JP2003031178A - Quadrupole mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quadrupole mass spectrometer suppressing the noise caused by the light generated at an area to be measured or at an ion source, with few sensitivity loss. SOLUTION: For the quadrupole mass spectrometer, impressing high frequency voltage to a quadrupole electrode 10 composed of 4 pieces of rod-shaped electrodes arranged parallel with each other, emitting only the ion having specified mass, ionized at an ionizing part, from an outlet of the quadrupole electrode 10, and detecting the emitted ion by an ion detector 11 located at the back side of an outlet part as a current, a light receiving surface 16 of the ion detector 11 is formed into ring-shape, and the center axis of the light receiving surface 16 and the axis of the quadrupole electrode 10 are arranged so as to coincide with each other, and an electric field, guiding the ion to the part located between the outlet of the quadrupole electrode 10 and the light receiving surface 16 of the ion detector 11, is formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a quadrupole mass spectrometer, and more particularly to a quadrupole mass spectrometer for measuring the mass of ions or ionized neutral molecules.

[0002]

2. Description of the Related Art Conventionally, a quadrupole mass spectrometer, which is also called a mass filter, has been popular as a mass spectrometer for measuring the mass of ions and ionized neutral molecules due to its small size and simple structure. . The quadrupole electrode is composed of four rod-shaped electrodes arranged in parallel in a highly precise positional relationship, and a high-frequency voltage and a DC voltage of, for example, about 1 to 5 kV are applied to each rod-shaped electrode. With this configuration, a time-varying quadrupole electric field is formed in the radial direction perpendicular to the axis of the region where the quadrupole electrode is provided, and ions existing in the vicinity of the axis are radially moved by the Coulomb force. It oscillates and ions other than a certain mass are diverged out of the axis. Regarding the direction of the axis, the moving ion is 10 eV (1 eV is about 1.
Since it has energy of about 60 × 10 ⁻¹⁹ J) and is advancing in the region of the quadrupole electrode at a constant speed, only specific ions pass through and are ejected from the outlet of the quadrupole electrode.

The directions of the ions ejected from the outlet of the quadrupole electrode are not only aligned in the direction of the above-mentioned axis, but are substantially radial. This has a velocity of only about 10 eV in the axial direction, while it has an energy of several hundreds eV in the radial direction, is vibrated at a large velocity, and is ejected as it is. Is. Moreover, since the vibrational conditions differ depending on the incident position, initial velocity, and phase of the ions, the ejection direction also differs for each ion. Therefore, when viewed as the entire flow of ions, the ions are ejected in a radial shape that is largely expanded in the radial direction.

This situation is shown in FIG. FIG. 13 is a schematic diagram showing the flow of ions passing through the quadrupole electrode and ejected from the outlet. The ions that have entered the quadrupole electrode 100 vibrate in the radial direction and move forward. Specific ions are ejected from the exit aperture 101 of the quadrupole electrode 100. At this time, as shown by an arrow 102 in FIG. 13, the ejection direction of the ions spreads in the radial direction.

This is a phenomenon peculiar to a quadrupole mass spectrometer. For example, in another typical mass spectrometer, a magnetic field sector mass spectrometer, the axial velocity is 1 ke.
The velocity corresponds to energy of about 10 eV in the radial direction above V, and the directions of the ions are very well aligned in the axial direction.

In FIG. 13, an ion detector (not shown in FIG. 13) is usually installed at the exit of the quadrupole electrode 100, and the ions reaching the light receiving surface of the ion detector are detected as a current. There are two types of ion detectors that differ greatly.

The former is usually called a Faraday type, and the light receiving surface is simply a conductive plate. The ions that have reached the light receiving surface generate a current due to the charge exchange on the surface of the plate-like object, so this current is taken out and used as a detection signal. Since it has a simple structure, it is used as a simple ion detector.

The latter is called an electron multiplier tube,
The light receiving surface is an opening in which a substance that easily emits secondary electrons is applied to the inner wall surface. The ions reaching the light receiving surface emit secondary electrons on the inner wall, and the secondary electrons generate a plurality of secondary electrons. A large current amplified by this repetition is taken out and used as a detection signal. Although the structure is complicated and high voltage is required, it is used as a highly sensitive detector because it can detect a small amount of ions.

