ASTM E334-01(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: E334 − 01 (Reapproved 2021)
Standard Practice for
General Techniques of Infrared Microanalysis
This standard is issued under the fixed designation E334; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope ric Analysis (TGA) Coupled With Infrared Analysis
(TGA/IR)
1.1 Thispracticecoverstechniquesthatareofgeneralusein
E2106 Practice for General Techniques of Liquid
securing and analyzing microgram quantities of samples by
Chromatography-Infrared (LC/IR) and Size Exclusion
infrared spectrophotometric techniques. This practice makes
Chromatography-Infrared (SEC/IR) Analyses
repetition of description of specific techniques unnecessary in
individual infrared methods.
3. Terminology
1.2 These recommendations are supplementary to Practices
3.1 Definitions and Symbols—For definitions of terms and
E168,E573,andE1252,whichshouldbereferredtofortheory,
symbols, refer to Terminology E131.
general techniques of sample preparation, and calculations.
3.2 Beam Condenser—Aspecializedaccessorydesignedfor
1.3 This standard does not purport to address all of the
analysis of samples of a microgram or less, comprising an
safety concerns, if any, associated with its use. It is the
analyte area or volume of 2.0 mm diameter or less.
responsibility of the user of this standard to establish appro-
4. Contamination
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
4.1 Although the presence of contaminants is a general
1.4 This international standard was developed in accor-
problem in any type of analysis, contamination can be particu-
dance with internationally recognized principles on standard-
larly severe in micro work. For example, minor impurities in a
ization established in the Decision on Principles for the
solvent can become major components of a residue remaining
Development of International Standards, Guides and Recom-
after solvent evaporation. Materials extracted from thin-layer
mendations issued by the World Trade Organization Technical
chromatographic materials, from the paper used in paper
Barriers to Trade (TBT) Committee.
chromatography, and from solid adsorbents in general, may
include particular contaminants of concern. It should also be
2. Referenced Documents
noted that the gas-chromatographic stationary phase may lead
2.1 ASTM Standards: to significant contamination. Consideration of these and other
E131Terminology Relating to Molecular Spectroscopy
sources of contamination must always enter interpretation of
E168Practices for General Techniques of Infrared Quanti- results in microanalysis. Erroneous results can be minimized
tative Analysis
by the use of pure reagents, extreme care in sample handling,
E573Practices for Internal Reflection Spectroscopy andthefrequentuseof“blanks”inthecourseofseparationand
E1252Practice for General Techniques for Obtaining Infra-
subsequent recording of spectra.
red Spectra for Qualitative Analysis
5. General Microspectroscopic Techniques
E1642Practice for General Techniques of Gas Chromatog-
raphy Infrared (GC/IR) Analysis
5.1 Spectroscopic techniques used for the examination of
E2105Practice for General Techniques of Thermogravimet-
microsamples are usually adaptations of comparable macro
techniques, and many have been described in the literature (1,
2).
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
5.2 In computerized dispersive spectrometers or Fourier
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
transform-infrared (FT-IR) instruments, computer routines for
Current edition approved April 1, 2021. Published April 2021. Originally
multiple scanning, signal averaging, absorbance subtraction,
approved in 1990. Last previous edition approved in 2013 as E334–01 (2013).
andscaleexpansioncanbeusedveryeffectivelytoenhancethe
DOI: 10.1520/E0334-01R21.
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 practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E334 − 01 (2021)
observed signal-to-noise ratio of weak bands and increase 5.4 Largeenergylossesbecauseofbeamattenuationmaybe
sensitivity (3, 4). Absorbance subtraction is also commonly avoided by the use of a beam-condensing accessory. This type
usedtoeliminateinterferingbandsfromthesamplematrixand ofaccessoryisdesignedtocondensethesampleradiationbeam
thus lower the limits of detection (see Practices E168). to an analyte area of 2 mm or less, accommodating the smaller
size of a microsample. A4× beam condenser is adequate for
5.3 Use of Masking Apertures—The aperture of sample
most microsample analyses.
