Detection member for volatile fatty acid sensor, method for manufacturing the same, and volatile fatty acid detection device

Abstract

The present invention provides a member for detecting volatile fatty acids with high sensitivity. In the detection member for a volatile fatty acid detection sensor according to one embodiment of the present invention, a portion that makes contact with outside air is formed from a hydrophobic swellable rubber. In the volatile fatty acid detection device according to one embodiment of the present invention, the aforementioned detection member for a volatile fatty acid detection sensor according to the present invention is disposed inside a capsule, which is a housing, and a water-repellent filter that allows the passage of volatile fatty acids is disposed in at least a part of a surface, in contact with the external environment, of the capsule.

Description

Technical Field

[0001] The present invention relates to a detection member for a volatile fatty acid detection sensor, a method for manufacturing the same, and a volatile fatty acid detection device.

Background Art

[0002] Volatile fatty acids (VFA) such as propionic acid, butyric acid, and acetic acid are substances that greatly affect the productivity and quality improvement of dairy farming such as cows. In addition, cows emit a large amount of methane gas that promotes global warming when digesting food, but there is a report that this emission can be significantly reduced by controlling VFA in the bovine rumen (the first stomach). Against this background, there is a need for a method and a device therefor to detect and quantitatively measure VFA, particularly VFA volatilized from the liquid part of the bovine rumen.

[0003] As a gas detection method, a method using an adsorbent that directly adsorbs gas components is known, and for example, it is disclosed in Patent Document 1. For this reason, a method has been tried in which VFA is adsorbed on an adsorbent, and the weight change of the adsorbent and the change in the infrared absorption spectrum due to the adsorption of VFA are monitored to detect and measure VFA. However, this method has problems of low sensitivity and a relatively large device. As for the sensitivity, a concentration of 25 mM (millimole) in the liquid in the bovine rumen is required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a detection member for a volatile fatty acid detection sensor that can detect VFA with high sensitivity despite its small size, a method for manufacturing the same, and a volatile fatty acid detection device. Another object of the present invention is to provide a small-sized device capable of highly sensitively detecting VFA in bovine rumen liquid.

Means for Solving the Problems

[0006] The configuration of the present invention is shown below. (Configuration 1) A detection member for a volatile fatty acid detection sensor made of a swelling rubber in which the portion exposed to the outside air is hydrophobic. (Configuration 2) A detection member for a volatile fatty acid detection sensor made of a swelling rubber in a swollen state, on which dodecane is adhered to the portion exposed to the outside air. (Configuration 3) The detection member for a volatile fatty acid detection sensor according to Configuration 1 or 2, wherein the swelling rubber is acrylonitrile-butadiene rubber. (Configuration 4) A capsule having a filter that is permeable to volatile fatty acids and water-repellent, and disposed on at least a part of the surface in contact with the outside world, A volatile fatty acid detection device, wherein the detection member for a volatile fatty acid detection sensor according to any one of Configurations 1 to 3 is disposed inside the capsule. (Configuration 5) The volatile fatty acid detection device according to Configuration 4, further comprising a weight change measuring device disposed inside the capsule in contact with the detection member for a volatile fatty acid detection sensor to measure a weight change. (Configuration 6) The volatile fatty acid detection device according to Configuration 4, wherein an infrared irradiation device and an infrared light receiving device are disposed inside the capsule with the detection member for a volatile fatty acid detection sensor interposed therebetween. (Configuration 7) The volatile fatty acid detection device according to Configuration 4, wherein an infrared reflection plate in contact with the detection member for the volatile fatty acid detection sensor, an infrared irradiation device, and an infrared light receiving device are arranged on the same side of the detection member via the infrared reflection plate inside the capsule. (Configuration 8) The volatile fatty acid detection device according to any one of Configurations 5 to 7, wherein a transmission device for wirelessly transmitting information obtained by the weight change measurement device or the infrared light receiving device to the outside of the capsule is arranged inside the capsule. (Configuration 9) Preparing a swellable rubber, Immersing the swellable rubber in a solution containing dodecane and a swelling liquid, Drying the solution, which is a method for manufacturing a detection member for a volatile fatty acid detection sensor. (Configuration 10) The method for manufacturing a detection member for a volatile fatty acid detection sensor according to Configuration 9, wherein the swelling liquid is hexane. (Configuration 11) The method for manufacturing a detection member for a volatile fatty acid detection sensor according to Configuration 9 or 10, wherein the swellable rubber is acrylonitrile-butadiene rubber. (Configuration 12) When the main volatile fatty acids in the gas phase of the target are either acetic acid or propionic acid, using the volatile fatty acid detection device according to Configuration 8, estimating whether the main volatile fatty acid in the gas phase of the target is acetic acid or propionic acid by utilizing the difference in the time change of the detection sensitivity of acetic acid and propionic acid, which is a method for estimating the main volatile fatty acids in the gas phase.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a detection member for a volatile fatty acid detection sensor that detects VFA with high sensitivity despite its small size, a method for manufacturing the same, and a volatile fatty acid detection device. In addition, according to the present invention, it is possible to provide a small-sized device capable of detecting VFA with high sensitivity in the liquid part of the bovine rumen.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0009] (Embodiment 1) In Embodiment 1, the VFA detection member of the present invention will be described.

