JP3572256B2 - Chemical substance detection device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chemical substance detection device, and more particularly to a chemical substance detection device capable of detecting a specific chemical substance with high accuracy.
[0002]
[Prior art]
Trace amounts of harmful chemical substances, such as chlorobenzenes and dioxins, are contained in exhaust gas discharged from combustion furnaces and metal refining furnaces and are discharged. There is a particularly strong demand for accurate detection and concentration measurement of such trace harmful substances.
[0003]
As a device for detecting the above-described chemical substances and measuring the concentration, gas chromatograph methods and those using conventional techniques such as mass spectrometry are known. Among them, the mass spectrometry method is compared with the gas chromatograph method. It is excellent in that the measurement time is short.
[0004]
In mass spectrometry, a sample gas is ionized using plasma generated by RF discharge (high-frequency discharge), an electron beam from an electron gun, and the like, and the ions are instantaneously accelerated to perform mass separation, and a flight time corresponding to the mass number This is a method of identifying the substance by measuring the amount of the substance.
[0005]
Time-of-flight mass spectrometry, as described above, is a process in which a sample gas is ionized. In addition, the fragments generated by the decomposition are complicated, and it is difficult to identify a specific substance, resulting in a decrease in the measurement sensitivity.
[0006]
For this reason, techniques for preventing ionization of substances other than the substance to be measured in the sample gas have been developed. In addition, a resonance multiphoton ionization method is known in which a laser beam is radiated according to a light absorption wavelength of a substance to be measured, and the substance is selectively multiphoton ionized.
[0007]
[Problems to be solved by the invention]
However, the resonance multiphoton ionization method that can increase measurement sensitivity is based on the fact that, among chlorobenzenes and dioxins, the more chlorine-containing substances such as dichlorobenzene and trichlorobenzene, the lower the ionization efficiency. Since sensitivity is reduced, an ultrashort pulse laser is required to compensate for the reduction in ionization efficiency. For this reason, the conventional apparatus is an expensive apparatus for measuring the specific substance as described above.
[0008]
Therefore, the applicant has improved the measurement sensitivity by increasing the ionization efficiency of a specific substance, preventing the ionization of another substance having ionization energy higher than the photon energy, and suppressing the fragmentation of the specific substance. Filed a patent application for a chemical substance detection device (Japanese Patent Application No. 2000-178985) capable of reducing the cost and simplifying the method.
[0009]
The chemical substance detection device of the prior application is an ionization means for ionizing a sample gas with vacuum ultraviolet light, an ion trap for accumulating ions of a specific mass among ions ionized by the vacuum ultraviolet light, and Time-of-flight mass spectrometry means for accelerating the accumulated ions and identifying the chemical substance of the specific mass in the sample gas based on the time of flight of the accelerated ions.
[0010]
An object of the present invention is to improve a chemical substance detection device of the prior application, and to provide a chemical substance detection device capable of detecting a specific chemical substance with high accuracy.
[0011]
[Means for Solving the Problems]
To achieve the above object, the invention according to claim 1 has the following configuration. That is, the ionization means is partitioned into a first space for ion generation and a second space for ion accumulation by a partition wall having a hole through which ions pass, and the first space includes the vacuum ultraviolet light. Generating means, wherein the ion trap is disposed in the second space, and a drawing electrode for drawing ions generated in the first space into the ion trap in the second space. Is provided.
[0012]
As a result, according to the first aspect of the present invention, the first space and the second space are separated by the partition wall, so that the function of the ion trap in the second space is not impaired. (Gas density) can be increased. Further, by separating the vacuum ultraviolet light generating means on the first space side and the ion trap on the second space side by a partition wall, the irradiation volume of the sample gas with vacuum ultraviolet light can be increased in the first space. . By increasing the gas pressure and the irradiation volume of vacuum ultraviolet light, the amount of generated ions increases. For this reason, the measurement sensitivity of the time-of-flight mass spectrometer is improved, and accordingly, a specific chemical substance can be detected with high accuracy.
[0013]
The invention according to claim 2 is characterized in that a differential exhaust means is provided for lowering the pressure in the second space than the pressure in the first space.
