JPH07161336A - Mass spectrometric method and apparatus therefor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a highly sensitive mass spectrometric method and an apparatus therefor, which can realize the analysis of a sample that exists only in an extremely small amount. [Composition] An ionization section in which ions are intermittently generated,
In a mass spectrometer having an ion trap section for accumulating or mass separating the generated ions, and a detection section for detecting the ions, the time during which the ions are generated in the ionization section or the number of times of ion generation is measured, A mass spectrometric method and apparatus for accumulating a required amount of ions in an ion trap section and mass-separating the accumulated ions at once.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass spectrometric method and an apparatus therefor, and particularly to highly sensitive analysis of biological substances such as nucleic acids, proteins, peptides, lipids, sugars and their complexes, which can be obtained only in trace amounts. The present invention relates to a mass spectrometry method using an ion trap, and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, Review of Scientific Instruments 60 (1992), pages 4277 to 4284.
Page (Review of Scientific Instruments 60 (1992) p
p.4277-4284) describes a mass spectrometer that combines an ion trap and a time-of-flight mass spectrometer. However, in this technique, the ions to be mass analyzed are irradiated with the pulsed laser light once on the gaseous sample at the ionization section.
It is generated by performing (multiphoton ionization).

[0003]

In the above-mentioned conventional technique, only a part of the sample molecules introduced into the ionization section is involved in the ionization. Therefore, when a sample with a very small amount of ions that determines the signal level (S) in the mass spectrum is analyzed, the amount of ions will be insufficient and ion detection will not be possible. Since the noise level (N) of the mass spectrum is often determined by the dark current of the detector, the S / N ratio in the mass spectrum cannot be improved even if the same measurement is repeated and averaged. The present invention has been made in view of the above circumstances, and an object thereof is to solve the above-mentioned problems in the conventional technique and to realize the analysis of a sample that exists only in an extremely small amount.
It is to provide a highly sensitive mass spectrometry method and an apparatus therefor.

[0004]

The above objects of the present invention are as follows:
In a mass spectrometer having an ionization section for intermittently generating ions, an ion trap section for accumulating the generated ions or separating the mass of the ions, and a detection section for detecting the ions, a plurality of times in the ionization section The ion generated in the ion trap section is accumulated in the ion trap section, and then the accumulated ion is introduced into the detection section for mass separation, and in the mass spectrometer, the ionization is performed. Mass spectrometer having means for accumulating ions generated by a plurality of ionizations in the ion trap section in the ion trap section, and then controlling the accumulated ions to be introduced into the detection section for mass separation. Achieved by

[0005]

In the mass spectrometry method and apparatus according to the present invention, in order to realize high-sensitivity detection, sample molecules introduced into the ionization section are all ionized by a plurality of ionizations, and the generated ions are ionized. After the mixture is accumulated and mixed in the trap portion, mass separation is performed at once. This significantly increases the signal level as compared to the case where only ions generated by one-time ionization are subjected to mass spectrometry. Therefore, the S / N ratio of the obtained mass spectrum is significantly improved, and the detection limit can be reduced.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 shows a block diagram of a mass spectrometer according to an embodiment of the present invention. The sample is mixed with the matrix and applied on the surface of the sample holder 1 in a volume of about 1 μl. At the time of sample introduction, the ionization section is exposed to atmospheric pressure, and the sample holder 1 can be replaced.
At this time, by the vacuum valve 2 having a shutter function,
The vacuum of the analysis unit including the ion trap 5 and the detection unit 6 is maintained. After introducing the sample, the ionization unit including the sample holder 1 is evacuated to a vacuum. By irradiating the laser light from the pulse laser 3, 100 near the surface of the sample holder 1
Ions are generated only for about ns. A voltage is applied to the sample holder 1, and the ions are introduced into the ion trap 5 through the electrostatic lens 4. A heater is installed in the ion trap 5 to prevent surface contamination.

The diameter of the spot of the laser light focused by the lens (not shown) on the sample holder 1 is usually 100 μm or less, which is smaller than the spread of the applied sample. Therefore, by finely moving the sample holder 1 with a piezoelectric element or the like, the laser irradiation position in the sample holder 1 is changed, and all the applied sample can be spent for ion generation. Ions generated by laser light irradiation a plurality of times (for example, several tens of times) are mixed and accumulated in the ion trap 5. The accumulation time of the ions accumulated in the ion trap can be designated in advance. The accumulated ions are emitted from the ion trap 5 and detected by the detector 6 when a designated time described later has elapsed after the start of laser irradiation. It is also possible to use an atomic beam or an ion beam instead of the laser beam.

