JP2004119040A - 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. Opposed electrodes of the same shape are disposed at positively opposite positions of the electrodes, the pulse valve is disposed rear of the opposed electrodes. A cylindrical potential switch is disposed rear of the lead-out electrodes, the detector is further disposed rear of the potential switch, the detector is disposed rear of the switch, holes of the drawer electrodes and the opposed electrodes, a jet port of the valve, and the detector are coaxially disposed. <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]
In a general Jet-REMPI apparatus, as shown in FIG. 1, a laser ionization region 5 is usually sandwiched between parallel plate electrodes (extrusion electrode (opposite electrode) 7, extraction electrode 1) centered on two meshes. Put in space. 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 directly is also a plate electrode having a mesh.
[0007]
The particles ejected from the pulse valve 10 are introduced into the laser ionization region 5. 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 an apparatus capable of further high-sensitivity analysis in supersonic molecular jet multiphoton absorption ionization mass spectrometry (Jet-REMPI) in order to solve the conventional problems described above.
[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 a conventional supersonic molecular jet multiphoton absorption ionization mass spectrometer (Jet-REMPI) apparatus, since all ions ionized by the pulse ionization source reach the detector, the signal of the molecule of interest is not counted. If the output of the pulse ionization source is reduced to avoid this, there is a problem that a signal of an ultra-trace component cannot be detected.
[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 saturation of the mass spectrometer by selectively detecting generated ions, and detecting ions of interest more quantitatively and with high sensitivity.
However, even with the Jet-REPMI apparatus proposed by the present inventors in Japanese Patent Application No. 2001-207261, since the sample gas is injected in a direction orthogonal to the mass spectrometer, it is orthogonal to the mass spectrometer. When a molecular flow is jetted in the direction, there is a problem that the momentum of the molecule slightly affects the trajectory of the laser ionized particles, which affects the efficiency introduced into the mass spectrometer.
[0013]
Therefore, the present inventors, in order to solve the above-mentioned problems, to study an optical system for efficiently introducing the sample gas to the detector, that is, to study an optical system for ejecting the sample gas toward the mass spectrometer, In a conventional Jet-REMPI apparatus composed of parallel plate electrodes (extrusion electrode (counter electrode), extraction electrode) centered on a normal two-mesh, a sample gas is introduced into a laser ionization region, and the sample gas is introduced into a mass spectrometer. An experiment to generate a molecular flow in the opposite form was attempted.
[0014]
In order to generate a molecular flow in a form directly facing the mass spectrometer, it is necessary to provide a skimmer or a pulse valve upstream of the pushing electrode (counter electrode). However, if a skimmer or a pulse valve is installed on the upstream side of the extrusion electrode (counter electrode) and a molecular flow is jetted toward the extraction electrode having the mesh, the molecule collides with the mesh and the molecular motion is hardly cooled, Re-emission of the adsorbed molecules and ionization thereof cause noise, dielectric breakdown, and the like. Then, the present inventors removed the electrostatic mesh from the center of the push-out electrode (counter electrode) to leave a hole in the structure, and changed the structure without collision with molecules. However, in the case of a flat electrode having holes without a mesh, disturbance of the electric field (lens effect) appears around the holes, and the hole diameter of the pushing electrode (counter electrode) and the distance between the tip of the nozzle and the pushing electrode (counter electrode). As a result, the spread of the beam changes greatly.
