ASTM E2224-02

Standard Guide for Forensic Analysis of Fibers by Infrared Spectroscopy

SIGNIFICANCE AND USE
Fiber samples may be prepared and mounted for microscopical infrared analysis by a variety of techniques. Infrared spectra of fibers are obtained using an IR spectrophotometer coupled with an IR microscope. Fiber polymer identification is made by comparison of the fiber spectrum with reference spectra.
Consideration should be given to the potential for additional compositional information that may be obtained by IR spectroscopy over polarized light microscopy alone (see Microscopy Guidelines). The extent to which IR spectral comparison is indicated will vary with specific sample and case evaluations.
The recommended point for IR analysis in a forensic fiber examination is following visible and UV comparison microscopy (fluoresence microscopy), polarized light microscopy, and UV/visible spectroscopy, but before dye extraction for thin-layer chromatography. This list of analytical techniques is not meant to be totally inclusive or exclusive.
The following generic types of fiber are occasionally encountered in routine forensic examinations: Anidex, Fluorocarbon, Lastrile, Novoloid, Nytril, Polycarbonate, PBI, Sulfar, Vinal, and Vinyon.
Exemplar data, reference standards, and/or examiner experience may be inadequate for characterization of these fibers by optical microscopical and microchemical techniques. For these fiber types, IR spectroscopic confirmation of polymer type is advisable.
Because of the large number of subgeneric classes, forensic examination of acrylic fibers is likely to benefit significantly from IR spectral analysis (11).
Colorless manufactured fibers are lacking in the characteristics for color comparison available in dyed or pigmented fibers. The forensic examination of these fibers may, therefore, benefit from the additional comparative aspect of IR spectral analysis.
If polymer identification is not readily apparent from optical data alone, an additional method of analysis should be used such as microchemical tests, melting point, p...
SCOPE
1.1 Infrared (IR) spectrophotometery is a valuable method of fiber polymer identification and comparison in forensic examinations. The use of IR microscopes coupled with Fourier transform infrared (FT-IR) spectrometers has greatly simplified the IR analysis of single fibers, thus making the technique feasible for routine use in the forensic laboratory.
1.2 This guideline is intended to assist individuals and laboratories that conduct forensic fiber examinations and comparisons in the effective application of infrared spectroscopy to the analysis of fiber evidence. Although this guide is intended to be applied to the analysis of single fibers, many of its suggestions are applicable to the infrared analysis of small particles in general.

General Information

• Status: Historical
• Publication Date: 09-Jul-2002
• ICS: 07.140 - Forensic science
• ICS: 71.040.50 - Physicochemical methods of analysis
• Technical Committee: E30 - Forensic Sciences
• Drafting Committee: E30.01 - Criminalistics

Relations

• Replaced By: ASTM E2224-10 - Standard Guide for Forensic Analysis of Fibers by Infrared Spectroscopy
• Effective Date: 15-Sep-2010
• Referred By: ASTM E3233-20 - Standard Practice for Forensic Tape Analysis Training Program
• Effective Date: 10-Jul-2002
• Referred By: ASTM E2225-23 - Standard Guide for Forensic Examination of Fabrics and Cordage
• Effective Date: 10-Jul-2002
• Referred By: ASTM E3260-21 - Standard Guide for Forensic Examination and Comparison of Pressure Sensitive Tapes
• Effective Date: 10-Jul-2002
• Referred By: ASTM E1732-22 - Standard Terminology Relating to Forensic Science
• Effective Date: 10-Jul-2002
• Referred By: ASTM E2227-23e1 - Standard Guide for Forensic Examination of Dyes in Textile Fibers by Thin-Layer Chromatography
• Effective Date: 10-Jul-2002
• Referred By: ASTM F3416-21 - Standard Guide for Using Fourier Transform Infrared Spectrometry to Evaluate Synthetic Equine Surface Components
• Effective Date: 10-Jul-2002
• Referred By: ASTM E3085-17 - Standard Guide for Fourier Transform Infrared Spectroscopy in Forensic Tape Examinations
• Effective Date: 10-Jul-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E2224–02
Standard Guide for
Forensic Analysis of Fibers by Infrared Spectroscopy
This standard is issued under the fixed designation E2224; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.5 attenuated total reflection (ATR)—reflection that occurs
when an absorbing coupling mechanism acts in the process of
1.1 Infrared (IR) spectrophotometery is a valuable method
total internal reflection to make the reflectance less than unity.
of fiber polymer identification and comparison in forensic
3.6 background—apparent absorption caused by anything
examinations.The use of IR microscopes coupled with Fourier
other than the substance for which the analysis is being made.
transforminfrared(FT-IR)spectrometershasgreatlysimplified
3.7 cellulosic fiber—fiber composed of polymers formed
the IR analysis of single fibers, thus making the technique
from glucose subunits.
feasible for routine use in the forensic laboratory.