[0010] <Structure> The VFA detection member of the present invention is made of a swelling rubber in which the portion in contact with the outside air is hydrophobic. As shown in FIG. 1, the structure of the VFA detection member 101 is composed of a swelling rubber 11 having a large number of voids 12, and the portion of the swelling rubber 11 in contact with the outside air is hydrophobic. Here, the portion in contact with the outside air refers to the gas adsorption surface, and includes not only the surface forming the so-called outer shape, but also the inner surface of the voids 12. Further, in the present specification, "swelling rubber" means a rubber having the property of swelling, and includes both those in a swollen state and those in a non-swollen state when the VFA detection member 101 is in use.

[0011] Generally, as shown in FIG. 2, the rubber 102 has a structure in which the polymers 13 constituting the rubber are intricately intertwined. For this reason, many spaces 14 are formed between the rubber polymers 13. When the rubber 102 is immersed in a liquid (swelling liquid) having a high affinity for the rubber polymer 13, an absorption force is generated and the liquid is drawn into the space 14 between the rubber polymers 13, and the space 14 expands and swells. Even after drying to remove the swelling liquid, the space 14 is not completely blocked. Therefore, the space 14 shown in FIG. 2 can be considered as a form of the voids 12 shown in FIG. 1, both in the state before swelling and in the state after swelling. That is, the voids 12 in the swelling rubber 11 may be in the form of pores or may be irregular spaces formed between the polymers constituting the rubber. In the aspect where the swelling rubber 11 is in a swollen state, examples of the swelling liquid include hexane, toluene, xylene, etc. Among these, hexane is easy to handle and can be preferably used. As the swelling rubber, acrylonitrile-butadiene rubber (NBR) is preferably used because it has high VFA detection sensitivity, the raw material rubber is inexpensive, the quality variation is small, and it is easy to handle. However, it is not limited to NBR, and nitrile isoprene rubber, epichlorohydrin rubber, acrylic rubber, chloroprene rubber, etc. can also be used.

[0012] As a method for making the portion of the swelling rubber 11 that touches the outside air hydrophobic, there is a method of using a rubber 102 composed of a rubber polymer 13 with strong hydrophobicity having an SP (Solubility Parameters) value exceeding 7.5 and being 8.5 or less as the swelling rubber 11, and a method of immersing the swelling rubber 11 in a lipophilic liquid to deposit a lipophilic substance on the rubber polymer of the swelling rubber 11. Here, as the lipophilic liquid, it is preferable to use a liquid with a high boiling point in order to suppress disappearance due to vaporization during use, and examples thereof include dodecane, liquid paraffin, and squalene. Among these, dodecane can be preferably used because of its low viscosity.

[0013] The inventor has found that by using the swelling rubber 11 as the detection member 101, the polarity of the portion of the swelling rubber 11 that touches the outside air changes according to the amount of VFA in the gas phase. In other words, it changes from hydrophobic to hydrophilic, and the amount of water drawn into the detection member 101 changes, enabling the detection of VFA with high sensitivity. Specifically, according to the detection member 101, high-sensitivity detection of VFA is possible by the following mechanism. The swelling rubber 11 that constitutes the detection member 101 has the property that when a small amount of VFA is adsorbed, the polarity of the portion of the swelling rubber 11 that touches the outside air changes, and the amount of water adsorbed (co-adsorbed) there changes significantly. Water exists in a large amount in the outside air (in the gas phase) in the form of water vapor. In an environment where VFA coexists in the gas phase, an absorption force is generated in the voids 12 hydrophilized by a small amount of VFA present in the gas phase, so that a large amount of water is drawn into the swelling rubber 11, and the weight of the detection member 101 and the infrared absorption amount at a specific wavelength change significantly. As a result, the detection member 101 functions as a detection member suitable for highly sensitive VFA detection. Here, in order to increase the amount of water adsorbed due to the change in polarity of the portion of the swelling rubber 11 that touches the outside air and enhance the detection sensitivity, the swelling rubber 11 constituting the detection member 101 is preferably a porous body. When the swelling rubber 11 is a porous body, the surface area per unit volume becomes larger, so that it becomes possible to adsorb more water.

