JP2011146180A - Time-of-flight mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure ions in a wide mass charge ratio range with high resolution by forming a flight orbit which has a long flight distance and never causes passing of ions by a simple electrode structure. <P>SOLUTION: One of sector electric fields E1, E2 capable of forming multi-revolution orbits is disposed with shift by a distance d in a direction orthogonal to parallel linear flight portions 11, 12, and induction decelerators 7, 8 for decelerating ions by a fixed degree are disposed on the linear flight portions 11, 12, whereby a quasi-orbit portion 4 is formed. Ions are decelerated before incident on the sector electric fields E1, E2, whereby the ions are flown along a circular orbit the radius of which is reduced by d for each half round, and ions which have arrived at the inner periphery in the sector electric field E1 reaches an ion detector 10 without entering to the next sector electric field E2. Thus, a flight orbit having a long traversable flight distance which is constant for all ions can be formed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a time-of-flight mass spectrometer, and more particularly to a time-of-flight mass spectrometer that forms a flight trajectory of ions using a plurality of sector electric fields.

  In general, a time-of-flight mass spectrometer measures the time required for ions to fly through a flight space of a certain distance based on the principle that ions accelerated with a constant energy have a flight speed corresponding to the mass. The mass-to-charge ratio (m / z value) of ions is calculated from the flight time. Therefore, the mass resolution can be improved as the flight distance of ions is increased. Utilizing this, a multi-turn time-of-flight mass spectrometer that achieves high mass resolution by extending the flight distance of ions by increasing the number of turns using a multi-turn ion optical system that makes multiple turns of ions along a closed orbit Have been developed (see Patent Documents 1, 2, 3, etc.).

  Although the multi-round time-of-flight mass spectrometer can achieve high mass resolution, there is a drawback derived from the fact that the ion flight path is a closed orbit. The drawback is that, as the ions circulate, ions that fly faster because the mass-to-charge ratio is small overtake slower ions on a closed orbit because the mass-to-charge ratio is large. When the time-of-flight spectrum is measured in a state where the overtaking of ions occurs in this way, peaks corresponding to different laps, that is, peaks corresponding to different flight distances are mixed on the spectrum. In that case, since the mass-to-charge ratio of ions and the flight distance cannot be uniquely determined, the mass spectrum cannot be obtained directly from the time-of-flight spectrum.

  Due to the above-mentioned drawbacks, the conventional multi-orbit time-of-flight mass spectrometers have only observed ions with a narrow mass-to-charge ratio range that do not pass on the orbit among the ions generated by the ion source. It is common to use

  Further, in order to solve the above-mentioned problem, there has been conventionally known a mass spectrometer that forms a one-stroke-like trajectory instead of a completely closed trajectory by shifting the trajectory little by little in each round. In the mass spectrometer described in Patent Document 4, a spiral trajectory is formed by slightly shifting the trajectory for each revolution in a direction orthogonal to the surface on which the orbit is placed. However, in such an ion optical system that forms a spiral orbit, it is difficult to introduce ions into the orbit and to extract ions from the orbit, and there is a problem that an electrode for forming an electric field becomes large. .

  On the other hand, in the mass spectrometer described in Patent Document 5, a spiral electric trajectory is formed by passing a different electric sector electric field every time an ion circulates. However, in order to form such an orbit, an electrode having a complicated structure in which a plurality of cylindrical electric fields that are concentric and slightly different in radius of rotation are stacked in multiple layers is used, and the electrode becomes considerably heavy and large. In addition, it is difficult to produce an electrode, and it is inevitable that the electrode becomes quite expensive.

  Furthermore, in the mass spectrometer described in Patent Document 5, the time convergence of ions having the same mass-to-charge ratio (the time-of-flight width of ion packets having the same mass-to-charge ratio on the reference plane on the orbit is made constant regardless of the orbit. Can be ensured, but the circulation time of ions having the same mass-to-charge ratio changes for each revolution (that is, there is no isochronism). Therefore, the data processing for conversion from the time-of-flight spectrum to the mass spectrum is complicated. Further, if the circulation of ions having the same mass-to-charge ratio is isochronous, for example, Fourier transform or an alternative analysis method based on the multiple circulation signal obtained by the ion nondestructive detector for the circulating ions Although it is possible to calculate the mass-to-charge ratio of various ions using (see, for example, Non-Patent Document 1), there is also a problem that such a method cannot be used due to lack of isochronism.

Japanese Patent Laid-Open No. 11-1335060 Japanese Patent Application Laid-Open No. 11-135061 JP-A-11-195398 JP 2000-243345 A JP 2000-243346 A

Nishiguchi, Ueno, “New Multiple Circulation Mass Spectrometry Using Multiple Circulation Ion Optics”, Shimazu Review, Vol. 66, No. 1, No. 2, September 30, 2009

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to use an ion optical system with a simple structure that can be manufactured easily and at a low cost, and is long in accordance with a circular orbit. To provide a time-of-flight mass spectrometer capable of analyzing ions with a wide mass-to-charge ratio range with high mass resolution by forming a flight trajectory that does not cause overtaking of ions while ensuring a flight distance. .

  Another object of the present invention is to realize an orbit capable of obtaining a long flight distance according to the orbit while ensuring isochronous orbit of ions having the same mass-to-charge ratio, and uses an ion nondestructive detector. It is an object of the present invention to provide a time-of-flight mass spectrometer capable of acquiring a mass spectrum with a high mass resolution for a wide mass-to-charge ratio range using ion detection and data processing.

