ASTM E2224-23ae1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: E2224 − 23a An American National Standard
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.
ε NOTE—Subsections 5.2 and 5.6.2 were editorially updated in October 2023.
1. Scope priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 Infrared (IR) spectroscopy is a valuable method of fiber
1.7 This international standard was developed in accor-
polymer identification and comparison in forensic examina-
dance with internationally recognized principles on standard-
tions. The use of IR microscopes, coupled with Fourier
ization established in the Decision on Principles for the
transform infrared (FTIR) spectrometers, has greatly simplified
Development of International Standards, Guides and Recom-
the IR analysis of single fibers, thus making the technique
mendations issued by the World Trade Organization Technical
feasible for routine use in the forensic laboratory. This guide
Barriers to Trade (TBT) Committee.
provides basic recommendations and information about IR
spectrometers and accessories, with an emphasis on sampling
2. Referenced Documents
techniques specific to fiber examinations. The particular meth-
od(s) employed by each examiner or laboratory will depend 2.1 ASTM Standards:
upon available equipment, examiner training, sample D123 Terminology Relating to Textiles
suitability, and sample size. E131 Terminology Relating to Molecular Spectroscopy
E620 Practice for Reporting Opinions of Scientific or Tech-
1.2 This guide is intended for examiners with a basic
nical Experts
knowledge of the theory and practice of IR spectroscopy, as
E1421 Practice for Describing and Measuring Performance
well as experience in the handling and forensic examination of
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
fibers. In addition, this guide is to be used in conjunction with
eters: Level Zero and Level One Tests
a broader analytical scheme.
E1459 Guide for Physical Evidence Labeling and Related
1.3 If polymer identification is not readily apparent from
Documentation
optical data alone, an additional method of analysis, such as
E1492 Practice for Receiving, Documenting, Storing, and
microchemical tests, melting point, IR spectroscopy, Raman
Retrieving Evidence in a Forensic Science Laboratory
spectroscopy, or pyrolysis gas chromatography, should be
E2228 Guide for Microscopical Examination of Textile Fi-
used. An advantage of IR spectroscopy is that the instrumen-
bers
tation is readily available in most forensic laboratories and the
E2917 Practice for Forensic Science Practitioner Training,
technique is minimally destructive.
Continuing Education, and Professional Development
1.4 Units—The values stated in SI units are to be regarded Programs
as standard. No other units of measurement are included in this
2.2 Other Documents:
standard.
ISO 17025 Testing and calibration laboratories
1.5 This standard is intended for use by competent forensic
science practitioners with the requisite formal education, 3. Terminology
discipline-specific training (see Practice E2917), and demon-
3.1 Definitions—For definitions of terms used in this guide,
strated proficiency to perform forensic casework.
refer to Terminologies D123 and E131.
1.6 This standard does not purport to address all of the
3.2 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This guide is under the jurisdiction of ASTM Committee E30 on Forensic contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved May 1, 2023. Published May 2023. Originally the ASTM website.
approved in 2002. Last previous edition approved in 2023 as E2224 – 23. DOI: Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/E2224-23AE01. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E2224 − 23a
3.2.1 aperture, n—an opening in an optical system that 3.2.12 sub-generic class, n—a group of fibers within a
controls the amount of light passing through a system. generic class that share the same base-polymer composition;
sub-generic names include, for example, nylon 6 and nylon 6,6.
3.2.2 attenuated total reflection (ATR), n—a method of
spectrophotometric analysis based on the reflection of energy
4. Summary of Guide
at the interface of two media which have different refractive
4.1 This guide covers the collection and comparison of IR
indices and are in intimate contact with each other.
absorption spectra obtained from fibers and can be applied to a
3.2.3 background, n—apparent absorption caused by any-
wide range of IR spectrometers and accessory configurations.
thing other than the substance for which the analysis is being
This guide is not meant to be the first step in the process of a
made. E131
fiber examination (4).