[0015]
Therefore, the present inventors further performed ion trajectory calculation while fixing the distance between the nozzle tip (diameter 0.5 mm) and the extrusion electrode (counter electrode) to 5 mm. The reason why the distance is fixed to 5 mm is that when the distance is further increased, a discharge easily occurs between the pulse valve or the skimmer (ground) and the pushing electrode (counter electrode) (applying 3 kV). When the hole diameter of the extrusion electrode (counter electrode) is 6 mm under these conditions, the beam diameter of the laser-ionized particles is about 1.5 mm on the detector of the electrostatic reflection time-of-flight mass spectrometer, and the hole diameter is 10 mm. It was found to be 2.0 mm. Increasing the hole diameter further increases the beam diameter and may exceed the effective diameter of the detector. On the other hand, by increasing the pore size, the molecular jet can be introduced into the laser ionization region without any obstacle. For the above reasons, the inventors of the present invention set the hole diameter of the pushing electrode (counter electrode) to the nozzle diameter when the distance between the tip of the nozzle and the pushing electrode (counter electrode) is the closest distance at which no discharge occurs between them. By setting the thickness to 10 mm or less, it has been found that the disturbance of the electric field around the hole of the extrusion electrode (counter electrode) can be sufficiently suppressed, and the organic compound of interest can be detected with high sensitivity.
[0016]
In addition, the present inventors used a nostril-shaped electrode proposed in Japanese Patent Application No. 2001-207261, installed a skimmer or a pulse valve on the upstream side of the counter electrode, and moved from the hole of the counter electrode to the hole of the extraction electrode. By injecting a molecular flow and measuring with a detector arranged coaxially, it has been found that the ion collection efficiency can be higher than that of the conventional parallel plate type.
Furthermore, the present inventors have studied the structure of the gas introduction unit that can directly detect the atmosphere in the incinerator and the flue.As a result, by attaching a differential exhaust chamber using a skimmer or orifice, the detection system It has been found that the organic compound of interest can be detected with high sensitivity while maintaining the degree of vacuum while reflecting the concentration in the high-temperature reactor.
[0017]
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 an extraction electrode of the ion optical system has a nose-out shape, and a positive electrode of the extraction electrode. A counter electrode of the same shape is arranged at a position opposite thereto, a pulse valve is arranged behind the counter electrode, a cylindrical potential switch is arranged behind the extraction electrode, and the detector is arranged further behind the potential switch. And high sensitivity wherein the holes of the extraction electrode and the counter electrode, the injection port of the pulse valve, and the detector are coaxially arranged. Supersonic molecular jet multiphoton absorption ionization mass spectrometer.
(2) 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 hole and a mesh in a hole. A counter electrode having a hole of the same shape at a position facing the extraction electrode is arranged in parallel, a pulse valve is arranged behind the counter electrode, and the detector is arranged behind the extraction electrode, And a hole for the extraction electrode and the counter electrode, an injection port for the pulse valve, and the detector are coaxially arranged. Multi-photon absorption ionization mass spectrometer.
(3) The high-sensitivity supersonic molecular jet according to (1) or (2), wherein the pulse valve has a structure of a gas introduction chamber connected to a flue via a gate valve. Multiphoton absorption ionization mass spectrometer.
(4) The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass according to (3), wherein the gas introduction chamber is further connected to an inert gas supply device via a gas introduction valve. Analysis equipment.
(5) The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to (3), wherein a filter is provided in the gas introduction chamber or in a flue immediately before the gate valve.
(6) The high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to (1) or (2), wherein the sample gas is a gas released from a high-temperature furnace or a combustion furnace.
(7) The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to (6), wherein the sample gas contains fly ash.
[0018]
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.
The outline of the ion optical system of the Jet-REMPI apparatus according to the present invention will be described. As the electrode constituting the ionization region according to the present invention, a conventional parallel plate type electrode or 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. Furthermore, as will be described later, the laser ionization beam can be once focused within the electrode, so that a differential pumping system is configured in the gas inlet, and a high degree of vacuum can be maintained, thereby reducing the load on the mass spectrometer. Small, advantageous for continuous gas introduction systems utilizing skimmers or orifices. In addition, it has a counter electrode, electrostatic mesh, and guide electrode provided to further suppress noise, and selectively detects generated ions to avoid saturation of the mass spectrometer and focus on more quantitative and high sensitivity. Particles can be detected.
[0019]
First, an outline of an ion optical system using a nose-shaped electrode according to the present invention will be described. FIG. 2 shows an outline of an ion optical system using a nasal electrode according to the present invention.
