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EM - Dissertações de Mestrado

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Browsing EM - Dissertações de Mestrado by Subject "2-phenoxyethanol"

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  • Dating of writing inks based on the study of volatile compounds / Datação forense de escrita manual através da análise de componentes voláteis de tintas
    Publication . Leal, Teresa Fernandes Argente; Bernardo, Maria Alexandra; Ferreira, Carla
    Background: One of the major challenges in forensic document analysis is estimating the age of an ink deposition on a manually written document. Objective: The present work aims to develop and optimize a methodology based on the evaporation of volatile compounds over time that can be used to solve real forensic case studies. Materials and methods: Nine pens (5 viscous inks + 4 liquid inks), purchased in commercial areas, were preliminarily analysed, and ink deposition began in September 2016. Initial volatile solvent screening was performed by GC/MS and GC-FID. Samples of the 5 viscous pen inks were further analysed by GC/MS. 20 microdiscs were subjected to n-hexane extraction in the presence of an internal standard (ethyl benzoate) using ultrasound and thermo-agitation, and finally derivatized with 95MSTFA: 5TMCS (TMS). The method was optimized for 2-phenoxyethanol (PE). Subsequently, the aging curve was studied for the black crystal BIC® pen (nr 2). Data were treated with Microsoft Excel® and later analysed on GraphPad Prism 8. Results: The developed method presents, for the (PE-TMS area/IS area) values which were linear between 0.008 and 1.37 (y = 0.0278x-0.0119; R2 = 0.9995), a LOD of 0.026 and a LOQ of 0.104. Through pen nr.2, GC/MS analysis, it was possible to characterize the decay of PE-TMS over time, which reveals a two phase decay behaviour and stabilized after the 33th day, and allowed to detect the presence of PE-TMS until 3 years. Two unknown compounds were also present and allowed to identify three dating time frames for the same ink stroke: (i) between time 0 and ca 33 days; (ii) between time ca 34 and 109 days; (iii) more than ca 109 days. Conclusion: This methodology allowed to characterize the behaviour of PE solvent over time and to establish a relative dating in three time frames.
    2019-12Master thesis Restricted access Show more