A Further Analysis of Laser-Induced Breakdown Spectroscopy Ink Pens' Spectra Using Principal Component Analysis (PCA) for Forensic Characterization

Because characterization of ink pens on documents represents an important forensic discipline, the need of legal systems for faster, in-situ and more accurate technique that identify and differentiate questioned documents involved in criminal or legal matters is of great interest. Laser-induced breakdown spectroscopy (LIBS) was experimentally proved to be a promising technique emerging in the field of forensic applications, specifically, questioned documents despite being from the same source or different source. However, the call for newly improved data analysis is unlimited and the need to know if the used ink has the same principal components or not. In the present work, the application of PCA has been demonstrated as statistics-based spectral analysis of the output resultant LIBS spectra for the forensic questioned documents analysis. The LIBS spectra were acquired from IR laser induced plasmas of black ink on regular document paper of ten brands of black gel inks commercially available in the Egyptian market. The idea behind principal component analysis is based on the loadings for the first three principal components. The obtained results have been shown to characterize ink pens used in the analysis. However, the first principal component encompasses the dominant characterization for the used pens. The results of this study indicate that Laser Induced Breakdown Spectroscopy (LIBS) of ink pens aided with PCA technique can promote the LIBS capability to faster, error-free and automatic elemental identification and differentiation for in-situ forensic purposes, specifically, questioned documents.