FIG. 1 shows a block diagram of a control system of the mass spectrometer based on the embodiment shown in FIG. An external trigger for laser oscillation in the pulse laser 3 is generated by the pulse generator 7. Part of the output of the pulse generator 7 is input to the fine movement mechanism 8 of the sample holder 1 of the ionization unit. As a result, the sample holder 1 periodically moves slightly. A part of the laser light is photoelectrically converted by the photodiode 9. The output from the photodiode 9 is sent to the delay circuit 10 as a start signal, where the time from the start of laser oscillation is measured. When a predetermined time elapses in the delay circuit 10, the ion trap power supply 1
The output signal is sent to 1. In the ion trap power supply 11, when an input signal is input from the delay circuit 10, a certain time (1
After a delay of ms or more, for example, 5 ms, a voltage for ejecting ions from the ion trap 5 is generated.

A part of the output of the delay circuit 10 and the output of the detector 6 are sent to the data processing section 12 to obtain a mass spectrum. The output of the pulse generator 7 can be directly input to the delay circuit 10. According to the present embodiment, it is possible to obtain a high-sensitivity mass spectrometer capable of realizing the analysis of a sample that exists in a very small amount. FIG. 3 shows a block diagram of a mass spectrometer in which an ion trap and a time-of-flight mass spectrometer are combined according to another embodiment of the present invention. The sample is applied to the surface of the sample holder 1 together with a matrix that efficiently absorbs laser light. Ions are generated near the surface of the sample holder 1 by the laser light irradiation from the pulse laser 3. A voltage is applied to the sample holder 1, and ions are introduced into the ion trap 5 through the electrostatic lens 4.

Ions are generated a plurality of times by a plurality of times of laser light irradiation linked to the fine movement of the sample holder 1, and these ions are mixed and accumulated in the ion trap 5. The number of times of ion generation can be designated in advance.
The accumulated ions are released from the ion trap 5 and are accelerated by the accelerating electrode 13 after a lapse of a fixed time after the introduction of the ions into the ion trap portion is completed, and a constant kinetic energy is obtained. Ions pass through the electrostatic lens 14 and then the electrode 1
After being deflected by 5 and reflected by the reflector 16, it is detected by the detector 6. The mass of the ion is detected by the detector 6
Is determined by the time difference of the ions that reach the. Here, the acceleration electrode 13 described above and the mesh 13 behind it are used.
A, the electrostatic lens 14, the electrode 15, the reflector 16 and the detector 6 constitute a reflection type time-of-flight mass spectrometer. The reflector 16 not only has the effect of downsizing the time-of-flight mass spectrometer, but also has the effect of canceling the velocity difference of the ions emitted from the ion trap section.

When mass separation is performed by the ion trap 5
(See FIG. 2) However, the mass of the ion may not be accurately determined due to the space charge effect. However, in the present embodiment, the mass of the ion is different from that of the ion trap 5 for the mass separation. It has the advantage that it is always accurately determined. FIG. 4 shows a block diagram of a control system of the mass spectrometer based on the embodiment shown in FIG. An external trigger for laser oscillation in the pulse laser 3 is generated by the pulse generator 7. Part of the output of the pulse generator 7 is input to the fine movement mechanism 8 of the sample holder 1 of the ionization unit. In this case, the fine movement of the sample holder 1 does not necessarily have to be periodic. The same effect can be obtained even when the sample holder 1 is kept stationary and the irradiated laser beam is finely moved by a mechanism such as a mirror.

A part of the laser light is photoelectrically converted by the photodiode 9. The output from the photodiode 9 is sent to the counter 18, where the number of laser oscillations is counted. When the number of input signals from the pulse generator 7 reaches the designated count number, output signals are sent to the ion trap power supply 11 and the ion acceleration power supply 17. In the ion trap power supply 11, when an input signal is input from the counter 18, in order to improve the resolution on the mass spectrum in the time-of-flight mass spectrometer 19, as described above, the ion trap 5 outputs a fixed time delay of 1 ms or more. A voltage is generated to eject the ions. Further, a high voltage is applied from the ion acceleration power supply 17 to the ion acceleration electrode 13 in a pulsed manner. A part of the output of the counter 18 and the output of the time-of-flight mass spectrometer 19 are sent to the data processing unit 12. According to the present embodiment, it is possible to obtain the effect of realizing a high-sensitivity mass spectrometer capable of realizing the analysis of a sample that exists only in an extremely small amount, which makes use of the characteristics of the time-of-flight mass spectrometer 19. .

FIG. 5 is a block diagram showing another embodiment of the present invention.
The block diagram of the mass spectrometer which combined the ion trap and the magnetic field type mass spectrometer is shown. The ions accumulated in the ion trap 5 are released from the ion trap 5 after a fixed time has elapsed after the introduction of the ions into the ion trap 5 is completed,
It is accelerated by the acceleration electrode 13 to obtain a constant kinetic energy. After the ions pass through the electrostatic lens 14, the electric field electrode 2
It is deflected by 0, is further mass-separated by the magnetic field of the electromagnet 21, and is detected by the detector 6. The detector 6 is an array type, and the mass of the detected ions is determined by the position of the surface of the detector 6. According to the present embodiment, it is possible to obtain the effect of realizing a high-sensitivity mass spectrometer that makes it possible to analyze a sample that is present in an extremely small amount, by making the most of the characteristics of the array-type detector 6.

