1、Designation: E 2224 02Standard Guide forForensic Analysis of Fibers by Infrared Spectroscopy1This standard is issued under the fixed designation E 2224; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 Infrared (IR) spectrophotometery is a valuable methodof fiber polymer identification and comparison in forensicexaminations. The use of
3、 IR microscopes coupled with Fouriertransform infrared (FT-IR) spectrometers has greatly simplifiedthe IR analysis of single fibers, thus making the techniquefeasible for routine use in the forensic laboratory.1.2 This guideline is intended to assist individuals andlaboratories that conduct forensic
4、 fiber examinations andcomparisons in the effective application of infrared spectros-copy to the analysis of fiber evidence. Although this guide isintended to be applied to the analysis of single fibers, many ofits suggestions are applicable to the infrared analysis of smallparticles in general.2. R
5、eferenced Documents2.1 ASTM Standards:E 1421 Practice for Describing and Measuring Performanceof Fourier Transform Infrared (FT-IR) Spectrometers:Level Zero and Level One Tests2E 1459 Guide for Physical Evidence and Labeling andRelated Documentation3E 1492 Practice for Receiving, Documenting, Storin
6、g, andRetrieving Evidence in a Forensic Laboratory33. Terminology3.1 absorbance (A)the logarithm to the base 10 of thereciprocal of the transmittance, (T); A = log10(1/T) = -log10T.3.2 absorption banda region of the absorption spectrumin which the absorbance passes through a maximum.3.3 absorption s
7、pectruma plot, or other representation, ofabsorbance, or any function of absorbance, against wavelength,or any function of wavelength.3.4 absorptivity (a)absorbance divided by the product ofthe sample pathlength (b) and the concentration of the absorb-ing substance (c); a = A/bc3.5 attenuated total
8、reflection (ATR)reflection that occurswhen an absorbing coupling mechanism acts in the process oftotal internal reflection to make the reflectance less than unity.3.6 backgroundapparent absorption caused by anythingother than the substance for which the analysis is being made.3.7 cellulosic fiberfib
9、er composed of polymers formedfrom glucose subunits.3.8 far-infraredpertaining to the infrared region of theelectromagnetic spectrum with wavelength range from ap-proximately 25 to 300 m (wavenumber range 400 to 30 cm-1).3.9 Fourier transforma mathematical operation that con-verts a function of one
10、independent variable to one of adifferent independent variable. In FT-IR spectroscopy, theFourier transform converts a time function (the interferogram)to a frequency function (the infrared absorption spectrum).Spectral data are collected through the use of an interferometer,which replaces the monoc
11、hrometer found in the dispersiveinfrared spectrometer.3.10 Fourier transform infrared (FT-IR) spectrometryaform of infrared spectrometry in which an interferogram isobtained; this interferogram is then subjected to a Fouriertransformation to obtain an amplitude-wavenumber (or wave-length) spectrum.3
12、.11 generic classa group of fibers having similar (but notnecessarily identical) chemical composition. A generic nameapplies to all members of a group and is not protected bytrademark registration. Generic names for manufactured fibersinclude, for example, rayon, nylon, and polyester. (Genericnames
13、to be used in the United States for manufactured fiberswere established as part of the Textile Fiber Products Identifi-cation Act enacted by Congress in 1954 (1).43.12 infraredpertaining to the region of the electromag-netic spectrum with wavelength range from approximately0.78 to 1000 m (wavenumber
14、 range 12 800 to 10 cm-1).3.13 infrared spectroscopyto spectroscopy in the infraredregion of the electromagnetic spectrum.3.14 internal reflection spectroscopy (IRS)the techniqueof recording optical spectra by placing a sample material incontact with a transparent medium of greater refractive indexa
15、nd measuring the reflectance (single or multiple) from theinterface, generally at angles of incidence greater than thecritical angle.3.15 manufactured (man-made) fiberany fiber derived bya process of manufacture from any substance that, at any pointin the manufacturing process, is not a fiber.1This
16、guide is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved July 10, 2002. Published September 2002.2Annual Book of ASTM Standards, Vol 03.06.3Annual Book of ASTM Standards, Vol 14.02.4Th
17、e boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.16 mid-infraredpertaining to the infrared region of theelectromagnetic spectrum with wavel
18、ength range from ap-proximately 2.5 to 25 m (wavenumber range 4000 to 400cm-1).3.17 near-infraredpertaining to the infrared region of theelectromagnetic spectrum with wavelength range from ap-proximately 0.78 to 2.5 m (wavenumber range 12 820 to 4000cm-1).3.18 spectrometerphotometric device for the
