Discrimination of Colorless Fibers by UV-VIS Microspectrophotometry and Microspectrofluorimetry

Fiber evidence is frequently encountered in forensic casework, and part of a typical fiber analytical scheme involves the detailed study of the color and other physical properties, optical properties, and chemical composition of the fibers in question. Microspectrophotometry (MSP) is commonly used to provide objective color measurements of fibers, eliminating subjectivity that may be present in visual color examinations. MSP can produce color measurements over the ultraviolet (UV) and visible (VIS) regions of the electromagnetic spectrum, as well as emission spectra from fluorescence measurements. In this research, colorless fibers were analyzed by MSP, using both transmission measurements in the UV-VIS region and fluorescence measurements, to evaluate the discrimination achieved for these fibers specifically lacking spectral characteristics in the VIS region. A combined discrimination power of MSP, using transmission and emission, was determined for the colorless fibers. The collected transmission spectra allowed discrimination, specifically in the UV region, of colorless fibers of the same type, as well as colorless fibers of different types. The collected emission spectra increased discrimination of the fibers, particularly when the transmission spectra did not show differences. The discrimination power of MSP in combination with polarized light microscopy (PLM) was 99.0%, and the MSP spectra were able to discriminate fibers not previously distinguished by physical and optical properties. The use of microspectrophotometry, in the UV-VIS region and with fluorescence measurements, in forensic laboratories has the potential to increase the discrimination of fiber evidence, even when evidence has limited physical properties and similar optical properties