Orthogonal acceleration time-of-flight mass spectrometer and lead-in electrode for the same

Abstract

A lead-in electrode, of an orthogonal acceleration time-of-flight mass spectrometer, includes: a main body having an ion passing part and a first member including a main-body accommodating part that is a through-hole. One surface of the first member includes an extension part to define a position of one surface of the main body. A second member is attached to the first member. A through-hole is provided at a position of the second member. One surface of the second member includes a first area in contact with a surface opposite to the one surface of the first member and a second area located inside with respect to the first area. The second area is formed lower than a surface, of the first area, in contact with the surface opposite to the one surface. A lead-in electrode elastic member is disposed, in the second area, between the first member and second members.

Claims

1. A lead-in electrode of an orthogonal acceleration time-of-flight mass spectrometer, the lead-in electrode comprising: (a) a main body having a plate shape, the main body having an ion passing part; (b) a first member which is a plate-shaped member in which there is provided a main-body accommodating part which is a through-hole and accommodates the main body, wherein on one surface of the first member there is provided an extension part to delimit a position of one surface of the main body accommodated in the main-body accommodating part; (c) a second member which is a plate-shaped member and is to be attached to the first member accommodating the main body in the main-body accommodating part, wherein a through-hole is provided at such a position of the second member that at least a part of the ion passing part is not blocked, and on one surface of the second member there are formed a first area which is in contact with a surface opposite to the one surface of the first member and a second area which is located inside with respect to the first area and is formed lower than a surface, of the first area, in contact with the surface opposite to the one surface of the first member; and (d) an elastic member disposed, in the second area, between the main body and the second member.

2. The lead-in electrode according to claim 1, wherein the second area is formed in a recessed shape.

3. An orthogonal acceleration time-of-flight mass spectrometer comprising: (e) an orthogonal accelerator section having the lead-in electrode according to claim 1 and an expulsion electrode; (f) a second accelerator section constituted by one or a plurality of electrodes; (g) a base plate; (h) a plurality of rod-shaped members provided to stand on the base plate; (i) first spacer members each of which is a member attached to a respective one of the plurality of rod-shaped members and defines a distance from the base plate to the lead-in electrode; (j) second spacer members each of which is a member attached to a respective one of the plurality of rod-shaped members and defines a distance from the lead-in electrode to the expulsion electrode; and (k) third spacer members each of which is a member attached to a respective one of the rod-shaped members and defines a distance from the base plate to an electrode which is one of the electrodes constituting the second accelerator section and is disposed at a position closest to the base plate.

4. The orthogonal acceleration time-of-flight mass spectrometer according to claim 3, wherein the second accelerator section includes a plurality of electrodes, and the orthogonal acceleration time-of-flight mass spectrometer further comprises: (l) fourth spacer members each of which is a member attached to a respective one of the rod-shaped members and defines the distances between the electrodes constituting the second accelerator section.

5. The orthogonal acceleration time-of-flight mass spectrometer according to claim 3, wherein the first spacer member and the second spacer member are made of ceramic.

6. An orthogonal acceleration time-of-flight mass spectrometer, comprising: (m) a high vacuum chamber in which an orthogonal accelerator section having the lead-in electrode according to claim 1 and an expulsion electrode is disposed; (n) an intermediate vacuum chamber provided on a former stage of the high vacuum chamber; and (o) an ion lens configured with: a former stage-side ion lens which is positioned relative to a member located inside the intermediate vacuum chamber and is constituted by one or a plurality of electrodes in each of which an ion passing opening is formed; and a subsequent stage-side ion lens which is positioned relative to a member located inside the high vacuum chamber and is constituted by one or a plurality of electrodes in each of which an ion passing opening is formed, wherein the ion passing opening in one of the electrodes located on a frontmost stage of the subsequent stage-side ion lens is larger than the ion passing opening of one of the electrodes located on a rearmost stage of the former stage-side ion lens.

7. The orthogonal acceleration time-of-flight mass spectrometer according to claim 6, wherein the ion passing opening of an electrode which is one of the electrodes constituting the ion lens and is located on a frontmost stage of the subsequent stage-side ion lens is a largest of the ion passing openings of all the electrodes constituting the ion lens.

