Forensic Evaluation of Ink Age by Raman Spectroscopy and Gas Chromatography-Mass Spectrometry (GC-MS)

Abstract

Ink age analysis is a hot but challenging topic in the practice of document inspection and identification in forensic sciences. Due to the influence of ink components, paper, and storage environment on the aging process, strict validation of laboratory methods is required. In this study, Raman spectroscopy was investigated to determine ink age by analyzing the peak intensity of carbon black in neutral signature pens and has been recently used as evidence in legal documents. Through statistical analysis of Raman peak heights of inks naturally aged from 3 days to 18 months, the results demonstrate this approach is unsuitable for forensic purposes. Hence, appraisal conclusions should also be rejected by the procuratorate in actual cases. In order to further explore the identification of ink age, the volatilization rates of cyclohexanone, 1-butanol, propylene glycol, ethylene glycol, benzyl alcohol, diethylene glycol, glycerol, phenoxyethanol, and triethylene glycol commonly used in pens as a function of time were investigated. The results show that gas chromatography-mass spectrometry (GC-MS) is reliable to characterize the volatilization of these alcohols in documents. The residual levels of characteristic solvents (triethylene glycol in two samples and diethylene glycol in one) decreased significantly within 6 months and may be used to evaluate the ink age in documents.