MULTI-TURN TIME-OF-FLIGHT MASS SPECTROMETER

Abstract

An MT-TOFMS which is one mode of the present invention includes: a linear ion trap (2) configured to temporarily hold ions to be analyzed, and to eject the ions through an ion ejection opening (211) having a shape elongated in one direction; a loop flight section (3) configured to form a loop path (P) capable of making ions repeatedly fly; and a slit part (5) located on an ion path in which the ions ejected from the linear ion trap (2) travel until the ions are introduced into the loop path, the slit part configured to block a portion of the ions in a longitudinal direction of the ion ejection opening (211).

Claims

1. A multi-turn time-of-flight mass spectrometer, comprising: a linear ion trap configured to temporarily hold ions to be analyzed, and to eject the ions through an ion ejection opening having a shape elongated in one direction; a loop flight section configured to form a loop path capable of making ions repeatedly fly; and a slit part located on an ion path in which the ions ejected from the linear ion trap travel until the ions are introduced into the loop path, the slit part configured to block a portion of the ions in a longitudinal direction of the ion ejection opening.

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

3. The multi-turn time-of-flight mass spectrometer according to claim 2, wherein the linear ion trap and the loop flight section are arranged relative to each other so that an ion which departed from a center in the longitudinal direction of the ion ejection opening enters the loop path at a central axis of the loop path, and the ion passage opening in the slit part has an asymmetrical shape in the longitudinal direction with respect to a position at which the ion which departed from the center in the longitudinal direction of the ion ejection opening passes through.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 is a schematic configuration diagram of a MT-TOFMS which is one embodiment of the present invention.

[0017] FIG. 2 is a model diagram showing the state of blockage of ions by a slit in the MT-TOFMS according to the present embodiment.

[0018] FIGS. 3A and 3B are graphs showing a comparison of mass spectra actually measured with and without the slit in the MT-TOFMS according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

[0019] One embodiment of the MT-TOFMS according to the present invention is hereinafter described with reference to the attached drawings.

[0020] FIG. 1 is a schematic configuration diagram of the MT-TOFMS according to the present embodiment.

[0021] The MT-TOFMS according to the present embodiment includes: an ion source 1 configured to generate ions originating from a sample; a linear ion trap 2 configured to capture and accumulate the generated ions by the effect of a radio-frequency electric field; a loop flight section 3 configured to form a loop path in which ions ejected from the linear ion trap 2 are made to fly an appropriate number of times; a detector 4 configured to detect ions which have finished flying in the loop path and have left the same path; and a slit part 5 located between the linear ion trap 2 and the loop flight section 3, having an ion passage opening of a predetermined size.

[0022] The linear ion trap 2 includes four plate electrodes 21-24 arranged around a linear central axis 20 and parallel to the same central axis 20 (in FIG. 1, the plate electrode 24 is located on the near side of the central axis 20); and a pair of end-cap electrodes 25 and 26 respectively arranged on the outside of the two ends of the four plate electrodes 21-24. In the end-cap electrode 25 closer to the ion source 1, an ion injection hole 251 of a predetermined size is formed, with its center on the central axis 20. In the plate electrode 21 closest to the loop flight section 3, an ion ejection opening 211 having an elongated rectangular shape extending parallel to the central axis 20 is formed. Additionally, a voltage generator (now shown) for applying predetermined voltages to the electrodes 21-24, 25 and 26, respectively, is provided.

[0023] As for the configuration of the linear ion trap 2, the plate electrodes 21-24 may be replaced by rod electrodes having a cylindrical (or columnar) cross section or rod electrodes whose surfaces facing the central axis 20 have a hyperbolic shape in the cross section.

[0024] The loop flight section 3 includes a plurality of pairs of loop electrodes 31, with each pair consisting of inner and outer electrodes 311 and 312 having a substantially sector form or parallel-plate form, as well as an entrance-side gate electrode 32 and an exit-side gate electrode 33. Additionally, a voltage generator (now shown) for applying predetermined voltages to the electrodes 31, 32 and 33, respectively, is provided. In the present example, a completely closed loop path P having a roughly elliptical shape is formed. Understandably, the shape of the loop path is not limited to this one. Furthermore, as already noted, it is natural that the loop path does not need to be a completely closed path.

[0025] As shown in FIG. 1, the loop path P is formed in a plane which contains the X and Y axes orthogonal to each other, with the X-axis direction defined as the direction in which ions are injected into the loop path P through the entrance-side gate electrode 32. Accordingly, in the present case, a plane orthogonal to the direction of travel of the ions at the point of injection of the ions into the loop path P is the Y-Z plane.

[0026] The slit part 5, which is arranged parallel to the Y-Z plane and close to the ion ejection opening 211 of the linear ion trap 2, has an ion passage opening 51 having a rectangular shape elongated in the Y-axis direction. As shown in FIG. 2, the longitudinal length L2 of the ion passage opening 51 is determined to be shorter than the longitudinal length Li of the ion ejection opening 211 of the linear ion trap 2.

