Classification of Document Papers by Infrared Spectroscopy and Multivariate Statistical Techniques

Abstract

Infrared (IR) spectra of different varieties of document papers were collected with the use of attenuated total reflectance (ATR, 4000-650 cm−1, eight paper varieties) and diffuse reflectance (DRIFTS, 9000-2500 cm−1, six paper varieties) techniques. The spectral data were classified by the application of soft independent modeling of class analogies (SIMCA), using principal components analysis (PCA) to estimate the distance of separation between the different classes of paper samples and discriminant analysis (DA) to obtain a probabilistic classification. The use of DA on spectral data needed a preliminary data reduction step, either by PCA-decomposition of spectra or the selection of discrete spectral features having maximum discriminating ability. The aim of this research was to evaluate these data-reduction techniques and compare the discriminating power of these two spectral techniques (DRIFTS and ATR) by the application of PCA and DA. The use of PCA scores as DA variables provided the best resolution (100% correct classification) for the DRIFTS spectra, while PCA on the ATR spectra resulted in the best discrimination, separating 67.86% paper pairs completely with the use of cross-validation. The results of this study reemphasize that infrared spectroscopy coupled with multivariate statistical methods of analysis could provide a powerful discriminating tool for the forensic questioned document examiner.

Forensic differentiation of paper by X-ray diffraction and infrared spectroscopy

“…A number of techniques have been proposed to carry out such investigations, among which X-ray diffraction [1][2][3][4], elemental analysis [5,6], IR spectroscopy [7][8][9], Raman spectroscopy [10], image analysis [11] and pyrolysis gas chromatography [12]. Physical testing, such as the measurement of density or of mechanical performance, are less viable since they require special apparatus and imply destructive tests.…”

“…with the possibility of examining the sheet's surface. Kher et al [8,9] emphasized that IR spectroscopy, coupled with multivariate statistical methods of analysis, is a powerful discriminating tool for the forensic questioned document examiner. They in fact demonstrated that all the samples in a set of six paper varieties could be differentiated by diffuse reflectance (DRIFTS) and 67.86% of the possible pairs within a population of 8 types of paper could be discriminated by ATR [8].…”

“…Kher et al [8,9] emphasized that IR spectroscopy, coupled with multivariate statistical methods of analysis, is a powerful discriminating tool for the forensic questioned document examiner. They in fact demonstrated that all the samples in a set of six paper varieties could be differentiated by diffuse reflectance (DRIFTS) and 67.86% of the possible pairs within a population of 8 types of paper could be discriminated by ATR [8]. In this article, a very simple quantitative approach to FTIR analysis of paper is presented, which is aimed at the differentiation of a larger population of white sheets of office paper, indistinguishable by visual examination.…”

Forensic differentiation of paper by ATR-FTIR spectroscopy technique and partial least-squares-discriminant analysis (PLS-DA)

“…Linear discriminant analysis (LDA) has been used quite frequently in forensic classification task [2][3][4]. However, one of the most popular analytical methods in forensic analysis, i.e.…”

Effects of scatter-correction pre-processing methods and spectral derivative algorithms on forensic classification of paper

“…Whereas derivatives have the capability to remove baseline effects and any offset differences between the data [10]. Pre-processing techniques were rarely applied in forensic studies involving instrumental techniques [11][12][13], except normalization, standardization [14][15] and derivatives [16][17]. In fact, the importance and benefits of preprocessing techniques should not be ignored by forensic scientists.…”