Acetic acid gas concentration measuring device, method for using same, and method for measuring acetic acid gas concentration

Abstract

One embodiment of the present invention provides an acetic acid gas concentration measuring device 101 comprising a capsule 22 which is provided, on at least a portion of a surface thereof that is in contact with the external environment, with a filter 21 that transmits acetic acid gas and repels water, and a droplet sensor unit 10 and a sensor signal processing unit 14 which are disposed within the capsule 22, wherein: the droplet sensor unit 10 comprises an insulating substrate 11 of which at least a surface 11A is composed of silica, first thin wire electrodes 12 which are disposed on the surface 11A and which include at least one of a first metal and carbon, and second thin wire electrodes 13 which include a second metal and which are arranged side-by-side alternately with the first thin wire electrodes 12 on the surface 11A; and the sensor signal processing unit 14 is configured to determine that acetic acid gas has been detected if a current flowing between the first thin wire electrodes 12 and the second thin wire electrodes 13 is equal to or greater than a predetermined current value, and to output a concentration calculated in accordance with the level of a response signal corresponding to the current, on the basis of an acetic acid gas concentration calibration characteristic obtained in advance.

Description

Acetic acid gas concentration measuring device, method of use thereof, and method of measuring acetic acid gas concentration REFERENCE TO RELATED APPLICATIONS

[0001] This application benefits from the priority of an earlier Japanese application, Patent Application No. 2023-156592 (filing date: September 22, 2023), the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an acetic acid gas concentration measuring device, a method for using the same, and a measuring method.

[0003] Volatile fatty acids (VFA) are volatile substances composed primarily of acetic acid, propionic acid, and butyric acid, which are produced by fermentation in the rumen of cattle, silage, etc. The composition ratio of VFA depends on the state of fermentation and is an important indicator of the condition of the cattle and their feed, as well as the amount of methane produced, a greenhouse gas.

[0004] Therefore, there is a high demand for methods to detect and analyze the components of VFA. However, because the molecular structures and molecular weights of the main components of VFA are similar, their detection and analysis require advanced analytical techniques such as various types of chromatography. As a result, conventional methods for detecting and analyzing the components of VFA require large, costly equipment and require a long analysis time. In particular, there has been no suitable method for measuring acetic acid gas in the rumen, which is in high demand, and this has been an issue for cattle breeding and for preserving the global environment.

[0005] International Publication No. 2016 / 013544

[0006] The problem to be solved by the present invention is to provide a small acetic acid gas concentration measuring device that can selectively detect and measure acetic acid gas, a method for using the same, and a method for measuring acetic acid gas concentration.

