Characterization of forced degradation products of torasemide through MS tools and explanation of unusual losses observed during mass fragmentation of drug and degradation products through density functional theory.

Mass spectrometry tools (HRMS/LC-HRMS, MSn, and/or on-line H/D exchange) were employed to establish mass fragmentation pattern of torasemide and to characterize its degradation products. During collision-induced dissociation, multiple rearrangement processes and unusual losses of sulfur (S), sulfanyl (HS), sulfur dioxide (SO2), sulphinic acid radical (HSO2), sulfur monoxide (SO), carbon monoxide (CO), formyl radical (CHO) and C5H3NOS were observed. The same were successfully explained by study of energy profiles, established by application of density functional theory (DFT).