In order to solve the above-mentioned problems, the present invention provides a final electric sector in which ions pass alternately between a fan-shaped electric field that draws an arc-shaped trajectory and a linear flight section that draws a linear trajectory between adjacent fan-shaped electric fields. A time-of-flight mass spectrometer using a plurality of sectoral electric fields capable of forming a flight trajectory in which ions can repeatedly circulate by re-entering the sectoral electric field where the ions exiting the electric field are first incident. In a time-of-flight mass spectrometer in which there are one or more pairs of straight flight parts parallel to each other,
1 to 2 included in the first group when a plurality of sector electric fields are divided into two groups of the first and second groups on the plane on which the straight flight units parallel to each other are placed. And the one or more fan-shaped electric fields included in the second group are shifted by a predetermined distance in a direction orthogonal to the parallel flight parts parallel to each other, and
Acceleration / deceleration means is provided on the trajectories of the linear flight parts parallel to each other to give constant energy to ions or to deprive ions of constant energy,
A spiral flight trajectory is formed by reducing or expanding the radius of curvature of an arc-shaped trajectory through which ions pass each time an ion enters a predetermined sectoral electric field, and for each revolution for ions having the same mass-to-charge ratio. The feature is that the lap times are equal.

  In the time-of-flight mass spectrometer according to the present invention, the flight trajectory formed by a plurality of sector electric fields does not go around the same trajectory, but at least the same ions return to the sector electric field where the ions first entered. Since it is incident again on the sector electric field, the formed orbit is called a quasi-circular orbit.

  In the time-of-flight mass spectrometer according to the present invention, the shape (rotation angle and rotation radius) of the plurality of fan electric fields is the same as that in the case of forming a circular orbit capable of multiple laps, but the relative positions of the plurality of fan electric fields. The relationship is different from the case where a multi-circular orbit is formed. That is, in general, when a multi-circular orbit is formed, ions are incident on the central axis (a center line between a pair of outer electrodes and inner electrodes) of a sector electric field, and the center from the sector electric field Ions exit along the axis. On the other hand, in the time-of-flight mass spectrometer according to the present invention, the one or more sector electric fields included in the first group and the one or more sector electric fields included in the second group are shifted by a predetermined distance. Therefore, the central axes of the two sector electric fields belonging to different groups across the straight flight part do not exist on a straight line. Therefore, when ions exit from the sector electric field belonging to one group along the central axis and enter the sector electric field belonging to the other group, the ions cannot enter the central axis of the sector electric field, The light enters the outer peripheral side or the inner peripheral side with respect to the central axis. That is, ions are incident at a position where the orbit radius (curvature radius) is different from the central axis.

  When ions are not accelerated or decelerated in the middle, ions that are incident off the central axis of the sector electric field as described above cannot maintain the orbital radius at the time of incidence in the sector electric field. On the other hand, in the time-of-flight mass spectrometer of the present invention, ions are accelerated (when the orbit shifts to the outer peripheral side when entering the next sector electric field) or decelerated (incident to the next sector electric field) in the straight flight part. When the trajectory is shifted to the inner circumference side), the ions incident on the electric sector form an arc-shaped trajectory while maintaining the same trajectory radius as the incident time. As a result, the radius of curvature of the arc-shaped trajectory through which the ions pass is reduced or expanded every time the ions are incident on at least the same sector electric field, and as a result, the outer peripheral side is directed to the inner peripheral side or the inner peripheral side is changed to the outer peripheral side. A spiral quasi-circular orbit toward the side is formed.

  Further, in such a spiral quasi-circular orbit, the flight distance of one round of ions changes every round (each time it enters the same electric sector), but when the flight distance of ions becomes short, for example, The ions are decelerated by the amount and the flight speed is slowed down. For this reason, the flight time of ions required for one round is the same for ions having the same mass to charge ratio. That is, the isochronism of the lap is maintained.

  Since the mass-to-charge ratio of the ions to be analyzed covers a wide range, the ions fly on the quasi-circular orbit with a wide time spread at various speeds. In order to accurately obtain the mass-to-charge ratio from the flight time, it is necessary to provide isochronism for all the ions to be analyzed and to maintain time convergence. For this purpose, it is preferable that the amount of change in ion kinetic energy during acceleration and deceleration is constant without depending on the mass-to-charge ratio or the flight speed. Therefore, it is preferable to use a DC acceleration / decelerator instead of a high-frequency accelerator / decelerator for the acceleration / deceleration means. Specifically, it is possible to use one that generates an electric field that is constant in the ion traveling direction, specifically, that has a constant time derivative.

  According to this, ion packets having the same mass-to-charge ratio have isochronism and time convergence is maintained regardless of the number of circulations. Therefore, for example, when converting a time-of-flight spectrum obtained based on a detection signal obtained by detecting ions after a predetermined number of times of orbiting the quasi-circular orbit into a mass spectrum, the processing is facilitated and the accuracy is improved.

  Further, as one aspect of the time-of-flight mass spectrometer according to the present invention, the plurality of sector electric fields are respectively cylindrical, spherical, or toroidal inner and outer electrodes having concentric and equal rotation angles and radii of curvature. It can be formed between a pair of electrodes.

