Patent ID: 8373121

Claim:
A magnetic mass spectrometer with double focusing comprising an ion source, an entry slit, an electrostatic section, a magnetic section and means for simultaneous detection of at least one ion mass, comprising: a first electrostatic device placed between the ion source and the exit of the electrostatic section, focusing the beam of ions onto the main axis of the mass spectrometer; a second electrostatic device disposed downstream of the magnetic section, creating in the longitudinal plane of symmetry a radial electric field that is higher the further the point in question is from the axis and whose respective signs, on the side of the low masses and on the side of the high masses, are opposing; wherein the electrostatic section is a truncated spherical electrostatic section comprising an external electrode to which a +Ve voltage is applied, and an internal electrode to which a −Ve voltage is applied, the external electrode and the internal electrode furthermore comprising a pair of external parallel plates disposed on either side of the external electrode and to which a voltage V ext is applied, and a pair of internal parallel plates disposed on either side of the internal electrode and to which a voltage V int is applied, said pairs of internal and external parallel plates forming the first electrostatic device; the voltages V ext , V int respectively applied to the external and internal parallel plates being adjusted by the same voltage difference ΔV each time that the second electrostatic device is activated, in order to modulate the dispersion in mass or in order to cancel the off-axis chromatism, in such a manner that the beam of ions corresponding to the on-axis mass always remains focused on the main axis.