JP7682519B2 - Gas detection device and gas detection method - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies (1) Published on November 30, 2020 at http://www.siej.org/2020_taikai/proceeding2020.pdf. (2) Published at the 2020 Indoor Environment Society Academic Conference on December 4, 2020. (3) Published in the Proceedings of the 68th Chemical Sensor Research Presentation Conference, Chemical Sensors, Vol. 37, Supplement A (2021), pages 52-54, on March 9, 2021. (4) Published at the 68th Chemical Sensor Research Presentation Conference on March 22, 2021. (5) Presented in the Proceedings of the 68th Chemical Sensors Research Conference on March 9, 2021, Chemical Sensors, Vol. 37, Supplement A (2021), pages 55-57. (6) Presented at the 68th Chemical Sensors Research Conference on March 22, 2021.

The present invention relates to a gas detection device and a gas detection method for detecting a specific gas contained in a gas, such as a biological gas such as exhaled breath.

In recent years, biogas analysis, particularly breath analysis, has attracted attention as a health management method because it is a non-invasive analytical method, and breath analyzers have been developed. For example, Patent Document 1 reports a breath analyzer, but the semiconductor sensor for detection has a cavity separate from the gas flow path to precisely control the flow rate. Patent Document 2 also reports a passive sampler for collecting gas, but in this case, a porous diffusion plate or filter is provided to eliminate the effects of wind speed, and the sampler is exposed to the gas.

JP 2020-204533 A JP 2020-139740 A

When attempting to collect gases such as human breath released as biological gases and precisely analyze the specific gas components to be detected within the gas, if a semiconductor sensor or the like is used as the gas detection element, it is necessary to precisely control the flow rate in order to accurately grasp the amount of gas that comes into contact with the sensor in order to perform accurate gas detection, which requires a precise design of the collection device and a special structure in addition to the flow path. In addition, in the case of a passive sampler, it is necessary to install a diffusion plate that requires precise machining, as well as multiple diffusion control methods.

The present invention has been made to solve the above problems, and aims to provide a gas detection device and a gas detection method that can detect a specific gas to be detected in a gas stream in a simple manner with good sensitivity.

In order to solve the above problems, the gas detection device of the present invention comprises a container for storing collected gas, a tube having one end communicating with the container, a pump connected to the other end of the tube for drawing in the gas in the container through the tube, and a gas detection element disposed in a flow path in the tube through which gas flows and for detecting a specific gas contained in the gas, the gas detection element having a porous structure carrying a gas detection agent that reacts with the specific gas, and the pump draws in the gas so that the flow rate of the gas is diffusion-limited .

In addition, the gas detection method of the present invention comprises a storage step of storing the collected gas in a container, a suction step of connecting the container to one end of a tube and sucking the gas in the container so that it flows through the tube using a pump connected to the other end of the tube, and a detection step of exposing the gas to a gas detection element arranged in a flow path in the tube through which the gas flows by the suction step, and detecting a specific gas contained in the gas based on a change in characteristics of the gas detection element, wherein the gas detection element has a porous structure carrying a gas detection agent that reacts with the specific gas, and the pump sucks the gas so that the flow rate of the gas is diffusion-limited .

According to the gas detection device and gas detection method of the present invention, a gas detection element is placed inside a tube through which gas passes, with one end connected to a container that contains gas and the other end connected to a pump, and the gas is sucked in by the pump or the like. This allows detection to be performed by the diffusion rate-limiting factor of the gas to be detected, which has the excellent effect of making it possible to easily improve accuracy without the need to precisely control the flow rate of the gas. In addition, by making the tube transparent, measurements can be performed simultaneously with the flow of gas without removing the gas detection element from the tube, which has the excellent effect of allowing measurements to be performed with high accuracy.

