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

Light-induced degradation (LID) strongly depends on experimental conditions, among which the presence of oxygen is a major parameter. Elucidating LID processes is of high concern to many areas of interest, e.g., for the conservation of cultural heritage, safety and shelf life of food, and UV-disinfection methods for water purification. Recently, we presented a new, fully automated tool to study molecular photodegradation in solution. The tool employs a gas-permeable liquid-core waveguide (LCW) as a light-exposure cell with in-situ absorption spectroscopy for real-time monitoring, coupled on-line to liquid chromatography (LC) with diode-array (DAD) and mass spectrometry (MS) for characterization of the photodegradation products. The current work reports on the assessment of the potential of the LCW in a tube-in-tube geometry for studying the role of oxygen in photodegradation processes, using Riboflavin and Eosin Y as model compounds. The LID results obtained for Riboflavin and Eosin Y using the LCW set-up were in line with reported data obtained with conventional approaches. On-line LC-MS analysis allowed semi-quantitative monitoring of LID differences under oxic and anoxic circumstances. An increase in degradation by 9% and 30% for Riboflavin and Eosin Y, respectively, was observed after 10 min under anoxic conditions. Moreover, for the first time, the fully debrominated species of Eosin Y (i.e. fluorescein), was identified as a photodegradation product in solution. The presented set-up can be highly useful for the investigation of photodegradation mechanisms and kinetics in solution, including the role of oxygen while increasing analytical efficiency and reducing time spent in the lab.