Guidelines for minimal destructive forensic examination of inkjet printer documents with (MA)LDI mass spectrometry and Raman spectroscopy

摘要

This work demonstrates the complementarities of three techniques: Raman spectroscopy, LDMS as well as MALDI-MS. It is preferable to try Raman spectroscopy first as it is a non-destructive approach and is adapted to the analysis of colored documents in most cases. If more information is necessary, laser desorption mass spectrometry is well adapted to the analysis of an inkjet document. However, contrary to all expectations, a matrix (9-aminoacridin) is required to desorb and ionize dyes from most inkjet printed documents (except Epson ones). Positive LDMS is the only way available to discriminate black inks due to the detection of polyethylene glycol polymer which has different mass distributions and end groups for each brand. It is not well understood why a matrix is needed for MS analyses of most color inkjet inks. Several explanations are possible, such as an ion signal suppression from the vehicle of the inks or the chemical structure of the dyes or a particular interaction between dyes and papers? TLC-LDI and AFM experiments as well as analyses of standard solutions of some identified dyes and pigments are current practices. Imaging mass spectrometry or Raman spectroscopy can also be easily performed if the spatial distribution of one ink is necessary.