JP6836071B2 - Gas analyzer and gas analysis method - Google Patents

Description

This case relates to a gas analyzer and a gas analysis method.

A technique for detecting each gas type for a gas containing a plurality of gas types is disclosed (see, for example, Patent Documents 1 to 3).

Japanese Unexamined Patent Publication No. 3-163343 Japanese Unexamined Patent Publication No. 2008-292344 Japanese Unexamined Patent Publication No. 2000-55853

However, with the above technique, it is difficult to obtain high measurement accuracy for a measurement target gas containing a plurality of gas types.

In one aspect, it is an object of the present invention to provide a gas analyzer and a gas analysis method capable of obtaining high measurement accuracy for a gas to be measured containing a plurality of gas types.

In one embodiment, the gas analyzer is provided for a chamber, three or more gas sensors provided within the chamber, each with a gas sensitive material having a different material composition, and a plurality of gas types having known components and concentrations. , A storage unit that stores information for converting the response of each gas sensor of the three or more gas sensors into a concentration in advance, and detects the response of each gas sensor of the three or more gas sensors to the gas to be measured. The conversion concentration of the plurality of gas types is calculated using the detection unit, the information stored in the storage unit, and the response detected by the detection unit, and each conversion concentration of the specific gas sensor among the three or more gas sensors is calculated. It is provided with a gas type specifying unit for specifying the gas type having the smallest variation among the differences between the gas sensor and each of the corresponding conversion concentrations of the other two or more gas sensors.

High measurement accuracy can be obtained for the measurement target gas containing a plurality of gas types.

It is a figure which illustrates the gas component of exhaled breath. It is a schematic diagram which illustrates the whole structure of a gas analyzer. (A) is a diagram illustrating the overall structure of the gas sensor, (b) is a top view of the substrate, and (c) is a bottom view of the substrate. It is a figure which illustrates the resistance change rate _{of CuBr, SnO 2} and WO ₃ with respect to a gas component. It is a figure which illustrates the flowchart which shows the analysis example of the gas type contained in the measurement target gas. (A) to (d) are diagrams showing an analysis example. It is a figure which shows the analysis example.

First, the outline of gas analysis will be described. The gas to be measured in the following embodiments includes a plurality of different gas types, for example, biogas (exhaled breath, body odor, urine, flatulence, stool) released from the body or excrement of humans or animals. is there. The gas analyzer and gas analysis method according to the present embodiment are, for example, a gas analyzer and a gas analysis method for medical / healthcare that specify each gas type of biological gas.

With the aging society accelerating, the total amount of medical expenses of the people is increasing year by year. According to the statistics of the Ministry of Health, Labor and Welfare in 2015, the total amount of medical expenses of the people exceeded 40 trillion yen in 2013, which has become a social problem. By disease, the proportion of diseases caused by lifestyle-related diseases such as hypertension, diabetes, and cancer occupy the top position. Therefore, there is an increasing need for early detection of lifestyle-related diseases. Against this background, breath analysis, which examines indicators of body condition from biogas, and research on diagnostic methods based on it are being conducted.

As illustrated in FIG. 1, the breath of humans and animals contains very low concentrations of gas species released by vaporization of chemicals in the blood in the lungs. Some of these are closely related to biological activity and illness. For example, ammonia gas contained in human breath is said to have a correlation with liver metabolism and Helicobacter pylori infection, which is a risk factor for gastric cancer. Nonanal, which is an aldehyde, is a candidate for a lung cancer marker substance.

In breath analysis, by analyzing these gas types, it is effective for screening for lifestyle-related improvement and early detection of illness by a simple means that does not cause physical restraint or pain of blood collection just by breathing. We aim to detect specific substances.

However, biogas contains a large number of volatile gas species (more than 200 in one theory). Most biogas are reducing gases such as organic molecules (hydrocarbons) and have similar chemical properties. There are roughly two types of methods for analyzing such gas species.