[0014]
As a result, according to the second aspect of the invention, the gas pressure in the first space can be increased by the differential pumping means without increasing the gas pressure in the second space. For this reason, the generation amount of ions further increases, and a specific chemical substance can be detected with high accuracy.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a chemical substance detection device according to the present invention will be described below with reference to the accompanying drawings. The embodiment is not intended to limit the chemical substance detection device.
[0016]
(Description of Configuration of Embodiment)
In FIG. 1, reference numeral 1 denotes ionization means for ionizing a sample gas by vacuum ultraviolet light. The ionization means 1 mainly includes an ionization chamber 2, a sample gas introduction tube 3, an ion acceleration electrode 4, and a lamp 5 as a vacuum ultraviolet light generation means. A sample gas (not shown) is introduced into the ionization chamber 2 through the sample gas introduction pipe 3. The ion accelerating electrode 4 is disposed between an ion trap 9 described later and a time-of-flight mass spectrometer 19 described later.
[0017]
The lamp 5 discharges a supplied lamp gas 6 (for example, H ₂ / He) with a microwave to generate vacuum ultraviolet light 7 having a specific emission line energy of H ₂ of 10.2 eV. is there. This lamp 5 can change the type of the lamp gas 6 to be discharged, thereby changing the amount of photon energy of the generated vacuum ultraviolet light 7 and selecting a substance to be ionized. The pressure in the lamp 5 is reduced to, for example, about 10 Torr or less.
[0018]
The lamp 5 is arranged in the ionization chamber 2 via a MgF ₂ window 8. The vacuum ultraviolet light 7 is applied to the ionization chamber 2 through the MgF ₂ window 8. The MgF ₂ window 8 has good transmittance of the vacuum ultraviolet light 7.
[0019]
In FIG. 1, reference numeral 9 denotes an ion trap for accumulating ions of a specific mass among ions ionized by the vacuum ultraviolet light 7. This ion trap 9 is composed of two end cap electrodes 10 and 11 and one ring electrode 12, as shown in FIG. The ion trap 9 has a space 24 surrounded by the electrodes 10, 11, and 12.
[0020]
The inner surfaces of the end cap electrodes 10 and 11 and the ring electrode 12 are convex. At a substantially center of one of the two end cap electrodes 10, a hole for drawing in the generated ions 28 described later, that is, a drawing hole 13 is provided. In addition, a hole for extracting the accumulated ions 18 to the outside, that is, a drawing hole 14 is provided at substantially the center of the other end 11 of the two end cap electrodes.
[0021]
An insulator 15 (for example, a ceramic insulator) is fixed between the end of the end cap electrodes 10 and 11 and the end of the ring electrode 12. The end cap electrodes 10 and 11, the ring electrode 12 and the insulator 15 are held by a holder 16.
[0022]
As shown in FIG. 1, a high-frequency power supply 17 for applying a high-frequency voltage is connected to the end cap electrodes 10 and 11 and the ring electrode 12. By adjusting the frequency and voltage of the high-frequency voltage applied from the high-frequency power supply 17, ions 18 having a specific mass among the drawn ions 28 can be selectively accumulated in the space 24. That is, the ions 18 having a specific mass are held and accumulated by convection on the ion orbit by the high-frequency electric field whose frequency and voltage are adjusted. Other ions disappear on the electrodes 10, 11 and 12.
[0023]
The accumulation time of the ions in the ion trap 9 varies depending on the chemical substance to be accumulated, but is about 1 to 2 seconds. At the end of the accumulation time, a voltage is applied to the ion acceleration electrode 4 to apply an electric field. Then, the ions 18 accumulated in the ion trap 9 are drawn out from the extraction hole 14 and accelerated.
[0024]
A partition wall 25 is arranged in the ionization chamber 2. Thus, the inside of the ion chamber 2 is partitioned into a first space 26 for generating ions and a second space 27 for storing ions. The partition wall 25 is provided with a hole 29 through which the ions 28 pass.
