JP2002181786A - Detector for chemical substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detector by which a chemical substance is detected with high accuracy. SOLUTION: An ion trap 9 which is partitioned with reference to an ionization means 1 and a time-of-flight mass spectrometry means 19 is filled directly with a sample gas through a sample-gas introduction tube 3. As a result, a gas pressure in the ion trap 9 can be increased, and a gas pressure in the ionization means 1 and the means 19 can be maintained at a prescribed pressure or less. Thereby, the generation amount of ions 18 in the ion trap 9 is increased, and the chemical substance can be detected with high accuracy. Since the gas pressure in the ionization means 1 and the means 19 is maintained at the prescribed pressure or less, there is no fear that a trouble is generated with reference to the enhancement of the measurement sensitivity of the means 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical substance detecting device, and more particularly to a chemical substance detecting device capable of detecting a specific chemical substance with high accuracy.

[0002]

2. Description of the Related 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 and measuring the concentration of a chemical substance as described above, devices using conventional techniques such as gas chromatography and mass spectrometry are known. Of these, mass spectrometry is based on gas chromatography. It is superior in that the measurement time is short as compared with.

[0004] In the mass spectrometry, a sample gas is ionized using plasma by RF discharge (high frequency discharge), an electron beam from an electron gun, etc., and the ions are instantaneously accelerated to perform mass separation and correspond to the mass number. This is a method of identifying the substance by measuring the time of flight.

The time-of-flight mass spectrometry described above is a process of ionizing a sample gas. In the process of ionizing a sample gas, a substance other than a substance to be detected is ionized, and a substance or an atom having a smaller mass of the substance to be detected or a substance not to be detected is smaller. 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.

For this reason, techniques for preventing ionization of substances other than the substance to be measured in the sample gas have been developed. Also known is a resonance multiphoton ionization method in which a laser beam is radiated in accordance with the light absorption wavelength of a substance to be measured, and the substance is selectively multiphoton ionized.

[0007]

However, the resonance multiphoton ionization method capable of increasing the measurement sensitivity is based on dichlorobenzene, chlorobenzene or dioxin.
A substance containing a larger amount of chlorine, such as trichlorobenzene, has a lower ionization efficiency and lower measurement sensitivity. Therefore, an ultrashort pulse laser is required to compensate for the lower ionization efficiency. For this reason, the conventional apparatus is an expensive apparatus for measuring the specific substance as described above.

Therefore, the applicant of the present invention has improved the ionization efficiency of a specific substance, prevented the ionization of another substance having an ionization energy higher than the photon energy, and improved the measurement sensitivity by suppressing the generation of fragments of the specific substance. And a chemical substance detection device (Japanese Patent Application No. 2000-178985) capable of reducing the cost and simplifying the device.

[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 the ions ionized by the vacuum ultraviolet light, and an ion trap. Time-of-flight mass analysis means for accelerating the ions accumulated in the trap and identifying the chemical substance having the specific mass based on the time of flight of the accelerated ions.

An object of the present invention is to improve a chemical substance detecting apparatus of the prior application and to provide a chemical substance detecting apparatus capable of detecting a specific chemical substance with high accuracy.

[0011]

In order to achieve the above object, the present invention is characterized in that a sample gas introduction pipe for directly introducing a sample gas into an ion trap is connected to the ion trap. I do.

As a result, according to the present invention, the sample gas can be directly charged into the ion trap partitioned by the ionization means and the time-of-flight mass spectrometry means via the sample gas introduction pipe. For this reason, the gas pressure (gas density) in the ion trap can be increased, and the gas pressure in the ionization means and the time-of-flight mass spectrometry means can be maintained at a predetermined pressure or less.

[0013] Thus, the gas pressure in the ion trap, that is, the sample gas density, which is the ionization region, can be increased, so that a large amount of ions are ionized by vacuum ultraviolet light in the ion trap. As a result, the measurement sensitivity of the time-of-flight mass spectrometer is improved, and a specific chemical substance can be detected with high accuracy. Further, even if the gas pressure in the ion trap is increased, the gas pressure in the ionization means and the time-of-flight mass spectrometer is maintained at a predetermined pressure or less, so that the measurement sensitivity of the time-of-flight mass spectrometer is improved. There is no risk of causing any trouble.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a chemical substance detecting apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that this embodiment does not limit the chemical substance detection device.

(Description of the Configuration of the 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. The ion accelerating electrode 4 is disposed between an ion trap 9 described later and a time-of-flight mass spectrometer 19 described later.

The lamp 5 is provided with a supplied lamp gas 6.
(E.g., H ₂ / He, etc.) were discharged at μ-wave, H
_It generates vacuum ultraviolet light 7 having _two specific emission line energies of 10.2 eV. In the lamp 5, a substance to be ionized can be selected by changing the amount of photon energy of the generated vacuum ultraviolet light 7 by changing the type of the lamp gas 6 to be discharged. The pressure in the lamp 5 is reduced to, for example, about 10 Torr or less.

