Application of Multivariate Statistics (PCA and HCA) on ballpoint pen ink Infrared spectra for dating of forensic relevant documents

In the normal casework of Forensic Document Examiners (FDEs), a common type of forgery is the alteration of the date of creation of a document through the erasure and addition of another date with ballpoint pen of color similar to the original. The chronology of manuscripts in a document has been a concern within the FDE community. Recently, Infrared spectroscopy (IR) and multivariate statistical analysis have been used to differentiate pens, but this paper aimed to develop an IR method that could also date a manuscript by multivariate statistic. Ballpoint pen lines from different brands made in different kinds of papers (office white and recycled), with variable ages, were analyzed by Infrared Spectroscopy with Total Attenuated Reflectance Accessory. The spectra obtained were analyzed with multivariate statistical analysis, especially Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). This study concludes that different kinds of paper do not influence the characterization of the pens by IR-ATR. The method was able to characterize the variables that were responsible for the discrimination of ballpoint pens from different brands/models and for differentiation of samples of different ages. The HCA and PCA were able to group pens with similar ages, and differentiate lines recently wrote from older lines. Within the loadings that are responsible for the differentiation, it was possible to identify absorption peaks from 2-phenoxyethanol, a solvent whose evaporation from the ink could indicate the line age. Further studies regarding other pen samples and multivariate statistical approaches could be conducted to confirm these findings.