  Further, in the time-of-flight mass spectrometer according to the present invention, by relatively shifting the two sector electric fields sandwiching the straight flight part, through the open space formed in front of the incident end surface or the exit end surface of the opposing sector electric field, A configuration may be adopted in which ions are incident on a position serving as an entrance end of a one-stroke writing flight trajectory, or ions are ejected from a position serving as an exit end of a one-stroke writing flight trajectory.

  According to this configuration, when introducing ions from an external ion source or the like into the flight trajectory as described above formed by a sector electric field, or when taking ions out of the flight trajectory in time, Does not require electric fields that change (eg, turn on and off). Therefore, the configuration of the entire electrode for forming the flight trajectory is simplified, and the radius of curvature of the trajectory is reduced or increased every time ions are incident on a different group of electric electric fields or in each lap, Eventually, when the radius of curvature of the orbit becomes less than a certain value or more than a certain value, the ions do not enter the next sector electric field and go off the quasi-circular orbit and go straight to the detector. be able to. According to this, the distance of the flight path can be made the same for all ions, and the relationship between the mass-to-charge ratio and the flight time can be uniquely determined.

  Also, as one aspect of the time-of-flight mass spectrometer according to the present invention, an ion detector that detects non-destructively ions that circulate in a spiral flight trajectory, and a periodic detection signal by the ion detector is processed. And a data processing means for obtaining a mass-to-charge ratio of each ion.

  As the ion detector, an induced charge detector, an induced current detector, or the like can be used. Further, the data processing means may perform an operation for converting a periodic component included in the signal into a time component by using, for example, Fourier transform or autocorrelation function. According to this, since the detection frequency of the same ions increases to twice the number of times of rotation, the S / N of the detection signal can be improved in principle, and an improvement in the accuracy of the mass spectrum can be expected.

  The ion nondestructive detector as described above does not destroy ions when detecting the presence of ions, but deprives part of the kinetic energy of ions. On the other hand, in the time-of-flight mass spectrometer according to the present invention, it is possible to impart kinetic energy to ions by acceleration / deceleration means. Therefore, the ions move to compensate for the energy lost from the ions by ion detection. Isochronism can be maintained by applying energy.

  Furthermore, in one aspect of the time-of-flight mass spectrometer according to the present invention, the one or more sector electric fields included in the first group are compared with one or more sector electric fields included in the second group. Control means for controlling the acceleration / deceleration means so as to change the energy imparted to or taken away from the ions as the distance is changed by the moving means, and the moving means for moving in a direction orthogonal to the straight flight parts parallel to each other. And means.

  According to this configuration, it is possible to change the number of times the ions orbit around the quasi-circular orbit by appropriately adjusting the amount of movement by the moving means (that is, the amount of deviation of the opposing electric field between the two groups). It is. For example, in the device described in Patent Document 5, the number of laps is uniquely determined in terms of the device configuration, but in the above configuration according to the present invention, the number of laps can be changed, so that the mass resolution can be changed according to the analysis purpose. . Further, by setting the amount of deviation of the opposing electric sector fields between the two groups to zero, it is possible to form a complete circular orbit instead of a spiral quasi-circular orbit.

  In principle, there is no limit to the number of laps when a complete orbit is used, but in this case, overtaking of ions occurs, so that the ion nondestructive detector described above may be used for ion detection. As described above, the loss of kinetic energy of ions accompanying non-destructive detection of ions can be compensated by the acceleration / deceleration means. Therefore, even if ion nondestructive detection is performed, isochronism is not impaired, and therefore a detection signal without an upper limit in the number of circulations can be obtained, and high mass resolution can be achieved.

  According to the time-of-flight mass spectrometer of the present invention, ions are swirled in a spiral shape, so that overtaking of ions does not occur during flight while ensuring a long flight distance, and ions in a wide mass-to-charge ratio range are high. It can be measured with mass resolution. Further, the shape of the sector electric field may be the same as that of a conventional full-circulation time-of-flight mass spectrometer, and a structure that is much simpler than the conventional multilayer electrode described in Patent Document 5 for forming a spiral trajectory. Therefore, the cost is low, and it is advantageous for light weight and downsizing. In addition, since it is a spiral flight trajectory, it is possible to ensure isochronism of the orbit, so conversion from a time-of-flight spectrum to a mass spectrum is easy, and in addition to periodic detection signals obtained by ion nondestructive detection It is also easy to obtain a mass spectrum by performing an analysis process.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram centering on the ion optical system of the time-of-flight mass spectrometer by 1st Example of this invention. Schematic of the induction speed reducer in FIG. The schematic block diagram centering on the ion optical system of the time-of-flight mass spectrometer by 2nd Example of this invention. FIG. 4 is a partial schematic view of an outer electrode of the cylindrical electrode in FIG. 3. The schematic block diagram centering on the ion optical system of the time-of-flight mass spectrometer by 3rd Example of this invention. The schematic block diagram centering on the ion optical system of the time-of-flight mass spectrometer by 4th Example of this invention. The schematic block diagram which shows an example of the state which moved the stage in the time-of-flight mass spectrometer by 4th Example. The schematic block diagram centering on the ion optical system of the time-of-flight mass spectrometer by 5th Example of this invention. Schematic which shows the example in the case of forming a multiple circulation orbit using the sector electric field shown in FIG.

