JP3652922B2 - Chemical substance detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a chemical substance detection apparatus and a concentration measurement method thereof, and more particularly to a chemical substance detection apparatus and concentration measurement method for detecting trace molecules such as halogenated organic chemical substances with high accuracy. About.
[0002]
[Prior art]
The detection of trace harmful substances is particularly strongly demanded. Trace amounts of harmful chemical substances such as chlorobenzenes and dioxins are contained in exhaust gas discharged from combustion furnaces and metal smelting furnaces. Conventional techniques such as gas chromatography and mass spectrometry are known as devices for detecting such chemical substances or measuring their concentrations. Mass spectrometry is superior to gas chromatography in that the measurement time is short.
[0003]
Mass spectrometry uses plasma by RF discharge (high frequency discharge), electron beam from an electron gun, etc., ionizes sample gas, instantaneously accelerates the ions to perform mass separation, and flight corresponding to the mass number It is a method of identifying the substance by measuring time. This type of flight mass spectrometry is a process of ionizing a sample gas. Substances other than the detection target substance are ionized, or the detection target substance and the non-detection target substance are decomposed into molecules and atoms that are smaller in mass. As a result, the generated fragments are complicated, making it difficult to identify a specific substance, resulting in a decrease in measurement sensitivity. In particular, chlorobenzenes and dioxins are easily decomposed in the process of ionization.
[0004]
A technique for preventing ionization of substances other than the measurement target substance in the sample gas is known. In general, it is effective to use a laser in order to increase the energy level of only the substance to be measured and ionize only that substance. However, in the laser ionization method that can increase the measurement sensitivity, the substance containing more chlorine such as dichlorobenzene and trichlorobenzene among chlorobenzenes and dioxins has a lower ionization efficiency and lowers the measurement sensitivity. Therefore, it cannot be said that it is effective for measurement of such a specific substance.
[0005]
Assuming that the irradiation energy is adjusted for the ionization energy of a specific substance and an electron beam that selectively ionizes the substance is used, the ionization efficiency of the specific substance is increased and the decomposition probability of the specific substance is reduced. It is desired to increase the detection sensitivity (presence detection sensitivity) of the measurement target substance by suppressing ionization of other substances, and further to increase the detection sensitivity of the concentration.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to improve the ionization efficiency of a specific substance on the premise that the irradiation energy is adjusted with respect to the ionization energy of the specific substance and an electron beam that selectively ionizes the substance is used. An object of the present invention is to provide a chemical substance detection apparatus and a concentration measurement method thereof that can reduce the probability of decomposition and suppress ionization of other substances.
Another object of the present invention is to improve the ionization efficiency of a specific substance on the premise that an electron beam for selectively ionizing the substance is used by adjusting the irradiation energy with respect to the ionization energy of the specific substance. An object of the present invention is to provide a chemical substance detection apparatus and its concentration measurement method capable of reducing the decomposition probability of a substance, suppressing ionization of another substance, and further enhancing the detection sensitivity of the concentration.
[0007]
[Means for Solving the Problems]
Means for solving the problem is expressed as follows. The technical matters corresponding to the claims in the expression are appended with numbers, symbols, etc. in parentheses (). The number, symbol, etc. clarify the correspondence / correspondence between the technical matters corresponding to the claims and the technical matters of at least one of the forms / implementations. It is not intended to show that the technical matter is limited to the technical matter of the embodiment.
[0008]
An apparatus for detecting a chemical substance according to the present invention includes an apparatus (6) for generating an electron beam (7) of a predetermined energy level, and a sample gas (8) ionized by the electron beam (7). It comprises a device (9) and a width adjusting device for actively narrowing the energy width of the electron beam (7). Means for determining the mass by measuring the time of flight of a substance whose electron beam energy has been accelerated and identifying the substance are conventional means. The specific substance is selectively ionized by reducing its decomposition probability by adjusting, and further, the probability is selectively further reduced by adjusting its width. The means for determining the mass by measuring the time of flight of the accelerated substance and identifying the substance is conventional means.
[0009]
The width adjusting device includes a grid electrode (13) and an applying device (15) for applying a voltage to the grid electrode (13), and the applying device (15) positively operates the adjusting device for adjusting the voltage. Have it. The application device (15) can adjust not only the width but also the absolute value of the energy of the electron beam.
