Ion detector and mass spectrometer

Abstract

The invention provides an ion detector and a mass spectrometer. The ion detector includes: a conversion dynode having a conversion region; an electron multiplication unit having a first dynode; a box-type electrode having a first opening through which ions traveling to the conversion region pass and a second opening through which electrons traveling from the conversion region to the first-stage dynode pass; a conductive shield part disposed in the first opening and having a gap through which ions traveling toward the conversion region pass; and a potential application unit that applies a first potential to the conversion dynode, applies a second potential to the first dynode, applies a third potential to the box electrode, and applies a fourth potential to the shield unit, the first potential and the third potential being opposite to the polarity of the ions, the second potential being higher than the first potential, and the third potential and the fourth potential being substantially the same potential.

Description

Technical Field

[0001] The present invention relates to an ion detector and a mass analysis device. Background Art

[0002] As an ion detector for detecting positive ions, there is known a structure including: a conversion dynode that releases electrons when ions are incident; an electron multiplying section that multiplies the electrons released from the conversion dynode; and a box electrode that accommodates the conversion dynode and has a first opening for allowing ions traveling toward the conversion dynode to pass and a second opening for allowing electrons traveling from the conversion dynode to the first-stage dynode to pass (for example, see Japanese Patent Application Publication No. 2011-086403). In such an ion detector, a box electrode is sometimes used to suppress the incidence of stray light that may become noise on the conversion dynode. Summary of the invention

[0003] In the above-mentioned ion detector, in order to detect not only positive ions but also negative ions, it is considered to enable the potential given to the conversion dynode to be switched. Specifically, it is considered to give a positive potential to the conversion dynode so that the positive ions released from the conversion dynode by the incidence of negative ions are incident on the first-stage dynode. In this case, since the conversion efficiency from negative ions to positive ions is low, there is a problem that the detection efficiency of negative ions may decrease as a result.

[0004] An object of the present invention is to provide an ion detector and a mass spectrometer capable of improving the ion detection efficiency for each of positive ions and negative ions.

[0005] An ion detector according to one aspect of the present invention includes: a conversion dynode having a conversion region that releases electrons by ion incidence; an electron multiplying section having a first-order dynode into which the electrons are incident; a box electrode that accommodates the conversion dynode and has a first opening through which the ions traveling toward the conversion region pass and a second opening through which the electrons traveling from the conversion region to the first-order dynode pass; a conductive shielding section that is arranged at the first opening and has a gap through which the ions traveling toward the conversion region pass; and a potential imparting section that imparts a first potential to the conversion dynode, a second potential to the first-order dynode, a third potential to the box electrode, and a fourth potential to the shielding section, wherein the first potential and the third potential are opposite to the polarity of the ions, the second potential is higher than the first potential, and the third potential and the fourth potential are substantially the same potential.

[0006] A mass spectrometer according to one aspect of the present invention includes an ionization section, a mass separation section, and an ion detector, wherein the ion detector includes: a conversion dynode having a conversion region that releases electrons by ion incidence; an electron multiplying section having a first-stage dynode on which the electrons are incident; a box electrode that accommodates the conversion dynode and has a first opening through which the ions traveling toward the conversion region pass and a second opening through which the electrons traveling from the conversion region to the first-stage dynode pass; a conductive shielding section that is disposed at the first opening and has a gap through which the ions traveling toward the conversion region pass; and a potential imparting section that imparts a first potential to the conversion dynode, a second potential to the first-stage dynode, a third potential to the box electrode, and a fourth potential to the shielding section, wherein the first potential and the third potential are opposite to the polarity of the ions, the second potential is higher than the first potential, and the third potential and the fourth potential are substantially the same potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a structural diagram of an ion detector according to an embodiment. Figure 2A and Figure 2B This is a diagram showing an example of the electric field distribution formed in the ion detector. Figure 3A and Figure 3B This is a diagram showing an example of the electric field distribution formed in the ion detector. Figure 4A and Figure 4B This is a diagram showing the detection efficiency of ions in the ion detector. Figure 5 This is a block diagram of a mass spectrometer according to one embodiment. DETAILED DESCRIPTION

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are given to the same or corresponding parts in each figure, and repeated descriptions are omitted. [Ion Detector According to One Embodiment]

[0009] like Figure 1 As shown, the ion detector 1 includes a partition 2, a conversion dynode 3, an electron multiplier 4, a box electrode 5, a shield 6, a deflection electrode 7 and a potential imparting unit 8. The ion detector 1 is housed in a box 201 (see FIG. 201 ) in a mass spectrometer 200. Figure 5) inside, and is arranged in a vacuum space. The material of the partition 2 is, for example, a metal such as stainless steel. A slit (aperture) 21a is formed in the wall portion 21 of the partition 2. The slit 21a has a center line (second center line) A1 parallel to the X-axis direction. The shape of the slit 21a when viewed from the X-axis direction is, for example, circular. Hereinafter, a direction perpendicular to the X-axis direction is referred to as the Y-axis direction, and a direction perpendicular to both the X-axis direction and the Y-axis direction is referred to as the Z-axis direction.

[0010] In the present embodiment, the ion detector 1 is used as a part of the mass spectrometer 200. In the mass spectrometer 200, the sample is ionized by the electrospray ionization method. The mass spectrometer 200 selects the ions P as the detection object from the generated ions by using a quadrupole. The ions P as the detection object are introduced into the ion detector 1 through the slit 21a. The ion detector 1 detects the injected ions P. In the present embodiment, the ions P can be either positive ions or negative ions. In addition, the housing 201 (refer to Figure 5 ) is recorded as the ground potential.

[0011] The conversion dynode 3 has a surface including a conversion region 3a. The conversion region 3a releases electrons E by the incidence of positive ions or negative ions. The conversion region 3a is a concave region on the opposite side of the space where the electrons E are released. The material of the conversion dynode 3 is, for example, a metal such as stainless steel. The conversion dynode 3 is supported by a supporting member (not shown) in the box electrode 5. The conversion dynode 3 is arranged on one side in the Y-axis direction relative to the center line A1. The conversion region 3a is on a plane α including the center line A1 and perpendicular to the Z-axis direction, facing one side in the X-axis direction (the side of the gap 21a). The conversion region 3a has a center line (first center line) A2 parallel to the X-axis direction.

[0012] The first potential is given to the conversion dynode 3 by the potential giving section 8. The first potential is a potential of opposite polarity to the polarity of the ion P. As an example, when the ion P is a positive ion, the first potential is -10 kV. In this case, the ion P is incident on the conversion region 3a with an energy of, for example, 10 keV, and the electron E is released from the conversion region 3a. As an example, when the ion P is a negative ion, the first potential is +5.5 kV. In this case, the ion P is incident on the conversion region 3a with an energy of, for example, 5.5 keV, and the electron E is released from the conversion region 3a. Generally, when the ion P is any of a positive ion and a negative ion, the amount of the released electron E is greater the higher the energy of the ion P incident on the conversion region 3a. That is, the higher the absolute value of the first potential is, the higher the conversion efficiency from the ion P to the electron E can be.