[0007] The present invention has the following configurations: (Configuration 1) An acetic acid gas concentration measuring device comprising: a capsule having a filter that is permeable to acetic acid gas and repels water on at least a portion of its surface that contacts the outside world; a droplet sensor unit disposed within the capsule; and a sensor signal processor disposed within the capsule, wherein the droplet sensor unit comprises: an insulating substrate having at least a surface made of silica; first thin-wire electrodes disposed on the surface of the substrate and including at least one of a first metal and carbon; and second thin-wire electrodes disposed on the surface of the substrate alternately with the first thin-wire electrodes and including a second metal that is different from the first metal; and the sensor signal processor is configured to determine that acetic acid gas has been detected when a current flowing between the first thin-wire electrodes and the second thin-wire electrodes is equal to or greater than a predetermined current value, and to output a concentration calculated in accordance with the level of a response signal corresponding to the current, based on predetermined acetic acid gas concentration calibration characteristics. (Configuration 2) The acetic acid gas concentration measuring device according to Configuration 1, wherein the distance between the first thin wire electrode and the second thin wire electrode is constant. (Configuration 3) The acetic acid gas concentration measuring device according to Configuration 2, wherein the distance between adjacent first thin wire electrodes and the second thin wire electrodes is 100 nm or more and 1000 nm or less. The acetic acid gas concentration measuring device according to Configuration 1, wherein the distance between the first thin wire electrode and the second thin wire electrode is constant in the region. (Configuration 4) The acetic acid gas concentration measuring device according to any one of Configurations 1 to 3, wherein the first metal is selected from the group consisting of gold, platinum, silver, and titanium. (Configuration 5) The acetic acid gas concentration measuring device according to any one of Configurations 1 to 4, wherein the second metal is selected from the group consisting of silver, copper, iron, zinc, nickel, cobalt, aluminum, tin, chromium, molybdenum, manganese, magnesium, and alloys thereof. (Configuration 6) An acetic acid gas concentration measuring device according to any one of configurations 1 to 5, wherein the first thin wire electrode and the second thin wire electrode extend from opposite directions toward each other and are arranged parallel to each other.(Configuration 7) The acetic acid gas concentration measuring device according to any one of Configurations 1 to 6, wherein the filter is made of one or more selected from the group consisting of a polytetrafluoroethylene porous membrane, a polyvinylidene fluoride porous membrane, and a nonwoven fabric treated with a fluorine compound for water repellency. (Configuration 8) The acetic acid gas concentration measuring device according to any one of Configurations 1 to 7, wherein the capsule is made of one or more selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, vinyl chloride, ABS resin, ASA resin, PLA resin, acrylic resin, epoxy resin, and high-strength glass. (Configuration 9) The acetic acid gas concentration measuring device according to any one of Configurations 1 to 8, further comprising a transmitter unit disposed within the capsule and capable of transmitting the concentration to the outside of the capsule. (Configuration 10) The acetic acid gas concentration measuring device according to any one of Configurations 1 to 8, further comprising a memory unit disposed within the capsule and capable of storing the concentration. (Configuration 11) A method for using the acetic acid gas concentration measuring device according to any one of Configurations 1 to 10, wherein the acetic acid gas concentration in the stomach is measured by placing the acetic acid gas concentration measuring device according to any one of Configurations 1 to 10 in the stomach. (Configuration 12) A method for measuring an acetic acid gas concentration by using the acetic acid gas concentration measuring device according to any one of Configurations 1 to 10. (Configuration 13) A method for measuring an acetic acid gas concentration by using the acetic acid gas concentration measuring device according to any one of Configurations 1 to 10. The method includes the steps of exposing a droplet sensor unit to a gas to be measured, the droplet sensor unit including: an insulating substrate having at least a surface made of silica; first thin-wire electrodes including at least one of a first metal and carbon arranged on the surface of the substrate; and second thin-wire electrodes arranged on the surface of the substrate alternately with the first thin-wire electrodes and including a second metal different from the first metal; and measuring a current flowing between the first thin-wire electrodes and the second thin-wire electrodes until the current reaches a predetermined value I. ｔｈ and determining whether the current is equal to or greater than a predetermined value I ｔｈ If the current is less than the predetermined value I, an output is made indicating that the acetic acid gas concentration is below the detection limit. ｔｈ In the above cases, the method for measuring the concentration of acetic acid gas outputs the result of the concentration of acetic acid gas according to the level of the response signal corresponding to the current, based on the previously determined calibration characteristic of the concentration of acetic acid gas.

[0008] The present invention provides a small acetic acid gas concentration measuring device capable of selectively detecting and measuring acetic acid gas, a method for using the same, and a method for measuring acetic acid gas concentration. This enables, for example, efficient and high-quality cattle breeding, and further contributes to the preservation of the global environment.

[0009] FIG. 1 is a structural diagram showing the schematic configuration of an acetic acid gas concentration measurement device according to an embodiment. FIG. 2 is an explanatory diagram explaining the measurement principle of the droplet sensor unit according to an embodiment. FIG. 3 is a diagram showing the configuration of an acetic acid gas concentration measurement device according to an embodiment, focusing on electrical connections. FIG. 4 is an explanatory diagram explaining the reason for the high detection sensitivity of acetic acid. FIG. 5 is a flowchart showing an acetic acid gas concentration measurement method according to an embodiment. FIG. 6 is an equipment diagram showing an outline of the experimental equipment used in the examples. FIG. 7(a) is a graph showing the measurement results when propionic acid was measured as a volatile fatty acid (VFA) sample using the experimental equipment used in the examples, and FIG. 7(b) is a characteristic diagram showing the concentration dependence of the current value at that time. FIG. 8(a) is a characteristic diagram showing the measurement results of test sensitivity when water, FIG. 8(b) is a characteristic diagram showing propionic acid, FIG. 8(c) is a characteristic diagram showing butyric acid, and FIGS. 8(d) and 8(e) are characteristic diagrams showing the measurement results of test sensitivity when acetic acid was measured using the experimental equipment used in the examples.