3.2.4 cellulosic fiber, n—fiber composed of polymers
4.2 This guide focuses on the classification of manufactured
formed from glucose subunits (for example, vegetable, rayon/
textile fiber types (with the exception of inorganic fibers).
Lyocell).
Although natural fibers can also be analyzed by IR
3.2.5 delustrant, n—a pigment, usually titanium dioxide,
spectroscopy, light microscopy is the primary method for the
used to dull the luster of a manufactured fiber. E2228
classification of natural fiber types.
3.2.6 diffraction, n—phenomenon that arises as a result of
5. Significance and Use
passing radiation through the “lens” of the microspectrometer
and past the edges of objects such as apertures and the
5.1 This guide is designed to assist an examiner in the
specimen. It causes radiation to deviate from its usually
selection of appropriate sample preparation methods for the
straight line causing blurring of what should be sharp images
analysis, comparison, and identification of fibers using IR
(1).
spectroscopy. IR spectroscopy can provide additional compo-
sitional information than is obtained using polarized light
3.2.7 exclusionary difference—a difference in one or more
microscopy alone. The extent to which IR spectral comparison
characteristics between compared items that is sufficient to
is conducted will vary with specific sample and case evalua-
determine that the compared items did not originate from the
tions.
same source, are not the same source, or do not share the same
composition or classification.
5.2 IR analysis should follow visible and fluorescence
3.2.7.1 Discussion—What is sufficient depends on the per-
comparison microscopy, polarized light microscopy, and ultra-
formance and limitations of the method used on the material in
violet (UV)/visible spectroscopy. If no exclusionary differ-
question. (2)
ences are noted between the known and unknown samples in
3.2.8 generic class, n—as used with textile fibers, a group- optical properties, then proceed to IR spectroscopy as the next
ing having similar chemical compositions or specific chemical step in the analytical scheme, as applicable.
characteristics. D123
NOTE 1—IR analysis generally follows the aforementioned techniques
3.2.8.1 Discussion—A generic name applies to all members
since sample preparation (for example, flattening) irreversibly changes
of a group and is not protected by trademark registration.
fiber morphology.
Generic names for manufactured fibers include, for example,
5.3 IR spectroscopy should be conducted before dye extrac-
rayon, nylon, and polyester. Generic names used in the United
tion for chromatography due to the semi-destructive nature of
States for manufactured fibers were established as part of the
the extraction technique. Because of the large number of
Textile Fiber Products Identification Act enacted by Congress
sub-generic classes, forensic examination of acrylic and mo-
in 1954 (3).
dacrylic fibers is likely to benefit significantly from IR spectral
3.2.9 interference fringes, n—the pattern that results from
analysis (5). Useful distinctions between subtypes of nylon and
constructive and destructive interference of light waves.
polyester fibers can also be made by IR spectroscopy.
3.2.10 manufactured fiber, n—a class name for various
5.4 IR spectroscopy can provide molecular information
genera of filament, tow, or staple produced from fiber-forming
regarding major organic and inorganic components. Compo-
substances which can be (1) polymers synthesized from
nents in lesser amounts are typically more difficult to identify.
chemical compounds, (2) modified or transformed natural
Reasons for this include interference of the absorption bands of
polymers, or (3) glass.
the major components with the less-intense bands of minor
3.2.10.1 Discussion—Acrylic, nylon, polyester, olefin,
components, and sensitivity issues whereby the minor compo-
urethane, and polyvinyl are examples of fiber synthesized from
nents are present at concentrations below the detection limits of
chemical compounds. Cellulose-based fibers, such as acetate
the instrument.
and rayons, and alginate fibers are examples of modified or
5.5 Fiber samples are prepared and mounted for microscopi-
transformed polymers. D123
cal IR analysis by a variety of techniques. IR spectra of fibers
3.2.11 mid-infrared, n—pertaining to the IR region of the
are obtained using an IR spectrometer coupled with an IR
electromagnetic spectrum with wavelength range from ap-
microscope, ATR, or diamond compression cell with beam
proximately 2.5 to 25 μm (wavenumber range approximately
condenser.