1 is a diagram showing a first exemplary configuration of a gas detection device according to an embodiment of the present invention; FIG. 4 shows a second exemplary configuration of a gas detection device according to an embodiment of the present invention. FIG. 13 is a diagram showing a third exemplary configuration of a gas detection device according to an embodiment of the present invention. 2 is a flowchart showing a gas detection method according to an embodiment of the present invention. FIG. 13 is a graph showing the measurement results of the amount of change in absorbance of the gas detection element corresponding to the suction speed of the pump. FIG. 13 is a diagram showing the measurement results of the amount of change in RGB value of the gas detection element corresponding to the suction speed of the pump. FIG. 13 is a graph showing the results of measuring the amount of change in absorbance of a plurality of gas detection elements corresponding to the suction speed of a pump.

The best mode of the present invention will be described below with reference to the drawings. However, such examples do not limit the technical scope of the present invention.

Figure 1 is a diagram showing a first example of the configuration of a gas detection device in an embodiment of the present invention. The gas detection device 1 is configured to include a container 2 that contains sampled gas, a tube 3 whose one end (gas inlet side) is connected to the container 2, a pump 4 that is connected to the other end (gas outlet side) of the tube 3 and draws the gas in the container 2 through the tube 3, and a gas detection element 5 that is disposed in the flow path in the tube 3 through which the gas in the container 2 flows. Note that Figure 1(a) shows a configuration in which one gas detection element 5 is disposed in the tube 3, and Figure 1(b) shows a configuration in which two (multiple) gas detection elements 5 are disposed in the tube 3.

The container 2 is preferably a gas collection bag (sampling bag) that collects and stores gas, particularly biological gas such as exhaled air. The material of the gas collection bag 2 may be any material that does not adsorb the specific gas to be detected that is contained in the gas, and for example, a bag coated with Teflon (registered trademark) is used.

The tube 3 through which the gas passes is, for example, cylindrical or rectangular. If cylindrical, the cross-sectional shape is circular or elliptical, and if rectangular, the cross-sectional shape may be square, polygonal including rectangular, or any other shape. A gas collection bag 2 containing the collected gas is attached to one end of the tube 3 so that the gas can flow into the tube 3. A valve 9 may be provided to open and close the flow path of the tube 3 relative to the container 2.

For example, a transparent glass tube can be used for the tube 3. In the case of a transparent glass tube, as described below, by installing a light source, such as an LED light source, and a photodetector, such as a photodiode, outside the tube, the state of the gas detection element 5 can be measured in real time and without exposing it to the outside air after exposure, allowing results to be obtained quickly and allowing highly accurate measurements by avoiding contamination by the outside air. In addition, by acquiring an image of the gas detection element 5 through the transparent glass tube, the color information of the gas detection element 5 can be converted into the gas concentration of a specific gas by image processing, making measurements easier.

The material of the tube 3 may be any material that does not adsorb the specific gas, such as a glass tube, a quartz tube, or a Teflon tube.

The diameter of the tube 3 through which the gas passes can be any size that allows the gas detection element 5 to be inserted, and can be, for example, 10 mm to 20 mm.

The pump 4 is attached to the other end of the tube 3 and draws gas from the container 2 attached to one end into the tube 3. The suction of the pump 4 causes the gas in the container 2 to flow from one end of the tube 3 to the other end.

The pump 4 may be one that can draw in gas at a flow rate (amount of suction) of, for example, 0.05 L/min to 2.0 L/min. The flow rate is proportional to the flow rate, with the cross-sectional area of the tube being a constant. If the flow rate is too low, gas detection will not be diffusion-limited but supply-limited, and the output of the gas detection element 5 will depend on the flow rate. If the flow rate is too high, however, a large amount of gas will need to be collected, which may result in large errors and further difficulty in collection. For this reason, the pump 4 of the present invention draws in gas so that the flow rate of the gas flowing through the tube 3 is diffusion-limited.

The pump 4 may be any pump whose flow rate can be controlled, such as a small pump used for environmental measurement using a detector tube, or it may be a manually operated pump.

