1、Designation: E2224 10Standard Guide forForensic Analysis of Fibers by Infrared Spectroscopy1This standard is issued under the fixed designation E2224; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num
2、ber in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 IR
3、 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 fi
4、ber 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.1.3 The
5、 values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.2. Referenced Documents2.1 ASTM Standards:2D123 Terminology Relating to TextilesE1421 Practice for Describing and Measuring Performanceof Fourier Transform Mid-Infrared (FT-MIR) Spect
6、rom-eters: Level Zero and Level One TestsE1459 Guide for Physical Evidence Labeling and RelatedDocumentationE1492 Practice for Receiving, Documenting, Storing, andRetrieving Evidence in a Forensic Science Laboratory3. Terminology3.1 DefinitionsFor definitions of terms used in this guide,refer to Ter
7、minology D123.3.2 Definitions of Terms Specific to This Standard:3.2.1 absorbance (A)the logarithm to the base 10 of thereciprocal of the transmittance, (T):A 5 log101/T! 5 log10T3.2.2 absorption banda region of the absorption spectrumin which the absorbance passes through a maximum.3.2.3 absorption
8、 spectruma plot, or other representation,of absorbance, or any function of absorbance, against wave-length, or any function of wavelength.3.2.4 absorptivity (a)absorbance divided by the productof the sample pathlength (b) and the concentration of theabsorbing substance (c):a 5 A/bc3.2.5 attenuated t
9、otal reflection (ATR)reflection that oc-curs when an absorbing coupling mechanism acts in theprocess of total internal reflection to make the reflectance lessthan unity.3.2.6 backgroundapparent absorption caused by anythingother than the substance for which the analysis is being made.3.2.7 cellulosi
10、c fiberfiber composed of polymers formedfrom glucose subunits.3.2.8 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).3.2.9 Fourier transforma mathematical operation thatconverts a func
11、tion of one independent variable to one of adifferent independent variable.3.2.9.1 DiscussionIn FT-IR spectroscopy, the Fouriertransform converts a time function (the interferogram) to afrequency function (the infrared absorption spectrum). Spectraldata are collected through the use of an interferom
12、eter, whichreplaces the monochrometer found in the dispersive infraredspectrometer.3.2.10 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-wavenum
13、ber (or wave-length) spectrum.3.2.11 generic classa group of fibers having similar (butnot necessarily identical) chemical composition; a genericname applies to all members of a group and is not protected bytrademark registration.1This guide is under the jurisdiction of ASTM Committee E30 on Forensi
14、cSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Sept. 15, 2010. Published October 2010. Originallyapproved in 2002. Last previous edition approved in 2002 as E2224 02. DOI:10.1520/E2224-10.2For referenced ASTM standards, visit the ASTM web
15、site, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United Sta
16、tes.3.2.11.1 DiscussionGeneric names for manufactured fi-bers include, for example, rayon, nylon, and polyester. Genericnames 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).33.2.12 infr
17、aredpertaining to the region of the electromag-netic spectrum with wavelength range from approximately0.78 to 1000 m (wavenumber range 12 800 to 10 cm-1).3.2.13 infrared spectroscopypertaining to spectroscopy inthe infrared region of the electromagnetic spectrum.3.2.14 internal reflection spectrosco
18、py (IRS)the techniqueof recording optical spectra by placing a sample material incontact with a transparent medium of greater refractive indexand measuring the reflectance (single or multiple) from theinterface, generally at angles of incidence greater than thecritical angle.3.2.15 manufactured (man
19、-made) fibera class name forvarious genera of filament, tow, or staple produced from fiberforming substance which may be (1) polymers synthesizedfrom chemical compound, (2) modified or transformed naturalpolymers, or (3) glass.3.2.16 mid-infraredpertaining to the infrared region of theelectromagneti
20、c spectrum with wavelength range from ap-proximately 2.5 to 25 m (wavenumber range 4000 to 400cm-1).3.2.17 near-infraredpertaining to the infrared region ofthe electromagnetic spectrum with wavelength range fromapproximately 0.78 to 2.5 m (wavenumber range 12 820 to4000 cm-1).3.2.18 spectrometerphot
21、ometric device for the measure-ment of spectral transmittance, spectral reflectance, or relativespectral emittance.3.2.19 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 tere
22、phthalate).3.2.20 transmittance (T)the ratio of radiant power trans-mitted by the sample, I, to the radiant power incident on thesample, Io:T 5 I/Io3.2.21 wavelengththe distance, measured along the line ofpropagation, between two points that are in phase on adjacentwaves.3.2.22 wavenumberthe number
23、of waves per unit length,in a 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
24、 infrared spectrophotometery and microscopeconfigurations. Additional information on infrared and micro-scopical analyses can be found in the sources listed in theBibliography at the end of this guide.4.2 Spectra may also be obtained by a variety of alternativeIR techniques. Other techniques (not co
25、vered in the scope ofthis guideline) include: micro internal reflection spectroscopy(MIR), which differs from attenuated total reflectance (ATR) inthat the infrared radiation is dependent upon the amount ofsample in contact with the surface of the prism (2):4.2.1 Diamond cell (medium or high pressur
26、e) 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 mechanicallyprepared (8).4.2.3 Lead foil technique (6).4.2.4 Micro potassium bromide (micro-KBr) (or other ap-propriate salt)
