JP2003022777A - High sensitivity supersonic molecule-jet multiphoton absorption ionization mass spectroscope device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a supersonic molecule-jet multiphoton absorption ionization mass spectroscope device which has high ion extraction efficiency, and has high sensitivity while avoiding saturation of a signal amplifier. SOLUTION: The supersonic molecule-jet multiphoton absorption ionization mass spectroscope device comprises a pulse valve which introduces sample gas in the device, an ionization domain which ionizes the sample gas emitted from the pulse valve by an ion source, an ion optical system which introduces the ions generated in the ionization domain into an ion detector, and the detector which detects the ions extracted from the ion optical system. The device is constituted of an extraction electrode of the above ion optical system, which has a projecting-part type electrode form, and a cylinder-like potential switch is arranged behind the extraction electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supersonic molecular jet multiphoton absorption ionization mass spectrometer for detecting an extremely small amount of organic compounds with high sensitivity.

[0002]

2. Description of the Prior Art Dioxin is an abbreviation for polychlorinated dibenzoparadioxin, and there are 75 kinds of homologues and isomers depending on the difference in the number of chlorine substitution and the position. Polychlorinated dibenzofuran is also polluting the environment with these,
It has 135 homologues and isomers. These two are collectively called dioxins. The effects of these dioxins on human health are various, and the toxicity factor relatively evaluated for 2,3,7,8-TCDD, which is the most toxic, and the total toxicity obtained using it are used. . From the above, it can be seen that an evaluation method having high sensitivity and high chemical species selectivity is required for dioxins evaluation.

The conventional official measurement and analysis method of dioxin is shown as a measurement standard method in "Guideline for Prevention of Generation of Dioxins" compiled by the Ministry of Health, Labor and Welfare.
This method extracts dioxins with an organic solvent,
After concentration / separation by various chromatographic methods, it is analyzed by gas chromatograph mass spectrometry (GC / MS). This test analysis process requires a great deal of measurement time and cost. On the other hand, as there is a strong concern that the effects of organochlorine compounds such as dioxins on the human body are strongly concerned, even one example of obtaining information necessary for incinerator design and operation management can It is desired to develop a new evaluation technique that enables selective and quantitative on-site real-time analysis. The supersonic molecular jet multiphoton absorption ionization mass spectrometry (Jet-REMPI) method is attracting attention as an analytical method that can detect with high sensitivity and high chemical species selectivity without requiring a concentration pretreatment technique like the official method. .

Generally, an organic molecule has an electronic state due to its molecular skeleton, and a vibrational level, a rotational level and the like interact in a complicated manner in the state. Absorption spectroscopy using infrared rays, ultraviolet rays, and the like is a method of identifying existing molecular species by utilizing light absorption due to the difference in the molecular skeleton of such organic molecules. The Jet-REMPI method is expected to make it possible to select and detect an organic molecule in real time by utilizing this excited state peculiar to the molecule. This principle will be briefly described.

The Jet-REMPI method is a combination of the resonant multiphoton absorption ionization (REMPI) method and the supersonic molecular jet (Jet) method. REMPI
(Resonance Enhanced Multi
-Photon Ionization) method, when exciting an organic molecule with a laser beam, tunes a laser wavelength to an excitation level peculiar to a molecule of interest to selectively ionize only a specific molecular species (resonant multiphoton absorption ionization). Then, the ions are detected using a mass spectrometer.

To ionize a sample by light absorption,
From the viewpoint of the absorption cross section (absorption efficiency), the wavelength near the peak observed in the absorption spectrum is used. However, the peak width of the absorption spectrum of an organic compound at room temperature and pressure is
It becomes wider due to overlapping transitions from vibration and rotation levels,
The absorption peaks of isomers with similar structures cannot be separated. On the other hand, when this molecule is cooled to near absolute zero (several K), the electrons are located in the true ground state, which does not oscillate or rotate, and due to the transition selectivity, they are excited only at a specific level. As a result, only a few sharp peaks are observed. The peak width depends on the cooled temperature, but is usually about 0.01 nm. By using a wavelength tunable laser, even if the isomers are very similar in structure, if the peak width is in this order,
It can be selectively excited and ionized.

On the other hand, the supersonic molecular jet (Jet) method is one method of cooling molecules to an extremely low temperature. In this method, vaporized sample molecules are ejected into a vacuum from a pinhole together with a rare gas such as helium or argon, and adiabatic expansion cooling and collision with the rare gas instantly cool the sample molecules to near absolute zero. Is the way. It is called the supersonic molecular jet method because the speed of molecules reaches several tens of times the speed of sound.