One is a method of performing a measurement targeting a specific gas type by using a large-scale analyzer typified by gas chromatography. Although this method can analyze the gas type in detail, it requires expert operation, takes several hours or more to obtain the result, and is an expensive and large-sized device. Therefore, this method is mainly used for research purposes because the burden of inspection is heavy.

The other is a method of analyzing the difference in the response pattern of the sensors due to gas by using a device in which a large number of gas sensors are integrated. With this method, it takes a short time to obtain the analysis result, it is portable, and it is easy to use. On the other hand, the difference in sensitivity of the sensor is small, and it is difficult to distinguish a specific gas type from another gas type. Therefore, this method was not sufficient as a breath analysis for examining an index of physical condition.

Many conventional gas sensors are based on tin oxide. Each gas type can be specified by heating gas molecules and oxygen with a heater and detecting the amount of active oxygen adsorbed on the gas-sensitive material as a change in resistance of the semiconductor material. Selectivity (difference in response strength depending on the gas type) can be realized by selecting the type of the main metal, containing a noble metal having a gas catalytic action, the amount of heating of the heater, and the like. However, in any case, only the balance between reducing property and oxygen was measured, and the selectivity was not large. For example, the selection ratio was less than 10, and there was almost no orthogonality of the eigenvectors.

For example, it is conceivable to use the techniques of Patent Documents 1 to 3. However, although the gas species can be classified by statistical processing, the main component direction moves for each population. Therefore, it was difficult to obtain a concentration index of a specific gas. That is, the reproducibility was poor and there was no quantitativeness. On the other hand, in the optical type and the vibration type, the unit system of the measurement result is completely different due to the difference in the principle, and data conversion is required. For this reason, quantitative statistical processing has been difficult. Moreover, due to the difference in principle, it could not be formed integrally.

Therefore, in the following embodiments, a gas analyzer and a gas analysis method capable of obtaining high measurement accuracy for a gas to be measured containing a plurality of gas types will be described.

(Embodiment)
FIG. 2 is a schematic diagram illustrating the overall configuration of the gas analyzer 100. The gas to be measured by the gas analyzer 100 (hereinafter referred to as the gas to be measured) includes a plurality of types of gas. For example, the gas to be measured includes both a reducing gas and a basic gas. The reducing gas is a gas that is easily oxidized by oxygen, and is an organic compound such as alcohols and ketones, hydrogen sulfide, and the like. The reducing gas is particularly one generated in the process of decomposition of hydrocarbons by a living body. The basic gas is a gas having basicity, and in particular, ammonia or the like generated in the process of decomposition of proteins by a living body. In the present embodiment, as an example, the gas to be measured contains ammonia as a basic gas and hydrogen, acetone, ethanol or the like as a reducing gas.

As illustrated in FIG. 2, the gas analyzer 100 includes a purge gas supply unit 20 outside the chamber 10. Further, the gas analyzer 100 includes a first gas sensor 30a, a second gas sensor 30b, a third gas sensor 30c, a fourth gas sensor 40, a temperature / humidity sensor 50, and the like inside the chamber 10. Further, the gas analyzer 100 includes a calculation unit 60 outside the chamber 10. The calculation unit 60 includes an impedance measurement circuit 61, a calculation circuit 62, a memory 63, a transmission / reception unit 64, and the like. A processor or the like may be used as each circuit.

A first inlet 11, a second inlet 12, and an outlet 13 are formed in the chamber 10. The first inlet 11 is an opening for supplying the purge gas into the chamber 10. The second inlet 12 is an opening for supplying the gas to be measured into the chamber 10. The outlet 13 is an opening for discharging the purge gas or the gas to be measured from the chamber 10.

A pipe from the purge gas supply unit 20 is connected to the first inlet 11. The second inlet 12 is provided with a check valve 14. The check valve 14 is configured to suppress gas outflow from the chamber 10 through the second inlet 12. The outlet 13 is provided with a check valve 15. The check valve 15 is configured to suppress gas inflow from the outside of the chamber 10 through the outlet 13.

