JP2010286476A - Highly sensitive gas analyzer, gas quantitative method and gas analyzer system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable measurement of a trace gas up to ppm order without upsizing a device and increasing a cost with an improved accuracy in measurement values. <P>SOLUTION: A highly-sensitive gas analyzer for quantitatively measuring a trace gas includes a gas-to-be measured reservoir 21 to store the gas, a small container 23 to connect the gas reservoir through a first opening and closing valve, a buffer tank 25 with a volume greater than 2,000 times of that of the small container, to connect the small container through a second opening and closing valve, a manifold 27 to connect the buffer tank through piping, a quadrupole type mass spectrometer 30 with an evacuation device composed of a turbo molecular pump and a diaphragm pump having a third opening and closing valve interposed on an inlet port side, to connect the manifold, an orifice to flow the gas in the quadrupole type mass spectrometer, and bypass piping 38 with a fourth opening and closing valve interposed, to connect the manifold and the turbo molecular pump. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas analyzer, a gas quantification method, and an analyzer system that can repeatedly quantify a minute amount of gas contained in the atmosphere or the like with high sensitivity. Specifically, mass spectrometry that can measure trace gases such as specified gases in the atmosphere, harmful gases in automobile exhaust gases, specified gases in exhaled breath, specified gases contained in structural materials with high sensitivity on the order of ppm The present invention relates to a gas analyzer, a gas determination method and an analyzer system.

When measuring trace gases in the atmosphere by mass spectrometry, it is necessary to continuously flow the atmosphere (measuring gas) containing the gas to be measured (target gas) into the ion source of the mass spectrometer. is there. However, since it is necessary to make a difference of 100 million times (10 ⁸ ) or more between the gas pressure to be measured at or near atmospheric pressure and the pressure at which the mass spectrometer operates normally, several stages of differentials are required. While evacuating, the pore diameter of the gas inlet to the mass spectrometer ion source is extremely reduced to create a measurement pressure of 10 ⁻² Pa or less suitable for the operation of the mass spectrometer.

  That is, the conventional gas analyzer is configured as shown in FIG. The apparatus includes a measured gas reservoir 1, a variable leak valve 2, a manifold 3, a vacuum exhaust device 6 including a turbo molecular pump 4 and a diaphragm pump 5, a pipe 7 a connecting the measured gas reservoir 1 and the manifold 3, and a manifold 3 and the turbo molecular pump 4, a quadrupole mass spectrometer 11 with a vacuum pumping device 10 comprising a turbo molecular pump 8 and a diaphragm pump 9, and part of the measured gas from the manifold 3 The material constituting the hose is composed of an orifice 13 for flowing into the ion source 12 of the quadrupole mass spectrometer 11, which is a polyester material, and a pressure gauge 14 attached to the manifold 3.

  The flow of the gas to be measured in such an apparatus is as follows. That is, first, both the vacuum exhaust devices 6 and 10 exhaust the downstream pipe of the variable leak valve 2 and the quadrupole mass spectrometer 11 to a high vacuum, and put the quadrupole mass spectrometer 11 into an operating state. . Next, the variable leak valve 2 is appropriately opened so that the indication of the pressure gauge 14 attached to the manifold 3 becomes a predetermined value. This predetermined value is set in advance so that the pressure of the ion source 12 of the quadrupole mass spectrometer 11 becomes an optimum value for measurement based on this value, the conductance of the orifice 13, and the effective exhaust speed of the exhaust device. This analyzer is unique.

  In this state, a part of the measurement gas released from the measurement gas reservoir 1 flows into the ion source 12 of the quadrupole mass spectrometer 11 from the orifice 13 provided near the manifold 3, so that the mass spectrum of the gas By analyzing the above, the concentration of the target gas in the gas to be measured can be measured.