[0027] An analytical operation in the MT-TOFMS according to the present embodiment is hereinafter described.

[0028] The ion source 1 produces ions originating from a sample. The generated ions are introduced through the ion injection hole 251 into the inner space of the linear ion trap 2, to be accumulated within the inner space by the effect of the radio-frequency electric field. The linear ion trap 2 additionally allows for the dissociation of the ions by collision induced dissociation or similar methods. After a sufficient amount of ions have been accumulated within the inner space of the linear ion trap 2, the radio-frequency voltages applied to the plate electrodes 21 and 23 facing each other are replaced by predetermined DC voltages. Due to the thereby created acceleration electric field, kinetic energy is imparted to the ions which have been accumulated until then. Consequently, the ions are simultaneously ejected through the ion ejection opening 211.

[0029] In the process of accumulating ions within the linear ion trap 2, the accumulated ions are spread along the direction of the central axis 20 (Y-axis direction) within the inner space of the linear ion trap 2. Therefore, at the moment of the ion ejection, a packet-like mass of ions roughly extending in the Y-axis direction are ejected from the almost entire area of the ion ejection opening 211. Accordingly, the area within which the ions are present on a plane orthogonal to the direction of travel of the ions (Y-Z plane) has a rectangular shape elongated in the Y-axis direction, as shown in FIG. 2. When this packet of ions arrives at the split part 5, ions which are present at or near the ends of the packet are blocked and cannot pass through the ion passage opening 51 since the length L.sub.2 of the ion passage opening 51 in the Y-axis direction is shorter than the length L.sub.1 of the ion ejection opening 211. Therefore, the area within which ions are present on the plane orthogonal to the direction of travel of the packet of ions travelling through the ion passage opening 51 toward the loop flight section 3 is shaped into a rectangular area which is shorter in the Y-axis direction than the area where the ions forming the original packet are present. The amount of ions is also decreased through this process.

[0030] In the loop flight section 3, a loop path P in which ions can repeatedly turn a large number of times is formed by the sector electric fields and linear electric fields created by the plurality of pairs of loop electrodes 31. The packet of ions which have passed through the ion passage opening 51 in the slit part 5 mentioned earlier is guided into the loop path P by the entrance-side gate electrode 32. Ideally, the kinetic energy is equally imparted to the ions when they are ejected from the linear ion trap 2, making each ion fly at a speed corresponding to its mass-to-charge ratio; i.e., the smaller the mass-to-charge ratio is, the higher the flying speed of the ion is. The ions fly along the loop path P. During this flight, the packet of ions is broken apart, ahead and behind in their direction of travel, according to the speeds of respective flying ions, or mass-to-charge ratios.

[0031] In the plane orthogonal to the central axis of the loop path P, the area within which ions can ideally pass through, i.e., the area within which ions can pass through in a highly time-focused form, is limited to a certain extent. Allowing the entry of ions outside this area would make it impossible to maintain the degree of time focusing of the ions. However, in the present MT-TOFMS, since the spread of the ions, particularly in the Y-axis direction, is restricted at the slit part 5, most of the ions introduced into the loop path P can enter the aforementioned area within which ions can pass through in a highly time-focused form.

[0032] If an excessive amount of ions were introduced into the loop path P, like-charged ions would repel each other, so that even ions having the same mass-to-charge ratio would vary in position in the direction of travel. However, since the entire volume of the ions is also decreased at the slit part 5, the positional variation due to the space-charge effect of the ions is less likely to occur. Therefore, ions having the same mass-to-charge ratio will fly in a highly time-focused form.

[0033] The ions which have thus made a predetermined number of turns in the loop path P leave the same path P, pass through the exit-side gate electrode 33 and travel toward the detector 4. The detector 4 produces a detection signal corresponding to the amount of incident ions. As just described, ions having the same mass-to-charge ratio are maintained in a highly time-focused form during their flight along the loop path P in the loop flight section 3. Therefore, ions originating from the sample and having the same mass-to-charge ratio almost simultaneously arrive at the detector 4. Therefore, the intensity signal of the ions originating from the sample and having the same mass-to-charge ratio appears as a narrow peak in the detection signal produced by the detector 4.

[0034] FIGS. 3A and 3B show a comparison of mass spectra actually measured with and without the slit part 5 in the MT-TOFMS according to the present embodiment. When the slit part 5 is omitted and all ions ejected from the linear ion trap 2 are introduced into the loop path P, a significant tailing will be observed in the peak of a specific ion originating from the sample, as shown in FIG. 3A. This demonstrates that some ions are delayed during their flight due to various factors. By comparison, when the spread of the ions is restricted by providing the slit part 5, the tailing is almost eliminated and a narrow, sharp peak can be observed, as shown in FIG. 3B.

