JP4553782B2 - Time-of-flight mass spectrometer - Google Patents

Description

  The present invention provides a flight time in which ions ejected from an ion source draw a spiral orbit by drawing a spiral orbit while drawing a circular orbit by the action of a sectoral electric field and shifting the orbital plane in a direction orthogonal to the orbital plane of the orbit. Type mass spectrometer.

A time-of-flight mass spectrometer (Time Of Flight Mass Spectrometer, hereinafter abbreviated as TOFMS) is used for quantitative analysis, qualitative simultaneous analysis, or structural analysis of sample ions. In TOFMS, the mass of ions is measured, but the resolution of this mass is
(Mass resolution) = (T / 2) × ΔT
It is expressed by the following formula. Here, T is the total flight time of ions, and ΔT is the time width of the measured electrical waveform. According to this equation, a high mass resolution can be obtained by keeping the time width ΔT constant and making the total flight time T long. In TOFMS, the total flight distance is increased in order to increase the total flight time T. However, in order to increase the total flight distance, it has been necessary to increase the size of the apparatus in the linear and reflective TOFMS.

  Here, in order to avoid an increase in the size of the apparatus and to realize high mass resolution, a multi-circular TOFMS is used. In this multi-turn type TOFMS, a toroidal electric field is generated by four cylindrical sector electrodes combined with Mazda plates, and ions are repeatedly caused to fly on the same round orbit of an 8-shaped shape, thereby performing multiple rounds of ions. . As a result, the total flight distance of ions can be increased and the total flight time T can be extended without increasing the size of the apparatus. In this multi-circular TOFMS, the spatial spread and the temporal spread on the detection surface due to the initial position, initial velocity, and initial kinetic energy can be converged to the first order term.

  However, this multi-circular TOFMS has a problem of overtaking ions. That is, when multiple types of ions repeatedly fly on the same orbit, light ions with high speed overtake heavy ions with low speed of circulation delay. By this overtaking, the order of ions input to the detector is not in the order from light to heavy, and as a result, it is difficult to specify the type of ions from the temporal input order.

  This difficulty is solved using a helical orbital TOFMS. The spiral trajectory type TOFMS shifts the starting point and end point of the circular orbit in a direction perpendicular to the circular orbital surface, and flies ions in a spiral orbit. As a result, even when ions perform multiple rounds, fast ions do not overtake slow ions, and the type of ions can be determined from the input order of ions to the detector.

Here, in order to realize the spiral trajectory of ions,
(1) When ions are incident on the spiral orbital TOFMS, they are incident obliquely (for example, see Patent Document 1).
(2) The ions on the orbit are shifted by a deflector in a direction perpendicular to the orbital plane (see, for example, Patent Document 2).
Is done.
JP 2000-243345, (first page, FIG. 1) Japanese Patent Laid-Open No. 2003-86129, (first page, FIG. 1) Journal of Mass Spectrometry (Vol. 38), 2003, p. 1125 to 1142

  However, according to the background art described above, it is not easy to change the number of times of ion circulation. That is, in the above-described method (1) in which the ions are incident obliquely, the number of turns can be changed by changing the incident angle. However, when ions are incident at an angle, there is no spatial and temporal convergence in the direction orthogonal to the orbital plane, and ions with different circulation numbers are incident on the same detector when the velocity distribution in the orthogonal direction is large. there's a possibility that.

  In addition, when the ions on the circular orbit are shifted in the direction orthogonal to the circular orbital plane by the deflector of (2) described above, the spiral trajectory is fixed by the deflector. Cannot make changes.

  In the spiral orbital TOFMS, it is useful to change the number of ion circulations. Changing the number of laps means changing the total flight distance. On the other hand, the total flight distance affects the sensitivity and the mass resolution. The longer the total flight distance, the lower the sensitivity and the higher the mass resolution. Therefore, by changing the number of laps, the conflicting sensitivity and mass resolution can be adjusted to be optimal for ion analysis.

