bands to yield the spectrum of only the sample materials because pertinent spectral data may be masked by
itself. When a spectrometer that is capable of storing digital solvent absorption. It is not possible to compensate fully
−1 −1
data is employed, the desired spectrum is obtained by a absorbing bands such as CS (|;1400cm to 1600 cm ),
−1 −1 −1
computer-assisted subtraction of the stored data for the solvent CCl (|;730cm to 800 cm ), and CHCl (about 790cm
4 3
−1
from the data for the solution. The user should refer to the to 725 cm ) when using a 0.1mm path length.
E1252 − 98 (2021)
NOTE 2—Attempted compensation of such totally absorbing bands can
6.5.3 Analysis of Aqueous Solutions: Internal Reflection
obscure sample bands.
Cells—Water is not generally recommended as an infrared
solventbecauseitisstronglyabsorbingthroughoutmostofthe
6.5.1.4 Often the same IR spectrum can be recorded using
1% solutions in 1.0mm sealed cells as with 10% solutions in useful mid-IR region and because it attacks many of the
window materials commonly used in transmission cells.When
0.1mm cells. Interferences from the solvents, however, are
larger with 1mm cells (see Table 2). In cases where there is aqueous solutions are the most convenient form to handle
particular materials, however, internal reflection cells with a
strong intermolecular association, such as intermolecular hy-
drogen bonding between solute molecules, the resulting IR short enough effective pathlength to permit recording of
−1
spectra from the near infrared to about 850 cm (except
spectra obtained with 1% solutions will be different from the
−1 −1
ones obtained with the 10% solutions, because of the different between about 3800cm and 2900 cm and between about
−1 −1
1700cm and 1600 cm ) can be used. These cells are
concentration of unassociated solute molecules, and in the
different concentrations of intermolecularly hydrogen bonded commonly cylindrical or rectangular. The water background
can be subtracted in FT-IR and computer-assisted dispersive
dimeric, trimeric, tetrameric, etc., solute molecules.
instruments. The spectrum of the solute obtained by this
6.5.1.5 A distinct advantage is gained by recording IR
methodwillusuallybequitedifferentfromthespectrumofthe
spectraunderasetofstandardconditions,suchas5%to10%
dry solute so that a library of aqueous solution spectra is
solutions in a 0.1mm path length sealed cell. This practice
ordinarily required for the identification materials dissolved in
allows approximate quantitative analyses to be readily per-
water.
formed at a future date on samples where the utmost accuracy
6.5.4 Analysis of Water-Containing Solutions: Disposable
is not required. Moreover, for qualitative analyses, the spectra
IR Card—This technique would be appropriate for samples
recorded will have comparable band intensities, assuming that
such as latexes, mayonnaise, and other colloidal or emulsion
identicalconcentrationsandpathlengthsareemployedandthat
type samples. For many such samples there is also an organic
the instrumental parameter settings are identical.
modifier present, such as a surfactant or organic liquid, which
6.5.1.6 Spectra that are to be used for computer searches
facilitateswettingofthesampleapplicationarea.Inthesecases
should be measured carefully. The search algorithms typically
a drop of the sample is applied to the sample application area
normalize the strongest spectral feature to an arbitrary absor-
as in 6.5.2.1, or it is smeared on as in 6.4.
bance level. Because of this, the spectrum of the solute should
be measured using a concentration/path length combination
7. Analysis of Solids
that results in the strongest solute band having an absorption
that does not exceed an absorbance of 1.0.