8. The orthogonal acceleration time-of-flight mass spectrometer according to claim 6, wherein an ion passing opening having a slit shape is formed in at least one of the electrodes that constitutes the subsequent stage-side ion lens and that is other than an electrode located on the frontmost stage of the subsequent stage-side ion lens.

9. The orthogonal acceleration time-of-flight mass spectrometer according to claim 6, wherein the subsequent stage-side ion lens and the orthogonal accelerator section are fixed to a same member directly or indirectly to be positioned to each other.

10. The orthogonal acceleration time-of-flight mass spectrometer according to claim 6, wherein one electrode which is one of the electrodes constituting the subsequent stage-side ion lens and whose ion passing opening is smaller than the ion passing opening formed in the electrode located on the frontmost stage constitutes a part of a vacuum bulkhead between the high vacuum chamber and the intermediate vacuum chamber.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic configuration view of a conventional orthogonal acceleration time-of-flight mass spectrometer.

(2) FIG. 2 is a breakdown perspective view of a conventional lead-in electrode.

(3) FIG. 3 is a perspective view of the conventional lead-in electrode.

(4) FIGS. 4A and 4B are cross-sectional views of the conventional lead-in electrode.

(5) FIG. 5 is a diagram illustrating a fixing mechanism of a conventional orthogonal accelerator section and a second accelerator section.

(6) FIG. 6 is a schematic configuration view of an embodiment of an orthogonal acceleration time-of-flight mass spectrometer according to the present invention.

(7) FIG. 7 is a breakdown perspective view of an embodiment of a lead-in electrode according to the present invention.

(8) FIG. 8 is a perspective view of the lead-in electrode of the present embodiment.

(9) FIGS. 9A and 9B are each a cross-sectional view of the lead-in electrode of the present embodiment.

(10) FIGS. 10A, 10B, and 10C are diagrams illustrating steps of fixing an orthogonal accelerator section and a second accelerator section in the orthogonal acceleration time-of-flight mass spectrometer of the present embodiment.

(11) FIG. 11 is a diagram illustrating a fixing mechanism of the orthogonal accelerator section and the second accelerator section in the orthogonal acceleration time-of-flight mass spectrometer of the present embodiment.

(12) FIG. 12 is a partially enlarged diagram of the orthogonal acceleration time-of-flight mass spectrometer of the present embodiment.

(13) FIG. 13 is a diagram illustrating a configuration of an ion lens of the orthogonal acceleration time-of-flight mass spectrometer of the present embodiment.

(14) FIGS. 14A and 14B are diagrams each illustrating a shape of an ion passing opening of the ion lens of the present embodiment.

DESCRIPTION OF EMBODIMENTS

(15) Embodiment of a lead-in electrode according to the present invention and a time-of-flight mass spectrometer including the lead-in electrode will be described below with reference to the drawings. Time-of-flight mass spectrometer of the present embodiment is an orthogonal acceleration type time-of-flight mass spectrometer (in the following, also referred to as simply a “time-of-flight mass spectrometer”).

(16) FIG. 6 shows a schematic configuration of a time-of-flight mass spectrometer 1 of the present embodiment. This time-of-flight mass spectrometer includes a first intermediate vacuum chamber 11 and a second intermediate vacuum chamber 12 disposed between an ionization chamber 10 and an analysis chamber 13 such that degrees of vacuum in the chamber are higher stepwise in this order. In the ionization chamber 10 there is disposed an electrospray ion (ESI) source 101 that applies electric charge to a liquid sample and nebulize the charged liquid sample so that the liquid sample is ionized. In this embodiment, the ion source is an ESI source, but another ion source (such as an atmospheric pressure chemical ion source) may be used. Further, the ion source may be an ion source that ionizes a gas sample and a solid sample.

(17) The ions generated in the ionization chamber 10 is drawn into the first intermediate vacuum chamber due to a pressure difference between a pressure in the ionization chamber 10 (approximately, the atmospheric pressure) and a pressure in the first intermediate vacuum chamber 11. At this time, the ions pass through inside a heated capillary 102, so that a solvent is removed. In the first intermediate vacuum chamber 11 there is disposed an ion lens 111, and the ion lens 111 converges an ion beam in the vicinity of an ion optical axis C. The ion beam converged in the first intermediate vacuum chamber 11 enters the second intermediate vacuum chamber 12 through a hole at a top part of a skimmer cone 112 provided at a bulkhead part between the first intermediate vacuum chamber 11 and the second intermediate vacuum chamber 12.

