Ion transport apparatus and mass spectrometer using the same

Abstract

An off-axis ion transport optical system (20) including a front-stage quadrupole ion guide (21), a rear-stage quadrupole ion guide (22), and an ion deflector (23) is disposed inside an intermediate vacuum chamber (2) in a stage next to an ionization chamber (1) maintained at an atmospheric pressure. Both of the quadrupole ion guides (21 and 22) have the same configuration as that of a conventional ion guide that transports ions while trapping the ions using a radio-frequency electric field. The ion deflector (23) includes a pair of parallel flat electrodes (231 and 232) and deflects ions using a direct-current electric field. By causing the deflected ions to reach the ion receiving range of the rear-stage quadrupole ion guide (22), it is possible to efficiency introduce ions while deflecting the ions. Meanwhile, the ions and neutral particles are separated from each other in the ion deflector (23). This provides an off-axis structure ion transport optical system that achieves a high ion transmission efficiency with a simple structure.

Claims

1. An off-axis structure ion transport apparatus that emits ions entering along a first ion beam axis along a second ion beam axis not lying on a same line as the first ion beam axis, the ion transport apparatus comprising: a) a front-stage ion transport unit for transporting the ions while focusing the ions along the first ion beam axis by an effect of radio-frequency electric field; b) a rear-stage ion transport unit for transporting the ions while focusing the ions along the second ion beam axis by an effect of radio-frequency electric field; and c) an ion deflector disposed between the front-stage ion transport unit and the rear-stage ion transport unit, the ion deflector for deflecting a traveling direction of the ions by an effect of a direct-current electric field so that the ions emitted from the front-stage ion transport unit reach an ion receiving range of the rear-stage ion transport unit.

2. The ion transport apparatus according to claim 1, wherein at least one of the front-stage ion transport unit and the rear-stage ion transport unit is a multipole-rod ion guide.

3. The ion transport apparatus according to claim 1, wherein at least one of the front-stage ion transport unit and the rear-stage ion transport unit is a multipole-array ion guide including a number of virtual rod electrodes each of which is composed of a number of plate electrodes arranged substantially in parallel to each other.

4. The ion transport apparatus according to claim 1, wherein at least one of the front-stage ion transport unit and the rear-stage ion transport unit is an ion funnel.

5. The ion transport apparatus according to claim 1, wherein the rear-stage ion transport unit is a radio-frequency carpet.

6. The ion transport apparatus according to claim 1, wherein the first ion beam axis and the second ion beam axis are parallel to each other.

7. The ion transport apparatus according to claim 6, wherein the ion deflector includes parallel flat electrodes provided so as to be orthogonal to a plane including the first ion beam axis and the second ion beam axis.

8. The ion transport apparatus according to claim 1, wherein the rear-stage ion transport unit is disposed so as to be off an extended line of the first ion beam axis.

9. A mass spectrometer including the ion transport apparatus according to claim 1, the mass spectrometer comprising n intermediate vacuum chambers (n is an integer equal to or greater than one) disposed between an ion source and an analysis chamber and having degrees of vacuum in an ascending order, the ion source being for ionizing a sample component under a substantially atmospheric pressure, the analysis chamber including a mass separation unit for separating ions in accordance with a mass-to-charge ratio and maintained at a high degree of vacuum, wherein the ion transport apparatus is disposed inside a first intermediate vacuum chamber next to the ion source.

10. The mass spectrometer according to claim 9, wherein a central axis of an ion introduction unit for sending ions from the ion source to the first intermediate vacuum chamber is located on a line of the first ion beam axis, and a central axis of an ion passage opening portion for sending ions from the first intermediate vacuum chamber to a next second intermediate vacuum chamber or the analysis chamber is located on a line of the second ion beam axis.

11. A mass spectrometer including the ion transport apparatus according to claim 1, the mass spectrometer comprising a first mass separation unit for selecting ions having a specific mass-to-charge ratio from among ions originating from a sample component, a collision cell for dissociating the ions selected by the mass separation unit, and a second mass separation unit for separating ions generated by dissociation in the collision cell in accordance with a mass-to-charge ratio, wherein the ion transport apparatus is disposed inside the collision cell.

12. The mass spectrometer according to claim 11, wherein the first ion beam axis and the second ion beam axis in the ion transport apparatus intersect with each other, and the first mass separation unit and the second mass separation unit are nonlinearly disposed across the collision cell.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic configuration diagram of an ion transport optical system of a first embodiment of an ion transport apparatus according to the present invention.

(2) FIG. 2 is a schematic perspective view of an electrode unit of the ion transport optical system in the first embodiment.

