Figure 3.

Time-resolved photocatalyzed oxidation LAESI-MS of verapamil using a TiO₂ nanoparticle suspension. (a) The formation of the N-dealkylation product (m/z 291.21) of verapamil. (b) The formation of the demethylation product of verapamil (m/z 441.28). (c) The product of both the N-dealkylation and demethylation (m/z 277.19), which starts to appear around ~ 25 min (intensity shown at secondary y-axis). The 365-nm UV lamp was switched ON after 2 min. All lines were normalized to verapamil [M+H]⁺. Data were averaged (n = 3, for clarity, error bars are not shown), individual data are shown in Figure S14