The present invention provides a method for acquiring fragment ion mass spectra with a time-of-flight mass spectrometer, whereby mixed mass spectra with fragment ions of different parent ion species are acquired and compared with each other in such a way that the signals of those fragment ions which originate from the same parent ion species are determined. The time-of-flight mass spectrometer contains an ion source, a flight path, a reflector and an ion detector. The flight path is preferably field-free and is positioned before the reflector, and the reflector preferably has a quadratically increasing reflection potential.