[0013] The electron multiplier 4 is arranged on one side in the Y-axis direction relative to the center line A2 (the opposite side to the center line A1). In the present embodiment, the electron multiplier 4 has a metal wall portion 41, a plurality of dynodes 42 and an anode 43. The electron multiplier 4 is supported by a supporting member (not shown). An electron passage 41a for passing electrons E is formed in the wall portion 41. The electron passage 41a is open in the Y-axis direction. The shape of the electron passage 41a when viewed from the Y-axis direction is, for example, a quadrilateral. The plurality of dynodes 42 and the anode 43 are arranged on a plane α. The material of each dynode 42 and the anode 43 is, for example, a metal such as stainless steel. Among the plurality of dynodes 42, the first-stage dynode 42a is opposite to the electron passage 41a in the Y-axis direction. In the electron multiplier 4, secondary electrons (not shown) are released from the first-stage dynode 42a by the electrons E after passing through the electron passage 41a being incident on the surface of the first-stage dynode 42a. The secondary electrons are multiplied by the dynodes 42 at the subsequent stage and enter the anode 43. The anode 43 is connected to a signal processing circuit via a capacitor (not shown). The anode 43 outputs the secondary electrons as a pulse signal.

[0014] The first-stage dynode 42a is given a second potential by the potential-giving section 8. The second potential is higher than the first potential of the conversion dynode 3. As an example, the second potential is +7 kV regardless of whether the ion P is a positive ion or a negative ion. The dynodes 42 other than the first-stage dynode 42a are given a predetermined potential by the potential-giving section 8 in such a manner that the secondary electrons released from the first-stage dynode 42a travel sequentially to the dynodes 42 of the subsequent stage. As an example, the dynodes 42 other than the first-stage dynode 42a are given a potential higher than +7 kV regardless of whether the ion P is a positive ion or a negative ion. The anode 43 is given a predetermined potential by the potential-giving section 8. As an example, the predetermined potential is +9 kV regardless of whether the ion P is a positive ion or a negative ion. In the ion detector 1, the wall 41 of the electron multiplier 4 is given a second potential by the potential-giving section 8. That is, in the present embodiment, regardless of the polarity of the ions P, the electron multiplying section 4 floats at a positive polarity.

[0015] The box electrode 5 accommodates the conversion dynode 3 in a manner that is separated into a space in which the conversion dynode 3 is arranged and a space in which the electron multiplier 4 is arranged. The box electrode 5 is arranged on one side (the conversion dynode 3 side) in the Y-axis direction relative to the center line A1, and is arranged between the center line A1 and the electron multiplier 4 on the plane α. The shape of the box electrode 5 is, for example, a rectangular box. The material of the box electrode 5 is, for example, a metal such as stainless steel. The box electrode 5 is supported by a supporting member (not shown). When viewed from the X-axis direction, the box electrode 5 does not overlap with the gap 21a, but overlaps with the wall 21. As a result, stray light that is generated in the mass spectrometer 200 and may become noise can be suppressed from entering the box electrode 5.

[0016] An ion passage opening (first opening) 51a is formed on the wall portion 51 to allow the ions P traveling toward the conversion region 3a to pass through. The ion passage opening 51a is formed at a corner on the side of the slit 21a of the box-type electrode 5 on the plane α when viewed from the Z-axis direction. The ion passage opening 51a is arranged on one side (the side of the center line A1) relative to the center line A2 when viewed from the Z-axis direction (the direction perpendicular to the center line A2). The ion passage opening 51a is inclined in a manner that the closer it is to the center line A1, the farther it is away from the slit 21a when viewed from the Z-axis direction (the direction perpendicular to the center line A1). The shape of the ion passage opening 51a when viewed from the direction perpendicular to the ion passage opening 51a is, for example, a quadrilateral.

[0017] The wall portion 51 is provided with an electron passage opening (second opening) 51b through which electrons E traveling from the conversion region 3a to the first-stage dynode 42a of the electron multiplying section 4 pass. The electron passage opening 51b is arranged on the other side (the electron multiplying section 4 side) relative to the center line A2 when viewed from the Z-axis direction (the direction perpendicular to the center line A2). The electron passage opening 51b is opposite to the electron passage opening 41a on the plane α. The shape of the electron passage opening 51b when viewed from the Y-axis direction is, for example, circular.

[0018] The third potential is given to the box-type electrode 5 by the potential-giving portion 8. The third potential is a potential with a polarity opposite to that of the ion P. The third potential is substantially the same potential as the first potential. Here, substantially the same potential means that, when the first potential is 100%, the third potential is greater than 90% and less than 110%. In the present embodiment, the third potential is the same potential as the first potential. As an example, the third potential is -10 kV when the ion P is a positive ion. As a result, the injected positive ions gradually move away from the center line A1 of the slit 21a to one side in the Y-axis direction and move toward the ion passage 51a. As an example, the third potential is +5.5 kV when the ion P is a negative ion. As a result, the injected negative ions gradually move away from the center line A1 of the slit 21a to one side in the Y-axis direction and move toward the ion passage 51a.

[0019] The shielding part 6 is arranged at the ion passage 51a, and is electrically connected to the box electrode 5, for example, by contacting with the box electrode 5. Like the ion passage 51a, the shielding part 6 is inclined in a manner that the closer it is to the center line A1, the farther it is from the gap 21a when viewed from the Z-axis direction (the direction perpendicular to the center line A1). The material of the shielding part 6 is a conductive material, for example, a metal such as stainless steel. The shielding part 6 has a plurality of gaps 6a through which the ions P traveling toward the conversion region 3a pass. The plurality of gaps 6a are arranged two-dimensionally along the ion passage 51a. In the present embodiment, the shielding part 6 is a grid-like component, and the plurality of gaps 6a are arranged in a matrix. The total area of ​​the plurality of gaps 6a is, for example, greater than 50% and less than 97% of the area of ​​the ion passage 51a.

[0020] In the shielding part 6, the fourth potential is imparted by the potential imparting part 8 through the box electrode 5. The fourth potential is a potential with a polarity opposite to that of the ion P. The fourth potential is substantially the same potential as the third potential. Here, substantially the same potential means that, when the third potential is 100%, the fourth potential is greater than 90% and less than 110%. In the present embodiment, the fourth potential is the same potential as the third potential. As an example, the fourth potential is -10 kV when the ion P is a positive ion. As an example, the fourth potential is +5.5 kV when the ion P is a negative ion.

