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

Abstract

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.

A Review of Laser-Induced Breakdown Spectroscopy (LIBS) for Document Examination: Fundamentals, Mechanism, and Application

“…Several researchers used Czerny-Turner [2,11,34,40,54,55], Echelle [4,7,47] and Ocean Optics [46,50] spectrometers in their studies. Czerny-Turner spectrometer is commonly used in LIBS.…”

“…A forensic document examiner (FDE) typically begins the examination of a questioned document by identifying the device used to produce the document (e.g., printers, pens, pencils, etc. ), followed by an analysis of the ink's physical properties and chemical composition [4]. Questioned documents refer to any form of written or printed text with questionable authenticity that can be treated as evidence in criminal and/or civil cases [4].…”

“…), followed by an analysis of the ink's physical properties and chemical composition [4]. Questioned documents refer to any form of written or printed text with questionable authenticity that can be treated as evidence in criminal and/or civil cases [4]. These documents are submitted to forensic document examiners (FDEs) in order to ascertain the authenticity of documents [1].…”

Interpol review of questioned documents 2016–2019

“…Several studies [ [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] ] have been published concerning the analysis and discrimination of writing inks with several kind of instruments. Some papers focused on only one analytical method while others compared a method to another, or combined them to find a methodology to discriminate inks.…”

“…Multivariate data analyses or chemometrics are one of the most studied fields. Concerning pen inks, 15 papers refer to this topic [ 3 , [5] , [6] , [7] , [8] , 11 , 14 , [16] , [17] , [18] , 20 , 23 , 24 , 26 , 33 ]. A chemometric approach is primarily used to classify samples or to discriminate them.…”