JP2008117546A - Time-of-flight mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect ions by separating ions having different masses mixed by catching up and passing while circling on an circular orbit. <P>SOLUTION: The ions separated from the circular orbit P are passed through a uniform magnetic field B formed between a pair of flat magnetic poles 7, and they are deflected in the direction perpendicular to their travelling direction in accordance with the masses of the ions by Lorentz's force. An array-shaped detector 6 is disposed so as to detect the ions which have single-dimensionally spread by this deflection. Thereby, the ions are three-dimensionally (in terms of time to reach the detector 6) separated in their travelling direction in accordance with the masses, and are three-dimensionally separated in the direction perpendicular to the travelling direction. In this manner, ions having different masses mixed while circling the circular orbit P can be surely detected, and thereby, analysis with high mass resolution can be performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a time-of-flight mass spectrometer, and more particularly to a time-of-flight mass spectrometer having a trajectory for orbiting ions.

  Generally, in a time-of-flight mass spectrometer, ions given a constant kinetic energy by an electric field are introduced into a flight space having a predetermined flight distance, and various ions are collected according to the flight time until reaching the detector. Separately detected for each mass to charge ratio. Since the difference in time of flight for two types of ions having a certain mass difference increases as the flight distance increases, the flight distance may be increased in order to obtain high mass resolution. However, due to physical restrictions such as the size of the apparatus, there is a limit in extending the flight distance in the conventional linear type or reflectron type configuration.

  In order to solve these problems, a multi-circulation type configuration has been proposed in recent years. For example, in the apparatus described in Patent Document 1, an elliptical circular orbit is formed using a plurality of toroidal sector electric fields, and ions are repeatedly circulated many times along the orbit to increase the flight distance. In such a configuration, the greater the number of times that the ions orbit the orbit, the longer the flight distance, and accordingly, the flight time becomes longer as a whole. Therefore, the mass resolution improves as the number of laps increases. However, in the configuration in which the same orbit is repeatedly flying as described above, ions with a smaller mass have a higher speed, so that ions with a smaller mass catch up with or overtake ions with a larger mass during the cycle. I will.

  Therefore, in order to avoid such a problem, Patent Document 2 proposes a configuration in which a spiral flight trajectory is formed by gradually shifting the trajectory for each lap instead of the same trajectory. In this device, a flight space that can circulate in a substantially regular hexagonal shape is formed by connecting six sector electric fields, a deflection electric field is provided between two adjacent sector electric fields, and ions passing therethrough are fan-shaped by the deflection electric field. The electric field is gradually shifted in the axial direction. When the ion trajectory is thus spiral, the arrival position of the ions is slightly shifted in the axial direction of the electric field for each round, so when ions are emitted from a predetermined position of the electric sector and guided to the detector, the predetermined number of times Only circulating ions can be introduced into the detector.

  However, in the above conventional configuration, in order to shift the flight trajectory in the axial direction of the sector electric field, a pair of parallel plane electrodes for forming a deflection electric field is required for each turn. A set of parallel planar electrodes will be required. Therefore, the structure becomes more complicated as the number of laps N is increased to increase the flight distance. In order to simplify the structure, only one set of parallel plate electrodes may be arranged in the deflection direction to form a deflection electric field. However, with such a structure, sufficient electric field strength cannot be obtained and the shape of the electric field ( Since equipotential lines are also disturbed, ions are not deflected as ideally, leading to performance degradation.

JP-A-11-195398 JP 2003-86129 A

  The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to fly in a circular orbit in a time-of-flight mass spectrometer that makes ions fly one or more times along a circular orbit. Time-of-flight mass spectrometry that ensures high mass separation performance by separating and detecting these ions with a simple structure even when catching up or overtaking ions with different masses Is to provide a device.

In order to solve the above-mentioned problems, the present invention is directed to a time-of-flight mass spectrometer that detects ions by detaching ions from the orbit after one or more turns along a predetermined orbit. ,
a) ion deflection means for forming a magnetic field or an electric field for dispersing ions separated from the circular orbit in a direction orthogonal or oblique to the traveling direction according to the mass;
b) detection means for detecting ions spatially dispersed by the ion deflection means;
It is characterized by having.

  In the time-of-flight mass spectrometer according to the present invention, the ion deflection unit may form a magnetic field in which ions are dispersed by Lorentz force with respect to passing ions.

  When ions with various masses (strictly, mass-to-charge ratio) are introduced into the orbit, the smaller the mass, the faster the flight speed. Large ions are delayed. That is, ions are separated according to their mass spatially when viewed on the entire orbit, and temporally when focusing on a certain point on the orbit. However, if the number of laps is large, ions with a high speed catch up with ions with a low speed and further overtake, and ions of different masses are mixed.