[First embodiment]
A first embodiment of a time-of-flight mass spectrometer according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram centering on an ion optical system of a time-of-flight mass spectrometer according to the first embodiment, and FIG. 2 is a schematic diagram of an induction speed reducer in FIG.

  The time-of-flight mass spectrometer of the first embodiment includes an ion source 1, an ion guide 2, an ion trap 3, and sector electric fields E1 and E2 formed by cylindrical electrodes and induction speed reducers 7 and 8. A quasi-circular orbit 4, an ion extraction auxiliary magnet 9, and an ion detector 10 are provided.

  The ion source 1 generates ions to be analyzed from a target sample, and the ionization method is not particularly limited. For example, in a configuration in which this mass spectrometer is used as a detector for a gas chromatograph, the ion source 1 ionizes gas molecules by an electron impact ionization method or a chemical ionization method. In a configuration in which this mass spectrometer is used as a detector for liquid chromatography, the ion source 1 ionizes liquid molecules by atmospheric pressure chemical ionization or electrospray ionization. Furthermore, MALDI (Matrix Assisted Laser Desorption / Ionization) may be used when the analysis target molecule is a high molecular compound such as protein.

  The ion trap 3 is, for example, a three-dimensional quadrupole ion trap, which cools and temporarily accumulates ions generated in the ion source 1 and applies various kinetic energy at a predetermined timing to collect all ions at once. The light is emitted. That is, in this time-of-flight mass spectrometer, the ion trap 3 becomes a flight start point (starting point) of ions with respect to a one-stroke quasi-circular orbit described later.

  The quasi-circular orbit 4 includes two sets of cylindrical electrodes 5 and 6 and two induction decelerators 7 and 8 for forming sector electric fields E1 and E2, respectively. Each of the cylindrical electrodes 5 and 6 has a shape obtained by cutting a concentric double cylindrical body by a plane including a central axis of a concentric circle so that the rotation angle is 180 °, and the inner electrodes 5a and 6a and the outer electrodes 5b having different curvature radii. , 6b is a pair. That is, the cylindrical electrodes 5 and 6 have exactly the same shape. For example, in the cylindrical electrode 5, when a predetermined DC voltage is applied to each of the inner electrode 5a and the outer electrode 5b, a sector electric field E1 having a rotation angle of 180 ° is formed in a space between the electrodes 5a and 5b. Is done. Similarly, in the cylindrical electrode 6, when a predetermined DC voltage is applied to each of the inner electrode 6a and the outer electrode 6b, a sector electric field E2 having a rotation angle of 180 ° is formed in a space between the electrodes 6a and 6b. It is formed.

  As shown in FIG. 9, the cylindrical electrodes 5 and 6 (that is, the sector electric fields E1 and E2) used here can theoretically form a complete orbit capable of circulating ions indefinitely. is there. That is, as shown in FIG. 9, when a complete orbit is formed, ions are traveling straight between the ion incident end face E1in of the sector electric field E1 and the ion exit end face E2out of the sector electric field E2 without the action of an electric field or magnetic field. The ion incidence end face E2in of the sector electric field E2 and the ion emission end face E1out of the sector electric field E1 are opposed to each other across the straight flight part 12 where the ions travel straight without an electric or magnetic field acting. Opposite. Then, the ions pass through the arc-shaped center line (the center line between the inner electrode 5a and the outer electrode 5b) in the sector electric field E1 and go straight in the straight flight part 12, and the ions are arc-shaped in the sector electric field E2. Pass through the center line. Then, the ion travels straight at the straight flight part 11 and returns to the same position as the previous one again at the incident end face E1in of the sector electric field E1. This is because one round orbit is formed to achieve spatial convergence. In general, one round orbit is formed to achieve time convergence.

  On the other hand, in the time-of-flight mass spectrometer of the present embodiment, the cylindrical electrode 5 is in the state of plan view as shown in FIG. They are shifted by a distance d in a direction (vertical downward direction in FIG. 1) perpendicular to the traveling direction (horizontal direction in FIG. 1). In addition, an induction speed reducer 8 for decelerating the ions is arranged in the straight flight part 12 until the ions exiting the sector electric field E1 enter the sector electric field E2, and the ions exiting the sector electric field E2 enter the sector electric field E1. Similarly, the induction speed reducer 7 for decelerating the ions is also arranged in the straight flight part 11 up to this point. The configuration of the induction speed reducers 7 and 8 will be described later.

  The ion extraction auxiliary magnet 9 is configured so that after the ions flying along the quasi-circular orbit formed by the sector electric fields E1 and E2 substantially leave the quasi-circular orbit, The light is deflected slightly in the direction and guided to the ion detector 10. Of course, instead of deflecting ions by a magnetic field, ions may be deflected by an electrostatic field. The ion extraction auxiliary magnet 9 is provided because the ion detector 10 has a certain size or more and the installation place is limited, and the ion emission end face E1out of the sector electric field E1. If the ions that have exited from the inner peripheral side and proceed straight through the straight flight part 12 can be introduced into the ion detector 10 as they are, the ion extraction auxiliary magnet 9 and the electric field forming electrode that replaces the ion extraction auxiliary magnet 9 are unnecessary.

  The ion detector 10 is a detector such as a microchannel plate (MCP) having a high time resolution.

