Radiosensitizers are important compounds used in radiotherapy to enhance tumor control of radioresistant hypoxic tumors. Despite their use in biological applications, little is known about the fundamental properties of these compounds. Nevertheless, understanding the ionization reactions of these compounds is crucial in evaluating the potential of radiosensitizers and in developing new and more effective drugs. The present study investigates the positive and negative electrospray ionization and subsequent low-energy collision-induced dissociation reactions of ions derived from 1-methyl-5-nitroimidazole, metronidazole, ronidazole, ornidazole and nimorazole using a hybrid quadrupole time of flight mass spectrometer equipped with an electrospray ionization source (ESI-Q-TOF). Quantum chemical calculations are performed to obtain in addition the proton affinities, deprotonation energies, and electron affinities of the investigated compounds.