Photofading of Ballpoint Dyes Studied on Paper by LDI- and MALDI-MS Analysis

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 is to characterise the degradation processes of methyl violet and ethyl violet, two typical ballpoint dyes, by using LDI and MALDI mass spectrometry and to evaluate the possible application of the method to the forensic examination of documents. The mass spectrometric methods were first tested and were found adequate for the purpose of this work. Moreover it is possible to analyse the dye from a stroke directly from the paper (LDI-MS), so the sample preparation is minimised. The degradation of the dyes methyl violet and ethyl violet in strokes from a ballpoint BIC® pen was studied under laboratory conditions influenced by different factors such as light, wavelength of light, heat and humidity. Then strokes from the same ballpoint were aged naturally in the dark or under the influence of light over one year and then analysed. The results show that the degradation of these dyes strongly depends on light fluence. Humidity also increases degradation, which can be explained by the basicity of the paper. The influence of heat on the degradation process was found to be rather weak. It was also observed that the dyes from the ink strokes did not show significant degradation after one year of storage in the dark. As a conclusion, the storage conditions of a questioned document and the initial composition of the dyes in the ink have to be known for correct interpretation of the age of an ink entry. Measurements over longer period of time are necessary to follow the degradation of dyes exempt from light exposure. LDI was found adequate and very useful for the analysis of ballpoint dyes directly from paper without further pretreatment