Infrared multiple photon dissociation spectroscopy of ciprofloxacin: Investigation of the protonation site

► IRMPD spectroscopy of protonated ciprofloxacin electrosprayed from methanol solution. ► Quantum chemical calculations to identify the possible isomers differing in the protonation site. ► Bands are assigned to the isomer protonated. ► Bands are assigned to the isomer protonated at the piperazinyl amino group.