The purge gas supply unit 20 includes a filter 21 and a blower pump 22. The purge gas is not particularly limited, but is air or the like. The blower pump 22 sucks the purge gas through the filter 21 and supplies the purge gas into the chamber 10 via the pipe. The filter 21 removes dust and the like in the purge gas. By supplying the purge gas into the chamber 10 by the blower pump 22, the internal pressure of the chamber 10 rises, and the gas inflow from the second inlet 12 is suppressed by the action of the check valve 14. When the internal pressure in the chamber 10 rises, the check valve 15 does not operate, so that the purge gas is discharged from the outlet 13. Thereby, the inside of the chamber 10 can be purged.

When analyzing the gas to be measured, the gas to be measured flows in from the second inlet 12. The check valve 14 suppresses the outflow of the gas to be measured from the second inlet 12. The gas to be measured flows in the chamber 10 and is discharged from the outlet 13.

The first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c have a configuration in which a heater 32 is provided on the lower surface of the substrate 31, and an electrode 33, a gas sensor 34, and an electrode 35 are provided on the upper surface of the substrate 31. FIG. 3A is a diagram illustrating the overall structure of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c. The substrate 31, the heater 32, the electrode 33, the gas sensitive material 34, and the electrode 35 illustrated in FIG. 2 are arranged in a housing 36 having an opening in a part thereof. FIG. 3B is a top view of the substrate 31. FIG. 3C is a bottom view of the substrate 31. The substrate 31 is made of an insulating material such as alumina. The heater 32 is made of a material that generates heat by supplying electricity, and is a NiCr thin film or the like. The electrode 33 is provided at one end of the gas sensitive material 34. The electrode 35 is provided at the other end of the gas sensitive material 34. Each of the electrodes 33 and 35 is connected to a terminal on the lower surface of the substrate 31 via a via. As a result, the heater 32 and the gas sensitive material 34 are connected in parallel.

The fourth gas sensor 40 has a configuration in which an electrode 42, a gas sensor 43, and an electrode 44 are provided on the upper surface of the substrate 41. The electrode 42 is provided at one end of the gas sensitive material 43. The electrode 44 is provided at the other end of the gas sensitive material 43.

The gas sensitive material 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c has different material configurations. Further, the gas sensitive material 43 of the fourth gas sensor 40 has a material composition different from that of each gas sensitive material 34. As a result, the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 have different selection ratios for the sensitivity to the gas to be measured including a plurality of gas types.

In the present embodiment, as an example, the gas-sensitive material 34 is made of a material having high sensitivity to the reducing gas concentration. The gas-sensitive material 34 is an oxide semiconductor of at least one of Sn (tin), W (tungsten), Zn (zinc) and In (indium), or a semiconductor whose main material is C (carbon). When the gas molecules and oxygen in the housing 36 are heated by the heater 32, the amount of active oxygen adsorbed on the gas sensitive material 34 changes. When the amount of active oxygen adsorbed changes, the resistance of the gas sensitive material 34 changes. By detecting this resistance change, the gas concentration to be measured can be detected.

By changing the type and composition ratio of the metals constituting the oxide semiconductor, the gas-sensitive material 34 can be made selective (difference in the strength of response to the gas type). Alternatively, the gas-sensitive material 34 can be made selective by containing a noble metal having a gas catalytic action in the gas-sensitive material 34, or by changing the type and composition ratio of the noble metal. For example, the selection ratio between gas types is determined by incorporating an additive metal such as a noble metal such as Pd (palladium) or Pt (platinum) or a base metal such as Al (aluminum) or Pb (lead) into the gas sensitive material 34. can do. Alternatively, the gas sensitive material 34 can be made selective by changing the heating amount of the heater 32. It is preferable to increase the sensitivity with respect to acetone, ethanol, etc. by about 0.1 to 10 times.

An organic thin film may be formed on the gas sensitive material 34 in order to provide a difference in sensitivity to VOCs (volatile organic compounds). Since the sensitivity of the gas sensitive material 34 is relatively lowered when the organic thin film is formed, it is desirable to form the organic thin film as thin as possible. For example, a monomolecular layer may be formed by applying gold particles to the surface of the gas-sensitive material 34 and exposing it to a polymer gas. For example, it is preferable to use an amine-based, thiol-based, silane-based or other coupling material.