3.8 far-infrared—pertaining to the infrared region of the
1.2 This guideline is intended to assist individuals and
electromagnetic spectrum with wavelength range from ap-
laboratories that conduct forensic fiber examinations and
-1
proximately25to300µm(wavenumberrange400to30cm ).
comparisons in the effective application of infrared spectros-
3.9 Fourier transform—a mathematical operation that con-
copy to the analysis of fiber evidence. Although this guide is
verts a function of one independent variable to one of a
intended to be applied to the analysis of single fibers, many of
different independent variable. In FT-IR spectroscopy, the
its suggestions are applicable to the infrared analysis of small
Fourier transform converts a time function (the interferogram)
particles in general.
to a frequency function (the infrared absorption spectrum).
2. Referenced Documents Spectraldataarecollectedthroughtheuseofaninterferometer,
which replaces the monochrometer found in the dispersive
2.1 ASTM Standards:
infrared spectrometer.
E1421 Practice for Describing and Measuring Performance
3.10 Fourier transform infrared (FT-IR) spectrometry—a
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
form of infrared spectrometry in which an interferogram is
eters: Level Zero and Level One Tests
obtained; this interferogram is then subjected to a Fourier
E1459 Guide for Physical Evidence Labeling and Related
transformation to obtain an amplitude-wavenumber (or wave-
Documentation
length) spectrum.
E1492 Practice for Receiving, Documenting, Storing, and
3.11 generic class—agroupoffibershavingsimilar(butnot
Retrieving Evidence in a Forensic Science Laboratory
necessarily identical) chemical composition. A generic name
3. Terminology
applies to all members of a group and is not protected by
trademark registration. Generic names for manufactured fibers
3.1 absorbance (A)—the logarithm to the base 10 of the
include, for example, rayon, nylon, and polyester. (Generic
reciprocal of the transmittance, (T); A = log (1/T) = -log T.
10 10
names to be used in the United States for manufactured fibers
3.2 absorption band—a region of the absorption spectrum
were established as part of the Textile Fiber Products Identifi-
in which the absorbance passes through a maximum.
cation Act enacted by Congress in 1954 (1).
3.3 absorption spectrum—a plot, or other representation, of
3.12 infrared—pertaining to the region of the electromag-
absorbance,oranyfunctionofabsorbance,againstwavelength,
netic spectrum with wavelength range from approximately
or any function of wavelength.
-1
0.78 to 1000 µm (wavenumber range 12 800 to 10 cm ).
3.4 absorptivity (a)—absorbance divided by the product of
3.13 infrared spectroscopy—to spectroscopy in the infrared
the sample pathlength (b) and the concentration of the absorb-
region of the electromagnetic spectrum.
ing substance (c); a = A/bc
3.14 internal reflection spectroscopy (IRS)—the technique
of recording optical spectra by placing a sample material in
This guide is under the jurisdiction of ASTM Committee E30 on Forensic
contact with a transparent medium of greater refractive index
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
Current edition approved July 10, 2002. Published September 2002. DOI:
10.1520/E2224-02.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to the list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2224–02
and measuring the reflectance (single or multiple) from the 4.3 This analytical method covers manufactured textile
interface, generally at angles of incidence greater than the fibers (with the exception of inorganic fibers), including, but
critical angle. not limited to:
Acetate Modacrylic Polyester Vinal (5)
3.15 manufactured (man-made) fiber—any fiber derived by
Acrylic Novoloid (5) Rayon Vinyon
a process of manufacture from any substance that, at any point
Anidex Nylon Saran
in the manufacturing process, is not a fiber. Aramid Nytril Spandex
Azlon (5) Olefin Sulfar
3.16 mid-infrared—pertaining to the infrared region of the
Fluorocarbon Polybenzimidazole Triacetate
electromagnetic spectrum with wavelength range from ap- (PBI)
Lastrile Polycarbonate Rubber
proximately 2.5 to 25 µm (wavenumber range 4000 to 400
-1
cm ). Although natural fibers may also be analyzed by IR spec-
troscopy, they are excluded from this guideline because no
3.17 near-infrared—pertaining to the infrared region of the
additional discriminating compositional information of the
electromagnetic spectrum with wavelength range from ap-
fiber is provided over that yielded by light microscopy.