[0035] This fact shows that the partial blocking of the ions by the slit part 5 placed in the ion path between the ion ejection opening 211 of the linear ion trap 2 and the entrance-side gate electrode 32 of the loop flight section 3 produces an unmistakable effect of improving the mass-resolving power and mass accuracy. Although the height of the peak in FIG. 3B is lower than that in FIG. 3A, the extent of the decrease is approximately 30%. Thus, the extent of decrease in ion intensity due to the provision of the slit part 5 is not significantly large, and therefore, the MT-TOFMS according to the present embodiment can achieve a high level of detection sensitivity by making use of the advantageous feature of the linear ion trap 2 which has a large capacity for accumulating ions.

[0036] In the MT-TOFMS according to the previously described embodiment, the opening shape of the ion passage opening 51 in the slit part 5 on the X-Y plane is symmetrical with respect to the line connecting the center in the longitudinal direction of the ion ejection opening 211 of the linear ion trap 2 and the central axis of the loop path P at the entry point of the ions which have passed through the entrance-side gate electrode 32. However, the opening shape may be asymmetrical. That is to say, the condition for allowing the ions to pass through the plane orthogonal to the central axis of the loop path P is not strictly symmetrical since there is a difference in terms of the ion passage condition between the inner and outer areas of the sector electric field created by the loop electrodes 31. Therefore, making the opening shape of the ion passage opening 51 in the slit part 5 be asymmetrical to fit for the ion passage condition will make it possible to achieve a higher degree of time focusing while decreasing the loss of the ions.

[0037] It is evident that the previously described embodiment is one example of the present invention and will fall within the scope of claims of the present application even if any modification, change or addition is appropriately made within the gist of the present invention.

[0038] [Various Modes]

[0039] A person skilled in the art can understand that the previously described illustrative embodiment is a specific example of the following modes of the present invention.

[0040] (Clause 1) A multi-turn time-of-flight mass spectrometer according to one mode of the present invention includes:

[0041] a linear ion trap configured to temporarily hold ions to be analyzed, and to eject the ions through an ion ejection opening having a shape elongated in one direction;

[0042] a loop flight section configured to form a loop path capable of making ions repeatedly fly; and

[0043] a slit part located on an ion path in which the ions ejected from the linear ion trap travel until the ions are introduced into the loop path, the slit part configured to block a portion of the ions in a longitudinal direction of the ion ejection opening.

[0044] The multi-turn time-of-flight mass spectrometer described in Clause 1 can achieve a high level of detection sensitivity by introducing an adequate amount of ions into the loop path while ensuring the time focusing of the ions having the same mass-to-charge ratio during their flight. This reduces the peak width of a peak originating from ions having the same mass-to-charge ratio in a mass spectrum, so that high levels of mass accuracy and mass-resolving power can be achieved.

[0045] (Clause 2) In the multi-turn time-of-flight mass spectrometer described in Clause 1, the loop path may be formed on a flat plane, and an ion passage opening in the slit part may have a shape elongated in one direction on the flat plane.

[0046] By the multi-turn time-of-flight mass spectrometer described in Clause 2, in particular, the dispersion in time of flight of the ions having the same mass-to-charge ratio due to the influence of the sector electric field for bending the direction of travel of the ions can be reduced. This is effective for improving the mass accuracy and mass-resolving power.

[0047] (Clause 3) In the multi-turn time-of-flight mass spectrometer described in Clause 2, the linear ion trap and the loop flight section may be arranged relative to each other so that an ion which departed from the center in the longitudinal direction of the ion ejection opening enters the loop path at a central axis of the loop path, and the passage opening in the slit part may have an asymmetrical shape in the longitudinal direction with respect to a position at which the ion which departed from the center in the longitudinal direction of the ion ejection opening passes through.

[0048] In the multi-turn time-of-flight mass spectrometer described in Clause 3, ions can be effectively blocked according to the ion passage condition which can vary due to the sector electric fields for creating the loop path or other factors. This makes it possible to realize high levels of mass accuracy and mass-resolving power while reducing the loss of the ions to ensure the highest possible level of detection sensitivity.

REFERENCE SIGNS LIST

[0049] 1 . . . Ion Source

[0050] 2 . . . Linear Ion Trap

[0051] 20 . . . Central Axis

[0052] 21-24 . . . Plate Electrode

[0053] 211 . . . Ion Ejection Opening

[0054] 25,26 . . . End-Cap Electrode

[0055] 251 . . . Ion Injection Hole

[0056] 3 . . . Loop Flight Section

[0057] 31 . . . Loop Electrode

[0058] 32 . . . Entrance-Side Gate Electrode

[0059] 33 . . . Exit-Side Gate Electrode

[0060] 4 . . . Detector

[0061] 5 . . . Slit Part

[0062] 51 . . . Ion Passage Opening

[0063] P . . . Loop Path