Multi-surrounding time-of-flight mass spectrometer

Abstract

The MT-TOFMS of one embodiment of the present invention comprises: a linear ion trap (2) for temporarily holding ions to be analyzed and ejecting the ions through an ion ejection opening (211) which is elongated in one direction; an ion orbit (P) for forming an ion orbit that enables the ions to fly repeatedly; and a slit portion (5) arranged in the ion path from the time when the ions are ejected from the linear ion trap (2) to the time when they are introduced into the ion orbit, for shielding a portion of the ions in the length direction of the ion ejection opening (211).

Description

Technical Field

[0001] The present invention relates to a time-of-flight mass spectrometer, and more particularly to a multi-surrounding time-of-flight mass spectrometer. Background Art

[0002] In a time-of-flight mass spectrometer (hereinafter sometimes referred to as "TOFMS"), a fixed energy is given to ions from components contained in a sample and put into a flight space, and the ions are detected and the flight time is measured after flying a fixed distance. Since the flight speed of the ions in the flight space corresponds to the mass-to-charge ratio of the ions (strictly speaking, it is the italicized "m / z", but it is recorded here as the conventional "mass-to-charge ratio"), the mass-to-charge ratio of the ions can be calculated based on the measured flight time. In TOFMS, the longer the flight distance of the ions, the higher the mass resolution, but generally speaking, if the flight distance is extended, the device will become larger.

[0003] In contrast, as one type of TOFMS, a multi-turn (multi-ring) TOFMS (Multi Turn-Time of Flight Mass Spectrometer: hereinafter sometimes referred to as "MT-TOFMS") is known (see Patent Document 1, etc.). In MT-TOFMS, by making ions orbit along a closed orbit such as a roughly circular shape, a roughly elliptical shape, an 8-shaped shape, or an orbit based on an orbit such as a spiral orbit (hereinafter, such an orbit is referred to as an orbit), it is possible to ensure an exceptionally long flight distance in a relatively narrow space.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-99424 Summary of the invention

[0007] Technical problem to be solved by the invention

[0008] In order to achieve a higher detection sensitivity in MT-TOFMS, it is desirable to put as many ions as possible into the orbit. As a method for this, an attempt has been made to combine a linear ion trap that can accumulate a larger amount of ions than a 3D quadrupole ion trap with MT-TOFMS. However, according to experiments by the inventors, when ions ejected from the linear ion trap are introduced into the orbit of MT-TOFMS for mass analysis, the deviation of the flight time of ions with the same mass-to-charge ratio becomes larger (i.e., the time convergence decreases), resulting in a problem that the width of the peak on the mass spectrum becomes wider.

[0009] The present invention is made to solve the above-mentioned technical problems, and its object is to provide a multi-surrounding time-of-flight mass spectrometer that can improve detection sensitivity while achieving high mass accuracy and mass resolution.

[0010] Method for solving the above technical problems

[0011] One embodiment of the multi-surrounding time-of-flight mass spectrometer of the present invention completed in order to solve the above-mentioned technical problems is to include:

[0012] A linear ion trap temporarily holds ions to be analyzed and ejects the ions through an ion ejection opening that is elongated in one direction;

[0013] The orbiting flight section forms an orbiting track for the ions to fly repeatedly;

[0014] The slit portion is disposed in an ion path from the ions ejected from the linear ion trap to the ions introduced into the orbit, and shields a portion of the ions in the longitudinal direction of the ion ejection opening.

[0015] The above-mentioned orbital track can be a completely closed orbit in which ions flying from a certain point on the orbit return to the same point after circling the orbit once, or it can be an orbital track that is not a completely closed orbit as described above, but a orbital track in which the ions gradually deviate from their orbits each time they orbit, such as in a spiral shape.

[0016] Effects of the Invention

[0017] In the MT-TOFMS of the above aspect of the present invention, when ions are ejected from the linear ion trap, the ions are ejected in a bag shape with a rod-like or elongated rectangular extension in a plane perpendicular to the traveling direction, but a portion of the ions in the longitudinal direction are shielded by the slit.