From these facts, it is important how to realize a time-of-flight mass spectrometer that can change the number of turns of ions that draw a spiral trajectory.
The present invention has been made to solve the above-described problems caused by the background art, and an object of the present invention is to provide a time-of-flight mass spectrometer capable of changing the number of ions that draw a spiral trajectory.

In order to solve the above-described problems and achieve the object, a time-of-flight mass spectrometer according to the first aspect of the present invention is such that ions ejected from an ion source fly in a circular orbit by the action of a sector electric field. Meanwhile, a part of the orbit, a time-of-flight mass spectrometer that draws a spiral orbit by shifting the orbital plane in a direction orthogonal to the orbital plane of the orbit, located on the orbit, A detector for detecting ions, and detector moving means for moving the detector in the orthogonal direction while maintaining the position on the orbital plane;
It is characterized by providing.

In the first aspect of the present invention, the detector moving means moves the detector of ions located on the circular orbit in the orthogonal direction while maintaining the position of the circular orbit.
According to a second aspect of the present invention, in the time-of-flight mass spectrometer according to the first aspect of the present invention, the detector includes an electrical impedance matching circuit.

  A time-of-flight mass spectrometer according to a third aspect of the present invention is the time-of-flight mass spectrometer according to the first or second aspect, wherein the detector moving means moves the detector to an in-plane perpendicular to the orbital plane. It is characterized by comprising a support arm which is supported by

In the third aspect of the invention, the detector is supported by the support arm.
According to a fourth aspect of the present invention, in the time-of-flight mass spectrometer according to the third aspect of the invention, the detector moving unit includes a driving unit that moves the support arm in the orthogonal direction. It is characterized by.

According to the fourth aspect of the present invention, the support arm is moved by the driving means.
A time-of-flight mass spectrometer according to a fifth aspect of the invention is the time-of-flight mass spectrometer according to the fourth aspect of the invention, wherein the driving means supports the support arm and has a screw hole and the support pedestal. Is provided with a threaded rod penetrating the screw hole for moving the screw in the orthogonal direction.

In the fifth aspect of the present invention, the driving means supports the support arm by the support base having a screw hole, and moves the support base through the threaded rod passing through the screw hole.
A time-of-flight mass spectrometer according to a sixth aspect of the present invention is the time-of-flight mass spectrometer according to the fifth aspect of the present invention, wherein the threaded rod includes a handle for manually rotating the thread groove.

In the invention according to claim 6, the threaded rod is rotated by the handle.
A time-of-flight mass spectrometer according to a seventh aspect of the invention is the time-of-flight mass spectrometer according to the fourth aspect of the invention, wherein the drive means includes automatic movement means for automatically moving the support arm in the orthogonal direction. It is characterized by that.

In the invention according to claim 7, the driving means moves the support arm by the automatic moving means.
A time-of-flight mass spectrometer according to the invention described in claim 8 is the time-of-flight mass spectrometer according to claims 5 and 7, wherein the automatic moving means is mechanically connected to the threaded rod. It is a motor that rotates a thread groove.

In the invention according to claim 8, the automatic moving means is a motor mechanically connected to the threaded rod.
The time-of-flight mass spectrometer according to the invention described in claim 9 is the invention according to claim 7 or 8, wherein the time-of-flight mass spectrometer determines the position of the detector in the orthogonal direction. The apparatus further includes a control unit that automatically controls the ions based on the number-of-circulations information that the ions repeatedly fly in the orbit.

  In the invention according to claim 9, the time-of-flight mass spectrometer automatically controls the position of the detector in the orthogonal direction based on the number-of-times information of ions.

  As described above, according to the first aspect of the present invention, the detector moving means moves the ion detector located on the orbit in the orthogonal direction while maintaining the position of the orbit. Therefore, a detector is placed at a position in the orthogonal direction according to the number of orbits of the orbit where ions fly, making the total flight distance of the ions variable, and thus making the mass resolution of the time-of-flight mass spectrometer variable and optimal. Can be.

  According to the second aspect of the present invention, the detector includes the electrical impedance matching circuit, so that reflection of the electrical signal can be suppressed, and generation of a pseudo ion peak can be prevented.