[0010] The following describes an acetic acid gas concentration measurement device, a method for using the device, and a method for measuring acetic acid gas concentration according to an embodiment of the present invention. Fig. 1 is a structural diagram showing the schematic configuration of the acetic acid gas concentration measurement device according to this embodiment, Fig. 2 is an explanatory diagram explaining the measurement principle of the droplet sensor unit according to this embodiment, and Fig. 3 is a diagram showing the configuration of the acetic acid gas concentration measurement device according to this embodiment, focusing on the electrical connections. Fig. 4 is an explanatory diagram explaining the reason for the high detection sensitivity of acetic acid, and Fig. 5 is a flowchart showing the acetic acid gas concentration measurement method according to this embodiment.

[0011] 1, the acetic acid gas measurement device 101 according to this embodiment includes a droplet sensor unit (acetic acid gas sensor unit) 10, a sensor signal processing unit 14, a transmitter unit 15 and / or a memory device unit 15A, and these units are housed in a capsule 22 with a filter 21. Signal lines 16 and 17 electrically connect the acetic acid gas sensor unit 10 and the sensor signal processing unit 14, and the sensor signal processing unit 14 and the transmitter unit 15 or the memory device unit 15A, respectively.

[0012] The acetic acid gas sensor unit 10 is a galvanic current detection type droplet sensor. As shown in FIG. 2 , which illustrates the operating principle of the galvanic current detection type droplet sensor, a first thin-wire electrode 12 and a second thin-wire electrode 13 made of different metals (metals A and B) are arranged side by side. When a conductive droplet, such as a water droplet, comes into contact with the first thin-wire electrode 12 and the second thin-wire electrode 13, the sensor detects the galvanic current flowing between the two thin-wire electrodes, thereby detecting the presence or generation of the conductive droplet, such as water. This sensor is disclosed, for example, in Patent Document 1. Here, the first thin-wire electrode 12 and the second thin-wire electrode 13 are formed on the surface 11A of a substrate 11, at least the surface 11A of which is made of an insulating material. Metals A and B may be alloys. Furthermore, either metal A or B may be carbon, a metal carbide, or a carbide alloy.

[0013] The acetic acid gas sensor unit 10 is characterized in that the surface 11A of the substrate 11 is made of silica (SiO ２ The silica surface enhances the adhesion of acetic acid and the interaction between the adhered acetic acid and water, producing a large response current to acetic acid and enabling the detection of acetic acid with high selectivity.

[0014] The reason why a droplet sensor using surface 11A of substrate 11 made of silica can detect acetic acid with high selectivity will be explained with reference to Fig. 4. Fig. 4 shows a state in which carbon 51, oxygen 52, hydrogen 53, acetic acid 54, water 55, and propionic acid 56 are attached and adsorbed to surface 11A of substrate 11 made of silica.

[0015] Acetic acid and propionic acid are ＋) and the amount of protons responsible for charge transport increases. This increases the sensor's response current. Propionic acid forms dimers, but since this requires protons, the number of protons responsible for charge transport decreases. In contrast, acetic acid does not form dimers. As a result, the magnitude relationship of the sensor's response current is acetic acid > propionic acid > water.

[0016] As shown in Fig. 1, the acetic acid gas sensor unit 10 is preferably disposed within the capsule 22 so that the first thin-wire electrode 12 and the second thin-wire electrode 13 face the filter 21. By disposing the first thin-wire electrode 12 and the second thin-wire electrode 13 in this manner, acetic acid gas can easily come into contact with the first thin-wire electrode 12 and the second thin-wire electrode 13. In Fig. 1, the substrate 11 is disposed substantially parallel to the filter 21, and the first thin-wire electrode 12 and the second thin-wire electrode 13 are disposed on the surface 11A of the substrate 11 facing the filter 21. The sensor signal processing unit 14 and the transmitter unit 15 are disposed on the back side of the substrate 11, opposite the surface 11.

[0017] The thickness of the substrate 11 is not particularly limited, but is preferably 500 μm or less from the viewpoint of heat conduction and heat control, and more preferably 200 μm or less or 50 μm or less.

