1、Designation: E334 01 (Reapproved 2013)Standard Practice forGeneral Techniques of Infrared Microanalysis1This standard is issued under the fixed designation E334; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This practice covers techniques that are of ge
3、neral use insecuring and analyzing microgram quantities of samples byinfrared spectrophotometric techniques. This practice makesrepetition of description of specific techniques unnecessary inindividual infrared methods.1.2 These recommendations are supplementary to PracticesE168, E573, and E1252, wh
4、ich should be referred to for theory,general techniques of sample preparation, and calculations.2. Referenced Documents2.1 ASTM Standards:2E131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE573 Practices for Internal Reflection
5、 SpectroscopyE1252 Practice for General Techniques for Obtaining Infra-red Spectra for Qualitative AnalysisE1642 Practice for General Techniques of Gas Chromatog-raphy Infrared (GC/IR) AnalysisE2105 Practice for General Techniques of Thermogravimet-ric Analysis (TGA) Coupled With Infrared Analysis(T
6、GA/IR)E2106 Practice for General Techniques of LiquidChromatography-Infrared (LC/IR) and Size ExclusionChromatography-Infrared (SEC/IR) Analyses3. Terminology3.1 Definitions and SymbolsFor definitions of terms andsymbols, refer to Terminology E131.3.2 Beam CondenserAspecialized accessory designed fo
7、ranalysis of samples of a microgram or less, comprising ananalyte area or volume of 2.0 mm diameter or less.4. Contamination4.1 Although the presence of contaminants is a generalproblem in any type of analysis, contamination can be particu-larly severe in micro work. For example, minor impurities in
8、 asolvent can become major components of a residue remainingafter solvent evaporation. Materials extracted from thin-layerchromatographic materials, from the paper used in paperchromatography, and from solid adsorbents in general, mayinclude particular contaminants of concern. It should also benoted
9、 that the gas-chromatographic stationary phase may leadto significant contamination. Consideration of these and othersources of contamination must always enter interpretation ofresults in microanalysis. Erroneous results can be minimizedby the use of pure reagents, extreme care in sample handling,an
10、d the frequent use of “blanks” in the course of separation andsubsequent recording of spectra.5. General Microspectroscopic Techniques5.1 Spectroscopic techniques used for the examination ofmicrosamples are usually adaptations of comparable macrotechniques, and many have been described in the litera
11、ture (1,2).35.2 In computerized dispersive spectrometers or Fouriertransform-infrared (FT-IR) instruments, computer routines formultiple scanning, signal averaging, absorbance subtraction,and scale expansion can be used very effectively to enhance theobserved signal-to-noise ratio of weak bands and
12、increasesensitivity (3, 4). Absorbance subtraction is also commonlyused to eliminate interfering bands from the sample matrix andthus lower the limits of detection (see Practice E168).5.3 Use of Masking AperturesThe aperture of sampleholders used for microspectroscopic study (without the use ofan in
13、frared microscope) are usually significantly smaller thanthe beam at the sample position of the instrument. As aconsequence of these small apertures, steps need to be taken toensure that the best quality spectra be obtained, and thetechniques used will depend on the type of spectrometer beingused. I
14、n general, the use of a beam condensing accessory willgreatly improve the results obtained (see 5.4).1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.03 on Infrared and Near Infrared S
15、pectroscopy.Current edition approved Jan. 1, 2013. Published January 2013. Originallyapproved in 1990. Last previous edition approved in 2007 as E334 01 (2007).DOI: 10.1520/E0334-01R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceast
16、m.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of references at the end ofthis practice.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
17、n, PA 19428-2959. United States15.3.1 When a double-beam dispersive spectrometer that isnot equipped for control by minicomputer is used, the refer-ence beam should be masked to a corresponding aperture. Thiscan be accomplished by using an opaque sheet of stiff materialpunched with an appropriate op
18、ening, with reference screens,or with commercially available optical attenuators.Attenuationof the reference beam affects instrument performance, andappropriate adjustment of the instrument settings (that is, widerslits or higher gain) is necessary to produce reliable spectra atthe lower energy leve
