JP2004119026A - High sensitivity supersonic speed molecule jet multiphoton absorption ionization mass spectroscopic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high sensitivity supersonic speed molecule jet multiphoton absorption ionization mass spectroscopic apparatus which has excellent detection of ultramicroscopic gas, high boiling point gas or unstable gas existing in a high temperature furnace or a flue. <P>SOLUTION: The supersonic speed molecule jet multiphoton absorption ionization mass spectroscopic apparatus includes a pulse valve for introducing a sample gas into the apparatus, an ionization region for ionizing the gas discharged from the valve, an ion optical system for introducing ion generated in the ionization region to a detector, and an ion detector for detecting the ion drawn from the optical system. In this apparatus, a lead-out electrode of the system is formed in a protruding electrode shape. 15≤X/D≤50 is satisfied, wherein D (mm) is an opening diameter of the pulse valve jet port, and X (mm) is a distance from the jet port to a center of the ionization region. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a supersonic molecular jet multiphoton absorption ionization mass spectrometer for detecting a trace amount of gas, a gas having a high boiling point, and an unstable gas emitted from a high-temperature furnace or a combustion furnace with high sensitivity.
[0002]
[Prior art]
The conventional official measurement and analysis method of dioxin is shown as a standard measurement method in the "Guidelines for Prevention of Dioxins" compiled by the Ministry of Health, Labor and Welfare. In this method, dioxins are extracted with an organic solvent, concentrated and separated by various chromatographic methods, and then analyzed by gas chromatography / mass spectrometry (GC / MS). This test analysis process requires a great deal of measurement time and cost.
On the other hand, at present, there is a strong concern that the effects of organic chlorine compounds such as dioxins on the human body are insignificant. The development of a new evaluation technique that enables selective and quantitative on-site real-time analysis is desired.
[0003]
In general, an organic molecule has an electronic state due to its molecular skeleton, and a vibration level, a rotational level, and the like interact in a complicated manner in that state. Absorption spectroscopy using infrared rays, ultraviolet rays, or the like is a method of identifying existing molecular species by utilizing light absorption due to the difference in molecular skeleton of organic molecules. The supersonic molecular jet multiphoton absorption ionization mass spectrometry (Jet-REMPI) method is expected to be able to select and detect an organic molecule in real time by utilizing the excited state inherent to the molecule. . The Jet-REMPI method is attracting attention as an analytical method that does not require a pretreatment method for concentration like the official method and can detect with high sensitivity and high chemical species selectivity. This principle will be briefly described.
[0004]
The Jet-REMPI method is a method that combines the resonance multiphoton absorption ionization (REMPI) method and the supersonic molecular jet (Jet) method.
Resonance enhanced multi-photon ionization (REMPI) is a technique in which, when an organic molecule is excited by laser light, only a specific molecular species is tuned by tuning a laser wavelength to an excitation level peculiar to a molecule of interest. In this method, ions are selectively ionized (resonant multiphoton absorption ionization) and ions are detected using a mass spectrometer. In order to ionize a sample by light absorption, a wavelength near a peak observed in an absorption spectrum is used from the viewpoint of an absorption cross section (absorption efficiency). However, the peak width of the absorption spectrum of an organic compound at normal temperature and normal pressure becomes wider due to the overlap of transitions from vibrational and rotational levels, and it is not possible to separate the absorption peaks of isomers having similar structures. On the other hand, when this molecule is cooled to near absolute zero (several K), the electrons are located in the true ground state without vibration or rotation, and are excited only to a specific level by the selectivity of transition. As a result, only a few sharp peaks are observed. The peak width is determined by the cooling temperature, but is usually about 0.01 nm. With this peak width, isomers having very similar structures can be selectively excited and ionized by using a wavelength tunable laser.
[0005]
The supersonic molecular jet (Jet) method is one method of cooling molecules to extremely low temperatures. 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 the sample molecules are instantaneously cooled to near absolute zero by adiabatic expansion cooling and collision with the rare gas. Is the way. Since the speed of molecules reaches several tens of times the speed of sound, it is called the supersonic molecular jet method.