The extraction electrode 1 has a nose-out shape, and has a cylindrical guide electrode 2 surrounding the extraction electrode 1 concentrically on the outside thereof. A cylindrical electrostatic mesh 3 surrounds the outside. Further, an Einzel lens 4 is provided downstream of the extraction electrode 1. An opposing electrode 7 is provided at four symmetrical positions of the extraction electrode portion with respect to the laser ionization region 5 by four support rods 6 shared with the extraction electrode. The counter electrode 7 has a guide electrode 2 ′, an electrostatic mesh 3 ′, and an Einzel lens 4 ′ similarly to the extraction electrode 1, and a pulse valve 10 is attached to a stage subsequent to the counter electrode 7.
[0020]
Since the pulse valve 10 operates at the ground potential, the pulse valve 10 maintains insulation from the push-out electrode (counter electrode) 7. Here, a cylindrical Teflon (registered trademark) block 19 in which a hole having a size equal to the diameter of the counter electrode 7 is passed through the center of the block 19 is attached and fixed concentrically with the center of the nozzle hole of the pulse valve 10. This material is not limited to Teflon, and any material may be used as long as it is less degassed in a vacuum, has high insulation properties, easily obtains processing accuracy, and does not deform even if a hole is formed. The shape may be a block shape or a disk shape. Further, the pore diameter is not particularly limited as long as it does not maintain the insulating property and does not hinder the injection of the sample gas.
[0021]
The Einzel lens 4 ′ of the counter electrode 7 does not contribute to ion detection, but is provided so that the lens can be replaced immediately when the Einzel lens 4 in the extraction electrode 1 breaks down. 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. , The center of the hole of the Einzel lens 4, the Y-axis deflector 11, the X-axis deflector 12, the center of the potential switch 9, the nozzle hole of the pulse valve 10, and the hole of the Teflon block 19. The two electrostatic meshes 3, 3 'are separated by about 5 to 100 mm. It is preferably about 5 to 20 mm, and about 10 mm is optimal for most efficiently capturing ions from the laser ionization region.
[0022]
From the pulse valve 10, a supersonic molecular jet stream is jetted. The holes of the two electrodes are always coaxial, and the laser ionization region 5 is located at the midpoint 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, it is necessary to maintain a positional relationship in which the two electrodes are held by the support rod 6.
[0023]
The degree of vacuum in the laser ionization region 5 is set at 10 to increase the probability of surviving the ions generated by the laser before reaching the detector. ^-2 It is necessary to make it Pa or less. In order to reduce the noise of the detector, 10 ^-5 A vacuum degree of Pa or less is required. Therefore, even if differential pumping is performed, the degree of vacuum in the laser ionization chamber is 10 ^-3 About Pa is required. On the other hand, it is important for increasing the sensitivity to increase the number of particles introduced into the laser ionization region. From the above, the degree of vacuum in the laser ionization chamber is 10 ^-3 Approximately Pa is optimal.
[0024]
A potential switch 9 is provided downstream of the Einzel lens 4. The potential switch is a cylindrical electrode. Here, let us consider a case where a common measurement condition 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 at −2 kV feel the anti-power generation level, wander in the cavity of the potential switch 9, and are not extracted to the mass spectrometer. 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 speed. However, at the moment of leaving the exit of the potential switch 9, the deflectors 11 and 12 and the grounded mass spectrometer which are almost non-potential are felt, and they also scatter and cannot reach the detector.
[0025]
In view of this, the present inventors have proposed in Japanese Patent Application No. 2001-207261 to apply a pulsed high voltage to the potential switch 9 having a cylindrical shape, whereby the above-described problem can be solved. That is, it can be achieved by raising the potential of the potential switch 9 to the ground potential in a pulsed manner at the time when the target particle reaches the inside of the potential switch 9 to which -2 kV is applied. 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, at the outlet of the potential switch 9, the deflectors 11 and 12 The constant velocity motion is continued without feeling the ground potential of the meter, and reaches the detector.
