JPH0349177B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field to Which the Invention Pertains] The present invention relates to a mass spectrometer that measures the mass of ions. In particular, it relates to a magnetic field type mass spectrometer that passes an accelerated ion stream through a narrow slit, passes through a deflection magnetic field, captures it with an ion detector, and analyzes the mass of the ions by changing the strength of the deflection magnetic field. [Description of Prior Art] In a magnetic field mass spectrometer, the slit width of the ion source is s, the slit width of the ion detector is d, the mass dispersion coefficient is Aγ, the image magnification is Ax, and the image spread due to aberration is Δ. , its resolution R (=M/ΔM) is
Generally, it is given by R=Aγ/Ax・s+Δ+d...(1). To detect ions efficiently, d=Ax·s+Δ. In order to increase the resolution R, each constant must be set such that the numerator and denominator in equation (1) are made large and small, but if the slit width s of the ion source is made small, the sensitivity decreases. Therefore, in order to reduce the denominator of equation (1), it is desirable to reduce the image magnification Ax and at the same time reduce the aberration Δ. On the other hand, the ion stream emitted from the slit of the ion source passes through the deflection magnetic field, but as the ion stream advances, it diverges and its width increases. On the other hand, if the mass of the ions to be analyzed is large, the magnetic field needs to be made stronger, and therefore the magnetic pole spacing must be made smaller. In the conventional device, the ion flow is in the direction perpendicular to the orbital plane (y-direction).
The width is set to 15 mm, but in order to measure polymers with molecular weights of ions reaching several thousand, the magnetic pole spacing must be narrower to increase the magnetic field strength, and a portion of the ion flow is It will only be available. The applicant of the present application filed a patent application (Japanese Patent Application No. 118645/1983, filed on July 29, 1981, hereinafter simply referred to as the earlier application) in order to improve this. This is an electrostatic quadrupole lens that is placed between the slit of the ion source and the deflection magnetic field, giving the passing ion stream a focusing property in the direction perpendicular to its trajectory plane and a diverging property in its radial direction. It has a structure in which multiple pieces are arranged at intervals. This made it possible to reduce the spacing between the magnetic poles that create the deflection magnetic field, and at the same time improve detection sensitivity and resolution. As a result of further research into this technology, the inventor found the following. That is, when the magnetic pole spacing of the deflecting magnetic field is made small, the ion flow after passing through the deflecting magnetic field diverges. It was described in the specification of the prior application that in order to focus the ions and simultaneously satisfy the double focusing conditions, it is preferable to use a toroidal electrode and pass the ion flow through the toroidal electrode to provide focusing properties.
However, when the toroidal electrode is manufactured into a device, its workability is extremely poor, and the cost becomes too high to make it into a practical product. For this reason, an attempt was made to provide a cylindrical electrode in place of the toroidal electrode and allow the ion stream to pass through it after passing through the deflection magnetic field, thereby achieving double focusing (direction and energy focusing). However, as a matter of course, this is not sufficient because the cylindrical electrode can provide focusing in the radial direction of the ion flow, but cannot provide focusing in the direction perpendicular to the trajectory plane. It was hot. [Object of the Invention] An object of the present invention is to provide an efficient mass spectrometer that uses a cylindrical electrode that is easy to work with and focuses an ion flow that has passed through a deflection magnetic field. [Features of the Invention] The present invention provides a method between the ion source slit and the deflection magnetic field, which gives the passing ion flow a focusing property in a direction perpendicular to its trajectory plane and a divergent property in its radial direction. It has a structure in which multiple electrostatic quadrupole lenses are arranged at intervals, and a cylindrical electric field is provided as a deflection electric field to provide double focusing of radial direction convergence and energy convergence to the ion flow that has passed through the deflection magnetic field. , Further, between this cylindrical electric field and the deflection magnetic field, another electrostatic quadrupole lens is provided which gives focusing property to the ion flow passing through this cylindrical electric field in a direction perpendicular to its orbit plane. . [Description by Example] Next, the present invention will be described in more detail with reference to the drawings of the example. FIG. 1 is an apparatus configuration diagram showing a first embodiment of the present invention. The ion source 1 includes an ionization chamber 2 and a plurality of acceleration electrodes 3, and an accelerated ion stream is emitted from an ion source slit 4. This ion flow is 2