As described above, the supersonic molecular jet multiphoton absorption ionization mass spectrometry (Jet-REMPI) method freezes the vibration / rotation level of a molecule of interest and assigns the energy of a tunable laser to the resonance excitation level of the molecule of interest. This is a method in which only specific molecules are selectively ionized by tuning, and mass analysis is performed.
[0006]
FIG. 1 shows an outline of a general Jet-REMPI apparatus. The laser ionization region 5 is usually formed in a space sandwiched between parallel plate-shaped electrodes (extruded electrode (opposite electrode) 7 and extraction electrode 1) centered on two meshes. The mesh is provided so that the ions generated in the extraction electrode 1 can be introduced into the mass spectrometer with high transmittance, and that the electric field formed by the parallel plate type electrodes is not disturbed. Therefore, the push-out electrode (opposite electrode) 7 facing the same is also a flat plate electrode having a mesh.
The particles ejected from the pulse valve 10 are introduced into the laser ionization region 5. A supersonic molecular jet can be obtained via a skimmer 8. The effect of the differential evacuation of the apparatus can be enhanced by the interposition of the skimmer 8 to achieve a high vacuum (about 10 ⁻³ Pa during the pulse valve operation), but the tip of the pulse valve and the laser ionization region cannot be brought close to each other.
[0007]
Using a nonlinear optical crystal, a visible light (ω) generated from a dye laser is used to generate a second harmonic (ω / 2), which is a selective excitation wavelength of a molecule of interest, and is inserted into a laser ionization region 5. Thereby, selective ionization of only the molecule of interest can be caused. The generated ions are accelerated by the parallel plate type electrodes 1 and 7, converged and deflected through the Einzel lens 4 and the deflectors 11 and 12, and reach the detector 13. The detected ion signal is amplified by a preamplifier 15 through a resistance divider 14 and measured by a digital oscilloscope 16. Alternatively, the signal is integrated by the BOXCAR integrator 17. The dependence of the integrated signal intensity on the laser wavelength is observed by the personal computer 18.
[0008]
Attempts to use the Jet-REMPI method having such characteristics as an on-line real-time analysis method for harmful organic compounds have been actively studied in recent years, and Oser et al. Report that about 10 ppt of dichlorodioxin can be detected. (For example, see Non-Patent Document 1).
On the other hand, the regulated concentration of harmful organic compounds such as dioxin is changed from ppt to ppq level, and it is necessary to consider further increasing the sensitivity. It should be noted that the development of a high-sensitivity analyzer is strongly desired not only for dioxin analysis but also for general gas analysis.
[0009]
[Non-patent document 1]
H. Oser, R .; Thanner, H .; H. Grotheer, B.S. K. Gillett, N.W. B. French, and D.C. Natscke, Proc. 16 ^th Int. Conf. on Inclusion and Thermal Treatment Technologies (1997)
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a supersonic molecular jet multiphoton absorption ionization mass spectrometer capable of further high-sensitivity analysis in the Jet-REMPI method in order to meet the above demand.
[0011]
[Means for Solving the Problems]
As described above, the regulated concentration of harmful organic compounds such as dioxin changes from the ppt level to the ppq level, and it is necessary to consider further increasing the sensitivity. However, in the conventional supersonic molecular jet multiphoton absorption ionization mass spectrometry (Jet-REMPI) apparatus, particularly when analyzing ultratrace components such as dioxins, it is the pulse ionization source that reaches the detector. Since all ions are ionized, there is a high possibility that the signal of the molecule of interest will be counted down.In order to avoid this, if the output of the pulse ionization source is reduced, signals of ultra-trace components cannot be detected. there were.
[0012]
On the other hand, the present inventors have disclosed in Japanese Patent Application No. 2001-207261, in order to solve the problems of the conventional Jet-REMPI device, efficiently introduce generated ions into a detector, and achieve high ion detection efficiency. Propose a system to achieve. That is, the ion optical system of the device has a nose-shaped extraction electrode that efficiently guides generated ions to the detector, the efficiency is higher, and a counter electrode provided to further suppress noise, an electrostatic electrode, This system has a mesh and a guide electrode, and has a feature of avoiding the saturation of the mass spectrometer by selectively detecting the generated ions to detect the ion particles of interest more quantitatively and with high sensitivity.