  According to the third aspect of the invention, since the detector is supported by the support arm, the detector moving means can be disposed without obstructing the trajectory of ions flying in the spiral trajectory.

According to the fourth aspect of the present invention, since the support arm is moved by the driving means, the detector can also be moved in the orthogonal direction.
According to the fifth aspect of the present invention, the drive means supports the support arm by the support base having the screw hole, and moves the support base through the threaded rod passing through the screw hole. A highly accurate movement can be performed with a simple configuration.

According to the sixth aspect of the present invention, since the threaded rod is rotated by the handle, it is possible to manually change the position of the support pedestal and thus the detector.
According to the seventh aspect of the invention, since the driving means moves the support arm by the automatic moving means, the position of the detector can be changed without manual intervention.

  According to the invention described in claim 8, since the automatic moving means is a motor mechanically connected to the threaded rod, the threaded rod can be rotated using an electrical signal.

  According to the ninth aspect of the invention, the time-of-flight mass spectrometer automatically controls the position of the detector in the orthogonal direction based on the information on the number of circulations of the ions by the control unit. In addition, the number of laps can be changed, and hence the mass resolution can be changed.

  The best mode for carrying out a time-of-flight mass spectrometer (abbreviated as TOFMS) according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited thereby.

  First, the overall configuration of the TOFMS according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating an appearance of the TOFMS according to the present embodiment. The TOFMS includes an ion optical system 10 and an ion source 20. Here, the ion optical system 10 and the ion source 20 form a vacuum container, and the inside is in a high vacuum state. The ion source 20 uses an ionized gas as a sample, forms an ion beam in which the gas is focused and accelerated, and injects the ion beam into the ion optical system 10. The ion optical system 10 causes an ion beam to fly on a circular orbit and separates and detects elements having different masses contained in the ion beam. Note that the xyz coordinate axes depicted in FIG. 2 are the same as the xyz coordinate axes shown in the drawings to be described later, and indicate common directions in the respective drawings.

  FIG. 3 is a diagram showing a cross section of the ion optical system 10 in the xz-axis direction. The ion source 20 emits an ion beam 22. The ion optical system 10 includes fan-shaped cylindrical electrodes 11 to 14 covered with a Mazda plate, deflectors 15 to 16 and a detection unit 17. The cylindrical electrodes 11 to 14 generate a cylindrical electric field inside and bend the traveling direction of the ion beam 22. Here, the cylindrical electrodes 11 to 14 are arranged at the four corners of the rectangular ion optical system 10 so that the flight path of the ion beam 22 draws an 8-shaped orbit.

  The deflectors 15 and 16 are disposed on the flight path between the cylindrical electrodes 12 and 13, and move the ion beam 22 in the y-axis direction orthogonal to the xz-axis cross section shown in FIG. 4 is a cross-sectional view showing the structures of the cylindrical electrodes 12 and 13 and the deflectors 15 and 16 on the xy-axis cross section orthogonal to the xz-axis cross section shown in FIG. In the deflectors 15 and 16, a plurality of paired electrode plates are arranged in the y-axis direction, and voltages having different polarities are applied to the deflector 15 and 16 on the paired electrode plates. The ion beam 22 that has passed through the cylindrical electrode 12 is bent in the positive direction of the y-axis by the deflector 15 and moves on the circular orbital surface, and then bent in the negative direction of the y-axis by the deflector 16 and is incident on the cylindrical electrode 13. Then, the flight of the new orbital surface moved in the y-axis direction is continued.

  In this way, the ion beam 22 draws a spiral trajectory that moves the orbital plane in the y-axis direction while flying in an 8-shaped orbit. The ion beam 22 sequentially moves in the y-axis direction along the orbital surface according to the number of orbits of the orbit, and maintains different flight paths while ensuring a long total flight distance. As a result, ions with different velocities are prevented from flying on the same flight path with a delay in circulation, and ions with different velocities, that is, masses, are measured in a temporal order proportional to the masses.

