Mass analysis equipment

Abstract

To reduce contamination of an ion optical element and the like by a neutral particle.SOLUTION: An aspect of a mass spectrometer according to the present invention, is a mass spectrometer having: ion sources (11 and 2) generating an ion derived from a sample component in an atmospheric pressure atmosphere; one or more intermediate vacuum chambers (12 and 13) from a space of a vacuum chamber (14) where a mass separator (7) separating an ion by mass separation is arranged. The mass spectrometer comprises: an ion transport part (3) that includes an ion outlet (3a) into a first intermediate vacuum chamber (12) which is a next step of an ion source, and transmits the ion into the first intermediate vacuum chamber from the ion source; an exhaust open part (12d) that exhausts in vacuum in the first intermediate vacuum chamber provided to a position at a front side of an ion flow discharged into the first intermediate vacuum chamber from the ion outlet; ion transfer open parts (5 and 5a) that is provided to a position on a line crossed to a straight line connecting the ion outlet and the exhaust open part, and transmits the ion to the next step from the first intermediate vacuum chamber; and an ion guide (4) that guides the ion transfer output part while focusing the ion discharged from the ion outlet by an action a high frequency electric field.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to mass spectrometers, and more particularly to mass spectrometers having atmospheric pressure ion sources. [Background technology]

[0002] Mass spectrometers using atmospheric pressure ion sources such as electrospray ion sources generally employ a multistage differential pumping system configuration in which two or more intermediate vacuum chambers are arranged between an ionization chamber where the atmospheric pressure ion source is located and is at approximately atmospheric pressure, and an analysis chamber where a mass separator and an ion detector are located and is at high vacuum. In such mass spectrometers, an ion guide, which is a type of ion optical element, is used to efficiently collect ions in each intermediate vacuum chamber and send them to the next stage.

[0003] In intermediate vacuum chambers with a low vacuum where the gas pressure is about 100 Pa and intermediate vacuum chambers with a medium vacuum where the gas pressure is about 1 Pa, multipole RF ion guides such as quadrupole and octapole types are widely used, which capture and transport ions by the action of a radio frequency electric field (RF electric field).

[0004] For example, in the mass spectrometer described in Patent Document 1, an ion introduction port, which is the outlet of a desolvation tube through which ions are introduced from the ionization chamber, is disposed on a wall surface adjacent to the ionization chamber in a first intermediate vacuum chamber of low vacuum, and an ion passage hole (an orifice at the top of the skimmer) that sends ions from the first intermediate vacuum chamber to a second intermediate vacuum chamber at the next stage is provided on a wall surface opposite the first intermediate vacuum chamber and positioned coaxially with the ion introduction port. An RF ion guide is provided within the first intermediate vacuum chamber to converge ions emitted from the ion introduction port and pass them through the ion passage hole.

[0005] In a mass spectrometer configured as described above, ions introduced into the first intermediate vacuum chamber can be sent to the next stage with little loss, but neutral particles such as non-ionized component molecules introduced into the first intermediate vacuum chamber together with the ions also tend to enter the second intermediate vacuum chamber, causing contamination of the walls of the second intermediate vacuum chamber and the subsequent analysis chamber, as well as the ion optical elements arranged in these chambers. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 110264 [Patent Document 2] International Publication No. 2012 / 081122 [Patent Document 3] International Publication No. 2020 / 129199 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, in order to prevent neutral particles from entering the intermediate vacuum chamber or analysis chamber at the next stage, an off-axis type ion transport optical system has been used in which the ion inlet and the ion passage hole are not located on a straight line but are offset from each other. However, even with this configuration, it is difficult to completely prevent neutral particles from entering the subsequent vacuum chamber.

[0008] Furthermore, in conventional mass spectrometers, most of the neutral particles introduced into the first intermediate vacuum chamber together with the ions circulate within the first intermediate vacuum chamber before being exhausted to the outside through the exhaust port. Therefore, if a large number of neutral particles enter the first intermediate vacuum chamber, there is a problem in that the walls of the intermediate vacuum chamber and the ion optical elements arranged within the vacuum chamber are likely to become contaminated.

[0009] If the inner walls of the intermediate vacuum chamber or the analysis chamber or the ion optical elements arranged in these chambers become contaminated, the state of the electric field that controls the ion trajectories may change, potentially resulting in performance degradation such as a drop in sensitivity, etc. Furthermore, the frequency of equipment maintenance such as cleaning of contaminated components increases, which causes problems such as increased costs and further increases equipment downtime, reducing the operating efficiency of the equipment.

