This article reports a method for the extraction and subsequent analysis of dyes directly from fibers.
Colorants from dyes observed on fibers and hairs in trace evidence examinations are commonly compared via polarized light microscopy, comparison microscopy, microspectrophotometry, and in some cases, chromatography. Some of the most difficult samples to evaluate and compare by these methods include lightly dyed fibers (which result in a “noisy” and nearly featureless spectrum due to a low signal-to-noise ratio), heavily dyed fibers (resulting in the nearly complete absorption of the incident illumination), and heterogeneously dyed fibers, e.g., vegetable fibers, which provide a range of spectral intensities that complicate interpretation. Here the authors present a method for the extraction and subsequent analysis of dyes directly from fibers. This approach relies upon the use of a borosilicate glass flat microcapillary cell (i.e., a low volume, fixed-path length cell) to hold the extract that can then be analyzed by a microspectrophotometer (MSP). This capillary microspectrophotometry (cMSP) method provides a means to obtain reproducible spectra of the dyes from many problematic fibers. (publisher abstract modified)