However, in Japanese Patent Application No. 2001-207261, the shape and the position of the gas injection port are not examined. As a result of the investigation by the present inventors, the cooling of the gas injected by the shape and the position of the gas injection port is performed. When the state changes greatly and the opening diameter of the gas injection port is D (mm) and the distance between the gas injection port and the center of the laser ionization region is X (mm), when 15 ≦ X / D ≦ 50, We have newly obtained the knowledge that the ion particles of interest can be detected with high sensitivity.
[0013]
The present invention has been made based on the above findings, and the gist is as follows.
(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, and an ion optical system for introducing ions generated in the ionization region to a detector; A supersonic molecular jet multiphoton absorption ionization mass spectrometer comprising an ion detector for detecting ions extracted from the ion optical system, wherein the extraction electrode of the ion optical system has a nasal electrode shape, and the extraction electrode A counter electrode of the same shape is arranged at a position directly opposite to the above, a cylindrical potential switch is arranged behind the extraction electrode, the detector is arranged further behind the same, and holes of the extraction electrode and the counter electrode are arranged. , The detector is arranged on the same straight line, and the opening diameter of the pulse valve injection port is D (mm). A high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer characterized by satisfying 15 ≦ X / D ≦ 50, where X (mm) is the distance to the center of the ionization region.
(2) The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to (1), wherein an orifice is provided near a focus of ions inside the extraction electrode.
(3) The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to (1) or (2), wherein X (mm) satisfies 15 ≦ X ≦ 45.
(4) The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to (1) or (2), wherein X (mm) satisfies 15 ≦ X ≦ 25.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below. Note that the present invention is not limited to the conditions shown here.
FIG. 2 shows a schematic diagram of an ion optical system of a supersonic molecular jet multiphoton absorption ionization mass spectrometer (Jet-REMPI) apparatus according to the present invention. This figure is a diagram of the optical system viewed from the jet flow jetting direction, that is, a diagram of the pulse valve 10 (not shown) viewed from the jet flow jetting direction in the upward direction on the paper surface. As an electrode constituting the ionization region according to the present invention, a nose-shaped electrode proposed by the present inventors in Japanese Patent Application No. 2001-207261 is used. The nasal electrode can increase the ion collection efficiency as compared with the conventional parallel plate type. The generated ions are focused inside the nasal exit electrode, converted into a parallel beam by the Einzel lens 4, and introduced into the mass spectrometer. Therefore, by providing the orifice 19 through which ions can sufficiently pass near the focal point of the ions inside the nose-shaped electrode, it becomes possible to perform differential evacuation between the ionization region and the mass spectrometer, and to maintain a high degree of vacuum. it can. Accordingly, the load on the mass spectrometer is reduced, which is advantageous for a continuous gas introduction system using a skimmer or an orifice. Further, in order to further suppress noise, a counter electrode, an electrostatic mesh, and a guide electrode are attached, and by selectively detecting the generated ions, saturation of the mass spectrometer can be avoided, and quantitative and high Particles of interest for sensitivity can be detected.
[0015]
The extraction electrode 1 according to the present invention has a nasal shape, and has a cylindrical guide electrode 2 surrounding the extraction electrode 1 concentrically outside. Further, a cylindrical electrostatic mesh 3 surrounds the outside thereof. Further, an Einzel lens 4 is provided downstream of the extraction electrode 1. A counter electrode 7 is provided at four symmetrical positions with respect to the extraction electrode portion around the laser ionization region 5 by four support rods 6 shared with the extraction electrode portion. The counter electrode 7 has a guide electrode 2 ′, an electrostatic mesh 3 ′, and an Einzel lens 4 ′, similarly to the extraction electrode 1. Here, the Einzel lens 4 ′ of the counter electrode 7 does not contribute to ion detection, but is provided so that it can be immediately replaced when the Einzel lens 4 at the subsequent stage of the extraction electrode 1 is replaced. .
