Microspectrophotometry is a quick, accurate, and reproducible method to compare colored fibers for forensic purposes. Applying chemometric techniques to spectroscopic data can provide valuable information, especially when looking at a complex dataset. In the current project, systematic changes in the wavelength of maximum absorption, peak shape, and signal-to-background ratio were noted as dye loading increased. In general, classifying the samples into 10 groups (one for each exemplar) had poor accuracy (i.e., 51 percent); however, classification was more accurate (i.e., 96 percent) using three classes of fibers that were identified by AHC as having low (0.10-0.20 wt percent), medium (0.40-0.75 wt percent), and high (1.5-3.5 wt percent) dye loadings. An external validation with additional fibers and data generated by independent analysts confirmed these findings. Lastly, it was also possible to discriminate pairs of exemplars with small differences in dye loadings as a simulation of questioned (Q) versus known (K) comparisons. (publisher abstract modified)
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