JP3683761B2 - Time-of-flight mass spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a time-of-flight mass spectrometer (TOFMS).
[0002]
[Prior art]
In a time-of-flight mass spectrometer (TOFMS), based on the fact that sample ions accelerated with a constant acceleration energy have a flight speed corresponding to the mass, the time of flight required to fly a certain distance is measured and the mass is measured. Ask.
[0003]
The resolution of this time-of-flight mass spectrometer is proportional to the flight distance of ions when the ion source conditions are the same. Therefore, in order to achieve high resolution, the flight distance may be increased, but this usually leads to an increase in the size of the apparatus.
[0004]
Therefore, in order to achieve both a long flight distance and a reduction in the size of the apparatus, for example, a U-turn is performed by changing the flight direction of ions using an electric field. Furthermore, there is an attempt to realize a long flight distance by constructing a closed trajectory by increasing the number of electric fields and circulating ions one or more times on this trajectory.
[0005]
[Problems to be solved by the invention]
In this way, when configuring a circular orbit, the key is a mechanism for entering and exiting ions with respect to a closed orbit. That is, there are a mechanism for injecting ions into a closed ion trajectory and a technique for ejecting ions from the circular trajectory toward the detector.
[0006]
In view of the above-described points, the object of the present invention is to have a closed trajectory around which ions circulate, and by implanting ions into this closed trajectory and taking them out, the flight distance can be increased and the apparatus can be downsized. It is to provide a time-of-flight mass spectrometer.
[0007]
[Means for Solving the Problems]
In order to achieve this object, the present invention is characterized in that an ion trap is disposed on the orbit in a time-of-flight mass spectrometer that performs mass analysis by flying sample ions along a closed orbit.
[0008]
The ion trap is composed of a pair of end cap electrodes arranged opposite to each other and a ring electrode arranged between the end gap electrodes, and the pair of end gap electrodes has a passage opening through which ions pass. It is characterized by being provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an ion optical diagram showing an example of a time-of-flight mass spectrometer embodying the present invention. In FIG. 1, four fan-shaped electric fields E1, E2, E3, and E4 whose turning angles are smaller than 180 ° are arranged in a curved portion of the figure 8, thereby forming a closed ion trajectory A having a figure eight shape. . This orbit A is composed of circular orbits A1 to A3 in the four sector electric fields E1 to E4 and four rectilinear orbits A12, A23, A34 and A41 connecting the sector electric fields.
[0010]
An ion trap 1 is disposed in the middle of the straight trajectory A41 between the sector electric fields E1 and E4. As a basic configuration, the ion trap 1 is opposed to a ring electrode 2 disposed so that an ion trajectory (straight traveling trajectory A41) passes through the center axis of the ring, and spaced apart so as to sandwich the ring electrode 2 therebetween. And a pair of end cap electrodes 3 and 4. A space surrounded by the end cap electrodes 3 and 4 inside the ring electrode 2 becomes a trap region. Passage ports 5 and 6 are provided at positions intersecting the ion trajectories of the end cap electrodes 3 and 4 so that ions can pass through the ion trap. Furthermore, an introduction tube 7 for introducing the sample gas into the trap region and an electron gun 8 for ionizing the introduced sample gas by electron impact are provided.
[0011]
FIG. 2 is a diagram showing an outline of a circuit configuration for supplying power to the ion trap 1. As shown in FIG. 2, the ring electrode 2 and the end cap electrodes 3 and 4 are supplied with voltages (including ground) in three types of modes a, b, and c via three-contact changeover switches S2, S3, and S4 that are linked. Are supplied respectively. That is, in the a mode, the end cap electrodes 3 and 4 are set to the ground potential, and a high frequency voltage for trapping is supplied from the high frequency power source 9 to the ring electrode 2. In the b mode, DC voltages V2, V3, and V4 are respectively supplied from the DC power supplies 10, 11, and 12 to the ring electrode 2 and the end cap electrodes 3 and 4, respectively. Further, in c mode, all electrodes are grounded.
[0012]
The straight trajectory A12 is provided with a sector electric field 13 for extracting ions to the outside of the orbit and an ion detector 14 for detecting the extracted ions. The sectoral electric field 13 is energized when taking out, and is not energized at other times, and the ions travel straight through a passage provided in the sectoral electric field.
[0013]
The operation in the above configuration will be described. First, the changeover switches S2, S3, S4 are set to the a mode. In the a mode, a quadrupole electric field that stably traps ions in the trap region is formed. Then, ions (positive ions) generated when the gas introduced into this region from the introduction tube 7 is bombarded by electrons from the electron gun 8 are accumulated in this trap region.
[0014]
