Weyermann Céline, Kirsch Dieter, Costa Vera César, Spengler Bernhard
Institute of Inorganic and Analytical Chemistry, Justus-Liebig University Giessen, Schuberstr. 60, Bldg. 16, D-35392 Giessen, Germany.
Forensic Sci Int. 2007 May 24;168(2-3):119-27. doi: 10.1016/j.forsciint.2006.06.076. Epub 2006 Aug 9.
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 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 1.5 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 strokes 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 possible pathways have to be considered.
确定可疑文件上墨水字迹的书写时间，在法医学中往往是一个至关重要且颇具争议的问题。因此，了解墨水中不同成分的老化过程十分重要。本研究旨在探究圆珠笔墨水的干燥过程，其特点是墨水字迹中挥发性溶剂的消失。苯氧乙醇尤其值得关注，因为在超过80%的蓝色圆珠笔中都能发现它，且浓度各异。采用液液萃取后，在选择离子模式下进行不分流气相色谱/质谱分析，以测量用派克蓝色圆珠笔书写的墨水字迹中溶剂的定量减少情况。研究了高达1.5年的墨水字迹中乙氧基乙氧基乙醇、二丙二醇、苯氧乙醇和苯氧乙氧基乙醇的含量，从而能够计算出这支特定圆珠笔的老化曲线。发现低含量的溶剂（对于1厘米长的圆珠笔字迹，含量在微克范围内）在墨水沉积到纸张上后，通过蒸发和扩散的竞争过程迅速减少。几秒钟后，观察到溶剂损失高达75%。乙氧基乙醇的含量在大约10天后停止下降（对于1厘米长的圆珠笔字迹，含量达到纳克范围），而二丙二醇、苯氧乙醇和苯氧乙氧基乙醇的老化曲线在2周后明显趋于平稳。据观察，如果放置得足够近（例如在一本书或一叠纸中），乙氧基乙醇、二丙二醇和苯氧乙醇也会从一张纸迁移到另一张纸上，因此对于这些溶剂，必须考虑来自其他纸张上新墨水笔画的污染。在本文中，我们证明了在实验室储存条件下，能够区分新鲜墨水（<2周）和陈旧墨水。对于实际案件样本，还需要研究更多参数，并考虑其他可能的途径。