[0021] The deflection electrode 7 is arranged on the other side (opposite to the box-type electrode 5) relative to the center line A1 when viewed from the Z-axis direction (the direction perpendicular to the center line A1). The material of the deflection electrode 7 is, for example, a metal such as stainless steel. The deflection electrode 7 is supported by a supporting member (not shown) so as to be located on the plane α. When viewed from the Z-axis direction, a portion of the deflection electrode 7 extends in the Y-axis direction. When viewed from the Z-axis direction, the other portion of the deflection electrode 7 extends from the portion toward the wall portion 21 in the X-axis direction. When viewed from the X-axis direction, the deflection electrode 7 does not overlap with the gap 21a, but overlaps with the wall portion 21. When viewed from the Y-axis direction, at least a portion of the deflection electrode 7 overlaps with the ion passage 51a.

[0022] The deflection electrode 7 is given a ground potential or a potential having the same polarity as that of the ions P by the potential applying section 8. As an example, this potential is +500 V when the ions P are positive ions. As an example, this potential is -500 V when the ions P are negative ions.

[0023] The potential-applying section 8 applies a predetermined potential to the conversion dynode 3, the electron multiplier section 4, the box electrode 5, and the deflection electrode 7, respectively. The potential-applying section 8 applies a predetermined potential to the shield section 6 via the box electrode 5. The potential-applying section 8 is electrically connected to the conversion dynode 3, the electron multiplier section 4, the box electrode 5, and the deflection electrode 7, respectively, through wiring or the like. As described above, when the ions P are positive ions, the potential-applying section 8 applies a first potential (e.g., -10 kV) to the conversion dynode 3, applies a second potential (e.g., +7 kV) higher than the first potential to the first-stage dynode 42a of the electron multiplier section 4, applies a third potential (e.g., -10 kV) which is the same potential as the first potential to the box electrode 5, applies a fourth potential (e.g., -10 kV) which is the same potential as the third potential to the shield section 6, and applies, for example, +500 V to the deflection electrode 7. When the ions P are negative ions, the potential imparting section 8 imparts a first potential (e.g., +5.5 kV) to the conversion dynode 3, imparts a second potential (e.g., +7 kV) higher than the first potential to the first-stage dynode 42a of the electron multiplier section 4, imparts a third potential (e.g., +5.5 kV) which is the same potential as the first potential to the box electrode 5, imparts a fourth potential (e.g., +5.5 kV) which is the same potential as the third potential to the shielding section 6, and imparts, for example, -500 V to the deflection electrode 7. That is, the potential imparting section 8 can switch the polarity of the first potential and the third potential, and change the value of each potential, according to the polarity of the ions P to be detected. As an example, the potential imparting section 8 is composed of a plurality of power supplies or a combination of a power supply and a resistor divider.

[0024] In this embodiment, the first-stage dynode 42a is opposite to the electron passage opening 51b with the electron passage opening 41a sandwiched therebetween. When viewed from the Y-axis direction, the outer edge of the electron passage opening 41a is located inside the outer edge of the electron passage opening 51b. When viewed from the Y-axis direction, at least the conversion region 3a of the conversion dynode 3 is located inside the outer edge of the electron passage opening 51b.

[0025] In the ion detector 1 constructed as described above, when detecting positive ions, the potential imparting section 8 imparts a predetermined potential to the conversion dynode 3, the electron multiplier section 4, the box electrode 5, the shield section 6, and the deflection electrode 7, respectively. As a result, an electric field is formed that causes positive ions to enter the conversion region 3a and an electric field that causes electrons E to enter the first-stage dynode 42a. In this state, positive ions enter from the slit 21a, and the positive ions pass through the ion passage 51a of the box electrode 5. In addition, positive ions enter the conversion region 3a of the conversion dynode 3. Electrons E are released from the conversion region 3a by the incidence of positive ions. Since an electric field is formed that causes electrons E to enter the first-stage dynode 42a, the electrons E released from the conversion region 3a pass through the electron passage 51b of the box electrode 5 and the electron passage 41a of the electron multiplier section 4, and enter the first-stage dynode 42a. When the electron E enters the first-stage dynode 42a, secondary electrons (not shown) are released from the first-stage dynode 42a. The secondary electrons are multiplied by the subsequent dynodes 42 and enter the anode 43. Then, the anode 43 outputs the secondary electrons as a pulse signal, and the ion detector 1 detects positive ions.

[0026] In the ion detector 1, when detecting negative ions, a predetermined potential is applied to the conversion dynode 3, the electron multiplier 4, the box electrode 5, the shield 6, and the deflection electrode 7 by the potential applying section 8. As a result, an electric field is formed to cause negative ions to enter the conversion region 3a and an electric field is formed to cause electrons E to enter the first-stage dynode 42a. In this state, negative ions enter from the slit 21a, and negative ions pass through the ion passage 51a of the box electrode 5. Moreover, negative ions enter the conversion region 3a of the conversion dynode 3. Electrons E are released from the conversion region 3a by the negative ion incidence. Since an electric field is formed to cause electrons E to enter the first-stage dynode 42a, the electrons E released from the conversion region 3a pass through the electron passage 51b of the box electrode 5 and the electron passage 41a of the electron multiplier 4, and enter the first-stage dynode 42a. When the electron E is incident on the first-stage dynode 42a, secondary electrons (not shown) are released from the first-stage dynode 42a. The secondary electrons are multiplied by the dynodes 42 of the subsequent stage and are incident on the anode 43. Then, the secondary electrons are output as pulse signals through the anode 43, and the ion detector 1 detects negative ions. That is, in the ion detector 1, since the electron multiplier 4 floats in the positive polarity, the electrons E released from the conversion region 3a can also be incident on the first-stage dynode 42a when detecting negative ions.

[0027] As described above, in the ion detector 1, when positive ions are detected, the first potential, which is a negative potential, is given to the conversion dynode 3, and the second potential, which is higher than the first potential, is given to the first-stage dynode 42a of the electron multiplier 4. At this time, the third potential, which is a negative potential, is given to the box electrode 5 that accommodates the conversion dynode 3, and the fourth potential, which is substantially the same as the third potential, is given to the shielding portion 6 disposed at the ion passage 51a of the box electrode 5. Thus, positive ions can be made incident on the conversion region 3a of the conversion dynode 3 through the plurality of gaps 6a of the shielding portion 6 disposed at the ion passage 51a of the box electrode 5. In addition, the electrons E released from the conversion region 3a can be made incident on the first-stage dynode 42a through the electron passage 51b of the box electrode 5. At this time, since the mutual interference between the electric field that causes positive ions to enter the conversion region 3a and the electric field that causes electrons E to enter the first-stage dynode 42a is suppressed by the box-type electrode 5, positive ions can be reliably entered into the conversion region 3a, and electrons E can be reliably entered into the first-stage dynode 42a. Furthermore, since the formation of the electric field that attracts electrons E through the ion passage 51a in the box-type electrode 5 is suppressed by the shielding portion 6, electrons E can be reliably entered into the first-stage dynode 42a. Thus, by using the ion detector 1, it is possible to improve the detection efficiency of positive ions.