An analysis operation in the time-of-flight mass spectrometer of the present embodiment will be described.
Various ions generated by the ion source 1 are extracted from the ion source 1 and accumulated in the ion trap 3 through the ion guide 2. Then, the accumulated various ions are extracted from the ion trap 3 by a constant electric field at a predetermined timing and sent to the quasi-circular orbit unit 4. The ions first pass through the induction speed reducer 7 in the straight flight part 11 and enter the electric sector E1 formed by the cylindrical electrode 5. Due to the deviation of the distance d between the two sets of cylindrical electrodes 5 and 6 described above, the front of the outer peripheral portion of the incident end face E1in of the sector electric field E1 is an open space where the exit end face E2out of the sector electric field E2 does not exist. The ions that have passed through the straight flight unit 11 are incident as they are as shown in FIG. Therefore, in this configuration, an incident electrode or the like is not necessary in order to introduce ions from the outside (in this case, the ion trap 3) into the quasi-circular orbit.

  The curvature radius of the incident position of the first ion on the incident end face E1in of the sector electric field E1 is ρ, which is larger than the curvature radius of the center line of the sector electric field E1. However, by appropriately attenuating the kinetic energy of the ions incident through the induction decelerator 7, the ions travel in a trajectory having the same radius of curvature ρ in the sector electric field E1. As shown in FIG. 1, the ions exit the electric sector E <b> 1, are decelerated when passing through the induction speed reducer 8 in the linear flight unit 12, and enter the electric sector E <b> 2 formed by the cylindrical electrode 6. At this time, due to the displacement of the arrangement of the cylindrical electrodes 5 and 6 as described above, the incident end surface E2in of the sector electric field E2 is incident on the position closer to the inner electrode 6a by the distance d than the trajectory passed by the immediately preceding cylindrical electrode 5. . That is, the radius of curvature of the ion incident position on the incident end face E2in of the sector electric field E2 is ρ-d.

  The trajectory radius of ions in the sector electric field E1 immediately before is ρ, and if the kinetic energy of the ions remains as it is, the trajectory radius of ρ-d cannot be taken in the sector electric field E2. On the other hand, since the ions are decelerated (the kinetic energy is reduced) by the induction speed reducer 8 before entering the sector electric field E2, the orbital radius of ρ-d can be maintained in the sector electric field E2. .

  In the electric sector E 2, the ions travel after drawing a trajectory having the same radius of curvature ρ-d, are emitted, decelerated when passing through the induction speed reducer 7 in the linear flight unit 11, and formed again by the cylindrical electrode 5. Is incident on the electric sector E1. The incident position when re-entering the sector electric field E1 is offset by 2d toward the inner peripheral side from the first incident position. By decelerating ions by the induction speed reducer 7 before entering the electric sector E1, the orbital radius of ρ-2d can be maintained in the electric sector E1.

Here, the configuration and operation of the induction speed reducer (in this case, deceleration, but acceleration in the example described later) 7 and 8 will be described in more detail.
Since the mass-to-charge ratio m / z of the ions to be analyzed covers a wide range, the ions fly over the quasi-circular orbit as described above at various speeds with time spread. Since time convergence must be maintained for all the ions to be analyzed, the amount of change in ion kinetic energy during deceleration (or acceleration) must be constant regardless of the mass-to-charge ratio and flight speed. There is. Therefore, as the induction speed reducers 7 and 8, linear induction speed reducers having a configuration as shown in FIG. 2 are used.

This linear induction speed reducer is obtained by winding a coil around a donut-shaped wound core. A current i that changes at a constant rate is passed through the coil, thereby generating a constant electric field in the direction of ion travel. When the change amount of the kinetic energy of ions when passing through this induction decelerator is ΔW, the relationship between the change amount d of the orbital curvature radius per one cylindrical electrode and ΔW is given by the following equation (1).
(3-n) · (d / ρ) = ΔW / W (1)
Here, W is the kinetic energy of ions when entering the quasi-circular orbit. Further, n is an electric field gradient in the radial direction of the sector electric field, and is 1 when the cylindrical electrode is used as in the present embodiment, 2 when the spherical electrode is used, and 2 when the toroidal electrode is used. It has a corresponding value. The electric field gradient is given by the following equation (2).
n =-(ρ / E) · (∂Er / ∂r) (2)
Here, E is an electric field in the radial direction at the ion incident point.

  If the decelerating electric field of the induction decelerators 7 and 8 and the shift amount d of the position of the cylindrical electrodes 5 and 6 are set so as to satisfy the relationship of the expression (1), the radius of the quasi-circular orbit of the ions is 1 round. Decrease by 2d. In the first embodiment, since the quasi-circular orbit is formed by the two sector electric fields E1 and E2 having a rotation angle of 180 °, the radius of curvature is only d when ions are incident on one sector electric field from the other sector electric field. The light is incident on different positions, and the orbit radius decreases by d every half turn.

  That is, in the time-of-flight mass spectrometer of the present embodiment, as described above, the incident of ions that have returned to the sector electric field E1 again via the sector electric field E1 → the linear flight unit 12 → the sector electric field E2 → the linear flight unit 11. The position is guaranteed to shift by 2d toward the inner circumference. This is common to all ions, regardless of differences in mass to charge ratio or flight speed. In this way, the radius of the quasi-circular orbit of ions decreases by 2d for each turn, so that the gap (gap) width between the inner electrodes 5a, 6a of the cylindrical electrodes 5, 6 and the outer electrodes 5b, 6b is G, for example. In some cases, the ions will be emitted when they go around the quasi-circular orbit G / 2d. In this example, all the ions reach the emission point at the time of 3/2 rounds.