(18) In the second intermediate vacuum chamber 12, there are disposed: a quadrupole mass filter 121 to separate the ions depending on the mass-to-charge ratio; a collision cell 123 equipped with a multipole ion guide 122 inside the collision cell 123; and an ion lens 124 (a former stage part of an ion lens 130 which transports ions from the collision cell 123 to an orthogonal accelerator section 132) which transports the ions ejected from the collision cell 123. Inside the collision cell 123, there is supplied a collision-induced dissociation (CID) gas such as argon or nitrogen continuously or intermittently. Note that the multipole ion guide 122 disposed inside the collision cell 123 is disposed such that a space surrounded by a plurality of rod electrodes is gradually wider (spreads out wide) toward an exit of the collision cell 123. Since the above configuration is employed, only by applying a high-frequency voltage to each rod electrode, there is formed a potential gradient to transport the ions toward the exit of the collision cell 123.

(19) In the analysis chamber 13, there are provided: an ion lens 131 (a subsequent-stage part of the ion lens 130 to transport ions from the collision cell 123 to the orthogonal accelerator section 132) which transports the ions having entered from the second intermediate vacuum chamber 12 to the orthogonal accelerator section 132; the orthogonal accelerator section 132 constituted by two electrodes 132A and 132B disposed to sandwich an incident optical axis (the orthogonal acceleration region) of ions; the second accelerator section 133 which accelerates the ions sent out toward a flight space by the orthogonal accelerator section 132; a reflectron 134 (134A and 134B) which forms in the flight space a turnover trajectory of the ions; a flight tube 136 located on an outer periphery of a detector 135 and the flight space; and a back plate 137. The reflectron 134, the flight tube 136, and the back plate 137 define the flight space of the ions.

(20) An ion guide 111 disposed in the first intermediate vacuum chamber 11, the quadrupole mass filter 121, and the collision cell 123 disposed in the second intermediate vacuum chamber 12 are positioned each by being fixed to a wall surface of the corresponding vacuum chamber. Further, the ion lens 124 disposed in the second intermediate vacuum chamber 12 is positioned by being fixed to the collision cell 123. In the analysis chamber 13, a base plate 138 is fixed to a wall surface of the vacuum chamber, and members in the analysis chamber 13 are positioned by being directly or indirectly fixed to the base plate 138. The details will be described later.

(21) The time-of-flight mass spectrometer of the present embodiment is characterized in the followings: a structure of a lead-in electrode 132B constituting the orthogonal accelerator section 132; a mechanism to fix the orthogonal accelerator section 132 and the second accelerator section 133; and a configuration and an arrangement of the ion lens 130 (a former stage-side ion lens 124 and a subsequent stage-side ion lens 131). In the following, these points will be described.

(22) FIG. 7 is a breakdown perspective view of the lead-in electrode 132B of the present embodiment, FIG. 8 is a perspective view of the lead-in electrode 132B when assembled, and FIGS. 9A and 9B are cross-sectional views of the lead-in electrode 132B taken along line A-A′ (FIG. 9A) and line B-B′ (FIG. 9B).

(23) The lead-in electrode 132B has an upper member 132B1, a main body 132B2, and a lower member 132B3, which are all metal members, and has lead-in electrode elastic members 132B4. The main body 132B2 is rectangular plate-shaped member having: an ion passing part 132B2a in which many ion passing holes are formed to penetrate through in a thickness direction; and a peripheral part 132B2b formed to surround the ion passing part 132B2a. The upper member 132B1 is a plate-shaped member at whose center there is formed a through-hole 132B1a having a rectangular cross-section with a size corresponding to an outer shape of the main body 132B2, and on an upper surface of the upper member 132B1, extension parts 132B1b are formed to cover parts of the through-hole 132B1a (parts, on the long-side sides, of the peripheral part 132B2b of the main body 132B2 when accommodated in the through-hole 132B1a). The peripheral of the through-hole 132B1a is one step lower on the sides of the two sides, of the through-hole 132B1a, corresponding to the short sides of the rectangle than on the long-side sides of the rectangle, and has the same height as the lower surface of the extension parts 132B1b. That is, when the main body 132B2 is accommodated in the through-hole 132B1a, the parts of the peripheral, of the through-hole 132B1a, on the sides of the two sides, of the through-hole 132B1a, corresponding to the short sides of the rectangle have a height flush with the upper surface of the main body 132B2. Further, in four corners of the upper member 132B1, there are formed through-holes 132B1c through which rod-shaped members 139 for fixing the orthogonal accelerator section 132 to an orthogonal acceleration section positioning plate 140 (to be described later) are inserted. In addition, in a lower surface of the upper member 132B1, there are formed four bolt holes used to bolt the upper member 132B1 from a lower member 132B3 side.

