Incorporating a liquid-core-waveguide cell in recycling liquid chromatography for detailed studies of photodegradation reactions

In this work, a microfluidic photoreactor was embedded in a recycling liquid-chromatography system. Mixtures were separated on an analytical column and compounds of interest were subsequently introduced into the light-reactor cell. After degradation, the content of the light-reactor cell was reinjected onto the same column to separate the parent compound from its degradation products. A separated degradation product could be re-introduced into the photoreactor and irradiated again. The next generation of degradation products could again be separated on the same analytical column. This recycling procedure proved an excellent tool to elucidate degradation pathways. This was demonstrated using riboflavin, better known as vitamin B2. By degrading it in the first cycle, degradation products were isolated and subjected to a second degradation in the light-reactor cell. This allows pinpointing secondary products and connect these with primary degradation products. Compared to previous work, this configuration is simpler, cheaper, and more user-friendly, while offering the unique possibility to easily connect degradation products to the initial compounds in a mixture.