[0018] In MT-TOFMS, the shape and configuration of the electrode forming the orbital track, or the voltage applied to the electrode, etc. are designed so that the deviation of the initial position of the ion when the ion is accelerated and put into the orbital track, the deviation of the initial energy given to the ion, or the deviation of the initial direction of motion of the ion, etc., can ensure time convergence as much as possible, that is, ions with the same mass-to-charge ratio can arrive at the detector at the same time as much as possible. However, usually in MT-TOFMS, in the cross section orthogonal to its central axis on the orbital track, the range in which the ion can pass well, that is, with high time convergence, is relatively narrow. In contrast, in the MT-TOFMS of the above-mentioned scheme of the present invention, the extended shape of the ion in the plane orthogonal to the traveling direction of the ion is appropriately shaped by the slit portion. Therefore, the expansion of the ion converges to the range in which the ion can pass with time convergence in the orbital track.

[0019] In addition, if the amount of ions introduced into the orbit is too much, the more the ions are superimposed and orbited, the easier it is for ions with the same mass-to-charge ratio to expand forward and backward in the direction of travel due to the space charge effect of the ions that form a group. In contrast, in the MT-TOFMS of the above-mentioned scheme of the present invention, since the amount of ions is appropriately limited by shielding a part of the ions with the slit portion, it is difficult to produce an excessive space charge effect caused by the ions, and it is also difficult to cause the expansion of the flying ions in the direction of travel forward and backward.

[0020] Therefore, the MT-TOFMS according to the above scheme of the present invention can improve the detection sensitivity by introducing a certain amount of more ions into the orbit, while also ensuring the time convergence of ions with the same mass-to-charge ratio during flight, thereby achieving higher mass accuracy and mass resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the configuration of MT-TOFMS which is one embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram showing the shielding state of ions in the slit in the MT-TOFMS of the present embodiment.

[0023] Figure 3 This is a diagram showing a comparison of actually measured mass spectra in the case where a slit is provided and in the case where a slit is not provided in the MT-TOFMS of the present embodiment. DETAILED DESCRIPTION

[0024] An embodiment of the MT-TOFMS of the present invention will be described with reference to the drawings.

[0025] Figure 1 This is a schematic diagram of the configuration of the MT-TOFMS according to this embodiment.

[0026] The MT-TOFMS of this embodiment includes: an ion source 1, which generates ions from a sample; a linear ion trap 2, which captures and accumulates the generated ions under the action of a high-frequency electric field; an orbiting flight section 3, which forms an orbiting orbit in which the ions ejected from the linear ion trap 2 orbit for an appropriate number of times; a detector 4, which detects ions after they have orbited and left the orbit; and a slit section 5, which is arranged between the linear ion trap 2 and the orbiting flight section 3 and has an ion passage opening of a specified size.

[0027] The linear ion trap 2 includes four planar electrodes 21 to 24 (in the middle) surrounding a linear central axis 20 and arranged parallel to the central axis 20. Figure 1 , the flat electrode 24 is located near the front side of the central axis 20); a pair of end cap electrodes 25 and 26 are respectively arranged on the outside of the two ends of the four flat electrodes 21 to 24. An ion entrance hole 251 of a specified size centered on the central axis 20 is formed in the end cap electrode 25 located on the side of the ion source 1. In addition, an ion ejection opening 211 of an elongated rectangular shape extending in a direction parallel to the central axis 20 is formed in a flat electrode 21 located on the side of the surrounding flight portion 3. In addition, a voltage generating unit (not shown) is provided for applying a specified voltage to these electrodes 21 to 24, 25, and 26, respectively.

[0028] In addition, the linear ion trap 2 may be configured to use rod electrodes having a cylindrical (or columnar) cross section or a hyperbolic cross section on the surface facing the central axis 20 instead of the planar electrodes 21 to 24 .