[0018] As shown in Fig. 3, the distance d between the first thin-wire electrode 12 and the second thin-wire electrode 13 is preferably constant. A constant distance d can improve the detection sensitivity of acetic acid. The distance d is preferably 100 nm or more and 1000 nm or less. When the distance d is in this range, the detection sensitivity of acetic acid can be further improved. The lower limit of the distance d is more preferably 100 nm or more, and the upper limit is more preferably 500 nm or less.

[0019] Although there are no particular limitations on the line width of the first thin wire electrode 12 and the second thin wire electrode 13, it is preferable that the line width be, for example, 0.1 μm or more and 2 μm or less. If the line width is 0.1 μm or more, the first thin wire electrode 12 and the second thin wire electrode 13 can be easily manufactured and the electrical resistance of the first thin wire electrode 12 and the second thin wire electrode 13 can be prevented from increasing. If the line width is 2 μm or less, a large number of the first thin wire electrodes 12 and the second thin wire electrodes 13 can be arranged in a given area.

[0020] The thickness of the first thin wire electrode 12 and the second thin wire electrode 13 is not particularly limited, but is preferably, for example, 100 nm or more and 200 nm or less, respectively. If the thickness is 100 nm or more, the electrical resistance of the first thin wire electrode 12 and the second thin wire electrode 13 can be prevented from increasing, and if the thickness is 200 nm or less, liquid can easily enter and escape between the first thin wire electrode 12 and the second thin wire electrode 13.

[0021] The first thin wire electrode 12 and the second thin wire electrode 13 are made of materials with different electric potentials, including metals, alloys, metal carbides, and carbon. For example, the first metal-containing material constituting the first thin wire electrode 12 can be selected from the group consisting of gold (Au), platinum (Pt), silver (Ag), titanium (Ti), and alloys thereof. Among these, gold (Au) is preferred from the viewpoints of electrical conductivity and corrosion resistance, and platinum (Pt) is preferred from the viewpoint of catalytic activity. Alternatively, carbon (C) or metal carbides can be used as the first metal.

[0022] Examples of the material containing the second metal constituting the second thin wire electrode 13 include materials selected from the group consisting of silver (Ag), copper (Cu), iron (Fe), zinc (Zn), nickel (Ni), cobalt (Co), aluminum (Al), tin (Sn), chromium (Cr), molybdenum (Mo), manganese (Mn), magnesium (Mg), and alloys thereof. Among these, aluminum (Al) is preferred from the viewpoints of low electrode potential and corrosion resistance.

[0023] As shown in Fig. 3, at least one of the first thin wire electrodes 12 and the second thin wire electrodes 13 is preferably provided in a plurality of wires. In this case, it is more preferable that the first thin wire electrodes 12 and the second thin wire electrodes 13 are arranged parallel to each other by extending from opposite directions toward each other. This increases the packing density of the sensor device, and improves its sensitivity, reliability, and stability.

[0024] The first thin wire electrode 12 and the second thin wire electrode 13 can be formed by vapor deposition or sputtering.

[0025] As shown in FIG. 3 , the electrodes of the acetic acid gas sensor unit 10 are a first electrode 32 electrically connected to the first thin-wire electrode 12 and a second electrode 33 electrically connected to the second thin-wire electrode 13. As mentioned above, the metal (material) constituting the first thin-wire electrode 12 is different from the metal (material) constituting the second thin-wire electrode 13. From the standpoint of electrode fabrication, it is preferable that the first thin-wire electrode 12 and the first electrode 32, and the second thin-wire electrode 13 and the second electrode 33, are made of the same material. From the standpoint of convenience of the wiring drawn out from the acetic acid gas sensor unit 10, it is preferable that the first electrode 32 and the second electrode 33 are made of the same material. From the latter standpoint, the first electrode 32 and the second electrode 33 are preferably made of aluminum, which has low electrical resistance and can be kept relatively low cost.

[0026] The acetic acid gas sensor unit 10 is electrically connected to a sensor signal processing unit 14 via a signal line 16 (see FIGS. 1 and 3). As shown in FIG. 3, the sensor signal processing unit 14 has at least two functional units: a current value measuring unit 41 and a current value determining unit 42. The current value measuring unit 41 and the current value determining unit 42 are electrically connected to each other via a signal line 43.