The lamp 5 is arranged in the ionization chamber 2 through a MgF ₂ window 8. The vacuum ultraviolet light 7
Is irradiated into the ionization chamber 2 through the MgF ₂ window 8. The MgF ₂ window 8 has good transmittance of the vacuum ultraviolet light 7.

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 disposed in the ionization chamber 2. The ion trap 9 is composed of two end cap electrodes 10 and 11 and one ring electrode 12, as shown in FIG.

The inner surfaces of the end cap electrodes 10 and 11 and the ring electrode 12 have a convex curved surface. At a substantially center of the one end cap electrode 10, a small hole for irradiating the vacuum ultraviolet light 7, that is, an irradiation hole 13 is provided. At the substantially center of the other end cap electrode 11, a small hole for extracting the accumulated ions to the outside, that is, an extraction hole 14 is provided.

An insulator 15 (for example, a ceramic insulator) is fixed between the ends 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.

The tip of the sample gas inlet tube 3 is connected to the ring electrode 12 of the ion trap 9. As a result, the sample gas (not shown) is introduced into the ion trap 9 via the sample gas introduction pipe 3, that is,
It can be directly introduced into the space 24 formed by the end cap electrodes 10 and 11 and the ring electrode 12. The sample gas introduced into the space 24 is ionized by the vacuum ultraviolet light 7.

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 1 having a specific mass can be adjusted.
8 can be sorted and stored 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.

The time for accumulating 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 of the extraction hole 14 and accelerated.

In FIG. 1, reference numeral 19 denotes time-of-flight mass spectrometry means (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. A flight room 20 of the time-of-flight mass spectrometry means 19 is arranged in communication with the ionization room 2.

A pump 21 is connected to the flight room 20. By the operation of the pump 21, the pressure in the flight chamber 20 and the ionization chamber 2 communicating with each other is maintained at a high vacuum, for example, about 10 ^-5 Torr or less. This high vacuum is such that the ions 18 flying in the ionization chamber 2 and the flight chamber 20 do not collide with other molecules and disappear.

An ion detector 22 is provided in the flight room 20 at a location where the ions 18 reach. The ion detector 22 includes, for example, a microchannel plate (so-called MCP), an electron multiplier, and the like. This ion detector 22
As shown in FIG. 3, a signal is output when the ions 18 are detected. The level of the signal output of the ion detector 22 changes depending on the amount of the ions 18.

An oscilloscope 23 is connected to the ion detector 22. This oscilloscope 23
As shown in FIG. 3, the ions 18 are detected by the ion detector 22.
Is to display the time waveform of the signal to be output at the time when is detected.

(Explanation of the operation of the embodiment) The chemical substance detecting device in this embodiment has the above-described configuration, and the operation thereof will be described below. The chemical substance to be detected in this example is, for example, dioxins and their precursors.

First, a sample gas is directly introduced into the ion trap 9 through the sample gas introduction pipe 3. on the other hand,
The lamp 5 is operated to supply the vacuum ultraviolet light 7 to the MgF ₂ window 8.
And the irradiation hole 13 of the ion trap 9 in the ionization chamber 2 to irradiate the ion into the ion trap 9. Then, the sample gas is ionized by the vacuum ultraviolet light 7.

At this time, 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 generated by one-photon energy.
Since it is ionized, the ionization efficiency is good.

Among the ionized ions, 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.

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
Is extracted from the extraction hole 14 and accelerated.

The accelerated packet of the ions 18 flies through the ionization chamber 2 and the flight room 20 and travels through the ion detector 22.
To reach. A specific mass of chemical substance in the sample gas is identified based on the flight time of the 18 packets of the ions.

For example, as shown in FIG. 3, when the flight time (μs) is T1, the mass M1 (eg, 112)
Of the chemical substance X1 (for example, monochlorobenzene) are identified. When the flight time (μs) is T2, the chemical substance X2 (for example, 146) of mass M2 (for example, 146)
Dichlorobenzene) 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.

Further, 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, based on 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:
It becomes 2 ppm. Further, 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.

(Explanation of the effects of the embodiment)
In the chemical substance detection device according to this embodiment, the sample gas can be directly charged into the ion trap 9 partitioned by the ionization means 1 and the time-of-flight mass spectrometry means 19 via the sample gas introduction pipe 3. . For this purpose, the gas pressure in the ion trap 9 is reduced by the ionization means 1.
Gas pressure in the ionization chamber 2 and the flight chamber 20 of the time-of-flight mass spectrometry means 19 can be increased. For example, it can be estimated to be about 10 times higher.

