Problems of Forensic Sciences 2013 Vol. 95 (XCV) 627-641
RAMAN SPECTROSCOPY SUPPORTED BY OPTICAL METHODS OF EXAMINATION FOR THE PURPOSE OF DIFFERENTIATING BLUE GEL PEN INKS
Marcin KUNICKI1, Ewa FABIAŃSKA1, Andrzej PARCZEWSKI1, 2
1Institute of Forensic Research, Kraków, Poland
2Faculty of Chemistry, Jagiellonian University, Kraków, Poland
Streszczenie
This paper presents the results of analysis of 17 blue gel inks (of different brands) deposited on a paper surface. The studies were carried out using a RENISHAW Raman Spectroscope equipped with three sources of excitation – lasers of wavelengths 514, 633 and 785 nm. Measurements of Raman spectra were performed in the spectral range 400–2000 cm–1. The studied samples were arranged in 136 pairs, in order to check separately for each of them whether it is possible to differentiate them on the basis of comparing Raman spectra. The obtained results allowed us to calculate the discriminating power of Raman spectroscopy for each of the applied sources of excitation and overall for this technique. Identification of the pigments making up the studied inks was also carried out, at the same time analysing the changes in intensity of the main bands of Raman spectra of these pigments depending on the wavelength of the excitation light. It was established that Raman spectroscopy is a highly effective method in the analysis of blue gels, because thanks to good repeatability of the obtained spectra and a low level of noise, it is possible to distinguish them even on the basis of single bands of relatively low intensity and also to identify bands which do not originate from the main chromatic components. In the case of samples that were not differentiated by this technique, additional optical analyses were applied, using a Leica stereoscopic microscope and a VSC 2000 HR spectral comparator. It was ascertained that several of them could already be differentiated by microscopic observation at 10–20 magnification. However, analysis of absorption and luminescence in infrared did not provide further solutions.
Słowa kluczowe
Forensic science; Document examination; Raman spectroscopy; Writing materials; Dyes; Pigments; Optical methods.