Patent GB-1326279-A (GB)
Title: Mass spectrometers
IPC: H01J49/40
Filed: 1970-11-25
Abstract: 1326279 Mass spectrometers BENDIX CORP 25 Nov 1970 [31 Dec 1969] 55962/70 Heading H1D An apparatus for analysing charged particles according to their mass-to-charge ratios by measuring the time of flight of each charged particle travelling between two reference points, comprises a means 12 for creating a dynamic electric field, means for introducing charged particles into the dynamic field, said field having at least two components during at least a portion of the charged particles flight between said reference points, and means 37 for measuring the time of flight of each charged particle travelling between said injection and ejection points. In one arrangement, Fig. 1, gas from a source 34 is ionized in a region 22 by electrons emitted by a filament 24 under control of a pulsed grid 26 and passing through an electrostatic lens 28 to an anode'30. Pulses are applied to a second control grid 32 to inject ions from region 22 into a dynamic field provided by structure 12 of metal rings 39 and an earthed end-electrode 40 separated by dielectric spacers 43 and connected to a potential divider 44 supplied by circuitry 18 (Fig. 2, not shown). The dynamic field preferably comprises A.C. and D.C. components, but may be A.C. only. For any particular set of operating conditions established by the circuitry 18 ions within a certain range of m/e ratios undergo unstable motion and are lost to the electrodes 39, while ions within another range of ratios undergo stable motion and return to the detector 37 which may be an electron multiplier or a Faraday cage, and is connected to readout apparatus 38 comprising a wide-band amplifier and an oscilloscope. Different scanning methods may be employed by suitably controlling the A.C. and D.C. potentials and operating frequency. A sequential scan may be achieved by providing a narrow time gate at the output of the detector 37. In an alternative arrangement (Fig. 8, not shown) gas is led by a tube directly into the region 22, and the dynamic field is provided by a single tubular resistive electrode fed by modified circuitry (Fig. 9, not shown) in which the D.C. component is obtained from a rectifier. A further alternative arrangement (Fig. 10, not shown) includes a spiral detector, and the dynamic field is established between an earthed conical electrode and an electrode having a surface defining a hyperboloid of revolution. The circuitry (Fig. 11, not shown) in this arrangement includes programmed means for maximizing either the resolution between adjacent ion species or the signal strengths from the various species. In a further alternative arrangement, Fig. 13, a dynamic field having a zero component in the x direction so that no reflection of ions occurs, is provided by a monopole structure including a cylindrical or hyperbolic rod 130 and two converging plates 132, 134 (not shown) forming a slot into which ions are injected with a component of motion along the x axis and are collected by a detector 37. In a further alternative arrangement (Figs. 14 and 15, not shown), a mirror arangement of the structure 12 of Fig. 1 is arranged on the opposite side of the region 22 to provide ion storage capability. Stored ions are removed by pulsing a grid to direct ions to a detector located laterally of the region 22 or at either end of the combined field structure.