proximately0.78to2.5µm(wavenumberrange12 820to4000
-1 However, infrared spectrophotometery may provide signifi-
cm ).
cantlyusefulinformationiftherearedyespresentinthenatural
3.18 spectrometer—photometric device for the measure-
fiber and can serve to distinguish among similarly colored
ment of spectral transmittance, spectral reflectance, or relative
fibers.
spectral emittance.
5. Significance and Use
3.19 subgeneric class—a group of fibers within a generic
class that share the same polymer composition. Subgeneric
5.1 Fiber samples may be prepared and mounted for micro-
names include, for example, nylon 6, nylon 6,6, and poly(eth-
scopical infrared analysis by a variety of techniques. Infrared
ylene terephthalate). spectra of fibers are obtained using an IR spectrophotometer
coupled with an IR microscope. Fiber polymer identification is
3.20 transmittance (T)—the ratio of radiant power transmit-
made by comparison of the fiber spectrum with reference
ted by the sample, I, to the radiant power incident on the
spectra.
sample, I ; T = I/I
o o
5.2 Consideration should be given to the potential for
3.21 wavelength—the distance, measured along the line of
additional compositional information that may be obtained by
propagation, between two points that are in phase on adjacent
IR spectroscopy over polarized light microscopy alone (see
waves.
Microscopy Guidelines). The extent to which IR spectral
3.22 wavenumber—the number of waves per unit length, in
comparisonisindicatedwillvarywithspecificsampleandcase
-1
a vacuum, usually given in reciprocal centimeters, cm .
evaluations.
5.3 The recommended point for IR analysis in a forensic
4. Summary of Guide
fiber examination is following visible and UV comparison
microscopy (fluoresence microscopy), polarized light micros-
4.1 This guideline covers identification of fiber polymer
copy, and UV/visible spectroscopy, but before dye extraction
compositionbyinterpretationofabsorptionspectraobtainedby
for thin-layer chromatography. This list of analytical tech-
infrared microspectroscopy. It is intended to be applicable to a
niques is not meant to be totally inclusive or exclusive.
wide range of infrared spectrophotometery and microscope
5.4 The following generic types of fiber are occasionally
configurations.
encountered in routine forensic examinations:Anidex, Fluoro-
4.2 Spectra may also be obtained by a variety of alternative
carbon, Lastrile, Novoloid, Nytril, Polycarbonate, PBI, Sulfar,
IR techniques. Other techniques (not covered in the scope of
Vinal, and Vinyon.
this guideline) include: micro internal reflection spectroscopy
5.5 Exemplar data, reference standards, and/or examiner
(MIR),whichdiffersfromattenuatedtotalreflectance(ATR)in
experience may be inadequate for characterization of these
that the infrared radiation is dependent upon the amount of
fibers by optical microscopical and microchemical techniques.
sample in contact with the surface of the prism (2): Forthesefibertypes,IRspectroscopicconfirmationofpolymer
type is advisable.
4.2.1 Diamond cell (medium or high pressure) used with a
5.6 Because of the large number of subgeneric classes,
beam condenser (3-5) (This combination is frequently used
forensic examination of acrylic fibers is likely to benefit
with a spectrophotometer configured for mid- and far-IR).
significantly from IR spectral analysis (11).
4.2.2 Thin films: solvent (6,7), melt (4), or mechanically
5.7 Colorless manufactured fibers are lacking in the charac-
prepared (8).
teristics for color comparison available in dyed or pigmented
4.2.3 Lead foil technique (6).
fibers. The forensic examination of these fibers may, therefore,
4.2.4 Micro-KBr (or other appropriate salt) pellets (9,10). benefit from the additional comparative aspect of IR spectral
This list is not meant to be totally inclusive or exclusive. analysis.