The Jet-REMPI method freezes the vibrational / rotational level of the molecule of interest in this way and tunes the energy of the wavelength tunable laser to the resonant excitation level of the molecule of interest, so that only the specific molecule is selectively selected. This is a method of ionization and mass spectrometry. A technology for detecting chlorobenzene and chlorophenol, which are considered to be precursors for the generation of dioxins, by the Jet-REMPI method has been disclosed (Japanese Patent Laid-Open No. 9-
No. 243601, JP-A-10-74479). In addition, H. H. Grotheer et al., Jet-
By optimizing the REMPI device, we succeeded in creating a highly sensitive analyzer. Quantification of up to 0.1 ppb has been realized with dichlorotoluene (Japanese Patent Laid-Open No. 8-222181).

[0009]

On the other hand, since dioxins have extremely strong toxicity, the detection sensitivity that must be evaluated is 0.1 ng / Nm ^{3, which} is a very small amount, and further high sensitivity is required. Required. Oser et al. Reported a detection limit of about 10 ppt for dichlorodioxin,
It is the most sensitive report so far (H.
Oser, R .; Thanner, H .; H. Grothe
er, B.I. K. Gullett, N .; B. French
h, D. Natscke, Proc. 16th In
t. Conf. On Invention an
d Thermal Treatment Techn
LOGIES (1997)). However, this detection limit corresponds to almost 100 ng / Nm ³ , and in order to achieve the detection limit of 0.1 ng / Nm ³ that needs to be evaluated in the future, it is necessary to further increase the sensitivity by about 1000 times. .

Therefore, in order to solve the above-mentioned conventional problems, the present invention is a supersonic molecular jet multiphoton absorption ionization mass spectrometer having high ion extraction efficiency, avoiding saturation of a signal amplifier, and highly sensitive. The purpose is to provide.

[0011]

[Means for Solving the Problems] General Jet-REM
An outline of the PI device is shown in FIG. Particles ejected from the pulse valve are introduced into the ion irradiation region through the skimmer. Using the nonlinear optical crystal, the visible light (ω) generated from the dye laser is the second wavelength which is the selective excitation wavelength of the molecule of interest.
A harmonic wave (ω / 2) is generated and inserted into the laser ionization region. This allows selective ionization of only the target molecule. The generated ions are accelerated by the parallel plate type electrodes, converged and deflected through the Einzel lens and the deflector, and reach the detector. The detected ion signal is amplified by the preamplifier and measured by the digital oscilloscope. Or BO
The signal is integrated by the XCAR integrator.

However, the following problems are involved in the analysis of trace amounts of components such as dioxins. That is, in the conventional device, all the ions that have been ionized by the pulse ionization source reach the detector, so the signal of the molecule of interest is likely to be missed, and in order to avoid this, pulse ionization is performed. There was a problem that the signal of the trace amount component could not be detected when the output of the source was lowered. Therefore, an ion detection system having high ionization efficiency and capable of avoiding saturation of the detector is required.

The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer of the present invention efficiently guides generated ions to an ion detector in order to achieve high ion detection efficiency, which is the main object of the present invention. Mass analysis by selectively detecting generated ions, with a counter electrode, electrostatic mesh, and guide electrode that are provided to increase the efficiency and suppress noise even more It is characterized by detecting ion particles of interest more quantitatively and with high sensitivity while avoiding saturation of the meter.

According to the invention described in claim 1, a pulse valve for introducing a sample gas into the apparatus, an ionization region for ionizing the sample gas released from the pulse valve by a pulse ionization source, and an ionization region generated in the ionization region A supersonic molecular jet multiphoton absorption ionization mass spectrometer equipped with an ion optical system for introducing the extracted ions into a detector and an ion detector for detecting the ions extracted from the ion optical system, wherein the ion optical system The extraction electrode has a nasal electrode shape, and a cylindrical potential switch is arranged behind the extraction electrode. A high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer.

The invention according to claim 2 is the high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1, characterized in that it has means for adjusting the length of the potential switch.

Further, the invention according to claim 3 is characterized in that a plurality of the potential switches are arranged in series in a state of being insulated from each other, and a high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometry according to claim 1. It is a device.