[0010]
The width adjusting device further has a drawing hole (14) for drawing out electrons, and the drawing hole (14) is actively formed to be small. The sample gas (3) contains a halogenated organic chemical. In this case, in particular, the energy width is adjusted to be smaller than 2.0 eV. Furthermore, the energy is adjusted to be smaller than 20 eV.
[0011]
It is particularly effective to add an ion trap in which a high-frequency electric field is generated. The sample gas (8) accumulated in the ion trap is accelerated. In the ion trap, specific molecules selectively ionized are concentrated. This concentration dramatically increases the existence probability of specific ions. A specific substance that is selectively ionized by an electron beam having a small energy width and has a high existence probability is further concentrated, and the existence probability is increased in a multiplicative manner.
[0012]
Also in this case, it is experimentally confirmed that the sample gas contains a halogenated organic chemical, the energy width is smaller than 2.0 eV, and the energy is smaller than 20 eV. .
[0013]
The chemical substance concentration measurement method according to the present invention includes a step for irradiating a gasified substance to be detected with an electron beam, and a step for optimizing the energy of the electron beam and the width of the energy. The optimization is to increase the probability of selectively ionizing the detection target substance. If the energy level is extremely low, it can be negatively ionized.
[0014]
The detection target substance is a halogenated organic chemical substance, and its energy is desirably 20 eV or less, and its width is desirably 2 eV or less. Furthermore, as described above, it is particularly excellent that a step for concentrating a detection target substance irradiated with an electron beam in a high-frequency electric field is added.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Corresponding to the figure, in the embodiment of the chemical substance detection device according to the present invention, the ionization chamber is provided together with the gas introduction device. The gas introduction device 1 includes a gas injection pipe 2 as shown in FIG. The gas injection tube 2 is formed by an on-off valve or capillary tube using an orifice such as a pulse valve. A sample gas 3 introduced into the gas injection pipe 2 from the introduction side is introduced into the ionization chamber 4.
[0016]
The sample gas 3 is assumed to contain a halogenated organic compound (hereinafter referred to as a detection target substance) such as chlorobenzenes and dioxins. A heater 5 is provided around the gas injection pipe 2. The heater 5 is a heating device for preventing the detection target substance from adhering to the inner surface of the gas injection pipe 2.
[0017]
The ionization chamber 4 includes an electron gun 6. The electron gun 6 generates an electron beam 7. The sample gas 3 introduced into the ionization chamber 4 is irradiated with the electron beam 7, and then receives the energy to be ionized. The sample gas 8 ionized in this way is introduced into the mass spectrometer 9. The mass spectrometer 9 is adjacent to the ionization chamber 4. The ionized material receives an acceleration voltage instantaneously and is introduced into the mass spectrometer 9 and flies in the mass spectrometer 9. The flight time is measured. There is a highly accurate correspondence between the time of flight and the mass of the flying material.
[0018]
FIG. 2 shows an embodiment of the electron gun 6. The electron gun 6 includes a filament 11. A filament voltage 12 is applied to the filament 11. A grid electrode 13 is disposed in front of the filament 11. A lead-out hole 14 is formed in the grid electrode 13. An extraction voltage 15 is applied to the grid electrode 13.
[0019]
A thermoelectron group is generated from the filament 11 to which the filament voltage 12 is applied. The thermoelectron group is accelerated by the extraction voltage 15 applied to the grid electrode 13 and extracted from the extraction hole 14 to generate the electron beam 7. When the length of the filament 11 is short, the filament voltage 12 is low, or the extraction hole 14 is small, the energy width of the electron beam 7 is small. Further, the energy level of the electron beam 7 can be controlled to be low by adjusting the extraction voltage 15.
[0020]
[Example 1]
As sample gas 3, monochlorobenzene diluted with helium gas is used. Its density is adjusted. The sample gas 3 introduced into the gas injection tube 2 is introduced into the ionization chamber 4 after being heated by the heater 5. The sample gas 3 introduced into the ionization chamber 4 is ionized by being irradiated with the electron beam 7. The energy width of the electron beam 7 extracted from the extraction hole 14 adjusted to be small is adjusted to a value smaller than 0.5 eV. Further, the extraction voltage 15 is adjusted in the range of 0.5 eV to 10 eV.