Further, the gas pressure in the ionization chamber 2 of the ionization means 1 and the gas pressure in the flight chamber 20 of the time-of-flight mass spectrometry means 19 can be maintained at a predetermined pressure (about 10 ^-5 Torr) or less. Moreover, if the gas pressure in the ion trap 9 is made substantially the same as that of the conventional apparatus, the gas pressure in the ionization chamber 2 of the ionization means 1 and the flight chamber 20 of the time-of-flight mass spectrometry means 19 is reduced to about 10 ^-5 Torr. Than, for example, about 1
Since the noise can be reduced to 0 ^-6 Torr or less, noise in the ion detector 22 can be reduced correspondingly, and the measurement sensitivity can be improved.

In the ion trap 9, the gap between the end cap electrodes 10, 11 and the ring electrode 12 is closed by the insulator 15, so that the ion trap 9 has a small irradiation hole 13 and a draw-out hole. 14 are just established. As a result, due to the resistance between the small irradiation hole 13 and the extraction hole 14, a certain degree of confidentiality exists between the ion trap 9 and the ionization chamber 2 of the ionization means 1 and the flight chamber 20 of the time-of-flight mass spectrometry means 19. Can be kept.

As a result, the gas pressure in the ion trap 9, which is the ionization region, that is, the sample gas density can be increased, so that the amount of ions ionized by the vacuum ultraviolet light 7 in the ion trap 9 is large. Become.
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. Further, even if the gas pressure in the ion trap 9 is increased, the gas pressure in the ionization chamber 2 of the ionization means 1 and the gas pressure in the flight chamber 20 of the time-of-flight mass spectrometry means 19 becomes lower than a predetermined pressure (about 10 ^-5 Torr). Since the time-of-flight mass spectrometry means 19 is held, there is no risk that the measurement sensitivity of the time-of-flight mass spectrometry means 19 will be hindered at all.

In particular, 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.

In this embodiment, since the lamp 5 is used as the means for generating the vacuum ultraviolet light 7, the cost is very excellent. In addition, although the lamp 5 has a lower photon density than the pulse laser, the lamp 5 emits light continuously, so that the total amount of photons is substantially equal. Moreover,
Since ions are accumulated in the ion trap 9, the small photon density does not cause any particular problem.

Further, in this embodiment, as the time-of-flight mass spectrometer 19, a type in which the ions 18 travel straight is used. For this reason, compared with a time-of-flight mass spectrometer in which ions make a U-turn 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.

In this embodiment, the chemical substances to be detected are dioxins and their precursors, but the present invention can be applied to the detection of other chemical substances.

As shown by a broken line in FIG. 2, the irradiation holes 13 may be provided in a direction intersecting (perpendicular to) the direction in which the ions 18 are extracted. In this case, the vacuum ultraviolet light 7 is not irradiated to the ion acceleration region between the ion trap 9 and the ion acceleration electrode 4. As a result, there is no possibility that the sample gas existing in the ion acceleration region is ionized and becomes noise.

[0045]

As is apparent from the above description, the chemical substance detecting apparatus according to the present invention transfers a sample gas through a sample gas introduction pipe into an ion trap partitioned with respect to ionization means and time-of-flight mass spectrometry means. Can be filled directly. For this reason, the gas pressure in the ion trap can be increased, and the gas pressure in the ionization means and the time-of-flight mass spectrometry means can be maintained at a predetermined pressure or less.

As a result, the gas pressure in the ion trap, that is, the sample gas density, which is the ionization region, can be increased, so that a large amount of ions are ionized by the vacuum ultraviolet light in the ion trap. As a result, the measurement sensitivity of the time-of-flight mass spectrometer is improved, and a specific chemical substance can be detected with high accuracy. Further, even if the gas pressure in the ion trap is increased, the gas pressure in the ionization means and the time-of-flight mass spectrometer is maintained at a predetermined pressure or less, so that the measurement sensitivity of the time-of-flight mass spectrometer is improved. There is no risk of causing any trouble.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a chemical substance detection device of 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) 6 Lamp gas 7 Vacuum ultraviolet light 8 MgF ₂ window 9 Ion trap 10, 11 End cap electrode 12 Ring electrode 13 Irradiation hole DESCRIPTION OF SYMBOLS 14 Lead-out hole 15 Insulator 16 Holder 17 High-frequency power supply 18 Ion 19 Time-of-flight mass spectrometry means 20 Flight room 21 Pump 22 Ion detector 23 Oscilloscope 24 Space

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01J49 / 40 H01J49 / 40 (72) Inventor Kaorunori Tsuruga 1-8-1, Koura, Kanazawa-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory (72) Inventor Shima Makoto Kuribayashi 1-8-1, Koura, Kanazawa-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory F-term (reference) 5C038 EE01 EF01 GG07 GH04

Claims (1)

[Claims] 1. 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 said vacuum ultraviolet light, and said ion trapped in said ion trap. A time-of-flight mass spectrometer for accelerating ions and identifying the chemical substance of the specific mass in the sample gas based on the time of flight of the accelerated ions. Is connected to a sample gas introduction pipe for directly introducing the sample gas into the ion trap.