  However, in the conventional gas analyzer, it is difficult to finely adjust the flow rate in order to reduce the amount of gas released from the gas reservoir 1 to be measured by narrowing the variable leak valve 2, so that the reproducibility is poor. Conversely, if the variable leak valve 2 is opened and the amount of gas released from the gas reservoir 1 to be measured is increased, the pressure in the manifold portion increases, so that the orifice diameter must be made extremely small, and the conductance of the orifice 13 changes. Or the orifice 13 is clogged and the reproducibility is similarly deteriorated.

  Further, the conventional gas analyzer basically employs a method in which a gas to be measured is continuously flowed and measurement is performed in a steady state. Therefore, even if the reproducibility of the flow is ensured, there is a problem that the detection sensitivity of the target gas is remarkably lowered due to the influence of an adsorbing gas such as water vapor that is usually contained in a large amount in the gas to be measured.

That is, for example, when measuring a very small amount of hydrogen present in the gas to be measured, the analysis is performed by paying attention to the ratio of the mass number of ions to the charge m / e = 2 (H ₂ ⁺ ). However, if a large amount of water vapor is present in the gas to be measured, m / e = 1 (H ⁺ ) is generated, and if the value of m / e = 1 increases, the indication of m / e = 2 adjacent thereto will also be given. Influence. For this reason, an accurate value of m / e = 2 due to hydrogen of the target gas cannot be read, resulting in a decrease in detection sensitivity. Note that an adsorptive gas such as water vapor is easily adsorbed on a tube wall or an electrode of a mass spectrometer, and once adsorbed, it does not easily desorb unless heated to a high temperature.

  For this reason, the applicant first improves the accuracy (reproducibility) of measured values and measures trace gases up to the highest ppm order while minimizing the influence of adsorbent gases such as water vapor. The gas analyzer which enabled it was proposed (patent document 1). However, such an improved gas analyzer is equipped with a vacuum exhaust device consisting of a turbo molecular pump and a diaphragm pump connected to the manifold via a pipe, so that the gas analyzer is increased in size and cost. There was a problem.

Here, the reason why the gas analyzer has to be enlarged will be described.
1) If an adsorbing gas such as water vapor is contained in the gas to be measured, the detection sensitivity of the measurement target gas and the reproducibility of the measurement value are significantly reduced. The cause of this is as described below. That is, non-adsorbing gas such as hydrogen (H ₂ ) contained in the measurement target gas is immediately discharged and removed from the measurement area after measurement by the vacuum pump. However, even after the measurement is completed, the adsorbing gas such as water vapor stays in the measurement area repeatedly for a long time by repeating the adsorption / desorption phenomenon with the walls of the manifold 3 and the quadrupole mass spectrometer 11 and the tube wall surface. And a part of it accumulates on the instrument wall surface, and it is re-released irregularly from the instrument wall surface etc. at the next measurement, relative dilution (decrease in detection sensitivity) and background value of the measurement target gas concentration Cause irregular fluctuations (decrease in reproducibility).

  2) Therefore, the realistic evacuation condition for avoiding the adverse effects of these adsorptive gases at the next measurement is that the effective evacuation speed in the manifold 3 is 0.01 to 0.1 L / s and the pressure is attenuated. The time constant (see FIG. 4) is around 10 s. In order to realize this condition, a dedicated vacuum exhaust device 6 is connected by a pipe 7b to the manifold 3, and the adsorptive gas in the manifold 3 is continuously discharged and removed by the vacuum exhaust device 6 even during measurement. Gas detection sensitivity and reproducibility of measured values are maintained at high quality.

3) By the way, when the vacuum exhaust device 6 is not installed, these adsorptive gases must be discharged and removed only by the vacuum exhaust device 10 attached to the quadrupole mass spectrometer 11 of the gas analyzer. Specifically, the adsorptive gas is exhausted by the vacuum exhaust device 10 via the manifold 3, the orifice 13 and the ion source 12. The orifice 13 is a circular hole (diameter around 0.3 mm, conductance 8 × 10 ⁻³ L / s) and has the smallest conductance. In this case, the effective exhaust speed in the manifold 3 is 8 × 10 ⁻³ L / s, and the time constant of pressure decay (see FIG. 4) is around 120 s. It is theoretically known that the effective exhaust speed becomes the same value as the smallest conductance value.

