Abstract: A mass spectrometer operating according to the iso-tach principle in which a mass filter accelerates ions to nominally equal velocities irrespective of their mass-to-charge ratios. The mass spectrometer is provided with an improved detector based on an electrostatic lens arrangement made of a concave lens followed in the beam path by a convex lens. These lenses deflect ions away from the beam axis by a distance from the beam axis that is inversely proportional to their mass-to-charge ratios. The mass-to-charge ratio of the ions can then be determined by a suitable detector array, such as a multi-channel plate placed in the beam path. This provides a compact and sensitive instrument.

Abstract: A mass spectrometer comprises an ion source which provides a beam of ions; a mass filter comprising a pair of electrodes and a drive circuit, the drive circuit operable to apply a time varying voltage to the electrodes having a profile that accelerates the ions to equal velocities irrespective of their mass: charge ratios; and an ion detector for detecting the proportions of ions according to their mass-to-charge ratios. In one embodiment, the voltage profile is exponential. In another embodiment, the voltage profile is a sequence of constant amplitude and increasing repetition frequency pulses. The novel mass filter thus imparts equal velocities to all ion species irrespective of their mass. This allows the ion species to be discriminated at the detector by energy, enabling simple and compact detection schemes to be used.