[0028] In the ion detector 1, when detecting negative ions, a first potential as a positive potential is given to the conversion dynode 3, and a second potential higher than the first potential is given to the first-stage dynode 42a of the electron multiplier 4. At this time, a third potential as a positive potential is given to the box electrode 5 that accommodates the conversion dynode 3, and a fourth potential substantially the same as the third potential is given to the shielding portion 6 disposed at the ion passage 51a of the box electrode 5. Thus, negative ions can be made incident on the conversion region 3a of the conversion dynode 3 through the plurality of gaps 6a of the shielding portion 6 disposed at the ion passage 51a of the box electrode 5. In addition, electrons E released from the conversion region 3a can be made incident on the first-stage dynode 42a through the electron passage 51b of the box electrode 5. At this time, since the mutual interference between the electric field that causes the negative ions to be incident on the conversion region 3a and the electric field that causes the electrons E to be incident on the first-stage dynode 42a is suppressed by the box-type electrode 5, the negative ions can be reliably incident on the conversion region 3a, and the electrons E can be reliably incident on the first-stage dynode 42a. Furthermore, since the formation of the electric field that pushes the electrons E back through the ion passage 51a in the box-type electrode 5 is suppressed by the shielding portion 6, the electrons E can be reliably incident on the first-stage dynode 42a. Therefore, by using the ion detector 1, it is possible to achieve an improvement in the detection efficiency of negative ions. According to the above description, the ion detector 1 can improve the detection efficiency of ions for both positive ions and negative ions.

[0029] In the ion detector 1, the shielding part 6 has a plurality of gaps 6a arranged two-dimensionally along the ion passage 51a. Thus, when detecting positive ions, it is possible to reliably suppress the electric field that attracts the electrons E released from the conversion region 3a from being formed in the box-type electrode 5 through the ion passage 51a, and at the same time, the positive ions are reliably passed through the ion passage 51a. When detecting negative ions, it is possible to reliably suppress the electric field that pushes back the electrons E released from the conversion region 3a from being formed in the box-type electrode 5 through the ion passage 51a, and at the same time, the negative ions are reliably passed through the ion passage 51a. Therefore, it is possible to further improve the detection efficiency of ions for positive ions and negative ions, respectively.

[0030] In the ion detector 1, the ion passage 51a is arranged on one side relative to the center line A2 when viewed from a direction perpendicular to the center line A2 passing through the center of the conversion region 3a, and the electron passage 51b is arranged on the other side relative to the center line A2 when viewed from a direction perpendicular to the center line A2, and the first-stage dynode 42a and the electron passage 51b are opposite to each other. Thus, the first-stage dynode 42a and the electron passage 51b of the box electrode 5 are opposite to each other, so that an electric field that causes the electrons E to be incident on the first-stage dynode 42a can be easily and reliably formed, and the electrons E can be more reliably incident on the first-stage dynode 42a. In addition, since the ion passage 51a of the box-type electrode 5 is arranged on one side relative to the center line A2 of the conversion region 3a, and the electron passage 51b of the box-type electrode 5 is arranged on the other side relative to the center line A2 of the conversion region 3a, the electric field causing the electrons E to be incident on the first-stage dynode 42a can be suppressed from affecting the ions P of the detection object traveling toward the conversion region 3a, and the ions P of the detection object can be more reliably made to be incident on the conversion region.

[0031] In the ion detector 1 , the first potential and the third potential are substantially the same potential. This simplifies the structure of the potential applying unit 8 and facilitates switching of the polarities of the first potential and the third potential according to the polarity of the ions P to be detected.

[0032] In the ion detector 1, the total area of ​​the plurality of gaps 6a is 50% or more of the area of ​​the ion passage 51a. Thus, the ions P to be detected can be more reliably made incident on the conversion region 3a of the conversion dynode 3 through the plurality of gaps 6a of the shielding portion 6 disposed at the ion passage 51a of the box electrode 5. Therefore, the detection efficiency of the ions can be further improved for both positive ions and negative ions.

[0033] The ion detector 1 includes a partition 2 having a slit 21a through which ions P traveling toward an ion passage 51a pass. This can suppress the incidence of electrons or ions that may become noise on the conversion region 3a. Therefore, the detection accuracy of ions can be improved for both positive and negative ions.

[0034] The ion detector 1 includes a deflection electrode 7. When the box electrode 5 is viewed from a direction perpendicular to the center line A1 of the slit 21a, the box electrode 5 is arranged on one side relative to the center line A1. When the box electrode 5 is viewed from a direction perpendicular to the center line A1, the deflection electrode 7 is arranged on the other side relative to the center line A1. The potential imparting unit 8 imparts a ground potential or a potential of the same polarity as the polarity of the ion P to the deflection electrode 7. Thus, an electric field that causes the ions P of the detection object to travel toward the ion passage 51a of the box electrode 5 can be reliably formed, so that the ions P of the detection object can be more reliably incident on the conversion region 3a. Therefore, the detection efficiency of the ions can be further improved for positive ions and negative ions respectively.

[0035] In the ion detector 1, the ion passage 51a is inclined so that the closer it is to the center line A1, the farther it is from the slit 21a. Thus, the ions P of the detection object that have passed through the slit 21a can be reliably incident on the ion passage 51a of the box electrode 5, and thus the ions P of the detection object can be more reliably incident on the conversion region 3a. Therefore, the detection efficiency of the ions can be further improved for both positive ions and negative ions.

[0036] In the ion detector 1, the total area of ​​the plurality of gaps 6a is less than 97% of the area of ​​the ion passage 51a. Thus, in the case of detecting positive ions, it is possible to more reliably suppress the electric field that attracts the electrons E released from the conversion region 3a from being formed in the box electrode 5 through the ion passage 51a. In the case of detecting negative ions, it is possible to more reliably suppress the electric field that pushes back the electrons E released from the conversion region 3a from being formed in the box electrode 5 through the ion passage 51a. Therefore, it is possible to further improve the detection efficiency of ions for both positive ions and negative ions. [Example of electric field distribution]

[0037] Reference Figure 2A and Figure 2B The advantages of the shielding unit 6 described above when the ions P are positive ions will be described. Figure 2A In FIG. 1 , the electric field distribution formed in the ion detector 101 different from the above-mentioned ion detector 1 when the ions P are positive ions is represented by equipotential lines. The ion detector 101 is different from the ion detector 1 in that the shielding part 6 is not provided. Figure 2BIn FIG. 1 , the electric field distribution formed in the above-mentioned ion detector 1 when the ions P are positive ions is represented by equipotential lines. As described above, the first potential of the conversion dynode 3 is -10 kV, the second potential of the first-stage dynode 42a of the electron multiplier 4 is +7 kV, the third potential of the box electrode 5 is -10 kV, the fourth potential of the shielding part 6 is -10 kV, and the potential of the deflection electrode 7 is +500 V.

