Identifying Material Evidence From Crime Scene Carpets | Chemical & Engineering News
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Web Date: November 9, 2012

Identifying Material Evidence From Crime Scene Carpets

Forensic Science: Technique could help pinpoint fiber and dye makeup
Department: Science & Technology
News Channels: Analytical SCENE
Keywords: forensic science, mass spectrometry, fibers, TOF-SIMS
Forensic Fingerprint
New mass spectrometry technique can analyze the chemical makeup of the cross section of fibers to identify the fiber material in this case nylon (yellow, left) and the dye, which here is acid blue (blue, right).
Credit: Anal. Chem.
Two image from paper showing cross section of fibers.
Forensic Fingerprint
New mass spectrometry technique can analyze the chemical makeup of the cross section of fibers to identify the fiber material in this case nylon (yellow, left) and the dye, which here is acid blue (blue, right).
Credit: Anal. Chem.

Forensic scientists may have a new tool to analyze suspicious fibers from crime scenes. The mass spectrometry method identifies dyes on nylon, a common carpet material (Anal. Chem., DOI: 10.1021/ac3025569).

The technique could provide backup for existing forensic fiber analysis techniques, allowing investigators to compare fibers from crime scenes with those associated with suspects. This new method also consumes a very small amount of the evidence, says David Hinks, a textile chemist at North Carolina State University, who developed the method with chemist Chuanzhen Zhou and others.

“Sometimes you get very little evidence from a crime scene. We want to minimize destruction of fiber evidence, especially when it is trace evidence,” Zhou says.

With funding from the National Institute of Justice, the team developed the method, which involves first cleaning residues off the fiber’s surface using a beam of ionized C60 fullerenes. Then the researchers use time-of-flight secondary ion mass spectrometry (TOF-SIMS) to analyze the chemical fingerprint of the dye, fiber, and any trace chemicals on the fiber’s surface.

Most forensic labs currently employ polarized light microscopy to identify fibers. Some labs then extract the dye from the fiber and analyze it by thin-layer chromatography, Hinks says.

By analyzing fiber and dye at the same time with the new technique, researchers can also identify trace contaminants in the material from its industrial production process. Identifying these compounds could give investigators an idea of which company produced a particular piece of material, which would then improve the accuracy of comparisons of fibers found at a crime scene to ones from a suspect, he says.

“I’d like to see this applied to a real forensic case,” comments University of Manchester mass spectrometry expert John Vickerman. He agrees that TOF-SIMS could be useful for forensic scientists. “They’ve shown what might be possible, but it is not yet a proof of principle for all cases,” he adds.

Textile conservation scientist Mehdi Moini at the Smithsonian Museum Conservation Institute sees potential for the new technique in cultural heritage research, where scientists also want to minimize destruction of samples.

“Many forensic and conservation scientists shy away from using these ‘destructive techniques’ because they consume a small amount of the specimen,” he says. However, this work, he adds, “clearly demonstrates that the amount of accurate information obtained from these techniques justifies their minimally destructive nature.”

The North Carolina State team is now extending the method to polyester and cotton.

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
ROBERT BLACKLEDGE ACS ID: rblackle (September 19, 2018 9:47 PM)
There is an area of forensic fiber identification/comparison that has existed for decades but is still virtually ignored by the forensic fiber/fibre trace evidence specialists. Whether it be items of clothing, carpeting, draperies, or upholstery fabrics, most fabric items today have been treated with one or more surface-modifying chemicals. These extremely thin layers do not noticeably change the fabrics' appearance, microscopic image (including SEM), feel (hand), or draping characteristics. These layers are so thin that measurements such as a fiber's refractive index, infrared and Raman spectra, etc. are not noticeably changed. Even with pyrolysis gas chromatography-mass spectrometry the contributions from the pyrolysis fragments from the surface-modifying polymer layers on a single fiber (typical fiber trace evidence sample)are so small that they are lost in the noise. Were forensic science identifying and characterizing such surface modifications, it would greatly add to the ability to distinguish between fibers that have the same fiber core (examples - cotton and nylon fibers). [These surface modifications are often fluorocarbons. See Poster ThP 241 ASMS 2018.]

I would very much appreciate it if you would write a brief article pointing out this limitation. Some work in this area has been done, but it has been ignored by the world-wide forensic science community. and especially by the major U.S. Government forensic research funding agency, the National Institute of Justice.

The analytical method that on a single fiber basis both detects and chemically characterizes these very thin surface modification layers is X-ray Photoelectron Spectroscopy (XPS). If this interests you, I can provide you XPS results on fibers that have/have not received surface modifications, or fibers having the same core (cotton), but either do/do not have surface modification layers, or have different surface modifications from different manufacturers.

These XPS results have been reported by me at annual meetings of the American Academy of Forensic Science (AAFS) and semi-annual seminars of the California Association of Criminalists (ACS). Additionally, research grant proposals submitted (in collaboration with research university professors in different years to the NIJ have been turned down.

Why were they turned down? Although the reviewers' comments did not specifically say so, at that time no XPS instruments were in any forensic laboratories (I believe the FBI know has one), plus a full-service XPS system would cost ~ $500,000.

The above paragraph illustrates another problem that bedevils the forensic science community.
The majority of ambitious hard-chargers who volunteer to serve on research grant application review committees believe that all examinations of forensic physical evidence should be conducted by forensic laboratories rather than by specialists in advance analytical techniques at research universities. I disagree. Other than perhaps the FBI Lab, it would make no sense for forensic labs to acquire such specialized and complex instrumentation. Not only would it make no sense in terms of acquisition costs, annual costs, maintenance, and training costs. In a typical forensic lab, cases requiring such instruments would be rare, so with each one there would be a learning curve.

Robert ('Bob') D. Blackledge
Forensic Chemist Consultant
8365 Sunview Drive
El Cajon, CA 92021


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