holders used for microspectroscopic study (without the use of
5.4.1 The heat produced by the concentrated beam may be
an infrared microscope) are usually significantly smaller than
injurious to some samples, especially in the case of some
the beam at the sample position of the instrument. As a
dispersive instruments. If this difficulty is encountered, a thin
consequenceofthesesmallapertures,stepsneedtobetakento
germanium wafer between the source beam and the sample, or
ensure that the best quality spectra be obtained, and the
a stream of cooling air directed upon the sample, will provide
techniques used will depend on the type of spectrometer being
some protection for the sample.
used. In general, the use of a beam condensing accessory will
greatly improve the results obtained (see 5.4). 5.5 Examination of Liquid Samples—Direct examination of
liquidsamplescanbeaccomplishedbyusingsealedmicrocells
5.3.1 When a double-beam dispersive spectrometer that is
ormicrocavitycells,whicharecommerciallyavailableandare
not equipped for control by minicomputer is used, the refer-
characterized by small apertures and volumes of the order of a
encebeamshouldbemaskedtoacorrespondingaperture.This
few microlitres. Beam-condensing accessories are available
can be accomplished by using an opaque sheet of stiff material
that can accommodate such microcells. The volume of de-
punched with an appropriate opening, with reference screens,
mountable microcells that are suitable for liquids of low
orwithcommerciallyavailableopticalattenuators.Attenuation
volatility is about 0.5 µL when assembled with a 0.1mm
of the reference beam affects instrument performance, and
spacer. Micro quantities of non-volatile liquids can be conve-
appropriateadjustmentoftheinstrumentsettings(thatis,wider
niently examined using micro internal reflection spectroscopy
slits or higher gain) is necessary to produce reliable spectra at
(IRS) (see Practices E573). Sometimes the most convenient
the lower energy levels. Enhancement of sensitivity can be
way to handle microquantities of a volatile liquid is to contain
attained by the ordinate scale expansion feature available on
itinagascellhavingalargelength-to-volumeratio,sothatthe
most spectrometers.
material is examined in the vapor phase.
5.3.2 When using a single-beam spectrometer, the instru-
ment background spectrum should be recorded through an 5.6 Examination of Solid Samples—The conventional tech-
niques for handling macro amounts of solids are equally
aperture in the sample position that has dimensions no larger
applicable for microgram quantities when scaled down acces-
than those of the sample. Where appropriate, this can be done
sories are used. Just as for liquids, compensation for the
by using the empty sample holder itself.
sample-beam attenuation or the use of a beam condenser is
5.3.3 OnsomeFT-IRspectrometers,insertionofanaperture
necessary for the recording of useful spectra; ordinate scale
at the sample position will slightly change the observed
expansion, multiple scans, or signal averaging may be needed
frequency positions of bands, as a result of modification of the
to enhance the sensitivity.
optical path. Hence, sample and reference aperture must be
carefully aligned at the same position, particularly if computer
NOTE1—Arangeofaccessoriessuchasmicromullholders,micropellet
differencing is to be done.
holders, etc. are commercially available. Some are designed for specific
instruments but others have general utility.
5.3.4 Some FT-IR spectrometers (especially those equipped
with cooled mercury cadmium telluride (MCT) detectors) are
5.6.1 A small quantity of finely ground powder can be
so sensitive that under normal operating conditions (that is,
mulled in an agent such as mineral oil and smeared on a small
when examining macro samples or recording the reference sample plate about 3mm by 5mm by 1 mm.The sample plate
singlebeamspectrum)theenergythroughputoftheinstrument
is mounted in a holder as near as possible to the focal point of
needs to be restricted in order to avoid detector nonlinearity theconvergingsampleradiationbeamorinabeam-condensing
(5). This is typically done by insertion of an aperture or wire
unit.
screen into the path of the beam. However, when the same
5.6.2 Alkali halide disk or pellet techniques are of consid-
instrument is employed to examine microsamples using a
erableimportanceinmicrosampling.Compromisesintheusual
sample holder, which is in itself an aperture, this throughput
recommended procedures may be required to permit analysis
restriction should be removed.
of ultra-micro samples. It is advantageous to use an alkali
halide that has been maintained in a drying oven at 105°C to
5.3.5 When using an infrared microscope, it is normal to
110°C. Blank samples of the stored alkali halide should be
record the reference spectrum through the same aperture as is
used to obtain frequent reference spectra, in order to guard
used for a particular sample. To accomplish this, it is most
against contamination.