[0029] The orbiting flight unit 3 includes a plurality of sets of orbiting electrodes 31, each of which is a set of an inner electrode 311 and an outer electrode 312 in a substantially fan-shaped or parallel flat plate shape, an incident-side gate electrode 32, and an exit-side gate electrode 33. In addition, a voltage generating unit (not shown) is provided for applying a predetermined voltage to each of these electrodes 31, 32, and 33. In addition, in this example, a completely closed substantially elliptical orbiting track P is formed, but the shape of the orbiting track is of course not limited to this. In addition, as described above, the orbiting track may of course not be a completely closed orbiting track.

[0030] like Figure 1 As shown, the orbit P is formed on a plane including mutually orthogonal X-axis and Y-axis, and the incident direction of the ions passing through the incident side grid electrode 32 toward the orbit P is set to the X-axis direction. That is, here, the plane orthogonal to the ion travel direction at the ion incident position toward the orbit P is the YZ plane.

[0031] The slit portion 5 is arranged close to the ion ejection opening 211 of the linear ion trap 2 and parallel to the YZ plane, and has an ion passage opening 51 which is elongated in a rectangular shape in the Y-axis direction. Figure 2 As shown, the length L2 of the ion passage opening 51 in the longitudinal direction is set to be shorter than the length L1 of the ion ejection opening 211 of the linear ion trap 2 in the longitudinal direction.

[0032] The analysis operation in the MT-TOFMS of this embodiment will be described.

[0033] The ion source 1 generates ions from the sample, and the generated ions are introduced into the inner space of the linear ion trap 2 through the ion injection hole 251, and are accumulated in the inner space by the action of the high-frequency electric field. In addition, in the linear ion trap 2, ions can also be dissociated by collision-induced dissociation or the like. After a sufficient amount of ions are accumulated in the inner space of the linear ion trap 2, a predetermined DC voltage is applied to the opposed planar electrodes 21 and 23 respectively instead of the high-frequency voltage, and the acceleration electric field generated thereby is used to give kinetic energy to the ions accumulated so far. As a result, the ions are ejected all at once through the ion ejection opening 211.

[0034] When ions are accumulated in the linear ion trap 2, the internal space of the linear ion trap 2 expands in the direction of the central axis 20 (the Y-axis direction) to accumulate the ions. Therefore, when the ions are ejected, the ions are ejected in a packet shape extending substantially in the Y-axis direction from almost the entire ion ejection opening 211. Figure 2 As shown, the range where ions exist on the plane (YZ plane) perpendicular to the traveling direction of the ions becomes a range that is elongated in the Y-axis direction. If the packet-shaped ions reach the slit portion 5, since the length L2 of the ion passage opening 51 in the Y-axis direction is shorter than the length L1 of the ion ejection opening 211, the ions existing near the two ends of the packet-shaped ions cannot pass through the ion passage opening 51 and are shielded. Therefore, the range where ions exist on the plane perpendicular to the traveling direction of the packet-shaped ions passing through the ion passage opening 51 toward the surrounding flight portion 3 is shaped in the Y-axis direction into a rectangular range that is shorter than the previous range where the packet-shaped ions exist. In addition, the amount of ions is also reduced at this time.

[0035] In the orbiting flight section 3, a fan-shaped electric field and a linear electric field formed by a plurality of sets of orbiting electrodes 31 form an orbiting track P that allows ions to repeatedly orbit. The ions that have passed through the slit section 5 are guided by the incident side grid electrode 32 in the form of packets through the opening 51 to ride the orbit P. Ideally, the kinetic energy given to each ion when ejected from the linear ion trap 2 is the same, and each ion has a flight speed corresponding to its mass-to-charge ratio, that is, the smaller the mass-to-charge ratio, the greater the flight speed. The ions fly along the orbit P, and during the flight, a difference is generated in the front and back of the traveling direction corresponding to their respective flight speeds, that is, the mass-to-charge ratio.