[0014] <Manufacturing method> The VFA detection member 101 of the present invention can be manufactured by the following steps as shown in FIG. 3. First, a swelling rubber is prepared (step S12). As the swelling rubber, acrylonitrile-butadiene rubber (NBR) can be preferably used, but it is not limited to NBR, and nitrile isoprene rubber, epichlorohydrin rubber, acrylic rubber, chloroprene rubber, etc. may be used. Next, the swelling rubber is immersed in a solution containing dodecane (corresponding to the above-described lipophilic liquid) and a swelling liquid (step S13). Here, hexane can be preferably used as the swelling liquid, but it is not limited to hexane, and toluene, xylene, etc. may be used. Thereafter, the solution is dried (step S14). The drying method is not particularly limited, and examples include a nitrogen drying method and a vacuum drying method. By the above steps, it becomes possible to provide a VFA detection member that can detect VFA with high sensitivity and perform quantitative measurement. In the VFA detection member produced by the above steps, the swelling rubber is in a swollen state by immersion in a solution containing dodecane and a swelling liquid, and dodecane adheres to the portion that touches the outside air, so that the portion that touches the outside air becomes hydrophobic. On the other hand, when using a rubber composed of a rubber polymer with strong hydrophobicity that satisfies the above-described SP value conditions as the swelling rubber, steps S13 and S14 may be omitted.

[0015] <Application as a sensor> The VFA detection member 101 of the present invention can be incorporated into sensors using a weight measurement method or an infrared absorption measurement method to provide a highly sensitive VFA detection sensor. An example of a sensor 104 incorporating the detection member 101 of the present invention into a quartz crystal microbalance (QCM) is shown in FIG. 4. The sensor 104 has a VFA detection member 101 composed of a quartz crystal 21, a first electrode 22, a second electrode 23, and a swellable rubber 11. The detection member 101 is disposed on the surface of the electrode (i.e., in contact with the electrode), and may be disposed in contact with both the first electrode 12 and the second electrode 13 (sensor 104), or may be disposed in contact with either one of them. The former sensor 104 disposed in contact with both electrodes can ensure a wide area where substances can be adsorbed onto the swellable rubber 11 constituting the detection member 101, and thus has the characteristic of being easy to increase the detection sensitivity. The latter sensor disposed in contact with one electrode has the characteristics of high efficiency when only the side of the electrode where the detection member 101 is disposed is in contact with the gas phase (outside air) during use, and being easy to reduce costs. The swellable rubber 11 constituting the detection member 101 is a substance in which the amount of water adsorbed from the gas phase changes depending on the amount of VFA in the gas phase, and the use of this as a detection member for a VFA detection sensor is a feature of the present invention. On the other hand, a sensor having a normal QCM structure uses, as a detection member, a substance or a thin film (sensitive film) thereof that adsorbs the target substance instead of the swellable rubber 11. Here, QCM is a device that detects the amount of adhesion of a specific substance by utilizing the principle that when a substance adheres to the surface of the vibrating body of a quartz crystal, the resonance frequency changes according to the weight of the adherent, and is disclosed, for example, in Patent Document 2.

[0016] The inventor has found that when trying to detect VFA with high sensitivity using a QCM with a conventional VFA adsorbing substance, it is necessary to monitor an extremely small weight change, and it becomes difficult to avoid complications such as an increase in the size and cost of the device and suppression of noise.

[0017] On the other hand, when the detection member 101 of the present invention made of the swellable rubber 11 is used as the detection member, the polarity of the portion of the swellable rubber 11 that touches the outside air changes according to the amount of VFA in the gas phase, and the amount of water co-adsorbed on its surface changes. Since water is present in a large amount in the outside air, in an environment where water vapor and VFA coexist in the gas phase, a larger amount of water than the adsorption amount of VFA that can change its polarity is adsorbed (co-adsorbed) on the portion of the swellable rubber 11 that touches the outside air. As a result, the weight change of the detection member 101 becomes large, or the change in the infrared absorption amount at a specific wavelength becomes large, enabling highly sensitive detection of VFA.

[0018] In the sensor 104, the thickness of the swellable rubber 11 constituting the detection member 101 is not particularly limited, but it is preferably a thin film from the viewpoint of the detection speed, and for example, it can be 10 nm or more and 1 μm or less. The size of the swellable rubber 11 is not particularly limited either, but a larger size is preferable from the viewpoint of the detection sensitivity because the area for adsorbing substances becomes larger. In view of the balance with the miniaturization of the sensor, a size (width) similar to that of the first electrode 12 and the second electrode 13 is preferable.

[0019] The density of the voids 12 formed in the swellable rubber 11 (the space ratio with respect to the outer volume) is preferably as high as possible on the premise that the strength that does not significantly affect the measured Q value is maintained. Practically, as the density when the swellable rubber 11 is a thin film, it can be 0.5 g / cm 3 or more and 1.8 g / cm 3 or less.