[0025]
The first space 26 is connected to the sample gas inlet tube 3, the lamp 5, and the pump 30 respectively. The irradiation direction of the vacuum ultraviolet light 7 and the acceleration direction of the ions 18 are substantially orthogonal. That is, the lamp 5 is arranged at a position where the vacuum ultraviolet light 7 is not irradiated to the ion acceleration region between the ion trap 9 and the ion acceleration electrode 4. The first space 26 is filled with a sample gas (not shown). The sample gas filling the first space 26 is ionized by the vacuum ultraviolet light 7.
[0026]
The ion accelerating electrode 4 and the ion trap 9 are arranged in the second space 27. Further, a differential pump 31 is connected to the second space 27. The differential evacuation pump 31 reduces the pressure in the second space 27 to be lower than the pressure in the first space 26.
[0027]
Between the partition 25 and the ion trap 9 of the first space 26 and the second space 27, an ion drawing electrode 32 is disposed. The ion attracting electrode 32 is for attracting the ions 28 generated in the first space 26 through the ion passage holes 29 into the ion trap 9 in the second space 27.
[0028]
In FIG. 1, reference numeral 19 denotes a time-of-flight mass spectrometer (so-called TOFMS) for identifying a chemical substance having a specific mass in a sample gas based on the time of flight of the accelerated ions 18. The flight room 20 of the time-of-flight mass spectrometry means 19 is arranged in communication with the second space 27.
[0029]
A pump 21 is connected to the flight room 20. By the operation of the pump 21, the pressure in the flight room 20 and the second space 27 communicating with each other is maintained at a high vacuum, for example, about 10 ⁻⁵ Torr or less. The high vacuum is such that the ions 18 flying in the second space 27 and the flight chamber 20 do not disappear by colliding with other molecules.
[0030]
An ion detector 22 is installed in the flight room 20 where the ions 18 reach. The ion detector 22 includes, for example, a microchannel plate (so-called MCP), an electron multiplier, and the like. As shown in FIG. 3, the ion detector 22 outputs a signal when the ions 18 are detected. The level of the signal output of the ion detector 22 varies depending on the amount of the ions 18.
[0031]
An oscilloscope 23 is connected to the ion detector 22. As shown in FIG. 3, the oscilloscope 23 displays a time waveform of a signal output when the ions 18 are detected by the ion detector 22.
[0032]
(Explanation of the operation of the embodiment)
The chemical substance detection device according to this embodiment has the above-described configuration, and its operation will be described below. The chemical substance to be detected in this example is, for example, dioxins and their precursors.
[0033]
First, a sample gas is introduced into the first space 26 of the ionization chamber 2 via the sample gas introduction pipe 3. Then, the sample gas fills the first space 26 of the ionization chamber 2. At this time, the ionization chamber 2 is partitioned into a first space 26 and a second space 27, and the second space 27 is differentially evacuated by the differential evacuation pump 31. For this reason, the gas pressure in the first space 26 can be increased.
[0034]
On the other hand, the lamp 5 is operated to irradiate the vacuum ultraviolet light 7 into the first space 26 of the ionization chamber 2 through the MgF ₂ window 8. Then, the sample gas is ionized by the vacuum ultraviolet light 7. At this time, the irradiation volume of the vacuum ultraviolet light 7 into the first space 26 can be increased according to the size of the irradiation aperture of the lamp 5. Further, the vacuum ultraviolet light 7 is not applied to an ion acceleration region between the ion trap 9 and the ion acceleration electrode 4.
[0035]
In the irradiation with the vacuum ultraviolet light 7, the vacuum ultraviolet light 7 having a higher photon energy than the ionization energy of the chemical substance to be detected in the sample gas is irradiated. As a result, the chemical substance to be detected is ionized by one-photon energy, so that the ionization efficiency is high.
[0036]
The ions 28 ionized in the first space 26 are drawn into the ion trap 9 in the second space 27 through the ion passing hole 29 and the drawing hole 13 by the drawing electrode 32. Among the ions 28 drawn into the ion trap 9, the ions 18 having a specific mass are accumulated in the space 24 in the ion trap 9 for 1 to 2 seconds. Thereby, the density of the ions 18 increases.