[0036] If the ions ideally pass through the plane orthogonal to the central axis of the orbit P, that is, the range in which they can pass with high temporal convergence is limited to a certain extent, if the ions are incident on a position deviating from this range, the temporal convergence of the ions cannot be maintained. In contrast, in the MT-TOFMS, since the expansion of the ions in the Y-axis direction is particularly limited in the slit portion 5, almost all of the ions introduced into the orbit P can be incident on the range in which the ions can pass with high temporal convergence.

[0037] In addition, if the amount of ions introduced into the orbit P is excessive, since ions with the same polarity of charge repel each other, even ions with the same mass-to-charge ratio will have their positions deviated in the front-to-back direction. In contrast, the amount of ions in the slit portion 5 is reduced as a whole, so it is difficult to produce position deviations due to the space charge effect of the ions. As a result, ions with the same mass-to-charge ratio fly while having high temporal convergence.

[0038] In this way, the ions that have orbited the orbit P for a predetermined number of times are separated from the orbit P and travel toward the detector 4 via the exit side gate electrode 33. The detector 4 generates a detection signal corresponding to the amount of incident ions. As described above, since ions with the same mass-to-charge ratio maintain a high time convergence when flying along the orbit P in the orbiting flight section 3, ions with the same mass-to-charge ratio from the sample arrive at the detector 4 almost at the same time. Therefore, in the detection signal output from the detector 4, the intensity signal of ions with the same mass-to-charge ratio from the sample appears as a peak with a narrow width.

[0039] Figure 3 1 is a diagram showing a comparison of the mass spectra actually measured when the slit portion 5 is provided and when the slit portion 5 is not provided in the MT-TOFMS of the present embodiment. When the slit portion 5 is not provided and all the ions ejected from the linear ion trap 2 are introduced into the orbit P, as shown in FIG. Figure 3As shown in (a), a significant tail is observed in the peak of a specific ion from the sample. This indicates that the ion is delayed during flight due to various reasons. In contrast, when the slit portion 5 is provided to limit the expansion of the ions, as shown in FIG. Figure 3 As shown in (b), the tail almost disappears, and a sharp peak with a narrow width can be observed.

[0040] It can be seen from this that the effect of improving mass resolution and mass accuracy by configuring the slit portion 5 in the ion path between the ion ejection opening 211 of the linear ion trap 2 and the incident side gate electrode 32 of the surrounding flight unit 3 to shield part of the ions is obvious. Figure 3 (b), although with Figure 3 The peak height is lower than that of (a), but the degree of reduction is about 30%. In this way, the degree of reduction in ion intensity caused by setting the slit portion 5 is not that great. In the MT-TOFMS of this embodiment, the advantage of using the linear ion trap 2 that can accumulate a large amount of ions is utilized to achieve a higher detection sensitivity.

[0041] In addition, in the MT-TOFMS of the above-mentioned embodiment, the opening shape of the ion passage opening 51 of the slit portion 5 is set to a symmetrical shape with respect to the line connecting the center of the length direction of the ion ejection opening 211 of the linear ion trap 2 and the central axis of the orbit P at the incident point of the ions passing through the incident side gate electrode 32 on the XY plane, but the opening shape may be set to an asymmetrical shape. That is, strictly speaking, since the conditions for the passage of ions on the inner and outer sides of the fan-shaped electric field formed by the orbiting electrode 31 are different, the passage conditions of ions in the plane orthogonal to the central axis of the orbit P cannot be symmetrical. Therefore, in accordance with the ion passage conditions, setting the opening shape of the ion passage opening 51 of the slit portion 5 to an asymmetrical shape can achieve higher time convergence while suppressing the loss of ions to a lesser extent.

[0042] In addition, the above-mentioned embodiment is an example of the present invention, and it is obvious that appropriate corrections, changes, and additions made within the scope of the gist of the present invention are also included in the scope of the claims of the present application.

[0043] [Various options]

[0044] Those skilled in the art will appreciate that the above exemplary embodiments are specific examples of the following schemes.

