HPLC–HR-ESI–MS/MS identification of fluorescent dyes and optical brighteners and their degradation products in daylight fluorescent paints

Abstract

AbstractDaylight fluorescent paints are luminous colors that are increasingly used in contemporary art. The pigments consist of a synthetic resin in which fluorescent dyes and optical brighteners are embedded. In the recent years, several research articles have been published on the composition of daylight fluorescent pigments. Despite the growing research on the aging behavior of daylight fluorescent paints, little is known to date about the chemical processes involved in aging. In the research presented here, we used dialysis to separate the colorants from the resin. HPLC–HR-ESI–MS/MS was used to extend the elucidation of the dye composition. A variety of rhodamines and coumarins, an aminonaphthalimide dye and another optical brightener were determined. NMR was used to elucidate the structure of an additional hemicyanine dye not listed in the Colour Index. Furthermore, reference substances were artificially aged under visible light and UV radiation and the degradation products were analyzed accordingly. N-deethylation, hydroxylation and higher oxidation processes were found to be the main degradation pathways for all colorants. For most dyes and optical brighteners, there was no difference between aging under visible light and aging under UV radiation. When the results were checked on samples of aged paint mock-ups, it was found that only a few of the degradation products can still be detected in the case of very advanced aging even with the smallest sample quantities.