Monitoring photochemical reactions catalyzed by nano-titanium dioxide using electrospray laser desorption ionization...

Electrospray laser desorption ionization mass spectrometry (ELDI-MS) is a two-step ambient ionization method that can effectively analyze particle-rich samples. In ELDI-MS, analytes are first separated from the sample matrix through laser desorption, then post-ionized within an electrospray plume, and finally detected by a mass analyzer. A major advantage of this method is its ability to minimize matrix interference, since analytes are desorbed before ionization takes place. This benefit is particularly useful for monitoring photochemical reactions involving high concentrations of titanium dioxide nanoparticles (nano-TiO₂).

ELDI-MS was used for real-time monitoring of photochemical reactions catalyzed by nano-TiO₂. These reactions, initiated by nano-TiO₂ and ultraviolet (UV) light, occurred in a reaction vessel. The sample solution was drawn from the vessel by capillary action to the tip of a stainless-steel tube, where it was exposed to a pulsed laser. The laser desorbed analytes and microdroplets, which then interacted with charged droplets in an electrospray plume above the tube to produce analyte ions for mass spectrometric detection. ELDI-MS was applied to track the breakdown of two industrial dyes-acridine orange and rhodamine 6G-under UV light in the presence of TiO₂ nanoparticles as catalysts. The resulting mass spectra revealed stepwise N-demethylation of the dye reactants. For cytochrome c, the spectra showed that highly charged, denatured protein forms were generated during photocatalytic degradation in the presence of UV light and nano-TiO₂.

ELDI-MS has proven to be an effective real-time tool for monitoring photochemical reactions catalyzed by nano-TiO₂. This technique enables direct analysis of complex liquid samples without any pre-treatment, allowing fast and continuous detection of reactants, intermediates, and products throughout the reaction. These findings demonstrate that ELDI-MS is a simple, convenient, and robust platform for monitoring ongoing reactions in real time and gaining mechanistic insights into their progression without the need for sample preparation.