The gas type and gas concentration can be detected by detecting the change in the resistance value of the gas sensitive material 34 in the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c. In the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c, there is an optimum detection temperature according to the gas type to be detected. Therefore, when measuring the gas concentration, the inside of the housing 36 is set to the optimum detection temperature. Alternatively, the inside of the housing 36 is heated by the heater 32 to a detection temperature within the detection temperature range including the optimum detection temperature. On the other hand, when cleaning the gas-sensitive material 34, the temperature inside the housing 36 is raised to a cleaning temperature higher than the temperature at the time of gas detection to desorb pollutants adsorbed on the surface of the gas-sensitive material 34. Can be done.

On the other hand, in the present embodiment, as an example, the gas sensitive material 43 is made of a material having high sensitivity to the basic gas concentration. Copper ions (Cu ⁺ and Cu ²⁺ ) and silver ions (Ag ⁺ ) exhibit high affinity with basic gases by being present as easy-to-move ions. Therefore, in the present embodiment, the gas-sensitive material 43 uses a halide or oxide of copper or silver as a main material. As an example, copper (I) bromide (CuBr), which is a p-type semiconductor, can be used.

Since the copper ion and the silver ion have a high affinity for the basic gas, the basic gas is strongly adsorbed on the gas sensitive material 43. By detecting the change in resistance of the gas-sensitive material 43 in this case, the basic gas type and concentration can be measured. For example, copper and silver ions form a coordination bond with the nitrogen atom of the amine. As a result, copper and silver ions have a high affinity for nitrogen. Therefore, a basic gas such as ammonia can be measured by using copper ions or silver ions. The monovalent copper ion has a higher affinity for nitrogen than the divalent copper ion. Therefore, it is preferable to use a halide or oxide of monovalent copper ion.

Since the fourth gas sensor 40 utilizes the adsorption of gas molecules, heating by a heater is not essential. However, the sensitivity and responsiveness can be improved by raising the temperature to a low temperature during adsorption and a high temperature during detachment.

An organic thin film may be formed on the gas sensitive material 43 in order to provide a difference in sensitivity to VOCs (volatile organic compounds). Since the sensitivity of the gas sensitive material 43 is relatively lowered when the organic thin film is formed, it is desirable to form the organic thin film as thin as possible. For example, a monomolecular layer may be formed by applying gold particles to the surface of the gas-sensitive material 43 and exposing it to a polymer gas. For example, it is preferable to use an amine-based, thiol-based, silane-based or other coupling material.

The heat of the heater 32 may be transferred to the downstream side along the gas flow. Therefore, it is preferable that the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c are arranged closer to the outlet 13 than the fourth gas sensor 40. By doing so, the influence of the heat of the heater 32 on the fourth gas sensor 40 can be suppressed.

FIG. 4 is a diagram illustrating the rate of change in resistance _{of CuBr, SnO 2} and WO _{3 for each gas type.} The vertical axis is the normalized value of the resistance change rate. MOS in the figure is a metal oxide semiconductor (Metal Oxide Semiconductor). The rate of change in resistance is normalized based on the rate of change in resistance with respect to 1 ppm of ammonia.

As illustrated in FIG. 4, SnO ₂ and WO ₃ have a large resistance change rate for a plurality of gas types. Therefore, the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c _{including SnO 2} and WO _{3 as the gas sensitive material 34 have a low selection ratio.} However, the rate of change in resistance differs depending on the gas type. Based on this difference, the concentration of each gas species can be accurately measured. In addition, the rate of change in resistance for each gas type _{differs between SnO 2} and WO _3. Therefore, _{by using both SnO 2} and WO _3, the concentration measurement for each gas type becomes more accurate.