7.1 High-PressureDiamondAnvilCells—Samplescanoften
6.5.2 Analysis of Materials Soluble in Volatile Organic
beruninahigh-pressurediamondanvilcellinaccordancewith
Solvents: Use of Disposable IR Cards—Many solid samples
Practice E334.
are soluble in volatile organic solvents which easily wet the
7.2 Alkali Halide Pressed Pellet Technique:
sample application area of an IR transparent window or a
7.2.1 This technique involves grinding a solid sample,
disposable IR card. Any solvent may be utilized that totally
mixing it with an alkali halide powder, and pressing the
dissolves the component(s) of interest, is volatile enough to
resulting mixture into a pellet or disk. Scattering of IR
quicklyevaporateaftersampleapplication,isnotreactivewith
radiation is reduced by having the sample particles embedded
thesample,anddoesnotreactwiththesampleapplicationarea.
in a matrix of comparable refractive index. Alkali halides are
NOTE 3—A spectrum obtained using the disposable IR Card can be
used because they have properties of cold flow and absence of
compensated for the polymer bands to yield the spectrum of only the
absorption in a wide spectral region. KBr is the most com-
sample. When a spectrometer that is capable of storing digital data is
monly used, but KCl and CsI are also used for better matching
employed, the desired spectrum is obtained by a computer-assisted
of refractive index, extended spectral range, or to avoid ion
subtraction of the stored data for the blank sample card from the data for
exchangewithanotherhalidesaltsample.Thepellettechnique
theappliedsample.Theusershouldrefertothemanufacturer’smanualfor
each instrumental system to perform the computer-assisted manipulation
is applicable to many organic materials, but there are limita-
of the spectral data necessary for hard copy presentation.
tions associated with several chemical types of materials.
Amine salts, carboxylic acid salts, and some inorganic com-
6.5.2.1 A solution of the sample in appropriate solvent is
prepared usually in the 10% or greater weight/volume range, pounds may react with alkali halides and produce a spectrum
that does not represent the original sample.
andisshakentoensureuniformsolution.Adropofthesolution
is applied to the center of the sample application area using a 7.2.2 Because the spectrum obtained depends on particle
cleanpipette,orsyringe.Ifnecessary,thesamplecanbespread size, it is important to prepare both sample and reference
out on the substrate surface using the blunt applicator tip such materialsinthesamemannerinordertoensurethattheparticle
as from an disposable pipette. The solvent(s) used for sample size distributions are reproduced. It should also be noted that
dissolution are allowed to evaporate, leaving a deposit of the the crystal structure of a compound may be changed by
grinding or by the high pressure exerted in forming the pellet,
solid or liquid sample on the sample application area. In many
cases, the solvents used will evaporate quickly. If evaporation causing an alteration of the IR spectrum.
time needs to be reduced, a gentle stream of clean dry air or 7.2.3 Both the sample and the alkali halide powder must be
nitrogen can be blown across the surface or the card can be dry in order to produce a clear pellet. Usually, the ratio of the
heatedgentlyinanovenorwithaninfraredheatlampforvery quantities of sample to KBr powder should be the range from
short duration. 1/50 to 1/1000, depending on the type of sample. The solid
E1252 − 98 (2021)
TABLE 3 Mulling Agents
sample is ground using a mortar and pestle or a mechanical
vibrating mill until the particle size is smaller than the
NOTE1—Fortheleastamountofabsorptionfromthemullingagent,use
−1 −1
wavelength of the IR radiation (for example, <2 µm) to
Nujol™ in the region of approximately 1350cm to 400 cm and
−1 −1
Fluorolube™ in the region 4000cm to 1350 cm . It is recommended
minimize the scattering of IR radiation. The mortar and pestle
that IR reference spectra be recorded of the mulling agents used in your
should be made of agate, alumina, or boron carbide to avoid
laboratory.
contamination of the sample during grinding.Adequate grind-
Maximum Peaks of
ing will usually produce a glossy layer adhering to the mortar. Mulling Agents
−1
Absorption; cm
TheKBr(orotheralkalihalide)isaddedandthoroughlymixed
A
Mineral Oil (Nujol ) 2952
with the sample. The KBr sample mixture is then placed in a
special die and compressed to a small disk with a thickness of
about 1 mm. The amount of force applied depends on the
diameter of the die. The best pellets are formed by evacuating
the die filled with the KBr sample mixture before applying
B
Fluorocarbon Oil (Fluorolube ) 1275
pressure. This process minimizes the amount of water in the
pressed pellet.