(24) The lower member 132B3 is a plate-shaped member at whose center there is formed a circular through-hole 132B3a having a diameter that is longer than a short side of the main body 132B2 having a rectangular plate shape and a long side of the ion passing part but is shorter than a length of a long side of the main body 132B2 in the center of the lower member 132B3. That is, the through-hole 132B3a of the present embodiment is provided at such a position that an entire part of the ion passing part is not blocked. In two part, of a peripheral part of the through-hole 132B3a, located to sandwich a center of the through-hole 132B3a, recessed parts 132B3b (second area) are formed one step lower than the other part (the first area). Each of the recessed parts 132B3b accommodates the lead-in electrode elastic members 132B4. In the present embodiment, each recessed part 132B3b accommodates two O-rings (as a result, four O-rings are used in total), but other members than O-rings may be used as the lead-in electrode elastic members 132B4, and it is possible to change the number of the members as necessary. In four corners of the lower member 132B3, there are formed through-holes 132B3c in which the above rod-shaped members 139 are inserted. Further, at positions, on the lower member 132B3, corresponding to the bolt holes formed in the lower surface of the upper member 132B1, there are formed four through-hole 132B3d through which bolts are inserted.

(25) The lead-in electrode elastic members 132B4 are disposed in the recessed parts 132B3b of the lower member 132B3, the main body 132B2 is puts on the lead-in electrode elastic members 132B4, the upper member 132B1 is placed on the main body 132B2, so that the main body 132B2 is accommodated in the through-hole 132B1a of the upper member 132B1. Then, bolts are inserted in the through-holes 132B3d of the lower member 132B3 to bolt the bolts in the bolt holes in the lower surface of the upper member 132B1. In this way, the lead-in electrode 132B is assembled.

(26) As shown in the cross-sectional view in FIG. 9B taken along line B-B′, the lower surface of the main body 132B2 is pushed up by the lower member 132B3 via the lead-in electrode elastic members 132B4. Further, as shown in the cross-sectional view in FIG. 9A taken along line A-A′, the upper surface of the main body 132B2 is pushed against the lower surface of the extension parts 132B1b of the upper member 132B1. In the above lead-in electrode 132B, even in a case where the main body 132B2 has a thickness unevenness, since the lead-in electrode elastic members 132B4 deform corresponding to the unevenness, the upper surface of the main body 132B2 is surely pressed against the lower surfaces of the extension parts 132B1b, thereby preventing the upper surface from being inclined. As described above, the conventional lead-in electrode 232B has a following problem. The lower surface of the lower member 232B3 is curved when the lead-in electrode 232B is assembled, and an electric field formed between the lead-in electrode 232B and the second accelerator section 233 is distorted; therefore, it is difficult to accelerate the ions uniformly. In contrast, in the case of the lead-in electrode 132B of the present embodiment, since the lower surface of the upper member 132B1 and the upper surface of the lower member 132B3 are fixed to each other while the both surfaces are in contact with each other, the lower surface of the lower member 132B3 is not curved, and such a conventional problem as described above does not occur. It is preferable that the lead-in electrode elastic members 132B4 be disposed also between the upper member 132B1 and the lower member 132B3 as in the present embodiment; however, if the lead-in electrode elastic members 132B4 are inserted at least between the main body 132B2 and the lower member 132B3, it can provide the above effect.