[0020] The crystal oscillator 21 is not particularly limited, but an AT-cut type crystal oscillator can be preferably used. Here, AT-cut means that the cutting angle is in a specific orientation with respect to the crystal axis, and the AT-cut type crystal oscillator has the characteristic of excellent temperature stability because the change in the temperature coefficient becomes extremely small near room temperature. The first electrode 22 and the second electrode 23 are not particularly limited as long as they can apply an alternating voltage to the crystal oscillator 21. For example, gold (Au), silver (Ag), platinum (Pt), copper (Cu), tungsten (W), aluminum (Al), titanium (Ti), chromium (Cr), nickel (Ni), their alloys, their metal compounds such as Al - Si, doped silicon (Si), and doped polysilicon (PolySi) can be mentioned. The electrode does not have to be a single substance. It is preferable to have an underlying layer of Ni or Cr to improve adhesion to the crystal and a top surface of Au or Ag to prevent oxidation. The first electrode 22 and the second electrode 23 preferably have a high Q - value of resonance of the crystal oscillator 21, can follow the movement of the crystal oscillator 21, and have a sensitivity in nanograms (ng). The thickness of the first electrode 22 and the second electrode 23 is not particularly limited, but is preferably a thin film for improving the Q - value, and can be, for example, 10 nm or more and 150 nm or less.

[0021] By applying an alternating voltage to the first electrode 22 and the second electrode 23 of the sensor 104 and measuring the change in the vibration frequency of the crystal oscillator 21, specifically, the change in the resonance frequency, it is also possible to detect VFA in the gas phase with high sensitivity and determine its amount. The sensor 104 provides a sensor that is small in size and has high VFA detection sensitivity.

[0022] (Embodiment 2) In Embodiment 2, a VFA detection device suitable for detecting and quantifying VFA in a solution environment where VFA is dissolved, such as bovine rumen liquid, will be described.

[0023] As shown in FIG. 5, in the VFA detection device 105 of Embodiment 2, the VFA detection member 101 of the present invention described in Embodiment 1 is disposed inside the capsule 56. Further, a filter 55 that allows VFA gas to permeate but blocks liquid is disposed on at least a part of the surface of the capsule 56, more specifically, on the surface of the capsule 56 that contacts the outside world (the environment outside the capsule). The material of the capsule 56 is not particularly limited, but it is preferably a material that is not corroded or destroyed in the digestive organs such as the bovine rumen. For example, polyethylene terephthalate, vinyl chloride, high-strength glass, etc. can be mentioned. Also, it is desirable that the inside of the capsule 56 is subjected to a hydrophobic coating so that water vapor does not condense. By using the housing of the VFA detection device as a capsule, it can be ingested by cows as a capsule tablet, and then the detection device can be recovered and the detection member 101 stored inside can be subjected to gravimetric analysis or infrared analysis to detect and measure VFA. The VFA detection device 105 is small, inexpensive, and easy to handle, so it is suitable for managing a large number of cows.

[0024] Here, as the material of the filter 55, a porous material or fiber having superhydrophobicity and permeable to gas, such as a superhydrophobic non-woven fabric, can be used. Here, in order to maintain the strength of the non-woven fabric and improve its durability, it is preferable to deposit a net-like metal on the non-woven fabric. More specifically, for the filter 55, for example, a gas-permeable superhydrophobic multilayer film in which both sides of a microporous PTFE (polytetrafluoroethylene) ultrafiltration membrane are sandwiched between PET (polyethylene terephthalate) non-woven fabrics having superhydrophobicity can be preferably used.

[0025] (Embodiment 3) In Embodiment 3, a VFA detection device that is particularly suitable for detecting and quantifying VFA in a solution environment in which VFA is dissolved, such as the liquid part of the bovine rumen, and that enables rapid measurement and real-time measurement will be described.

[0026] As shown in FIG. 6, the VFA detection device 106 according to Embodiment 3 includes a QCM device 52 disposed inside a capsule 56 with a swelling rubber 51 as the VFA detection member 101 of the present invention described in Embodiment 1 in contact with one electrode. A frequency measurement device 53 is arranged to receive the output from the QCM device 52 via a signal line 57, measure the vibration frequency of the crystal oscillator, process the data, and send the data to a transmission device 54 that transmits the data wirelessly via a signal line 58. Further, a filter 55 that allows VFA gas to pass through but blocks liquid is disposed on the surface of the capsule 56, more specifically, at least a part of the surface of the capsule 56 that is in contact with the outside world (the environment outside the capsule). Regarding the material of the capsule 56 and the like, it is the same as that in Embodiment 2, so the description thereof is omitted. The same applies to the capsule 56 used in Embodiment 3 described later and the capsule 61 used in Embodiment 3. Here, as the material of the filter 55, similar to Embodiment 2, a porous material having superhydrophobicity and permeable to gas, or a superhydrophobic nonwoven fabric made of fibers can be used. Here, in order to maintain the strength of the nonwoven fabric and improve its durability, it is preferable to deposit a net-like metal on the nonwoven fabric. More specifically, for the filter 55, for example, a gas-permeable superhydrophobic multilayer film in which both sides of a microporous PTFE (polytetrafluoroethylene) ultrafiltration membrane are sandwiched between PET (polyethylene terephthalate) nonwoven fabrics having superhydrophobicity can be preferably used.