(3) FIG. 3 is a schematic configuration diagram of an atmospheric pressure ionization mass spectrometer using the ion transport optical system in the first embodiment.

(4) FIG. 4 is a schematic configuration diagram of an ion transport optical system of a second embodiment of the ion transport apparatus according to the present invention.

(5) FIG. 5 is a schematic perspective view of an electrode unit of a quadrupole array ion guide used in the ion transport optical system in the second embodiment.

(6) FIG. 6A and FIG. 6B are diagrams illustrating the result of ion path simulation calculation for the ion transport optical system of the second embodiment.

(7) FIG. 7 is a schematic configuration diagram of an ion transport optical system of a third embodiment of the ion transport apparatus according to the present invention.

(8) FIG. 8 is a schematic perspective view of an electrode unit of a radio-frequency carpet used in the ion transport optical system in the third embodiment.

(9) FIG. 9 is a schematic configuration diagram of an ion transport optical system of a fourth embodiment of the ion transport apparatus according to the present invention.

(10) FIG. 10 is a schematic configuration diagram of an ion transport optical system of a fifth embodiment of the ion transport apparatus according to the present invention.

(11) FIG. 11 is a schematic configuration diagram of an ion transport optical system of a sixth embodiment of the ion transport apparatus according to the present invention.

(12) FIG. 12 is a schematic configuration diagram of an ion transport optical system of a seventh embodiment of the ion transport apparatus according to the present invention.

(13) FIG. 13A and FIG. 13B are diagrams illustrating another configuration example of the ion deflector used in the ion transport optical systems in the first to seventh embodiments.

(14) FIG. 14 is a schematic configuration diagram of an embodiment of a tandem quadrupole mass spectrometer including the ion transport apparatus according to the present invention.

DESCRIPTION OF EMBODIMENTS

(15) Several embodiments of an ion transport apparatus according to the present invention as well as a mass spectrometer using this ion transport apparatus are described with reference to the attached drawings.

First Embodiment

(16) An atmospheric pressure ionization mass spectrometer, which is a mass spectrometer using one embodiment (a first embodiment) of an ion transport apparatus according to the present invention, is described. FIG. 1 is a schematic configuration diagram of an ion transport optical system in the first embodiment, FIG. 2 is a schematic perspective view of an electrode unit of the ion transport optical system in the first embodiment, and FIG. 3 is a schematic configuration diagram of an atmospheric pressure ionization mass spectrometer using the ion transport optical system in the first embodiment.

(17) In FIG. 3, an ionization chamber 1 is maintained at a substantially atmospheric pressure, and an analysis chamber 4 is maintained at a high degree of vacuum by evacuation using a high-performance vacuum pump (normally, a combination of a turbo-molecular pump and a rotary pump), which is not illustrated. Between the ionization chamber 1 and the analysis chamber 4, a first intermediate vacuum chamber 2 maintained at a low degree of vacuum, and a second intermediate vacuum chamber 3 maintained at a degree of vacuum between those of the first intermediate vacuum chamber 2 and the analysis chamber 4, are provided. In other words, this mass spectrometer has the structure of a multistage differential pumping system in which the degree of vacuum is increased in a stepwise manner in the traveling direction of ions from the ionization chamber 1.

(18) Within the ionization chamber 1, a liquid sample containing a sample component is sprayed from an electrospray nozzle 5 while the sample component is subjected to biased electric charges from this nozzle. The sprayed droplets with electric charges come in contact with the ambient air and become even smaller droplets, and in the process of the vaporization of the solvent, sample component molecules leave with electric charges to be ionized. It is also possible to adopt a different atmospheric pressure ionization technique instead of the electrospray ionization (ESI) described here, such as the atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI).

(19) The ionization chamber 1 communicates with the first intermediate vacuum chamber 2 through a thin heated capillary 6. Mainly due to the pressure difference between the two open ends of this capillary 6, ions originating from the sample component produced within the ionization chamber 1 are drawn into the heated capillary 6. Then, the ions are ejected into the first intermediate vacuum chamber 2 together with gas stream from the outlet end of the heated capillary 6. In a partition wall that separates the first intermediate vacuum chamber 2 and the second intermediate vacuum chamber 3, a skimmer 7 having a small-diameter orifice 71 at its apex is provided. Within the first intermediate vacuum chamber 2, an off-axis ion transport optical system 20 having a characteristic configuration to be described later. Ions introduced into the first intermediate vacuum chamber 2 are guided to the orifice 71 of the skimmer 7 by this off-axis ion transport optical system 20 and sent through the orifice 71 to the second intermediate vacuum chamber 3.