19、measure-ment of spectral transmittance, spectral reflectance, or relativespectral emittance.3.19 subgeneric classa group of fibers within a genericclass that share the same polymer composition. Subgenericnames include, for example, nylon 6, nylon 6,6, and poly(eth-ylene terephthalate).3.20 transmitt
20、ance (T)the ratio of radiant power transmit-ted by the sample, I, to the radiant power incident on thesample, Io; T = I/Io3.21 wavelengththe distance, measured along the line ofpropagation, between two points that are in phase on adjacentwaves.3.22 wavenumberthe number of waves per unit length, ina
21、vacuum, usually given in reciprocal centimeters, cm-1.4. Summary of Guide4.1 This guideline covers identification of fiber polymercomposition by interpretation of absorption spectra obtained byinfrared microspectroscopy. It is intended to be applicable to awide range of infrared spectrophotometery a
22、nd microscopeconfigurations.4.2 Spectra may also be obtained by a variety of alternativeIR techniques. Other techniques (not covered in the scope ofthis guideline) include: micro internal reflection spectroscopy(MIR), which differs from attenuated total reflectance (ATR) inthat the infrared radiatio
23、n is dependent upon the amount ofsample in contact with the surface of the prism (2):4.2.1 Diamond cell (medium or high pressure) used with abeam condenser (3-5) (This combination is frequently usedwith a spectrophotometer configured for mid- and far-IR).4.2.2 Thin films: solvent (6,7), melt (4), or
24、 mechanicallyprepared (8).4.2.3 Lead foil technique (6).4.2.4 Micro-KBr (or other appropriate salt) pellets (9,10).This list is not meant to be totally inclusive or exclusive.4.3 This analytical method covers manufactured textilefibers (with the exception of inorganic fibers), including, butnot limi
25、ted to:Acetate Modacrylic Polyester Vinal (5)Acrylic Novoloid (5) Rayon VinyonAnidex Nylon SaranAramid Nytril SpandexAzlon (5) Olefin SulfarFluorocarbon Polybenzimidazole(PBI)TriacetateLastrile Polycarbonate RubberAlthough natural fibers may also be analyzed by IR spec-troscopy, they are excluded fr
26、om this guideline because noadditional discriminating compositional information of thefiber is provided over that yielded by light microscopy.However, infrared spectrophotometery may provide signifi-cantly useful information if there are dyes present in the naturalfiber and can serve to distinguish
27、among similarly coloredfibers.5. Significance and Use5.1 Fiber samples may be prepared and mounted for micro-scopical infrared analysis by a variety of techniques. Infraredspectra of fibers are obtained using an IR spectrophotometercoupled with an IR microscope. Fiber polymer identification ismade b
28、y comparison of the fiber spectrum with referencespectra.5.2 Consideration should be given to the potential foradditional compositional information that may be obtained byIR spectroscopy over polarized light microscopy alone (seeMicroscopy Guidelines). The extent to which IR spectralcomparison is in
29、dicated will vary with specific sample and caseevaluations.5.3 The recommended point for IR analysis in a forensicfiber examination is following visible and UV comparisonmicroscopy (fluoresence microscopy), polarized light micros-copy, and UV/visible spectroscopy, but before dye extractionfor thin-l
30、ayer chromatography. This list of analytical tech-niques is not meant to be totally inclusive or exclusive.5.4 The following generic types of fiber are occasionallyencountered in routine forensic examinations: Anidex, Fluoro-carbon, Lastrile, Novoloid, Nytril, Polycarbonate, PBI, Sulfar,Vinal, and V
31、inyon.5.5 Exemplar data, reference standards, and/or examinerexperience may be inadequate for characterization of thesefibers by optical microscopical and microchemical techniques.For these fiber types, IR spectroscopic confirmation of polymertype is advisable.5.6 Because of the large number of subg
32、eneric classes,forensic examination of acrylic fibers is likely to benefitsignificantly from IR spectral analysis (11).5.7 Colorless manufactured fibers are lacking in the charac-teristics for color comparison available in dyed or pigmentedfibers. The forensic examination of these fibers may, theref
33、ore,benefit from the additional comparative aspect of IR spectralanalysis.5.8 If polymer identification is not readily apparent fromoptical data alone, an additional method of analysis should beused such as microchemical tests, melting point, pyrolysisinfrared spectrophotometry, or pyrolysis gas chr
34、omatography.Infrared analysis offers the advantage of being the leastdestructive of these methods.6. Sample Handling6.1 The general handling and tracking of samples shouldmeet or exceed the requirements of Practice E 1492 and GuideE 1459.6.2 The quantity of fiber used and the number of fibersamples