The light passes through the electrostatic quadrupole lenses 5 and 6 and enters the deflection magnetic field 7. The ion stream is deflected in this deflecting magnetic field 7, and those passing through the detector slit 8 are captured by the ion detector 9. This deflection magnetic field 7 is configured so that its strength can be changed from the outside (not shown), and the position of the detector slit 8 is fixed. Further, the ion flow is accelerated so that the kinetic energy of the ions incident on the deflection magnetic field 7 is constant. Ions that enter the deflection magnetic field 7 have different momentum depending on their mass, so they are deflected at different angles depending on their mass. Therefore, when the strength of the deflection magnetic field 7 is changed, the ions captured by the ion detector 9 have different masses, and the masses of the ions can be analyzed. Note that each device in this figure is placed in a vacuum, and the vacuum partition wall is omitted from the figure. The first feature of the present invention in this device is that electrostatic quadrupole lenses 5 and 6 are provided between the ion source slit 4 and the deflection magnetic field 7; and 6 are set so as to give convergence to the passing ion flow in the direction perpendicular to the orbital plane and divergence in the radial direction. Furthermore, the second feature of the present invention is that the ion flow that has passed through the deflection magnetic field 7 is passed through a cylindrical electric field 11 in order to satisfy the double focusing conditions of radial direction convergence and energy convergence. This cylindrical electric field 11 is generated by two concentric cylindrical electrodes 11A and 11B.
formed by Furthermore, the third feature of the present invention is that the cylindrical electric field 11 is
Another electrostatic quadrupole lens 1 that provides focusing to the ion stream incident on the ion stream in a direction perpendicular to its trajectory plane.
It is located where 2 was set up. FIG. 2 is a diagram showing a cross-sectional structure of this electrostatic quadrupole lens 5 and a configuration example of an electric circuit that applies a potential to it. The electrostatic quadrupole lens 5 consists of four vertically divided cylindrical electrodes as shown in FIG. 2 when taken in a cross section perpendicular to the direction in which the ion flow passes (the cross section shown in FIG. A positive potential is applied to electrodes facing each other in a direction perpendicular to the trajectory plane of the ion flow (y direction), and a negative potential is applied to electrodes facing each other in the radial direction (x direction) of the ion flow. Assuming that the radius of the inscribed circle of the four electrodes is r ₀ , the outer diameter of each electrode is designed to be 1.13r ₀ in this example. Two potentiometers 15 and 1 from a power supply 14 whose midpoint is grounded
6 applies positive and negative voltages to the electrostatic quadrupole lens 5. The electrostatic quadrupole lenses 6 and 12 have a similar structure and are similarly applied with a voltage. The voltages can be equal or set separately. FIG. 3 is a BB sectional structural diagram of the cylindrical electrodes 11A and 11B. The qualitative operating principle of the apparatus constructed in this way will be explained with reference to the ion trajectory diagram shown in FIG. In Fig. 4, the left end is the ion source slit 4, and among the ions emitted from this, the ions emitted at an angle β ₀ from the center point of the ion source slit 4 to the axis of this system, and the ions The emission parallel to the axis of the system from the upper end y ₀ of the source slit 4 is shown in particular. As shown in FIG. 4, two electrostatic quadrupole lenses 5
and 6 are placed between the ion source slit 4 and the deflection magnetic field ₇ , and the potential, spacing, or position of the ions are adjusted appropriately _. Both ions emitted can also be passed through the deflection magnetic field 7. That is, if the angle and position of the two ions passed through the ion source slit 4 are set as the upper limit, all ions within this range are
This means that it can be used effectively without colliding with the magnetic poles. Conversely, this shows that since the width of the ion flow becomes narrower, the magnetic field can be strengthened by reducing the spacing between the magnetic poles. Furthermore, such electrostatic quadrupole lenses 5 and 6 have the effect of diverging the ion flow in the radial direction (x direction) of the ion flow. Thereby, a virtual image of the slit 4 is created as if the ion source 1 were equivalently close to the deflection magnetic field 7, so that the image magnification Ax of the mass spectrometer can be reduced and the resolution R can be improved. However, when the ion flow incident on the deflection magnetic field 7 is focused by the above method, the ion flow gradually diverges in the y direction from the exit point of the deflection magnetic field. In contrast, another electrostatic quadrupole lens 12 is provided and serves to focus this. With this configuration, after the ion flow passes through an extremely narrow interval by the deflection magnetic field 7, it is efficiently focused and captured by the ion detector 9. Furthermore, in this first embodiment device, an electrostatic octupole lens 1 is provided between the electrostatic quadrupole lens 6 and the deflection magnetic field 7.