19、ls. Enhancement of sensitivity can beattained by the ordinate scale expansion feature available onmost spectrometers.5.3.2 When using a single-beam spectrometer, the instru-ment background spectrum should be recorded through anaperture in the sample position that has dimensions no largerthan those o
20、f the sample. Where appropriate, this can be doneby using the empty sample holder itself.5.3.3 On some FT-IR spectrometers, insertion of an apertureat the sample position will slightly change the observedfrequency positions of bands, as a result of modification of theoptical path. Hence, sample and
21、reference aperture must becarefully aligned at the same position, particularly if computerdifferencing is to be done.5.3.4 Some FT-IR spectrometers (especially those equippedwith cooled mercury cadmium telluride (MCT) detectors) areso sensitive that under normal operating conditions (that is,when ex
22、amining macro samples or recording the referencesingle beam spectrum) the energy throughput of the instrumentneeds to be restricted in order to avoid detector nonlinearity(5). This is typically done by insertion of an aperture or wirescreen into the path of the beam. However, when the sameinstrument
23、 is employed to examine microsamples using asample holder, which is in itself an aperture, this throughputrestriction should be removed.5.3.5 When using an infrared microscope, it is normal torecord the reference spectrum through the same aperture as isused for a particular sample. To accomplish thi
24、s, it is mostconvenient to use visual observation to select the aperture sizerequired to mask the sample area of interest. The single-beamspectrum of this sample area is recorded, and the referencesingle-beam background spectrum is then recorded afterwards.The transmittance (or absorbance) spectrum
25、of the sample isobtained by using the instrument software to calculate the ratioof the two single-beam spectra.5.4 Large energy losses because of beam attenuation may beavoided by the use of a beam-condensing accessory. This typeof accessory is designed to condense the sample radiation beamto an ana
26、lyte area of 2 mm or less, accommodating the smallersize of a microsample. A4 beam condenser is adequate formost microsample analyses.5.4.1 The heat produced by the concentrated beam may beinjurious to some samples, especially in the case of somedispersive instruments. If this difficulty is encounte
27、red, a thingermanium wafer between the source beam and the sample, ora stream of cooling air directed upon the sample, will providesome protection for the sample.5.5 Examination of Liquid SamplesDirect examination ofliquid samples can be accomplished by using sealed microcellsor microcavity cells, w
28、hich are commercially available and arecharacterized by small apertures and volumes of the order of afew microlitres. Beam-condensing accessories are availablethat can accommodate such microcells. The volume of de-mountable microcells that are suitable for liquids of lowvolatility is about 0.5 L whe
29、n assembled with a 0.1-mmspacer. Micro quantities of non-volatile liquids can be conve-niently examined using micro internal reflection spectroscopy(IRS) (see Practices E573). Sometimes the most convenientway to handle microquantities of a volatile liquid is to containit in a gas cell having a large
30、 length-to-volume ratio, so that thematerial is examined in the vapor phase.5.6 Examination of Solid SamplesThe conventional tech-niques for handling macro amounts of solids are equallyapplicable for microgram quantities when scaled down acces-sories are used. Just as for liquids, compensation for t
31、hesample-beam attenuation or the use of a beam condenser isnecessary for the recording of useful spectra; ordinate scaleexpansion, multiple scans, or signal averaging may be neededto enhance the sensitivity.NOTE 1Arange of accessories such as micromull holders, micropelletholders, etc. are commercia
32、lly available. Some are designed for specificinstruments but others have general utility.5.6.1 A small quantity of finely ground powder can bemulled in an agent such as mineral oil and smeared on a smallsample plate about 3 by 5 by 1 mm. The sample plate ismounted in a holder as near as possible to
33、the focal point of theconverging sample radiation beam or in a beam-condensingunit.5.6.2 Alkali halide disk or pellet techniques are of consid-erable importance in microsampling. Compromises in the usualrecommended procedures may be required to permit analysisof ultra-micro samples. It is advantageo
34、us to use an alkalihalide that has been maintained in a drying oven at 105 to110C. Blank samples of the stored alkali halide should be usedto obtain frequent reference spectra, in order to guard againstcontamination.5.6.3 Commercial micropellet dies usually produce disks ofeither 0.5 or 1.5-mm diame
