2.4.3. Step III: structure assignment and confirmationUM-PPS was used without the “relative reasoning mode” [16]to predict two generations of TPs for each pharmaceutical. Thislist was complemented with TPs previously described in literature[10,17–31,33–36,39]. The candidates retained from step II werecompared to this list on the basis of their exact mass, and – in caseof a match – were annotated as tentatively identified TPs. For theremaining components, annotated as potential TPs, their chro-matographic and spectral information as well as time-trends weremanually inspected and the most plausible molecular formulawas assigned to each component (see Supplementary Material fordetails).Commercially available reference standards were purchased forthe tentatively identified TPs. Mass spectra were recorded with flowinjection (concentration: 1000 ng mL−1in MeOH), and a series ofcalibration standards (concentration range: 5–200 ng mL−1) wereanalyzed to confirm RT.