[0010] The present invention has been made in view of these problems, and its main object is to provide a mass spectrometer that can reduce contamination of the inner walls of the vacuum chamber and ion optical elements arranged in the vacuum chamber, which is mainly caused by neutral particles. [Means for solving the problem]

[0011] One aspect of the mass spectrometer according to the present invention, which has been made to solve the above problems, is a mass spectrometer having one or more intermediate vacuum chambers between an ion source that generates ions derived from sample components in an atmospheric pressure environment and a vacuum chamber in which a mass separator that separates the ions by mass is disposed, an ion transport unit having an ion outlet in a first intermediate vacuum chamber next to the ion source, for transporting ions from the ion source to the first intermediate vacuum chamber; an exhaust opening for evacuating the first intermediate vacuum chamber, the exhaust opening being provided at a position ahead of the ion flow emitted from the ion outlet into the first intermediate vacuum chamber; an ion outlet opening for sending ions from the first intermediate vacuum chamber to a next stage, the ion outlet opening being located on a line intersecting a line connecting the ion outlet and the exhaust opening; an ion guide that guides the ions emitted from the ion outlet to the ion outlet opening while converging the ions by the action of a radio frequency electric field; Equipped with. [Effects of the Invention]

[0012] According to the above-described aspects of the mass spectrometer of the present invention, ions introduced into the first intermediate vacuum chamber can be efficiently transported to the next stage, while at the same time, the intrusion of neutral particles, such as sample component molecules, introduced into the first intermediate vacuum chamber together with the ions into the next or subsequent vacuum chambers can be reduced. Furthermore, neutral particles sent from the ion source into the first intermediate vacuum chamber together with the ions can be separated from the ions and quickly evacuated. This reduces contamination caused by neutral particles adhering to the inner walls of the first intermediate vacuum chamber and the next or subsequent vacuum chambers, as well as to the ion optical elements disposed in those vacuum chambers. As a result, degradation of the device's performance, such as a decrease in sensitivity, can be avoided, and the frequency of device maintenance can be reduced, thereby reducing running costs and downtime. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of a mass spectrometer according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic perspective view of an ion guide in the mass spectrometer of the present embodiment. [Figure 3] FIG. 2 is a schematic diagram of the inside of a first intermediate vacuum chamber in the mass spectrometer of the present embodiment, viewed in the Y-axis direction. [Figure 4] FIG. 10 is a partial configuration diagram of a modified example of the mass spectrometer of the present embodiment. [Figure 5] FIG. 10 is a schematic diagram of a first intermediate vacuum chamber in another modified example of the mass spectrometer of the present embodiment. [Figure 6] FIG. 1 is a configuration diagram of a main part, centered on a first intermediate vacuum chamber, in a conventional general mass spectrometer. DETAILED DESCRIPTION OF THE INVENTION

[0014] A mass spectrometer according to an embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a schematic diagram of the mass spectrometer of this embodiment. Fig. 2 is a schematic perspective view of an ion guide in the mass spectrometer of this embodiment. Fig. 3 is a schematic diagram of the inside of a first intermediate vacuum chamber in the mass spectrometer of this embodiment as viewed in the Y-axis direction.

[0015] The mass spectrometer of this embodiment is a single-type quadrupole mass spectrometer equipped with an atmospheric pressure ion source. For convenience of explanation, three mutually orthogonal axes, X, Y, and Z, are defined in space as shown in FIG.

[0016] In this mass spectrometer, four chambers are provided inside the chamber 1: an ionization chamber 11, a first intermediate vacuum chamber 12, a second intermediate vacuum chamber 13, and an analysis chamber 14. The inside of the ionization chamber 11 is at approximately atmospheric pressure, and the inside of the first intermediate vacuum chamber 12 is evacuated by a rotary pump (RP) 9. The second intermediate vacuum chamber 13 and the analysis chamber 14 are evacuated by a turbomolecular pump (TMP) 10 and the rotary pump 9 acting as a roughing pump, respectively. This mass spectrometer is configured as a multi-stage differential pumping system in which the degree of vacuum increases in order from the ionization chamber 11 to the first intermediate vacuum chamber 12, the second intermediate vacuum chamber 13, and the analysis chamber 14. As an example, the gas pressure in the first intermediate vacuum chamber 12 is about 100 Pa, the gas pressure in the second intermediate vacuum chamber 13 is about 1 Pa, and the gas pressure in the analysis chamber 14 is about 10 -2 ~10 -4 It is about Pa.