(20) Within the second intermediate vacuum chamber 3, a multipole (e.g., octupole) ion guide 8 is arranged. Owing to the effect of a radio-frequency electric field created by the ion guide 8, ions are focused and sent to the analysis chamber 4. Within the analysis chamber 4, the ions are introduced into the space extending along the longitudinal axis of a quadrupole mass filter 9. Owing to the effect of an electric field created by the radio-frequency voltage and the direct-current voltage applied to the quadrupole mass filter 9, only ions having a specific mass-to-charge ratio pass through the quadrupole mass filter 9 and reach an ion detector 10. The ion detector 10 generates a detection signal corresponding to the amount of ions reached, and sends the signal to a data processor, which is not illustrated. By allowing only the target ions among the ions derived from the sample component within the ionization chamber 1 to reach the ion detector 10 while suppressing the loss of the target ions as much as possible, the mass spectrometry with high sensitivity can be achieved.

(21) The off-axis ion transport optical system arranged within the first intermediate vacuum chamber 2 is hereinafter described in detail.

(22) This off-axis ion transport optical system 20 includes a front-stage quadrupole ion guide 21 in which four columnar-shaped rod electrodes 211, 212, 213, and 214 are disposed in a rotationally symmetric manner around a linear first ion beam axis C1, and a rear-stage quadrupole ion guide 22 in which four columnar-shaped rod electrodes 221, 222, 223, and 224 are disposed in a rotationally symmetric manner around a linear second ion beam axis C2 that does not lie on the extended line of the first ion beam axis C1 but is parallel to the ion beam axis C1. The front-stage quadrupole ion guide 21 is disposed immediately behind the outlet end of the heated capillary 6. The central axis of the outlet of the heated capillary 6 lies on a straight line with the first ion beam axis C1. The rear-stage quadrupole ion guide 22 is disposed directly in front of the skimmer 7. The central axis of the orifice 71 lies on a straight line with the second ion beam axis C2.

(23) In the space between the front-stage quadrupole ion guide 21 and the rear-stage quadrupole ion guide 22, an ion deflector 23 is disposed that deflects the traveling direction of ions. The ion deflector 23 includes a pair of parallel flat electrodes 231 and 232 orthogonal to a plane including the first ion beam axis C1 and the second ion beam axis C2 (the x-z plane in this embodiment) and provided being separated from each other in the X direction so as to sandwich both the ion beam axes C1 and C2.

(24) A first radio-frequency/direct-current voltage generator 31 applies high-frequency voltages +V1 cos t having the same amplitude, frequency, and phase to two rod electrodes 211 and 213 out of the four rod electrodes 211 to 214 of the front-stage quadrupole ion guide 21, the two rod electrodes 211 and 213 facing each other across the first ion beam axis C1, and applies, to the other two rod electrodes 212 and 214 adjacent to these rod electrodes 211 and 213 in a circumferential direction, high-frequency voltages V1 cos t having the same amplitude and phase, and having a phase inverted (i.e., different by 180 degrees) from that of +V1 cos . In addition to the above-described high-frequency voltages, the first radio-frequency/direct-current voltage generator 31 applies a predetermined direct-current bias voltage VDC1 to the four rod electrodes 211 to 214 in common.

(25) A second radio-frequency/direct-current voltage generator 32 applies high-frequency voltages +V2 cos 2t having the same amplitude, frequency, and phase to two rod electrodes 221 and 223 out of the four rod electrodes 221 to 224 of the rear-stage quadrupole ion guide 22, the two rod electrodes 221 and 223 facing each other across the second ion beam axis C2, and applies, to the other two rod electrodes 222 and 224 adjacent to these rod electrodes 221 and 223 in a circumferential direction, high-frequency voltages V2 cos 2t having the same amplitude and phase, and having a phase inverted from +V2 cos 2t. In addition to the above-described high-frequency voltages, the second radio-frequency/direct-current voltage generator 32 applies a predetermined direct-current bias voltage VDC2 to the four rod electrodes 221 to 224 in common.

(26) A deflection direct-current voltage generator 33 applies predetermined direct-current voltages to the pair of parallel flat electrodes 231 and 232, respectively.

(27) All of these voltage generators 31, 32, and 33 generate the respective voltages under control by the controlling unit 30.