[0037]
After the ions 18 are accumulated in the ion trap 9, a voltage is applied to the ion acceleration electrode 4. Then, 18 packets (group) of ions in the ion trap 9 are drawn out from the extraction hole 14 and accelerated. At this time, the direction of accelerating the extraction of the ions 18 and the direction of irradiation of the vacuum ultraviolet light 7 are substantially orthogonal to each other.
[0038]
The accelerated ion 18 packet flies through the second space 27 of the ionization chamber 2 and the flight room 20 and reaches the ion detector 22. A specific mass of the chemical substance in the sample gas is identified based on the flight time of the ion 18 packet.
[0039]
For example, as shown in FIG. 3, when the flight time (μs) is T1, the chemical substance X1 (for example, monochlorobenzene) having the mass M1 (for example, 112) is identified. When the flight time (μs) is T2, the chemical substance X2 (for example, dichlorobenzene) having the mass M2 (for example, 146) is identified. Here, in FIG. 3, time 0 refers to a point in time when a voltage is applied to the ion acceleration electrode 4.
[0040]
Moreover, as shown in FIG. 3, the concentration of the chemical substance to be detected is determined from the level of the signal output from the ion detector 22. For example, from the density characteristics, the density of the reference signal output level (the minimum triangular level in FIG. 3) is 1 ppm. In this case, since the signal output level S1 at the flight time T1 is twice the reference signal output level, the concentration of the chemical substance X1 in the mass M1 is 2 ppm. In addition, since the signal output level S2 at the flight time T2 is three times the reference signal output level, the concentration of the chemical substance X2 of the mass M2 is 3 ppm.
[0041]
(Explanation of effects of the embodiment)
As described above, the chemical substance detection device according to the present embodiment separates the first space 26 and the second space 27 in the ionization chamber 2 by the partition wall 25, thereby providing the function of the ion trap 9 in the second space 27. The gas pressure in the first space 26 can be increased to such an extent that is not impaired. In addition, the irradiation volume of the vacuum ultraviolet light 7 to the sample gas in the first space 26 is increased by partitioning the lamp 5 on the first space 26 side and the ion trap 9 on the second space 27 side by the partition wall 25. be able to.
[0042]
Increasing the gas pressure and the irradiation volume of the vacuum ultraviolet light 7 increases the amount of ions 28 generated. For this reason, the measurement sensitivity of the time-of-flight mass spectrometer 19 is improved, and accordingly, a specific chemical substance can be detected with high accuracy.
[0043]
In particular, in the chemical substance detection device according to this embodiment, the gas pressure in the second space 27 is increased by the differential pump 31 that makes the pressure in the second space 27 lower than the pressure in the first space 26. Without this, the gas pressure in the first space 26 can be increased. For this reason, the generation amount of the ions 28 is further increased, and a specific chemical substance can be detected with high accuracy.
[0044]
As described above, the chemical substance detection device according to the present embodiment is configured such that the region for ionizing the sample gas by the vacuum ultraviolet light 7 is provided in the first space 26 of the ionization chamber 2 which is separated from the ion trap 9. It is. For this reason, the generation amount of the ions 28 is increased under a restriction less strict than the restriction on the gas pressure of the ion trap 9 and the restriction on the irradiation volume of the vacuum ultraviolet light 7.
[0045]
Further, in this embodiment, the sample gas is ionized by one-photon energy of the vacuum ultraviolet light 7, so that the ionization efficiency is high.
[0046]
Further, in this embodiment, since the lamp 5 is used as a means for generating the vacuum ultraviolet light 7, the cost is very excellent. In addition, the lamp 5 has a lower photon density than the pulse laser, but emits light continuously, so that the total amount of photons is substantially equal. In addition, since the ions are accumulated in the ion trap 9, the small photon density does not cause any particular problem.
[0047]
Furthermore, in this embodiment, as the time-of-flight mass spectrometer 19, a linear type in which the ions 18 travel straight is used. For this reason, compared with a reflectron-type time-of-flight mass spectrometer in which ions are reflected by the electrodes, the amount of ions that collide with the electrodes and disappear is small. As a result, in this embodiment, the detection of the ions 18 by the ion detector 22 becomes accurate.