The pair of electrodes (the extraction electrode 1 and the counter electrode 7) need to be installed at positions completely symmetrical with respect to the laser ionization region 5, and the holes at the center of both nasal electrodes 1 and 7 are the extraction electrodes. 1, the center of the hole of the Einzel lens 4, the Y-axis deflector 11, the X-axis deflector 12, and the center of the potential switch 9 are on the same straight line.
[0016]
The two electrostatic meshes 3, 3 'are preferably separated by 5 to 100 mm depending on the size of the nasal electrode. More preferably, it is 5 to 20 mm, and particularly, about 10 mm is optimal for most efficiently capturing ions from the laser ionization region. A supersonic molecular jet stream is jetted toward the center from the pulse valve 10 in the upward direction on the paper. The holes of the two electrodes 1 and 7 are always on the same straight line, and the laser ionization region 5 is located at the midpoint of the distance between the holes. The extraction electrode 1 and the counter electrode 7 have a pair of symmetric structures centered on the laser ionization region 5, and when this structure is broken, the electric field is broken and ions cannot reach the detector with high efficiency. Therefore, a structure for maintaining the positional relationship holding the two electrodes by the support rod 6 is required.
[0017]
FIG. 3 shows an example of a schematic diagram of a Jet-REMPI apparatus according to the present invention. This figure is a diagram of the optical system viewed from the jet flow jetting direction, that is, a diagram viewed from the jet flow jetting direction of the pulse valve in the upward direction on the paper surface. This device irradiates an organic molecule released into a vacuum together with an inert gas such as He from a pulse valve with an ultraviolet laser for resonance selective excitation, and ionizes it through a multiphoton absorption process. The ionized organic molecules are mass-analyzed and detected by a time-of-flight mass spectrometry (TOF-MS), so that isomers and the like are selected based on the difference in resonance wavelength, and different mass numbers are used. Different organic molecules with are separable. In addition, by using the electrostatic reflection type TOF-MS, ions generated in the vicinity of the pulse valve or in collision with the extraction electrode can be separated, and noise can be reduced without reaching the detector.
[0018]
The degree of vacuum in the laser ionization region 5 according to the present invention needs to be 10 ⁻² Pa or less in order to increase the probability of surviving the ions generated by the laser to reach the detector. Further, in order to reduce noise of a detector installed in an adjacent TOF-MS, a degree of vacuum of 10 ⁻⁵ Pa or less is required in the TOF-MS. Therefore, even if differential evacuation is performed between the ionization region and the TOF-MS, the degree of vacuum in the laser ionization region needs to be about 10 ⁻⁵ Pa. Further, it is important to increase the number of particles to be introduced into the laser ionization region for higher sensitivity. Therefore, the degree of vacuum in the laser ionization region is optimally about 10 ⁻³ Pa.
[0019]
A potential switch 9 is provided downstream of the Einzel lens 4 according to the present invention. The potential switch is a cylindrical electrode. Here, let us consider a case in which the common measurement conditions of +2 kV of the counter electrode and -2 kV of the extraction electrode are applied. When the potential switch 9 is grounded, the ions extracted from the extraction electrode 1 at −2 kV feel an anti-power generation level, wander in the cavity of the potential switch 9, and are not extracted to the TOF-MS. On the other hand, if −2 kV is applied to the potential switch 9, ions pass through the potential switch 9 having the same potential as the extraction electrode 1 at a constant velocity. However, at the moment of leaving the outlet of the potential switch 9, the deflectors 11 and 12 having almost no potential and the grounded TOF-MS are felt, and also scatter and cannot reach the detector.
[0020]
Then, the present inventors applied a pulse-like high voltage to the cylindrical potential switch 9 in Japanese Patent Application No. 2001-207261, that is, the target particle reached the potential switch 9 to which −2 kV was applied. It is proposed that the potential of the potential switch 9 be stepped up to the ground potential in a pulsed manner over time, thereby solving the above-mentioned problem. That is, the ions arriving in the potential switch 9 are moving at a constant speed at a potential of -2 kV, but are boosted to the ground potential in a pulsed manner. As a result, the deflectors 11, 12 and TOF -Continue the constant velocity motion without feeling the ground potential of the MS and reach the detector.