[0021]
The sample gas 8 ionized by irradiation with the electron beam 7 is subjected to mass analysis by the mass analyzer 9. The minimum detected concentration of monochlorobenzene obtained as a result of mass spectrometry was 0.5 ppm as shown in FIG. In the figure, the result of mass spectrometry by the conventional method is shown, and the minimum detection concentration is 1 ppm. In the conventional method, the energy level of the sample gas 8 was adjusted to 100 eV.
[0022]
FIG. 4 shows another embodiment of the chemical substance detection apparatus according to the present invention. The gas introduction device 1, the ionization chamber 4, the heater 5, and the electron gun 6 are exactly the same as those shown in FIG. The electron gun 6 is exactly the same as the above-described embodiment in that the one shown in FIG. 2 is used.
[0023]
In the embodiment shown in FIG. 4, an ion trap 16 is further added. The ion trap 16 is a conventional technique. A high frequency voltage 17 is applied to the ion trap 16. There is a correspondence between the frequency and voltage of the high-frequency voltage 17 and the mass number of ions concentrated and accumulated in the ion trap 16. Other substances that are not specific substances that are accumulated in response to a voltage of a specific frequency are ejected from the ion trap 16, and the specific substances are concentrated in the electric field of the high-frequency voltage 17.
[0024]
After the concentrated specific substance is accumulated for a certain period of time (several seconds later), the concentrated specific ionized substance is introduced into the mass spectrometer 9 by applying an acceleration voltage to the specific substance, and the mass spectrometer Fly in 9. The flight time is measured. There is a more precise correspondence between time of flight and mass of flying material. Such a mass spectrometer or mass spectrometry method is a conventional means called a time-of-flight mass spectrometer or a time-of-flight mass spectrometry method.
[0025]
[Example 2]
Just as in the first embodiment, the energy width and the energy level of the electron beam 7 are adjusted. The time during which ionized monochlorobenzene, which is a specific substance, is accumulated in the ion trap 16 upon receiving an applied voltage of a specific frequency is 2 seconds. The analysis result by the flight-type mass spectrometer is shown in FIG. According to the method of the present invention, the minimum detected concentration is 0.01 ppm. According to the conventional method in which an ion trap is added as in the present invention, the minimum detection concentration is 0.1 ppm.
[0026]
Thus, in the previous embodiment, the method of the present invention has double detection accuracy compared to the conventional method, but in the later embodiment, the method of the present invention has detection accuracy 10 times that of the conventional method. have.
[0027]
【The invention's effect】
The chemical substance detection apparatus and the concentration measurement method according to the present invention improve the chemical substance concentration detection accuracy. By using an ion trap, the detection sensitivity is dramatically increased.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a chemical substance detection apparatus according to the present invention.
FIG. 2 is a circuit diagram showing an electron gun.
FIG. 3 is a table showing experimental results.
FIG. 4 is a sectional view showing another embodiment of the chemical substance detection apparatus according to the present invention.
FIG. 5 is another table showing experimental results.
[Explanation of symbols]
3, 8 ... Sample gas 6 ... Electron beam generator 7 ... Electron beam 9 ... Accelerator (flight type mass spectrometer)
13 ... Grid electrode 14 ... Lead-out hole 15 ... Application device

Claims (3)

An apparatus for generating an electron beam of a predetermined energy level;
An acceleration device for accelerating the sample gas ionized by the electron beam;
An adjustment device for adjusting the magnitude of the energy of the electron beam and the width of the energy to be small;
With an ion trap that generates a high-frequency electric field inside,
The existence probability of a specific molecule in the sample gas ionized by the electron beam having the energy and the energy width adjusted by the adjustment device is increased, and then the existence probability is multiplied by the ion trap. The specific molecules accumulated further increased by the acceleration device,
The specific molecule includes a halogenated organic chemical,
An apparatus for detecting a chemical substance, wherein the magnitude of the energy is smaller than 20 eV, and the width of the energy is adjusted to be smaller than 2.0 eV. In claim 1,
The adjusting device is
A grid electrode;
An application device for applying a voltage to the grid electrode,
The application device has a voltage adjustment device for adjusting the voltage. A chemical substance detection device. In claim 2,
The adjustment device further has a drawing hole for drawing out electrons. The chemical substance detection device.

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