Study of chemical profile and of lines crossing using blue and black ink pens by LDI (+) MS and LDI (+) imaging

Add time:07/19/2019    Source:sciencedirect.com

The determination of the chemical characterization and the order of ink crossing by ballpoint pens have received increasing and important attention in forensic analysis due to forgery or alteration of documents strongly related to their use. The examination of these cases must be using non-destructive methods, in order to preserve the integrity of the evidence present in the documents. Laser desorption ionization mass spectrometry (LDI-MS) and LDI mass spectrometry imaging (LDI-MSI) have been widely applied in forensic document analysis by offering specific information on the chemical composition of the material from the mass to charge ratio (m/z) of the dyes without destroying the spatial location of the analytes. In this work, the combination of LDI data with statistical treatment, such as principal components analysis, classified the blue and black pen inks according to their 11 brands and 18 models studied. The interpretation of the LDI mass spectra allowed a chemical profile analysis relating the concept of relative ion intensity of the following dyes: methyl violet (m/z 372), ethyl violet (m/z 456), basic blue 26 (m/z 470), and basic blue 7 (m/z 478). In addition, the order of ink crossing (pen over pen, pen over printer and vice versa) was determined by monitoring the ions: methyl violet dye (m/z 372), their homologues (m/z 358, 344, 330, 316) and basic blue 7 (m/z 478) for the pens; and the ions of m/z 285 and 355, for inkjet and laserjet printers, respectively, by the LDI (+) MSI.

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