There are various types of the electron multiplier tube type, and there are a multi-stage type having a single opening and a plurality of electrodes and a continuous type having one semiconductive (semimetal such as antimony) electrode. is there. There is also a microchannel plate (MCP) which is a kind of continuous type but has a large number of openings. Microchannel plates have been increasingly used in recent years because they contribute greatly to miniaturization, but each aperture is very small, so there is a limit to the amplification capability of each aperture. Therefore, it is very important to distribute the ions to be detected as evenly as possible on the light receiving surface.
If the ions continue to reach the limited aperture,
It is known that problems occur in the linearity of life and amplification factor.

Each of the above-mentioned two types of ion detectors has a problem that when not only ions but also light having high energy reaches the light receiving surface, secondary electrons are emitted to give a false signal. This problem is particularly remarkable in the electron multiplier type. Especially, in the quadrupole mass spectrometer, since the quadrupole electrode has a straight line from the entrance to the exit, light generated in the region to be measured or the ion source easily enters the ion detector and becomes noise. Therefore, conventionally, the ion detectors are arranged in parallel with each other so that the light receiving surface of the ion detector cannot be expected from the entrance of the quadrupole electrode, or the mounting direction is set to be perpendicular to the quadrupole electrode. These examples are shown in FIG. 14 and FIG.
This will be described with reference to FIG.

FIG. 14 is a diagram of a conventional quadrupole mass spectrometer in which the ion detectors are arranged in parallel with each other, and FIG.
FIG. 5 is a diagram of a conventional quadrupole mass spectrometer in which an ion detector is attached in a direction perpendicular to the quadrupole electrode. As shown in FIG. 14, the light receiving surface 104 of the ion detector 103 has an exit aperture 10 provided at the exit of the quadrupole electrode 100.
It is shifted parallel to the opening of No. 1. In the figure, reference numeral 104 is a shield electrode. Further, in this figure, the ion detector 1
A microchannel plate is used as 03.
In FIG. 15, the light receiving surface 105 of the ion detector 103 is arranged at right angles to the exit aperture 101 of the quadrupole electrode 100. Thus, in the arrangement of the ion detector 103 as shown in FIGS. 14 and 15, the ion detector 103
Since the light-receiving surface 105 of 1 cannot be seen from the entrance of the quadrupole electrode 100, the light generated in the region to be measured or the ion source does not reach the ion detector.

However, since a negative potential of 1 kV is usually applied to the light-receiving surface 105 of the electron multiplier tube type ion detector 103, positively charged ions can be attracted by this potential, so that FIG. 14 and FIG. Even in these positional relationships shown by, the exit aperture 1 of the quadrupole electrode 100
Ions ejected from 01 reach the light receiving surface of the ion detector and are detected.

Although FIG. 14 and FIG. 15 show a microchannel plate as an ion detector, it may actually be an electron multiplier tube of another type.

[0014]

The direction of the ions ejected from the exit aperture 101 of the quadrupole electrode 100 is radial with the axis of the quadrupole electrode 100 as the center.
Outlet of Quadrupole Electrode 100 and Ion Detector 10 in Conventional Example
In the space between 3 there is an electric field in a direction deviated parallel to the axis of the quadrupole electrode 100, or in a direction perpendicular to the axis. Therefore, there is a problem that all the ions ejected from the outlet of the quadrupole electrode 100 are not detected. Ions are strongly ejected radially and have a large velocity corresponding to energy of several hundreds eV in the radial direction.
This is because it is not possible to attract all the ions with an electric field of about 1 kV due to 5. Therefore, sensitivity loss occurs.

In the conventional example, the ions are detected by the ion detector 10
Many ions reach only a part of the light receiving surface 105 of No. 3, and the ions are not uniformly distributed over the entire light receiving surface. Therefore, in the microchannel plate, there are problems in the life and the linearity of the amplification factor. A proposal for solving this problem is Japanese Patent Application Laid-Open No. 4-132152 (“charged particle detection device”).
Is disclosed in. According to this, a lens system for diverging a charged particle beam is arranged in front of the microchannel plate so that the charged particle beam to be detected is incident on the entire light receiving surface of the microchannel plate in a dispersed manner. The common anode receives electrons emitted from each channel. However, this proposal has a new problem that the sensitivity loss becomes larger than usual because it is necessary to pass through a plurality of holes.