The gas detection element 5 is a gas detection element having a porous structure carrying a gas detection agent that reacts with a specific gas component to be detected. The specific gas is, for example, a ketone such as acetone, an aldehyde such as formaldehyde, or nitrogen oxide. In the gas detection element 5 having a porous structure, the pore size of the porous body is, for example, 4 nm, and may be within the range of 4 nm to 100 nm, and the pore size of the porous body may be small enough to detect the gas at the diffusion rate limiting the gas.

The gas detection element 5 is placed in the flow path in the tube 3 so that its detection surface is, for example, parallel to the longitudinal direction of the tube 3. That is, the gas in the tube 3 flows across the detection surface of the gas detection element 5 from one end to the other. If the detection surfaces are the top and bottom surfaces when placed parallel, gas diffusion occurs at the top and bottom surfaces. Alternatively, the gas detection element 5 is placed in the flow path in the tube 3 so that it is, for example, perpendicular to the longitudinal direction. In this case, since the conductance of the detection element is very small, the gas in the tube 3 collides with the detection surface of the gas detection element 5 and then flows up, down, left and right across the surface of the detection element. Here, gas diffusion occurs into the detection element from the contact surface between the detection element and the gas.

Also, as shown in FIG. 1(b), multiple gas detection elements 5, each of which reacts to a different specific gas component, may be arranged in parallel within the tube 3. This makes it possible to detect multiple types of specific gases simultaneously.

Figure 2 is a diagram showing a second example of the configuration of a gas detection device according to an embodiment of the present invention. Compared to the first example, the second example further includes a light source 6 and a photodetector 7. The tube 3 is a transparent tube or a tube that is capable of transmitting the light to be detected to a certain extent. The light source 6 and the photodetector 7 are arranged on either side of the gas detection element 5 arranged in the tube 3, and the light emitted by the light source (e.g., an ultraviolet light-emitting diode) 6 irradiates the gas detection element 5 arranged in the tube 3. The photodetector 7 is, for example, a photodiode or a detection unit of a spectrophotometer, and detects the light that has passed through the gas detection element 5. This makes it possible to measure the absorbance of the gas detection element 5 while the gas detection element 5 is arranged in the tube 3.

In addition, after flowing gas into the tube 3 and exposing the gas to the gas detection element 5 placed in the tube 3, the gas detection element 5 may be removed from the tube 3 and placed in a predetermined position, and the absorbance of the gas detection element 5 may be measured using the light source 6 and the photodetector 7.

Figure 3 is a diagram showing a third example configuration of a gas detection device according to an embodiment of the present invention. Compared to the first example configuration, the third example configuration further includes an imaging device (camera or scanner) 8. Furthermore, the tube 3 is a transparent tube or a tube capable of acquiring a detection image to some extent. The imaging device 8 is positioned so that it can image the detection surface of the gas detection element 5 through the transparent tube 3, and by imaging the detection surface of the gas detection element 5 with the imaging device 8, color information (e.g., RGB values) of the gas detection element 5 can be measured from the image data.

In addition, after flowing gas into the tube 3 and exposing the gas to the gas detection element 5 placed in the tube 3, the gas detection element 5 may be removed from the tube 3 and placed in a predetermined position, and the gas detection element 5 may be imaged by the imaging device 8, and color information may be obtained from the image data.

Figure 4 is a flow chart of the gas detection method using the gas detector of the present invention. In the gas detection method, first, a gas, which is a biological gas such as exhaled air, is collected and stored in a container 2 (S100). Then, the container 2 is attached to one end of a tube 3 so that the gas can communicate with the tube, and a pump 4 connected to the other end of the tube 3 is used to suck the gas from the container 2 so that the gas flows through the tube (S102). In other words, the gas is forced to flow through the tube 3 by suction using the pump 4. The gas is exposed to a gas detection element 5 arranged in the tube 3 through which the gas flows at a predetermined flow rate by the suction operation (S104), and a specific gas contained in the gas is detected based on the change in the characteristics of the gas detection element 5 exposed to the gas (S106).