[0045] (Item 1) A multi-surrounding time-of-flight mass spectrometer according to one embodiment of the present invention comprises:

[0046] A linear ion trap temporarily holds ions to be analyzed and ejects the ions through an ion ejection opening that is elongated in one direction;

[0047] The orbiting flight portion forms an orbiting orbit capable of causing the ions to repeatedly fly;

[0048] The slit portion is disposed in an ion path from the ions ejected from the linear ion trap to the ions introduced into the orbit, and shields a portion of the ions in the longitudinal direction of the ion ejection opening.

[0049] According to the multi-orbital time-of-flight mass spectrometer described in item 1, it is possible to improve the detection sensitivity by introducing a certain amount of ions into the orbital track, while also ensuring the time convergence of ions with the same mass-to-charge ratio during flight. As a result, the peak width of the peak from ions with the same mass-to-charge ratio in the mass spectrum can be narrowed, achieving higher mass accuracy and mass resolution.

[0050] (Item 2) In the multi-orbital time-of-flight mass spectrometer described in Item 1, the orbital track is formed on a plane, and the ion passage opening in the slit portion can be set to an opening with a slender shape in one direction on the plane.

[0051] The multi-orbit time-of-flight mass spectrometer described in item 2 can suppress the flight time deviation of ions with the same mass-to-charge ratio caused by the influence of the sector electric field for bending the traveling direction of the ions, which is effective in improving the mass accuracy and mass resolution.

[0052] (Item 3) In the multi-orbital flight time-of-flight mass spectrometer described in Item 2, the linear ion trap and the orbital flight portion are arranged relative to each other in such a manner that ions ejected from the center in the length direction of the ion ejection opening are incident on the central axis of the orbital orbit, and the passing opening of the slit portion can be set to be an asymmetric shape in the length direction with the position through which ions ejected from the center in the length direction of the ion ejection opening pass as the center.

[0053] According to the multi-orbital time-of-flight mass spectrometer described in item 3, ions can be effectively shielded according to the ion passing conditions under the influence of the fan-shaped electric field, etc., used to form the orbital orbits. Thus, high mass accuracy and mass resolution can be achieved while suppressing ion loss and ensuring high detection sensitivity as much as possible.

[0054] Description of Reference Numerals

[0055] 1 Ion source

[0056] 2 Linear ion trap

[0057] 20 Center axis

[0058] 21~24 Flat electrode

[0059] 211 Ion ejection opening

[0060] 25, 26 End cap electrode

[0061] 251 Ion entrance hole

[0062] 3 Orbiting flight unit

[0063] 31 Surround electrode

[0064] 32 Incident side gate electrode

[0065] 33 Output side gate electrode

[0066] 4 Detector

[0067] 5 Slit

[0068] 51 Ions pass through opening

[0069] P orbits around.

Claims

1. A multi-surround time-of-flight mass spectrometer, characterized in that: have: A linear ion trap temporarily holds ions to be analyzed and ejects the ions through an ion ejection opening that is elongated in one direction; The orbiting flight portion forms an orbit that enables the ions to fly repeatedly; A slit portion is arranged in the ion path from the ions ejected from the linear ion trap to the ions introduced into the orbit, the slit portion has an ion passage opening, the length of the ion passage opening in one direction is shorter than the length of the ion ejection opening in one direction, and the slit portion shields a portion of the ions in the ion ejection opening in the one direction.

2. The multi-orbit time-of-flight mass spectrometer according to claim 1, wherein: The orbit is formed on a plane, and the ion passage opening has an elongated shape in the one direction on the plane.

3. The multi-orbit time-of-flight mass spectrometer according to claim 2, wherein: The linear ion trap and the orbiting flight portion are arranged relative to each other in such a manner that ions ejected from the center in the length direction of the ion ejection opening are incident on the central axis of the orbiting track, and the ion passage opening of the slit portion is asymmetrical in the length direction with the position through which ions ejected from the center in the length direction of the ion ejection opening pass as the center.

Images