Next, CuBr can obtain a significantly larger resistance change rate with respect to the basic gas (ammonia) as compared with other gas types. On the other hand, CuBr has almost no change in resistance to the reducing gas. This is because copper or silver halides or oxides have a low affinity for reducing gases. Therefore, the fourth gas sensor 40 including CuBr as the gas sensitive material 43 has a high selectivity. By using a gas sensor provided with CuBr as the gas sensitive material 43, the basic gas concentration can be accurately measured.

In this way, by making the material composition of each gas sensor 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c different, the selection ratio of these gas sensors can be made different. Further, by making the material composition of the gas sensor 43 of the fourth gas sensor 40 different from the material composition of each gas sensor 34, the selection ratio of the fourth gas sensor 40 can be changed to the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 40. It can be different from the selection ratio of the gas sensor 30c.

By making the material composition of each gas sensor different, the selection ratio of the fourth gas sensor 40 can be made larger than the selection ratio of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c. For example, by using the gas-sensitive material 43 as a main material of a halide or oxide of Cu or Ag, the fourth gas sensor 40 has low sensitivity to reducing gas and particularly high to basic gas. Becomes sensitive. That is, the selection ratio of the fourth gas sensor 40 becomes large. By using an oxide semiconductor whose main material is at least one of Sn, W, Zn and In, or a semiconductor whose main material is C, the gas sensitive material 34 is a first gas sensor 30a, a second gas sensor 30b, and a third gas sensor. While 30c has high sensitivity to reducing gas, it also has high sensitivity to basic gas. As a result, the selection ratio of the fourth gas sensor 40 becomes larger than the selection ratio of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c.

With reference to FIG. 2 again, the electrodes of the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 are connected to the impedance measurement circuit 61. As a result, the impedance measurement circuit 61 measures the resistance of each gas sensitive material. Specifically, the impedance measurement circuit 61 measures the impedance of the gas sensor 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c, and measures the impedance of the gas sensor 43 of the fourth gas sensor 40. .. The impedance measurement circuit 61 transmits the measurement result to the arithmetic circuit 62. The calculation circuit 62 calculates the concentration of each gas type of the gas to be measured. The transmission / reception unit 64 transmits the calculation result of the arithmetic circuit 62 to an external device.

Subsequently, an analysis example of the gas type contained in the measurement target gas will be described with reference to the flow of FIG. Here, as an example, it is assumed that the gas to be measured contains ammonia as a basic gas and a plurality of reducing gases such as hydrogen, acetone, and ethanol as reducing gases.

Each gas sensor is not only sensitive to a particular gas type. That is, even if the resistance change of the gas sensitive material of each gas sensor is measured, it is difficult to specify which gas type the resistance change is for. Therefore, in the present embodiment, information to be converted into the concentration of each gas type is stored in the memory 63 in advance by performing statistical processing or machine learning on the measurement result of the impedance of the gas sensitive material of each gas sensor. deep.

First, the learning results of the rate of change of the response (impedance) of the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 with respect to each of the gas types 1 to m having known components and concentrations are obtained. It is stored in the memory 63 as matrix data (step S1).

For example, a set as illustrated in FIG. 6A is used as element data. Each element of the set of impedance changes is the rate of change of impedance over time for each of the plurality of gas species. For example, the amount of impedance change from the introduction of the gas type into the chamber 10 to the lapse of a specified time. Alternatively, the correlation between the gas concentration and the amount of impedance change with respect to the reference gas type (for example, ammonia) may be investigated, and the data converted into the concentration using the correlation may be used as the element data.

Next, a correction-type database when each gas type is introduced into the chamber 10 is created in advance (step S2). For example, _{a function f such that Δz n0 m} = f (C _m0 ) is defined. However, C _m0 is the gas concentration (initial value) in the gas type m. n is a gas sensor number (1 to 4).

Next, the arithmetic circuit 62 changes the response rate (time change rate of impedance) of the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 to the measurement target gas x whose component and concentration are unknown. Is measured (step S3). FIG. 6B is a diagram illustrating the measurement result. As illustrated in FIG. 6B, the impedance change rate of the first gas sensor 30a is Δz _1x . The impedance change rate of the second gas sensor 30b is Δz _2x . The impedance change rate of the third gas sensor 30c is Δz _3x . The impedance change rate of the fourth gas sensor 40 is Δz _4x .