  4) Therefore, when the adsorbing gas is exhausted and removed only through the orifice 13 without the dedicated vacuum exhaust device 6, the time constant of pressure decay becomes about 120s / 10s = 12 times longer. That is, the removal of the adsorptive gas through the orifice 13 alone takes too much time and is not realistic.

Japanese Patent No. 4052597

  The present invention has been made in consideration of such circumstances, and while improving the accuracy of measured values without incurring an increase in the size and cost of the apparatus, the influence of an adsorbing gas such as water vapor is minimized. An object of the present invention is to provide a high-sensitivity gas analyzer, a gas determination method, and an analyzer system capable of measuring trace gases up to the highest ppm order.

  The high-sensitivity gas analyzer according to the present invention is a high-sensitivity gas analyzer for quantitatively measuring a trace gas, and is connected to a gas reservoir to be measured that contains the gas to be measured, and the gas reservoir to be measured and the first on-off valve. A small container, a buffer tank connected to the small container via a second on-off valve, having a capacity of 2000 times or more the capacity of the small container, a manifold connected to the buffer tank via a pipe, and the manifold A quadrupole mass spectrometer with a vacuum exhaust system consisting of a turbo molecular pump and a diaphragm pump with a third on-off valve on the inlet side, and a gas to be measured into a quadrupole mass spectrometer It is characterized by comprising an orifice for inflowing, and a bypass pipe connecting a manifold and a turbo-molecular pump and having a fourth on-off valve interposed therebetween.

  The gas quantification method according to the present invention is a gas quantification method using the high-sensitivity gas analyzer, and operates the first and second on-off valves for the measurement gas stored in the measurement gas reservoir. The process of collecting a constant volume of gas to be measured in a small container, and after operating the vacuum exhaust device, the first on-off valve is closed and then the second on-off valve is opened to measure the inside of the small container. A step of diffusing the gas into the buffer tank, a step of transferring the diffused gas to be measured to the manifold via a pipe between the buffer tank and the manifold, and a mass analysis of the gas to be measured in the manifold via the orifice Supplying the ion source of the meter to ionize the gas to be measured, and measuring the ion current of the ionized gas to be measured to measure the target gas in the gas to be measured. If the measured gas pressure in the hold exceeds the upper limit of the normal operating pressure of the mass spectrometer, characterized by discharging the excess amount of measurement gas via a bypass pipe to the outside of the system.

  Furthermore, the high-sensitivity gas analyzer system according to the present invention includes the high-sensitivity gas analyzer, a host computer that analyzes the analysis by the high-sensitivity gas analyzer, and an analysis between the high-sensitivity gas analyzer and the host computer. And a wired or wireless contact mechanism for exchanging information and analysis result information.

  According to the present invention, measurement accuracy can be improved without increasing the size and cost of the apparatus, and measurement of trace gases up to the highest ppm order while minimizing the influence of adsorbent gas such as water vapor. A highly sensitive gas analyzer, gas determination method and analyzer system that can be obtained can be obtained.

FIG. 1 is a schematic view of a highly sensitive gas analyzer according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a highly sensitive gas analyzer system according to the present invention. FIG. 3 is a schematic view of a conventional gas analyzer. FIG. 4 is a diagram schematically showing temporal changes in pressure in the buffer tank and the manifold of the high sensitivity gas analyzer according to the present invention.

Hereinafter, the highly sensitive gas analyzer, gas determination method, and analyzer system of the present invention will be described in more detail.
In the present invention, the reason why the capacity of the buffer tank is 2000 times or more the capacity of the small container is as follows.
The quadrupole mass spectrometer, which is one configuration of the analyzer according to the present invention, allows an ionized (charged) gas to be measured to pass through an electric field region in which a high-frequency electric field and a DC electric field are superimposed. This is a device that detects separately the component gas species in the mixed gas by utilizing the fact that the flight trajectory of ions varies with the difference in weight (molecular weight). Therefore, in a quadrupole mass spectrometer, it is extremely important to ionize an electrically neutral measurement gas.