[0017] An ESI (ElectroSpray Ionization) probe 2 is provided as an ion source in the ionization chamber 11. The ionization chamber 11 and the first intermediate vacuum chamber 12 are connected via a small-diameter desolvation tube 3. In this example, the central axis of the ESI probe 2 is parallel to the Y axis, the central axis of the ion inlet of the desolvation tube 3 is parallel to the Z axis, and the two central axes are perpendicular to each other, but this is just an example and can be changed as appropriate.

[0018] The first intermediate vacuum chamber 12 has a substantially rectangular parallelepiped shape, and the ion outlet 3a of the desolvation tube 3 is located on a first wall surface 12a among the multiple wall surfaces that define the first intermediate vacuum chamber 12. An exhaust opening 12d connected to the rotary pump 9 is provided on a second wall surface 12b that faces the first wall surface 12a and is located approximately on an extension of the central axis C1 of the ion outlet 3a. Furthermore, a skimmer 5 having an ion passage hole 5a formed at its top for sending ions to the next stage is provided on a third wall surface 12c that is neither the first wall surface 12a nor the second wall surface 12b. In this example, the first wall surface 12a and the second wall surface 12b are surfaces parallel to the XY plane, and the third wall surface 12c is a surface parallel to the XZ plane.

[0019] A multipole RF ion guide 4 is disposed within the first intermediate vacuum chamber 12. The multipole RF ion guide 4 bends the trajectory of ions introduced through the ion outlet 3a by approximately 90°, as indicated by reference symbol C2 in FIG. 1, and guides the ions to the ion passage aperture 5a. As shown in FIG. 2, the RF ion guide 4 includes eight curved rod electrodes 41 to 48. Ion guides made of curved rod electrodes are known in the art, as described in, for example, Patent Document 2. However, in this example, a pole-changing RF ion guide is used, rather than a simple RF ion guide, which has an octupole structure on the ion inlet side and a substantially quadrupole structure on the ion outlet side. This point will be described in detail later.

[0020] As shown in FIG. 1 , the central axis C1 of the desolvation tube 3 extends substantially parallel to the Z axis, while the ion optical axis C in the second intermediate vacuum chamber 13 and the analysis chamber 14 extends substantially parallel to the Y axis. A multipole RF ion guide 6 is disposed within the second intermediate vacuum chamber 13. Unlike the RF ion guide 4, this RF ion guide 6 includes multiple linear rod electrodes. A quadrupole mass filter 7 and an ion detector 8 are disposed within the analysis chamber 14 along the ion optical axis C. In this example, the quadrupole mass filter 7 consists of a main rod electrode and a pre-rod electrode disposed in front of it, although the pre-rod electrode can be omitted.

[0021] Here, a pole-changing type RF ion guide used as the RF ion guide 4 will be described. An example of a pole number-changing RF ion guide is described in Patent Document 3. In a typical RF ion guide, multiple (even number) linear rod electrodes are arranged around a linear ion optical axis in parallel to the ion optical axis. RF voltages of opposite polarity, that is, 180° out of phase, are applied to two adjacent rod electrodes around the ion optical axis, thereby forming a multipole RF electric field in the space surrounded by the rod electrodes. For example, in the case of an octopole ion guide, an octopole RF electric field is formed at the entrance of the ion guide, and a similar octopole RF electric field is also formed at the exit of the ion guide. In other words, the number of poles remains constant throughout the entire ion guide, from the entrance to the exit.

[0022] In contrast to this, in one pole number changing type RF ion guide described in Patent Document 3, some of the multiple linear rod electrodes arranged around the linear ion optical axis are arranged so as to be inclined with respect to the ion optical axis. This makes it possible to form an octupole RF electric field at the entrance of the ion guide, and a substantially quadrupole RF electric field at the exit of the ion guide. In other words, the number of poles changes from the entrance to the exit of the ion guide.

[0023] Multipole RF fields, such as hexapole and octopole RF fields, have a stronger ion confinement effect and better ion acceptance than quadrupole RF fields. Therefore, to effectively capture ions arriving from the front in a somewhat expanded state and introduce them into the internal space, a hexapole or higher multipole RF field is preferable to a quadrupole RF field. On the other hand, although the quadrupole RF field has a weaker ion confinement effect than a hexapole or higher multipole RF field, it has a stronger effect of converging ions near the central axis. Therefore, to converge ions transported through a space surrounded by multiple rod electrodes near the central axis and pass through a small aperture with low loss, a quadrupole RF field is preferable to a hexapole or higher multipole RF field. The pole-number-changing ion guide has the advantage that, by changing the number of poles at the ion inlet and outlet as described above, RF fields suitable for efficient ion transport can be formed in each region.

