Gas-permeable liquid-core waveguide coupled to LC-MS for studying the influence of oxygen on photodegradation processes

Chemical Mapping of the Degradation of Geranium Lake in Paint Cross Sections by MALDI-MSI

“…As the fully debrominated product (m/z 332.63) is also detected in the sample without LW, this may indicate that the loss of bromine is initiated by the light and presence of oxygen as suggested in previous studies modeling the degradation of eosin in aqueous solution. 34,36 The mapping of this ion in a solid sample provides for the first time direct evidence of this phenomenon, where eosin loses bromine before the cleavage of the chromophore.…”

“…These signals were assigned by comparison with data reported previously, , analyzing their isotopic patterns and distributions, and evaluating the possible additions to the most intense and monoisotopic ions based on mass differences. As GL was widely used by Van Gogh, its degradation pathway has been extensively investigated in solution and mock-up samples. ,,− These studies have revealed that an intermediate mechanism can be associated with the debromination process of the eosin molecule before leading to the breakdown of the xanthene moiety that causes total discoloration. ,, The ability to perform distribution analysis of the intact eosin monomer and its known degradation products on paint cross sections was evaluated next. 10 μm spatial resolution ion images of these characteristic ions in samples GL100 and GL50 are presented in Figure B,C.…”

“…The discoloration mechanism of eosin has been documented, in solution and oil paint models, ,− showing that eosin exhibits a multistep degradation process, where initially a debromination takes place, while the chromophore remains essentially intact; further degradation steps lead to the breakdown of the chromophore responsible for the red-pink color. This multistep degradation mechanism resembles the photodegradation of other organic dyes such as Rhodamine B, in which the subsequent loss of N -ethyl functional groups takes place before the cleavage of the chromophore and subsequent mineralization .…”