FR2486713A1 - MASS SPECTROMETER IN FLIGHT TIME - Google Patents

Abstract

FLIGHT TIME MASS SPECTROMETER INCLUDING A SOURCE OF ION AND DEVIATION AND FOCUSING DEVICES, IN WHICH DIFFERENT MASS AND ENERGY IONS ARE LAUNCHED FROM A STARTING POINT ON A TRACK AT THE END OF WHICH IS AVAILABLE. ION COLLECTOR. THE TRAJECTORY IS INFLECHED OR DEVIED BY SEVERAL IONIC MIRRORS 16, WHICH ARE DIMENSIONED AND CONTROLLED SO THAT THE FLIGHT TIME OF THE IONS BETWEEN THE DEPARTURE POINT S AND THE COLLECTOR 20 IS INDEPENDENT OF THEIR ENERGY.

Description

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  The present invention relates to a time-of-flight mass spectrometer comprising an ion source and deflection devices

  and focusing, in which ions of different mass and energy

  Annuities are launched from a starting point on a trajectory at the end of which is disposed an ion collector. Time-of-flight mass spectrometers separate ions of the same energy but of different mass by making them travel the same length at a different speed, to reach successively

  an ion collector or an ion photomultiplier. It is essential

  all the ions are launched at the same time, at the beginning of the course. Soviet Patent No. 198,034 describes a particular time-of-flight mass spectrometer assembly (FIG. 1), in which the energy of all the ions does not have to be equal anymore.

  (See B. A. Mamyrin et al., Zh Tekh Fiz 41 (1971), 1498 - Sov.

  Phys.-Tech. Phys. 16 (1972, 1177). After crossing the path (L), the ions are indeed deviated by almost 1800 by an electrostatic mirror and must thus perform the path in the opposite direction, before they can be recorded by an ion photomultiplier, placed right next to the source ion. It is essential that slightly higher energy ions penetrate deeper

  in the ion mirror formed by grids; they must therefore be

  in total a greater distance than the ions of slightly lower energy. An appropriate distribution of the potential in the ion mirror has made it possible to obtain that the time of flight of the ions between the source and the photomultiplier depends solely on their mass and not their energy, at the cost, however, of great losses.

ion current.

  Since the mass resolution of a time-of-flight mass spectrometer is proportional to the length of the path, it is desirable to increase this length. Even with a Mamyrin ionic mirror, that is to say with a double use of the constructive length, we still obtain extended systems, including the collector and the

  ionic mirror must besides be of large diameter. The introduction

  focusing elements, such as electrostatic lenses,

  symmetrical ticks, certainly reduces at least the collector

  ions, but the diameter of the ion mirror remains high.

  The aim of the invention is to improve a time-of-flight mass spectrometer of the type previously described, to reduce ionic current losses and to obtain a higher resolution power with a

  simpler and more compact constitution, while avoiding the incon-

come from the prior art.

  According to an essential characteristic of the invention, the trajec-

  It is inflected or deflected by several ion mirrors, which are dimensioned and controlled so that the ion flight time between the starting point and the collector is independent of their energy. The step of the folded beam several times is essential for the time-of-flight mass spectrometer according to the invention; this repeated deviation or inflection of the trajectory is equivalent to the serial assembly of several time-of-flight (simple) mass spectrometers with ionic mirrors. With a relatively weak apparatus, the trajectory of the ions is lengthened and consequently the resolution of the

  complete system improved, for the same duration of the ionic peaks.

  The use of N ion mirrors of this type (having a reflection of 100%) makes it possible to use the constructive length not only twice, but (N + 1) times. The number N of ionic mirrors can be

even or odd. -

  The mass resolution of a time-of-flight mass spectrometer increases as the duration of an ion pulse decreases. intensity

  ionic decreases with the duration of an ion pulse.

  According to another characteristic of the invention, it is possible to combine a high mass resolution and a high intensity by providing an additional path of length D between the ion source and the beginning of the path of length L (FIG. ) instead of using a pulsed ion source, directly upstream in a time-of-flight mass spectrometer according to Mamyrin et al. At the beginning of a pulse, the source can then emit weak ions

  energy, then ions of energy and consequently of increasing velocity.

  In the case of appropriate sizing and control, the faster ions have caught up at point E the slower, launched ions

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  previously. A much shorter pulse of ions, whose energy width has however increased, is thus produced at point E without loss of ionic current. This phenomenon is called "production

  ion packets "in the art of particle accelerators.

  The duration of the pulse is D.AU at the catch-up point E, where AU is the. inevitable energy width of the ions leaving the source at a given moment. D is as low as possible in order to make the pulse duration as short as possible at the catch-up point E; in some cases, when the production of ions is limited for a short time for example, it is possible to neglect totally

  this catch-up effect by adopting hence D = 0.

  In a time-of-flight mass spectrometer of the type shown in FIGS. 1 and 2, the diameter of the ion beam increases with the length of the ion trajectory. To oppose this effect, he

  It is possible to insert a focusing lens on the beam path.

  which reduces the diameter of the beam at the location of the

ion reader.