[0024] The RF ion guide 4 employed in the mass spectrometer of this embodiment is configured such that at least some of the eight curved rod electrodes 41-48 arranged around the ion optical axis, which is curved in a substantially arcuate shape, are arranged so that their distance from the ion optical axis varies along the ion optical axis. As a result, as shown in FIG. 2 , at the ion entrance 4A, the eight curved rod electrodes 41-48 are arranged equidistant from the central axis (ion optical axis), while at the ion exit 4B, only the four curved rod electrodes 43, 44, 47, and 48 located inside a square 4B1 are arranged equidistant from the central axis (ion optical axis). Of the eight curved rod electrodes 41-48, RF voltages of opposite polarities are applied to two curved rod electrodes circumferentially adjacent to each other at the ion entrance 4A. This RF ion guide 4 also generates an octupole RF electric field at the ion entrance 4A and a quadrupole RF electric field at the ion exit 4B. This makes it possible to utilize both the strong ion confinement effect of the octupole RF electric field and the strong ion focusing effect of the quadrupole RF electric field, as described above.

[0025] 3 when viewed in the Y-axis direction. That is, none of the curved rod electrodes 41 to 48 exists on a plane including an extension C1 of the central axis of the ion outlet 3a of the desolvation tube 3 and a curved ion optical axis C2 in the RF ion guide 4. This is to prevent the curved rod electrodes 41 to 48 from being positioned so as to block the flow of gas containing neutral particles that is expelled together with ions from the ion outlet 3a, as will be described later.

[0026] Next, the analytical operation of the mass spectrometer of this embodiment will be described. The ESI probe 2 ionizes various components contained in the sample liquid by spraying the sample liquid into the ionization chamber 11 as minute charged droplets. The generated ions are drawn into the desolvation tube 3, mainly by a gas flow formed by the pressure difference between both end openings of the desolvation tube 3. At this time, along with the ions derived from the sample components, minute charged droplets from which the solvent has not yet been fully vaporized and neutral particles such as unionized component molecules (or component molecules that have been ionized but generated by recombination with electrons) are also drawn into the desolvation tube 3. The desolvation tube 3 is heated to a predetermined temperature, and when charged droplets from which the solvent has not yet been fully vaporized are drawn into the desolvation tube 3, the evaporation of the solvent is promoted as the droplets pass through the desolvation tube 3, generating ions.

[0027] The ions and neutral particles sucked into the desolvation tube 3 are released together with the gas from the ion outlet 3a into the first intermediate vacuum chamber 12. At this time, the gas flow becomes a supersonic free jet, and the ions tend to spread due to the barrel shock. However, as described above, the RF electric field at the ion inlet 4A of the RF ion guide 4 is an octupole RF electric field with a strong ion-confining effect, so the ions are efficiently captured (i.e., with low loss) by the RF electric field and taken into the internal space of the RF ion guide 4. The ions then bend their trajectories along the RF ion guide 4 and reach the ion outlet 4B. Because a quadrupole RF electric field is formed at the ion outlet 4B, the ions are focused near the ion optical axis C and sent to the second intermediate vacuum chamber 13 through the ion passing hole 5a.

[0028] On the other hand, the gas molecules and neutral particles discharged from the ion outlet 3a into the first intermediate vacuum chamber 12 are not affected by the electric field of the RF ion guide 4. Therefore, the gas flow containing the neutral particles spreads but travels generally straight, as shown by the dotted arrows in Figure 1, and is separated from the ion flow. Because an exhaust opening 12d is provided ahead of the gas flow in the direction of travel, the neutral particles are discharged to the outside of the chamber 1 together with the gas through the exhaust opening 12d.

[0029] For comparison with the mass spectrometer of this embodiment, FIG. 6 shows a configuration diagram of the main components of a typical conventional mass spectrometer, centered on the first intermediate vacuum chamber 12. In FIG. 6, components corresponding to those shown in FIG. 1 are denoted by the same reference numerals. As indicated by the dotted arrows in FIG. 6, in this configuration, the gas flow containing neutral particles directly hits the skimmer 5, which has an ion passage hole 5a formed therein for sending ions into the second intermediate vacuum chamber 13. As a result, some of the neutral particles easily enter the second intermediate vacuum chamber 13 through the ion passage hole 5a. Furthermore, many of the remaining neutral particles ride the gas flow and circulate within the first intermediate vacuum chamber 12, easily contaminating the inner wall of the first intermediate vacuum chamber 12 and components within the vacuum chamber 12.

