ASTM E334-01(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E334 − 01 (Reapproved2007)
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 Department of Defense.
1. Scope 4. Contamination
1.1 Thispracticecoverstechniquesthatareofgeneralusein 4.1 Although the presence of contaminants is a general
securing and analyzing microgram quantities of samples by problem in any type of analysis, contamination can be particu-
infrared spectrophotometric techniques. This practice makes larly severe in micro work. For example, minor impurities in a
repetition of description of specific techniques unnecessary in solvent can become major components of a residue remaining
individual infrared methods. after solvent evaporation. Materials extracted from thin-layer
chromatographic materials, from the paper used in paper
1.2 These recommendations are supplementary to Practices
chromatography, and from solid adsorbents in general, may
E168,E573,andE1252,whichshouldbereferredtofortheory,
include particular contaminants of concern. It should also be
general techniques of sample preparation, and calculations.
noted that the gas-chromatographic stationary phase may lead
2. Referenced Documents to significant contamination. Consideration of these and other
2 sources of contamination must always enter interpretation of
2.1 ASTM Standards:
results in microanalysis. Erroneous results can be minimized
E131Terminology Relating to Molecular Spectroscopy
by the use of pure reagents, extreme care in sample handling,
E168Practices for General Techniques of Infrared Quanti-
andthefrequentuseof“blanks”inthecourseofseparationand
tative Analysis
subsequent recording of spectra.
E573Practices for Internal Reflection Spectroscopy
E1252Practice for General Techniques for Obtaining Infra-
5. General Microspectroscopic Techniques
red Spectra for Qualitative Analysis
5.1 Spectroscopic techniques used for the examination of
E1642Practice for General Techniques of Gas Chromatog-
microsamples are usually adaptations of comparable macro
raphy Infrared (GC/IR) Analysis
techniques, and many have been described in the literature (1,
E2105Practice for General Techniques of Thermogravimet-
2).
ric Analysis (TGA) Coupled With Infrared Analysis
5.2 In computerized dispersive spectrometers or Fourier
(TGA/IR)
E2106 Practice for General Techniques of Liquid transform-infrared (FT-IR) instruments, computer routines for
Chromatography-Infrared (LC/IR) and Size Exclusion multiple scanning, signal averaging, absorbance subtraction,
Chromatography-Infrared (SEC/IR) Analyses andscaleexpansioncanbeusedveryeffectivelytoenhancethe
observed signal-to-noise ratio of weak bands and increase
3. Terminology
sensitivity (3, 4). Absorbance subtraction is also commonly
3.1 Definitions and Symbols—For definitions of terms and usedtoeliminateinterferingbandsfromthesamplematrixand
symbols, refer to Terminology E131. thus lower the limits of detection (see Practice E168).
3.2 Beam Condenser—Aspecializedaccessorydesignedfor
5.3 Use of Masking Apertures—The aperture of sample
analysis of samples of a microgram or less, comprising an
holders used for microspectroscopic study (without the use of
analyte area or volume of 2.0 mm diameter or less.
an infrared microscope) are usually significantly smaller than
the beam at the sample position of the instrument. As a
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
consequenceofthesesmallapertures,stepsneedtobetakento
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
ensure that the best quality spectra be obtained, and the
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
techniques used will depend on the type of spectrometer being
Current edition approved March 1, 2007. Published March 2007. Originally
used. In general, the use of a beam condensing accessory will
approved in 1990. Last previous edition approved in 2001 as E334–01. DOI:
10.1520/E0334-01R07.
greatly improve the results obtained (see 5.4).
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
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.
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E334 − 01 (2007)
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 0.1-mm
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-
5.6 Examination of Solid Samples—The conventional tech-
ment background spectrum should be recorded through an
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
NOTE1—Arangeofaccessoriessuchasmicromullholders,micropellet
carefully aligned at the same position, particularly if computer
holders, etc. are commercially available. Some are designed for specific
differencing is to be done.
instruments but others have general utility.
5.3.4 Some FT-IR spectrometers (especially those equipped
5.6.1 A small quantity of finely ground powder can be
with cooled mercury cadmium telluride (MCT) detectors) are
mulled in an agent such as mineral oil and smeared on a small
so sensitive that under normal operating conditions (that is,
sample plate about 3 by 5 by 1 mm. The sample plate is
when examining macro samples or recording the reference
mountedinaholderasnearaspossibletothefocalpointofthe
singlebeamspectrum)theenergythroughputoftheinstrument
converging sample radiation beam or in a beam-condensing
needs to be restricted in order to avoid detector nonlinearity
unit.