[0021]
Since the nose-shaped electrode according to the present invention has the electrostatic mesh grounded on the outer peripheral portion, the pulse valve can be brought closer to the vicinity of the laser ionization region. Further, the nasal-shaped electrode according to the present invention does not require a skimmer to be provided in front of the bulb, so that a free molecular flow (Free jet) can be used. Therefore, the molecular flow can be efficiently cooled, and the valve can be arranged at a position close to the ionization region. This means that it is possible to detect a supersonic molecular flow at a position several millimeters immediately below the nozzle with the highest density, which is extremely advantageous for increasing the sensitivity.
[0022]
In the Jet-REMPI apparatus according to the present invention, assuming that the nozzle opening diameter of the pulse valve is D and the distance from the nozzle tip to the state where the molecular flow is most cooled is Y, the optimal setting value of Y / D is 15 ≦ It is in the range of Y / D ≦ 50.
Since the molecular concentration in the molecular flow decreases in inverse proportion to the square of the distance as Y increases, there is an optimum range. An optimum range similarly exists for cooling the molecular flow. For example, when He is used as the cooling gas, the cooling of the molecular flow is almost completed when Y / D = 40. However, the cooling condition of the molecular flow depends on the degree of vacuum, the evacuation speed of the evacuation pump, the type of cooling gas, and the like. For example, when air or the like is used, the cooling speed decreases. Therefore, it is preferable that Y / D has a certain range. Specifically, the upper limit of Y / D is preferably 50. When Y / D is more than 50, the cooling effect of the molecular flow is saturated, and the molecular concentration in the molecular flow is undesirably reduced. The lower limit of Y / D is due to restrictions on the device.
[0023]
Assuming that the distance between the pulse valve injection port and the center of the laser ionization region is X (mm), the center of the laser ionization region of the Jet-REMPI device according to the present invention reaches a state where the molecular flow is most cooled from the nozzle tip. Therefore, X = Y, and the optimal set value of X / D exists in the range of 15 ≦ X / D ≦ 50 for the above-described reason.
[0024]
Further, the nozzle opening diameter D of the pulse valve according to the present invention varies depending on the type of the pulse valve. However, if the nozzle opening diameter D is too large, a large load is imposed on the exhaust of the chamber, which is not realistic. If the diameter D is too small, the ejection pressure is too high, which is not preferable. Therefore, a preferable range of the nozzle opening diameter D is 0.4 mm ≦ D ≦ 1.5 mm. Considering an appropriate range of the nozzle opening diameter of the pulse valve, the distance X (mm) between the pulse valve injection port and the center of the laser ionization region is particularly preferably 15 ≦ X ≦ 45. If X is more than 45 mm, the molecular jet spreads and noise is generated by particles colliding with the nose-shaped electrode, which is not preferable. On the other hand, the lower limit of X is due to restrictions on the apparatus.
Since the cooling effect is saturated when the molecular flow exceeds 25 mm, 15 ≦ X ≦ 25 mm is particularly preferable for high sensitivity detection.
[0025]
【Example】
Hereinafter, the present invention will be described based on examples.
(Example 1)
Using the optical system shown in FIG. 2, the change in resonance multiphoton absorption ionization (REMPI) spectrum of phenol was observed using the Jet-REMPI apparatus shown in FIG. The distance from the pulse valve tip to the center of the laser ionization region was set to 25, 45, and 65 mm. The nozzle opening diameter of the pulse valve was 0.5 mm, and the distance between the electrostatic mesh and the center of the laser ionization region was 20 mm. For this reason, the distance from the tip of the pulse valve to the center of the laser ionization region could not be less than 25 mm.
[0026]
FIG. 4 shows the measurement results. It can be seen that even when the distance between the pulse valve injection port and the center of the laser ionization region is changed, the half width of the spectrum hardly changes. From the half width of the obtained spectrum, it was confirmed that the supersonic molecular jet was cooled to 6 K, and it was confirmed that the conditions were such that the molecular selectivity was sufficiently secured by tuning the laser wavelength.
This is probably because the distance from the electrostatic mesh to the center of the laser ionization region was 20 mm, and the gas flow ejected from the pulse valve was already sufficiently cooled.
