Mass Spectrometric Investigation of the Aging Processes of Ballpoint Ink for the Examination of Questioned Documents.


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PhD thesis: a PhD thesis.
Mass Spectrometric Investigation of the Aging Processes of Ballpoint Ink for the Examination of Questioned Documents.
Weyermann C.
Spengler B.
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Universität Giessen
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summa cum laude
Since its beginnings, the field of forensic questioned documents has been concerned with the dating of inks. Ink aging processes follow complex paths and disagreements about the feasibility of current methods have been voiced worldwide among the scientific community. This controversy has been the starting point of the present work. Its aim was that of actually studying the aging processes of the dyes and the solvents found in ballpoint pens by modern mass spectrometric methods in order to evaluate the potentiality and limitations of dynamic dating methods.
Laser Desorption Ionisation, Electrospray Ionisation and Gas Chromatography Mass Spectrometry proved to be more adequate and powerful tools than standard methods used today in the analysis of ballpoint dyes and solvents. These techniques yield a sensitive, reproducible, discriminating, rapid and easy analysis with minimal sample preparation. They provide useful information about the compounds found in inks and may be of use in the establishment of an ink database that is essential for static and dynamic dating methods.
Scanning Microprobe LDI-MS, a new non destructive method, has been proposed for determining the crossing sequence of lines on paper, and has given encouraging preliminary results in instances when the ink constituting the lines were not entirely mixed at the intersection.
Many factors influencing the fading of dyes and the drying of solvents over time have been identified, and to some extent measured and evaluated in standard conditions. Variations in ballpoint pen type (ink composition and concentration) and storage conditions (light, temperature, humidity, air flow, paper type) lead to very complex processes resulting in different aging states for an identical point in time. Also, contamination through migration of solvents from one sheet of paper to another was quantified, and should not be underestimated. Without precise knowledge of these variables and of the extent of their influence, it will not possible to deliver a scientific result for the age of an ink entry. Any established dating method based on the fading of dyes or the drying of solvents has to be checked for reliability through indications of reproducibility, by valid answers in blind testing and by measuring errors that are lower than predictable variations.
On the other hand, the question about the age of an ink entry lies more on the inference of sources rather than the technological or analytical aspects. One can therefore argue that an unequivocal conclusion about the age of an entry will ever be possible in practical forensic cases, as the nature of the samples (small amounts and complex ink-substrate matrix) and the influence of the storage conditions (stack of paper in a file or plastic folder) may actually yield larger differences in the dyes and solvents fractions of the ink entry than the ones provoked by time. The measurement however precise would give no indication about the true age of the ink.
ink, mass spectrometry, forensic
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27/02/2009 9:52
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20/08/2019 17:01
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