Next, the arithmetic circuit 62 uses the measured value of FIG. 6B and the correction type database created in step S2, and each gas type contained in the measurement target gas x is each gas type on the database. The concentration conversion value when it is assumed to exist is calculated (step S4). The inverse function can be expressed as _{C mx} = f ^-1 (Δz _nx). FIG. 6C is a calculation result of the concentration conversion value.

Next, the arithmetic circuit 62 calculates the difference between the concentration conversion value of each of the first gas sensor 30a to the third gas sensor 30c and the corresponding concentration conversion value of the fourth gas sensor 40 (step S5). FIG. 6D is a diagram illustrating the calculation result of the difference. In addition, the difference can be calculated using the following formula.
(A ₁₁ , A ₁₂ , ..., A _{1 m} ) = (C ₁₁ , C ₁₂ , ..., C _{1 m} )-(C ₄₁ , C ₄₂ , ..., C _{4 m} )
(A ₂₁ , A ₂₂ , ..., A _2m ) = (C ₂₁ , C ₂₂ , ..., C _2m )-(C ₄₁ , C ₄₂ , ..., C _4m )
(A ₃₁ , A ₃₂ , ..., A _3m ) = (C ₃₁ , C ₃₂ , ..., C _3m )-(C ₄₁ , C ₄₂ , ..., C _4m )

The arithmetic circuit 62 has the same gas (same row) elements (A ₁₁ , A ₂₁ , A ₃₁ ), (A ₁₂ , A ₂₂ , A ₃₂ ), ..., (A _{1 m} , A _{2 m} , A _{3 m} ). Search for the gas type k with the smallest variation (step S6). At this time, it is preferable to exclude the element including the negative value or set it to 0. For the variation, for example, (maximum value-minimum value) / median value may be used as an index, or the variance may be obtained to find the minimum value. In the example of FIG. 7, for example, gas type 2 is searched for as the gas type having the smallest variation.

Next, the arithmetic circuit 62 specifies the gas type k as the main component of the gas types other than ammonia among the gas types contained in the gas to be measured, and calculates _{the converted gas concentration of the gas type k = A xx.} To do. The highest accuracy can be ensured by _{assuming that x has the highest sensitivity (Δz n0m} ) among the first gas sensor 30a to the third gas sensor 30c. However, the average value of the first gas sensor 30a to the third gas sensor 30c may be adopted.

Next, the transmission / reception unit 64 _{outputs C 41 as the ammonia concentration and outputs A xx} as the main component gas concentration (step S7). By the above processing, the analysis of the gas to be measured is completed.

According to the present embodiment, the gas sensitive material 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c has different material configurations. Further, the gas sensitive material 43 of the fourth gas sensor 40 has a material composition different from that of each gas sensitive material 34. As a result, the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 have different selection ratios.

Next, by calculating the difference between the concentration conversion values of the first gas sensor 30a to the third gas sensor 30c and the corresponding concentration conversion values of the fourth gas sensor 40 with respect to the gas to be measured, the fourth gas sensor 40 has high sensitivity. Gases with can be excluded. Next, by searching for the gas type having the smallest variation in the difference, the main component gas type other than the gas type having high sensitivity can be estimated by the fourth gas sensor 40. As a result, high measurement accuracy can be obtained for the measurement target gas containing a plurality of gas types. In such a process, the calculation is simple, so that the power consumption can be suppressed. As a result, it can be applied to constant monitoring. Moreover, since it is not necessary to use a large-scale arithmetic unit, the device can be miniaturized.

By making the selection ratio of the fourth gas sensor 40 larger than the selection ratio of the first gas sensor 30a to the third gas sensor 30c, the concentration measurement accuracy of the gas type having high sensitivity of the fourth gas sensor 40 is improved.