[0027]
On the other hand, if the distance between the tip of the pulse valve and the center of the laser ionization region is increased, the spectrum tends to be tailed due to collision with an electrode or the like. This is because the molecules in the jet collide with the electrostatic mesh, preventing the cooling of the molecules, and when the molecules collide with the electrostatic mesh, the molecules previously adsorbed on the electrostatic mesh are released. This is considered to be due to ionization and noise entering the mass spectrometer.
Therefore, when the nozzle opening diameter of the pulse valve is 0.5 mm and the distance between the electrostatic mesh and the center of the laser ionization region is 20 mm, the optimal distance between the pulse valve injection port and the center of the laser ionization region is 25 mm. It was confirmed.
[0028]
(Example 2)
Under the same apparatus and conditions as in Example 1, the distance between the pulse valve injection port and the center of the laser ionization region was set to the optimum distance of 25 mm obtained in Example 1, and the concentration dependence of the signal intensity of chlorobenzene was measured. . Further, as Comparative Example 1, the Jet-REMPI apparatus disclosed by the present inventors in Japanese Patent Application No. 2001-207261 was used, and the distance between the pulse valve injection port and the center of the laser ionization region was determined by the optimum value obtained in Example 1. Similar experiments were performed outside the distance range.
FIG. 5 shows the correlation between the chlorobenzene concentration and the detection signal. As can be seen from the figure, in the measurement at the optimum distance, an ultra-trace gas can be measured with a detection sensitivity 2 to 5 times higher than that in Comparative Example 1, and the detection limit is about 0.1 ppt.
[0029]
【The invention's effect】
According to the present invention, it is possible to provide a high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer that is excellent in detecting an ultra-trace gas, a high-boiling gas, and an unstable gas existing in a high-temperature furnace or a flue.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a conventional supersonic molecular jet multiphoton absorption ionization mass spectrometer using parallel plate electrodes.
FIG. 2 is a schematic diagram of an optical system of a supersonic molecular jet multiphoton absorption ionization mass spectrometer according to the present invention.
FIG. 3 is a schematic diagram of a supersonic molecular jet multiphoton absorption ionization mass spectrometer according to the present invention.
FIG. 4 shows the distance dependence of the REMPI signal spectrum of phenol obtained using the nasal electrode according to the present invention between the pulse valve and the laser ionization region.
FIG. 5 shows a calibration curve of monochlorobenzene obtained with the Jet-REMPI apparatus of the present invention (Example 2) and a calibration curve obtained with the Jet-REMPI apparatus shown in Japanese Patent Application No. 2001-207261 by the present inventors. It is a figure which shows the comparison of a line (comparative example 1).
[Explanation of symbols]
1: Leader electrode 2, 2 ': Guide electrode 3, 3': Electrostatic mesh 4, 4 ': Einzel lens 5: Laser ionization area 6: Support rod 7: Counter electrode 8: Skimmer 9: Potential switch 10: Pulse Valve 11: Y axis deflector 12: X axis deflector 13: Detector 14: Resistance divider 15: Preamplifier 16: Digital oscilloscope 17: BOXCAR integrator 18: Personal computer

Claims (4)

A pulse valve for introducing a sample gas into the apparatus, an ionization region for ionizing the sample gas released from the pulse valve, an ion optical system for introducing ions generated in the ionization region to a detector, and the ion optics A supersonic molecular jet multiphoton absorption ionization mass spectrometer comprising an ion detector for detecting ions extracted from the system, wherein the extraction electrode of the ion optical system has a nasal electrode shape, and faces the extraction electrode. A counter electrode of the same shape is disposed at the position, a cylindrical potential switch is disposed behind the extraction electrode, and the detector is disposed further behind the extraction switch, and holes of the extraction electrode and the counter electrode are detected. Are arranged on the same straight line, and the opening diameter of the pulse valve injection port is D (mm). When the distance to the center of the area to X (mm),
15 ≦ X / D ≦ 50
A high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer characterized by the following. The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1, wherein an orifice is provided near a focus of ions inside the extraction electrode. 3. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1, wherein the X (mm) satisfies 15 ≦ X ≦ 45. 4. 3. The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1, wherein the X (mm) satisfies 15 ≦ X ≦ 25.

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