(28) In the front-stage and rear-stage quadrupole ion guides 21 and 22, the high-frequency voltages applied to the rod electrodes 211 to 214 and 221 to 224 create quadrupole radio-frequency electric fields in spaces surrounded by these rod electrodes 211 to 214 and 221 to 224, respectively. Owing to the effects of these radio-frequency electric fields, introduced ions are captured within predetermined ranges around the ion beam axes C1 and C2 while oscillating with the ion beam axes C1 and C2 as a center. If the ions have excessive energies, the ions are hard to be captured within the radio-frequency electric fields. However, the first intermediate vacuum chamber 2 is in a low vacuum state, and the ions have many opportunities to come into contact with residual gas. Therefore, the energies of the ions are easily reduced by the cooling effect made by contact with the residual gas, and thus the ions are efficiently captured within the radio-frequency electric fields. The ions introduced into the front-stage and rear-stage quadrupole ion guides 21 and 22 with a predetermined energy travel while being focused around the ion beam axes C1 and C2.

(29) The ions ejected from the outlet end of the heated capillary 6 together with the gas travel while spreading out, but many of them enter the ion receiving range on the inlet side of the front-stage quadrupole ion guide 21. The ions are thus efficiently captured within the radio-frequency electric field of the front-stage quadrupole ion guide 21, and travel along the first ion beam axis C1 to be emitted from the outlet end of the front-stage quadrupole ion guide 21. Immediately afterward, these emitted ions receive force by a direct-current deflecting electric field created between the parallel flat electrodes 231 and 232. This force acts in the direction illustrated by the white thick arrow in FIG. 1 (in the negative direction of the X axis in FIG. 2). The traveling direction of the ions thereby gradually bends as illustrated bold solid lines in FIG. 1 and FIG. 2. In the direct-current deflecting electric field, no focusing action acts on the ions, and thus the ions spread out as traveling. However, many of them enter the ion receiving range on the inlet side of the rear-stage quadrupole ion guide 22. The ions are thus efficiently captured within the radio-frequency electric field of the rear-stage quadrupole ion guide 22.

(30) Into the front-stage quadrupole ion guide 21, various kinds of non-ionized molecules and neutral particles such as metastable molecules are injected together with the ions. These neutral particles are not affected by the radio-frequency electric field and thus travel almost straight ahead through the internal space of the front-stage quadrupole ion guide 21. Many of the neutral particles thus travel straight ahead in the vicinity of the first ion beam axis C1 and are injected into a space between the parallel flat electrodes 231 and 232 of the ion deflector 23. The neutral particles are not affected by the direct-current deflecting electric field either and thus pass almost straight ahead outside the rear-stage quadrupole ion guide 22. Therefore, in the ion deflector 23, the neutral particles are separated from the ions and mostly discharged from the first intermediate vacuum chamber 2 with the residual gas. In such a manner, various neutral particles, which are to be a cause of noise, introduced together with the ions are eliminated in the first intermediate vacuum chamber 2.

(31) The ions captured in the radio-frequency electric field of the rear-stage quadrupole ion guide 22 with their traveling direction changed into a direction along the second ion beam axis C2, and are emitted from the outlet end of the rear-stage quadrupole ion guide 22 while being focused around the second ion beam axis C2. Then, the ions pass through the orifice 71 to be sent to the second intermediate vacuum chamber 3.

(32) In such a manner, in this off-axis ion transport optical system, with a combination of a quadrupole ion guide and parallel flat electrodes, all of which are simply structured, it is possible to efficiently guide target ions originating from a sample component and send them to the rear stage while reliably eliminating neutral particles.

(33) In this off-axis ion transport optical system in the first embodiment, the front-stage and rear-stage quadrupole ion guides 21 and 22 can be replaced with different multipole ion guides, such as an octupole ion guide, having different number of rod electrodes. In terms of performance, the quadrupole ion guides having a small number of electrodes sufficiently achieve the effect, and a small number of electrodes advantageously reduce the cost. As will be described later, the ion deflector 23 may be any electrodes other than the parallel flat electrodes. However, the parallel flat electrodes have a simple structure and a simple condition of applied voltage, which also advantageously reduces the cost.

Second Embodiment

(34) In place of the front-stage and rear-stage quadrupole ion guides 21 and 22 in the off-axis ion transport optical system in the first embodiment, quadrupole array ion guides having rod electrodes replaced with virtual rod electrodes consisting of plate electrodes, or multipole array ion guides other than quadrupole ones can be used. FIG. 4 illustrates the schematic configuration of an off-axis ion transport optical system 20A in a second embodiment using quadrupole array ion guides. FIG. 5 is a schematic perspective view of an electrode unit of a quadrupole array ion guide. In FIG. 4, the same components as those of the off-axis ion transport optical system in the first embodiment are denoted by the same reference signs.