[0038] like Figure 2A As shown in FIG. 1 , in the ion detector 101, an electric field EF1 is formed to make the electron E incident on the first-stage dynode 42a, and at the same time, it is an electric field EF1 that expands from the electron passage port 51b into the box-type electrode 5. In addition, in the ion detector 101, an electric field EF2 is formed to attract the electron E, and at the same time, it is an electric field EF2 that expands from the ion passage port 51a into the box-type electrode 5. As a result, the electron E is affected not only by the electric field EF1 but also by the electric field EF2, so the electron E is attracted to the ion passage port 51a side. As a result, in the ion detector 101, it is difficult for the electron E to be incident on the first-stage dynode 42a.

[0039] like Figure 2B As shown, in the ion detector 1, an electric field EF3 is formed to make the electrons E incident on the first-stage dynode 42a, and at the same time, the electric field EF3 is expanded from the electron passage port 51b into the box-type electrode 5. In the ion detector 1, since the shielding part 6 is arranged at the ion passage port 51a, the formation of an electric field that attracts the electrons E in the box-type electrode 5 is suppressed, unlike the ion detector 101. As a result, compared with the case of the ion detector 101, the electrons E released from the conversion region 3a can be made to be incident on the first-stage dynode 42a more reliably.

[0040] for Figure 2A The ion detector 101 and Figure 2B The ion detector 1 shown simulates the incidence efficiency of the electrons E released from the conversion region 3a onto the first-stage dynode 42a. The value obtained by dividing the mass of the ion P by the charge of the ion P (hereinafter referred to as "m / z") is 50. The incidence efficiency in the ion detector 101 is 76.1%, while the incidence efficiency in the ion detector 1 is 99.8%. From the results of this simulation, it can be seen that when the ions P are positive ions, the amount of electrons E incident on the first-stage dynode 42a increases by configuring the shielding part 6 at the ion passage port 51a.

[0041] Reference Figure 3A and Figure 3B The advantages of the shielding unit 6 described above when the ions P are negative ions will be described. Figure 3A In FIG. 1 , the electric field distribution formed in the above-mentioned ion detector 101 when the ions P are negative ions is represented by equipotential lines. Figure 3B In FIG. 1 , the electric field distribution formed in the above-mentioned ion detector 1 when the ions P are negative ions is represented by equipotential lines. As described above, the first potential of the conversion dynode 3 is +5.5 kV, the second potential of the first-stage dynode 42a of the electron multiplier 4 is +7 kV, the third potential of the box electrode 5 is +5.5 kV, the fourth potential of the shielding part 6 is +5.5 kV, and the potential of the deflection electrode 7 is -500 V.

[0042] like Figure 3A As shown in FIG. 1 , in the ion detector 101, an electric field EF4 is formed to make the electron E incident on the first-stage dynode 42a, and at the same time, it is an electric field EF4 that expands from the electron passage port 51b into the box-type electrode 5. In addition, in the ion detector 101, an electric field EF5 is formed to push the electron E back, and at the same time, it is an electric field EF5 that expands from the ion passage port 51a into the box-type electrode 5. As a result, the electron E is not only affected by the electric field EF4 but also by the electric field EF5, so the electron E is pushed back to the opposite side of the ion passage port 51a. As a result, in the ion detector 101, it is difficult for the electron E to be incident on the first-stage dynode 42a.

[0043] like Figure 3B As shown, in the ion detector 1, an electric field EF6 is formed to make the electrons E incident on the first-stage dynode 42a, and at the same time, the electric field EF6 is extended from the electron passage port 51b into the box-type electrode 5. In the ion detector 1, since the shielding part 6 is arranged at the ion passage port 51a, the electric field that pushes back the electrons E is suppressed from being formed in the box-type electrode 5, unlike the ion detector 101. As a result, compared with the case of the ion detector 101, the electrons E released from the conversion region 3a can be made to be incident on the first-stage dynode 42a more reliably.

[0044] for Figure 3A The ion detector 101 and Figure 3B The ion detector 1 shown simulates the incidence efficiency of the electrons E released from the conversion region 3a to the first-stage dynode 42a. The m / z value of the ion P is 50. The incidence efficiency is 69.1% in the ion detector 101, while the incidence efficiency is 91.2% in the ion detector 1. From the results of this simulation, it can be seen that when the ions P are negative ions, the amount of electrons E incident on the first-stage dynode 42a increases by configuring the shielding part 6 at the ion passage 51a. [Ion detection example]

[0045] Reference Figure 4A and Figure 4B , the ion intensity of ions detected by the ion detector 1 will be described. Figure 4A The results when positive ions are detected by the ion detector 1 are shown. Figure 4B The results are shown when negative ions are detected by the ion detector 1 . Figure 4A and Figure 4B Each vertical axis of represents a value (intensity ratio) obtained by dividing the ion intensity detected by the ion detector 1 by the ion intensity detected by an example of a conventional ion detector (hereinafter referred to as “conventional example”), Figure 4A and Figure 4B Each horizontal axis represents a value (m / z) obtained by dividing the mass of the ion to be detected by the charge of the ion. The conventional example does not include the box electrode 5 , the shielding unit 6 , and the deflection electrode 7 , and the potential applied to each component in the conventional example is different from that of the ion detector 1 .

[0046] right Figure 4A The potentials of the components of the ion detector 1 are described below. In the ion detector 1, the first potential of the conversion dynode 3 is -10 kV, the second potential of the first-stage dynode 42a of the electron multiplier 4 is +7 kV, the potential of the anode 43 is +9 kV, the third potential of the box electrode 5 is -10 kV, the fourth potential of the shielding part 6 is -10 kV, and the potential of the deflection electrode 7 is +500 V. Figure 4A The potential of each component of the prior art example is described below. In the prior art example, the potential of the conversion dynode is -10 kV, the potential of the first stage dynode of the electron multiplication unit is -2 kV, and the potential of the anode is the ground potential. Figure 4A As shown, when detecting positive ions, the detection efficiency of the ion detector 1 is comparable to that of the conventional example.