7.2.4 For routine qualitative analysis of many compounds,
adequate grinding and mixing can be realized by grinding the
KBr-sample mixture in a vibrating mill for 30s to 60s.
7.2.5 Alkalihalidepowdermaybeusedasagentleabrasive
to collect samples of surface layers of materials such as paint.
Pellets made from these powders have been used to study
environmental exposure of surface finishes, and for forensic
comparison of automotive finishes.
7.2.6 Aminiaturepressisoftenemployedtopresspelletsas 519
A
small as 0.5mm diameter. The quality of the spectrum ob-
Formerly trademarked by Stanco Incorporated, New York, NY, expired 1996.
B
Trademark by Gabriel Performance Products, LLC, in Baton Rouge, LA.
tained is improved by placing the small pellet in a beam
condenser in the IR spectrometer sample compartment. This
results in an additional focusing of the IR beam, usually by a
low-density polyethylene (LDPE) windows are useful below
factor of 4 to 6 in the linear dimension.
−1
200 cm ) and spread uniformly across the middle section of
7.3 Polymer Matrix Technique—Powdered low-density
the plate. A second flat plate is used to squeeze the paste into
polyethylene can be used as the matrix material in the region
a thin film by gently rotating the top plate, with the exception
−1 −1
500cm to 50 cm . Because absorption bands in the far IR
that IR cards and LDPE windows do not require this step. At
usually have low intensity, a relatively high sample-to-
this point, a properly prepared mull should be reasonably
polyethylene powder ratio is required. The well-dispersed
transparent to visible light (a frosty or cloudy appearance
sample-polyethylene mixture is placed in a die and heated to
means that further grinding is needed).
90°C. This results in a pressed film with evenly dispersed
7.4.3 For split mulls, two mortars and pestles are useful for
sample. This procedure is applicable only to compounds that
working with the two mulling agents. The difficult part of this
are stable at 90°C.
process is adjusting the mull film thicknesses so that the band
7.4 Mull Technique:
absorbances in both spectral regions yield true relative values.
7.4.1 This technique involves grinding a solid sample with
This is accomplished by selecting a sample band that is free
a small amount of a liquid known as a mulling agent. from interference in both mulling fluids and in adjusting the
−1 −1
Fluorocarbonoilisusedfortheregion4000cm to1300cm
film thicknesses so that the absorbances of this band are
−1 −1
and mineral oil is used for the region 1300cm to 50 cm . essentially identical in the spectra of the two mulls. The
Split mulls using both liquids are necessary to obtain an adjustment of film thicknesses is simplified by the use of an
optimal complete spectrum. Qualitative spectra can be ob- instrument(FT-IRordispersive),capableofstoringdigitaldata
tained using only one of the mulling agents (usually mineral and thus enabling the adjustment to be made by computer-
oil), provided that absorption by the mulling agent used does assisted calculations based on a sample band that is free from
not mask spectral regions of analytical importance. interference. The user should refer to the manufacturer’s
7.4.2 Approximately 3mg to 10 mg of sample is placed in manual in order to perform the calculations for each type of
anagate,alumina,orboroncarbidemortar,groundtoaparticle system employed.
size less than 2µm diameter, and spread uniformly over the 7.4.4 Another technique that has been used to prepare
surface of the mortar. At this stage, the sample should have a high-quality mulls is to grind the sample and mulling agent
glossy appearance. One to a few drops of the mulling fluid is with a grinder having two motor-driven rotating ground-glass
added,andvigorousgrindingiscontinueduntilalltheparticles plates. This method is useful for preparing mulls of many
are suspended in the mulling agent and the mixture is a paste organic materials. It is not recommended for hard materials,
of creamy consistency. This paste is then transferred with a since glass may be introduced into the sample as a contami-
clean rubber policeman onto a flat NaCl, KBr, or other plate nant. Grinding may also be done manually with large diameter
(disposable IR cards are useful for the mid-IR to far IR, while ground glass joints.