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4000 to 400 cm ).
5.6 IR spectroscopy can be used to obtain spectra for
elucidation of the chemical composition of the fiber and for
The boldface numbers in parentheses refer to a list of references at the end of
this standard. comparison of two or more fiber samples.
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E2224 − 23a
5.6.1 When used to characterize the fiber type, the spectrum surface technique, contaminants on the surface of the fiber can
can be compared to reference spectra obtained from authenti- make a more significant contribution to the spectrum as
cated samples or reference standards. compared to using a transmission method.
5.6.2 When used for spectral comparisons, the objective is
6.7 The flattened fiber can be mounted across an aperture,
to determine whether any exclusionary differences exist be-
on an IR window, or between IR windows. The choice of
tween the samples.
window material should not reduce the effective spectral range
of the detector being used. Common IR window materials used
6. Sample Handling
for this purpose include, but are not limited to, potassium
6.1 The general collection, handling and tracking of
bromide (KBr), cesium iodide (CsI), barium fluoride (BaF ),
samples should meet or exceed the requirements of Practice
zinc selenide (ZnSe), and diamond. When the fiber is mounted
E1492 and Guide E1459.
between two IR windows, a small KBr crystal should be placed
next to the fiber. The background spectrum should be acquired
6.2 The work area and tools used for the preparation of
through this crystal to avoid interference fringes that would
samples shall be free of any materials that could transfer to the
arise if the spectrum were acquired through the air gap between
sample.
the two IR windows.
6.2.1 Useful sample preparation accessories include, but are
not limited to, forceps, sample supports, IR windows, presses,
6.8 When several fibers are mounted on or in a single
dies, rollers, scalpels, and tungsten probes.
mount, they should be physically separated so that their
positions can be unambiguously documented for later retrieval,
6.3 The quantity of fiber used and the number of fiber
samples required will differ according to the following: reanalysis, or both, and to prevent spectral contamination from
stray light that might pass through another fiber.
6.3.1 Specific technique and sample preparation,
6.3.2 Sample composition (for example, fabrics comprised
of multiple fiber types),
7. Analysis
6.3.3 Condition of the sample, and
7.1 Equipment:
6.3.4 Other case-dependent analytical conditions, concerns,
7.1.1 A mid-infrared spectrometer (FTIR is the current
or both.
standard, but dispersive IR is not excluded) and an IR
6.4 When necessary to ensure reproducibility and evaluate
microscope that is compatible with the spectrometer or dia-
intra-sample variations, repeat analysis of samples is
mond compression cell with beam condenser are recommended
recommended, if possible. The number of replicates is depen-
(8). The lower frequency cutoff varies with the microscope
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dent on factors such as sample size, composition, and
detector used, and should be no higher than 750 cm .
condition, and is evaluated on a case-by-case basis.
7.2 Instrument Parameters:
6.5 IR analysis can be performed using either transmittance
7.2.1 All spectrometer and microscope components should
or reflectance. These measurements can be taken with a variety
be turned on and allowed to reach thermal stability prior to
of equipment configurations and accessories, the most common
commencement of performance verification and operational
being the use of a diamond compression cell, ATR or an IR
runs. It should be noted that some FTIR instruments are
microscope.
designed to work best when left on or in the standby mode
6.5.1 ATR, also known as internal reflection spectroscopy
24 hours a day. Refer to the manufacturer’s guidelines for the
(IRS), is a rapid sampling method that enables the examiner to
optimum performance of their instruments.
collect IR spectra from manufactured textile fibers with mini-
7.2.2 It is essential that instrument performance be evalu-
mal sample preparation.
ated routinely (for example, once a month or before use, if used
less frequently), in a comprehensive manner, and according to
6.6 Fiber samples being compared shall be prepared and
the laboratory’s operation manual or the manufacturer’s guide-
analyzed in the same manner. Generally, fibers should be
lines.
flattened prior to analysis. The sample needs to be thin enough
7.2.3
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