35、required will differ according to:6.2.1 Specific technique and sample preparation,6.2.2 Sample homogeneity,6.2.3 Condition of the sample, and6.2.4 Other case dependent analytical conditions and/orconcerns.6.3 Sample preparation should be similar for all fibers beingE2224022compared. Fibers should be
36、 flattened prior to analysis in orderto obtain the best quality absorption spectra. Flattening thefibers can alter the crystalline/amorphous structure of the fiberand result in minor differences in peak frequencies andintensities. This must be taken into consideration when makingspectral comparisons
37、 (12). Leaving the fiber unflattened, whileallowing crystallinity-sensitive bands to be observed unaltered,results in distortion of peak heights due to variable pathlengths(13). In certain situations, a combination of both approaches isadvisable.6.4 Because flattening the fiber is destructive of mor
38、phol-ogy, the minimum length of fiber necessary for the analysisshould be used. A typical IR microscope is optimized for a 100m-spot size, thus little beam energy passes through a pointthat is farther than 50 m from the center of the field of view.Hence, analytical performance will not necessarily b
39、e im-proved with the use of fibers greater than 100 m in length.6.5 The flattened fiber may be mounted across an aperture,on an IR window, or between IR windows. Common IRwindow materials used for this purpose include, but are notlimited to, KBr, CsI, BaF2, ZnSe, and diamond. The choice ofwindow mat
40、erial should not reduce the effective spectral rangeof the detector being used. When the fiber is mounted betweentwo IR windows, care must be taken to avoid light by-passaround the fiber; otherwise an interference pattern will beintroduced in the spectrum of the sample. Where the fiber ismounted bet
41、ween two IR windows, a small KBr crystal shouldbe placed next to the fiber. The background spectrum should beacquired through this crystal to avoid interference fringes,which would arise if the spectrum of an air “gap” between thetwo IR windows was acquired or if the fringes would distortthe ratioed
42、 spectrum.6.6 Where several fibers are mounted on or in a singlemount, they should be well separated (microscopically) so thattheir positions can be unambiguously documented for laterretrieval and/or reanalysis, and to prevent spectral contamina-tion from stray light that might pass through another
43、fiber. It isimportant that the longitudinal plane (flattened surface) of thefiber be as nearly parallel to the IR window or other mount aspossible.7. Analysis7.1 A mid-infrared spectrophotometer (FT-IR is the currentstandard, but dispersive IR is not excluded) and an infraredmicroscope that is compa
44、tible with the mid-range spectropho-tometer is recommended. The lower frequency cutoff will varywith the microscope detector used (preferably no higher than750 cm-1).7.1.1 Useful sample preparation accessories include, but arenot limited to, sample supports, infrared windows, presses,dies, rollers,
45、scalpels, and etched-tungsten probes.7.2 All spectrophotometer and microscope componentsshould be turned on and allowed to reach thermal stability priorto commencement of calibration and operational runs. Thismay take up to several hours. It should be noted that mostFT-IR instruments are designed to
46、 work best when left on or inthe standby mode 24 hours a day.7.3 It is essential that instrument performance and calibra-tion be evaluated routinely, at least once a month, in acomprehensive manner.7.4 The preferred performance evaluation method is inaccordance with Practice E 1421, Sections 17, 9.5
47、, and 9.5.1.In brief, this includes:7.4.1 System throughput,7.4.2 Single-beam spectrum,7.4.3 100 % T line, and7.4.4 Polystyrene reference spectrum.7.5 The apertures that control the areas (fields) of sampleillumination and detector measurement in an IR microscopemay be of fixed or variable size, and
48、 may be either rectangularor circular in shape. Variable rectangular apertures are recom-mended, because they can be more closely matched to the fibershape. Light throughput, stray light reduction, and aperturefocus in the sample image plane are some of the considerationsin selecting aperture parame
49、ters and positioning. Fiber width,flatness, and linearity will usually limit the size of the illumi-nation and detector apertures used for analysis. In general, theilluminating and detector fields should lie within the bound-aries of the fiber edges.7.6 Not all systems provide for the control of both illumi-nation and detector measurement fields; the following recom-mendations can be modified to suit the constraints of aparticular system design.7.7 The objective and/or condenser should be adjusted (ifpossible) for any IR window that lies between the optic and
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