In addition, in the measurement result of the fourth gas sensor 40, the error for the gas type having low sensitivity becomes large. In this case, the gas type having the smallest variation in the difference between the concentration conversion value of each of the first gas sensor 30a to the third gas sensor 30c with respect to the gas to be measured and the corresponding concentration conversion value of the fourth gas sensor 40 is searched for. Therefore, the estimation accuracy of the main component gas type other than the gas type having high sensitivity of the fourth gas sensor 40 is improved.

In the above analysis example, the fourth gas sensor 40 uses a gas sensor 43 containing a halide or oxide of Cu or Ag as a main material. The gas-sensitive material 43 has a high sensitivity to a basic gas and a low sensitivity to a reducing gas. As a result, high measurement accuracy with respect to the basic gas concentration can be obtained. In the above analysis example, the concentration of ammonia can be measured with high accuracy.

By the way, in the body of animals including humans, nitrogen is generated as ammonia during the decomposition of proteins in the digestive tract. Alternatively, microorganisms and anaerobic bacteria living in the gastrointestinal tract use urease enzyme to decompose urea to generate ammonia. Some of these ammonia are absorbed into the blood and the rest are excreted to the outside as excrement. Blood containing nutrients absorbed from the digestive system is collected in the liver as a portal vein.

In the liver, nutrients are absorbed and toxins are metabolized with a detoxifying function. In the case of ammonia, it is the latter, and it is metabolized in a cycle called the urea cycle in the liver and converted to urea. This urea is then filtered by the kidneys and excreted with urine. In addition, when muscles are tired due to strenuous exercise, ammonia is generated in the blood, and it is metabolized in the liver through veins in the urea cycle and converted to urea.

With such a metabolic function, the ammonia concentration in the living body is kept below a certain level. Therefore, when there is a disease in the metabolic function of the liver and the liver function is lowered, the ammonia concentration is high, and in the undernutrition state, the ammonia concentration is low. However, it can be said that organisms always contain ammonia in their blood as long as they are accompanied by nutrients and exercise. Since this ammonia is vaporized by the capillaries of the lungs and skin, the exhaled breath and sweat of living organisms always contain a small amount of ammonia.

In addition, alcohols such as ethanol are generated in the process of decomposing hydrocarbons. In addition, ketones such as acetone are generated during the decomposition of sugars. When cholesterol is decomposed, isoprene and the like are generated. Further, in diseases such as cancer, various VOCs are generated due to oxidative stress in the affected area and vaporize in the lungs and skin through blood.

According to this embodiment, by using a gas-sensitive material 43 whose main material is a halide or oxide of Cu or Ag, it is possible to separate ammonia from various metabolic gases. .. Further, in addition to the concentration of the gas (ammonia) to be constantly monitored, the most concentrated gas type and concentration can be estimated as the main components. It is possible to improve the estimation accuracy by excluding ammonia. By applying this embodiment and further installing a gas sensor, it is possible to increase the types of gas that can be detected and realize an electronic nose. By using these, it is possible to construct an electronic nose called a breath print sensor by a gas sensor array for grasping the characteristics of breath and sweat components like a fingerprint.

The convenience of this embodiment makes it possible to continuously investigate changes in breath components due to lifestyle habits without causing pain such as blood sampling. In addition, a breath print sensor can be mounted on a smart device or a wearable device to provide a means for continuing to analyze these gases as easily as a thermometer. In addition, this technology can be used as a screening means for improving lifestyle habits and early detection of diseases.

In the above embodiment, the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 are provided in the chamber, and three or more gas sensors including gas sensing materials made of different materials are provided. This is an example. The fourth gas sensor 40 is an example of a specific gas sensor among the three or more gas sensors. The first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c are examples of two or more gas sensors other than the specific gas sensor. The memory 63 is an example of a storage unit that stores in advance information for converting the response of each gas sensor of the three or more gas sensors into a concentration for a plurality of gas types having known components and concentrations. The impedance measurement circuit 61 is an example of a detection unit that detects the response of each gas sensor of the three or more gas sensors to the gas to be measured. The arithmetic circuit 62 calculates the conversion concentration of the plurality of gas types using the information stored in the storage unit and the response detected by the detection unit, and converts each of the specific gas sensors among the three or more gas sensors. This is an example of a gas type specifying unit that specifies the gas type having the smallest variation among the differences between the concentration and each corresponding conversion concentration of the other two or more gas sensors.