  Even in the quasi-circular orbit, the greater the number of laps, the longer the flight distance, but the number of laps is determined by the shift amount d of the sector electric fields E1 and E2. Therefore, in order to increase the number of turns, it is necessary to reduce the shift amount d. This shift amount d is determined by the spread of the ion flux in the horizontal direction (in the paper of FIG. 1) when ions are incident on the incident end face E1in and the thickness of the outer electrode 6b. Therefore, it is desirable to construct an ion optical system that minimizes the horizontal spread of the ion flux at the ion incident point. Thereby, the shift amount d of the two cylindrical electrodes 5 and 6 can be made as small as possible, and the number of laps can be increased to extend the flight distance.

  As described above, in the time-of-flight mass spectrometer according to the present embodiment, various ions emitted from the ion trap 3 are spirally formed from the outer circumference side to the inner circumference side in the quasi-circular orbit portion 4, that is, It flies along a one-stroke path where the flight paths do not overlap in the middle, and reaches the ion detector 10 via the magnet 9. Therefore, the flight distance is the same for all ions, and no overtaking of ions occurs due to a difference in flight speed on the way, and therefore, on the time-of-flight spectrum created based on the detection signal obtained by the ion detector 10. Can uniquely determine the flight time and the mass-to-charge ratio.

[Second Embodiment]
Next, a time-of-flight mass spectrometer according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a schematic configuration diagram focusing on the ion optical system of the time-of-flight mass spectrometer according to the second embodiment. FIG. 4 is a partial schematic view of the outer electrode of the cylindrical electrode in FIG. Components that are the same as or correspond to the components described in the first embodiment are denoted by the same reference numerals.

  The major difference from the first embodiment described above is that the dedicated deflection electrode 13 is used to inject ions into the quasi-circular orbit 4 and no ion extraction auxiliary magnet is provided. In the second embodiment, ions are made incident on the inner peripheral side by the deflecting electrode 13, and the inductive decelerator is applied to the linear flight units 11 and 12 so that the orbit radius is increased every time the ions enter the next electric sector. Instead, induction accelerators 14 and 15 are provided to accelerate ions. However, the configurations of the induction accelerators 14 and 15 are the same as those of the induction reducers 7 and 8 described above, except that the direction of the electric field generated by changing the direction of the current flowing through the coil is reversed.

An analysis operation in the time-of-flight mass spectrometer of the present embodiment will be described.
When ions are incident on the quasi-circular orbit 4 from the ion trap 3, it can be considered that the various ions do not spread in the time direction (in practice, when the distance from the ion trap 3 to the deflection electrode 13 is reached). Therefore, the deflection electric field is generated by applying a predetermined voltage to the deflection electrode 13 only while the ion group extracted from the ion trap 3 passes. Thereby, it can be considered that the deflection electrode 13 does not exist after ions are incident on the quasi-circular orbit from the ion trap 3.

  As in the first embodiment, each time the ions pass through the induction accelerators 14 and 15, the kinetic energy of the ions is increased by a fixed amount, so that the orbit radius is increased by d every time the electric fields E1 and E2 are passed. increase. Then, when the ions circulate around the quasi-circular orbit by the sector electric fields E1 and E2 2.5 times, the sector electric field E2 does not exist in front of the emission end face E1out of the sector electric field E1, and the ions traveling straight through the straight flight section 12 are cylindrical electrodes. 6 reaches the ion detector 10 by passing further outside the outer electrode 6b. However, in this example, since the shift amount d is small and the outer electrode 6b at the ion emission point may interfere with the ions, as shown in FIG. 4, a groove portion 61 through which ions pass is formed on the outer surface of the outer electrode 6b. It is formed. Thereby, the flight distance can be extended and the mass resolution can be improved as compared with the configuration of the first embodiment.

  In this embodiment, the ions fly two or more quasi-circular orbits by the sector electric fields E1 and E2, and the flight distance is longer in the second round than in the first round. In other words, in order to make ions fly in a spiral shape, the flight distance of ions is different for each lap, which is different from a complete lap orbit as shown in FIG. Therefore, if the flight speed of ions is constant, the time required for one lap will change for each lap, but in the present invention, when the flight distance of one lap is shortened for each lap, The flight speed is decreased step by step, and conversely, if the flight distance of one lap becomes longer for each lap, the flight speed of the ions is increased step by step, so the time required for one lap of the ions is kept constant. Can keep. Of course, the time itself depends on the mass-to-charge ratio of ions, and the smaller the mass-to-charge ratio, the shorter the time.

  That is, the time-of-flight mass spectrometer according to the present invention is characterized in that the isochronism of the lap is ensured despite the spiral flight trajectory. If the time-of-flight spectrum is not isochronous, the process of converting the time-of-flight spectrum into a mass spectrum must take into account changes in the time-of-flight for each lap that varies depending on the mass-to-charge ratio. Become. On the other hand, if the isochronism of the lap is ensured, the process of converting the time-of-flight spectrum into the mass spectrum is easy. In addition, since there is a particularly isochronous circulation, a configuration as in the following third embodiment is possible.

