Pyrolysis gas chromatography - mass spectrometry of triarylmethane dyes

Triarylmethane (TAM) dyes are commonly used in modern inks and paints and are of large interest in different fields of application such as cultural heritage, forensic sciences, dying industry. Here, a systematic pyrolysis - gas chromatography-mass spectrometry study of eight commonly used green, blue and violet triarylmethane dyes (Basic Violet 1, Basic Violet 3, Basic Violet 14, Basic Blue 11, Acid Green 5, Acid Blue 9, Acid Blue 22 and Basic Green 1) is presented. Pyrolysis temperatures ranging from 300 °C up to 800 °C were applied in order to study the pyrolysis products generated at each temperature. Low temperatures (300 and 400 °C) were not sufficient to distinguish between the different TAMs, whereas at 550 °C, a common temperature in paint analysis, a series of specific compounds useful in differentiation is formed, although at 700 °C a larger number of markers is generated. Py-GC-MS of two blue felt-tip pen inks used by modern artists was also carried out in order to verify the possibility to detect low amounts of TAMs in complex matrices. Although not all the pyrolysis products of the reference TAMs could be detected, efficient identification of the dyes could be accomplished thanks to the presence of specific markers.