  When the mixed ions leave the orbit and go into an ion deflecting means, for example, a uniform magnetic field in which the magnetic lines of force are directed in a direction perpendicular to the direction of ion travel, the ions that are charged particles are affected by the magnetic field. The trajectory bends due to the Lorentz force in a direction perpendicular to both of the directions. Since the trajectory curve at this time depends on the mass or velocity of the ions, the ions are spatially dispersed according to the mass when passing through the ion deflection means. The detection means detects all or part of the spatially dispersed ions and outputs a detection signal corresponding to the amount of ions. If it is desired to detect ions only by focusing on a specific mass, it is sufficient to detect only a part of the ions. For the purpose of creating a mass spectrum in a predetermined mass range, all or spatially predetermined An array-like detection means in which a plurality of detection units are arranged in a straight line so as to detect ions in a range may be used.

  That is, in the time-of-flight mass spectrometer according to the present invention, ions are separated with high mass resolution in accordance with the mass while orbiting the orbit, and at that time, ions having different masses mixed due to the orbit characteristics. Are separated by the ion deflection means. The ion deflecting unit only needs to be able to separate ions having a relatively large mass, and therefore does not require high mass separation performance. As described above, according to the time-of-flight mass spectrometer according to the present invention, it is possible to sufficiently utilize the high mass resolution that is exhibited by rotating the ions many times along the orbit, and the mass of the ions is highly accurate. And a high-accuracy mass spectrum can be created.

  An electrode that generates an electric field instead of a magnetic pole that generates a magnetic field can also be used as the ion deflecting means. However, if the kinetic energy of ions incident in a uniform DC electric field is the same, it depends on the mass. Ion separation is not possible. Therefore, in that case, an operation that changes the magnitude of the orbital curvature according to the mass of ions (or the velocity of incident ions) may be performed, such as scanning the voltage applied to the electrodes.

  When the ion deflecting means is a magnetic pole, either a permanent magnet or an electromagnet may be used. However, if the magnetic field intensity is changed using an electromagnet, the mass resolution can be changed by changing the deflection amount for ions of the same mass. Can do.

  An embodiment of a time-of-flight mass spectrometer according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an ion optical system of a time-of-flight mass spectrometer according to the present embodiment. The three-dimensional coordinate axes of the X axis, the Y axis, and the Z axis that are orthogonal to each other are set as shown in FIG.

  In the time-of-flight mass spectrometer of this embodiment, a plurality of sets of circular electrodes 4 each having a fan-shaped inner electrode and an outer electrode as a set are arranged in the flight space 3 and formed by the respective circular electrodes 4. A circular orbit P in which ions can circulate many times is formed by the electric sector E. Ions emitted from the ion source 1 provided outside the circular orbit P are guided to enter the circular orbit P by the incident-side gate electrode 2, and ions orbiting the one or more circular orbits P are emitted from the emission side. The gate electrode 5 leaves the orbit P. In order to achieve such ion flight, a voltage generator (not shown) for applying a voltage to each of the circular electrode 4, the incident side gate electrode 2, and the emission side gate electrode 5 is provided.

  Ions having various masses are emitted from the ion source 1 at the same time under the same acceleration voltage, and are introduced into the orbit P through the incident-side gate electrode 2. The ion velocity depends on the mass, and the smaller the mass, the greater the velocity. Therefore, ions having a small mass are preceded while turning around the orbit P, and ions having a large mass are delayed. The difference in the distance on the orbit P is increased as the number of laps is increased. That is, the mass resolution improves as the number of turns increases.

  However, if the preceding ions catch up with the slow ions and further overtake them, ions of different masses are mixed on the circular orbit P, and the ions are removed from the circular orbit P by the exit-side gate electrode 5 at a certain timing. When separated, ions with different masses may be emitted simultaneously. Therefore, in this time-of-flight mass spectrometer, two parallel plate-shaped magnetic poles 7, one of which is the S pole and the other is the N pole, sandwiching the trajectory Q in which ions released from the circular orbit P travel linearly. Is arranged. The trajectory Q is parallel to the Z axis, the two magnetic poles 7 extend along the X axis-Z axis plane, and the direction of the magnetic lines of force in the magnetic field B formed between the magnetic poles 7 is the Y axis direction. Furthermore, an array-like detector 6 in which a large number of ion detectors are arranged one-dimensionally in the X-axis direction is disposed at the point where ions pass through the magnetic field B. FIG. 2 is a schematic perspective view of the magnetic pole 7 and the detector 6.

