Evaluation of the Photodegradation of Crystal Violet upon Light Exposure by Mass Spectrometric and Spectroscopic Methods

Abstract

Crystal violet is a very common dye in ballpoint ink. Recent research suggests that the degradation of triarylmethane dyes gives an indication of the age of a ballpoint pen entry on a document. The main problem for the quantitative evaluation of the degradation is that it is highly dependent on the exposure to light. Moreover additional factors, such as additives and substrate play an important role in this process. The aim of this work is to compare the degradation pathways of the pure dye in water and ethanol upon exposure to xenon light by UV ⁄ VIS spectrophotometry and laser desorption ionization. Significant differences have been observed in the products and the kinetics of the degradation. N-demethylation, an expected decomposition process, was found to take place only in aqueous solution and kinetics calculations showed that the degradation occurred 2.5 times faster in ethanol compared to water. The degradation of crystal violet in inks from four ballpoint pens on paper was also studied for entries made over 2-3 years. It was observed that degradation reactions were quenched by the presence of another dye due to competitive absorption. It was also observed that the thickness of a stroke (concentration of ink) influenced the degradation process. In the absence of light only one ballpoint pen showed slight degradation. A better understanding of the influence of the paper, ink composition, and storage conditions is necessary to interpret correctly the age of an ink based on the degradation of dyes.

Differentiation of blue ballpoint pen inks by positive and negative mode LDI-MS

“…The graph confirms that the molecular ion RPA values of the triphenylmethane cationic dye BV3 (RPA 372 ) decreased in correlation to nominal laser irradiance, while degradation products were formed (i.e., increasing values of RPA 358 and RPA 344 ). Similar observations were previously reported in the literature [19,20] and demonstrate that dependence between laser irradiance and degradation of cationic dyes is a consequence that have to be considered if LDI-MS is used to discriminate inks. No information of this type was yet proposed for negative ions.…”

“…This ensures high discrimination power considering that combinations of organic dyes and inorganic pigments are highly variables in ink formulations [15]. Secondary ion mass spectrometry (SIMS) [4], field desorption (FD) [5], electrospray ionization (ESI) [7], laser desorption/ionization (LDI) [6,12,[16][17][18][19][20], matrix-assisted laser desorption/ionization (MALDI) [19,21], direct analysis in real time (DART) [8] and desorption electrospray ionization (DESI) [22,23] were proposed for ballpoint inks examination. In addition to classical methods, mass spectrometry may yield information on the structure of the analyzed molecules (i.e., mass or/and fragmentation pattern).…”

The investigation of dye aging dynamics in writing inks using Raman spectroscopy

“…Here, the photoreduction of the excited dye cation is achieved by the addition of an electron to dye photoexcited states or by photochemical hydrogenation of a dye [9,13].…”

“…Moreover, materials of paper documents can also be very different in their structure and chemical composition. Therefore, it is quite important to study in detail the aging process of dyes taking into account all aforementioned factors [13].…”

Minimum requirements for application of ink dating methods based on solvent analysis in casework

“…It was based on the changes in the extractability of the ink supposedly caused by the hardening of the resins [10,[21][22][23][24]. The use of this technique in caseworks was reported in the literature [18,25], but it was followed by a vigorous controversy among the scientific community about the limitations of this approach [5,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. Several researchers tried reproducing the results obtained in previous studies and reported the methods to be unreliable [28,[34][35][36], while other scientists debated about the necessity for inter-laboratory validation before their use in casework [4,27,[31][32][33]38,41].…”