Forensic Fibre Analysis by UV-Visible Microspectrophotometry

Abstract

ABSTRACTThis study evaluated various aspects of UV-VIS microspectrophotometry for routine colour analysis of fibres in a forensic laboratory, and was compared to visible microspectrophotometry. Quartz plates and glycerine mounting medium do not absorb within the spectral range of 240 nm to 380 nm. However, glass and XAM™ mounting medium, which are routinely used for microscopic fibre analysis and visible microspectrophotometry, were found to absorb substantially below 320 nm. The spectral interference from the polymeric composition of fibres was also studied. Wool, silk, polyester and acrylics with methylvinylpyridine(MVP) are highly absorbing below 310 nm, so dye colour analysis could not be applied in that region for these fibre types. Acetates, nylons, modacrylics and acrylics with polyvinylpyrrolidone (PVP) have low or moderate absorbance below 310 nm, which causes some interference. Cotton, rayon, and olefins do not absorb in the UV range. Analysis of glass-mounted fibres in the UV-VIS range can provide increased discrimination over analysis in the visible range. A flowchart decision tree was developed to guide the analyst in the application of UV-VIS microspectrophotometry for fibre analysis. Dyed fibres could initially be analysed under glass mount by UV-VIS microspectrophotometry from 320 nm to 770 nm. For fibre types with little or no polymeric UV spectral interference, additional spectral information could be obtained from UV-VIS analysis on quartz slides, measured from 240 nm to 770 nm.