(35) In the second embodiment, a front-stage quadrupole array ion guide 21A and a rear-stage quadrupole array ion guide 22A both include virtual rod electrodes each of which consists of four disk-shaped electrodes. In FIG. 5, four virtual rod electrodes 211A, 212A, 213A, and 214A disposed around a first ion beam axis are each composed of four disk-shaped electrodes. By applying the same high-frequency voltages to the four disk-shaped electrodes included in one virtual rod electrode, it is possible to create a radio-frequency electric field almost the same as that in the quadrupole ion guide 21 or 22 in the first embodiment, in the space surrounded by the four virtual rod electrodes. Therefore, the motion of ions injected into the front-stage and rear-stage quadrupole array ion guides 21A and 22A are almost the same as in the case of the first embodiment. Thus, the traveling direction of ions transported by the front-stage quadrupole array ion guide 21A bends in the ion deflector 23 to reach the ion receiving range at the inlet of the rear-stage quadrupole array ion guide 22A, and is transported in the rear-stage quadrupole array ion guide 22A while being focused. Additionally, the motion of neutral particles is almost the same as in the case of the first embodiment.

(36) Now, an ion path simulation performed to verify the effect of the ion transport apparatus according to the present invention is described. FIG. 6A is a plan view of the result of the ion path simulation for the off-axis ion transport optical system 20A in the second embodiment, and FIG. 6B is a perspective view of the result. It is assumed here that the quadrupole array ion guides 21A and 22A each include virtual rod electrodes each of which consists of three disk-shaped electrodes. Additionally, of the parallel flat electrodes constructing the ion deflector 23, the flat electrode 231 on the upper side is longer than the flat electrode 232 on the lower side and extends toward the rear-stage quadrupole array ion guide 22A so that the front part of the rear-stage quadrupole array ion guide 22A is covered with the flat electrode 231. In FIG. 6A and FIG. 6B, to avoid making the ion paths difficult to understand, some of the virtual rod electrodes and the disk-shaped electrodes are not illustrated, but of course, these components are factored into the calculation of the simulation.

(37) The high-frequency voltage applied to the virtual rod electrodes of the front-stage and rear-stage quadrupole array ion guides 21A and 22A has an amplitude of 150 [V] and a frequency of 800 [kHz]. The deflection direct-current voltage has a value appropriately adjusted so that an ion transmission efficiency becomes best. Referring to the ion paths illustrated in FIG. 6A and FIG. 6B, it is confirmed that the ions transported by the front-stage quadrupole array ion guide 21A are deflected by the ion deflector 23 so as to travel toward the rear-stage quadrupole array ion guide 22A, and are captured and focused in the rear-stage quadrupole array ion guide 22A. The calculation from this paths simulation shows an ion transmission efficiency of about 98%, thereby confirming that it is possible to implement an off-axis-structure ion transport apparatus that gives a high ion transmission efficiency while having a simple structure.

(38) Although this result of the simulation based on the off-axis ion transport optical system 204 in the second embodiment, it is clear for the previously-described reason that the off-axis ion transport optical system 20 in the second embodiment can give almost the same ion transmission efficiency.

(39) In the above-described first and second embodiments, quadrupole ion guides and quadrupole array ion guides are used as ion transport units using radio-frequency electric fields in order to simplify the electrode structures and the applied voltage conditions. As these ion transport units, a conventionally known ion funnel, radio-frequency carpet, or the like can be used. Hereinafter, embodiments using such configurations are described.

Third Embodiment

(40) FIG. 7 is a schematic configuration diagram of an off-axis ion transport optical system 20B in a third embodiment. In this embodiment, a quadrupole ion guide 21 is used as a front-stage ion transport unit, and a radio-frequency carpet 22B is used as a rear-stage ion transport unit. FIG. 8 is a schematic perspective view of an electrode unit of this radio-frequency carpet 22B.

(41) The radio-frequency carpet 22B is composed of a number of (five in this embodiment) ring electrodes 22B1, 22B2, 22B3, 22B4, and 22B5 disposed concentrically. High-frequency voltages +V cos t and V cos t are applied to the ring electrodes neighboring each other in a radial direction, for example, to the ring electrodes 22B1 and 22B2, respectively, where the high-frequency voltages +V cos t and V cos t have the same amplitude and frequency but have phases inverted from each other. Specifically, +V cos t is applied to some of the ring electrodes alternately positioned in the radial direction (the ring electrodes 22B2 and 22B4 in the example illustrated in FIG. 8), and V cos t is applied to the others (the ring electrodes 22B1, 22B3, and 22B5 in the example illustrated in FIG. 8). A radio-frequency electric field created by the high-frequency voltages applied to the ring electrodes 22B1 to 22B5 in such a manner has an effect of capturing ions in the vicinities of locations fittingly separated from the ring electrodes 22B1 to 22B5.