  As a method of ionizing an electrically neutral gas to be measured, thermoelectrons are emitted from a metal filament heated at a high temperature of about 1000 ° C. or more, and an external voltage is applied thereto to accelerate the thermoelectrons. For example, electrons can be struck out from neutral gas molecules by colliding with a gas to be measured, and changed to ions having a positive charge.

  Therefore, in the ion source of the quadrupole mass spectrometer, a metal filament such as tungsten heated at a high temperature of about 1000 ° C. or higher is lit to generate the thermoelectrons necessary for the operation of the quadrupole mass spectrometer. . It is known that when a reactive gas other than inert gas, such as oxygen and halogen, is present in the ion source above a certain upper limit pressure, the high-temperature metal filament undergoes an abrupt corrosion reaction and the filament leads to corrosion breakage. . This interrupts the generation of thermionic electrons from the hot metal filament and impedes normal operation of the quadrupole mass spectrometer.

It has been empirically known that the upper limit pressure of the reactive gas at which this corrosion reaction occurs remarkably does not depend much on the reaction gas species, and is about 50 Pa. Therefore, in order to suppress this corrosion reaction, The gas inlet of the source needs to be about 50 Pa or less. For this reason, in the present invention, it is necessary to reduce the pressure of the gas to be measured collected in the small container under the atmospheric pressure (approximately 1 atm, 0.1 MPa) to about 50 Pa or less. Therefore, the capacity of the buffer tank is set to about 2000 times that of the small container (0.1 × 10 ⁶ Pa / 50 Pa = 2000 times), and the gas to be measured is introduced and expanded from the small container into the buffer tank. The pressure is adjusted to about 50 Pa at the part.

  In the present invention, the bypass pipe having the fourth on-off valve interposed between the manifold and the turbo molecular pump is generally provided with a large amount of gas to be measured in the gas reservoir to be measured. This is because the gas pressure to be measured in the manifold may exceed the upper limit of the normal operating pressure of the quadrupole mass spectrometer.

(First embodiment)
Please refer to FIG.
Reference numeral 21 in the figure indicates a gas reservoir to be measured that accommodates the gas to be measured in an atmospheric pressure (0.1 MPa) state. A small container 23 (internal volume: about 0.1 ml) is connected to the measured gas reservoir 21 via a first on-off valve 22. A buffer tank 25 (internal volume: about 200 ml) is connected to the small container 23 via a second opening / closing valve 24. A manifold 27 having a pressure gauge (not shown) is connected to the buffer tank 25 through a pipe 26 having a large conductance. Here, a measured gas flow path 28 is constituted by the measured gas reservoir 21, the small container 23, the buffer tank 25 and the manifold 27. Here, the capacity of the buffer tank 25 is 2000 times or more the capacity of the small container 23.

  A quadrupole mass spectrometer 30 with an evacuation device is connected to the manifold 27 via a pipe 29. On the downstream side of the mass spectrometer 30, there is a vacuum exhaust device 31 composed of a turbo molecular pump 32 having a third on-off valve 36 on the inlet side and a diaphragm pump 33 connected to the turbo molecular pump 32. Has been placed. Here, the effective exhaust speed of the vacuum exhaust device 31 is 20 to 100 L / s. The intake port of the manifold 27 and the turbo molecular pump 32 is connected by a bypass pipe 38 having a fourth open / close valve 37 located on the manifold side. The mass spectrometer 30 includes an ion source 34. A thin metal plate (orifice) 35 having a circular hole (diameter of about 0.3 mm) is disposed in the pipe 29 connecting the manifold 27 and the mass spectrometer 30. A part of the gas to be measured is introduced into the ion source 34 of the mass spectrometer 30 from the middle of the gas flow path 28 to be measured by the orifice 35.