E2224–02
5.8 If polymer identification is not readily apparent from 7. Analysis
optical data alone, an additional method of analysis should be
7.1 A mid-infrared spectrophotometer (FT-IR is the current
used such as microchemical tests, melting point, pyrolysis
standard, but dispersive IR is not excluded) and an infrared
infrared spectrophotometry, or pyrolysis gas chromatography.
microscope that is compatible with the mid-range spectropho-
Infrared analysis offers the advantage of being the least
tometer is recommended. The lower frequency cutoff will vary
destructive of these methods.
with the microscope detector used (preferably no higher than
-1
750 cm ).
6. Sample Handling
7.1.1 Useful sample preparation accessories include, but are
6.1 The general handling and tracking of samples should
not limited to, sample supports, infrared windows, presses,
meet or exceed the requirements of Practice E1492 and Guide
dies, rollers, scalpels, and etched-tungsten probes.
E1459.
7.2 All spectrophotometer and microscope components
6.2 The quantity of fiber used and the number of fiber
shouldbeturnedonandallowedtoreachthermalstabilityprior
samples required will differ according to:
to commencement of calibration and operational runs. This
6.2.1 Specific technique and sample preparation,
may take up to several hours. It should be noted that most
6.2.2 Sample homogeneity,
FT-IR instruments are designed to work best when left on or in
6.2.3 Condition of the sample, and
the standby mode 24 hours a day.
6.2.4 Other case dependent analytical conditions and/or
7.3 It is essential that instrument performance and calibra-
concerns.
tion be evaluated routinely, at least once a month, in a
6.3 Sample preparation should be similar for all fibers being
comprehensive manner.
compared. Fibers should be flattened prior to analysis in order
to obtain the best quality absorption spectra. Flattening the 7.4 The preferred performance evaluation method is in
accordance with Practice E1421, Sections 1–7, 9.5, and 9.5.1.
fibers can alter the crystalline/amorphous structure of the fiber
and result in minor differences in peak frequencies and In brief, this includes:
intensities.This must be taken into consideration when making
7.4.1 System throughput,
spectral comparisons (12). Leaving the fiber unflattened, while
7.4.2 Single-beam spectrum,
allowing crystallinity-sensitive bands to be observed unaltered,
7.4.3 100 % T line, and
results in distortion of peak heights due to variable pathlengths
7.4.4 Polystyrene reference spectrum.
(13). In certain situations, a combination of both approaches is
7.5 The apertures that control the areas (fields) of sample
advisable.
illumination and detector measurement in an IR microscope
6.4 Because flattening the fiber is destructive of morphol-
may be of fixed or variable size, and may be either rectangular
ogy, the minimum length of fiber necessary for the analysis
or circular in shape. Variable rectangular apertures are recom-
should be used.Atypical IR microscope is optimized for a 100
mended, because they can be more closely matched to the fiber
µm-spot size, thus little beam energy passes through a point
shape. Light throughput, stray light reduction, and aperture
that is farther than 50 µm from the center of the field of view.
focus in the sample image plane are some of the considerations
Hence, analytical performance will not necessarily be im-
in selecting aperture parameters and positioning. Fiber width,
proved with the use of fibers greater than 100 µm in length.
flatness, and linearity will usually limit the size of the illumi-
6.5 The flattened fiber may be mounted across an aperture,
nation and detector apertures used for analysis. In general, the
on an IR window, or between IR windows. Common IR
illuminating and detector fields should lie within the bound-
window materials used for this purpose include, but are not
aries of the fiber edges.
limited to, KBr, CsI, BaF , ZnSe, and diamond. The choice of
7.6 Not all systems provide for the control of both illumi-
window material should not reduce the effective spectral range
nation and detector measurement fields; the following recom-
of the detector being used. When the fiber is mounted between
mendations can be modified to suit the constraints of a
two IR windows, care must be taken to avoid light by-pass
particular system design.
around the fiber; otherwise an interference pattern will be
7.7 The objective and/or condenser should be adjusted (if
introduced in the spectrum of the sample. Where the fiber is
possible) for any IR window that lies between the optic and the
mounted between two IR windows, a small KBr crystal should
sample in the beam path. This compensation reduces spherical
beplacednexttothefiber.Thebackgroundspectrumshou
...