[0027] The current value measurement unit 41 measures the value of the galvanic current flowing between the first thin-wire electrode 12 and the second thin-wire electrode 13. The current value measurement unit 41 may measure the galvanic current using an ammeter that directly measures the galvanic current, or may measure the galvanic current by amplifying it with an amplifier. The former method of directly measuring the current is a simple method that can be manufactured at low cost, while the method using an amplifier is suitable for improving measurement accuracy.

[0028] The current value determination unit 42 determines the measured current value I ｍｅａｓｕｒｅ and the threshold I obtained through calibration curve creation experiments, etc. ｔｈ , or / and a calibration curve, and outputs the results. ｔｈ If the concentration is less than the threshold value I, the acetic acid concentration is determined to be equal to or less than the lower limit of measurement. ｔｈ In the above cases, it is determined that acetic acid has been detected, and the current value I ｍｅａｓｕｒｅ The acetic acid concentration C calculated according to ＡＡ where the acetic acid concentration C ＡＡ is the calibration curve C obtained in a previous experiment ＡＡ = f(I ｍｅａｓｕｒｅ ) to find the answer.

[0029] The output result of the current value determination unit 42 is sent to the transmission device unit 15 via a signal line 44. The transmission device unit 15 has a function of wirelessly transmitting data, and transmits the data sent from the current value determination unit 42 to the outside of the capsule 22. The transmitted data is received by a computer such as a personal computer (PC) outside the subject to be measured, such as a cow, and is analyzed. This method has the advantage of being able to perform analysis in real time.

[0030] The storage device 15A may be used instead of the transmission device 15. Alternatively, the transmission device 15 and the storage device 15A may be used together. The storage device 15A has a storage unit such as an SSD or flash memory, and stores the data sent from the current value determination unit 42 in the storage unit. The capsules 22 are swallowed by the cows, and the capsules 22 are then collected in the form of feces or the like, and the information stored in the storage device 15A is read out and data analysis is performed. The system using the storage device 15A is small, inexpensive, and easy to handle, making it suitable for managing large numbers of cows.

[0031] The material of the capsule 22 is not particularly limited, but it is preferable to use a material that will not corrode or be destroyed in the digestive tract such as the cow's rumen, and examples of such materials include polyethylene terephthalate, polypropylene, polycarbonate, vinyl chloride, ABS resin, ASA resin, PLA resin, acrylic resin, epoxy resin, and high-strength glass. In addition, the inside of the capsule is preferably coated with a hydrophobic coating to prevent water vapor from condensing.

[0032] The filter 21 can be made of a porous material or fiber with ultra-water-repellent properties that is gas-permeable, such as an ultra-water-repellent nonwoven fabric. Specifically, the material can be one or more selected from the group consisting of a polytetrafluoroethylene porous membrane, a polyvinylidene fluoride porous membrane, and a nonwoven fabric treated with a fluorine compound to make it water-repellent. Here, to maintain the strength and improve durability of the nonwoven fabric, it is preferable to coat the nonwoven fabric with a metal mesh. For example, a gas-permeable, ultra-water-repellent multilayer film made of a porous PTFE (polytetrafluoroethylene) ultrafiltration membrane sandwiched between ultra-water-repellent PET (polyethylene terephthalate) nonwoven fabrics is particularly preferred for the filter 21.

[0033] According to this embodiment, the present invention includes a capsule 22 having a filter 21 that is permeable to acetic acid gas and repels water on at least a portion of a surface that contacts the outside world, and a droplet sensor unit 10 and a sensor signal processing unit 14 that are disposed within the capsule 22. The droplet sensor unit 10 is disposed on a surface 11A of an insulating substrate 11, at least a surface 11A of which is made of silica, and includes first thin wire electrodes 12 that contain at least one of a first metal and carbon, and second thin wire electrodes 13 that are disposed on the surface 11A of the substrate 11 alternately with the first thin wire electrodes 12 and contain a second metal that is a metal different from the first metal. The sensor signal processing unit 14 is configured to process a current flowing between the first thin wire electrodes 12 and the second thin wire electrodes 13 when the current flowing between the first thin wire electrodes 12 and the second thin wire electrodes 13 reaches a predetermined current value (threshold value) I ｔｈ In the above cases, the device is configured to determine that acetic acid gas has been detected, and to output the concentration calculated according to the level of the response signal corresponding to the current based on the acetic acid gas concentration calibration characteristics obtained in advance, thereby providing a small acetic acid gas concentration measuring device 101 that can selectively detect and measure acetic acid gas.