[0048]
In addition, in the chemical substance detection device according to the present embodiment, the direction in which the ions 18 are extracted and accelerated is orthogonal to the direction in which the vacuum ultraviolet light 7 is irradiated. Is not irradiated to the ion acceleration region between For this reason, it is possible to suppress the sample gas existing in the ion acceleration region from being ionized by the vacuum ultraviolet light 7 and becoming a noise. As a result, the measurement sensitivity of the time-of-flight mass spectrometry means 19 is improved, and accordingly, a specific chemical substance can be detected with high accuracy.
[0049]
(Examples other than the embodiment)
In this embodiment, the chemical substance to be detected is a dioxin or a precursor thereof, but the present invention can be applied to the detection of other chemical substances.
[0050]
Further, in this embodiment, the differential exhaust pump 31 is connected to the second space 27, but in the present invention, in particular, the differential exhaust pump 31 is not connected to the second space 27. Is also good.
[0051]
Further, in this embodiment, the irradiation direction of the vacuum ultraviolet light 7 and the extraction direction of the ions 18 are orthogonal, but in the chemical substance device of the present invention, the irradiation direction of the vacuum ultraviolet light 7 and the ions 18 May be the same direction.
[0052]
【The invention's effect】
As is clear from the above, in the chemical substance detection device according to the present invention (claim 1), the function of the ion trap in the second space is impaired by dividing the first space and the second space by the partition wall. The gas pressure in the first space can be increased to the extent that it does not occur. Further, by separating the vacuum ultraviolet light generating means on the first space side and the ion trap on the second space side with a partition wall, the irradiation volume of the sample gas with vacuum ultraviolet light can be increased in the first space. . By increasing the gas pressure and the irradiation volume of vacuum ultraviolet light, the amount of generated ions increases. For this reason, the measurement sensitivity of the time-of-flight mass spectrometer is improved, and accordingly, a specific chemical substance can be detected with high accuracy.
[0053]
Further, the chemical substance detection device according to the present invention (claim 2) is provided with a differential exhaust unit that makes the pressure in the second space lower than the pressure in the first space. By this differential evacuation means, the gas pressure in the first space can be increased without increasing the gas pressure in the second space. For this reason, the generation amount of ions further increases, and a specific chemical substance can be detected with high accuracy.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an embodiment of a chemical substance detection device according to the present invention.
FIG. 2 is a vertical sectional view showing the ion trap.
FIG. 3 is a graph showing a signal output from an ion detector and a flight time of ions displayed on an oscilloscope.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ionization means 2 Ionization chamber 3 Sample gas introduction pipe 4 Ion acceleration electrode 5 Lamp (vacuum ultraviolet light generation means)
Reference Signs List 6 lamp gas 7 vacuum ultraviolet light 8 MgF ₂ window 9 ion trap 10, 11 end cap electrode 12 ring electrode 13 lead-in hole 14 lead-out hole 15 insulator 16 holder 17 high-frequency power source 18 ion 19 time-of-flight mass spectrometer 20 flight room 21 Pump 22 Ion detector 23 Oscilloscope 24 Space 25 Partition wall 26 First space 27 Second space 28 Ions 29 Ion passage hole 30 Pump 31 Differential pump 32 Ion pull-in electrode

Claims (2)

Ionization means for ionizing the sample gas with vacuum ultraviolet light generated from the vacuum ultraviolet light generation means,
Of the ions ionized by the vacuum ultraviolet light, an ion trap that accumulates ions of a specific mass,
Time-of-flight mass spectrometry means for accelerating the ions accumulated in the ion trap and identifying the chemical substance of the specific mass in the sample gas based on the time of flight of the accelerated ions,
In the chemical substance detection device provided with
The ionization means is partitioned into a first space for ion generation and a second space for ion accumulation by a partition wall having a hole through which ions pass, and the first space has the vacuum ultraviolet light generation space. Means are provided, and the ion trap is disposed in the second space, and a drawing electrode for drawing ions generated in the first space into the ion trap in the second space is provided. A chemical substance detection device provided. The chemical substance detection device according to claim 1, further comprising a differential exhaust unit configured to lower a pressure in the second space from a pressure in the first space.

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