JPH0421304B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an ion detector used in mass spectrometers and the like.

(b) Prior art and its problems Some conventional time-of-flight mass spectrometers use a microchannel plate as an ion detector.

When detecting ions by directly colliding ions emitted from a sample with this microchannel plate, only a small number of secondary electrons are emitted, especially if the incident ions are slow and high mass. Detection efficiency becomes extremely poor.
For this reason, in the conventional technology, a converter plate with high electron emission efficiency is placed in front of the microchannel plate, and the ions emitted from the sample are first collided with this converter plate, which excites and generates secondary electrons. There is a method that increases the detection efficiency of ions by detecting them with a microchannel plate. As shown in FIG. 2, such an ion detector includes a so-called Venetian blind type converter-equipped ion detector in which a plurality of converter plates C are arranged in a blind manner in front of a microchannel plate MCP.

However, when this ion detector with a Venetian blind converter is used in a time-of-flight mass spectrometer, as shown in FIG. Therefore, even if ions of the same mass are generated from the sample at the same time, there will be a difference in flight distance △l depending on the location where they collide with the converter plate C. As a result, the secondary radiation detected by the microchannel plate This causes a problem in that the incident time of electrons becomes different and the mass resolution decreases.

In order to solve this problem, an ion detector as shown in FIG. 4 has been proposed. In this ion detector, the converter plate C is arranged perpendicular to the direction of ion incidence, and a magnetic field is applied perpendicular to the plane of the paper, and the secondary electrons generated from the converter plate C are transferred to the microchannel plate.
It is configured to lead to MCP. If the converter plate C is arranged perpendicular to the direction of ion incidence in this way, the flight distance to the converter plate will be the same for ions of the same mass generated at the same time from the sample, increasing the mass resolution to a certain degree. becomes possible.

However, in the above configuration, a large magnet is required to generate the magnetic field, and if the area of the converter plate is increased to increase detection sensitivity, the effective area of the microchannel plate must also be increased accordingly. However, there is a problem that the entire device becomes larger.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide an ion detector with high mass resolution and high detection sensitivity despite its simple and compact structure. do.

(C) Means for Solving the Problems In order to achieve the above object, the ion detector of the present invention is provided with a converter plate for ion-electronic conversion arranged perpendicularly to the direction of ion incidence. An electron deflection electrode plate is disposed perpendicular to the converter plate, and an electron multiplier is provided at a position opposite to the electron deflection electrode plate, while a first mesh is disposed at a position opposite to the converter plate, and an electron deflection A second mesh is arranged in front of the electron multiplier at a position opposite to the electrode plate, and a voltage is applied to the converter plate, the electron deflection electrode plate, and the first and second meshes to form an electric field. I have to.

(d) Effect Since the converter plate is arranged perpendicular to the direction of ion incidence, the incident ions collide with the converter plate without causing any difference in flight time. The secondary electrons generated thereby are absorbed by an electron multiplier arranged opposite to the electron deflection electrode plate by a lens effect due to the potential distribution formed by the converter plate, the electron deflection electrode plate, and the first and second meshes. is efficiently converged.

(E) Embodiment FIG. 1 is a sectional plan view of an ion detector according to an embodiment of the present invention. In the figure, reference numeral 1 is an ion detector, and 2 is a metal plate having an inverted L-shaped cross section.
This metal plate 2 includes an opposing wall 4 disposed perpendicularly to the direction of ion incidence, a parallel wall 6 perpendicular to the opposing wall 4, and a projecting wall 8 projecting from the opposing wall 6 in parallel to the parallel wall 6. are integrally formed. A converter plate 10 made of an oxidized Cu/Be alloy plate with excellent electron emission efficiency is fixed to the inner surface of the opposing wall 4 for ion-electron conversion, and the parallel wall 6 is connected to an electron deflection electrode plate 6. be done.

Reference numerals 12 and 14 indicate first electrodes disposed at opposing positions of the opposing wall 4 and the parallel wall 6, respectively, for forming an electric field.
This is a second mesh, and the interior surrounded by the first and second meshes 12 and 14 and the metal plate 2 is a space 15 for forming an electric field.