  The flow of the gas to be measured in such a gas analyzer is as follows. That is, first, the gas to be measured contained in the gas reservoir 21 to be measured is opened in the first on-off valve 22 (the second on-off valve 24 is closed). , 0.1 MPa) to be measured. Subsequently, after confirming that the vacuum exhaust device 31 is operating, the first on-off valve 22 is closed, and then the second on-off valve 24 is fully opened at high speed. As a result, the gas to be measured in the small container 23 quickly diffuses into the buffer tank 25. At this time, as shown in FIG. 4, the pressure in the buffer tank 25 once reaches a maximum value, and after that, since it is exhausted by the vacuum exhaust device 31, it gradually decreases. Since the buffer tank 25 and the manifold 27 are connected by a pipe 26 having a large conductance, the pressure in the manifold 27 changes almost the same as the pressure in the buffer tank 25. Therefore, the pressure in the buffer tank 25 and the manifold 27 immediately after opening the second on-off valve 24 is approximately 50 Pa.

  Thereafter, the gas to be measured diffused into the buffer tank 25 is transferred to the manifold 27. Next, the gas to be measured in the manifold 27 is supplied to the ion source 34 of the quadrupole mass spectrometer 30 through the orifice 35 to ionize the electrically neutral gas to be measured. Here, the ion current of the ionized measurement gas is measured, and the target gas in the measurement gas is quantified repeatedly. When the gas pressure to be measured in the manifold 27 exceeds the upper limit of the normal operating pressure of the quadrupole mass spectrometer 30, the fourth on-off valve 37 is opened / closed to bypass the bypass pipe 38. A quantity of gas to be measured is discharged out of the system.

  As described above, the high-sensitivity gas analyzer according to the embodiment includes the gas reservoir 21 to be measured, the small container 23 connected to the gas reservoir 21 to be measured via the first on-off valve 22, and the small container 23. A buffer tank 25 having a capacity of about 2000 times the capacity of the small container 23 connected through the second opening / closing valve 24, a manifold 27 connected to the buffer tank 25 via a pipe 26, and a connection to the manifold 27 A quadrupole mass spectrometer 30 having a vacuum exhaust device 31 comprising a turbo molecular pump 32 and a diaphragm pump 33 having a third opening / closing valve 36 on the intake side, and a part of the gas to be measured A bypass pipe 38 having a fourth on-off valve 37 connecting the orifice 35 flowing into the mass spectrometer 30, the manifold 27 and the turbo molecular pump 32. It is provided.

  According to such a high-sensitivity gas analyzer, the capacity of the buffer tank 25 is set to 2000 times the capacity of the small container 23, so that measurement can be performed without using a conventional vacuum exhaust device connected to the manifold via a pipe. In addition to improving the accuracy of the values, it is possible to measure trace gases up to the highest ppm order while minimizing the influence of adsorptive gases such as water vapor. Moreover, since the said vacuum exhaust apparatus can be removed, the structural member of an apparatus can be simplified and the enlargement and cost increase of an apparatus can be avoided. Furthermore, in the gas analyzer of the present invention, by providing a bypass pipe 38 between the manifold 27 and the turbo molecular pump 32, the gas pressure to be measured in the manifold 27 increases the upper limit of the normal operating pressure of the quadrupole mass spectrometer 30. When it exceeds, an excess amount of the gas to be measured is discharged and removed from the system via the bypass pipe 38 by opening and closing the fourth on-off valve 37. In this case, in response to the opening or closing operation of the fourth opening / closing valve 37, the third opening / closing operation is such that the operation of the third opening / closing valve 36 is always the opposite closing or opening operation of the fourth opening / closing valve 37. By operating the valve 36 and the fourth on-off valve 37 in conjunction with each other, it is possible to prevent the removed gas to be measured from flowing back into the quadrupole mass spectrometer 30.

