In the forensic examination of documents the legitimacy of the age of an ink entry is often an essential question. Ball-point ink contains equivalent amounts of dyes, solvents and resins. After the ink is deposited on paper, its composition begins to change qualitatively and quantitatively.
The degradation of dyes contained in ballpoint ink will be described. The aim is to study aging processes of dye with minimal or without chemical treatment. Thus methyl violet, a common dye used in ballpoint ink and blue ink paste (source Bundeskriminalamt, Wiesbaden, Germany), were exposed to heat (oven 100°C) or light (high pressure Xenon and UV lamps) over defined periods of time. Then they were analysed by MALDI- and LDI-MS. Finally ink aging under these conditions was studied using the measured mass spectra.
In the second part of this work, ink entries were directly analysed on paper. The entries were made over several months with blue pall points on white paper. One batch of samples was kept in a cupboard, while the other was fixed to a window and exposed to day light. A small piece of paper was then cut and mounted directly on the target. LDI measurements were obtained and compared.
The aging curves show a strong correlation of degradation to the duration of light exposure, which is not observed for exposure to heat. The difficulties of determining the age of ink entries will be discussed.
Moreover our results demonstrate that LDI is a better method than MALDI for analysis of these types of dyes. A stronger initial degradation was observed for the samples prepared with matrix. It was also observed that the laser irradiance is an important variable, that can cause degradation of the dye during the initial processes of MALDI/LDI.