[0026]
FIG. 3 shows an ion orbit simulation result of laser ionized positive ions when the nose-shaped electrode according to the present invention is used. The simulation was performed using SIMION 7.0 under the conditions of applying the above-described voltage. The generated ions were focused inside the extraction electrode 1, turned into a parallel beam by the Einzel lens 4, and introduced into the mass spectrometer. You. Therefore, by arranging an orifice through which ions can sufficiently pass near the focal point of the ions inside the nose-shaped extraction electrode 1, it becomes possible to perform differential evacuation between the ionization region and the mass spectrometer. As described above, a nasal discharge electrode in which the degree of vacuum in the mass spectrometer is maintained and the differential exhaust is easily used to obtain measurement conditions with low signal noise is very effective.
[0027]
Next, an outline of an ion optical system using the parallel plate type electrode according to the present invention will be described. FIG. 4 shows an outline of an ion optical system using the parallel plate type electrode according to the present invention.
The push-out electrode (opposite electrode) 7 of the parallel plate electrode has no mesh in the hole at the center, and has a mesh only on the extraction electrode 1 side. Further, as described above, when the distance between the tip of the nozzle and the pushing electrode (counter electrode) is the closest distance at which no discharge occurs between them, as described above, the hole diameter of the pushing electrode (counter electrode) 7 Are conditions that can sufficiently converge. A pulse valve 10 is provided behind the push-out electrode (counter electrode) 7.
[0028]
Since the diameter of the head portion of the pulse valve is usually much smaller than that of the push-out electrode (counter electrode) 7, when a voltage is applied to the push-out electrode (counter electrode) 7 as it is, the electric field is disturbed due to non-uniform shape. Occurs. Therefore, a disk 20 having substantially the same shape as the push-out electrode (counter electrode) 7 was attached to the head of the pulse valve 10. A hole was made in the center of the disk 20 so that the nozzle hole of the pulse valve was not blocked. In order to prevent the disk from colliding with the molecular jet, the hole was made as large as possible, and the end portion was tapered (gently slanted polishing). The material of this disk may be an organic substance such as metal, ceramics, and Teflon.
[0029]
Next, the gas introduction section of the Jet-REMPI apparatus of the present invention will be described.
The gas introduced from the flue has almost the same composition as the atmosphere, and the cooling efficiency of the molecular jet is poor, so that the molecular selectivity may be degraded. In this case, the cooling efficiency can be improved by diluting the atmosphere of the gas introduced from the flue to a specific concentration with the inert gas. For cooling the molecular flow, an inert gas (rare gas) having a large specific heat becomes the most excellent medium, and He, Ne, Ar, and Xe are preferable. Generally, a supersonic molecular jet uses He gas containing an organic compound of interest.
[0030]
In the present invention, a gas introduction valve is installed in the gas introduction chamber. FIG. 5 shows an example of the outline from the flue to the gas introduction chamber according to the present invention. As shown in FIG. 5, the gas introduction valve 21 is installed in the gas introduction chamber. The subject gas from the flue 22 is introduced into the sample introduction chamber via the pipe via the gate valve 24. The rare gas whose flow rate is controlled by the mass flow meter 25 from the rare gas cylinder 26 is introduced from the gas introduction valve 21, mixed with the test gas in the gas introduction chamber, and introduced into the pulse valve 10. Thereby, it is also possible to grasp the detection limit of the specific organic compound and determine the lower limit of quantification.