[0034] This acetic acid gas concentration measuring device 101 is suitable for selectively detecting and measuring acetic acid gas in the stomach of a mammal, particularly in the rumen of a cow.

[0035] <Acetic Acid Gas Concentration Measurement Method> The acetic acid gas concentration measurement method according to this embodiment will be described with reference to the flowchart of Fig. 5. First, a sensor unit 10 having a structure in which first thin-wire electrodes 12 made of a material containing at least one of a first metal and carbon and second thin-wire electrodes 13 made of a material containing a second metal different from the first metal are alternately arranged on the surface of an insulating substrate 11, at least the surface of which is made of silica, is exposed to a gas to be measured, and a current I flowing between the first thin-wire electrodes 12 and the second thin-wire electrodes 13 is measured. ｍｅａｓｕｒｅ is measured (step S11).

[0036] Next, the measured current I ｍｅａｓｕｒｅ is a predetermined value (threshold value) I ｔｈ It is determined whether the current value is equal to or greater than this (step S12).

[0037] Finally, the current I ｍｅａｓｕｒｅ is a predetermined value I ｔｈIf the value is less than the lower limit of acetic acid gas detection, the output is that the concentration is below the lower limit of acetic acid gas detection, and the current I ｍｅａｓｕｒｅ is a predetermined value I ｔｈ In the above cases, the acetic acid gas concentration result is output in accordance with the level of the response signal corresponding to the current, based on the previously determined acetic acid gas concentration calibration characteristics (step S13).

[0038] The above steps provide a method for measuring the concentration of acetic acid gas, which can selectively detect and measure acetic acid gas in, for example, the lumen, using a small and simple device.

[0039] In the examples, VFA detection characteristics were investigated under a simulated lumen environment, and the results revealed that acetic acid gas could be selectively detected with high sensitivity. Figure 6 is a diagram showing an outline of the experimental equipment used in the examples, Figure 7 (a) is a graph showing the measurement results when propionic acid was measured as a volatile fatty acid (VFA) sample using the experimental equipment used in the examples, and Figure 7 (b) is a characteristic diagram showing the concentration dependence of the current value at that time. Figure 8 (a) is a characteristic diagram showing the measurement results of the test sensitivity when water, Figure 8 (b) is propionic acid, Figure 8 (c) is butyric acid, and Figures 8 (d) and 8 (e) are measured using the experimental equipment used in the examples.

[0040] As shown in Figure 6, the apparatus 200 used in the examples was composed of a sample gas supply equipment 202, an oven 201 containing a droplet sensor (acetic acid gas sensor) 10A, a current measuring device, and an analysis device (PC) (not shown).

[0041] A container 204 containing a VFA sample solution was housed in the sample gas supply equipment 202, and a filter 205 was formed on a part of the wall surface of the sample gas supply equipment 202. The filter 205 was made of nonwoven polytetrafluoroethylene fabric having an average pore size of 200 nm and a thickness of 260 μm.

[0042] The acetic acid gas sensor 10A was a galvanic current sensor in which a first thin-wire electrode 12 and a second thin-wire electrode 13 were formed on the surface of a silica substrate 11 with a thickness of approximately 200 μm. The first thin-wire electrode 12 was made of platinum (Pt) and had a line width of 1 μm, a thickness of 150 nm, and 92 wires. The second thin-wire electrode 13 was made of aluminum (Al) and had a line width of 1 μm, a thickness of 150 nm, and 92 wires. The distance between the first thin-wire electrode 12 and the second thin-wire electrode 13 was 500 nm. The first thin-wire electrode 12 and the second thin-wire electrode 13 were formed on the surface of the substrate 11 by vapor deposition.

[0043] The acetic acid gas sensor 10A was connected to a current measuring device via a cable, and the output of the current measuring device was sent to a PC, which was an analytical device. The current measuring device was custom-made (custom-made).

[0044] Then, using such an apparatus 200, measurements were carried out according to the following measurement procedure. First, a VFA sample 203 prepared to a predetermined concentration with water was placed in a container 204. As the VFA sample, acetic acid (CH ３ COOH), propionic acid (CH ３ CH ２ COOH) and butyric acid (CH ３ CH ２ CH ２ COOH) was used.