[Third embodiment]
FIG. 5 is a schematic block diagram centering on the ion optical system of the time-of-flight mass spectrometer according to the third embodiment of the present invention. Since the basic ion optical system is the same as that of the second embodiment, description thereof is omitted. This time-of-flight mass spectrometer is characterized by ion detection and detection signal processing. That is, in order to detect ions flying along the quasi-circular orbit, an ion nondestructive detector 31 is installed on the orbit. The ion nondestructive detector 31 is, for example, an inductive charge detector, and outputs a detection signal corresponding to the charge induced in the conductor when ions that are charged particles pass therethrough. Although there is no destruction of ions due to the detection, a part of the kinetic energy of the ions is lost. Therefore, the induction accelerators 14 and 15 generate an acceleration electric field larger than that of the second embodiment so as to compensate for the lost kinetic energy. provide. Thereby, the isochronism of the circulation is ensured.

  Since the ion nondestructive detector 31 can obtain a periodically multiplexed signal, the data processing unit 32 obtains the time of flight of each ion by performing, for example, a Fourier transform process for converting a frequency component into a time component, and further from here on. The mass to charge ratio of each ion is calculated. Based on this, a mass spectrum is created. Use various signal analysis methods used in mass spectrometers that combine general multi-circular ion optics and ion nondestructive detectors, such as using autocorrelation functions instead of Fourier transforms. Can do.

  For ease of explanation, the same ion optical system as in FIG. 3 is used in FIG. 5, but in order to perform accurate conversion using Fourier transform or autocorrelation function, the number of turns is considerably large. There is a need to. Therefore, in practice, the distance d is further reduced. In the third embodiment, since the ion detector 10 can be omitted, it is not necessary to consider taking out ions from the quasi-circular orbit.

[Fourth embodiment]
The distance d which is the deviation between the two sets of cylindrical electrodes 5 and 6 and the amount of change in the kinetic energy of ions when passing through the induction decelerator (or induction accelerator), ΔW, has the relationship of the above equation (1). Since the radius of curvature of the ion trajectory in the sector electric fields E1 and E2 is reduced or enlarged by a distance d every half turn, the number of turns can be increased by reducing d. The flight distance from when ions exit from the ion source 1 to reach the ion detector 10 depends on the number of laps, and the mass resolution improves as the number of laps increases. On the other hand, increasing the number of laps increases the time taken to obtain the mass spectrum. Therefore, it may be convenient to adjust the mass resolution according to the purpose of analysis. The fourth embodiment shown in FIG. 6 is an example of a time-of-flight mass spectrometer with variable mass resolution.

  The cylindrical electrode 5 (5a, 5b) is installed on a stage 41 that can move in a direction orthogonal to the straight flight units 11 and 12, and the stage 41 is driven by a stage drive unit 42 including a motor and the like. On the other hand, the induction accelerators 14 and 15 form an electric field that accelerates ions by the current supplied from the acceleration / deceleration current supply unit 43. The control unit 44 controls the operations of the stage drive unit 42 and the acceleration / deceleration current supply unit 43 based on, for example, an instruction of the required mass resolution given from the input unit 45, so that the flight trajectory that can realize the required mass resolution is obtained. Form. For example, FIG. 6 shows an example in which ions are detected by being emitted from a quasi-circular orbit after 2.5 laps, as in FIG. On the other hand, when the required mass resolution is lowered, the control unit 44 increases the distance d by the stage driving unit 42. Further, the acceleration / deceleration current supply unit 43 is controlled so as to adjust the kinetic energy so as to satisfy the expression (1) according to the distance d. As a result, as shown in FIG. 7, the ions are changed so as to be detected after being emitted from the quasi-circular orbit after 1.5 laps. Of course, also at this time, the kinetic energy imparted to the ions can be adjusted as appropriate to ensure isochronism of the circulation.

  By setting the distance d to 0 in the configuration of FIG. 6, it is possible to form a complete orbit instead of a spiral orbit. In this case, since a problem of overtaking of ions occurs, it is preferable to perform ion detection by an ion nondestructive detector as in the third embodiment.

[Fifth embodiment]
Each of the first to fourth embodiments is an example in which the shapes of the two sector electric fields E1 and E2 (that is, the cylindrical electrodes 5 and 6) forming the quasi-circular orbit are the same. It is possible to adopt a configuration in which is 3 or more and the shapes are not the same. FIG. 8 shows one example of such a configuration, in which three sector electric fields E2, E3, and E4 are used.

  More specifically, in the time-of-flight mass spectrometer of the fifth embodiment, the ion optical system of the first embodiment and the sector electric field E2 are the same, and the sector electric field E1 is divided into two sector electric fields E3 and E4. Has been. The sum of the rotation angles of the sector electric field E3 formed by the cylindrical electrode 20 (inner electrode 20a, outer electrode 20b) and the sector electric field E4 formed by the cylindrical electrode 21 (inner electrode 21a, outer electrode 21b) is 180 °. The positions of the incident end face E3in of the sector electric field E3 and the exit end face E4out of the sector electric field E4 need to be matched with the incident end face E1in and the exit end face E1out of the sector electric field E1. Therefore, here, the rotation angles of the cylindrical electrodes 20 and 21 are both set to 90 °, and the radius of curvature of their center lines is made smaller than the radius of curvature of the cylindrical electrode 5 so that the linear flight portion 22 is formed between the sector electric fields E3 and E4. Secured.