[0031]
The technology of the present invention described above relates to the detection of ultra-trace gas, high boiling point gas, and unstable gas in a high-temperature furnace or in a flue, but in the flue, in addition to the gas components, fly ash and the like. Solid components are also convective. Such a solid component causes a problem of clogging of the pulse valve or becomes a source of contamination of the vacuum chamber. Therefore, the filter 23 is installed in the gas introduction chamber or in the flue immediately before the gas introduction chamber, and before being introduced into the vacuum chamber. , So that solid components can be removed. Further, by heating the filter 23, adsorption of gas components and condensation of moisture can be prevented. In general, it is better to make the heating temperature substantially equal to the ambient gas temperature in the flue. In particular, when the temperature is 100 ° C. or higher, condensation of moisture can be prevented by heating the filter. The filter may be made of any material as long as it has characteristics such as resistance to heating at 200 ° C. or more, processing into a mesh, and resistance to acid. Also, this filter is preferably replaceable. In the present invention, the filter itself is heated and held at about 170 ° C. so that gas components are not adsorbed to the filter 23 made of stainless steel and having a mesh of 40 to 200 μm in the examples described later.
[0032]
The organic molecules emitted from the pulse valve are irradiated with a laser to be ionized. The laser is typically Nd with a nanosecond pulse width. ³⁺ : A dye laser excited by a YAG laser is used. The wavelength to be subtracted needs to be changed according to the electronic excitation energy level of the molecule of interest. For example, it is 269.8 nm for chlorobenzene and 287.2 nm for p-chlorophenol. Therefore, it is necessary to tune the wavelength of the dye laser depending on the compound of interest and replace the dye in some cases. In recent years, an optical parametric oscillator (OPO) has been developed, and it has become possible to continuously extract the wavelength of laser light in a wavelength range of 2 μm to 200 nm.
[0033]
On the other hand, highly toxic environmental hormones, such as 2,3,7,8-tetrachlorodioxin, are not limited to polycyclic polyhalogen aromatics. When a compound in which a large number of halogen atoms are bonded to an aromatic ring absorbs laser light and is excited to the lowest excited state, intersystem crossing from a singlet state to a triplet state occurs, and finally fragmentation (cleavage) occurs. )Resulting in. This is called the heavy atom effect. It is known that the laser ionization probability of these polycyclic polyhalogen aromatic molecules is extremely reduced due to the heavy atom effect. In order to suppress this heavy atom effect, it is necessary to irradiate the molecule with a laser light pulse width of several to several hundred psec or less, which is the relaxation lifetime of intersystem crossing. However, when the pulse width is made extremely short, the energy resolution of the laser beam increases in inverse proportion to the uncertainty principle. Decrease in energy resolution may cause loss of molecular selectivity and structural isomer selectivity. Therefore, the energy resolution is 5 cm which can maintain the structural isomer selectivity. ^-1 It is better to use a wavelength tunable laser with a pulse width of up to 10 nsec, with 3 psec being the shortest.
[0034]
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 separated by a difference in resonance wavelength, and different masses are separated. Different organic molecules with numbers can be separated. 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.
[0035]
【Example】
Hereinafter, the present invention will be described based on examples.
(Example 1)
Using He as a rare gas, the correlation between the detected amount of chlorobenzene and the concentration of chlorobenzene in the gas was measured. For the measurement, a pulse valve was installed in the coaxial direction as shown in FIG. 4, and a parallel plate electrode-shaped ion optical system was used, and the distance between the pulse valve and the laser ionization region was set to 25 mm. The chlorobenzene concentration in He was changed by controlling the flow rate of He gas through a gas introduction valve. The chlorobenzene concentration of the He dilution introduced from the skimmer was quantified using a permeator. FIG. 6 shows the results obtained by mixing the gas in the permeator and the gas from the gas introduction valve into the gas introduction chamber, introducing the gas into the Jet-REMPI apparatus using a pulse valve, and obtaining the correlation between the concentration and the detection signal.
[0036]
As Comparative Example 1, a similar experiment was performed using a conventional orthogonal Jet-REMPI apparatus (pulse valve-laser ionization region distance: 55 mm) in which a pulse valve was installed above a parallel plate electrode as shown in FIG. FIG. 6 also shows the results of the above.
