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The value of evidence in ballpointink analysis

analysing dyes in questioned documents with LC-PDA/MS/MS

Rechten: Alle rechten voorbehouden

The value of evidence in ballpointink analysis

analysing dyes in questioned documents with LC-PDA/MS/MS

Rechten: Alle rechten voorbehouden

Samenvatting

Abstract
The NFI contains 40 forensic disciplines, including the department of Questioned Documents, which focus on the investigation of threatening- and ransom letters, forged documents and documents that have been damaged by water or fire. The authenticity’s of a document, based on handwriting investigation in combination with ink analysis, can give an indication of the extent of falsification or fraud. In questioned documents investigations the most common type of ink is ballpoint ink. It has been stated that at least 80% of all evidence requiring ink analysis contains ballpoint pen ink. Ballpoint ink contains many different functional ingredients, of which the most common ingredients are organic compounds. The combination of all of these ingredients allow the forensic investigator to determine the differences or similarities between inks using optical methods and soft ionization methods.
In this study, the value of evidence in ballpoint ink is investigated with the analyses of dyes in questioned documents by using dimethylformamide (DMF) extraction, LC-PDA/MS/MS analysis and a suitable statistical analysis, resulting in discrimination powers (DP), accuracy, sensitivity and specificity as high as possible. During the Xmas period, the department questioned documents requested the employees of the NFI to collect their envelopes in which they receive their Xmas cards. It is assumed that this is a relevant sample to gain insight to the variation of dyes and pigments in ballpoint ink from pens in the Netherlands. The envelopes are categorized, counted and numbered in different groups, based on the type of pen, the colour of the pen, the colour of the envelope and nationality. During the analyses of the envelopes, this research project has been divided into multiple stages: performing the analytical method and the detection and identification of various dyes in black- and blue- ballpoint ink, analysing and processing the results during data analysis, and interpreting and presenting the results during the multivariate statistical analysis. In order to find patterns and relationships in the amount of ink results, a multivariate statistical analysis, such as the cluster analysis (CA) is required for the analysis of the data. The degree of similarity is quantified by using different measurements, such as the Manhattan distance-, Euclidean distance-, Chebyshev distance metric and the Pearson correlation, resulting in within- and- between variations.
Research has shown that, despite the fact that the results are discrete values, the Euclidean distance is the most suitable distance measure for the similarity between blue- and-black- ballpoint ink comparison, with a high discrimination power (DP), accuracy, specificity and sensitivity. Furthermore, from this research it can be concluded that due to the invalidated and non-optimized database and analysis method, this method for ink comparison in questioned documents is not suitable yet for case studies.
The information that the research has provided, offers a number of recommendations, which are valuable to consider. It is recommended to increase the sample size in order to increase the statistical power, which increases the reliability of the statistical analyses. Furthermore, it is advisable to increase the sample concentration, in order to increase the signal-to-noise (s/n) ratio, which results in less false positive an false negative peaks. In addition, it is recommended to analyse the positively charged dyes with the orbitrap, to obtain high mass accuracy, which ensures good distinction between different dyes. For further studies it would be a recommendation to take into account that when the dyes would not be grouped, but were counted as individual dyes, this could produce a higher discrimination power and wider spreading. Moreover it should be considered that for discriminating dyes in black and blue ball point ink, continuous values, such as the peak intensity or the mass (m/z) value of a dye, are preferred. Closing off, optimization and validation of the database and the analysis method is recommended, making the database and analysis method suitable and reliability for future casework. In addition, it is recommended to measure the validity and reliability of the likelihood ratio by using the log-likelihood-ratio cost (Cllr)[33]

Toon meer
OrganisatieAvans Hogeschool
OpleidingChemie-Breda
AfdelingATGM Academie voor de technologie van Gezondheid en Milieu
PartnersAvans Hogeschool
Jaar2013
TypeBachelor
TaalOnbekend

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