  Since the radius of curvature of the center line of the sector electric field E2 is different from the radius of curvature of the center lines of the sector electric fields E3 and E4, the degree of deceleration in the induction decelerators 7 and 8 is not the same, and is appropriately adjusted according to the radius of curvature. Although it is necessary, the radius of the orbit decreases by d every time it makes a semicircular orbit, so that a one-stroke flight trajectory can be formed as in the first embodiment.

  Furthermore, it is possible to adopt a configuration in which the number of sector electric fields is increased, but in order to form the quasi-circular orbit as described above, the following conditions must be satisfied. That is, as shown in FIG. 1, FIG. 3, and FIG. 5, a plurality of sector electric fields can form a multi-circular flight trajectory, and there are at least one set of straight flight parts parallel to each other. Is essential. In that case, a plurality of sector electric fields can be divided into two groups with the one set of straight flight sections as a boundary, and the entire sector electric field belonging to one group is compared to the sector electric field belonging to the other group. What is necessary is just to arrange | position by the distance d in the direction orthogonal to this straight flight part. There is no upper limit to the number of sector electric fields that belong to one group. In addition, in the linear flight part connecting between different groups as described above, an induction accelerator is arranged when the orbit radius is increased for each lap, and an induction decelerator is arranged when the orbit radius is reduced for each lap, A certain amount of kinetic energy is increased or decreased in the passing ions.

  The above-described embodiments are merely examples of the present invention, and it is obvious that changes, modifications, and additions are appropriately included in the scope of the claims of the present application within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Ion source 2 ... Ion guide 3 ... Ion trap 4 ... Semi-circular orbit part E1, E2, E3, E4 ... Fan-shaped electric field 5, 6, 20, 21 ... Cylindrical electrode 5a, 6a, 20a, 21a ... Inner electrode 5b, 6b, 20b, 21b ... outer electrode 61 ... groove 7, 8 ... induction speed reducer 9 ... ion extraction auxiliary magnet 10 ... ion detector 11, 12, 22 ... linear flight part 13 ... deflection electrodes 14, 15 ... induction accelerator 31 ... Ion non-destructive detector 32 ... Data processing part 41 ... Stage 42 ... Stage drive part 43 ... Acceleration / deceleration current supply part 44 ... Control part 45 ... Input part

Claims (6)

Ions that alternately pass through a fan-shaped electric field in which an ion forms an arc-shaped trajectory and a linear flight section in which ions form a linear trajectory between adjacent fan-shaped electric fields, and the ions that have exited the last fan-shaped electric field first A time-of-flight mass spectrometer using a plurality of sectoral electric fields that can form a flight trajectory in which ions can repeatedly circulate by re-entering the incident sectoral electric field, wherein the orbits that can be circulated are parallel to each other In a time-of-flight mass spectrometer where one or more straight flight parts exist,
1 to 2 included in the first group when a plurality of sector electric fields are divided into two groups of the first and second groups on the plane on which the straight flight units parallel to each other are placed. And the one or more fan-shaped electric fields included in the second group are shifted by a predetermined distance in a direction perpendicular to the straight flight parts parallel to each other, and
Acceleration / deceleration means for imparting energy to ions or depriving energy from ions is provided on the trajectories of the linear flight parts parallel to each other,
Each time an ion enters a predetermined sectoral electric field, the radius of curvature of the arcuate trajectory through which the ion passes is reduced or expanded to form a spiral flight trajectory, and for each revolution for ions of the same mass to charge ratio A time-of-flight mass spectrometer characterized in that the lap times are equal. The time-of-flight mass spectrometer according to claim 1,
The time-of-flight mass spectrometer is characterized in that the acceleration / deceleration means generates a predetermined electric field in the traveling direction of ions. The time-of-flight mass spectrometer according to claim 1 or 2,
Each of the plurality of sector electric fields is formed between a pair of electrodes made of a cylindrical, spherical, or toroidal inner electrode and outer electrode having concentric and equal rotation angles and curvature radii. A time-of-flight mass spectrometer. The time-of-flight mass spectrometer according to any one of claims 1 to 3,
By displacing the two sectoral electric fields sandwiching the straight flight part, ions pass through the open space formed in front of the incident end face or the exit end face of the opposing sectoral electric field at the position that becomes the entrance end of the spiral flight trajectory. A time-of-flight mass spectrometer characterized in that ions are emitted from a position that becomes an exit end of a spiral flight trajectory. A time-of-flight mass spectrometer according to any one of claims 1 to 4,
An ion detector that non-destructively detects ions circulating in a spiral flight trajectory, and a data processing means for obtaining a mass-to-charge ratio of each ion by processing a periodic detection signal from the ion detector; A time-of-flight mass spectrometer. A time-of-flight mass spectrometer according to any one of claims 1 to 5,
Moving means for moving one or more fan electric fields included in the first group in a direction perpendicular to the mutually parallel straight flight sections with respect to one or more fan electric fields included in the second group;
Control means for controlling the acceleration / deceleration means so as to change energy applied to or taken away from ions as the distance is changed by the moving means;
A time-of-flight mass spectrometer.

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