(27) Next, with reference to FIGS. 10A, 10B, 10C, and 11, a fixing mechanism of the orthogonal accelerator section 132 and the second accelerator section 133 will be described. FIGS. 10A, 10B, and 10C are diagrams showing the fixing mechanism while being assembled, and FIG. 11 is a diagram showing the fixing mechanism after assembled. As described above, in the analysis chamber 13, the base plate 138 is fixed to the vacuum chamber, and the orthogonal accelerator section 132 and the second accelerator section 133 are positioned with reference to the base plate 138. Note that the detector 135 is directly fixed on the base plate 138 as shown in FIG. 11 in the present embodiment; however, the detector 135 may be fixed via a detachable positioning plate for the detector, or also the detector 135 may be fixed on the orthogonal acceleration section positioning plate 140 to be described later. To the base plate 138, the orthogonal acceleration section positioning plate 140 (in the following, also referred to as a “positioning plate”) is detachably attached.

(28) When the orthogonal accelerator section 132 and the electrodes constituting the second accelerator section 133 are attached, the rod-shaped members 139 (only two of them are shown in FIGS. 10A, 10B, and 10C) in each of whose outer circumferences a thread groove is formed are fixed to corresponding four bolt holes formed in the upper surface of the positioning plate 140. Next, first spacer members 141 in each of which a through-hole having a size corresponding to an outer circumference of the rod-shaped member 139 is formed are inserted into the rod-shaped members 139. The first spacer members 141 are attached one to each rod-shaped member 139 (in the same way, regarding second spacer members 142, third spacer members 143, fourth spacer members 144, and fifth spacer members 145 to be described later, one is attached to each rod-shaped member 139). Further, each spacer member used in the present embodiment is an insulating member made of ceramic. Resin members can be used as the spacer members, but if the spacer members are deformed, the positions of the members positioned via the spacer members are displaced. Therefore, it is preferable to use spacer members made of ceramic, which has higher stiffness than resin.

(29) Next, the third spacer members 143 in each of which a through-hole having a size corresponding to an outer circumference of the first spacer member 141 is formed are inserted into the first spacer members 141. Then, on the third spacer members 143, a second acceleration electrode 133D, which is one of second acceleration electrodes 133A to 133D constituting the second accelerator section 133 and is disposed on the side closest to the flight space, is inserted. In each of the second acceleration electrode 133A to 133D, there are formed four through-holes (the same number as the rod-shaped members 139) each having a size corresponding to the outer circumference of the first spacer members. FIG. 10A is a diagram showing a state where the second acceleration electrode 133D is inserted.

(30) After that, the fourth spacer members 144 and the second acceleration electrodes 133C, 133B, and 133A constituting the second accelerator section 132 are inserted into the first spacer members 141 alternately. After the second acceleration electrode 133A (which is the second acceleration electrode attached at the position most distant from the base plate 138) is attached, the fifth spacer members 145 are attached on the second acceleration electrode 133A, and a positioning and securing elastic members 146 (O-rings) are attached on the fifth spacer members 145. The positioning and securing elastic members 146 (O-ring) are attached one to each of the rod-shaped members 139. FIG. 10B is a diagram showing a state where the positioning and securing elastic members 146 are attached. Note that in the present embodiment, the second accelerator section 132 are constituted by four electrodes, and it is possible to change the number of the electrodes constituting the second accelerator section 132 as necessary.

(31) Subsequently, on the positioning and securing elastic members 146, the lead-in electrode 132B, in which four through-holes each corresponding to the outer shape of the rod-shaped member 139 are formed, is attached. Then, on the lead-in electrode 132B, the second spacer members 142 are attached. FIG. 10C is a diagram showing this state. Further, in the holes of the expulsion electrode 132A, the rod-shaped members are inserted to attach the expulsion electrode 132A. For example, by attaching nuts 147 to the rod-shaped members 139 from above the expulsion electrode 132A, or by another method, the orthogonal accelerator section 132 (the expulsion electrode 132A and the lead-in electrode 132B) and the second accelerator section 133 are fixed to the positioning plate 140. Finally, the positioning plate 140 is fixed to the base plate 138 (FIG. 11).