The invention according to claim 4 further comprises means for adjusting the timing of high-voltage pulse application between the potential switch and the pulse ionization source. High-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer.

Further, the invention according to claim 5 is characterized in that a counter electrode facing the extraction electrode and having the same nasal discharge electrode shape as the extraction electrode is provided on the same straight line centering on the ionization region. The highly sensitive supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of claims 1 to 4.

According to the sixth aspect of the present invention, the extraction electrode and the counter electrode have electrostatic shields coaxially with the respective electrodes, and the respective electrostatic shields are cylindrical and mesh-shaped. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of claims 1 to 5, wherein the electrostatic shield has a bilaterally symmetrical structure.

Further, according to a seventh aspect of the present invention, in order to correct the distortion of the applied electric field generated in the counter electrode and the extraction electrode, a cylindrical guide electrode is provided coaxially with the counter electrode and the extraction electrode. Claim 1 characterized by
The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of 6 above.

According to the present invention, the extraction electrode and the counter electrode each have a guide electrode, an electrostatic mesh, and an Einzel lens, and the extraction electrode and the counter electrode are symmetrical with respect to the ionization region. Placed,
8. A high-sensitivity supersonic molecular jet poly according to any one of claims 1 to 7, characterized in that each of these electrodes is fixed by a plurality of supporting members so as to be arranged on the same straight line. It is a photon absorption ionization mass spectrometer.

According to a ninth aspect of the present invention, the extraction electrode and the counter electrode have a bilaterally symmetrical structure with the ionization region sandwiched therebetween, and a counter electrode to which a positive potential is applied around the ground potential, The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass according to any one of claims 1 to 8, further comprising an extraction electrode applied with a negative potential whose absolute value is equal to that applied to the counter electrode. It is an analyzer.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION An outline of an ion optical system of a high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to the present invention will be described with reference to FIG. The extraction electrode 1 has a nasal shape, and has a cylindrical guide electrode 2 concentrically surrounding the extraction electrode 1 on the outside thereof.
Moreover, the cylindrical electrostatic mesh 3 surrounds the outer side thereof. Further, the Einzel lens 4 is installed in the subsequent stage of the extraction electrode 1. The counter electrode 7 is provided at the symmetrical position of the extraction electrode portion with the four support rods 6 shared with the extraction electrode 1 about the laser ionization region 5.
Is installed. The counter electrode 7 is the same as the extraction electrode.
It has a guide electrode 8, an electrostatic mesh 9, and an Einzel lens 10. Here, the Einzel lens 10 of the counter electrode 7 does not contribute to the detection of ions, but is provided so that the Einzel lens in the extraction electrode can be immediately replaced in case of failure. These two pairs of electrodes need to be installed in completely symmetrical positions with respect to the laser ionization region 5, and the holes at the center of both nasal electrodes are the Einzel lens 4 at the latter stage of the extraction electrode 1.
On the same straight line as the center of the hole, the Y-axis deflector 11, the X-axis deflector 12, and the center of the potential switch 13.

The two electrostatic meshes 3 and 9 are separated by about 10 mm. Generally, the ultimate vacuum degree of the laser ionization region evacuated by using a rotary pump and a turbo molecular pump is about 1E-5 to 1E-6Pa. The supersonic molecular jet stream 15 passes through the center of the drawing from above. In general, supersonic molecular jets
It can be obtained via the skimmer. Through the skimmer, the effect of differential pumping of the device can be enhanced, and high vacuum (about 1E-3Pa during pulse valve operation) can be achieved. However, the pulse valve tip and the laser ionization region cannot be brought close to each other. Since the device of the present invention is characterized by high-sensitivity detection, it is difficult to achieve high sensitivity when the distance from the valve tip to the laser ionization region is large. Therefore, the apparatus of the present invention uses a free molecular flow without using a skimmer.
However, when the pulse valve 14 and the ion extraction system come close to each other, the electric field is distorted, so that the particles ionized by the laser cannot be efficiently taken into the detector. Therefore, by disposing the electrostatic meshes 3 and 9 having the same electric potential as the valve, the equipotential surface is prevented from being distorted. However, if the distance between the meshes is too wide, the equipotential surface surrounding the electrodes is distorted, and when the pulse valve 14 approaches, the equipotential surface is distorted due to its shape. The guide electrodes 2 and 8 play a role of correcting the distortion of these electric fields and transmitting ions into the detector. Further, the laser for ionization is incident on the laser ionization region 5 from the direction perpendicular to the paper surface. The holes of the two electrodes are always on the same straight line, and the laser ionization region 5 is located at the midpoint between the holes.
Is located.