In the suction step (S102), the suction operation of the pump 4 is controlled so that the gas flows through the tube 3 at a flow rate equal to or greater than a certain value, so that the gas flow rate is diffusion-limited.

Also, if the gas is exhaled gas, a pump is not required as the person can exhale directly without collecting the gas, and the above process can be carried out by adjusting the amount of air exhaled by the person.

The change in the characteristics of the gas detection element 5 is, for example, a change in the degree of light absorption (absorbance) of the gas detection element 5. Based on the second configuration example of FIG. 2, the absorbance of the gas detection element 5 may be measured on the spot by using a transparent tube for the tube 3 and attaching a light source 6 and a photodetector 7 to the tube 3, or, according to the first configuration example described above, the gas detection element 5 may be exposed to gas in the tube 3, and then removed from the tube 3 and the absorbance may be measured using the light source 6 and the photodetector 7. The concentration of a specific gas can be determined according to the absorbance of the gas detection element 5.

For example, as shown in FIG. 2, a gas detection device using an acetone detection element that detects acetone as the gas detection element 5 may be configured such that the gas detection element 5 is disposed between a light source 6 such as an ultraviolet light-emitting diode with a central wavelength of 385 nm, and a photodetector as the light detector 7, so that the light transmitted through the gas detection element 5 can be detected by the photodetector, and the output signal from the photodetector is processed to output the change in absorbance of the gas detection element. With such a simple device configuration, the extremely small amount of acetone described above can be easily measured.

The characteristic change of the gas detector element 5 is, for example, a color change of the gas detector element 5. Based on the third configuration example of FIG. 3, color information of the gas detector element 5 is obtained by imaging the gas detector element 5 with the imaging device 8 and measuring the RGB values of the image data. An image of the gas detector element 5 may be obtained on the spot through the tube 3 using a transparent tube 3. According to the first configuration example, the gas detector element 5 may be exposed to gas in the tube 3, and then the gas detector element 5 may be removed from the tube 3 and the image of the gas detector element 5 may be taken with the imaging device 8, and color information (RGB values) may be obtained from the image data. The concentration of a specific gas may be determined according to the color information of the gas detector element 5.

The present invention will be specifically described below based on examples. Note that specific conditions are shown here to facilitate understanding of the invention, but the implementation of the present invention is not limited to the combinations or numerical ranges of the following examples.

The gas sensor element used was an acetone sensor element, which was fabricated by the method disclosed in, for example, the following document 1.
Reference 1: Microchemical Journal, 159, (2020)105428

Porous glass with a pore size of 4 nm was used as the substrate. The gas detector element, whose absorption spectrum (absorbance) from 300 nm to 2000 nm had been measured in advance using a spectrophotometer (photodetector), was placed parallel to the glass tube in a glass tube with an inner diameter of 12 mm. Air with a humidity of about 50% and an acetone concentration of 5 ppm was adjusted in a commercially available 2 L sampling bag. The cock of the sampling bag was connected to the glass tube using a silicon rubber stopper and Teflon tubing. The other end of the transparent glass tube was connected to a pump using a silicon rubber stopper and Teflon tubing. A suction pump for measuring atmospheric air was used as the pump. The pump was operated to allow aeration at a flow rate of 0.05 L/min for 5 minutes. The gas detector element was then removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer, and the difference in absorbance at 390 nm was calculated.

Next, a similar system was assembled, the pump was operated, and aeration was carried out for 5 minutes at a flow rate of 0.1 L/min. The gas detector element was then removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer, and the change in absorbance at 390 nm was calculated.

Next, a similar system was assembled, the pump was operated, and aeration was carried out for 5 minutes at a flow rate of 0.2 L/min. The gas detector element was then removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer, and the change in absorbance at 390 nm was calculated.

