Identification of ink degradation products by LC–MS
thesisposted on 15.08.2018, 10:33 by Abdulelah Alsuidan
The aging processes of ink dyes in ballpoint inks were determined using modem chromatographic and spectrometric methods with their possible application. Two main methods were applied IP–HPLC method with photodiode array detection for ink dyes separation and LC–MS method for the identification of ink degradation products as a function of age, for this purpose the two methods were developed and validated. The aging processes of standard dyes as reference substances at different conditions (light and heat) were investigated. These processes were used then on ink entries on paper. Dye components and their degradation products were successfully separated and identified by their retention time, UV-visible absorption profiles and mass spectra. Different blue ballpoint inks were identified and discriminated by comparing their relative peaks areas (RPA) to obtain the aging profiles. Moreover, other types of ink (gel pens, fibre tips and different colours) were also analysed and discriminated successfully by the developed method. In addition, several months’ entries from multiple inks entries exposed to normal sunlight and samples stored in the dark were compared. A typical and expected degradation of ink dyes was characterized by the de-alkylation process (loss of CH2– or CH2–CH3 groups). Crystal violet and Victoria blue dye groups, two major dyes used in ballpoint ink industries were thoroughly investigated. In this work, mass spectrometric methods were developed and validated to describe the ageing mechanism of ballpoint ink dyes. Furthermore, factors influencing the aging process (heat, light, natural aging factors) were studied. For real forensic cases the storage conditions of the paper and type of pen used should be known.
Saudi Arabia, Ministry of Interior, Forensic Science Department.