[0027] According to the configuration of the VFA detection device 106, the QCM device 52, the vibration frequency measurement device 53, and the wireless transmission device 54 housed therein can be miniaturized. By appropriately selecting the material of the capsule 56, the VFA gas can be drawn into the inside of the capsule 56 through the filter 55 without being corroded even in gastric juice, and the required detection and measurement can be performed. In addition, since the result measured by the vibration frequency measurement device 53 and transmitted from the transmission device 54 can be received externally by wireless or the like, the VFA detection device 106 is a useful device that can monitor the state of the bovine rumen liquid part in real time. In the VFA detection device 106 shown in FIG. 6, the swelling rubber 51, which is the detection member 101, is provided on the surface of one of the electrodes (the first electrode or the second electrode) of the QCM device 52. However, as shown in FIG. 7, it may be a VFA detection device 103 in which the swelling rubber 51 is provided on the surfaces of both electrodes (the first electrode and the second electrode).

[0028] (Embodiments 4 and 5) In Embodiments 4 and 5, a VFA detection device that uses an infrared sensor and is suitable for detecting and quantifying VFA in a solution environment in which VFA is dissolved, such as the bovine rumen liquid part, and can perform rapid measurement and real-time measurement will be described.

[0029] As shown in FIG. 8, the VFA detection device 107 of Embodiment 4 includes, inside the capsule 61, the VFA detection member 101 of the present invention described in Embodiment 1, an infrared irradiation device 62 and a light receiving device 64 sandwiching the detection member 101, a signal control and processing device 67, and a wireless transmission device 69. Further, a filter 70 that allows the VFA gas to pass through but blocks the liquid is disposed on the surface of the capsule 61, more specifically, at least a part of the surface of the capsule 61 that contacts the outside world (the environment outside the capsule). The infrared irradiation device 62, the light receiving device 64, and the wireless transmission device 69 are each connected to the signal control and processing device 67 via signal lines 65, 66, and 68. As shown in FIG. 9, in the VFA detection device 108 of Embodiment 5, an infrared irradiation device 62 and a light receiving device 64 for the light thereof are arranged inside the capsule 61 on the same side as the VFA detection member 101 of the present invention described in Embodiment 1 via an infrared reflector 109. The VFA detection device 107 of Embodiment 4 has a device configuration that employs a transmission type detection method, while the VFA detection device 108 of Embodiment 5 has a device configuration that employs a reflection type detection method. However, other configurations are the same. In the VFA detection device 108 of Embodiment 5, by bringing the filter 70 into contact with the detection member 101, it is desirable to minimize the space in contact with the swelling rubber constituting the detection member 101 (the range where outside air touches the outer surface of the swelling rubber).

[0030] The signal control and processing device 67 controls the infrared irradiation device 62 via the signal line 65 to irradiate the detection member 101 with infrared rays 63 of a predetermined wavelength, receives the output signal from the light receiving device 64 via the signal line 66, and performs signal processing and data analysis. Then, the result is sent to the wireless transmission device 69 via the signal line 68. The infrared rays irradiated by the infrared irradiation device 62 may be infrared rays of a single wavelength, infrared rays composed of a plurality of emission lines, or infrared rays having a broad wavelength range. However, from the viewpoint of passing through the detection member 101 and detecting water, it is preferable to use infrared rays including a wavenumber range of 3000 to 4000 cm -1 . Also, from the viewpoints of reducing the cost and power consumption of the device, infrared rays of a single wavelength or a narrow wavelength band are preferable. On the other hand, the infrared rays irradiated by the infrared irradiation device 62 may be in the range of 4500 to 6000 cm -1 . The infrared rays in this region are called near-infrared rays, and various commercially available light-emitting diodes can be used as the irradiation device.

[0031] Note that the light receiving device 64 in FIG. 8 detects infrared rays 63 as transmitted light through the detection member 101, and the light receiving device 64 in FIG. 9 reflects the infrared rays 63 with the infrared reflecting plate 109 and detects the reflected light. In the latter case, when the infrared rays 63 are reflected by the infrared reflecting plate 109, a part of them penetrates into the swelling rubber constituting the detection member 101. Therefore, it becomes possible to detect the change in the swelling rubber accompanying this with the light receiving device 64. Further, similar to the second embodiment, the filter 70 can be made of a super water-repellent porous material or fiber such as a super water-repellent nonwoven fabric that allows gas to pass through. Here, in order to maintain the strength of the nonwoven fabric and improve its durability, it is preferable to deposit a net-like metal on the nonwoven fabric. More specifically, for the filter 70, for example, a gas-permeable super water-repellent multilayer film in which both sides of a microporous PTFE (polytetrafluoroethylene) ultrafiltration membrane are sandwiched between PET (polyethylene terephthalate) nonwoven fabrics having super water-repellency can be preferably used.