(42) Additionally, different levels of direct-current voltages U1, U2, . . . are applied to the ring electrodes 22B1 . . . , respectively. These direct-current voltages U1, U2, . . . are determined so as to create a potential which is sloped downward from the outer ring electrode toward the inner ring electrode. The upward or downward slope should be determined depending on the polarity of the ions concerned. Therefore, the polarity of the direct-current voltages U1, U2, . . . are changed depending on the polarity of the ions to be analyzed. Ions located within a certain distance from the surfaces of the ring electrodes 22B1 to 22B5 by the effect of the radio-frequency electric field are affected by the aforementioned direct-current electric field showing the potential having the downward gradient, and thereby move along the gradient of that potential. As a result, the ions move from the outer circumference side to the inner circumference side of the radio-frequency carpet 22B, that is, come closer to the second ion beam axis C2.

(43) In the off-axis ion transport optical system 20B in the third embodiment, as in the above-described embodiments, ions deflected in the ion deflector 23 by the effect of the direct-current deflecting electric field are collected by the radio-frequency carpet 22B, focused in the vicinity of the second ion beam axis C2, and finally sent out from the orifice 71. In general, a radio-frequency carpet has a wider ion receiving range than the multipole ion guide or the like. Thus, even when an ion stream spreads out to some extent in the ion deflector 23 without the effect of focusing ions, it is possible to efficiently collect and transport the ions by the radio-frequency carpet 22B.

(44) As the radio-frequency carpet 22B, one having a configuration described in Patent Literature 2 can be used, and it is more preferable to use a radio-frequency carpet described in PCT/JP2003/066564 filed by the applicant of the present application.

Fourth Embodiment

(45) FIG. 9 is a schematic configuration diagram of an off-axis ion transport optical system 20C in a fourth embodiment. In this embodiment, the front-stage quadrupole ion guide 21 in the off-axis ion transport optical system 20B in the third embodiment is replaced with the quadrupole array ion guide 21A used in the second embodiment. Clearly, this configuration also achieves the same effect as that in the above-described embodiments.

Fifth Embodiment

(46) FIG. 10 is a schematic configuration diagram of an off-axis ion transport optical system 20D in a fifth embodiment. In this embodiment, the quadrupole ion guide 21 is used as a front-stage ion transport unit, and a typical ion funnel 22C described in Patent Literature 1 and the like is used as a rear-stage ion transport unit. As is well known, the ion funnel can efficiently focus introduced ions in such a manner as to narrow the ion stream to the vicinity of its central axis. Therefore, it is clear that this configuration also achieves the same effect as that in the above-described embodiments.

Sixth Embodiment

(47) FIG. 11 is a schematic configuration diagram of an off-axis ion transport optical system 20E in a sixth embodiment. In this embodiment, the quadrupole array ion guide 21A is used as a front-stage ion transport unit, and as in the fifth embodiment, the ion funnel 22C is used as a rear-stage ion transport unit. It is clear that this configuration also achieves the same effect as that in the above-described embodiments.

Seventh Embodiment

(48) FIG. 12 is a schematic configuration diagram of an off-axis ion transport optical system 20F in a seventh embodiment. In this embodiment, an ion funnel 21B and the ion funnel 22C are used as the front-stage and rear-stage ion transport unit, respectively. It is clear that this configuration also achieves the same effect as that in the above-described embodiments.

(49) As described in the above-described embodiments, as ion transport units respectively disposed in the front-stage and the rear stage across the ion deflector 23, any ion transport unit having various configurations can be used as long as the ion transport unit traps and transports ions using a radio-frequency electric field. Additionally, the ion deflector 23 is not limited to the aforementioned one using the simple pair of parallel flat electrodes 231 and 232.

(50) FIG. 13A and FIG. 13B are diagrams illustrating other configuration examples of the ion deflector used in the off-axis ion transport optical systems in the above-described embodiments. An ion deflector 23A illustrated in FIG. 13A includes a cylindrical outer electrode 233 and a flat-shaped inner electrode 234 disposed in the internal space of the outer electrode 233 being electrically insulated from (e.g., not being in contact with) the electrode 233. The inner electrode 234 is disposed so as to extend on the central axis of the outer electrode 233 and in parallel with the central axis. The insertion length of the inner electrode 234 into the internal space of the outer electrode 233 (a columnar-shaped space surrounded by the circumferential face and both open end faces of the outer electrode 233) may be from about of the distance between the inner electrode 234 and the outer electrode 233 in the internal space (denoted by reference sign d in FIG. 13A) to about a length L of the outer electrode 233.