convenient to use visual observation to select the aperture size
required to mask the sample area of interest. The single-beam
5.6.3 Commercial micropellet dies usually produce disks of
spectrum of this sample area is recorded, and the reference either 0.5mm or 1.5mm diameter.Astandard size 13mm die
single-beam background spectrum is then recorded afterwards. may be adapted for micropellet work by punching a small
The transmittance (or absorbance) spectrum of the sample is aperture in a disk of, for example, tinfoil, manila folder,
obtainedbyusingtheinstrumentsoftwaretocalculatetheratio blotting paper, or filter paper about 0.1 mm thick. About one
of the two single-beam spectra. third the usual pressure should be used for pressing the
E334 − 01 (2021)
micropellet.Thetinfoilorpaperservesasaholderforthepellet while polyethylene film is particularly useful for far-infrared
and can be positioned over the aperture of the micropellet measurements. Both materials withstand the effects of many
holder or on the beam-condenser unit. Commercially available corrosive samples.
lead micro disks are also available.
5.6.10 Another method for holding small solid samples in
the beam is to stick them on a translucent adhesive tape and
NOTE2—Stationerysupplystorescarrypaperpunchesofassortedsizes
placeanapertureoverthesample.Inthiscase,thespectrumof
and shapes that are suitable for making these apertures for micropellets.
NOTE 3—An aperture of 1mm by 4 mm is about the minimum size on the adhesive tape should be compensated for, either by placing
which some dispersive spectrometers can operate properly. If a beam
a similar aperture covered with adhesive tape in the reference
condensing accessory is used, the minimum aperture is reduced to the
beam or by computer subtraction of an adhesive tape spectrum
orderof0.5mmto1.0mmindiameter.Fouriertransforminstrumentscan
collected in a manner similar to that of the sample.
obtain spectra through a 0.5mm aperture, if necessary, without the use of
a beam condenser. 5.6.11 To avoid the need to computer-subtract the spectrum
of adhesive tape mentioned in 5.6.10, small pieces of salt
5.6.4 A very small sample may be made transferable by
window can be used to mount microsamples next to an
rubbing or abrasion, or both, using dry potassium bromide
aperture. The pieces of salt are cleaved from a used crystal by
(KBr) powder. Pellet grade KBr should be used, and subse-
using a razor blade, and can be as small as 1mm or 2 mm
quent grinding should be kept to the minimum necessary to
square.Transfer a few particles of adhesive from a (preferably
disperse the sample. This technique is also valuable for
old) piece of adhesive tape, using a probe, onto the extreme
removing a thin surface layer from a solid object.
edgesofthissaltcover.Placethesampleovertheaperture,and
5.6.5 A sample of a thin coating material may be obtained
cover with the salt plate. Pressure the salt cover onto the
by rubbing the surface with glass-paper or silicon carbide
aperture so that the adhesive holds it in place. Adhesive from
paper. The spectrum of the sample on the surface of the paper
a used piece of tape will allow the cover to be removed more
is obtained by using the diffuse reflectance technique, with a
easily after sample collection is completed.
clean piece of glass-paper or silicon carbide paper, as
5.6.12 IfusingIRSwithasmallsample,optimalresultswill
appropriate, being used as the reference.
beobtainedifthesmallsampleisplacedacrossthewidthofthe
5.6.6 Solidmaterialscanbeexaminedbyfirstdissolvingthe
internal reflection element (IRE). With very small samples,
material in a solvent (see 5.7). The resulting solution can be
optimal results will be obtained by placing the sample where
examined directly, or used to deposit the solute in a state more
thebeamenters,sothatthefirstreflectionisconcentratedatthe
advantageous for analysis, such as a thin film or in a halide
sample position (see Practices E573).
powder for the preparation of a KBr pellet or diffuse reflec-
5.6.12.1 MicroIRSaccessoriesarealsocommerciallyavail-
tance.Thesamesolventshouldbeusedtoobtainaspectrumof
able and are generally referred to as “micro-ATR” ac
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