(32) In the conventional configuration (see FIG. 5), the spacer members 242 and the electrodes 233 constituting the second accelerator section are alternately attached on the base plate 241, and the lead-in electrode 232B is attached on this assembly. In addition, the expulsion electrode 232A is attached and fixed on the lead-in electrode 232B via the spacer members 242. Due to such a configuration, errors of the spacer members 242 and the electrodes constituting the second accelerator section 233 are accumulated on the expulsion electrode 232A and the lead-in electrode 232B fixed at positions distant from the base plate, and there tends to occur deterioration in accuracy of the distances from the base plate 241 to the lead-in electrode 232B and the expulsion electrode 232A, in degrees of parallelism between the base plate 241 and the both electrodes, and in a degree of parallelism between the opposing surfaces of the expulsion electrode 232A and the lead-in electrode 232B. As a result, the ions are not accelerated uniformly, and the resolution power and the sensitivity are sometimes decreased.

(33) In contrast, in the configuration of the present embodiment, the distance from the base plate 138 (strictly, the positioning plate 140) to the lead-in electrode 132B is defined only by the first spacer members 141. Further, the distance from the base plate 138 (strictly, the positioning plate 140) to the expulsion electrode 132A is defined only by the first spacer members 141 and the second spacer members 142. That is, the accuracy of the distances from the base plate 138 to the expulsion electrode 132A and the lead-in electrode 132B, the degree of parallelism between the opposing surfaces of the both electrodes, and the degrees of parallelism between the base plate and the both electrodes are never influenced by dimension errors and flatness errors of the third spacer members 143, the fourth spacer members 144, and the fifth spacer members 145 at the time of manufacturing. Therefore, it is possible to improve, compared to before, the accuracy of the distances from the base plate 138 to the expulsion electrode 132A and the lead-in electrode 132B, the degrees of parallelism between the base plate and the both electrodes, and the degree of parallelism between the opposing surfaces of the expulsion electrode 132A and the lead-in electrode 132B, thereby improving the resolution power and the sensitivity. Note that in the present embodiment, the orthogonal acceleration section positioning plate 140 is used so that a work of fixing the orthogonal accelerator section 132 and the electrodes constituting the second accelerator section 133 can be performed outside the vacuum chamber. However, it is possible to fix the orthogonal accelerator section 132 and the second accelerator section 133 directly to the base plate 138 without using the positioning plate 140. Note that positioning and securing elastic members 146 are not essential, but the positioning and securing elastic members 146 surely absorb the thickness error and the flatness error, at the time of manufacturing, of the third spacer members 143, the fourth spacer members 144, and the fifth spacer member 145, so that the first spacer members 141 and the second spacer members 142 can position the orthogonal accelerator section 132 more accurately.

(34) Next, a description will be given on the ion lens 130 (124 and 131) disposed on a boundary portion between the second intermediate vacuum chamber 12 and the analysis chamber 13. FIG. 12 is an enlarged view of a vicinity of the boundary between the second intermediate vacuum chamber 12 and the analysis chamber 13. FIG. 13 is a diagram showing only a configuration of the ion lens 130.

(35) The ion lens 130 is used to converge the ion beam having passed through the collision cell 123 and to transport the ion beam to the orthogonal accelerator section 132. The collision cell 123 is disposed in the second intermediate vacuum chamber 12, and the orthogonal accelerator section 132 is disposed in the analysis chamber. Therefore, the ion lens 130 is disposed separately in the two spaces.

(36) The ion lens 130 of the present embodiment is configured with seven circular plate-shaped electrodes and is divided into the former stage-side ion lens 124 constituted by three electrodes 124a, 124b, and 124c on a former stage side (collision cell 123 side) and the subsequent stage-side ion lens 131 constituted by four electrodes 131a, 131b, 131c, and 131d on a subsequent stage side (orthogonal accelerator section 132 side). There is formed a circular ion passing opening 151 at a center of each of the electrodes 124a, 124b, and 124c constituting the former stage-side ion lens 124 and the electrode 131a, which is one of the electrodes constituting the subsequent stage-side ion lens 131 and is located on the frontmost stage side (FIG. 14A). On the other hand, there is formed a rectangular slit 152 at a center of each of the three electrodes 131b, 131c, and 131d, of the electrodes constituting the subsequent stage-side ion lens 131, located on the subsequent stage side (FIG. 14B). These electrodes also have a function of a slit to shape the ion beam. Further, the holes formed in the electrodes do not have the same size but have such sizes that each electrode has a converging property corresponding to a position of the each electrode (that is, each hole has such a size that when voltages are applied, the electrodes converge the ion beam toward the hole of the neighboring ion lens on the subsequent stage side).