Reference numeral 16 denotes a shielding mesh placed outside the first mesh 12, and 18 a microchannel plate as an electron multiplier placed opposite the electron deflection electrode plate 6 and outside the second mesh 14. .

In this example, the voltages applied to each part of the ion detector 1 are set as follows. A metal plate 2 including an electron deflection electrode plate 6, a converter plate 10 and a first
The same voltage of negative polarity is applied to both the meshes 12, the voltage of negative polarity and absolutely smaller than the voltage applied to the metal plate 2 is applied to the second mesh 14, and the shielding mesh 16 is set to earth potential. Ru. If the voltages in each part are set in this way, the potential distribution E in the space 15 will be shown by the broken line in the figure.

Therefore, when ions emitted from a sample (not shown) pass through the shielding mesh 16 and the first mesh 12 and enter the space 15, the incident ions collide with the converter plate 10. In this case, the converter plate 10 is perpendicular to the direction of ion incidence.
are arranged, so there is no difference in the flight time of the incident ions. When ions collide with the converter plate 10, from the converter plate 10,
This ion is excited and secondary electrons are emitted.
The generated secondary electrons are efficiently focused on the microchannel plate 18 by the lens effect caused by the potential distribution E formed in the space 15. Note that the flight distance of the secondary electrons generated from the converter plate 10 to reach the microchannel plate 18 varies depending on the position at which the ions collide with the converter plate 10, but the movement speed of the secondary electrons varies depending on the ion. Since it is much larger in comparison, it has little effect on resolution.

Although a microchannel plate is used as the electron multiplier in this embodiment, the present invention is not limited to this, and it is also possible to use a combination of a photomultiplier tube and a scintillator, for example. Further, in this embodiment, the space 15 is open at the top and bottom, but metal plates can also be provided at the top and bottom to increase the efficiency of convergence of secondary electrons. Also,
The electron deflection electrode plate 6 is configured separately from the metal plate 2, and the converter plate 10, the electron deflection electrode plate 6, the first and second
It is also possible to apply a predetermined voltage to each mesh individually so that the potential distribution can be adjusted as desired. moreover,
In order to increase the convergence efficiency of secondary electrons, the protruding wall 8
Although it is more preferable to provide this, it is also possible to omit this.

On the other hand, this ion detector 1 can be applied to a time-of-flight mass spectrometer, and can also be used as an ion detector for a quadrupole mass spectrometer or a magnetic field mass spectrometer. Further, if the voltage applied to the converter plate 10 and the electron deflection electrode plate 6 is set to a negative high voltage, it becomes possible to use it as a post acceleration detector.

(F) Effect As described above, according to the present invention, since the converter plate is arranged perpendicular to the direction of ion incidence, the converter plate can be used as an ion detector in a time-of-flight mass spectrometer. Resolution can be obtained.
In addition, the secondary electrons generated by the converter plate can be efficiently focused on the electron multiplier due to the lens effect of the electron deflection electrode plate, so detection sensitivity can be increased despite the simple structure. Excellent effects such as:

[Brief explanation of drawings]

FIG. 1 is a plan cross-sectional view of an ion detector according to an embodiment of the present invention, FIG. 2 is a configuration diagram of an ion detector using a conventional Venetian blind converter, and FIG.
This figure is an explanatory diagram of the flight distance difference of incident ions in the ion detector of FIG. 2, and FIG. 4 is a diagram of the configuration of another conventional ion detector. 1... Ion detector, 6... Electron deflection electrode plate, 10
...Converter plate, 18...Microchannel plate.

Claims (1)

[Claims] 1. A converter plate for ion-electron conversion is arranged perpendicularly to the direction of incidence of ions, an electron deflection electrode plate is arranged perpendicular to the converter plate, and the electron deflection electrode plate is an electron multiplier is provided at an opposing position, a first mesh is arranged at an opposite position to the converter plate, and a second mesh is arranged in front of the electron multiplier at an opposite position to the electron deflection electrode plate; An ion detector characterized in that an electric field is formed by applying a voltage to the converter plate, the electron deflection electrode plate, and the first and second meshes. 2. The ion detector according to claim 1, wherein the electron multiplier is a microchannel plate.