Next, a similar system was assembled, the pump was operated, and aeration was carried out for 5 minutes at a flow rate of 0.3 L/min. The gas detector element was then removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer, and the change in absorbance at 390 nm was calculated.

Figure 5 shows the measurement results of the change in absorbance of the gas detection element in response to the gas flow rate. The difference in absorbance is constant at all flow rates, and it has become clear that the detection of acetone with the detection element is diffusion-limited, and that fine control is not necessary if the flow rate is 0.05 L/min or higher. It has also been shown that measurements can be easily made using a small volume of gas with a simple system that only uses such a gas detection element and a tube.

The gas detector used was an acetone detector. The acetone detector was fabricated by the method disclosed in the above-mentioned document 1. The substrate was porous glass with a pore size of 4 nm. The gas detector, whose image had been captured in advance by a digital camera, was placed parallel to a glass tube with an inner diameter of 12 mm. Air was adjusted to a humidity of about 50% and an acetone concentration of 5 ppm in a commercially available 2 L sampling bag. The cock of the sampling bag was connected to the glass tube using a silicon rubber stopper and a Teflon tube. The other end of the glass tube was connected to a pump using a silicon rubber stopper and a Teflon tube. The pump used was a suction pump for measuring atmospheric air. The pump was operated to ventilate the sample at a flow rate of 0.05 L/min for 5 minutes. The gas detector was then removed and images were captured by a digital camera (imaging device). The images before and after exposure were analyzed using RGB, and the change in B/G value was calculated.

Next, a similar system was assembled, the pump was operated, and aeration was performed at a flow rate of 0.1 L/min for 5 minutes. The gas detection element was then removed and images were taken. The images before and after exposure were subjected to RGB analysis, and the change in the B/G value was calculated.

Next, a similar system was assembled, the pump was operated, and aeration was performed at a flow rate of 0.2 L/min for 5 minutes. The gas detection element was then removed and images were taken. The images before and after exposure were subjected to RGB analysis, and the change in the B/G value was calculated.

Next, a similar system was assembled, the pump was operated, and aeration was performed for 5 minutes at a flow rate of 0.3 L/min. The gas detection element was then removed and images were taken. The images before and after exposure were subjected to RGB analysis, and the change in the B/G value was calculated.

Figure 6 shows the measurement results of the change in color information (B/G value) of the gas detection element in response to the gas flow rate. The change in the B/G value was almost constant at all flow rates, and it was made clear that the detection of acetone with the detection element was diffusion-limited, and that fine control was not necessary if the flow rate was 0.05 L/min or higher. It was also shown that measurements can be easily made with small volumes of gas using a simple system that only uses such a gas detection element and a tube.

The gas detection elements used were an acetone detection element and a nitrogen dioxide detection element. The acetone detection element was fabricated, for example, by the method disclosed in the above-mentioned document 1. The nitrogen dioxide detection element was fabricated, for example, by the method disclosed in the following document 2.
Reference 2: Sensors and Actuators B 173, 191-196(2012)

Porous glass with a pore size of 4 nm was used as the substrate. Each gas detector element, whose absorption spectrum from 300 nm to 2000 nm had been measured in advance using a spectrophotometer, was placed in parallel with the glass tube with an inner diameter of 12 mm, 1 cm apart from the glass tube. A mixed air with a humidity of about 50%, an acetone concentration of 5 ppm, and a nitrogen dioxide concentration of 100 ppb was prepared in a commercially available 2 L sampling bag. The cock of the sampling bag was connected to the glass tube using a silicon rubber stopper and a Teflon tube. The other end of the glass tube was connected to a pump using a silicon rubber stopper and a Teflon tube. A suction pump for measuring atmospheric air was used as the pump. The pump was operated and aeration was performed for 5 minutes at a flow rate of 0.05 L/min. After that, each gas detector element was taken out and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer. The amount of change in absorbance at 390 nm for the acetone detector element and the amount of change in absorbance at 525 nm for the nitrogen dioxide detector element were calculated.