[0047] right Figure 4B The potentials of the components of the ion detector 1 are described in FIG. 1. In the ion detector 1, the first potential of the conversion dynode 3 is +5.5 kV, the second potential of the first-stage dynode 42a of the electron multiplier 4 is +7 kV, the potential of the anode 43 is +9 kV, the third potential of the box electrode 5 is +5.5 kV, the fourth potential of the shielding part 6 is +5.5 kV, and the potential of the deflection electrode 7 is -500 V. Figure 4B The potential of each component of the prior art example is described below. In the prior art example, the potential of the conversion dynode is +10 kV, the potential of the first-stage dynode of the electron multiplication unit is -2 kV, and the potential of the anode is the ground potential. Figure 4B As shown, when detecting negative ions, the detection efficiency of the ion detector 1 is better than that of the conventional example in the region where the value of the horizontal axis is 200 or less. [Mass Spectrometer According to One Embodiment]

[0048] Reference Figure 5, the specific structure of the mass spectrometer 200 described above is described. The mass spectrometer 200 includes an ion detector 1, a housing 201, an ionization unit 202, a first mass separation unit (mass separation unit) 203, a collision unit 204, a second mass separation unit (mass separation unit) 205, and a pulse counting detection unit 206. In the mass spectrometer 200, the first mass separation unit 203, the collision unit 204, and the second mass separation unit 205 are sequentially arranged in series. The ion detector 1 includes a detection unit 10 composed of a partition 2, a conversion dynode 3, an electron multiplier 4, a box electrode 5, a shielding unit 6, and a deflection electrode 7, and a potential applying unit 8. The housing 201 accommodates the detection unit 10, the ionization unit 202, the first mass separation unit 203, the collision unit 204, and the second mass separation unit 205. The potential applying unit 8 and the pulse counting detection unit 206 are arranged outside the housing 201.

[0049] The ionization section 202 generates ions from a sample introduced into the ionization section 202. As an example, a liquid sample is introduced from a liquid chromatograph into the ionization section 202. In the ionization section 202, the sample is ionized by, for example, electrospray ionization.

[0050] The first mass separation unit 203 selectively allows ions with a predetermined m / z value to pass through from the ions generated by the ionization unit 202. In the present embodiment, the first mass separation unit 203 is a quadrupole mass separation unit having four electrodes 203a. Each electrode 203a is a rod-shaped electrode, which is arranged around a predetermined central axis. A predetermined potential is given to each electrode 203a by a potential imparting unit (not shown in the figure), forming an electric field with a high-speed phase change. When the ions with a predetermined m / z value pass through the electric field, they vibrate stably, and thus can pass through the first mass separation unit 203.

[0051] The collision section 204 generates product ions by dissociating the ions (precursor ions) passing through the first mass separation section 203. The collision section 204 has a plurality of electrodes 204a and a collision chamber 204b. The number of the plurality of electrodes 204a is, for example, eight. Each electrode 204a is arranged around a predetermined central axis in the collision chamber 204b. In the collision chamber 204b, a collision gas for colliding with the precursor ions is introduced. As an example, the collision gas is argon gas. By colliding the precursor ions injected into the collision chamber 204b with the collision gas, the precursor ions are dissociated to generate product ions. A predetermined potential is given to each electrode 204a by a potential imparting section (not shown) to form a high-frequency electric field. The product ions are accelerated by the electric field and thus travel smoothly to the outside of the collision chamber 204b.

[0052] The second mass separation unit 205 selectively allows ions with a predetermined m / z value to pass through from the ions (product ions) generated by the collision unit 204. In the present embodiment, the second mass separation unit 205 is a quadrupole mass separation unit having four electrodes 205a. Each electrode 205a is a rod-shaped electrode, arranged around a predetermined central axis. A predetermined potential is given to each electrode 205a by a potential imparting unit (not shown in the figure), forming an electric field with a high-speed phase change. Ions with a predetermined m / z value vibrate stably when passing through the electric field, and thus can pass through the second mass separation unit 205.

[0053] The ions passing through the second mass separation section 205 are incident on the ion detector 1 as the detection object, i.e., the ions P. The pulse counting detection section 206 counts the pulse signals output from the above-mentioned anode 43. The mass spectrometer 200 is a quadrupole mass spectrometer having a first mass separation section 203 and a second mass separation section 205 as quadrupole mass separation sections. In the mass spectrometer 200, by using the first mass separation section 203 and the second mass separation section 205 to perform two-stage mass separation, it is possible to achieve an improvement in the signal-to-noise ratio (S / N). Therefore, the mass spectrometer 200 is suitable for the detection of trace components in a sample.

[0054] With the structure of the mass spectrometer 200 as described above, in the ion detector 1, the orbit of the electron E released from the conversion dynode 3 is optimized by applying appropriate potentials to the conversion dynode 3, the first-stage dynode 42a of the electron multiplier 4, the box electrode 5, and the shielding section 6. Thus, even when the energy distribution and spatial distribution of the ions passing through the first mass separation section 203 or the second mass separation section 205 are widely spread, the detection efficiency of the ions can be improved for both positive ions and negative ions.

[0055] In the mass spectrometer 200 , the first mass separation unit 203 is a quadrupole mass separation unit, and the second mass separation unit 205 is a quadrupole mass separation unit. Thus, the first mass separation unit 203 and the second mass separation unit 205 can be specifically configured. [Modifications]

[0056] The present invention is not limited to the above-mentioned embodiment. In the ion detector 1, one potential imparting section 8 imparts a predetermined potential to each of the conversion dynode 3, the electron multiplier section 4, the box electrode 5, the shield section 6, and the deflection electrode 7, and a plurality of potential imparting sections 8 may impart a predetermined potential to each of at least one of the conversion dynode 3, the electron multiplier section 4, the box electrode 5, the shield section 6, and the deflection electrode 7.

[0057] In the ion detector 1, the shielding part 6 is electrically connected to the box electrode 5, but the shielding part 6 may not be electrically connected to the box electrode 5. As an example, the shielding part 6 may be supported by a supporting member (not shown). In this case, the potential imparting part 8 may be electrically connected to the shielding part 6 via wiring, etc., and the fourth potential may be imparted to the shielding part 6.

[0058] In the ion detector 1, the shielding part 6 is a grid-shaped component, but it can also be a honeycomb-shaped component. The plurality of gaps 6a of the shielding part 6 are arranged in a matrix shape, but it can also be arranged in a two-dimensional shape in other ways. Further, the plurality of gaps 6a can also be arranged in a one-dimensional shape. In this case, each gap 6a can also be formed in a slit shape. The shielding part 6 only needs to have at least one gap 6a.

[0059] In the ion detector 1, the electron passage port 51b is arranged on the other side relative to the center line A2 when viewed from the Z-axis direction, and the first-stage dynode 42a is opposite to the electron passage port 51b, and the conversion region 3a, the electron passage port 41a, the first-stage dynode 42a and the electron passage port 51b can also be arranged on the plane α.