[0030] In contrast, in the mass spectrometer of this embodiment, the gas flow containing neutral particles is smoothly discharged within the first intermediate vacuum chamber 12. The smoother the gas flow from the ion outlet 3a to the exhaust opening 12d, the less likely the neutral particles are to spread within the first intermediate vacuum chamber 12. As shown in FIG. 3 , the curved rod electrodes 41-48 constituting the RF ion guide 4 are arranged so as not to obstruct the gas flow as much as possible, thereby reducing turbulence in the gas flow and allowing the neutral particles to be smoothly discharged without circulating within the first intermediate vacuum chamber 12. In addition, contamination of the curved rod electrodes 41-48 themselves due to adhesion of neutral particles can be suppressed. Since neutral particles are less likely to circulate within the first intermediate vacuum chamber 12, contamination of not only the RF ion guide 4 but also other components installed within the first intermediate vacuum chamber 12 and the inner wall of the first intermediate vacuum chamber 12 can be reduced.

[0031] Of the multiple rod electrodes that make up the RF ion guide 6 in the second intermediate vacuum chamber 13, RF voltages of opposite polarity are applied from a power supply unit (not shown) to rod electrodes that are adjacent to each other around the ion optical axis C. This forms a multipole RF electric field in the internal space of the RF ion guide 6. Ions sent to the second intermediate vacuum chamber 13 through the ion passing hole 5a are captured by this multipole RF electric field of the RF ion guide 6, and are then focused and sent to the analysis chamber 14.

[0032] A predetermined voltage is applied from a power supply (not shown) to the multiple rod electrodes that make up the quadrupole mass filter 7 in the analysis chamber 14. Due to the action of the electric field formed by this, only ions with a specific m / z value selectively pass through the quadrupole mass filter 7, while other ions dissipate along the way. The ion detector 8 detects ions that have passed through the quadrupole mass filter 7 and outputs a detection signal with an intensity corresponding to the quantity of ions.

[0033] This detection signal is input to a data processing unit (not shown), where data processing is performed. For example, when the voltage applied to the electrodes constituting the quadrupole mass filter 7 is scanned over a predetermined range, the m / z values ​​of the ions that can pass through the quadrupole mass filter 7 change. Therefore, the data processing unit processes the detection signal corresponding to this scanning of m / z values ​​to create a mass spectrum that shows the changes in ion intensity over a predetermined m / z range.

[0034] As described above, in the mass spectrometer of this embodiment, neutral particles introduced into the first intermediate vacuum chamber 12 together with ions are less likely to enter the second intermediate vacuum chamber 13, and are also more likely to be quickly expelled to the outside of the chamber 1 without circulating within the first intermediate vacuum chamber 12. This reduces contamination of the inner wall of the first intermediate vacuum chamber 12, components arranged within the first intermediate vacuum chamber 12, such as the RF ion guide 4, the inner wall of the second intermediate vacuum chamber 13, components arranged within the second intermediate vacuum chamber 13, such as the RF ion guide 6, and further components arranged within the analysis chamber 14, such as the inner wall of the analysis chamber 14 and the quadrupole mass filter 7. On the other hand, ions derived from sample components are efficiently transported from the first intermediate vacuum chamber 12 to the second intermediate vacuum chamber 13, thereby achieving high detection sensitivity.

[0035] [Variations] In the mass spectrometer of the above embodiment, the eight curved rod electrodes 41 to 48 constituting the RF ion guide 4 are arranged so as not to obstruct the gas flow, but one or more of the curved rod electrodes 41 to 48 constituting the RF ion guide 4 may be configured to have a recessed portion carved out at a location that may intersect with the gas flow exiting the ion outlet 3a and heading toward the exhaust opening 12d. In Fig. 4, the recessed portion formed by this carving is indicated by the symbol 4a.

[0036] Although this structure makes it difficult for the gas flow to come into contact with the curved rod electrodes 41-48, it may disrupt the RF electric field formed in the space surrounded by the curved rod electrodes 41-48, weakening the effect of bending the ion trajectories and making the ions more likely to dissipate. To address this issue, as shown in Fig. 4, a flat auxiliary electrode 400 may be placed parallel to the XZ plane at a certain distance from the gas flow, and a predetermined DC voltage (a DC voltage of the same polarity as the ions) may be applied to the auxiliary electrode 400 from a DC voltage source 401.