As can be seen from FIG. 6, the coaxial ion optical system of the present invention achieves about five times higher sensitivity than the conventional orthogonal type. This is considered to be largely affected by the fact that the coaxial type can shorten the distance between the pulse valve and the laser ionization region, so that a high-concentration molecular flow can be introduced into the laser ionization region. As can be seen from the figure, it was confirmed that an extremely linear calibration curve was obtained, and the detection limit was reduced from 10 ppt or less to about 2 ppt from the conventional signal / noise ratio.
[0037]
(Example 2)
In the same manner as in Example 1, the correlation between the detected amount of chlorobenzene and the concentration of chlorobenzene in the gas was measured using He as a rare gas. For the measurement, a nasal electrode as shown in FIG. 2 was used, and the distance between the pulse valve and the laser ionization region was set to 13 mm. As Comparative Example 2, a similar experiment was performed using an orthogonal Jet-REMPI apparatus (distance between a pulse valve and a laser ionization region: 25 mm) using a nasal electrode described in Japanese Patent Application No. 2001-207261. These results are also shown in FIG. As can be seen from the figure, a sensitivity improvement of about 5 times was confirmed.
The reason for this is that, as shown in Example 1 and Comparative Example 1, a similar improvement in sensitivity was observed in the case of the parallel plate electrode, but by further using the coaxial type, the distance between the pulse valve and the laser ionization region was reduced. It is considered that the reduction was almost halved. Since the molecular flow concentration of the jet is considered to be inversely proportional to the square of the distance, it can be said that the result is almost satisfactory.
[0038]
【The invention's effect】
According to the present invention, it is possible to provide a 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 supersonic molecular jet multiphoton absorption ionization mass spectrometer.
FIG. 2 is a schematic view of an ion optical system using a nose-shaped electrode according to the present invention.
FIG. 3 is an ion orbit simulation result of laser ionized positive ions when the nose-shaped electrode according to the present invention is used.
FIG. 4 is a schematic diagram of an ion optical system using a parallel plate electrode according to the present invention.
FIG. 5 is a schematic diagram from a flue to a gas introduction chamber according to the present invention.
FIG. 6 is a calibration curve of monochlorobenzene obtained by a high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer using a coaxial parallel plate electrode according to the present invention.
FIG. 7 is a calibration curve of monochlorobenzene obtained by a high-sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer using the coaxial nose-shaped electrode according to the present invention.
[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: Guide electrode
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
19: Teflon block 20: Disk
21: Gas inlet valve 22: Flue
23: Filter 24: Gate valve
25: Mass flow meter 26: Noble gas cylinder
27: Laser light

Claims (7)

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 nose-out shape, and is positioned at a position directly opposite to the extraction electrode. Arranging a counter electrode of the same shape, arranging a pulse valve behind the counter electrode, arranging a cylindrical potential switch behind the extraction electrode, further arranging the detector behind the same, and High sensitivity supersonic, wherein the extraction electrode and the counter electrode hole, the injection port of the pulse valve, and the detector are coaxially arranged. Child jet multiphoton absorption ionization mass spectrometer. 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 a system, wherein the extraction electrode of the ion optical system has a flat plate shape having holes and a mesh in a hole portion. A counter electrode having a hole of the same shape is arranged in parallel at a position facing the extraction electrode, a pulse valve is arranged behind the counter electrode, the detector is arranged behind the extraction electrode, and the A hole for an extraction electrode and a counter electrode, an injection port for the pulse valve, and the detector are coaxially arranged. DOO multiphoton absorption ionization mass spectrometer. The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1 or 2, wherein the pulse valve has a structure of a gas introduction chamber connected to a flue via a gate valve. apparatus. The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 3, wherein the gas introduction chamber is further connected to an inert gas supply device via a gas introduction valve. The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 3, wherein a filter is provided in the gas introduction chamber or in a flue immediately before the gate valve. The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 1 or 2, wherein the sample gas is a gas released from a high-temperature furnace or a combustion furnace. 7. The high sensitivity supersonic molecular jet multiphoton absorption ionization mass spectrometer according to claim 6, wherein the sample gas contains fly ash.

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