8 is provided to reduce third-order aberrations that occur in the ion flow. FIG. 5 is a CC cross-sectional structural diagram of this electrostatic octupole lens 18. Eight cylindrical electrodes 19 are configured to extend in the longitudinal direction in the ion flow direction so as to circumscribe a virtual cylinder with a radius r ₀ (a value standardized by the magnetic field radius rm). Potentials of +V and -V are alternately applied to each electrode. In the first embodiment shown in FIG. 1, the deflection angle of the deflection magnetic field 7 is 50 degrees, and the deflection angle of the cylindrical electric field 11 is 105 degrees. Further, in this example, the output point of the deflection magnetic field 7 is set at an output angle such that the boundary surface of the magnetic field is inclined by 20 degrees with respect to a plane perpendicular to the ion beam. This has the effect of adjusting the focus position of the ion stream to an appropriate location and suppressing aberrations of the entire system. FIG. 6 is a structural diagram of an apparatus according to a second embodiment of the present invention. In this example, electrostatic quadrupole lenses 5 and 6 are provided, a cylindrical electric field 11 is provided, and the cylindrical electric field 1
The structure is such that another electrostatic quadrupole lens 12 is provided in front of the cylindrical electric field 1, and the feature is that the deflection angle of the deflection magnetic field 7 is set to 30 degrees, and the deflection angle of the cylindrical electric field 11 is set to 70 degrees. This is intended to reduce the deflection angle of the deflection magnetic field 7 as much as possible, and also to downsize the magnet for creating the deflection magnetic field 7. Further, in this example, the incident angle and the exit angle of the deflection magnetic field 7 are each set to 24 degrees. Next, examples with specific numerical values and aberration coefficients according to the present invention will be shown. (a) and (b) of Table 1
are the numerical values of the apparatus of the first embodiment of the present invention shown in FIG. (c) of Table 1 is a specific example of the structure of the device according to the second embodiment of the present invention shown in FIG. For all lengths, values standardized by the radius of curvature r _n of the deflection magnetic field 7 are used.