[0032] The VFA detectors 107 and 108 can miniaturize the detection member 101, signal control and processing device 67, and wireless transmission device 69 housed therein. By appropriately selecting the material of the capsule 61, the VFA gas can be drawn into the interior of the capsule 61 through the filter 70 without corrosion even in gastric juice, and the required detection and measurement can be performed. In addition, since the results processed and analyzed by the signal control and processing device 67 transmitted from the transmission device 69 can be received externally by wireless or the like, the VFA detectors 107 and 108 are useful devices that can monitor the state of the bovine rumen liquid part in real time. In particular, in the VFA detectors 107 and 108 that adopt a detection method using an infrared sensor, as demonstrated in the examples described later, regarding the detection sensitivity of acetic acid and propionic acid, the time-varying behavior of the measurement results differs depending on the concentrations of acetic acid and propionic acid in the gas phase and the material of the swelling rubber (type of rubber polymer) constituting the detection member 101. Therefore, by monitoring the measurement results using a plurality of detection devices, it becomes possible to determine whether the main component of the VFA gas is propionic acid or acetic acid. This is an important index for evaluating the fermentation state in bovine rumen fluid.

Example

[0033] In the following examples, an example in which the detection member of the present invention is fabricated and its VFA detection characteristics are examined by a gravimetric method, an infrared (IR) measurement method, or a reflection infrared absorption (RAS) method will be described. However, of course, the present invention is not limited to such a specific form, and it should be noted that the technical scope of the present invention is defined by the scope of the claims. (Example 1) In Example 1, the detection member 101 described in Embodiment 1 was fabricated, and its VFA detection characteristics were examined by a gravimetric method.

[0034] At room temperature, 6 g of NBR (PN-20HA, manufactured by JSR), 1.5 g of dodecane, and 12 g of hexane were placed in a glass bottle with a capacity of 100 mL, mixed, sealed, and left for one day. Then, it was naturally dried in the atmosphere in a draft for three days to produce the detection member 101 made of swellable rubber. Here, the NBR used contained 41.5% acrylonitrile component, had a Mooney viscosity (ML1+4) of 85 at 100 °C, and was pulverized to a particle size of 100 to 500 μm. Thereafter, the detection member 101 (swellable rubber) was divided into small portions of about 0.2 g, placed in a sealed container with the lid on, and the first weighing was performed using an electronic balance (CP224S, manufactured by Sartorius). Next, a petri dish A with an internal volume of 400 mL was filled with 200 mL of VFA aqueous solution or water. The detection member 101 (swellable rubber) divided into small portions was placed in a petri dish B with an internal volume of 20 mL. Petri dish B was placed in petri dish A, covered, and then petri dish A and the lid were wrapped with Saran Wrap (registered trademark) and left at room temperature for 24 hours. In the preparation of the VFA aqueous solution, propionic acid, acetic acid, or butyric acid was used as the VFA. Thereafter, petri dish B was taken out from petri dish A, placed in a sealed container with the lid on in the same manner as the first weighing, and the second weighing was performed using an electronic balance. The weight difference of the sample of the detection member 101 (swellable rubber) was obtained from the difference between the first weighing and the second weighing.

[0035] The relationship between the amount of VFA in the VFA aqueous solution placed in petri dish A and the measured weight increase is shown in FIGS. 10 to 12. Here, FIGS. 10 to 12 show the cases where VFA is propionic acid, acetic acid, and butyric acid respectively, and the concentration of the VFA aqueous solution is also shown in mM units in each figure. From the results shown in FIGS. 10 to 12, for any VFA, a linear relationship is recognized between the concentration of VFA and the weight increase, and it can be seen that the concentration of VFA can be measured using such data as a calibration curve. Moreover, it can be seen that the produced detection member 101 (swellable rubber) can detect VFA even at a low concentration of 5 mM or less in the VFA aqueous solution. According to Example 1, it was demonstrated that the detection member of the present invention can detect VFA by the weight measurement method with extremely high sensitivity.

[0036] (Example 2) In Example 2, the detection member 101 described in Embodiment 1 was fabricated, and its VFA detection characteristics were examined by an infrared (IR) measurement method.

