Protonated and Sodiated Cyclophosphamide Fragmentation Pathways Evaluation by Infrared Multiple Photon Dissociation Spectroscopy.

Cyclophosphamide (CP or CTX) is a widely used antineoplastic agent, and the evaluation of its efficacy and its impacts on the environment are dependent on mass spectrometry (MS) techniques. Because there is no dedicated experimental study to characterize the actual molecular nature of the CP fragments upon collision-induced dissociation, this work evaluated the chemical structure of the fragments of protonated and sodiated CP and CP protonation sites by infrared multiple photon dissociation spectroscopy supported by density functional theory calculations. This study allowed us to propose a new fragment structure and confirm the nature of multiple fragments, including those relevant for transitions used for CP quantitative and qualitative analyses. Our results also show that there is no spectroscopic evidence that can rule out the existence of aziridinium fragments, making it clear that further studies on the nature of iminium/aziridinium fragments in the gas phase are necessary.