35、ter.Astandard size 13-mm die maybe adapted for micropellet work by punching a small aperturein a disk of, for example, tinfoil, manila folder, blotting paper,or filter paper about 0.1 mm thick. About one third the usualpressure should be used for pressing the micropellet. Thetinfoil or paper serves
36、as a holder for the pellet and can bepositioned over the aperture of the micropellet holder or on thebeam-condenser unit. Commercially available lead micro disksare also available.NOTE 2Stationery supply stores carry paper punches of assorted sizesand shapes that are suitable for making these apertu
37、res for micropellets.NOTE 3An aperture of 1 by 4 mm is about the minimum size on whichsome dispersive spectrometers can operate properly. If a beam condensingaccessory is used, the minimum aperture is reduced to the order of 0.5 to1.0 mm in diameter. Fourier transform instruments can obtain spectrat
38、hrough a 0.5-mm aperture, if necessary, without the use of a beamcondenser.5.6.4 A very small sample may be made transferable byrubbing or abrasion, or both, using dry potassium bromide(KBr) powder. Pellet grade KBr should be used, and subse-quent grinding should be kept to the minimum necessary toE
39、334 01 (2013)2disperse the sample. This technique is also valuable forremoving a thin surface layer from a solid object.5.6.5 A sample of a thin coating material may be obtainedby rubbing the surface with glass-paper or silicon carbidepaper. The spectrum of the sample on the surface of the paperis o
40、btained by using the diffuse reflectance technique, with aclean piece of glass-paper or silicon carbide paper, asappropriate, being used as the reference.5.6.6 Solid materials can be examined by first dissolving thematerial in a solvent (see 5.7). The resulting solution can beexamined directly, or u
41、sed to deposit the solute in a state moreadvantageous for analysis, such as a thin film or in a halidepowder for the preparation of a KBr pellet or diffuse reflec-tance. The same solvent should be used to obtain a spectrum ofthe solvent blank, either directly or as a deposit, as appropriate.5.6.6.1
42、WarningSolvent or melt recrystallization or ap-plication of pressure to samples may cause changes in thecrystalline structure of the material, and hence give changes tothe observed spectrum.5.6.7 Some solids can be heat-softened or melted by press-ing between two small heated KBr plates and then exa
43、mined ina demountable microcell holder (see 5.6.6.1). It is oftenadvantageous to perform the pressing operation with thesample between two sheets of aluminum foil first, so that morepressure can be exerted. The thin film is then peeled off the foiland examined between the salt windows. Some solid sa
44、mplesmay be cut into thin wafers that may then be mounted in amicropellet holder for subsequent analysis.5.6.8 Small flakes of material have been successfully exam-ined by supporting them on a salt plate and then placing anaperture over the sample. Both salt plate and aperture areplaced in the sampl
45、e beam. Static forces may be used to holdvery small samples inside a pinhole aperture. Stray light maybe observed under both types of sample mounting, since thesample does not normally fill the aperture completely. Im-proved spectral data are obtained by the use of a beamcondenser (see 5.4) or, even
46、 better, an infrared transmittingmicroscope (see Section 11).5.6.9 Samples can be held between two thin sheets of apolymeric material that has low infrared absorbance at thefrequencies of interest, instead of being on the surface of a saltplate as in 5.6.6-5.6.8. Fluorocarbon tape may be used to obt
47、ainspectra over large portions of the mid-infrared region, whilepolyethylene film is particularly useful for far-infrared mea-surements. Both materials withstand the effects of manycorrosive samples.5.6.10 Another method for holding small solid samples inthe beam is to stick them on a translucent ad
48、hesive tape andplace an aperture over the sample. In this case, the spectrum ofthe adhesive tape should be compensated for, either by placinga similar aperture covered with adhesive tape in the referencebeam or by computer subtraction of an adhesive tape spectrumcollected in a manner similar to that
49、 of the sample.5.6.11 To avoid the need to computer-subtract the spectrumof adhesive tape mentioned in 5.6.10, small pieces of saltwindow can be used to mount microsamples next to anaperture. The pieces of salt are cleaved from a used crystal byusing a razor blade, and can be as small as 1 or 2 mm square.Transfer a few particles of adhesive from a (preferably old)piece of adhesive tape, using a probe, onto the extreme edgesof this salt cover. Place the sample over the aperture, and coverwith the salt plate. Pressure the salt cover onto the aperture sothat the adhesive ho
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