(37) The ion lens 130 of the present embodiment has one feature in that the ion passing opening 151 of the electrode 131a, which is one of the electrodes constituting the subsequent stage-side ion lens 131 and is located on the frontmost stage side, is larger than the ion passing opening 151 of the electrode 124c, which is one of the electrodes constituting the former stage-side ion lens 124 and is located on the rearmost stage side.

(38) As shown in FIGS. 12 and 13, the three electrodes 124a, 124b, and 124c constituting the former stage-side ion lens 124 are fixed to one another via insulating members 161 made of resin or other materials. The electrode 124a located on the frontmost stage side of the former stage-side ion lens 124 is fixed to the collision cell 123 via the insulating members 161, and this arrangement positions the former stage-side ion lens 124. Note that the collision cell 123 is fixed to the vacuum chamber via a fixing member 164.

(39) In the same manner, the four electrodes 131a to 131d constituting the subsequent stage-side ion lens 131 are fixed to one another via the insulating members 161 made of resin or other materials. The electrode 131d located on the rearmost stage side of the subsequent stage-side ion lens 131 is fixed to the base plate 138 via the insulating members 161, and this arrangement positions the subsequent stage-side ion lens 131. In the present embodiment, the electrode 131d is fixed to the base plate 138 but may be fixed to the orthogonal acceleration section positioning plate 140. As described above, the orthogonal acceleration section positioning plate 140 is fixed to the base plate 138. The subsequent stage-side ion lens 131 is fixed to the base plate 138 directly or indirectly.

(40) As described above, the former stage-side ion lens 124 and the subsequent stage-side ion lens 131 are disposed independently from each other and are positioned relative to different members. For this reason, there is a possibility that there occurs misalignment between the ion optical axis of the former stage-side ion lens 124 and the ion optical axis of the subsequent stage-side ion lens 131. If, due to such misalignment of ion optical axis, a part of the ions having passed through the electrode 124c located on the rearmost stage side of the former stage-side ion lens 124 do not enter the ion passing opening 151 of the electrode 131a located on the frontmost stage side of the subsequent stage-side ion lens 131, the sensitivity is reduced by a magnitude corresponding to the ions which do not enter the ion passing opening 151.

(41) As described above, the ion lens 130 of the present embodiment is configured such that the ion passing opening 151 of the electrode 131a, which is one of the electrodes constituting the subsequent stage-side ion lens 131 and is located on the frontmost stage side, is larger than the ion passing opening 151 of the electrode 124c, which is one of the electrodes constituting the former stage-side ion lens 124 and is located on the rearmost stage side. That is, the ion lens 130 is divided into the former stage-side ion lens 124 and the subsequent stage-side ion lens 131 so that the ion beam narrowed down to have a small diameter by the electrode 124c enters the ion passing opening 151, of the electrode 131a, having a large diameter. Therefore, even if some misalignment of ion optical axis occurs between the former stage-side ion lens 124 and the subsequent stage-side ion lens 131 when these two ion lenses are fixed, a decrease in sensitivity due to loss of ions does not occur. In particular, the ion lens 130 of the present embodiment is configured such that the electrode 131a, which is one of the electrodes constituting the ion lens 130 and whose ion passing opening 151 has the largest diameter, is located on the frontmost stage side of the subsequent stage-side ion lens 131, and this configuration decreases the decrease in sensitivity due to the loss of ions as much as possible.

(42) Further, in the ion lens 130 of the present embodiment, the electrode 131b located on the second position, in the subsequent stage-side ion lens 131, from the former stage side is fixed also to a bulkhead member 163 via a seal member (for example, O-ring) 162, and the electrode 131b separates the second intermediate vacuum chamber 12 from an internal space of the analysis chamber 13. The ion passing opening 151 of the electrode 131b fixed to the bulkhead member 163 via the seal member 162 is smaller than the ion passing opening 151 of the electrode 131a located on the previous stage. Therefore, this configuration can keep larger the difference in degree of vacuum between the second intermediate vacuum chamber 12 and the analysis chamber 13 than in a configuration where the electrode 131a is fixed to the bulkhead member 163 (that is, this configuration can keep high the degree of vacuum in the analysis chamber 13).