After a sufficient amount of ions are accumulated, the gas introduction is stopped, and then the changeover switches S2, S3, S4 are set to the c mode after being set to the b mode for a short time. In this b mode, DC voltages V2, V3, and V4 are respectively supplied from the DC power sources 10, 11, and 12 to the ring electrode 2 and the end cap electrodes 3 and 4, but V2, V3, and V4 are V2>. Since the relationship of V3> V4 is given, an electric field that pushes positive ions upward in FIG. 1 is formed in the trap region, and the ions accumulated in the trap region are given equal energy by the electric field. It is pushed out from the ion trap 1 in a pulse manner and starts to fly toward the electric sector E1.
[0015]
The ions extracted in a pulse manner from the ion trap 1 in this manner sequentially return to the ion trap 1 through the sector electric fields E1, E2, E3, and E4. At this time, each electrode of the ion trap 1 is c Since the ground potential is set in the mode, the ions can pass through the ion trap through the passage ports 5 and 6 without being accelerated or decelerated. Then, the ions that have passed through the ion trap again pass through the sector electric fields E1, E2, E3, and E4 again, and repeat this to repeat the circulation. In the meantime, ions are developed according to their velocity.
[0016]
When the extraction electric field 13 is energized after an appropriate number of circulations, the extracted ions are extracted from the circular orbit one after another and enter the detector 14 for detection. Is done.
[0017]
It should be noted that the timing of energizing the extraction sector electric field 13 is the period from the time immediately before the head of the ions deployed with the lightest ion on the circular orbit reaching the sector to the end of the last passage. is there.
[0018]
As described above, in the present invention in which the ion trap is arranged on the orbit of the ion in the time-of-flight mass spectrometer, the ions accumulated in the ion trap are expelled onto the orbit of the time-of-flight mass spectrometer to perform mass analysis. It can be carried out. In addition to simply storing ions in the ion trap, various experiments (for example, selecting the mass of ions stored in advance by the ion trap, or irradiating the ions stored in the ion trap with laser light). It is also possible to mass-analyze the ions after they have been smashed).
[0019]
Furthermore, further experiments can be performed in the ion trap by capturing the specific ion species once mass-separated by being driven out on the orbit. In order to trap ions flying from outside in the ion trap, the acceleration voltage when the ions are expelled to each electrode of the ion trap is applied in a pulse manner at the moment when the ions enter the ion trap, and then the ring electrode A high frequency voltage is applied to the trap region to form a quadrupole electric field that stably traps ions.
[0020]
In the above-described embodiment, gas is introduced into the trap region and ionized, but ions generated in another place may be introduced into the trap region from the outside. FIG. 4 shows a configuration of another embodiment based on such a concept. In the present embodiment, there is provided a sector electric field 22 that guides ions generated by the external ion source 21 onto the ion orbit. Ions introduced onto the circular orbit by the electric sector 22 are introduced into the ion trap and accumulated. Further, in this embodiment, an extraction hole is provided in one of the electrodes for generating the sector electric field E2 without providing an extraction sector electric field, and ions are straightened with the intensity of the sector electric field E2 being zero at the time of extraction. Then, ions are taken out from the orbit around the take-out hole and guided to the ion detector for detection.
[0021]
In this embodiment, ions generated by the external ion source 21 are introduced and accumulated in the ion trap. After accumulation, the ions are extracted in a pulsed manner, placed on a circular orbit, and developed according to the mass and detected. Is exactly the same as the previous embodiment.
[0022]
【The invention's effect】
The time-of-flight mass spectrometer of the present invention is a time-of-flight mass spectrometer that performs mass analysis by flying sample ions along a closed trajectory. Thus, a time-of-flight mass spectrometer capable of extending the flight distance by increasing the number of laps is realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing an outline of a circuit configuration for supplying power to the ion trap 1;
FIG. 3 is a diagram showing an embodiment of the present invention.
[Explanation of symbols]
E1, E2, E3, E4: Fan electric field 1: Ion trap 14: Ion detector

Claims (6)

A time-of-flight mass spectrometer that performs mass analysis by flying sample ions along a closed orbit, wherein an ion trap is disposed on the orbit. The ion trap is composed of a pair of end cap electrodes arranged opposite to each other and a ring electrode arranged between the end gap electrodes, and the pair of end gap electrodes is provided with a passage through which ions pass. The time-of-flight mass spectrometer according to claim 1, wherein The time-of-flight mass spectrometer according to claim 1 or 2, wherein the ion trap is capable of generating ions therein. The high-frequency supply to the ion trap is stopped, and a pulse voltage is applied so that ions inside the ion trap can be taken out into an ion trajectory of a time-of-flight mass spectrometer. 3. A time-of-flight mass spectrometer according to 3. The time-of-flight mass spectrometer according to claim 3, wherein ions on the orbit can be trapped inside the ion trap by applying a pulse voltage to the electrodes constituting the ion trap. The time-of-flight mass spectrometer according to any one of claims 1 to 4, wherein the closed orbit is configured by a combination of a plurality of electric sector fields.

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