Iva Bogdanovic Radovic oral presentation (OA2-Mon3-3-3)
Utilisation of MeV Secondary Ion Mass Spectrometry for Forensic Document Examination
1 Rudjer Boskovic Institute, Bijenicka 54, 10000 Zagreb, Croatia (Hrvatska)
2 University of Surrey - Department of Chemistry, , Guildford, Surrey, United Kingdom
Analysis of ink in questioned documents is a highly important area of forensic science. Currently, there is no established standard technique for the determination of sequence deposition order of intersecting lines of optically indistinguishable ballpoint pens. It is estimated that ballpoint pens are used in approximately 80% of questioned documents , and as such non-destructive methods with high discrimination factor must be utilised in order to provide forensic document examiners with clear results.
In this work, potential of MeV Secondary Ion Mass Spectrometry (MeV-SIMS) to discern the deposition order of optically similar blue ballpoint pens was investigated. Focused 8 MeV Si4+ ions were utilised for the analysis of the ink on paper with a typical lateral beam resolution of approximately 5x5 μm2. First, a single line for different inks was prepared and MeV SIMS spectra were collected in order to determine ink molecular composition and to define differences in colorants among them. Then, samples containing ink intersection were prepared for different ink combinations and deposition orders. Taking into account that MeV SIMS is surface sensitive technique and by imaging one characteristic and unique m/z peak for each ink, 2D images (up to 1200x1200 μm2) of ink intersections were created clearly showing the deposition order.
Further, to test the MeV-SIMS sensitivity, the smallest possible amount of sample was taken from a piece of handwritten text keeping visually document integrity. It was shown that this small amount of sample was sufficient to identify used ink from a MeV SIMS spectrum.
As a conclusion, the use of MeV-SIMS as a tool for forensic document examiners is promising, although is not necessarily applicable for routine analysis due to high set-up and running costs. However, for situations of high importance, it may be an extremely useful tool when other non-destructive methods yield inconclusive results.
 J. Denman, W. M. Skinner, K. P. Kirkbride and I. M. Kempson, Appl. Surf. Sci., 2010, 256, 2155-2163