27、 pellets (9, 10). This list is not meant to be totallyinclusive or exclusive.4.3 This analytical method covers manufactured textilefibers (with the exception of inorganic fibers), including, butnot limited to:Acetate Modacrylic Polyester Vinal (5)Acrylic Novoloid (5) Rayon VinyonAnidel Nylon SaranAr
28、amid Nytril SpandexAzlon (5) Olefin SulfarFluorocarbon Polybenzimidazole(PBI)TriacetateLastrile Polycarbonate RubberAlthough natural fibers may also be analyzed by IR spec-troscopy, they are excluded from this guideline because noadditional discriminating compositional information of thefiber is pro
29、vided 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 among similarly coloredfibers.5. Significance and Use5.1 Fiber samples may be prepared and mounted
30、 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 by comparison of the fiber spectrum with referencespectra.5.2 Consideration should be given to the
31、potential foradditional compositional information that may be obtained byIR spectroscopy over polarized light microscopy alone (seeMicroscopy Guidelines). The extent to which IR spectralcomparison is indicated will vary with specific sample and caseevaluations.5.3 The recommended point for IR analys
32、is in a forensicfiber examination is following visible and ultraviolet (UV)comparison microscopy (fluoresence microscopy), polarizedlight microscopy, and UV/visible spectroscopy, but before dyeextraction for thin-layer chromatography. This list of analyticaltechniques is not meant to be totally incl
33、usive or exclusive.5.4 The following generic types of fiber are occasionallyencountered in routine forensic examinations: Anidel, Fluoro-carbon, Lastrile, Novoloid, Nytril, Polycarbonate, PBI, Sulfar,Vinal, and Vinyon.5.4.1 Exemplar data, reference standards, or examiner ex-perience, or combination
34、thereof, may be inadequate forcharacterization of these fibers by optical microscopical and3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E2224 102microchemical techniques. For these fiber types, IR spectro-scopic confirmation of polymer type is advis
35、able.5.5 Because of the large number of subgeneric classes,forensic examination of acrylic fibers is likely to benefitsignificantly from IR spectral analysis (11).5.6 Colorless manufactured fibers are lacking in the charac-teristics for color comparison available in dyed or pigmentedfibers. The fore
36、nsic examination of these fibers may, therefore,benefit from the additional comparative aspect of IR spectralanalysis.5.7 If polymer identification is not readily apparent fromoptical data alone, an additional method of analysis should beused such as microchemical tests, melting point, pyrolysisinfr
37、ared spectrophotometry, or pyrolysis gas chromatography.Infrared analysis offers the advantage of being the leastdestructive of these methods (12).6. Sample Handling6.1 The general handling and tracking of samples shouldmeet or exceed the requirements of Practice E1492 and GuideE1459.6.2 The quantit
38、y of fiber used and the number of fibersamples 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 or con-cerns, or both.6.3 Sample preparation should be similar
39、for all fibers beingcompared. Fibers should be 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
40、 consideration when makingspectral comparisons (13). Leaving the fiber unflattened, whileallowing crystallinity-sensitive bands to be observed unaltered,results in distortion of peak heights due to variable pathlengths(14). In certain situations, a combination of both approaches isadvisable.6.4 Beca
41、use flattening the fiber is destructive of morphol-ogy, the minimum length of fiber necessary for the analysisshould be used. A typical IR microscope is optimized for a100 m-spot size, thus little beam energy passes through apoint that is farther than 50 m from the center of the field ofview. Hence,
42、 analytical performance will not necessarily beimproved 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, caesium i
43、odide (CsI), barium fluoride (BaF2),zinc selenide (ZnSe), and diamond. The choice of windowmaterial should not reduce the effective spectral range of thedetector being used. When the fiber is mounted between two IRwindows, care must be taken to avoid light by-pass around thefiber; otherwise an inter
44、ference pattern will be introduced inthe spectrum of the sample. Where the fiber is mountedbetween two IR windows, a small KBr crystal should be placednext to the fiber. The background spectrum should be acquiredthrough this crystal to avoid interference fringes, which wouldarise if the spectrum of
45、an air “gap” between the two IRwindows was acquired or if the fringes would distort theratioed 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 or reanalysis
46、, or both, and to prevent spectral con-tamination from stray light that might pass through anotherfiber. It is important that the longitudinal plane (flattenedsurface) of the fiber be as nearly parallel to the IR window orother mount as possible.7. Analysis7.1 A mid-infrared spectrophotometer (FT-IR
47、 is the currentstandard, but dispersive IR is not excluded) and an infraredmicroscope that is compatible with the mid-range spectropho-tometer is recommended (15). The lower frequency cutoff willvary with the microscope detector used (preferably no higherthan 750 cm-1).7.1.1 Useful sample preparatio
48、n accessories include, but arenot limited to, sample supports, infrared windows, presses,dies, rollers, 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 operation
49、al runs. Thismay take up to several hours. It should be noted that mostFT-IR instruments are designed to 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 E1421, Sections 17, 9.5, 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
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