Investigating the in‐solution photodegradation pathway of Diamond Green G by chromatography and mass spectrometry

Abstract

Diamond Green G (CI 42040, Basic Green 1) is a triarylmethane dye mostly employed in the industrial dyeing of miscellaneous natural and artificial textile fibres, in the production of printing inks and as an anti‐fungal agent for aquaculture products. Diamond Green (DG) tends to fade under light irradiation, similar to several other dyes and pigments belonging to the triarylmethane family. In this paper, an in‐solution degradation study was carried out to shed light on DG photostability. The experiments were performed by artificially irradiating DG in water and dimethyl sulphoxide, and analysing aliquots sampled at different time intervals by ultra‐high performance liquid chromatography coupled with diode array detector quadrupole and time of flight tandem mass spectrometry. The degradation products formed were characterised and the product‐ion spectra discussed and interpreted. On the basis of the structure of the identified compounds and their kinetic trend in relation to the accelerated ageing time, degradation mechanisms were proposed for DG, taking into account the role played by the solvent. Finally, the dyeing formulation of an historical textile sample, collected from a stage costume worn in a Zeffirelli lyric opera, was determined utilising the information collected from the analysis of irradiated DG solutions.

An Introduction and Recent Advances in the Analytical Study of Early Synthetic Dyes and Organic Pigments in Cultural Heritage

“…Many synthetic colourants are renowned for being particularly light sensitive [6,23,24]. Studies on degradation mechanisms have elucidated some pathways that lead to the molecular degradation of ESDs and SOPs [11,62,65,96,147,200,[208][209][210][211][212]. Separation techniques are often required for such studies, as degradation products and their parent molecules often show similar spectral features.…”

“…The knowledge of the precise chemical formulation of reference materials and the creation of exhaustive databases is fundamental for the correct description of dye degradation pathways [20,21]. Several studies on dye degradation and the identification of the photo-oxidation products have been conducted by HPLC-DAD-MS/MS under photo-accelerated conditions in solution [26,62,173,197,200,211,213] or in painting/textile matrices [65,208,210] as well as with attention to other mechanisms not related to light exposure [212]. Some of the observations gathered are summarised in the following sections.…”

“…Dealkylation is a known photodegradation pathway of various classes of synthetic colourants [28], especially those containing N-alkylated functionalities, such as some triarylmethane dyes (Methyl Violets, Diamond Greens, Patent Blues, etc.) [20,173,197,211,213], as well as Rhodamines [187,208] and some azines [20,21]. These colourants are often detected as mixtures of differently alkylated molecules.…”

Liquid Core Waveguide Cell with In Situ Absorbance Spectroscopy and Coupled to Liquid Chromatography for Studying Light-Induced Degradation

“…With commonly used methods it is often difficult to find a strong link between the parent molecule and the degradation product(s). An example of such a method is where solutions are degraded in a beaker placed under a light source. − These experiments can take rather long as the irradiation (power per area) is often low; that is, Confortin et al irradiated a solution of crystal violet for at least 100 h, and Weyermann et al required 54 h. Besides, errors are easily introduced since samples are taken manually, and solvents may evaporate during irradiation, resulting in irreproducible results. Hence, efficient tools are needed to study photodegradation in a simple and repeatable manner, while including the most important parameters affecting photodegradation.…”