Although the examples of the present invention have been described in detail above, the present invention is not limited to the specific examples, and various modifications and modifications are made within the scope of the gist of the present invention described in the claims. It can be changed.

10 Chamber 11 1st inlet 12 2nd inlet 13 Outlet 14,15 Check valve 30a 1st gas sensor 30b 2nd gas sensor 30c 3rd gas sensor 32 Heater 34 Gas sensor 40 4th gas sensor 43 Gas sensor 60 Calculation unit 61 Impedance measurement Circuit 62 Arithmetic circuit 63 Memory 100 Gas analyzer

Claims (12)

With the chamber
Three or more gas sensors provided in the chamber and each having a gas sensitive material having a different material composition,
A storage unit that stores in advance information for converting the response of each gas sensor of the three or more gas sensors into a concentration for a plurality of gas types having known components and concentrations.
A detection unit that detects the response of each gas sensor of the three or more gas sensors to the gas to be measured, and
The conversion concentration of the plurality of gas types is calculated using the information stored in the storage unit and the response detected by the detection unit, and each conversion concentration of the specific gas sensor among the three or more gas sensors and the other two. A gas analyzer characterized by comprising a gas type specifying unit for specifying the gas type having the smallest variation among the differences from the corresponding conversion concentrations of the gas sensor described above. The gas analyzer according to claim 1, wherein the gas sensitive material of the specific gas sensor is mainly composed of a halide or oxide of Cu or Ag. The other two or more gas sensors include a heater for heating the gas sensitive material.
The gas analyzer according to claim 2, wherein the specific gas sensor is arranged on the upstream side in the gas flow direction in the chamber, as compared with the other two or more gas sensors. The gas-sensitive material of the other two or more gas sensors is an oxide semiconductor whose main material is at least one of Sn, W, Zn and In, or a semiconductor whose main material is C. The gas analyzer according to any one of 1 to 3. The gas analyzer according to any one of claims 1 to 4, wherein the selection ratio of the gas sensitive material of the specific gas sensor is larger than the selection ratio of the gas sensitive material of the other two or more gas sensors. .. The gas analyzer according to any one of claims 1 to 5, wherein the total number of the gas sensors is equal to or less than the total number of gas types stored in the storage unit. For a plurality of gas types having known components and concentrations, information for converting the response of each gas sensor of three or more gas sensors provided in the chamber and having a gas sensor having a different material composition into a concentration is obtained. , Pre-stored in the storage
The response of each gas sensor of the three or more gas sensors to the gas to be measured is detected.
The converted concentration of the plurality of gas types is calculated using the information stored in the storage unit and the detected response, and each converted concentration of the specific gas sensor among the three or more gas sensors and the other two or more. A gas analysis method characterized in that the gas type having the smallest variation among the differences from the corresponding conversion concentrations of the gas sensor is specified. The gas analysis method according to claim 7, wherein the gas sensitive material of the specific gas sensor is mainly composed of a halide or oxide of Cu or Ag. The other two or more gas sensors include a heater for heating the gas sensitive material.
The gas analysis method according to claim 8, wherein the specific gas sensor is arranged on the upstream side in the gas flow direction in the chamber as compared with the other two or more gas sensors. The gas-sensitive material of the other two or more gas sensors is an oxide semiconductor whose main material is at least one of Sn, W, Zn and In, or a semiconductor whose main material is C. The gas analysis method according to any one of 7 to 9. The gas analysis method according to any one of claims 7 to 10, wherein the selection ratio of the gas-sensitive material of the specific gas sensor is larger than the selection ratio of the gas-sensitive material of the other two or more gas sensors. .. The gas analysis method according to any one of claims 7 to 11 , wherein the total number of the gas sensors is equal to or less than the total number of gas types stored in the storage unit.

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