Dating inks on paper through chromatographic analysis of volatile compounds: a mini-review

Abstract

Introduction: Forensic research dating ballpoint pen inks on paper is among the most difficult and hardest problems. The two main challenges are to determine when the ink was manufactured and to determine time since deposition (TSD) of the ink on a handwriting document [1]. Ink´s TSD depends on internal ink properties and external factors, such as environmental conditions. Once a document has been handwritten the ink deposited starts the aging process, which involves solvent evaporation, dye degradation, polymerization and hardening of the resins [2]. The analysis of quantitative differences or chemical changes of solvents on a given set of environmental conditions can provide a measure of TSD. To obtain a chemical fingerprint of ink changes, chromatographic methods have been explored. The aim of this work is to do a review research that provides an overview of chromatographic procedures that allow ink dating, on paper, through ink pen solvent analysis.

Materials and methods: A review of the literature was performed at the b-on database, between October 2017 and April 2018. Articles were selected between 1985 and 2018 in English and Spanish. Search was conducted using the terms “writing inks” AND “dating” AND “solvents” AND “GC”. 343 articles have been found. According to the title/abstract, studies on volatile compounds present on pen inks were included while those on dating ink studies based on resins and dyes were excluded. After title/abstract analysis 28 studies were considered in this overview, including 6 review articles.

Results: The most used techniques to get a time frame of ink deposition on paper are based on Gas Chromatography (GC) coupled to an FID or an MS detector. Chromatographic techniques take advantage of getting ink dynamic profile with time to determine time since deposition values. Nowadays the elective technique is GC-MS. In GC-MS inks must be extracted from the paper with an extraction solution. Concerning the extraction method, 18 articles described the most commonly used solvents for the extraction (methanol, acetonitrile, chloroform/pyridine/MSTF, Dimetilformamide). 4 articles used headspace coupled to GC, to analyze the volatiles, instead of traditional extraction procedures. Overall the results presented in the previously mentioned papers show that it is possible to estimate the age of an ink when deposited in a document.

Discussion and conclusions: GC/MS and HS-GC-FID prove to be promising in the field of ink aging of a questioned entry, allowing getting information about solvents chemical changing and providing a measure of TSD [3]. Nevertheless, no solvent ink age standard method has been implemented in forensic sciences laboratories.