  According to another very advantageous characteristic of the invention,

  the ion mirror itself is used as a focusing element.

  It is not constituted in the usual way by metal networks.

  parallel lines, each representing a potential surface area

  undermined; according to another characteristic of the invention, it comprises a series of diaphragms, tubes or other elements, worn to various

  potential. Like a filter lens from Möllenstedt

  In transmission, such an ion mirror operating in reflection produces focussing effects, as a numerical calculation makes it possible to show it. Ionic mirrors consisting of focusing diaphragms furthermore eliminate the losses of the ion beam,

  unavoidable when the latter passes through conventional networks.

tional.

  Other features and advantages of the invention will be

  better understood using the detailed description below

  examples of embodiments and the accompanying drawings in which Figure 1 shows the diagram of a time-of-flight mass spectrometer according to the aforementioned prior art; 4-

  FIG. 2 represents the corresponding diagram of a part of a spectral

  time-of-flight mass trometer according to the invention; FIG. 3 represents a diagrammatic oblique view of a plane linear disposition time-of-flight mass spectrometer; FIG. 4 represents the oblique view of a time-of-flight mass spectrometer according to the invention, with a circular cylindrical arrangement; FIG. 5 represents the principle of a time-of-flight mass spectrometer according to the invention with switchable ion mirrors; and FIG. 6 represents the principle of a time-of-flight mass spectrometer according to the invention with ionic mirrors with electrostatic switching.

  The arrangement shown in Figure 1 corresponds to the reference

  mentioned above (Mamyrin et al.). The time-of-flight mass spectrometer comprises an ion source 12 and an ion beam guiding device 14, which an ionic mirror 16 with gates 18 deflects over an ion beam.

  ion collector 20 (photomultiplier).

  The parts of a mass spectrometer - time of flight according to the

  vention has the same appearance, as shown in Figure 2.

  The identical elements are designated by the same references. The spec-

  mass meter 10 again comprises an ion source 12 and a device 14 for guiding the ion beam, that the ion mirror 16

  deviates on a collector 20. However, the essential

  sioning and control such as at a first point E1 located downstream of the ion source 12, higher energy ions, launched later, catch up with ions of the same mass but of lower energy; previously launched on the trajectory. The ion mirror 16, constituted by diaphragms, tubes or similar elements (not shown), furthermore has a focusing action, so that ion packets reach a second catch-up point E2, on the ion collector 20. With the upstream path D (between the ion source 12 and the first catch point E1), this arrangement ensures that the total flight time on the following path L depends solely on the mass and not on the energy of the ions. , so that pulses of ions of duration

  are produced on the collector.

  potentials in series mounting of N ion mirrors 16

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  or Rt, R2, etc. produces a different penetration depth of the ions in each mirror. A catch-up point E2, E3, etc. is thus created after each mirror RI, R2, etc. It is even possible to obtain that the first catch point following that located at a distance D downstream of the ion source 12 is on the

ion collector 20.

  In series assemblies of N ion mirrors, focusing elements or focusing ion mirrors should be used. We obtain a minimum diameter of the mirrors or lenses

  when the focal length of all mirrors Rt, R2, etc. and len

  is equal to L / 2, where L is the distance between two mirrors facing each other. An extraction optic of the ion source 12 or an auxiliary lens makes it possible to obtain an image of the ion source 12 at the location of the inversion of the beam in the first mirror R2 of the plane II (FIG. and 5), while a pupil is necessary against the location of the inversion of the beam in the first mirror R1 of the plane 1, as in the case of circular accelerators,

  in order to adapt the beam to the center of the focal points

  tion. Ionic mirrors Ri, R2, etc. deviating the path of the beam can be arranged side by side on a line or in a plane (Figure 3), or on a circle or a cylinder (Figure 4). Every first

  mirror should generally be tilted or rotatable, electrostatic

  electromagnetically using an electro-

  nique, so that the ion beam is directed to the center of the (1 + 1) th following mirror. In the case of Figure 3, this means that the mirrors are arranged linearly and parallel in the two planes I and II, so that the ion beam is reflected in a transverse plane, with a movement back and forth , until it exits through the last ion mirror (R7) to reach a downstream ion collector. In the exemplary embodiment according to FIG. 4, the various ionic mirrors R1, R2, and so on. are arranged in a circle in each of the two planes I, II, so that

  the corresponding envelope may be a cylinder or a truncated cone.

  A substantially parallel arrangement of all the ionic mirrors is also possible in this case, with the interposition of an electrode

  repulsive 22 which, at each pass, deflects the ion beam sensi-

  to the center of the complete assembly.

  It can be seen that the assemblies according to FIGS. 3 and 4, using N ion mirrors, use (N + 1) times the constructive length, substantially equal to L, as the course of the ions. It is also possible according to the invention to circulate the ion beam N times between two ion mirrors Ri, R2 (Figure 5). However, devices are needed to introduce the ion packet on this course

  (a L), between the two mirrors RI, R2, then extract it.