In order to solve the above problems, it is an object of the present invention to provide a quadrupole mass spectrometer which suppresses noise due to light generated in the region to be measured, the ion source, etc. and has a small sensitivity loss. is there.

[0017]

The quadrupole mass spectrometer according to the present invention is configured as follows to achieve the above object.

In the first quadrupole mass spectrometer (corresponding to claim 1), a high frequency voltage is applied to a quadrupole electrode composed of four rod-shaped electrodes arranged in parallel, and ionized in the ionization section. Ion detection in a quadrupole mass spectrometer in which only ions of a specific mass are ejected from the outlet of the quadrupole electrode and the ions emitted by the ion detector located behind the outlet are detected as current. The detector has an annular light-receiving surface, and is arranged so that the central axis of the light-receiving surface and the axis of the quadrupole electrode coincide with each other, and the outlet of the quadrupole electrode and the light-receiving surface of the ion detector. It is characterized by the formation of an electric field that guides ions to the light receiving surface.

According to the first quadrupole mass spectrometer, the ion detector has a form in which the light receiving surface is annular, and the central axis of the light receiving surface and the axis of the quadrupole electrode coincide with each other. Since the electric field that guides ions to the light-receiving surface is formed between the exit of the quadrupole electrode and the light-receiving surface of the ion detector, the light generated in the area to be measured or the ion source is detected. Since it does not enter the light-receiving surface of the container, noise due to light can be suppressed. Further, since the radially ejected ions can reach the light receiving surface of the ion detector, the sensitivity loss can be reduced. Since the ionization section is premised on the generation of light or the like as described above, a mechanism based on electron impact ionization, chemical ionization, and atmospheric pressure ionization is assumed.

The second quadrupole mass spectrometer (corresponding to claim 2) is characterized in that, in the above configuration, the ion detector is preferably a microchannel plate (MCP). As a result, the present invention becomes a particularly effective means in suppressing noise due to light and reducing sensitivity loss.

The third quadrupole mass spectrometer (corresponding to claim 3) is preferably arranged such that the light receiving surface of the microchannel plate is provided on the side facing the outlet of the quadrupole electrode. It is characterized in that a shield electrode having a potential higher than the potential of the light receiving surface is arranged near the central axis of the light receiving surface.

The fourth quadrupole mass spectrometer (corresponding to claim 4) is preferably arranged such that the light-receiving surface of the microchannel plate faces the side opposite to the outlet of the quadrupole electrode. A shield cylindrical electrode having a potential higher than that of the light-receiving surface is disposed between the macro channel plates corresponding to the outlet portion, and a shield electrode having a potential higher than the potential of the light-receiving surface faces the light-receiving surface. It is characterized by being placed.

In a fifth quadrupole mass spectrometer (corresponding to claim 5), preferably, the ion detector is a cylindrical Faraday type ion detector, and the Faraday type ion detector is used. Is characterized in that a shield electrode having a potential higher than that of the light receiving surface is arranged at the exit of the.

The sixth quadrupole mass spectrometer (corresponding to claim 4) has the above-mentioned structure, and preferably the shield electrode has an auxiliary ion detector function independent of the light receiving surface of the ion detector. It is characterized by having.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

The configurations, shapes, sizes, and positional relationships described in the embodiments are merely schematic ones so that the present invention can be understood and implemented. Therefore, the present invention is
The present invention is not limited to the embodiments described below,
Various modifications can be made without departing from the scope of the technical idea shown in the claims.

1 to 4 are views showing a first embodiment of a quadrupole mass spectrometer according to the present invention. 1 is a sectional view of a main part, FIG. 2 is a perspective view of an ion detector, FIG. 3 is an enlarged sectional view of an ion detector showing an electric field distribution, and FIG. 4 is an enlarged sectional view of an ion detector. Is shown.
In the figure, 10 is a quadrupole electrode, and 11 is an electron multiplier tube type ion detector. 12 is the exit aperture, and 13 is the ions ejected from the quadrupole electrode. Reference numeral 14 is a microchannel plate, and 15 is a shield electrode. Reference numeral 16 is a light receiving surface of the microchannel plate, 17 is an electron output surface of the microchannel plate, 18 is an electron collector of the microchannel plate, and 19 is a signal output line.

