A comparative study of ballpoint ink ageing parameters using GC/MS

Abstract

For more than a decade scientists tried to develop methods capable of dating ink by monitoring the loss of phenoxyethanol (PE) over time. While many methods were proposed in the literature, few were really used to solve practical cases and they still raise much concern within the scientific community. In fact, due to the complexity of ink drying processes it is particularly difficult to find a reliable ageing parameter to reproducibly follow ink ageing. Moreover, systematic experiments are required in order to evaluate how different factors actually influence the results over time. Therefore, this work aimed at evaluating the capacity of four different ageing parameters to reliably follow ink ageing over time: (1) the quantity of solvent PE in an ink line, (2) the relative peak area (RPA) normalising the PE results using stable volatile compounds present in the ink formulation, (3) the solvent loss ratio (R%) calculated from PE results obtained by the analyses of naturally and artificially aged samples, (4) a modified solvent loss ratio version (R%*) calculated from RPA results. After the determination of the limits of reliable measurements of the analytical method, the repeatability of the different ageing parameters was evaluated over time, as well as the influence of ink composition, writing pressure and storage conditions on the results. Surprisingly, our results showed that R% was not the most reliable parameter, as it showed the highest standard deviation. Discussion of the results in an ink dating perspective suggests that other proposed parameters, such as RPA values, may be more adequate to follow ink ageing over time.

Ink dating, part I: Statistical distribution of selected ageing parameters in a ballpoint inks reference population

“…10 dots/punches were taken on different locations of the four lines for each set. For each dot taken for the "natural" set, a second was collected right next to it for the "heated" set in order to limit variations between the two sets [6,8,9,25].…”

“…64% of the inks contained less than 80 ng/cm tending to show that highly concentrated PE in inks are less frequent on the ink market than lower concentrations. Other compounds identified in the composition of the measured inks might also be useful for dating purposes, at least to normalise PE quantities through the calculation of RPA ratios [25]. While BA was present in all samples at time t=4 days, about 24% of the inks contained only traces of BA (i.e.…”

“…This step generally represents the easiest task and is well described in the (forensic) literature [13]. More recently proposed approaches focused on the analysis of ink volatile compounds, and mainly phenoxyethanol (PE) and its decrease over time [5][6][7][8][9][10][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. While gas chromatography coupled to mass spectrometry (GC/MS) was mainly used to analyse PE and other ink solvents, high performance liquid chromatography (HPLC) was also recently proposed to simultaneously analyse dyes and solvents [10,11,23].…”

“…Once the method is developed and validated, ageing parameters must be selected to monitor ageing according to the following criteria [12,25,34]:…”

“…In a previous paper using liquid extraction followed by GC/MS [25], four ageing parameters were tested over time under different influence factors: the quantity of PE, different relative…”