Next, a similar system was assembled, the pump was operated, and aeration was performed for 5 minutes at a flow rate of 0.1 L/min. After that, each gas detector element was removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer. The amount of change in absorbance at 390 nm was calculated for the acetone detector element, and the amount of change in absorbance at 525 nm was calculated for the nitrogen dioxide detector element.

Next, a similar system was assembled, the pump was operated, and aeration was performed for 5 minutes at a flow rate of 0.2 L/min. After that, each gas detector element was removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer. The amount of change in absorbance at 390 nm was calculated for the acetone detector element, and the amount of change in absorbance at 525 nm was calculated for the nitrogen dioxide detector element.

Next, a similar system was assembled, the pump was operated, and aeration was performed for 5 minutes at a flow rate of 0.3 L/min. After that, each gas detector element was removed and the absorption spectrum from 300 nm to 2000 nm was measured using a spectrophotometer. The amount of change in absorbance at 390 nm was calculated for the acetone detector element, and the amount of change in absorbance at 525 nm was calculated for the nitrogen dioxide detector element.

Figure 7 shows the measurement results of the change in absorbance of each gas detection element in response to the gas flow rate. The difference in absorbance of each element is constant at all flow rates, and it has become clear that the detection of acetone and nitrogen dioxide with the detection element is diffusion-limited, and that fine control is not necessary if the flow rate is 0.05 L/min or higher. It has also been shown that this simple system using multiple gas detection elements and tubes can easily and accurately measure each substance in a mixed gas using a small volume of gas.

The present invention is not limited to the above-described embodiment, and of course includes design changes that do not deviate from the gist of the invention, including various modifications and alterations that would occur to a person with ordinary knowledge in the field of the invention.

1: Gas detection device, 2: Container, 3: Tube, 4: Pump, 5: Gas detection element, 6: Light source, 7: Photodetector, 8: Imaging device, 9: Valve

Claims (7)

A container for containing the collected gas;
a tube having one end communicating with the container;
a pump connected to the other end of the tube and configured to draw gas from the container through the tube;
a gas detection element disposed in a flow path in the pipe through which a gas flows and detecting a specific gas contained in the gas ;
The gas detection element has a porous structure carrying a gas detection agent that reacts with the specific gas,
The gas detection device , wherein the pump draws in the gas so that the flow rate of the gas becomes diffusion rate-limited . The gas detection device according to claim 1, further comprising a light source that irradiates the gas detection element with light and a photodetector that detects the transmitted light from the gas detection element in order to measure the absorbance of the gas detection element. The gas detection device according to claim 1, further comprising an imaging device that images the gas detection element to obtain color information of the gas detection element. A process of storing the collected gas in a container;
a suction step of connecting the container to one end of a pipe and suctioning gas in the container by a pump connected to the other end of the pipe so that the gas flows through the pipe;
a detection step of exposing the gas to a gas detection element disposed in a flow path in the pipe through which the gas flows by the suction step, and detecting a specific gas contained in the gas based on a change in characteristics of the gas detection element ;
The gas detection element has a porous structure carrying a gas detection agent that reacts with the specific gas,
The gas detection method , wherein the pump draws in the gas so that the flow rate of the gas becomes diffusion rate-limiting . 5. The gas detection method according to claim 4, further comprising the step of detecting a specific gas contained in a gas based on a comparison between a characteristic value of the gas detection element measured before exposure to the gas and a characteristic value of the gas detection element measured while exposed to the gas. 6. The gas detection method according to claim 5, wherein the characteristic value of the gas detection element is the absorbance of the gas detection element, and the absorbance of the gas detection element is measured by irradiating the gas detection element with light from a light source and detecting the transmitted light from the gas detection element with a photodetector . 6. The gas detection method according to claim 5, wherein the characteristic value of the gas detection element is color information of the gas detection element, the gas detection element is imaged by an imaging device, and RGB values of the image data obtained by the image capture are measured.

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