[0037] The DC deflection electric field formed by the auxiliary electrode 400 exerts a force on ions traveling in approximately the same direction as the gas flow (Z-axis direction) to deflect the ions in the negative direction of the Y-axis (downward in FIG. 4). This compensates for the disturbance of the RF electric field and adjusts the direction of ion travel. Since the auxiliary electrode 400 is located at a certain distance from the gas flow and extends approximately parallel to the gas flow, contamination caused by neutral particles adhering to the auxiliary electrode 400 can also be reduced. However, the shape and position of the auxiliary electrode 400 are not limited to the example shown in FIG. 4 and can be modified as appropriate.

[0038] Furthermore, even in the mass spectrometer having the configuration shown in FIG. 1, i.e., a configuration in which recesses 4a are not provided in the curved rod electrodes 41 to 48, an auxiliary electrode 400 that forms a DC deflection electric field that deflects ions may be provided as shown in FIG. 4 to assist in bending the ions.

[0039] In the above embodiment, the pole-changing type curved RF ion guide 4 is used to separate the ions from the gas flow and guide the ions to the ion passage hole 5a, but it is not necessary to use a pole-changing type. That is, a curved RF ion guide having a quadrupole, hexapole, or octapole configuration may also be used.

[0040] Furthermore, instead of a multipole ion guide, an ion guide of another structure may be used as the RF ion guide 4. For example, an ion funnel may be used instead of a multipole ion guide. However, it is generally known that the performance of an ion funnel is easily degraded by contamination. Furthermore, since the electrode plates must be arranged at relatively narrow intervals along the ion optical axis, the gas flow that enters the internal space of the ion funnel is unlikely to escape to the outside. For these reasons, when forming a curved ion path that easily collides with neutral particles carried by the gas flow, as in this embodiment, it is considered preferable to use a multipole ion guide rather than an ion funnel.

[0041] In the above embodiment, as shown in Fig. 1, it is assumed that the first intermediate vacuum chamber 12 has a substantially rectangular parallelepiped shape and six wall surfaces, but the shape of the first intermediate vacuum chamber 12 is not limited to this. Fig. 5 is a schematic perspective view of the first intermediate vacuum chamber in another modified example of the mass spectrometer of this embodiment. In this figure, the RF ion guide is omitted.

[0042] In this modification, the first intermediate vacuum chamber 12A has a generally cylindrical shape with both open ends closed by flat surfaces. That is, the first intermediate vacuum chamber 12A is comprised of a cylindrical first wall surface 12Aa and flat second and third wall surfaces 12Ab and 12Ac. An ion outlet 3a at the end of the desolvation tube 3 is provided at a predetermined position on the first wall surface 12Aa, and an exhaust opening 12d is provided on the first wall surface 12Aa at a position substantially opposite (in front of) the ion outlet 3a. The skimmer 5 is provided on the third wall surface 12Ac, which is to the side of the gas flow from the ion outlet 3a toward the exhaust opening 12d.

[0043] In this example, too, the gas flow containing neutral particles expelled from the ion outlet 3a travels almost straight until it reaches the vicinity of the exhaust opening 12d and is smoothly expelled outside the chamber through the exhaust opening 12d. Meanwhile, ions derived from sample components introduced through the ion outlet 3a are separated from the gas flow and their trajectories are bent by the action of the electric field generated by the RF ion guide (not shown). The ions then pass through the ion passage hole 5a at the top of the skimmer 5 and are sent to the next stage. Thus, regardless of the shape and structure of the first intermediate vacuum chamber, it is clear that the above-described actions and effects can be achieved by appropriately arranging the ion outlet 3a, exhaust opening 12d, and ion passage hole 5a and using the RF ion guide 4 to guide the ions.

[0044] Furthermore, although the above explanation is based on the assumption that the gas flow emitted from the ion outlet 3a travels almost straight, the direction of travel of the gas flow may bend slightly depending on the shape and structure of the RF ion guide. Such bending of the direction of travel can be analyzed experimentally. Therefore, although the position of the exhaust opening 12d is in front of the ion flow discharged from the ion outlet 3a, it is not necessarily located on the central axis of the ion flow, and it can be positioned at an appropriate offset.

[0045] Furthermore, in the above embodiment and modified examples, the trajectory of the ions discharged from the ion outlet 3a is bent by approximately 90°, but this angle may be any angle that allows separation from the gas flow. Therefore, the skimmer 5 having the ion passing hole 5a may be located on the second wall surface 12b, instead of on the third wall surface 12c, which is different from both the first wall surface 12a and the second wall surface 12b, as in the configuration of FIG. 1. In other words, the ion passing hole 5a may be located on a straight line that intersects (orthogonal or oblique) with a straight line connecting the ion outlet 3a and the exhaust opening 12d.

