Identification of dye content in colored BIC ballpoint pen inks by Raman spectroscopy and surface-enhanced Raman scattering

摘要

Raman spectroscopy and surface-enhanced Raman scattering (SERS) were used for the elucidation of dye content in commercial BIC ballpoint pens. In contrast to the majority of studies in this field on black and blue inks of forensic interest, this paper targeted characterization of colored (red, pink, purple, and green) pen inks, increasingly used for artistic purposes. Because of its not invasive nature, the capabilities of Raman spectroscopy were initially tested. However, overall SERS provided enhanced spectral features and quenching of fluorescence necessary for the unequivocal identification of dye mixtures in all analyzed pens. SERS analysis was carried out in situ, by deposition of Ag nanopastes directly on pen colored paper surfaces. Rhodamine B was identified as the main dye component in red, pink, and purple inks, whereas phthalocyanine dye Blue 38 was identified in all green inks; excitation at different wavelengths revealed that the darker hue of purple ink was achieved by addition of crystal violet to red Rhodamine B and that green hues were achieved by addition of yellow dyes to Blue 38. UV-vis spectroscopy and thin-layer chromatography analyses complemented Raman/SERS measurements by revealing the presence of additional yellow/orange and blue components in red and green inks, respectively. The relevance of this analysis for art diagnostics was demonstrated through the real noninvasive analysis of BIC pens drawings, which led to successful identification of chemical ink composition and identification of production medium.