On the spectroscopic investigation of stamp inks using ATR-FTIR and chemometrics: Application in forensic document examination

Abstract

The identification and differentiation of stamp inks can be a crucial aspect to establish the authenticity of questioned documents, and thus plays a vital role in judicial expertise. Herein, 16 brands of blue stamp inks and 12 brands of red stamp inks have been investigated using Attenuated Total Reflectance – Fourier Transform Infrared (ATR FT-IR) Spectroscopy in the mid-IR range. Stamp inks of different brands were differentiated using visual inspection of spectra with discrimination power of 96.6% and 93.9% for blue and red stamp inks respectively. To get enhanced and better discrimination power, chemometric tools such as PCA, PCA-LDA, and PLS-DA were applied, which provided satisfactory results with higher accuracy rate. Further, to check the influence of substrates, imprinted stamp inks on different papers were also analyzed and results have been discussed. Henceforth, the obtained results in the current study illustrates that the technique ATR FT-IR spectroscopy is a sensitive and reliable tool with minimal sample preparation requirements to identify and differentiate different manufactures of stamp inks, thus extends a novel approach to judge the document’s authenticity.