The determination of the age of an ink entry from a questioned document is often an essential problem and a controversial issue in forensic sciences. Therefore it is important to understand the aging process of the different components found in ink. The aim of this work was to the study the drying process of ballpoint ink, characterised by the disappearance of volatile solvents from the ink entry. Phenoxyethanol is of particularly high interest as it is found in more than 80% of the blue ballpoint pens at different concentrations.
Liquid extraction followed by splitless gas chromatography / mass spectrometry in the selected ion mode was used to measure the quantitative decrease of solvents from ink entries made with a blue Parker® ballpoint pen. Quantities of ethoxyethoxyethanol, dipropylene glycol, phenoxyethanol and phenoxyethoxyethanol were studied in ink entries up to one and a half years old, thus allowing to calculate aging curves for this particular pen. The low quantities of solvents (in the microgram range for a 1 cm ballpoint entry) were found to decrease quickly after deposition of the ink on paper through the competitive processes of evaporation and diffusion. Losses of up to 75% of solvents were observed after a few seconds. The amount of ethoxyethanol stopped decreasing after about 10 days (quantities reached the nanogram range for a 1 cm ballpoint entry), while the aging curves of dipropylene glycol, phenoxyethanol and phenoxyethoxyethanol level off considerably after 2 weeks. It was observed that ethoxyethanol, dipropylene glycol and phenoxyethanol can also migrate from one sheet of paper to another if placed close enough (e.g. in a book or a stack of papers), therefore contamination from fresh ink stroke from other paper sheets has to be taken into account for those solvents.
In this paper we demonstrate that differentiation between fresh ink (< 2 weeks) and older inks is possible under laboratory storage conditions. For real cases samples, more parameters have to be studied and other possibilities have to be considered.