[0060] In the ion detector 1, the third potential is substantially the same as the first potential, but the third potential may not be substantially the same as the first potential. As an example, when the ions P are positive ions, the first potential may be -10 kV and the third potential may be -11.5 kV. As an example, when the ions P are negative ions, the first potential may be +5.5 kV and the third potential may be +6.1 kV.

[0061] In the ion detector 1 , the total area of ​​the plurality of gaps 6 a is equal to or greater than 50% of the area of ​​the ion passage opening 51 a , but the area of ​​the gaps 6 a may be smaller than 50% of the area of ​​the ion passage opening 51 a .

[0062] The ion detector 1 can be used as a part of a mass spectrometer using TOF (Time of Flight) or a part of a mass spectrometer using plasma as an ion source.

[0063] The mass spectrometer 200 includes the first mass separation unit 203 and the second mass separation unit 205 , but the mass spectrometer 200 only needs to include at least one of the first mass separation unit 203 and the second mass separation unit 205 . The mass spectrometer 200 may not include the collision unit 204 .

[0064] An ion detector according to one aspect of the present invention is [1] "an ion detector comprising: a conversion dynode having a conversion region that releases electrons upon ion incidence; an electron multiplying section having a first-stage dynode into which the electrons are incident; a box electrode that accommodates the conversion dynode and has a first opening through which the ions traveling toward the conversion region pass and a second opening through which the electrons traveling from the conversion region to the first-stage dynode pass; a conductive shielding section that is disposed at the first opening and has a gap through which the ions traveling toward the conversion region pass; and a potential imparting section that imparts a first potential to the conversion dynode, a second potential to the first-stage dynode, a third potential to the box electrode, and a fourth potential to the shielding section, wherein the first potential and the third potential are opposite to the polarity of the ions, the second potential is higher than the first potential, and the third potential and the fourth potential are substantially the same potential".

[0065] In the ion detector described in [1] above, when detecting positive ions, a first potential as a negative potential is given to the conversion dynode, and a second potential higher than the first potential is given to the first-stage dynode of the electron multiplier. At this time, a third potential as a negative potential is given to the box electrode that accommodates the conversion dynode, and a fourth potential substantially the same as the third potential is given to the shielding portion arranged at the first opening of the box electrode. As a result, positive ions can be made incident on the conversion region of the conversion dynode through the gap of the shielding portion arranged at the first opening of the box electrode. In addition, electrons released from the conversion region can be made incident on the first-stage dynode through the second opening of the box electrode. At this time, the mutual interference between the electric field that makes the positive ions incident on the conversion region and the electric field that makes the electrons incident on the first-stage dynode is suppressed by the box electrode, so that positive ions can be reliably made incident on the conversion region and electrons can be reliably made incident on the first-stage dynode. Furthermore, since the electric field that attracts electrons formed in the box electrode through the first opening is suppressed by the shielding portion, the electrons can be reliably incident on the first-stage dynode. Thus, the ion detector described in [1] can improve the detection efficiency of positive ions.

[0066] In the ion detector described in [1] above, when detecting negative ions, a first potential as a positive potential is given to the conversion dynode, and a second potential higher than the first potential is given to the first-stage dynode of the electron multiplier. At this time, a third potential as a positive potential is given to the box electrode that accommodates the conversion dynode, and a fourth potential substantially the same as the third potential is given to the shielding portion arranged at the first opening of the box electrode. Thus, negative ions can be made incident on the conversion region of the conversion dynode through the gap of the shielding portion arranged at the first opening of the box electrode. In addition, electrons released from the conversion region can be made incident on the first-stage dynode through the second opening of the box electrode. At this time, the mutual interference between the electric field that causes negative ions to be incident on the conversion region and the electric field that causes electrons to be incident on the first-stage dynode is suppressed by the box electrode, so that negative ions can be reliably made incident on the conversion region and electrons can be reliably made incident on the first-stage dynode. Furthermore, since the electric field that pushes back the electrons formed in the box electrode through the first opening is suppressed by the shielding portion, the electrons can be reliably incident on the first-stage dynode. Thus, the ion detector described in [1] can improve the detection efficiency of negative ions. According to the above description, the ion detector described in the above [1] can improve the ion detection efficiency for both positive ions and negative ions.

[0067] The ion detector of one aspect of the present invention may also be [2] "the ion detector described in [1] above, wherein the shielding portion has a plurality of gaps as the gaps two-dimensionally arranged along the first opening". When using the ion detector described in [2], when detecting positive ions, it is possible to reliably suppress the electric field that attracts electrons released from the conversion region from being formed in the box-type electrode through the first opening, while allowing positive ions to reliably pass through the first opening. When detecting negative ions, it is possible to reliably suppress the electric field that pushes back electrons released from the conversion region from being formed in the box-type electrode through the first opening, while allowing negative ions to reliably pass through the first opening. Therefore, it is possible to further improve the detection efficiency of ions for both positive and negative ions.

[0068] The ion detector of one aspect of the present invention may also be [3] "the ion detector described in [1] or [2] above, wherein the first opening is arranged on one side relative to the first center line when viewed from a direction perpendicular to the first center line passing through the center of the conversion region, the second opening is arranged on the other side relative to the first center line when viewed from the direction perpendicular to the first center line, and the first-stage dynode is opposite to the second opening". With the ion detector described in [3], the first-stage dynode is opposite to the second opening of the box electrode, so that an electric field that causes electrons to be incident on the first-stage dynode can be easily and reliably formed, and electrons can be more reliably caused to be incident on the first-stage dynode. In addition, since the first opening of the box-type electrode is arranged on one side relative to the first center line of the conversion area, and the second opening of the box-type electrode is arranged on the other side relative to the first center line of the conversion area, the electric field causing electrons to be incident on the first-stage dynode can be suppressed from affecting the ions of the detection object traveling toward the conversion area, and the ions of the detection object can be more reliably made to be incident on the conversion area.

[0069] The ion detector according to one aspect of the present invention may also be [4] "an ion detector as described in any one of [1] to [3] above, wherein the first potential and the third potential are substantially the same potential". By using the ion detector described in [4], it is possible to simplify the structure of the potential imparting portion and facilitate switching of the polarity of the first potential and the third potential corresponding to the polarity of the ions to be detected.

[0070] The ion detector according to one aspect of the present invention may also be [5] "the ion detector described in any one of [1] to [4] above, wherein the area of ​​the gap is at least 50% of the area of ​​the first opening". By using the ion detector described in [5], the ions of the detection object can be more reliably incident on the conversion region of the conversion dynode through the gap of the shielding portion arranged at the first opening of the box electrode. Therefore, the detection efficiency of ions can be further improved for both positive ions and negative ions.

