Weyermann Céline, Kirsch Dieter, Costa-Vera César, Spengler Bernhard
Institute of Inorganic and Analytical Chemistry, Justus Liebig University Giessen, Giessen, Germany.
J Am Soc Mass Spectrom. 2006 Mar;17(3):297-306. doi: 10.1016/j.jasms.2005.11.010. Epub 2006 Jan 27.
The determination of the age of an ink entry from a questioned document is often a major 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 characterize the degradation processes of methyl violet and ethyl violet, two typical ballpoint dyes by using laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS), and to evaluate the possible application of the method to forensic examination of documents. The mass spectrometric methods were first tested and were found to be adequate for the purpose of this work. Moreover, it is possible to analyze the dye from a stroke directly from the paper (LDI-MS), so the sample preparation is minimized. The degradation of the dyes methyl violet and ethyl violet in strokes from a ballpoint 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 analyzed. 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. In 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 periods 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.
从有疑问的文件中确定墨水痕迹的形成时间通常是法医学中的一个重大问题和有争议的议题。因此，了解墨水中不同成分的老化过程很重要。本研究的目的是通过激光解吸/电离（LDI）和基质辅助激光解吸/电离（MALDI）质谱法（MS）来表征甲基紫和乙基紫这两种典型圆珠笔染料的降解过程，并评估该方法在文件司法鉴定中的可能应用。首先对质谱方法进行了测试，发现其适用于本研究目的。此外，有可能直接从纸张上分析笔画中的染料（LDI-MS），因此样品制备被减到最少。在光照、光波长、热和湿度等不同因素影响的实验室条件下，研究了圆珠笔笔画中甲基紫和乙基紫染料的降解情况。然后，将同一支圆珠笔书写的笔画在黑暗中或光照影响下自然老化一年，然后进行分析。结果表明，这些染料的降解强烈依赖于光通量。湿度也会增加降解，这可以用纸张的碱性来解释。发现热对降解过程的影响相当小。还观察到，墨水笔画中的染料在黑暗中储存一年后没有显示出明显降解。总之，为了正确解读墨水痕迹的形成时间，必须了解有疑问文件的储存条件和墨水中染料的初始成分。需要进行更长时间的测量来跟踪未受光照的染料的降解情况。发现LDI足以直接从纸张上分析圆珠笔染料，无需进一步预处理，非常有用。