(Second Embodiment)
Please refer to FIG.
The high-sensitivity gas analyzer system according to the present embodiment includes a high-sensitivity gas analyzer 41, a host computer 42 that analyzes the analysis by the analyzer 41, analysis information between the high-sensitivity gas analyzer and the host computer, and A wired or wireless contact mechanism 43 that exchanges analysis result information. Here, examples of the contact mechanism 43 include a mobile phone, a personal computer, a FAX, and a net computer, but are not particularly limited as long as analysis information and analysis result information can be exchanged.

  According to the second embodiment, the analysis information by the operator using the high-sensitivity gas analyzer 41 can be sent to the host computer 42, and the analysis result of the analyzer by the host computer 42 can be transmitted to the operator. Can transmit the analysis result to the operator without going to the site where the high-sensitivity gas analyzer 41 is arranged. Therefore, even if the operator is not sufficiently mastered in the analysis by the apparatus 41, an accurate analysis result can be obtained in a short time, and the analyst can also go to the site and analyze it, thereby eliminating waste of travel time. Can do.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, the ratio between the capacity of the buffer tank and the capacity of the small container is not limited to the above ratio, and may be 2000 times or more.

  21 ... Gas reservoir to be measured, 22 ... First open / close valve, 23 ... Small container, 24 ... Second open / close valve, 25 ... Buffer tank, 26, 29 ... Piping, 27 ... Manifold, 28 ... Gas flow to be measured, DESCRIPTION OF SYMBOLS 30 ... Quadrupole-type mass spectrometer, 31 ... Vacuum exhaust apparatus, 32 ... Turbo molecular pump, 33 ... Diaphragm pump, 34 ... Ion source, 35 ... Orifice, 36 ... Third on-off valve, 37 ... Fourth on-off valve 38 ... Bypass piping, 41 ... High sensitivity gas analyzer, 42 ... Host computer, 43 ... Communication mechanism.

Claims (3)

In a high-sensitivity gas analyzer that quantitatively measures trace gases,
A gas reservoir to be measured for containing a gas to be measured;
A small container connected to the measured gas reservoir via the first on-off valve;
A buffer tank having a capacity of 2000 times or more the capacity of the small container, connected to the small container via a second on-off valve;
A manifold connected to the buffer tank via a pipe,
A quadrupole mass spectrometer with a vacuum exhaust system consisting of a turbo molecular pump and a diaphragm pump interposing a third on-off valve on the inlet side connected to the manifold;
An orifice for allowing the gas to be measured to flow into the quadrupole mass spectrometer,
A high-sensitivity gas analyzer comprising a bypass pipe connecting a manifold and a turbo molecular pump with a fourth on-off valve interposed therebetween. A gas quantification method using the highly sensitive gas analyzer according to claim 1,
Collecting the gas to be measured in a small volume by operating the first and second on-off valves for the gas to be measured stored in the gas reservoir to be measured;
A step of diffusing the gas to be measured in the small container into the buffer tank by closing the first on-off valve and then opening the second on-off valve after operating the vacuum exhaust device;
Transferring the measured gas diffused to the manifold via a pipe between the buffer tank and the manifold;
Supplying the gas to be measured in the manifold to the ion source of the mass spectrometer through the orifice to ionize the gas to be measured;
Measuring the ion current of the ionized measurement gas, and quantifying the target gas in the measurement gas,
When the measured gas pressure in the manifold exceeds the upper limit value of the normal operating pressure of the mass spectrometer, an excessive amount of measured gas is discharged out of the system via a bypass pipe. Gas determination method.   2. The high-sensitivity gas analyzer according to claim 1, a host computer that performs analysis of analysis by the high-sensitivity gas analyzer, and a wire that exchanges analysis information and analysis result information between the high-sensitivity gas analyzer and the host computer. Or a highly sensitive gas analyzer system comprising a wireless communication mechanism.

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