  The detection unit 17 is disposed on the flight path between the cylindrical electrode 11 and the cylindrical electrode 14 and detects ions flying on the circular orbit. FIG. 1 is an external view showing a configuration of the detection unit 17. The detection unit 17 includes a housing 46, a detector 41, and detector moving means. The detector moving means includes a support arm 42 and a driving means. The driving means includes a support pedestal 44, a guide rail 43. And a threaded rod 45. The drive means includes a handle 47 (not shown) which will be described later.

  The detector 41 is a detector for the ion beam 22 and uses a microchannel plate or the like. The support arm 42 is an arm that fixedly connects the detector 41 and the support pedestal 44, and the detector moving means including the support pedestal 44 does not interfere with the flight of the ion beam 22 located on the circular orbit in the z-axis direction. It is overhanging.

  The support base 44 supports the support arm 42 and the detector 41 and is movable in the y-axis direction along the guide rail 43 and the threaded rod 45. Here, the guide rail 43 prevents the support pedestal 44 from rotating in the xz axis plane, and as a result, the ion beam detection surface of the detector 41 is always orthogonal to the ion beam incident direction.

  The thread cutting bar 45 moves the support base 44 in the y-axis direction by the rotation operation of the thread groove by the operator. The support pedestal 44 is formed with a screw hole corresponding to the threaded rod 45. The casing 46 has a U-shape that fixes the detector moving means described above and does not obstruct the flight of the ion beam 22. The thread cutting bar 45 is rotated by a handle 47 on the back surface of the housing 46 (not shown).

  FIG. 5 is a cross-sectional view showing an xy-axis cross section of the detector 41. The detector 41 includes a microchannel plate 51, a matching circuit 52 and a shield 53. The microchannel plate 51 is an electron multiplier that detects ions. A large number of glass electrodes are arranged on the detection surface of the microchannel plate 51, and the incident ion beam 22 is detected and electronic amplification is performed.

  The matching circuit 52 is a matching circuit that performs electrical impedance matching between the input impedance of an electronic device such as an amplifier that is electrically connected to the subsequent stage via an electric cable and the output impedance of the microchannel plate 51. Compared with the input impedance of an electronic device such as an amplifier being about 50Ω, the electron current output from the microchannel plate 51 has characteristics as a current source and has a high output impedance. Therefore, when the microchannel plate 51 and the subsequent electronic device are electrically connected without passing through the matching circuit 52, reflection of the electric signal occurs.

  FIG. 6 is a diagram illustrating an example of an electrical signal detected by a subsequent electronic device when the matching circuit 52 does not exist. The vertical axis represents the signal intensity of the electric signal, and the horizontal axis represents the detection time of the electric signal. Here, the electric signal of the ion beam 22 detected by the microchannel plate 51 is shown as an ion peak 62. On the other hand, a reflected wave of an electric signal is generated at both ends of the connection due to a mismatch in electrical impedance between the microchannel plate 51 and the subsequent electronic device. The reflected wave generates a reflected pseudo ion peak 63 at a position on the time axis that is delayed from the ion peak 62 by about several tens of nsec, which is proportional to the length of the electric cable connecting the two. Here, the reflection quasi-ion peak 63 is not preferable in the case of TOFMS in which ions having different masses are separated and detected based on the position of the ion peak on the time axis.

  Returning to FIG. 5, the shield 53 is a metallic case including the microchannel plate 51 and the matching circuit 52. The shield 53 is electrically connected to the casing 46 and thus to the chassis of the ion optical system 10 to prevent an unnecessary electric field from being generated in the space near the shield 53. Thereby, the ion beam 22 passing through the vicinity of the detector 41 performs a stable flight without being affected by the orbit.

  Next, the operation of the detector moving means will be described with reference to FIG. FIG. 7 is a cross-sectional view showing a yz-axis cross section of the detection unit 17. The handle 47 connected to the housing 46 in FIG. 7 is connected to the threaded rod 45, and by manually rotating the handle 47, the support base 44 and thus the detector 41 move in the y-axis direction.

  Further, the plurality of ion beams 22 shown in FIG. 7 are beam positions for each turn of the ion beam 22 that moves in the y-axis direction on the orbital plane while drawing a helical orbit. Therefore, the position of the ion beam 22 having the number of circulations 1 to 5 is shown in order from the ion beam 22 located at the top.