[0037] First, 0.1 g of NBR (PN-20HA, manufactured by JSR) was pressed using a heater plate press machine (manufactured by NPE Systems) under the conditions of 200°C for 30 seconds. Next, the pressed NBR was placed in a petri dish, covered, and immersed in a mixed solution of 50 μL of dodecane and 500 μL of hexane at room temperature for 1 hour, and then naturally dried in a draft for 12 hours to obtain a swellable rubber. Thereafter, the swellable rubber was cut into a size for measurement to obtain a sheet-like sample A (detection member 101) made of the swellable rubber. The thickness of the sheet of sample A was about 30 μm. Next, a petri dish A with an internal volume of 400 mL was filled with 200 mL of an aqueous VFA solution or water, sample A was placed in a petri dish B with an internal volume of 20 mL, petri dish B was placed in petri dish A, covered, and then petri dish A and the cover were wrapped with Saran Wrap (registered trademark) and left at room temperature for 24 hours. In the preparation of the aqueous VFA solution, propionic acid was used as the VFA. Thereafter, sample A was taken out from petri dish B placed in petri dish A, and IR spectrum measurement was performed in a reflection measurement mode using an IR spectrum analyzer (FT / IR-6200, manufactured by JASCO Corporation).

[0038] The results of the IR spectrum measurement are shown in FIG. 13. In FIG. 13, the reference numerals 1 to 6 indicated by circled numerals respectively indicate the following conditions. 1: The fabricated sample A (sheet-like detection member 101 made of swellable rubber), 2: When water was placed in petri dish A, 3: When the amount of propionic acid in the aqueous VFA solution placed in petri dish A was 5 μL / 200 mL, 4: When the amount of propionic acid in the aqueous VFA solution placed in petri dish A was 10 μL / 200 mL, 5: When the amount of propionic acid in the aqueous VFA solution placed in petri dish A was 25 μL / 200 mL, 6: When the amount of propionic acid in the aqueous VFA solution placed in petri dish A was 50 μL / 200 mL. From the results of Fig. 13, a characteristic peak indicating water absorption appears at a wavenumber of 3500 cm -1 only when sample A is placed in an environment where water is present (the peak is not confirmed in the spectrum of sample A indicated by reference numeral 1), and it can be seen that the higher the concentration of propionic acid in the VFA aqueous solution, the higher this peak becomes. Fig. 14 is a graph showing the relationship between the peak intensity at a wavenumber of 3500 cm -1 in the spectra indicated by reference numerals 2 to 6 in Fig. 13, that is, the absorbance of water in the IR, and the concentration of propionic acid in the VFA aqueous solution. Since the absorbance of water in the IR increases monotonically with the concentration of propionic acid, it can be seen that quantitative measurement of propionic acid is possible by using this data as a calibration curve. Furthermore, it can be seen that in the measurement method of Example 2 using IR, even a very small amount of propionic acid of 0.34 mM can be detected. Example 2 demonstrated that VFA can be detected by IR measurement method with extremely high sensitivity.

[0039] Here, although it was evaluated at the concentration of the VFA aqueous solution used in the test, such as an aqueous propionic acid solution, in a low concentration range where the concentration of VFA is 25 mM, the relative concentration C V of VFA in the gas and its partial pressure P can be converted using Raoult's law. The relationship between the VFA aqueous solution concentration C L (unit: mM), the relative concentration C V (unit: %) and the partial pressure P (unit: Pa) at 25°C, taking propionic acid as an example, is as shown in the following formulas (2) and (3). Here, "relative" represents the ratio to water (water vapor). P = 5.6×10 -2 C L ···(2) C V = 1.8×10 -5 C L ···(3) That is, since VFA contained in an aqueous solution at a low concentration range as used in the test of this example can be considered to exist in the gas phase in a closed space at a relative concentration and partial pressure correlated with the concentration in the aqueous solution, it can be said that highly sensitive detection of VFA was achieved by the VFA detection member produced in this example.

[0040] (Example 3) In Example 3, the detection member 101 described in Embodiment 1 was produced, and its VFA detection characteristics were examined by the reflection infrared absorption (RAS) method.