  In a system according to FIG. 5, the potentials of the ion mirrors

  can be pulsed by an appropriate command, instead of being applied continuously. The ionic cloud can for example meet

  first the mirror Rt to the earth, that is to say, as if it did not exist

  was not, while the mirror R2 reflects the ions. The ionic cloud returning from the mirror R2 is then reflected by the mirror RI, connected in the meantime. After N crossings of the distance between the mirrors Ri and R2, the electronic control causes the ions reaching the mirror R2 for the (N + 1) th foix to find it in the earth, that is to say, as if it were did not exist. They can consequently go out and reach

the ion photomultiplier 20.

  The system according to FIG. 6 uses mirrors R1, R2, etc. a

  electronic control makes it possible to switch briefly and in-between

  which the potential distribution is briefly commanded so

  modifying the angle of reflection of the ion beam; it is then pos-

  It is possible to record in the first collector (ion photomultiplier) Ai a relatively high resolution mass spectrum. A brief rotation of the mirror Rt allows the ion beam to reach the mirror R2. The latter is inclined during the passage of the ionic cloud so as to deflect the beam on the mirror R3; the mirror R2 is then returned to its initial position and the ionic cloud reflected N times between. mirrors R2 and R3, until a brief pivoting of the mirror R3 directs the ion beam onto the second collector A2. The latter therefore records, with a high mass resolution, a small mass range extracted from the mass spectrum recorded by

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  the first collector AI. Such beam swivelings can also

  can be performed by additional failover elements

  (not shown), electrostatic or magnetic, for example.

  Of course, various modifications can be made by those skilled in the art to the principle and to the devices which have just been described by way of non-limiting examples, without

depart from the scope of the invention.

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Claims (16)

claims   A time-of-flight mass spectrometer comprising an ion source and deflection and focusing devices, in which ions of different mass and energy are launched from a starting point on a trajectory at the end of which an ion collector is arranged, said spectrometer being characterized in that the trajectory is inflected or deflected by a plurality of ion mirrors (16, R1, R2, etc.), which are dimensioned and controlled in such a way that   the ion flight time between the starting point (S) and the collector-   (A) is independent of their energy.   A mass spectrometer according to claim 1, characterized by dimensioning and controlling the ion mirrors (16, R1, R2, etc.) and their potential distribution such that the ions depart from the point (E) at which weak ions energy, previously produced, are caught by ions launched later, of the same mass but superior energy.   3. Mass spectrometer according to one of the characteristics 1 and 2,   characterized in that the ionic mirrors (16, R1, R2, etc.) comprise   diaphragms, tubes or other elements, to which various   Electrostatic heads can be applied.   4. Mass spectrometer according to claim 3, characterized in that grids seal the diaphragms, tubes or other elements, which   reflected ions can no longer or almost no longer reach.   Mass spectrometer according to any of claims 1   at 4, characterized by a geometry and mirror potentials such that the reflection of the ions is accompanied by a focus of the latter   between the starting point (S) and the collector (A).   6. Mass spectrometer according to any one of claims 1 to   , characterized in that the paths between two successive ion mirrors are always equal or that groups of ionic mirrors (16,   R1, R2, etc.) are provided with equal spacings (L); and the   focal ratio of the individual mirrors is equal to half of the (L) mirrors.   Mass spectrometer according to claim 6, characterized in that   that the necessary focal length (L / 2) is obtained with the aid of   symmetrical cells arranged upstream of the ion mirrors (16, RI, R2, etc.).   8. Mass spectrometer according to any one of claims 1   7, characterized by electrostatic or magnetic field control   time-varying ticks for the introduction and extraction of ions that travel more than one path with two mirrors   ionic or more (16, R1, R2, etc.).   9. Mass spectrometer according to claim 8, characterized, for the introduction and extraction of ions, by a control comprising additional electrostatic or magnetic deflection fields, pulsed and locally limited.   10. Mass spectrometer according to one of claims 8 and 9, characterized   in that the control of introduction and extraction of ions   includes a device for connecting and cutting off   tials of one or more ionic mirrors (16, Ri, R2, etc.); and that each mirror lets the incident ions pass for the duration of cut off its potential.   Mass spectrometer according to any one of claims 8 to   , characterized in that the ion introduction and extraction control comprises a device which varies briefly the angle of reflection of one or more ionic mirrors (16, Ri, R2, etc.) to   using potential variables over time.   Mass spectrometer according to any of claims 1   at 11, characterized by spherical equipotential surfaces in   the ionic mirrors (16, Ri, R2, etc.).   13. A mass spectrometer according to any of claims 1   at 12, characterized in that the ionic mirrors (16, Ri, R2, etc.)   are arranged facing each other in two planes (1, II).   14. Mass spectrometer according to claim 13, characterized in that the ionic mirrors (16, Ri, R2, etc.) of each plane (I, II)   are arranged linearly in a perpendicular plane.   15. Mass spectrometer according to claim 13, characterized in that the ionic mirrors (16, R1, R2, etc.) of each plane (1, II) are arranged in a circle.   16. Mass spectrometer according to any one of claims 13 24 8 6 7 1 3   at 15, characterized by at least one repulsive electrode (22) between   groups of ionic mirrors (16, R1, R2, etc.) opposite in both - plans (I, II).