[0046] Furthermore, although the above embodiment is a single-type quadrupole mass spectrometer, it is clear that the present invention is applicable to mass spectrometers in general that are equipped with an atmospheric pressure ion source, and may also be applied to other types of mass spectrometers, such as a triple quadrupole mass spectrometer or a quadrupole time-of-flight mass spectrometer.

[0047] Furthermore, the above-described embodiment and various modifications are merely examples of the present invention, and it is natural that any further appropriate modifications, alterations, or additions made within the spirit of the present invention will also be encompassed within the scope of the claims of the present application.

[0048] [Various aspects] It will be understood by those skilled in the art that the exemplary embodiments and variations described above are examples of the following aspects.

[0049] (Item 1) One aspect of the mass spectrometer according to the present invention is a mass spectrometer having one or more intermediate vacuum chambers between an ion source that generates ions derived from sample components in an atmospheric pressure environment and a vacuum chamber in which a mass separator that separates the ions by mass is disposed, an ion transport unit having an ion outlet in a first intermediate vacuum chamber next to the ion source, for transporting ions from the ion source to the first intermediate vacuum chamber; an exhaust opening for evacuating the first intermediate vacuum chamber, the exhaust opening being provided at a position ahead of the ion flow emitted from the ion outlet into the first intermediate vacuum chamber; an ion outlet opening for sending ions from the first intermediate vacuum chamber to a next stage, the ion outlet opening being located on a line intersecting a line connecting the ion outlet and the exhaust opening; an ion guide that guides the ions emitted from the ion outlet to the ion outlet opening while converging the ions by the action of a radio frequency (RF) electric field; Equipped with.

[0050] (Item 2) In the mass spectrometer described in item 1, the first intermediate vacuum chamber can be surrounded by three or more substantially planar walls, the ion outlet can be provided on a first wall of the plurality of walls, the exhaust opening can be provided on a second wall of the plurality of walls that faces the first wall, and the ion outlet opening can be provided on a third wall of the plurality of walls that is different from the first and second wall.

[0051] (Item 3) In the mass spectrometer described in item 2, the first wall surface and the second wall surface may be substantially parallel, and the third wall surface may be substantially perpendicular to the first wall surface. In the mass spectrometers described in items 2 and 3, the first intermediate vacuum chamber typically has a substantially rectangular parallelepiped shape.

[0052] The mass spectrometer described in paragraphs 1 to 3 can efficiently transport ions introduced into the first intermediate vacuum chamber to the next stage, while reducing the intrusion of neutral particles such as sample component molecules introduced into the first intermediate vacuum chamber together with the ions into the next or subsequent vacuum chambers. Furthermore, neutral particles sent from the ion source into the first intermediate vacuum chamber together with the ions can be separated from the ions and quickly evacuated. This reduces contamination caused by neutral particles adhering to the inner walls of the first intermediate vacuum chamber and the next or subsequent vacuum chambers, as well as ion optical elements disposed in those vacuum chambers. As a result, it is possible to avoid degradation of the device's performance, such as a decrease in sensitivity, and reduce the frequency of device maintenance, thereby reducing running costs and downtime.

[0053] (Item 4) In the mass spectrometer described in any one of Items 1 to 3, the ion guide may be an ion guide with a multipole structure in which a plurality of rod electrodes are arranged to surround the ion optical axis.

[0054] In a multipole ion guide, the rod electrodes extend in the ion travel direction overall, making it difficult for the gas flow emitted from the ion outlet to directly hit the rod electrodes. Furthermore, the gas flow emitted from the ion outlet into the space surrounded by the rod electrodes easily passes through the gaps between the rod electrodes and exits the space. Therefore, compared to other RF ion guides such as ion funnels, contamination of the rod electrodes due to the adhesion of neutral particles contained in the gas flow is less likely to occur. Therefore, the mass spectrometer described in paragraph 4 can further reduce contamination of the ion guide in the first intermediate vacuum chamber.

[0055] (Item 5) In the mass spectrometer described in item 4, the ion guide may be a multipole ion guide that has a substantially hexapole or greater multipole structure on the ion inlet side and a substantially quadrupole structure on the ion outlet side.

[0056] According to the mass spectrometer described in paragraph 5, ions that are released from the ion outlet and then expand as they travel can be trapped in the internal space surrounded by the rod electrodes with a high confinement effect. Meanwhile, ions that are trapped and transported in the internal space can be effectively focused near the ion optical axis and passed through the small-diameter ion outlet opening. This allows ions to be transported with low loss, improving the sensitivity of the device.