[0045] Next, the container 204 was placed in the sample gas supply equipment 202, and the temperature of the oven 201 was set to 39°C, which is the average temperature of the lumen.

[0046] The VFA sample volatilizes according to the concentration prepared in the sample gas supply equipment 202, and in the same temperature environment as the lumen (Fig. 8), the gaseous VFA reaches the acetic acid gas sensor 10A via the filter 205, as in the acetic acid gas measuring device 101 described in the embodiment, and the current value, which is the response signal (output signal) from the acetic acid gas sensor 10A, was monitored. Therefore, in this example, the VFA sample was measured in a simulated lumen environment.

[0047] The measurement data obtained by using the above-described device 200 and propionic acid (PA) as a VFA sample according to the above-described measurement method are shown in Fig. 7. Fig. 7(a) shows the raw measurement data, and Fig. 7(b) shows the saturated response signal value in a 39°C environment re-plotted with concentration as the horizontal axis. For reference, Fig. 7(b) also shows the measurement value in a room temperature (23°C) environment without the oven 201 turned on.

[0048] As shown in Figure 7(b), when the PA concentration is 60 mM or higher, the concentration and the detected current value have a linear relationship, and it can be seen that the concentration can be calculated accurately from the response signal. Furthermore, the response signal strength and the slope of the response signal (the differential value of the response signal strength) of the detection characteristic curve are greater at 39°C, which is the lumen environment, than at 23°C, and it can be seen that accurate calibration is possible in the lumen environment.

[0049] Here, we have shown an example of PA, which has a relatively small response signal strength, but similar concentration-response signal characteristics were obtained for both butyric acid and acetic acid. In particular, when acetic acid was used, a linear relationship was observed between the concentration and the detected current value at low concentrations of 1.5 mM or more, demonstrating that highly sensitive measurements are possible.

[0050] Response signal measurement data obtained using the above-described device 200 and VFA samples of acetic acid, propionic acid, and butyric acid according to the above-described measurement method are shown in Figure 8. Measurements were performed at room temperature, then the temperature was raised to 39°C, the rumen environment, and then lowered to room temperature. The concentrations of acetic acid, propionic acid, and butyric acid were each 150 mM (see Figures 8(b) to 8(d)). Acetic acid was also measured at a concentration of 1.5 mM (see Figure 8(e)).

[0051] In the measurement of acetic acid, the detection current response at room temperature was slower than when propionic acid or butyric acid was used (see Figures 8(b) to 8(d)). On the other hand, the detection sensitivity of acetic acid was about two orders of magnitude higher than that of propionic acid or butyric acid, even at room temperature in a steady state (see Figures 8(b) to 8(d)). At 39°C, the rumen environment, the detection current response to acetic acid was as fast as when propionic acid or butyric acid was used, and it can be seen that the detection current value for acetic acid, i.e., the detection sensitivity, was about two orders of magnitude higher than that of propionic acid or butyric acid.

[0052] Therefore, in the case of acetic acid, the response signal strength is two orders of magnitude greater than that of other VFAs at the same sample concentration, and the detected concentration at the same response signal level is two orders of magnitude smaller than that of other VFAs. Furthermore, the sensor responds quickly in the rumen temperature environment, providing excellent characteristics for a measurement device. This demonstrates that the measurement device used in the examples can selectively detect acetic acid with high sensitivity in a simulated rumen environment.

[0053] According to one aspect of the present invention, a small acetic acid gas concentration measuring device and measuring method are provided that selectively detect and measure acetic acid gas in the rumen. Therefore, the present invention enables efficient and high-quality cattle breeding, greatly improving the productivity and quality of dairy farming. Furthermore, it is believed that the present invention will be useful for preserving the global environment.