E1252 − 98 (2021)
7.5 Specular Reflection Spectroscopy—A flat surface will the sample using the IRS technique, it is possible to improve
allow an incident beam to be reflected off the surface at an the surface contact by warming both the IRE and the material
angle of reflection equal to the angle of incidence. The while in contact under pressure. However, this technique will
reflectance spectrum measured includes information on the often ruin the IRE.
absorbing properties of the material, and often appears to be
highly distorted. Application of the Kramers-Kronig transfor- 8. Analysis of Vapor-Phase Samples
mation to the observed spectrum can be used to extract the
8.1 Use of Simple Gas Cells:
normalabsorptionspectrumfromthisinformation(seePractice
8.1.1 Samples that are gases at ambient conditions of
E334).
temperature and pressure, or even liquids that have a vapor
7.6 Diffuse Reflection Spectroscopy: pressure as low as 0.1 torr (;13 Pa) at ambient temperature,
7.6.1 When used in conjunction with a Fourier Transform arereadilyexaminedbyIR.Aspectrumsatisfactoryforroutine
qualitative identification can be recorded of most gases by
infrared spectrometer, this technique is commonly referred to
as DRIFT (Diffuse Reflection Infrared Fourier Transform) purging, in a hood, a small-volume cell (one having, for
example, one 3mm pathlength) with the sample gas to flush
spectroscopy. It has gained wide acceptance for analysis of a
range of materials, due to its simplicity and ease of sample out the air. The stopcocks are then closed. Longer pathlengths
can be used if the goal is to identify impurities in the gaseous
preparation.Itisalsopreferredforsamplesthatstronglyreflect
or scatter infrared energy. sample.
8.1.2 A5cm or 10cm glass cell equipped with windows of
7.6.2 Thistechniqueisgenerallyapplicabletosolidsamples
KBr, CsI, or other suitable material, is frequently used to
that are ground (as in the preparation of an alkali halide pellet
record vapor-phase IR spectra. Several pressures may be
or a mull) and then mixed with KBr, KCl powder, or other
employedsothattheshapesofbothweakandstrongbandscan
optical transparent powdered materials, or combinations
−1
be observed. Band shapes and intensities in gas phase spectra
thereof. Spectra below 400 cm can be obtained using
vary with both the total pressure and with the nature of the
polyethylene powder. The mixture is loaded into a sample cup
diluent.Itisausefulprocedure,therefore,toobtaingasspectra
that is then placed in a diffuse reflectance accessory. The
adjusted to some constant dilution with an inert IR transparent
resultingspectracandiffersignificantlyfromthoseobtainedby
gas, such as nitrogen, for example, to a total pressure 600 torr.
transmission spectroscopy. For details and applications, see
Thisaspectisparticularlyimportantifquantitativeanalysesare
(17-29).
contemplated. Moreover, infrared spectra of strongly intermo-
7.6.3 Another method utilized to obtain solid samples for
lecular hydrogen bonded molecules, such as carboxylic acids
use in DRIFT spectroscopy relies on an abrasive pad sampler,
(monomer-dimer) are especially affected by both pressure and
made of silicon carbide, diamond, or other hard substance.
temperature.
These disposable sample holders, available from a number of
8.1.3 CertaingasessuchasNO orSO reactwiththealkali
sources, offer a simple means of sampling hard inorganics (for 2 2
halide windows, causing the formation of ionic species on the
example, minerals) and organics (for example, thermoset
windowsurface.Inthiscase,ZnSeoranothersubstancewhich
resins).
is not attacked by SO or NO , should be used as window
2 2
7.7 Reflection-Absorption Spectroscopy—This technique is
material if the artifact-bands interfere excessively with the
used to obtain absorption spectra of insoluble coatings on
sample spectrum.
reflecting substrates, such as smooth metallic surfaces. Spectra
8.1.4 A 10cm glass cell equipped with high-density poly-
of coatings as thin as 1 µm can be obtained using a spectral
ethylene windows several millimetres thick can be used to
reflectance attachment. (For details and applications, see (30-
−1
record vapor-phase IR spectra in the region 500cm to
33).)