[0057] (Item 6) In the mass spectrometer described in Item 4 or 5, the plurality of rod electrodes constituting the ion guide may not be located on a plane including a central axis of the ion outlet and an ion optical axis of the ions extending from the ion outlet to the ion exit aperture.

[0058] (Item 7) In the mass spectrometer described in any one of Items 4 to 6, the plurality of rod electrodes constituting the ion guide may have a shape in which a portion corresponding to a predetermined region around an extension line of the central axis of the ion outlet is missing.

[0059] According to the mass spectrometers described in paragraphs 6 and 7, the gas flow emitted from the ion outlet is less likely to directly impinge on the rod electrodes that make up the ion guide, further reducing contamination of the rod electrodes. Furthermore, since the gas flow is less likely to be disturbed by the rod electrodes, the gas is smoothly discharged from the first intermediate vacuum chamber and is less likely to spread within the first intermediate vacuum chamber. This further reduces contamination of the inner walls of the first intermediate vacuum chamber.

[0060] (Item 8) The mass spectrometer according to item 1 or 5 may further comprise an auxiliary electrode on the outside of the ion guide that forms a DC electric field that assists the ion guide in bending the direction of ion travel.

[0061] According to the mass spectrometer described in paragraph 8, even when the RF electric field of the ion guide is insufficient to bend ions, the ions can be effectively deflected by the action of the DC electric field from the auxiliary electrode, thereby further reducing ion loss during ion transport and improving the sensitivity of the device. [Explanation of symbols]

[0062] 1...Chamber 11...Ionization chamber 12, 12A...1st intermediate vacuum chamber 12a...First wall 12b...Second wall 12c...Third wall 12d...Exhaust opening 13...Second intermediate vacuum chamber 14…Analysis room 2. ESI probe 3...Desolvation tube 3a...Ion outlet 4...RF ion guide 41-48...Curved rod electrodes 4A...Ion inlet 4B...Ion outlet 4a...recess 400…Auxiliary electrode 401...DC voltage source 5. Skimmer 5a...Ion passage hole 6...RF ion guide 7...Quadrupole mass filter 8...Ion detector 9...Rotary pump 10...Pump C...Ion optical axis

Claims

1. A mass spectrometer having one or more intermediate vacuum chambers between an ion source that generates ions derived from sample components in an atmospheric pressure environment and a vacuum chamber in which a mass separator that separates the ions by mass is disposed, an ion transport unit having an ion outlet in a first intermediate vacuum chamber next to the ion source, for transporting ions from the ion source to the first intermediate vacuum chamber; an exhaust opening for evacuating the first intermediate vacuum chamber, the exhaust opening being provided at a position ahead of the ion flow emitted from the ion outlet into the first intermediate vacuum chamber; an ion outlet opening for sending ions from the first intermediate vacuum chamber to a next stage, the ion outlet opening being located on a line intersecting a line connecting the ion outlet and the exhaust opening; an ion guide that guides the ions emitted from the ion outlet to the ion outlet opening while converging them by the action of a radio frequency electric field, the ion guide having a multipole structure in which a plurality of rod electrodes are arranged to surround an ion optical axis; A mass spectrometer comprising:

2. the first intermediate vacuum chamber is surrounded by three or more substantially flat wall surfaces, the ion outlet is provided on a first wall surface of the plurality of wall surfaces; the exhaust opening is provided in a second wall surface of the plurality of wall surfaces that faces the first wall surface, The mass spectrometer according to claim 1 , wherein the ion outlet opening is provided on a third wall surface of the plurality of wall surfaces, the third wall surface being different from the first wall surface and the second wall surface.

3. The mass spectrometer according to claim 2 , wherein the first wall surface and the second wall surface are substantially parallel to each other, and the third wall surface is substantially perpendicular to the first wall surface.

4. 4. The mass spectrometer according to claim 1, wherein the ion guide is a multipole ion guide having a substantially hexapole or greater multipole structure on the ion entrance side and a substantially quadrupole structure on the ion exit side.

5. 5. The mass spectrometer according to claim 1, wherein the plurality of rod electrodes constituting the ion guide are not positioned on a plane including a central axis of the ion outlet and an ion optical axis of ions extending from the ion outlet to the ion exit opening.

6. 6. The mass spectrometer according to claim 1, wherein the plurality of rod electrodes constituting the ion guide are shaped such that a portion corresponding to a predetermined region around an extension line of the central axis of the ion outlet is missing.

7. 7. The mass spectrometer according to claim 1, further comprising an auxiliary electrode on the outside of said ion guide, said auxiliary electrode forming a DC electric field that assists said ion guide in bending the traveling direction of ions.

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