(51) The outer electrode 233 and the inner electrode 234 are disposed so that the circumferential face of the outer electrode 233 is parallel to the first ion beam axis C1, and the first ion beam axis C1 is located midway between the inner circumferential surface of the outer electrode 233 and the inner electrode 234 (i.e., as illustrated in FIG. 13A, the distance from the first ion beam axis C1 to the inner circumferential surface of the outer electrode 233 and the distance from the first ion beam axis C1 to the inner electrode 234 are substantially the same as d). In place of the flat-shaped inner electrode 234, a rod-shaped electrode may be used.

(52) The same direct-current voltage as that applied to the aforementioned pair of parallel flat electrodes 231 and 232 is applied to the outer electrode 233 and the inner electrode 234. This creates, in the space between the outer electrode 233 and the inner electrode 234, a direct-current electric field that deflects ions in a direction toward the inner electrode 234. Since the outer electrode 233 is cylindrical, the electric field created between the inner circumferential surface of the outer electrode 233 and the inner electrode 234 has the effect of pushing ions existing in the internal space of the outer electrode 233 in directions toward the central-axis of the outer electrode 233. Thus, ions being deflected and travelling are prevented from spreading out and focused around the central axis of the outer electrode 233. A gas stream containing neutral particles without electric charges is not affected by the electric field and travel straight ahead. Thus, the ions and the neutral particles are separated from each other, and the ions efficiently reach the ion receiving range of the rear-stage ion transport unit.

(53) An ion deflector 239 illustrated in FIG. 13B includes a semi-cylindrical outer electrode 235 but is otherwise the same as the ion deflector 23A.

(54) In all of the aforementioned off-axis ion transport optical systems in the first to seventh embodiments, the first ion beam axis C1 does not lie on a straight line with and is parallel to the second ion beam axis C2, but the first ion beam axis C1 and the second ion beam axis C2 are not necessarily parallel to each other and can be, for example, oblique or orthogonal to each other. Additionally, the first ion beam axis C1 and the second ion beam axis C2 do not necessarily intersect with each other (i.e., lie on the same plane), and the rear-stage ion transport unit may be disposed at a location that causes ions deflected by the ion deflector to reach the ion receiving range at the inlet of the rear-stage ion transport unit. One of advantages provided by disposing the first ion beam axis C1 and the second ion beam axis C2 so as not to intersect with each other or lie on the same plane in such a manner is to increase the flexibility of disposition of ion optical systems in front-stage and rear-stage rear stages across the off-axis ion transport optical system, whereby to downsize the apparatus.

(55) As an example of such a mass spectrometer, an example in which an off-axis ion transport optical system of an embodiment of the present invention is applied to a tandem quadrupole mass spectrometer is described with reference to FIG. 14. FIG. 14 is a diagram illustrating the schematic configuration of an analysis chamber 4 maintained at a high degree of vacuum in the tandem quadrupole mass spectrometer.

(56) Ions originating from a sample component are introduced into a front quadrupole mass filter 40 along a first ion beam axis C3. In accordance with voltage applied to the front quadrupole mass filter 40, only ions having a specific mass-to-charge ratio selectively pass through the front quadrupole mass filter 40 and enter the inside of a collision cell 41 disposed at the rear of the front quadrupole mass filter 40, through an ion entrance port 411 of the collision cell 41. In the collision cell 41, an off-axis ion transport optical system 42 including a front-stage quadrupole ion guide 43, a rear-stage quadrupole ion guide 44, and an ion deflector 45 is installed. In this off-axis ion transport optical system 42, as aforementioned, the first ion beam axis C3 on the entrance side and a second ion beam axis C4 on the emission side are not parallel to each other, but the ion beam axes C3 and C4 intersect with each other at a predetermined angle. By determining the positional relation between the ion deflector 45 and the rear-stage quadrupole ion guide 44 so that ions deflected in the ion deflector 45 reach the ion receiving range at the inlet of the rear-stage quadrupole ion guide 44, the deflected ions are efficiently collected in the rear-stage quadrupole ion guide 44.

(57) Into the collision cell 41, a predetermined collision-induced dissociation (CID) gas such as argon is continuously or intermittently introduced. The ions having the specific mass-to-charge ratio and introduced into the collision cell 41, namely, precursor ions come into contact with the CID gas in the collision cell 41 to be cleaved, whereby product ions are generated. This cleavage is advanced as the precursor ions travel in the collision cell 41, and thus ions containing the precursor ions and the product ions are deflected in the ion deflector 45 and sent to the rear-stage quadrupole ion guide 44. The cleavage is advanced during such flight of the ions, and the product ions originating from the precursor ions are sent out through an ion emission port 412 of the collision cell 41.

