Dyes at the Molecular Level Help ID Fibers

Through the National Criminal Justice Reference Service, NIJ has made available the following final technical report (this report is the result of an NIJ-funded project but was not published by the U.S. Department of Justice): Validation of Forensic Characterization and Chemical Identification of Dyes Extracted from Millimeter-length Fibers (pdf, 142 pages)

Stephen L. Morgan Ph.D.

The ubiquitous nature of textile fibers provides an information-rich evidence source for crime scene investigations. However, in cases of similarly dyed fibers, current fiber analysis techniques do not provide adequate chemical information for unambiguous match determinations to be made. The standard procedure for analyzing forensic textile fibers involves measurement of physical and optical properties in an attempt to exclude matches of known and questioned fibers, followed by visual color matching and infrared (IR) spectroscopy and UV/visible spectral comparisons.

The challenge of analyzing dye extracts from forensic fibers stems from the need to preserve the evidence as much as possible. Extraction of dyes is destructive to the fiber, and recovered trace evidence fibers are often as small as 2 mm in length and contain as little as 2 ng of dye2, thus very sensitive analysis techniques are needed.

The objective of this research was to validate analytical methods for the forensic chemical characterization of dyes extracted from trace evidence fibers, thereby enhancing discrimination for comparison of known and questioned casework fibers. This study focused on determining the optimum extraction conditions for each dye class and developing chromatographic methods with suitable resolution and sensitivity for trace analysis.

The author found that modern instrumental analysis of separated dye components increases the reliability of fiber examinations by providing discriminating information on dye characterization and allowing for possible identification of dyes at the molecular level from trace evidence fibers as small as 0.5 mm.

Download a PDF of this report. 

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