Abstract: A highly sensitive broad band mass spectrometer consists of a broad band selector of a low energy level beam of negative ions to be examined; a molecular disintegrator and charge changer which receives the negative ions and produces a beam of high-energy multiply charged positive ions free of molecules; and a broad band high-energy, continuously-operable isochronous time-of-flight mass spectrometer which receives the output from the molecular disintegrator. The disintegrator destroys molecules that would obscure the measurement of atomic species. Both selector and spectrometer preferably are electrostatic to avoid mass discrimination and maintain the broad band capability. The use of an isochronous time-of-flight mass spectrometer permits continuous operation which increases sensitivity. The ion selector may be of a magnetic type if a somewhat narrower band of masses is acceptable.