The shape of the microchannel plate 14 is an annular shape with a hole formed in the central portion, and the light receiving surface 16 of the microchannel plate 14, the output surface 17 of the microchannel plate 14, and the electron collector 18 of the microchannel plate 14 are formed. Both of them have an annular shape. These central axes are set so as to substantially coincide with the axes of the quadrupole electrode 10.

A negative potential of -1 kV is applied to the light receiving surface 16 of the microchannel plate 14 and a negative potential of -0.1 kV is applied to the electron output surface 17 of the microchannel plate 14 from a power supply line (not shown). When the ions reach the light receiving surface 16 of the microchannel plate 14, the microchannel plate 1 in which the electrons amplified from the electron output surface 17 of the microchannel plate 14 are 0V
4 into the electron collector 18 and is measured by an ammeter (not shown) connected via the signal output line 19.

The exit aperture 12 shields the electric field and light coming from the quadrupole electrode side, and ions are radially emitted from the central hole 12a. However, light that acts as noise is also emitted from the center hole 12a. The shield electrode 15 has a circular shape slightly larger than the central hole 12a of the exit aperture 12. These central axes are also set so as to substantially coincide with the axes of the quadrupole electrode 10.

Next, referring to FIG. 3 and FIG. 4, the electric field distribution and the state of ion detection are shown. The potential of the exit aperture 12 and the shield electrode 15 is 0V, the microchannel plate 1
Since the light receiving surface 16 of No. 4 has a voltage of -1 kV, as shown in FIG. 3, positive ions are symmetrically drawn into the light receiving surface 16 of the annular microchannel plate 14 in the space between them. Such an electric field E1 is formed.

As shown in FIG. 4, the ions 13 ejected from the quadrupole electrode 10 are originally in a radial shape that spreads around the axis of the quadrupole electrode 10. Therefore, the ions 13 ejected from the quadrupole electrode 10 reach the light-receiving surface 16 of the microchannel plate 14 in an axially symmetric manner without difficulty due to the electric field E1. Therefore, problems of sensitivity loss and linearity of life and amplification factor do not occur.
Since the light emitted from the central hole of the exit aperture 12 travels straight, it does not enter the light receiving surface 16 of the annular microchannel plate 14 and no noise is generated.

In the normal measurement, the shield electrode 15 exists only for forming an electric field. However, when high-sensitivity measurement is not required or the atmosphere pressure is high and the electron multiplier cannot be operated. It is also possible to connect an ammeter to the shield electrode 15 and use it as an auxiliary Faraday type ion detector.

5 to 8 are views showing a second embodiment of the quadrupole mass spectrometer according to the present invention, FIG. 5 is a cross-sectional view of a main part, and FIG. 6 is a perspective view of an ion detector. FIG. 7 is an enlarged cross-sectional view of the ion detector showing an electric field distribution, and FIG. 8 is an enlarged cross-sectional view of the ion detector showing ion trajectories. 5 to 8, the elements substantially the same as the elements described in FIGS. 1 to 4 are denoted by the same reference numerals. The exit aperture according to this embodiment is provided with a shield cylinder electrode 20 on its back side.

In the present embodiment, the light-receiving surface 16 of the microchannel plate 14 is not on the quadrupole electrode side but on the opposite side, and the electron output surface 17 of the microchannel plate 14 and the electron collector 18 of the microchannel plate 14 are arranged. Are located on the quadrupole electrode side. Further, the hole at the center of the microchannel plate 14 has the first
It is slightly larger than that used in the embodiment, and the outer diameter of the shield electrode 15 is considerably larger than that used in the first embodiment. All of these central axes are set so as to substantially coincide with the axes of the quadrupole electrode 10.

Next, FIG. 7 and FIG. 8 show how the electric field distribution and ions are detected. The potentials of the shield cylinder electrode 20, the exit aperture 12, and the shield electrode 15 are all 0V, and the light-receiving surface 16 of the microchannel plate 14 is -1kV.
Therefore, in the space between them, the microchannel plate 1 in which the positive ions are annular and the positive ions are annular
An electric field E2 is formed so as to be drawn into the light receiving surface 16 of No. 4. In the case of the present embodiment, unlike in FIGS. 3 and 4, the positive ions are drawn in a U-shape, but the ions 13 ejected from the quadrupole electrode 10 are reasonably axisymmetrical to the microchannel plate. Reaching the light receiving surface 16 of 14 is similar. In this structure, since the light-receiving surface 16 of the microchannel plate 14 exists on the opposite side of the quadrupole electrode 10, there is an advantage that the influence of light can be further reduced.