As described in detail above, in the mass spectrometric method and apparatus according to the present invention, for example, ions generated by several tens of times of ion generation are accumulated in an ion trap,
Since mass spectrometry can be performed, there is an effect that the detection sensitivity of the apparatus is improved by a factor of 10 as compared with the case of analyzing ions generated once. Further, the lower limit of the laser light intensity with which the sample holder 1 is irradiated is determined by the photon density per unit area. According to the present invention, the laser beam diameter in the sample holder 1 is about 1 μm due to the use of a lens or the like. Even if the sample is narrowed down to (1), all the sample on the sample holder 1 can be contributed to ionization by the fine movement mechanism 8 of the sample holder 1 and plural times of ionization, so that a compact laser with low output can be used. Further, according to the present invention, since a very small amount of the sample can be all contributed to the ionization, no special precision is required for the coating position and its size when introducing the sample into the apparatus, and the sample introduction There is also an advantage that the work is easy.

[0015]

As described above in detail, according to the present invention, it is possible to realize a highly sensitive mass spectrometric method and an apparatus therefor, which makes it possible to analyze a sample that exists in a very small amount. It has a great effect.

[Brief description of drawings]

FIG. 1 is a block diagram of a control system of the mass spectrometer shown in FIG.

FIG. 2 is a configuration diagram of a mass spectrometer according to an embodiment of the present invention.

FIG. 3 is a block diagram of a control system of the mass spectrometer shown in FIG.

FIG. 4 is a configuration diagram of a mass spectrometer according to another embodiment of the present invention.

FIG. 5 is a configuration diagram of a mass spectrometer according to still another embodiment of the present invention.

[Explanation of symbols]

 1 Sample Holder 2 Vacuum Valve 3 Pulse Laser 4 Electrostatic Lens 5 Ion Trap 6 Detector 7 Pulse Generator 8 Fine Adjustment Mechanism 9 Photodiode 10 Delay Circuit 11 Ion Trap Power Supply 12 Data Processing Section 13 Acceleration Electrode 14 Electrostatic Lens 15 Electrode 16 Reflector 17 Ion Acceleration Power Supply 18 Counter 19 Time-of-Flight Mass Spectrometer 20 Electric Field Electrode 21 Electromagnet

Claims (11)

[Claims] 1. A mass spectrometer having an ionization section for intermittently generating ions, an ion trap section for accumulating the generated ions or separating the mass of the ions, and a detection section for detecting the ions, wherein the ionization is performed. A method for mass spectrometry, comprising: accumulating ions generated by a plurality of ionizations in the ion trap section in the ion trap section, and introducing the accumulated ions into the detection section for mass separation. 2. The mass spectrometric method according to claim 1, wherein the time during which ions are accumulated in the ion trap portion can be measured. 3. The mass spectrometric method according to claim 2, wherein the time at which ions are accumulated in the ion trap portion can be designated in advance. 4. The mass according to claim 3, wherein the ions are introduced from the ion trap section to the detection section after the time for which the ions are accumulated in the ion trap section reaches a predetermined time. Analysis method. 5. The mass spectrometric method according to claim 1, wherein the number of times ions are generated in the ionization section can be counted. 6. The mass spectrometric method according to claim 5, wherein the number of times ions are generated in the ionization section can be designated in advance. 7. The mass spectrometer according to claim 6, wherein the ions are introduced from the ion trap unit to the detection unit after the number of times the ions are generated in the ionization unit reaches a preset number of times. Method. 8. A mass spectrometer having an ionization section for intermittently generating ions, an ion trap section for accumulating the generated ions or separating the mass of the ions, and a detection section for detecting the ions, wherein the ionization is performed. Mass spectrometer having means for accumulating ions generated by a plurality of ionizations in the ion trap section in the ion trap section, and then controlling the accumulated ions to be introduced into the detection section for mass separation. . 9. The ion accumulated in the ion trap section or the number of times ions are generated in the ionization section reaches a predetermined time or number of times, and the ions generated in the ionization section are the ions. 9. The mass spectrometer according to claim 8, further comprising means for controlling so that ions are introduced from the ion trap section to the detection section after a predetermined time has elapsed after the introduction into the trap section is completed. apparatus. 10. The mass spectrometer according to claim 9, wherein the predetermined time is 1 ms or more. 11. The sample holder of the ionization section is configured to be finely movable.
0. The mass spectrometer according to any one of 0.