[0071] The ion detector of one aspect of the present invention may also be [6] "the ion detector described in any one of [1] to [5] above, further comprising a partition having a slit through which the ions traveling toward the first opening pass". By using the ion detector described in [6], it is possible to suppress the incidence of electrons or ions that may become noise into the conversion region. Therefore, it is possible to improve the detection accuracy of ions for both positive ions and negative ions.

[0072] The ion detector of one aspect of the present invention may also be [7] "the ion detector described in [6] above, further comprising a deflection electrode, wherein the box-type electrode is arranged on one side relative to the second center line of the gap when viewed from a direction perpendicular to the second center line, and the deflection electrode is arranged on the other side relative to the second center line when viewed from the direction perpendicular to the second center line, and the potential imparting unit imparts a ground potential or a potential of the same polarity as the polarity of the ions to the deflection electrode". By using the ion detector described in [7], an electric field can be reliably formed that causes the ions of the detection object to travel toward the first opening of the box-type electrode, thereby more reliably causing the ions of the detection object to be incident on the conversion region. Therefore, the detection efficiency of ions can be further improved for both positive ions and negative ions.

[0073] The ion detector of one aspect of the present invention may also be [8] "the ion detector described in [6] or [7] above, wherein the first opening is inclined in such a manner that the closer it is to the second center line, the farther it is from the slit" when viewed from a direction perpendicular to the second center line of the slit. By using the ion detector described in [8], the ions of the detection object that have passed through the slit can be reliably incident on the first opening of the box electrode, thereby more reliably causing the ions of the detection object to be incident on the conversion region. Therefore, the detection efficiency of ions can be further improved for both positive ions and negative ions.

[0074] A mass spectrometer according to one aspect of the present invention is [9] "a mass spectrometer comprising: an ionization unit; a mass separation unit; and an ion detector, wherein the ion detector comprises: a conversion dynode having a conversion region for releasing electrons upon ion incidence; an electron multiplication unit having a first-stage dynode for incident electrons; a box-type electrode for housing the conversion dynode and having a first opening for allowing the ions traveling toward the conversion region to pass through and a second opening for allowing the electrons traveling from the conversion region to pass through the first-stage dynode. a second opening; a conductive shielding portion, which is arranged at the first opening and has a gap for allowing the ions traveling toward the conversion region to pass through; and a potential imparting portion, which imparts a first potential to the conversion dynode, a second potential to the first-stage dynode, a third potential to the box electrode, and a fourth potential to the shielding portion, wherein the first potential and the third potential are opposite to the polarity of the ions, the second potential is higher than the first potential, and the third potential and the fourth potential are substantially the same potential.

[0075] In the mass spectrometer described in [9], by applying appropriate potentials to the conversion dynode, the first-stage dynode of the electron multiplier section, the box electrode, and the shielding section, the trajectory of the electrons released from the conversion dynode is optimized. Thus, even when the energy distribution and spatial distribution of the ions passing through the mass separation section are widely spread, the detection efficiency of the ions can be improved for both positive ions and negative ions.

[0076] The mass spectrometer according to one aspect of the present invention may be

[10] "the mass spectrometer according to [9] above, wherein the mass separation unit is a quadrupole mass separation unit". The mass spectrometer according to

[10] can be specifically configured to form the mass separation unit.

[0077] According to the present invention, it is possible to provide an ion detector and a mass spectrometer capable of improving the detection efficiency of ions for both positive ions and negative ions.

Claims

1. An ion detector, characterized in that include: a conversion dynode having a conversion region for releasing electrons upon ion incidence; An electron multiplying section having a first-stage dynode into which the electrons are incident; a box-type electrode that accommodates the conversion dynode and has a first opening for allowing the ions traveling toward the conversion region to pass through and a second opening for allowing the electrons traveling from the conversion region toward the first-stage dynode to pass through; a conductive shielding portion disposed at the first opening and having a gap through which the ions traveling toward the conversion region pass; and a potential imparting unit that imparts a first potential to the conversion dynode, imparts a second potential to the first-stage dynode, imparts a third potential to the box electrode, and imparts a fourth potential to the shielding unit, The first potential and the third potential are polarities opposite to the polarity of the ions. The second potential is higher than the first potential, The third potential and the fourth potential are substantially the same potential.

2. The ion detector according to claim 1, characterized in that The shield portion includes a plurality of gaps as the gaps that are two-dimensionally arranged along the first opening.

3. The ion detector according to claim 1 or 2, characterized in that The first opening is arranged on one side relative to a first center line passing through the center of the conversion area when viewed from a direction perpendicular to the first center line. The second opening is arranged on the other side relative to the first center line when viewed from the direction perpendicular to the first center line. The first-stage dynode is opposite to the second opening.

4. The ion detector according to any one of claims 1 to 3, characterized in that The first potential and the third potential are substantially the same potential.

5. The ion detector according to any one of claims 1 to 4, characterized in that The area of ​​the gap is equal to or greater than 50% of the area of ​​the first opening.

6. The ion detector according to any one of claims 1 to 5, characterized in that The device further includes a partition having a slit through which the ions traveling toward the first opening pass.

7. The ion detector according to claim 6, characterized in that Also includes deflection electrodes, The box-type electrode is arranged on one side relative to the second center line when viewed from a direction perpendicular to the second center line of the gap, The deflection electrode is arranged on the other side relative to the second center line when viewed from the direction perpendicular to the second center line. The potential applying unit applies a ground potential or a potential having the same polarity as the polarity of the ions to the deflection electrode.

8. The ion detector according to claim 6 or 7, characterized in that The first opening is inclined so as to be farther away from the slit as it approaches the second center line when viewed from a direction perpendicular to the second center line of the slit.

9. A mass analysis device, characterized in that: include: Ionization unit; Mass separation section; and Ion detector, The ion detector comprises: a conversion dynode having a conversion region for releasing electrons upon ion incidence; An electron multiplying section having a first-stage dynode into which the electrons are incident; a box-type electrode that accommodates the conversion dynode and has a first opening for allowing the ions traveling toward the conversion region to pass through and a second opening for allowing the electrons traveling from the conversion region toward the first-stage dynode to pass through; a conductive shielding portion disposed at the first opening and having a gap through which the ions traveling toward the conversion region pass; and a potential imparting unit that imparts a first potential to the conversion dynode, imparts a second potential to the first-stage dynode, imparts a third potential to the box electrode, and imparts a fourth potential to the shielding unit, The first potential and the third potential are polarities opposite to the polarity of the ions. The second potential is higher than the first potential, The third potential and the fourth potential are substantially the same potential.

10. The mass spectrometer according to claim 9, wherein: The mass separation section is a quadrupole mass separation section.

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