(58) These product ions are introduced into a rear quadrupole mass filter 46 disposed in the rear stage of the collision cell 41 along the second ion beam axis C4. In accordance with voltage applied to the rear quadrupole mass filter 46, only product ions having a specific mass-to-charge ratio selectively pass through the rear quadrupole mass filter 46 and reach the ion detector 10 to be detected.

(59) For example, in the case where the tandem quadrupole mass spectrometer is used as a detector in a gas chromatograph, a noble gas such as helium used as a carrier gas in the gas chromatograph is introduced into an ion source. In this case, an ion source using electron ionization is often used, and the noble gas is easy to turn into a metastable atom (molecule) when receiving energy in the ion source. Thus, undesired metastable atoms generated in such a manner may be introduced into the collision cell 41 together with ions originating from a sample component. The metastable atoms are neutral particles and not affected by an electric field, and thus the ions (precursor ions, product ions) and the metastable atoms are separated from each other in the ion deflector 45, and the metastable atoms do not enter the rear quadrupole mass filter 46. This can avoid noise due to the metastable atom.

(60) Typically, in a tandem quadrupole mass spectrometer, the front quadrupole mass filter 40, the collision cell 41, and the rear quadrupole mass filter 46 are disposed on a substantially straight line, and thus it is inevitable that the analysis chamber 4 is made significantly long. However, the configuration illustrated in FIG. 14 allows the analysis chamber 4 to be short by deflecting ions in the collision cell 41. It is thereby possible to downsize the external shape of the apparatus as a whole, and for example, it is possible to reduce an installation space for the apparatus.

(61) Of course, an off-axis ion transport optical system installed in the collision cell 41 may naturally have one of the configurations described in the above-described second to seventh embodiments or a configuration obtained by modifying the configurations. The angle of intersection between the first ion beam axis C3 and the second ion beam axis C4 or the like can be determined as appropriate. Rather than the tandem quadrupole mass spectrometer, as a rear stage mass separator, a quadrupole time-of-flight (Q-TOF) mass spectrometer using a time-of-flight (TOF) mass analyser can naturally have the same configuration.

(62) Any of the previous embodiments is a mere example of the present invention, and any change modification or addition appropriately made within the spirit of the present invention will naturally fall within the scope of claims of the present application.

REFERENCE SIGNS LIST

(63) 1 . . . Ionization Chamber

(64) 2 . . . First Intermediate Vacuum Chamber

(65) 3 . . . Second Intermediate Vacuum Chamber

(66) 4 . . . Analysis Chamber

(67) 5 . . . Electrospray Nozzle

(68) 6 . . . Heated Capillary

(69) 7 . . . Skimmer

(70) 71 . . . Orifice

(71) 8 . . . Ion Guide

(72) 9 . . . Quadrupole Mass Filter

(73) 10 . . . Ion Detector

(74) 20, 20A, 20B, 20C, 20D, 20E, 20F . . . Off-Axis Ion Transport Optical System

(75) 21 . . . Front-Stage Quadrupole Ion Guide

(76) 211, 213, 214, 221, 222, 223, 224 . . . Rod Electrode

(77) 21A . . . Rear-Stage Quadrupole Array Ion Guide

(78) 211A, 212A, 213A, 214A . . . Virtual Rod Electrode

(79) 21B, 22C . . . Ion Funnel

(80) 22 . . . Rear-Stage Quadrupole Ion Guide

(81) 22A . . . Rear-Stage Quadrupole Array Ion Guide

(82) 22B . . . Radio-Frequency Carpet

(83) 22B1, 22B2, 22B3, 22B4, 22B5 . . . Ring Electrode

(84) 23, 23A, 23B . . . Ion Deflector

(85) 231, 232 . . . Flat Electrode

(86) 233, 235 . . . Outer Electrode

(87) 234 . . . Inner Electrode

(88) 30 . . . Controller

(89) 31 . . . First Radio-Frequency/Direct-Current Voltage Generator

(90) 32 . . . Second Radio-Frequency/Direct-Current Voltage Generator

(91) 33 . . . Deflection Direct-Current Voltage Generator

(92) 40 . . . Front Quadrupole Mass Filter

(93) 41 . . . Collision Cell

(94) 411 . . . Ion Entrance Port

(95) 412 . . . Ion Emission Port

(96) 42 . . . Off-Axis Ion Transport Optical System

(97) 43 . . . Front-Stage Quadrupole Ion Guide

(98) 44 . . . Rear-Stage Quadrupole Ion Guide

(99) 45 . . . Ion Deflector

(100) 46 . . . Rear Quadrupole Mass Filter

(101) C1, C3 . . . First Ion Beam Axis

(102) C2, C4 . . . Second Ion Beam Axis