−1
50cm and below.
7.8 Total Reflectance—Accessories are available that can
8.2 Use of Multipass Gas Cells:
measure both diffuse and specular components of the infrared
8.2.1 Long path length cells are required in order to record
reflectance spectrum. One special type of accessory is an
IR spectra of chemicals with low vapor pressure at ambient
integrating sphere, which captures reflected energy from all
temperatures. The same type of cell is employed in order to
angles, and often incorporates a purpose-built detector having
detect parts per million (ppm) levels of contaminants (impuri-
a large surface area. Under certain conditions, the specular
ties) in air or other gas. In the latter case, the H O and CO
2 2
component of the reflected energy can be reduced or even
presentinaircanbecompensatedbyplacingacomparablecell
removed before the energy reaches the detector. This type of
filled with ordinary air in the reference beam with the appro-
accessory if useful for measuring the total reflected energy
priate path length setting. For instruments capable of storing
fromasample,forexaminingsamples(suchasfabrics)thatare
digitalspectra,thesamecellcanbeusedtoobtainthereference
not easily handled in any traditional manner.
airspectrum,andthenthisspectrumcanbesubtractedfromthe
sample spectrum. The usual path length employed in trace
7.9 Internal Reflection Spectroscopy—Bulk samples, in-
cluding polymer films and liquids, can be analyzed by this analyses is ;20 m. A comparable path length setting is
required for chemicals with low vapor-pressure at ambient
techniqueifthesurfaceisrepresentativeofthesampleinterior.
For further information, see Practices E573. In the case of temperatures.
materials with hard surfaces where it may be difficult to get 8.2.2 A disadvantage of utilizing multipass cells is that the
goodcontactbetweentheinternalreflectionelement(IRE)and optics are in contact with the sample, and this can cause even
E1252 − 98 (2021)
the gold-coated mirrors to deteriorate.Another disadvantage is thickness of ;0.01 mm, a suitably dilute water solution of the
that certain samples adhere to the large cell surface area, polymer is prepared. Silver bromide is less sensitive to strong
causing a built-in memory when a different sample is intro- visible or ultraviolet light than silver chloride (AgCl), but it
duced into the cell. Extensive flushing with dry air or dry willdarkenwithtime.Theplates,therefore,shouldbestoredin
nitrogen with repeated cell evacuation is often necessary to
the dark when not in use. Only clear transparent AgBr plates
cleanoutthecell.Gentleheatingwithaheatlampmayalsoaid shouldbeusedforthesemeasurements.Moreover,flatAgBror
inreducingmemoryeffects.Inaddition,thecellwindowsoften
AgCl plates should be 2 mm thick in order to eliminate
become coated with materials used to seal the cell window. interference fringes. The plates are readily cleaned by redis-
Ignoring these factors will result in obtaining IR spectra of the
solving the cast film in water.
sample plus contaminants from previous runs.
9.1.2 Films of water-soluble polymers cast on glass are
readily examined by peeling off the film from the glass. Water
8.3 Use of Heated Gas Cells:
solublepolymersthatdonotformgoodfilmsmaybeexamined
8.3.1 Vapor-phase IR spectra of solids and high boiling
using the alkali halide pellet technique (7.2.1).
liquids can be examined at an elevated temperature (200°C
and above), using a relatively short path length vapor cell
9.1.3 Also see Practices E573 for details of the internal
(0.1m to 0.75 m). The IR spectra recorded in this manner are
reflection spectroscopy (IRS) technique.