As described above, the extraction electrode 1 and the counter electrode 7 have two pairs of symmetrical structures with the laser ionization region 5 as the center. If this structure is broken, the electric field is broken and the ions can be detected with high efficiency in the detector. I can't reach it. Therefore, it is necessary for the support rod 6 to have a structure in which the two electrodes are held in a positional relationship. On the other hand, the extraction electrode 1, the counter electrode 7, the electrostatic meshes 3, 9 and the guide electrodes 2, 8 are
Since it is close to the pulse valve 14, adsorption of the injected gas is unavoidable. Therefore, such contamination easily causes discharge when a high voltage is applied, and therefore periodic cleaning is necessary. For these reasons, the two electrostatic meshes 3, 9
It is preferable to use a structure in which two electrostatic meshes surrounding the respective electrodes are used instead of a structure in which holes are formed in the cylindrical mesh in the passage region of the supersonic molecular jet and the laser.

The reason for using this electrode shape is that the electrostatic meshes 3 and 9 are at the same potential as the pulse valve, so that the pulse valve 14 can be brought close to the laser ionization region 5 and that the laser ionization is wide. This is because the ions generated from the region 5 can be collected with high probability. This is an essential condition for detecting an extremely small amount of organic matter. However, in terms of equipment, some of the following major problems occurred.

(A) When a voltage of + X (V) is applied to the counter electrode and the extraction electrode is grounded, it becomes necessary for the electrostatic mesh and the pulse valve to apply a voltage of + X / 2 (V). (B) When a voltage of + X (V) is applied to the counter electrode and a voltage of -X (V) is applied to the extraction electrode, the electrostatic mesh and the pulse valve are grounded, but the Einzel lens behind the extraction electrode, The deflector and time-of-flight mass spectrometer need to have a floating potential, and the electrodes, lens, and detector need to apply a voltage on the floating potential. In addition, the circuit is very expensive. In addition, if the time-of-flight mass spectrometer does not have a double-tube structure, it poses a safety problem.

In order to solve the above problems, the present inventors newly installed a potential switch, which has not been used so far, in the latter stage of the Einzel lens. The potential switch is a cylindrical electrode. Here, let us consider the case where the counter electrode +2 KV and the extraction electrode -2 KV, which are general measurement conditions, are applied.

When the potential switch is grounded, the ions extracted at -2 KV feel the anti-power generation potential,
It wanders inside the cavity of the potential switch and is not drawn to the time-of-flight mass spectrometer. On the other hand, if −2 KV is applied to the potential switch, the ions pass through the potential switch having the same potential as the extraction electrode with constant velocity motion. However, at the moment of exiting the exit of the potential switch, I felt the almost potentialless deflector and the time-of-flight mass spectrometer that was grounded, and also scattered,
Cannot reach the detector.

Therefore, we solved the above-mentioned problem by applying a pulsed high voltage to a newly grounded cylindrical potential switch. That is, it can be achieved by raising the potential of the potential switch to the ground in a pulsed manner when the particle of interest reaches the potential switch to which −2 KV is applied. That is, although the ions that have reached the potential switch are moving at a constant potential of −2 KV at a constant speed, the ions are boosted to the ground potential in a pulse form. As a result, at the outlet of the potential switch, the constant velocity motion is continued without reaching the ground potential of the deflector and the time-of-flight mass spectrometer, and reaches the detector. Particles present in the potential switch at the time when the ground potential is applied in a pulsed manner are thus detected, other particles cannot reach the detector. In the supersonic molecular jet, the kinetic energy of particles (E = 1/2 mv ² : m
Are the mass numbers of particles, and v is the velocity). Therefore, the time to reach the potential switch from the ionization region is inversely proportional to the square root of the mass number of the particle. From this, it is also possible to detect only the mass range in the vicinity of the organic molecule of interest.
The mass range to be detected is determined by the voltage applied to the counter electrode and the extraction electrode, the length of the potential switch, and the timing of application of the high-voltage pulse with the pulse ionization source.

