Analytical Sciences

Analysis of Writing Ink Dyestuffs by TLC and FT-IR and Its Application to Forensic Science

Kazuhiro TSUTSUMI* and Kazuya OHGA**

*Criminal Investigation Laboratory, Oita Prefecture Police Headquarters, Otemachi, Oita 870, Japan
**Department of Applied Chemistry, Faculty of Engineering, Oita University Dannoharu, Oita 870-11, Japan

Black, blue and red writing pens were classified into various groups using the Rf values and color tones of dyestuff bands separated by normal-phase thin-layer chromatography (TLC) of their inks. The classification is effective for the prelimi-nary identification of pens used in crime scenes. A microsampling technique was proposed for the TLC analysis of minute quantities of inks on questioned documents. Furthermore, a combination of reflectance-mode microscope/Fourier transform infrared spectroscopy and the pin-point condensation technique was proved to be useful for the precise discrim-ination of trace amounts of analogous water-soluble dyestuffs on TLC plates. (Keywords: Forensic science, ink, dyestuff, thin-layer chromatography, Fourier transform infrared spectroscopy)

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