Journal of AOAC Article by Microtrace Scientists
Volume 101, 2018 of The Journal of AOAC International contains a special report devoted to the analysis and application of colorants and optical sensing markers. It features a research article co-authored by three Microtrace scientists: Ethan Groves, Skip Palenik, and Christopher S. Palenik. The article entitled, “A Generalized Approach to Forensic Dye Identification: Development and Utility of Reference Libraries,” approaches the difficult problem of identifying dyestuffs in textile fibers.
In forensic trace evidence examinations of fibers, dye identification often has great evidentiary potential; however, several analytical issues have limited the exploitation of dye identification in casework. These include: the low concentration of dyestuffs in a finished textile, the limited amount of sample available for analysis, the complexity of dye mixtures in a single fiber, and the large number of dyestuffs in commercial use. In the research article, the authors present an approach to dye identification that combines several analytical methods, is applicable to a wide range of dye chemistries, application glasses, and fiber types, and can be scaled down to forensic casework-sized samples. This approach permits the development and implementation of reference libraries to constrain the identity of, and in many cases, identify the dye (or dyes) present in textile fibers.
The full article can be found here.
While color is arguably the most important optical property of evidential fibers, the actual dyestuffs responsible for its expression in them are, in forensic trace evidence examinations, rarely analyzed and still less often identified. This is due, primarily, to the exceedingly small quantities of dye present in a single fiber as well as to the fact that dye identification is a challenging analytical problem, even when large quantities are available for analysis. Among the practical reasons for this are the wide range of dyestuffs available (and the even larger number of trade names), the low total concentration of dyes in the finished product, the limited amount of sample typically available for analysis in forensic cases, and the complexity of the dye mixtures that may exist within a single fiber. Literature on the topic of dye analysis is often limited to a specific method, subset of dyestuffs, or an approach that is not applicable given the constraints of a forensic analysis. Here, we present a generalized approach to dye identification that (1) combines several robust analytical methods, (2) is broadly applicable to a wide range of dye chemistries, application classes, and fiber types, and (3) can be scaled down to forensic casework-sized samples. The approach is based on the development of a reference collection of 300 commercially relevant textile dyes that have been characterized by a variety of microanalytical methods (HPTLC, Raman microspectroscopy, infrared microspectroscopy, UV-Vis spectroscopy, and visible microspectrophotometry). Although there is no single approach that is applicable to all dyes on every type of fiber, a combination of these analytical methods has been applied using a reproducible approach that permits the use of reference libraries to constrain the identity of and, in many cases, identify the dye (or dyes) present in a textile fiber sample.
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