Analysis of writing ink dyestuffs by TLC and FT-IR and its application to forensic science

Black, blue and red writing pens were classified into various groups using the R-f values and color tones of dyestuff bands separated by normal-phase thin-layer chromatography (TLC) of their inks. The classification is effective for the preliminary 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 discrimination of trace amounts of analogous water-soluble dyestuffs on TLC plates.