As described above, the above-mentioned problems are solved by the high-sensitivity supersonic molecular jet multiphoton absorption ionization apparatus of the present invention in which the nasal electrode and the potential switch are combined,
The following effects can be obtained. (A) High sensitivity can be achieved at low cost without complicating the system of the time-of-flight mass spectrometer in the latter stage. (B) Mass selection is possible without using a normally used assembly such as a mass gate. (C) Due to the higher sensitivity of (A), the signal amount per unit time is expected to increase and there is concern about saturation of the amplifier, etc., but (B) can selectively detect only the information of the molecule of interest. .

[0032]

EXAMPLES The present invention will be described below based on examples. FIG. 3 is a schematic diagram of a supersonic molecular jet multiphoton absorption ionization apparatus according to the present invention. Pulse valve from He
It is a device that inserts an ultraviolet laser that excites resonance selective excitation of organic molecules emitted in a vacuum together with a rare gas such as, and ionizes it through a multiphoton absorption process. The ionized organic molecule is a time-of-flight mass spectrometer (Time-of-Fi).
ght Mass Spectrometry: TOF
-MS) for mass spectrometry and detection. Therefore, isomers and the like are selected according to the difference in resonance wavelength, and different organic molecules having different mass numbers can be separated by a mass spectrometer. Further, by using the electrostatic reflection type TOF-MS, it is possible to separate ions generated near the pulse valve or colliding with the extraction electrode and to reduce noise without reaching the detector.

FIG. 4 shows the time sequence of the operation of the pulse valve, laser and potential switch. The pulse valve is opened, a supersonic molecular jet is generated in the vacuum chamber, and ions are generated by laser irradiation. After that, the potential switch applied with −2 KV is stepped up to 0 V in a pulse form. When this pulse voltage is applied, only the ions existing in the potential switch can reach the detector.

FIG. 5 shows a time-of-flight mass obtained when the pulse timing of the potential switch and the pulse laser was changed to 1, 2, 3 as shown in FIG. 4 by using monochlorobenzene as the sample. It shows the spectrum. An ultraviolet laser having a resonance excitation wavelength of 269.843 nm was used, and the laser light intensity was 6 mJ / pulse. Figure 5
As shown in, timing 1 of the potential switch
Then, all ions having a mass number of 10 or less to 160 are detected. Further, since the laser light intensity is high, fragment ions are detected at a very high intensity in addition to the parent ion of chlorobenzene (112 a.mu.u). On the other hand, at timing 2, fragment ions on the lower mass number side are no longer being detected. Further, at timing 3, all the ions with a mass number of 70 or less cannot reach the detector, and it can be seen that a condition can be set in which signals other than the parent ion of interest do not enter the detector. This allowed the establishment of optimum conditions that could be avoided from amplifier saturation.

According to the second aspect of the invention, the mass range of the above-mentioned ions is made variable by changing the length of the potential switch. In the invention according to claim 3, a plurality of insulated potential switches are used to detect a wide mass range, and the ions desired to be detected are controlled to a pulse timing that can be detected by the potential switch at the front stage. By grounding the potential switches other than the frontmost stage, it becomes possible to introduce signals of only desired ions into the detector. By using this, it is not necessary to use an expensive detector having a temporal gate in the subsequent stage. FIG. 6 shows mass spectra obtained when the upper stage (a) uses a plurality of insulated potential switches and the lower stage (b) uses only the frontmost potential switch. When the potential switch having an appropriate length is operated only in the frontmost stage, the mass range of a desired ion can be detected.

Using this apparatus and conditions, the correlation between the detected amount of chlorobenzene and the concentration of chlorobenzene in He gas was measured. The chlorobenzene concentration in He gas is
It was quantified using a permeator. FIG. 7 shows that the gas in the permeator was directly introduced into the Jet-REMPI device of the present invention to obtain the correlation between the concentration and the detection signal. Example 1 is a calibration curve (marked with a circle) obtained by the high-sensitivity supersonic molecular jet multiphoton absorption ionization apparatus developed by the present invention, and Comparative Example 1 shows a conventionally used parallel plate. It is a calibration curve (square mark) obtained by the supersonic molecular jet multiphoton absorption ionization device equipped with the extraction electrode of the mold.

As can be seen from FIG. 7, the device according to the present invention achieves higher sensitivity by one digit or more as compared with the conventional device. In the conventional method, the detection limit has already been reached, and linearity cannot be obtained in the concentration range of several ppt of the calibration curve. It is considered that the detection sensitivity of chlorobenzene was able to reach the level of 0.2 to 0.5 ppt with the device of the present invention.