especially useful in the identification of GC-IR fractions of
9.2 Polymers Soluble in Organic Solvents—A variety of
unknownmaterials,sincemostGC-IRspectraareconveniently
solvents such as 1,2-dichlorobenzene, toluene, methyl ethyl
recorded at high temperatures (see Practice E1642).
ketone, dimethylformamide, tetrahydrofuran (Note 3) can be
8.3.2 Recording IR spectra at high temperature, employing
used to cast polymeric films on an alkali halide plate. The
a dispersive instrument, requires that the IR radiation from the
solvent is removed by heating in a nitrogen atmosphere using
source be chopped ahead of the sample to avoid recording IR
an IR heat lamp or in an evacuated oven. The ideal cast
radiation emitted from the hot sample. Unless using very high
uniform film is ;0.01mm to 0.05 mm thick and has no
temperatures,thisisnotusuallyaproblemwhenemployingan
spectral evidence of solvent. In most cases, solutions of the
FT-IR spectrometer, provided that the sample is held between
polymer can be obtained only by heating; this necessitates
the interferometer (which is a wavenumber-selective chopper)
preheating the KBr or NaCl plate before the polymer solution
and the detector.
is applied to prevent fracturing the plate.ACsI plate allows a
9. Analysis of Polymers wider frequency range to be recorded, and it is not as sensitive
NOTE 4—See Refs (8) and (34) for general methods of IR analysis of
to thermal shock. Table 4 gives a list of solvents used to
polymers. See Refs (10-14) for compilations of polymer spectra.
dissolve different classes of polymers. Films can also be cast
9.1 Polymers Soluble in Water: fromanorganicsolventonaninternalreflectionelement(IRE)
9.1.1 Film forming polymers which are soluble in water are and qualitative spectra recorded using the IRS technique.
−1 −1
readily examined in the region 4000cm to 400 cm as cast Further, for those materials soluble in solvents which may
easily be volatilized at temperatures below 75°C, the dispos-
filmsonflatsilverbromide(AgBr)plates(seeTable1forother
window materials). In order to cast a film with a uniform able IR card method described in 6.5.4 may be used.
TABLE 4 Solvents Used in Casting Polymer Films
A
Class Generic Name Solvents
Acetate Resins Polyformaldehyde 1,2-dichlorobenzene
Acrylics ABS terpolymer 1,2-dichlorobenzene
Acrylic acid-ethylene copolymer 1,2-dichlorobenzene
Acrylonitrile-butadiene copolymer 1,2-dichlorobenzene
Polyacrylamide water
Polyethylacrylate 1,2-dichlorobenzene
Ethylacrylate 1,2-dichlorobenzene
Ethylacrylate-ethylene copolymer 1,2-dichlorobenzene
Polymethylacrylate 1,2-dichlorobenzene
Polymethylmethacrylate acetone
Methylmethacrylate-styrene copolymer 1,2-dichlorobenzene
Polyacrylonitrile dimethyl sulfoxide or dimethylformamide
Polymethacrylamide water
Polysodium acrylate water
B
Amino Resins Melamine-formaldehyde
B
Urea-formaldehyde
Cellulosics Cellulose acetate acetone
Cellulose acetate butyrate 1,2-dichlorobenzene or acetone
Cellulose nitrate acetone
Cellulose propionate acetone
Ethyl cellulose ethylene dichloride
Hydroxyethyl cellulose water
Methyl cellulose water
Sodium carboxymethyl cellulose water
Coumarone and Terpene Resins Coumarone-indene resin polyterpene 1,2-dichlorobenzene 1,2-dichlorobenzene
E1252 − 98 (2021)
TABLE 4 Continued
A
Class Generic Name Solvents
B
Epoxies Polymers based on the diglycidyl ether of bisphenol-A (cured)
(uncured) 1,2-dichlorobenzene
Epoxylated phenolformaldehyde acetone
Ethylene Polyethylene 1,2-dichlorobenzene
Polymers Ethylene-propylene copolymer 1,2-dichl
...