In the first and second embodiments described above, the potentials of the exit aperture 12, the shield electrode 15, and the shield cylinder electrode 20 are all set to 0V, but these electrodes are not necessarily limited to 0V. For example, when the light-receiving surface 16 has a normal level of about -1 kV, the potential may be higher than the potential of the light-receiving surface 16 such as -200V or + 100V. With such a potential, the ions receive the attractive force from the light-receiving surface 16 and receive the reaction force from each electrode while receiving the light-receiving surface 1.
Proceed to 6.

9 to 12 are views showing a third embodiment of a quadrupole mass spectrometer according to the present invention, FIG. 9 is a cross-sectional view of a main part, and FIG. 10 is a perspective view of an ion detector. FIG. 11 is an enlarged sectional view of the ion detector showing the electric field distribution, and FIG. 12 is an enlarged sectional view of the ion detector showing the trajectories of ions. 9 to 12, elements that are substantially the same as the elements described in FIGS. 1 to 4 are given the same reference numerals. In this embodiment, a Faraday type ion detector 21 is used, and 22 is an annular (cylindrical) shape.
Is the light receiving surface of. The potential of the shield electrode 15 is +1
It is kV.

As shown in FIG. 11, the light-receiving surface 22 and the exit aperture 12 are at 0 V, and the shield electrode 15 is at +1 kV.
Therefore, in the space between these, an electric field E3 is formed which is axially symmetrical and in which positive ions are radially drawn into the annular light-receiving surface 22. Further, as shown in FIG. 12, unlike the above-described respective embodiments, the annular light-receiving surface 22 does not have a low voltage, and therefore the light-receiving surface 22 itself does not strongly attract positive ions, but has a high voltage. Finally, the positive ions flow into the annular light-receiving surface 22 under the influence of the shield electrode 15 that is formed.

This embodiment is effective when high-sensitivity measurement is not required or when the atmosphere pressure is high and the electron multiplier cannot be used.

Although the present invention has been described in the above three embodiments, the present invention is not limited to these. For example,
In each case, the light-receiving surface itself was circular, but even if the surface that functions as a light-receiving surface is not circular and is disk-shaped, the light does not reach the center by hiding it with a shield electrode. In this way, the effective light-receiving surface may have a ring shape.

Although the potential of the exit aperture 12, the shield electrode 15, and the shield cylindrical electrode 20 is 0V in all cases, an electric field other than 0V may be formed as long as an electric field is formed so that the ions are directed to the annular light receiving surface. Good. Further, although all the ions are positively charged ions, they may be negative ions, and in that case, the polarity of each potential may be changed.

Although the shield electrode 15 has a disk shape in each case, it is sufficient if an electric field is formed on the light receiving surface having a conical shape so that the ions can be directed toward the axis.
It may be conical or the like. Similarly, the outlet aperture 12 is not limited to a disc shape, and may have a cylindrical edge, a conical shape, or a barrel shape. It is expected that the distribution of the ions reaching the light receiving surface will be made more uniform by optimizing these shapes and potentials or by additionally adding an auxiliary electrode.

Further, the ions that have reached the shield electrode 15 cause charge exchange on the surface of the shield electrode 15 to generate a current. By extracting this current and using it as a detection signal, the ions are detected in the shield electrode 15. An auxiliary ion detection function independent of the light receiving surface of the vessel can be provided.

[0045]

As is apparent from the above description, the present invention has the following effects.

Since the effective light receiving surface of the ion detector has a substantially annular shape and the ion detector is arranged so that the central axis of the light receiving surface and the axis of the quadrupole electrode coincide with each other, the region to be measured and the ion source The light generated by, for example, does not enter the light receiving surface of the ion detector, thereby suppressing the noise due to the light. Further, since the radially ejected ions can reach the light receiving surface of the ion detector, the sensitivity loss can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a first embodiment of a quadrupole mass spectrometer according to the present invention.

FIG. 2 is a perspective view of the ion detector of the first embodiment of the quadrupole mass spectrometer according to the present invention.