[0054] 10: Droplet sensor unit (acetic acid gas sensor unit), sensor unit 10A: Droplet sensor (acetic acid gas sensor) 11: Substrate 11A: Surface 12: First thin wire electrode 13: Second thin wire electrode 14: Sensor signal processing unit 15: Transmitter unit 15A: Memory device unit 16: Signal line 17: Signal line 21: Filter 22: Capsule 32: First electrode 33: Second electrode 41: Current value measuring unit 42: Current value determining unit 43: Signal line 44: Signal line 51: Carbon 52: Oxygen 53: Hydrogen 54: Acetic acid (monomer) 55: Water 56: Propionic acid (dimer) 101: Acetic acid gas measuring device 201: Oven 202: Sample gas supply equipment 203: Sample solution 204: Container 205: Filter

Claims

1. An acetic acid gas concentration measuring device comprising: a capsule having a filter that is permeable to acetic acid gas and repels water on at least a portion of its surface in contact with the outside world; a droplet sensor unit disposed within the capsule; and a sensor signal processing unit disposed within the capsule, wherein the droplet sensor unit comprises an insulating substrate having at least a surface made of silica, a first thin-wire electrode disposed on the surface of the substrate and containing at least one of a first metal and carbon, and a second thin-wire electrode disposed on the surface of the substrate alternating with the first thin-wire electrode and containing a second metal that is different from the first metal, wherein the sensor signal processing unit is configured to determine that acetic acid gas has been detected when the current flowing between the first thin-wire electrode and the second thin-wire electrode is equal to or greater than a predetermined current value, and to output a concentration calculated in accordance with the level of a response signal corresponding to the current based on predetermined acetic acid gas concentration calibration characteristics.

2. An acetic acid gas concentration measuring device as set forth in claim 1, wherein the distance between said first thin wire electrode and said second thin wire electrode is constant.

3. An acetic acid gas concentration measuring device according to claim 2, wherein the distance between adjacent first and second thin wire electrodes is 100 nm or more and 1000 nm or less.

4. An acetic acid gas concentration measuring device as claimed in any one of claims 1 to 3, wherein the first metal is selected from the group consisting of gold, platinum, silver, and titanium.

5. An acetic acid gas concentration measuring device as described in any one of claims 1 to 4, wherein the second metal is selected from the group consisting of silver, copper, iron, zinc, nickel, cobalt, aluminum, tin, chromium, molybdenum, manganese, magnesium and alloys thereof.

6. An acetic acid gas concentration measuring device as described in any one of claims 1 to 5, wherein the first thin wire electrode and the second thin wire electrode are arranged parallel to each other by extending from opposite directions toward each other.

7. An acetic acid gas concentration measuring device as described in any one of claims 1 to 6, wherein the filter is made of one or more materials selected from the group consisting of a polytetrafluoroethylene porous membrane, a polyvinylidene fluoride porous membrane, and a non-woven fabric treated with a fluorine compound to make it water-repellent.

8. An acetic acid gas concentration measuring device as described in any one of claims 1 to 7, wherein the capsule is made of one or more materials selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, polyvinyl chloride, ABS resin, ASA resin, PLA resin, acrylic resin, epoxy resin, and high-strength glass.

9. An acetic acid gas concentration measuring device as described in any one of claims 1 to 8, further comprising a transmitting device portion disposed within the capsule and capable of transmitting the concentration to the outside of the capsule.

10. An acetic acid gas concentration measuring device as described in any one of claims 1 to 8, further comprising a memory device unit disposed within the capsule and capable of storing the concentration.

11. A method for using an acetic acid gas concentration measuring device according to any one of claims 1 to 10, comprising placing the acetic acid gas concentration measuring device in a stomach and measuring the acetic acid gas concentration in the stomach.

12. A method for measuring an acetic acid gas concentration, comprising measuring the acetic acid gas concentration using an acetic acid gas concentration measuring device according to any one of claims 1 to 10.

13. A method for measuring a current flowing between the first thin-line electrode and the second thin-line electrode by exposing a droplet sensor unit including an insulating substrate having at least a surface made of silica, a first thin-line electrode including at least one of a first metal and carbon arranged on the surface of the substrate, and a second thin-line electrode arranged on the surface of the substrate alternately with the first thin-line electrode and including a second metal different from the first metal, to a gas to be measured; ｔｈ and determining whether the current is equal to or greater than a predetermined value I ｔｈ If the current is less than the predetermined value I ｔｈ In the above cases, the method for measuring the concentration of acetic acid gas outputs an acetic acid gas concentration result according to the level of a response signal corresponding to the current, based on a previously obtained acetic acid gas concentration calibration characteristic.

Images