JPS6245423Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a highly sensitive ion detector in a mass spectrometer or the like.

A conventional mass spectrometer is schematically shown in FIG. 1 in the figure ionizes the test sample with an ion source,
An ion beam I is formed by accelerating at a desired acceleration voltage. 2 disperses the velocity of the ion beam I using an electric field, and makes ions with uniform velocity incident on the analysis magnetic field 3. Ions that are subjected to mass dispersion by this magnetic field and are separated according to their mass-to-charge ratio are focused on a focusing surface outside the magnetic field. A minute slit 4 is fixed on this converging surface, and an ion collector 5 is installed behind it, and ions passing through the slit are detected.

In such a configuration, if the strength of the magnetic field 3 is swept over a certain range, ions with different mass-to-charge ratios will enter the collector 5 through the slit 4, and the output signal of this collector will be processed appropriately and sent to the recorder. If recorded, a mass spectrum can be obtained.

However, conventional devices require a slit 4 in front of the collector 5, but increasing the width of this slit lowers the resolution;
It is necessary to use one with a minute width of less than μm. In addition to the problem that such slits are difficult to process with high precision, they also block most of the incoming ions, which is the biggest reason why the sensitivity of the detection system cannot be improved.

Therefore, the purpose of this invention is to dramatically improve the sensitivity of the detection system, and its configuration includes a multi-channel secondary electron multiplier plate near the ion beam convergence plane and parallel to the convergence plane. ion, converts the ions into electrons and multiplies them, accelerates the electrons emitted from the plate, forms an image on an image sensor consisting of a large number of minute detection elements, and sequentially extracts signals from each detection element of the image sensor. This ion detector is characterized by the following characteristics.

The present invention will be described below based on embodiments shown in the drawings.

Figure 2 is a diagram of the main part, and 6 is a multi-channel secondary electron multiplier plate placed near the convergence plane (actually behind the convergence plane) by the analysis field 3, as in Figure 1. -15KV~- on the ion incidence side
A negative high voltage of 20KV (-15KV in Figure 4) is applied. In front of the secondary electron multiplier plate, as shown in FIG. 3, there are a plurality of slit-shaped electrodes 7a,
7b, 7c, and 7d are placed parallel to the convergence surface, and at least the electrode 7a at ground potential is placed in front of the convergence surface. A predetermined voltage is applied to each electrode from a power source 8, so that a uniform ion accelerating electric field is formed across the converging surface in a direction perpendicular to the converging surface. When ions are accelerated by such a uniform electric field, each ion follows a substantially identical parabola and converges to a new plane parallel to the original convergence plane. Therefore, the ion incidence surface of the multi-channel secondary electron multiplier plate is placed on this new focusing surface. Ions enter each channel (capillary) of a multichannel secondary electron multiplier plate and are converted into electrons. At this time, an ion-electron conversion surface may be formed on the front surface of the multiplication plate. Since an electron accelerating voltage of, for example, about 1 KV is applied to the output side of the secondary electron multiplier plate, the converted electrons are accelerated by the electric field inside the tube, and are multiplied each time they collide with the tube wall. At the exit, the gain is approximately 1000 times. FIG. 4 shows the potential gradient when the incident surface of the secondary electron multiplier plate is set at -15 KV and the exit surface at -14 KV. The inner diameter of the thin tube is approximately 10 μm, and the emitted electrons are emitted from the other end while maintaining the image of the incident ions. 9a, 9b, 9c,
Reference numeral 9d denotes an emitted electron accelerating electrode, which forms a uniform accelerating electric field between the image sensor 10 placed at ground potential and the multichannel secondary electron multiplier plate 6. The accelerated electrons form an electron image corresponding to the ion image on the sensor 10 by the lens magnetic field created by the converging coil 11. Image sensor 10
consists of a large number of tiny diode arrays (Fig. 5) that are sensitive to light and electrons, and a thin (about 1 μm) protective film is formed on the surface. The spacing τ between each diode detection element is 20 μm to 25
μm, and the number used is about 512 or 1024. Now, when using 512 elements,
Even if τ is 20 μm, the sensor length L will be 10 mm or more. Also, the length of the element, that is, the width W of the sensor is approximately
It is 2.5mm. When electrons with a certain energy (12KeV) or more are incident on such an image sensor,
The electrons pass through the protective film and reach the diode,
For example, for 15KV electrons, for one incident electron,
Generates about 1000 electrons. Therefore, by sequentially extracting the electrons accumulated in each diode as charges, the mass spectrum developed on the multichannel secondary electron multiplier plate can be sent out as an electrical signal.

When obtaining a mass spectrum using the above detector, as the intensity of the analysis magnetic field 3 is swept, ions with a specific mass-to-charge ratio that are incident on the multichannel secondary electron multiplier plate 6 are distributed from right to left. (or from left to right). Therefore, the signals (charges) charged in each element of the image sensor 10 are sequentially measured at high speed for each minute sweep of the analytical magnetic field, and this is repeatedly integrated and stored in the address corresponding to each mass-to-charge ratio of the storage element. As a result, at each address of the memory element, a conventional slit 4 is inserted into the image sensor 1.
A signal of the same intensity as when spread over a length of 0 (L in FIG. 5) will be accumulated. As mentioned above,
Since the width of the slit 4 is 100 μm or less and the length L of the image sensor 10 is 10 mm or more, the sensitivity of the detector of this embodiment is improved by more than 100 times compared to the conventional one.

With the configuration described in detail above, the present invention can improve sensitivity by more than two orders of magnitude compared to the conventional method without sacrificing resolution in any way, and can provide a high-speed, high-performance mass spectrometer.

Incidentally, the above is an illustration of the present invention, and various modifications thereof are possible. Especially electrodes 7a, 7b, 7c, 7
The shapes of d, 9a, 9b, 9c, and 9d, and the structure of the image sensor 10 are not limited to those shown in the drawings.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a conventional mass spectrometer, Fig. 2 is a diagram showing the main parts of an example of the present invention, and Fig. 3 is a schematic diagram showing a conventional mass spectrometer.
This figure shows electrodes for forming the ion accelerating electric field in FIG. 2, FIG. 4 shows the potentials of various parts in FIG. 2, and FIG. 5 shows an example of the image sensor shown in FIG. 2. 6: Multi-channel secondary electron multiplier plate, 7
a, 7b, 7c, 7d: slit-shaped electrode, 9a,
9b, 9c, 9d: acceleration electrode, 10: image sensor, 11: convergence coil.

Claims (1)

[Scope of utility model registration request] A multi-channel secondary electron multiplier plate is placed near the convergence plane of the ion beam emitted from the analysis field and parallel to the convergence plane, and a multichannel secondary electron multiplier plate is placed on the ion incidence side of the secondary electron multiplier plate in the direction perpendicular to the convergence plane. A negative high voltage is applied to form an ion accelerating electric field, and a positive voltage is applied to the electron exit side of the multiplier plate relative to the ion input side, so that the electrons emitted from the multiplier plate have an energy higher than a predetermined energy. An ion detector for use in a mass spectrometer, etc., configured to accelerate the ion beam, form an image, project it onto an image sensor consisting of a large number of minute detection elements, and sequentially extract signals from each detection element of the image sensor.