Evaluation of Raman Spectroscopy for the Analysis of Colored Fibers: A Collaborative Study

Abstract

A collaborative study on Raman spectroscopy was carried out by members of the ENFSI (European Network of Forensic Science Institutes) European Fibres Group (EFG) on three dyed fibers: two red acrylics and one red wool. Raman instruments from six different manufacturers were tested as well as nine different laser wavelengths ranging from blue (λ = 458 nm) to near infrared-NIR (λ = 1064 nm). This represents the largest comparison study of Raman analytical parameters carried out on identical fiber samples. For the chosen fiber and dye samples, red lasers (λ = 633 and 685 nm) gave the poorest spectral quality whereas blue (458 nm), green (514 nm) and near infrared lasers (785, 830 and 1064 nm) provided average results. Blue (488 nm) and green lasers (532 nm) globally gave the best quality spectra. Fluorescence problems were often encountered with some of the excitation wavelengths and therefore a flexible Raman instrument equipped with different lasers can be recommended to measure forensic fiber samples. The instrument should also be equipped with a Raman microscope in order to be able to focus on a single fiber. This study shows that Raman spectroscopy usually enables the identification of the main dye present in a colored fiber; however, minor dye components are much more difficult to detect. SERRS (Surface Enhanced Resonance Raman Scattering) techniques give an improvement of the dye's spectral intensity but no spectral improvement was observed for the two red acrylic and red wool fibers tested.

Micro-Raman and Micro-FT-IR Spectroscopic Investigation of Raw and Dyed Pan Fibers

“…[1][2][3][4][5][6][7] Raman and IR spectroscopic studies on fibers and dyed fibers showed that Raman data provided information about the dyes used in dyeing the fibers, but gave little information about the polymer, while IR spectra were found to be well suited for characterization of the polymer, but gave poor information on the dyes. 8 Some Raman experiments on dyed fibers have shown that this technique enables identification of the main dye present in colored fiber, but the components of the dyes are much more difficult to detect 9,10 because of their low overall content. Simultaneous application of both techniques could allow (in favorable cases) a characterization and identification of raw polymer-based fibers 7 and also, in the case of dyed fibers, the type of the dye used.…”

Forensic Analysis of Fibres by Vibrational Spectroscopy

“…The results of Massonnet et al [34] are probably highly dependent on the nature and colour of the particular dyes used in their study because other workers have concluded that longer wavelength NIR excitation is generally considerably better for dyed fibres and most likely to result in reduced fluorescence [31,35,36].…”

“…The most comprehensive evaluation of the application of Raman spectroscopy to the analysis of coloured fibres has been that of Massonnet et al [34] who studied acrylic and wool fibres dyed red with different dyes. They used a range of Raman instrumentation with excitation wavelengths varying between 458 and1064 nm.…”

Forensic comparison of synthetic fibers

“…The molecular structure data obtained with this instrument can complement IR analysis of molecular identifications. [44][45][46][47] Kalasinsky et al used FT-Raman with 1064-nm excitation to identify foreign materials in tissue specimen such as cholesterol and polytetrafluoroethylene in an implant case, PET and polyacrylonitrile in a pilonidalcyst, and carbenicillin in a skin biopsy. They showed that Raman spectra are important in identifying foreign materials in tissue and proving valuable information to the pathologist.…”