FIG. 3 shows an electric field distribution in an enlarged sectional view of the ion detector of the first embodiment of the quadrupole mass spectrometer according to the present invention.

FIG. 4 is a magnified sectional view of the ion detector of the first embodiment of the quadrupole mass spectrometer according to the present invention, showing an ion trajectory.

FIG. 5 is a cross-sectional view of essential parts of a second embodiment of a quadrupole mass spectrometer according to the present invention.

FIG. 6 is a perspective view of an ion detector of a second embodiment of the quadrupole mass spectrometer according to the present invention.

FIG. 7 shows an electric field distribution in an enlarged sectional view of an ion detector of a second embodiment of a quadrupole mass spectrometer according to the present invention.

FIG. 8 is an enlarged cross-sectional view of an ion detector of the second embodiment of the quadrupole mass spectrometer according to the present invention, showing an ion trajectory.

FIG. 9 is a cross-sectional view of essential parts of a third embodiment of a quadrupole mass spectrometer according to the present invention.

FIG. 10 is a perspective view of an ion detector of a third embodiment of a quadrupole mass spectrometer according to the present invention.

FIG. 11 shows an electric field distribution in an enlarged cross-sectional view of the ion detector of the third embodiment of the quadrupole mass spectrometer according to the present invention.

FIG. 12 is a magnified sectional view of an ion detector of a third embodiment of a quadrupole mass spectrometer according to the present invention, showing an ion trajectory.

FIG. 13 is a schematic diagram showing a flow of ions that pass through a quadrupole electrode and are ejected from an outlet.

FIG. 14 is a diagram of a conventional quadrupole mass spectrometer in which ion detectors are arranged in parallel with each other.

FIG. 15 is a diagram of a conventional quadrupole mass spectrometer in which the mounting direction of the ion detector is perpendicular to the quadrupole electrode.

[Explanation of symbols]

10 Quadrupole Electrode 11 Electron Multiplier Tube Ion Detector 12 Exit Aperture 13 Ions Emitted from Quadrupole Electrode 14 Micro Channel Plate 15 Shield Electrode 16 Light-Receiving Surface of Micro Channel Plate 17 Electron Output Surface of Micro Channel Plate 18 Electron Collector of Micro Channel Plate 19 Signal Output Line 20 Shield Cylindrical Electrode 21 Faraday Ion Detector 22 Ring-shaped Light-receiving Surface

Claims (6)

[Claims] 1. A high frequency voltage is applied to a quadrupole electrode composed of four rod-shaped electrodes arranged in parallel, and only ions of a specific mass ionized in the ionization section are ejected from the outlet section of the quadrupole electrode. In the quadrupole mass spectrometer that detects the ions emitted by the ion detector located on the rear side of the outlet as a current, the ion detector has a shape in which the light-receiving surface is annular. And is arranged so that the central axis of the light receiving surface and the axis of the quadrupole electrode coincide with each other, and the ions are received between the outlet of the quadrupole electrode and the light receiving surface of the ion detector. A quadrupole mass spectrometer characterized in that an electric field is formed on the surface. 2. The quadrupole mass spectrometer according to claim 1, wherein the ion detector is a microchannel plate. 3. The light-receiving surface of the microchannel plate is provided on a side of the quadrupole electrode facing the outlet portion, and a shield electrode having a potential higher than a potential of the light-receiving surface is provided near a central axis of the light-receiving surface. The quadrupole mass spectrometer according to claim 2, wherein the quadrupole mass spectrometer is arranged. 4. The light receiving surface of the microchannel plate is provided on a side of the quadrupole electrode facing the side opposite to the outlet portion, and the light receiving surface is provided between the microchannel plates in correspondence with the outlet portion. 3. The quadrupole type electrode according to claim 2, wherein a shield cylinder-shaped electrode having a potential higher than that of the light-receiving surface is disposed, and a shield electrode having a potential higher than the potential of the light-receiving surface is disposed so as to face the light-receiving surface. Mass spectrometer. 5. The ion detector is a cylindrical Faraday type ion detector, and a shield electrode having a potential higher than the potential of the light receiving surface is arranged at the exit of the Faraday type ion detector. The quadrupole mass spectrometer according to claim 1. 6. The four electrodes according to claim 3, wherein the shield electrode has an auxiliary ion detection function independent of a light receiving surface of the ion detector. Double pole mass spectrometer.