  FIG. 3 is an explanatory diagram of the behavior of ions in the magnetic field B formed by the magnetic pole 7. When the magnetic flux density of the magnetic field B by the magnetic pole 7 is b, the charge amount of ions incident on the magnetic field B is e, and the velocity of this ion is v, the force that the ions receive when passing through the magnetic field B, that is, the Lorentz force F becomes F = e · v · b. As described above, the traveling direction of the ions (the direction of velocity v) is the Z-axis direction, and the direction of the magnetic field lines is the Y-axis direction. Therefore, when the ions are positive ions (charges are positive), Acts in the X-axis direction. Therefore, by this Lorentz force, as shown in FIGS. 2 and 3, positive ions incident in the Z-axis direction are bent in the X-axis direction (upward) off the trajectory Q that can be taken when there is no magnetic field B. Proceed along the trajectory Q ′. Since the Lorentz force continues to act while passing through the magnetic field B, the ions draw a circular orbit with a radius R in the magnetic field B, and go straight after exiting the magnetic field B. This R is the cyclotron radius of the ion.

Now, as shown in FIG. 3, it is assumed that a uniform magnetic field exists in the Z-axis direction at 0 ≦ z ≦ 2l, and the detector 6 exists at a position of z = l + L. In this case, the ion deflection amount y2 at the position of the detector 6 by the magnetic field B is as follows.
y2≈L · α = L · (2l / v) · ωc (1)
Where ωc is the cyclotron frequency ωc = (e / m) · b (2)
Therefore, equation (1) can be rewritten as follows.
y2 = √ (e / 2m) · b / √V · 2lL (3)
However, l << L, V = m · v ² / 2e, and V is an ion incident voltage.

  In equation (3), since the ion incident voltage is constant, it can be seen that when the magnetic flux density b, that is, the strength of the magnetic field B is constant, the deflection amount y2 is inversely proportional to the square root of the mass m. That is, in a uniform magnetic field, the arrival position of ions in the X-axis direction is different on the detector 6 according to the ion mass m, and ions having different masses can be separated.

  Basically, the ions are separated according to the mass during many orbits around the orbit P as described above. At that time, a part of ions having different masses may be mixed due to catching up or overtaking of ions and may reach the magnetic pole 7 in this state, but such mixed ions are also separated for each mass when passing through the magnetic pole 7. Thus, it is detected by a different detection unit of the detector 6. Therefore, by analyzing the detection signals from the respective detection units of the detector 6, all or a desired mass range of ions can be separated for each mass, and the respective ion intensities can be calculated.

  As apparent from the equation (3), the deflection amount y2 also changes when the magnetic flux density b is changed. Therefore, if the magnetic pole 7 can be used as an electromagnet and the magnetic flux density can be changed by the applied voltage, the measurement can be performed more freely. You can raise the degree. Further, since the direction in which the Lorentz force acts is reversed depending on the polarity of the ions, when the ions are negative ions, the ions are deflected downward in FIG. Thus, if the magnetic pole 7 is used as an electromagnet so that the direction of the magnetic field (direction of the lines of magnetic force) can be reversed, it is possible to easily cope with both positive and negative ions.

  In the above embodiment, the array-like detector 6 is used. However, when measuring the ion intensity while paying attention only to a specific mass, one detector provided at an appropriate position on the X-axis. In this case, ions may be detected.

  As a method of deflecting ions that are charged particles as described above, it is also conceivable to use an electric field in addition to using a magnetic field. More specifically, for example, when parallel plate electrodes are arranged above and below the trajectory Q and a DC electric field is formed between the two electrodes, ions are deflected in the X-axis direction. However, since the amount of ion deflection does not depend on the mass in a DC electric field with a constant potential gradient, it is necessary to scan, for example, an applied DC voltage so that the amount of deflection changes according to the mass.

  It should be noted that the above embodiment is an embodiment of the present invention, and it is obvious that modifications, changes, additions, and the like as appropriate within the scope of the present invention are included in the scope of the claims of the present application.

The schematic block diagram of the ion optical system of the time-of-flight mass spectrometer by one Example of this invention. The schematic perspective view of the magnetic pole and detector in FIG. Explanatory drawing of the behavior of the ion within the magnetic field formed of a magnetic pole.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ion source 2 ... Incident side gate electrode 3 ... Flight space 4 ... Circulating electrode 5 ... Outgoing side gate electrode 6 ... Detector 7 ... Magnetic pole B ... Magnetic field E ... Fan-shaped electric field P ... Circulating orbit Q ... Orbit

Claims (2)

In a time-of-flight mass spectrometer that detects ions after they have made one or more rounds of flight along a predetermined orbit, and then desorbs ions from the orbit,
a) ion deflecting means for forming a magnetic field or an electric field for dispersing ions separated from the circular orbit in a direction orthogonal or oblique to the traveling direction according to its mass;
b) detection means for detecting ions spatially dispersed by the ion deflection means;
A time-of-flight mass spectrometer.   2. The time-of-flight mass spectrometer according to claim 1, wherein the ion deflection unit forms a magnetic field in which ions are dispersed by Lorentz force with respect to passing ions.

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