(43) In addition, in the present embodiment, the base plate 138 used as a reference for positioning of the subsequent stage-side ion lens 131 is also used for positioning of the orthogonal accelerator section 132 and the second accelerator section 133. That is, the configuration is made such that there occurs no misalignment of the ion optical axis C between the subsequent stage-side ion lens 131 and the orthogonal accelerator section 132 (in addition, the second accelerator section 133). Therefore, it is possible to precisely transport the ion beam, which is converged by the electrodes 131a to 131d of the subsequent stage-side ion lens 131 and is shaped by the slits 152 of the electrodes 131b, 131c, and 131d, to the orthogonal acceleration region in the orthogonal accelerator section 132. Further, because the base plate 138 positions also the reflectron 134, the flight tube 136, the back plate 137, and the detector 135, it is possible to guide the ions accelerated by the orthogonal accelerator section 132 and the second accelerator section 133 to the detector 135 by causing the ions to fly without deviating from a predetermined trajectory.

(44) The above embodiment is merely an example and can be modified as necessary without departing from the subject matter of the present invention. In the present embodiment, the through-hole 132B3a is provided at such a position that an entire part of the ion passing part is not blocked. However, this configuration is a preferable aspect, and when the through-hole 132B3a is provided at such a position that at least a part of the ion passing part is not blocked, it is possible to emit the ions from the lead-in electrode 132B. Further, in the present embodiment, the configuration is made such that the ions enter the orthogonal accelerator section 132 in the horizontal direction and such that the orthogonal accelerator section 132 and the second accelerator section 133 accelerate the ions downward. However, this configuration is an example, and the orthogonal accelerator section 132 and the second accelerator section 133 may accelerate the ions upward or in the horizontal direction. For example, in the case of accelerating the ions upward, the arrangement may be made to suspend, below the base plate 138 (and the orthogonal acceleration section positioning plate 140), the electrodes constituting the second accelerator section 133, the lead-in electrode 132B, and the expulsion electrode 132A. Further, in the present embodiment, a plurality of electrodes constitute the second accelerator section 133, but only one electrode may constitute the second accelerator section 133. In that case, the fourth spacer member 144 is not necessary. In addition, the present embodiment includes the quadrupole mass filter 121 and the collision cell 123, but a configuration similar to the above embodiment can be used in an orthogonal acceleration type time-of-flight mass spectrometer which has only one of the quadrupole mass filter 121 and the collision cell 123.

REFERENCE SIGNS LIST

(45) 1 . . . Orthogonal Acceleration Time-of-flight Mass Spectrometer 10 . . . Ionization Chamber 101 . . . Electrospray Ion Source 102 . . . Capillary 11 . . . First Intermediate Vacuum Chamber 111 . . . Ion Guide 112 . . . Skimmer Cone 12 . . . Second Intermediate Vacuum Chamber 121 . . . Quadrupole Mass Filter 122 . . . Multipole Ion Guide 123 . . . Collision Cell 124 . . . Former Stage-side Ion Lens 13 . . . Analysis Chamber 130 . . . Ion Lens 131 . . . Subsequent Stage-side Ion Lens 132 . . . Orthogonal Accelerator Section 132A . . . Expulsion Electrode 132B . . . Lead-in Electrode 132B1 . . . Upper Member 132B1a . . . Through-hole 132B1b . . . Extension Part 132B2 . . . Main Body 132B2a . . . Ion Passing Part 132B3 . . . Lower Member 132B4 . . . Lead-in Electrode Elastic Member 133 . . . Second Accelerator Section 134 . . . Reflectron 135 . . . Detector 136 . . . Flight Tube 137 . . . Back Plate 138 . . . Base Plate 139 . . . Rod-shaped Member 140 . . . Orthogonal Acceleration Section Positioning Plate 41 . . . First Spacer Member 142 . . . Second Spacer Member 143 . . . Third Spacer Member 144 . . . Fourth Spacer Member 145 . . . Fifth Spacer Member 146 . . . Positioning And Securing Elastic Member 147 . . . Nut 151 . . . Ion Passing Opening 152 . . . Slit 161 . . . Insulating Member 162 . . . Seal Member 163 . . . Bulkhead Member 164 . . . Fixing Member C . . . Ion Optical Axis