  First, the operator determines the number of revolutions of the ion beam 22 in consideration of the mass resolution and sensitivity of the sample to be analyzed. Thereafter, the operator rotates the handle 47 and sets the detector 41 to which the support pedestal 44 is fixed to the ion beam position of the target number of revolutions in the y-axis direction. FIG. 7 shows a case where the detector 41 is set at an ion beam position where the number of laps is 1, as an example. Thereafter, the operator starts the operation of TOFMS and analyzes the sample.

  As described above, in this embodiment, the detector 41 including the matching circuit 52 is constituted by the support arm 42, the support base 44, the threaded rod 45, the handle 47, the guide rail 43, and the housing 46 that are detector moving means. Is positioned on the orbit of the ion beam 22 corresponding to the number of laps, the total flight distance of the detected ion beam 22 can be made variable, and the operator can control the mass resolution or sensitivity. You can do what you want.

  In the present embodiment, the threaded rod 45 is manually rotated by the handle 47. However, the handle 47 can be replaced with a motor to automatically control the position of the detector 41. In this case, the position of the detector 41 in the y-axis direction is automatically set based on the number-of-turns information of the orbital track set in the control unit that automatically controls the motor. Furthermore, the number of turns can be determined from setting information such as mass resolution or sensitivity set in the control unit by the operator, and the position of the detector 41 can be automatically set.

It is a block diagram which shows the detection part of embodiment. It is an external view which shows the external appearance of a time-of-flight mass spectrometer (TOFMS). It is sectional drawing which shows the cross section of the orbital surface where the ion of TOFMS flies. It is sectional drawing which shows the cross section of the deflector of TOFMS. It is sectional drawing which shows the cross section of the detector of embodiment. It is explanatory drawing which shows an example of the electrical signal received when a matching circuit does not exist. It is explanatory drawing which shows the movement of the detector of embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ion optical systems 11-14 Cylindrical electrodes 15 and 16 Deflector 17 Detection part 20 Ion source 22 Ion beam 41 Detector 42 Support arm 43 Guide rail 44 Support base 45 Threaded rod 46 Housing 47 Handle 51 Micro channel plate 52 Matching circuit 53 Shield 62 Ion peak 63 Reflected pseudo ion peak

Claims (9)

Ions ejected from the ion source fly in a circular orbit by the action of a sector electric field and draw a spiral trajectory by shifting the orbital plane in a direction orthogonal to the orbital plane of the orbital orbit in part of the orbit. A time-of-flight mass spectrometer,
A detector located on the orbit and detecting the ions;
Detector moving means for moving the detector in the orthogonal direction while maintaining the position on the track surface;
A time-of-flight mass spectrometer.   The time-of-flight mass spectrometer according to claim 1, wherein the detector includes an electrical impedance matching circuit.   The time-of-flight mass spectrometer according to claim 1, wherein the detector moving unit includes a support arm that supports the detector in a plane orthogonal to the orbital plane.   The time-of-flight mass spectrometer according to claim 3, wherein the detector moving unit includes a driving unit that moves the support arm in the orthogonal direction.   The said drive means is provided with the threaded rod penetrated by the said screw hole which supports the said support arm, and has the screw hole which moves the said support base in the said orthogonal direction which has a screw hole. Time-of-flight mass spectrometer.   The time-of-flight mass spectrometer according to claim 5, wherein the threaded rod includes a handle for manually rotating the thread groove.   The time-of-flight mass spectrometer according to claim 4, wherein the driving unit includes an automatic moving unit that automatically moves the support arm in the orthogonal direction.   The time-of-flight mass spectrometer according to claim 5 or 7, wherein the automatic moving means is a motor that is mechanically connected to the threaded rod and rotates a thread groove of the threaded rod.   The time-of-flight mass spectrometer further includes a control unit that automatically controls the position of the detector in the orthogonal direction based on the number of laps information in which the ions repeatedly fly around the orbit by the automatic moving unit. The time-of-flight mass spectrometer according to claim 7 or 8,

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