(5). This is typically done by insertion of an aperture or wire
5.6.2 Alkali halide disk or pellet techniques are of consid-
screen into the path of the beam. However, when the same
erableimportanceinmicrosampling.Compromisesintheusual
instrument is employed to examine microsamples using a
recommended procedures may be required to permit analysis
sample holder, which is in itself an aperture, this throughput
of ultra-micro samples. It is advantageous to use an alkali
restriction should be removed.
halide that has been maintained in a drying oven at 105 to
5.3.5 When using an infrared microscope, it is normal to
110°C.Blanksamplesofthestoredalkalihalideshouldbeused
record the reference spectrum through the same aperture as is
to obtain frequent reference spectra, in order to guard against
used for a particular sample. To accomplish this, it is most
contamination.
convenient to use visual observation to select the aperture size
5.6.3 Commercial micropellet dies usually produce disks of
required to mask the sample area of interest. The single-beam
either0.5or1.5-mmdiameter.Astandardsize13-mmdiemay
spectrum of this sample area is recorded, and the reference
be adapted for micropellet work by punching a small aperture
single-beambackgroundspectrumisthenrecordedafterwards.
in a disk of, for example, tinfoil, manila folder, blotting paper,
The transmittance (or absorbance) spectrum of the sample is
or filter paper about 0.1 mm thick. About one third the usual
obtainedbyusingtheinstrumentsoftwaretocalculatetheratio
pressure should be used for pressing the micropellet. The
of the two single-beam spectra.
tinfoil or paper serves as a holder for the pellet and can be
5.4 Largeenergylossesbecauseofbeamattenuationmaybe
positionedovertheapertureofthemicropelletholderoronthe
avoided by the use of a beam-condensing accessory. This type
beam-condenserunit.Commerciallyavailableleadmicrodisks
ofaccessoryisdesignedtocondensethesampleradiationbeam
are also available.
toananalyteareaof2mmorless,accommodatingthesmaller
NOTE2—Stationerysupplystorescarrypaperpunchesofassortedsizes
size of a microsample. A4× beam condenser is adequate for
and shapes that are suitable for making these apertures for micropellets.
most microsample analyses.
NOTE3—Anapertureof1by4mmisabouttheminimumsizeonwhich
somedispersivespectrometerscanoperateproperly.Ifabeamcondensing
5.4.1 The heat produced by the concentrated beam may be
accessory is used, the minimum aperture is reduced to the order of 0.5 to
injurious to some samples, especially in the case of some
1.0 mm in diameter. Fourier transform instruments can obtain spectra
dispersive instruments. If this difficulty is encountered, a thin
through a 0.5-mm aperture, if necessary, without the use of a beam
germanium wafer between the source beam and the sample, or
condenser.
a stream of cooling air directed upon the sample, will provide
5.6.4 A very small sample may be made transferable by
some protection for the sample.
rubbing or abrasion, or both, using dry potassium bromide
5.5 Examination of Liquid Samples—Directexaminationof (KBr) powder. Pellet grade KBr should be used, and subse-
liquidsamplescanbeaccomplishedbyusingsealedmicrocells quent grinding should be kept to the minimum necessary to
E334 − 01 (2007)
disperse the sample. This technique is also valuable for Transfer a few particles of adhesive from a (preferably old)
removing a thin surface layer from a solid object. piece of adhesive tape, using a probe, onto the extreme edges
ofthissaltcover.Placethesampleovertheaperture,andcover
5.6.5 A sample of a thin coating material may be obtained
with the salt plate. Pressure the salt cover onto the aperture so
by rubbing the surface with glass-paper or silicon carbide
that the adhesive holds it in place.Adhesive from a used piece
paper. The spectrum of the sample on the surface of the paper
of tape will allow the cover to be removed more easily after
is obtained by using the diffuse reflectance technique, with a
sample collection is completed.
clean piece of glass-paper or silicon carbide paper, as
appropriate, being used as the reference. 5.6.12 IfusingIRSwithasmallsample,optimalresultswill
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-
tance.Thesamesolventshouldbeusedtoobtainaspectrumof 5.6.12.1 MicroIRSaccessoriesarealsocommerciallyavail-
thesolventblank,eitherdirectlyorasadeposit,asappropriate. able and are generally referred to as “micro-ATR” accessories.
The IRE of these accessories is only 1 to 3 mm in diameter
5.6.6.1 Warning: Solvent or melt recrystallization or appli-
with an effective sampling area of 0.5 to 2.0 mm in diameter,
cation of pressure to samples may cause changes in the
allowinganalysisofsmallersamplesand,withadiamondIRE,
crystalline structure of the material, and hence give changes to
greater contact pressures.
the observed spectrum.
5.6.12.2 Particular cautions should be observed when using
5.6.7 Some solids can be heat-softened or melted by press-
these types of accessories.Accessory design precludes control
ingbetweentwosmallheatedKBrplatesandthenexaminedin
over the incident beam angle penetrating the IRE crystal
a demountable microcell holder (see 5.6.6.1). It is often
surface, thus, a number of incident beam angles are directed
advantageous to perform the pressing operation with the
ontothesample-crystalinterface.Theresultantspectramaynot
samplebetweentwosheetsofaluminumfoilfirst,sothatmore
be directly comparable to spectra collected from a controlled
pressurecanbeexerted.Thethinfilmisthenpeeledoffthefoil
incident angle IRE accessory or spectra collected by transmis-
and examined between the salt windows. Some solid samples
sion.Additionally, if the active sampling area (0.5 to 2.0 mm)
may be cut into thin wafers that may then be mounted in a
is not completely filled by the sample, that is, the sample is
micropellet holder for subsequent analysis.
smaller than the crystal surface, stray-light effects can distort
5.6.8 Smallflakesofmaterialhavebeensuccessfullyexam-
the spectrum. In both cases, the “standard” ATR-correction
ined by supporting them on a salt p
...