GB969293A - Improvements in or relating to mass spectrometers - Google Patents

Abstract

969,293. Mass spectrometers. MAX-PLANCKGESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN e. V., and INSTITUT FUR PLASMAPHYSIK-G.m.b.H. Dec. 20, 1962 [Dec. 23, 1961], No. 48263/62. Heading H1D. In a mass spectrometer having a longitudinally extending vacuum tube, ions which have been caused to oscillate along a first portion of the length of the tube are supplied with high frequency energy to cause selective acceleration of those ions having a predetermined charge/ mass ratio; ions travelling above a predetermined velocity are then caused to enter a second portion of the tube where they again oscillate before being detected. As shown, the vacuum tube houses a plurality of apertured electrodes 1 to 30 which are connected to a voltage divider and potential supply arrangement 31 in such a manner that the potential distribution along the tube is in the form of first and second, preferably parabolic, potential troughs 33 and 34 with a normal intervening maximum 35<SP>1</SP>. Electrodes 1 to 7 inclusive and 8 to 12 inclusive are coupled to form two groups which are supplied with high frequency voltage from an oscillator 39. Ions produced in the first portion of the tube oscillate in the potential trough 33 with frequencies depending on the different charge/mass ratios. Ions whose frequency of oscillation coincides with the applied H.F. voltage accumulate energy and oscillate with increasing amplitude. These resonant ions are then allowed to pass into the influence of the second potential trough 34 by temporarily reducing the potential maximum between the troughs 33, 34 to a value 35<SP>11</SP> which can be surmounted by the resonant ions; this potential reduction is effected by applying a suitably phased voltage, derived over a phaseshifter 55 from the oscillator 39, to a ring electrode 54 situated inside electrode 15. The ions in the second portion of the tube oscillate in the potential trough 34 for detection. The detection arrangement may comprise a secondary electron multiplier 50 arranged after the last potential electrode 27 and having an output electrode 51, or it may comprise electrodes 24 to 27, which are interconnected by capacitors to form an electrostatic collector arrangement, an amplifier 48 and a measuring device 49. The electron gun system 40, shown enlarged in Fig. 1 and rotated through 180 degrees, which produces an ionizing electron beam perpendicular to the tube axis, includes a compensating electrode 45 to reduce undesirable effects arising from electric fields created by the system. Similar conditions prevailing in the region of the potential maximum 35 are compensated for by the provision of an electrode 13 connected over an attenuator 62 to the oscillator 39. An electrode 27<SP>1</SP>, similar in circuitry and function to the electrode 54, may be provided at the input to the multiplier 50.