[0038]

According to the present invention, it is possible to provide a supersonic molecular jet multiphoton absorption ionization apparatus suitable for detecting harmful organic compounds, which is essential for high sensitivity, without making the apparatus structure complicated. Moreover, the detection sensitivity of chlorobenzene can be as low as 0.1 ppt, and a detection limit higher than that of the conventional method can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a supersonic molecular jet multiphoton absorption ionization device.

FIG. 2 is a schematic diagram of an ion optical system of the present invention.

FIG. 3 is a schematic view of a supersonic molecular jet multiphoton absorption ionization apparatus of the present invention.

FIG. 4 is a diagram showing a time sequence of a pulse valve, a laser, and a potential switch according to an embodiment of the present invention.

FIG. 5 is a diagram showing a time-of-flight mass spectrum when the timing of a potential switch is changed.

FIG. 6 is a diagram showing mass spectra when a plurality of potential switches are operated and when a potential switch at the frontmost stage is operated.

FIG. 7 is a diagram showing a calibration curve of monochlorobenzene obtained by the high-sensitivity supersonic molecular jet multiphoton absorption ionization apparatus of the present invention and a calibration curve of a conventional apparatus.

[Explanation of symbols]

1: Extraction electrode 2, 8: Guide electrode 3, 9: Electrostatic mesh 4, 10: Einzel lens 5: Ionization region 6: Support rod 7: Counter electrode 11: Y-axis deflector 12: X-axis deflector 13: Potential switch 14: Pulse valve 15: Supersonic molecular jet flow

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shunichi Hayashi             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Tetsuya Suzuki             3-2-1 Sakado, Takatsu-ku, Kawasaki City, Kanagawa Prefecture             Ceremony Company Nippon Steel Techno Research (72) Inventor Morikihisa Saeki             38 Saigochu, Myodaiji Town, Okazaki City, Aichi Prefecture Okazaki National             Joint Research Institute, Institute for Molecular Science (72) Inventor Masaaki Fujii             38 Saigochu, Myodaiji Town, Okazaki City, Aichi Prefecture Okazaki National             Joint Research Institute, Institute for Molecular Science F-term (reference) 5C038 GH11 HH02

Claims (9)

[Claims] 1. A pulse valve for introducing a sample gas into the apparatus, an ionization region for ionizing the sample gas released from the pulse valve by a pulse ionization source, and ions generated in the ionization region for introduction into a detector. A supersonic molecular jet multiphoton absorption ionization mass spectrometer equipped with an ion optics system for detecting ions extracted from the ion optics system, wherein the extraction electrode of the ion optics system is a nasal electrode. A high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer characterized by arranging a cylindrical potential switch behind the extraction electrode. 2. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1, further comprising means for adjusting the length of the potential switch. 3. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1, wherein a plurality of the potential switches are arranged in series while being insulated from each other. 4. A high-sensitivity supersonic molecular jet multiphoton according to claim 1, further comprising adjusting means for adjusting the timing of high-voltage pulse application between the potential switch and the pulse ionization source. Absorption ionization mass spectrometer. 5. The counter electrode facing the extraction electrode and having the same nasal discharge electrode shape as the extraction electrode on the same straight line centering on the ionization region. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of claims 1. 6. The extraction electrode and the counter electrode have electrostatic shields coaxially with the respective electrodes, and the respective electrostatic shields are cylindrical and mesh-shaped, and the respective electrodes and electrostatic shields are symmetrical. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of claims 1 to 5, which has a structure. 7. A cylindrical guide electrode is provided coaxially with the counter electrode and the extraction electrode in order to correct the distortion of the applied electric field generated in the counter electrode and the extraction electrode. 6. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of 6 above. 8. The extraction electrode and the counter electrode each have a guide electrode, an electrostatic mesh, and an Einzel lens, and the extraction electrode and the counter electrode are symmetrically arranged with an ionization region in between, and the electrodes are The high-sensitivity supersonic molecular jet multiphoton absorption ionization according to any one of claims 1 to 7, which has a structure in which a plurality of supporting members are fixed so as to be arranged on the same straight line. Mass spectrometer. 9. The counter electrode, which has a structure in which the extraction electrode and the counter electrode are bilaterally symmetric with respect to the ionization region, and which has a positive potential applied around a ground potential, and a potential applied to the counter electrode. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to any one of claims 1 to 8, further comprising an extraction electrode applied with a negative potential having the same absolute value.