【table】

[Table] The symbols in this table are as follows. φm: Deflection angle of ion beam due to deflection magnetic field (°) φe: Deflection angle of ion beam due to cylindrical electric field (°) rm: Radius of orbit of ion beam in magnetic field re: Radius of orbit of ion beam in electric field Rm ₁ : Radius of curvature of the magnetic field end face at the point of incidence Rm ₂ : Radius of curvature of the end face of the magnetic field at the exit point ε ₁ : Incident angle of the ion beam into the magnetic field (°) ε ₂ : Output angle of the ion beam into the magnetic field (°) QK ₁ : Constant QK that indicates the potential gradient of the first electrostatic quadrupole lens ₂ : Constant QK that indicates the potential gradient of the second electrostatic quadrupole lens ₃ : Constant that indicates the potential gradient of the third electrostatic quadrupole lens Q _L : Static Length of electric quadrupole lens L ₁ : Distance from ion source slit to Q ₁ lens L ₂ : Distance from Q ₁ lens to Q ₂ lens L ₃ : Distance from Q ₂ lens to magnetic field entrance L ₄ : From magnetic field exit Distance to Q ₃ lens L ₅ : Distance from Q ₃ lens to electric field entrance L ₆ : Distance from electric field exit to detector slit Ax: Image magnification Aγ: Mass dispersion coefficient Aαα, Aαδ, Aδδ, Ayy, Ayβ, Aββ : Secondary aberration coefficient Ay: Coefficient of spread of image in the y direction due to y Aβ: Coefficient of spread of image in the y direction due to β g in the bottom row of Table 1 is the maximum spread width of the ion flow within the magnetic pole. As can be seen from this table, according to the present invention, the ratio Aγ/Ax between the mass dispersion coefficient and the image magnification is considerably large, and g (mm) is smaller than that of the conventional device. Therefore, a device with good sensitivity and a strong deflection magnetic field can be obtained. Furthermore, to explain the action of the electrostatic octupole lens 18 using numerical values, the potential applied alternately to each electrode is +V, -V, the ion acceleration voltage is U, and the radius of the inscribed circle of the electrode is r ₀ (magnetic field radius rm When k=2V/Ur ₀ , the third-order aberration coefficients Aααα, Aααδ, Aαδδ, Aδδ
δ
The result is as shown in Table 2. In this example, the lens length L ₈ is 0.2rm.

[Explanation of effects]

As described above, according to the present invention, the electrostatic quadrupole lens focuses the ion flow in the direction perpendicular to its orbital plane and diverges it in the radial direction, thereby creating a deflection magnetic field that deflects the ion flow. Reduce the magnetic pole spacing to improve detection sensitivity and measurement dispersion. In particular, by using a cylindrical electric field as a deflection electric field to focus the ion flow that has passed through the deflection magnetic field, and by providing an electrostatic quadrupole lens in front of this cylindrical electric field to provide focusing in a direction perpendicular to the trajectory plane of the ion flow, Since the convergence of the ions can be improved and aberrations can be kept small, the precision and efficiency of analysis can be improved. Further, since the cylindrical electrode that forms the cylindrical electric field is much easier to work with than the toroidal electrode, manufacturing costs can be kept low.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an apparatus according to a first embodiment of the present invention. Second
The figure shows an example of the cross-sectional structure of an electrostatic quadrupole lens and a voltage application circuit. Figure 3 is a cross-sectional structural diagram of a cylindrical electric field. FIG. 4 is an ion trajectory diagram for explaining the qualitative principle of operation. FIG. 5 is a cross-sectional structural diagram of an electrostatic octupole lens. FIG. 6 is a configuration diagram of an apparatus according to a second embodiment of the present invention. 1...Ion source, 4...Ion source slit,
5, 6... Electrostatic quadrupole lens, 7... Deflection magnetic field, detector slit, 9... Ion detector, 11... Cylindrical electric field, 12... Another electrostatic quadrupole lens, 18...
Electrostatic octupole lens.

Claims (1)

[Claims] 1. An ion source that emits accelerated ions, a slit through which the ions emitted from the ion source pass, a deflection magnetic field that deflects the ions that have passed through the slit, and a deflection magnetic field that deflects the ions that have passed through the slit. and an ion detector for detecting passing ions, and between the slit and the deflecting magnetic field, the passing ion flow is provided with focusing property in a direction perpendicular to its trajectory plane and in its radial direction. A plurality of electrostatic quadrupole lenses providing divergence are arranged at intervals, and a deflection electric field is provided to provide focusing in the radial direction of the ion flow passing between the deflection magnetic field and the ion detector. , in a mass spectrometer that performs mass analysis of ions reaching the ion detector by changing the strength of the deflection magnetic field, wherein the deflection electric field has a cylindrical shape, and the deflection electric field is located between the deflection electric field and the deflection magnetic field. , a mass spectrometer comprising another electrostatic quadrupole lens that provides focusing to a passing ion stream in a direction perpendicular to its trajectory plane. 2. The mass spectrometer according to claim 1, further comprising an electrostatic octupole lens for reducing third-order aberration of the ion flow at a position closer to the ion source than the point of incidence of the deflection magnetic field.