[0041] First, 0.1 g of medium-nitrile NBR (240S, manufactured by JSR) was pulverized to about 1 mm in diameter. On the other hand, a water-repellent PET nonwoven fabric (HIROSE-02, fluorine-processed product) manufactured by Hirose Paper was cut out into a sheet with a diameter of 28 mm, the above-mentioned medium-nitrile NBR was placed on it, and it was pressed at 160 °C for 1 minute under 10 MPa. As the press machine, a press machine manufactured by NPA System was used, and the pressing process was performed while sandwiching it between two Teflon (registered trademark) sheets. Thereby, an NBR film (detection member 101) with a film thickness of about 15 μm was produced on a water-repellent PET nonwoven fabric (film thickness of about 125 μm). Similarly, using 0.1 g of low-nitrile NBR (260S, manufactured by JSR), an NBR film (detection member 101) with a film thickness of about 15 μm was produced on a water-repellent PET nonwoven fabric. Here, the medium-nitrile NBR (240S) used contains 26% acrylonitrile component and has moderate water resistance. On the other hand, the low-nitrile NBR (260S) contains 15% acrylonitrile component and has strong water resistance. That is, the low-nitrile NBR has a property of being less likely to absorb water than the medium-nitrile NBR. In addition, since both the medium-nitrile NBR and the low-nitrile NBR are composed of rubber polymers that satisfy the above-mentioned SP value conditions, in this example, they were used in a non-swollen state (that is, without immersing them in a solution containing dodecane and a swelling liquid). Next, a water-repellent PET nonwoven fabric having the NBR film was fixed to the detection window of a reflection-type near-infrared spectroscopic module (C15714, wavelength range: 1750 to 2150 nm) manufactured by Hamamatsu Photonics. Here, with the surface of the water-repellent PET nonwoven fabric having the NBR film facing downward, it was brought into contact with the detection surface of the horizontally placed spectroscopic module, and water, an aqueous propionic acid solution, an aqueous acetic acid solution, or an aqueous butyric acid solution was dropped onto the surface without the NBR film (upper surface) and left for a certain period of time. The configuration of this experimental apparatus is shown in Fig. 15. Note that the water-repellent PET nonwoven fabric prevents the penetration of water and VFA aqueous solutions, and water and VFA aqueous solutions do not directly touch the NBR film. That is, in the experimental apparatus shown in Fig. 15, the NBR film (detection member 101) is configured to be able to come into contact with water vapor and VFA gas derived from water or VFA aqueous solution dropped onto its upper surface via the water-repellent PET nonwoven fabric.

[0042] Fig. 16 shows the measurement results of the near-infrared absorption spectra obtained for the NBR film (detection member 101) prepared using medium-nitrile NBR (240S). When water, 0.2% aqueous acetic acid solution, 0.2% aqueous propionic acid solution, and 0.2% aqueous butyric acid solution were dropped onto the water-repellent PET nonwoven fabric and measured 10 minutes later (i.e., with the contact time between the NBR film and the gas from the sample solution being 10 minutes), the detection sensitivity of near-infrared light decreased in the order of water, acetic acid, propionic acid, and butyric acid. This indicates that, in the order of water, aqueous acetic acid solution, aqueous propionic acid solution, and aqueous butyric acid solution, the amount of near-infrared light absorbed by the PET nonwoven fabric containing the NBR film increased as these sample solutions were dropped onto the water-repellent PET nonwoven fabric. The characteristic absorption band of water is broadly present around 1940 nm (5155 cm -1 ) but is not significantly detected because the absorption coefficient is small. However, when water is absorbed by the NBR film, the NBR film swells or bends, reducing the amount of the NBR film present in the detection layer (range within approximately less than 1.0 μm from the detection surface) near the detection surface of the spectroscopic module. As a result, the detection sensitivity of near-infrared light by the PET nonwoven fabric containing the NBR film decreases. In Fig. 16, the difference in detection sensitivity near 2100 nm when the sample solution is water and an aqueous solution of butyric acid is about 150 counts, which corresponds to 1.7% of the detection counts in the case of the aqueous solution of butyric acid. In the case of butyric acid, which is the most hydrophobic among the VFAs used, the decrease in the count number is the largest. In the case of acetic acid, the amount of decrease is smaller compared to propionic acid and butyric acid.

[0043] Fig. 17 shows the measurement results of the near-infrared absorption spectra obtained for an NBR membrane (detection member 101) made using medium-nitrile NBR (240S), with the concentration of the VFA aqueous solution being 0.02% and the contact time between the NBR membrane and the gas from the sample solution being 60 minutes. As described above, since the medium-nitrile NBR (240S) used has medium water resistance, it can be seen that even if the amount of VFA contained in the VFA aqueous solution is small (that is, even if the VFA concentration is low), the detection sensitivity of near-infrared rays decreases significantly compared to the case of water. The concentrations of acetic acid, propionic acid, and butyric acid in a 0.02% aqueous solution are 3.3 mM, 2.7 mM, and 2.3 mM, respectively. The difference in detection sensitivity near 2100 nm when the sample solution is water and an aqueous solution of butyric acid is about 600 counts, which corresponds to 6.9% of the detection counts in the case of the aqueous solution of butyric acid. This indicates that in the presence of a very small amount of butyric acid, the NBR membrane absorbs a large amount of water, causing swelling and bending. However, since the characteristic absorption of water near 1940 nm is small, it is considered that the influence of bending is greater. Interestingly, in the case of medium-nitrile NBR (240S), the detection sensitivity of propionic acid is about half that of butyric acid. In Fig. 16, when the detection sensitivity of acetic acid is low and the contact time between the NBR membrane and the gas from the sample solution is short, the detection sensitivity of propionic acid is high. However, when this contact time is lengthened, a result with a high detection sensitivity of acetic acid is obtained. This means that by monitoring the time change of the detection sensitivity of near-infrared rays, it is possible to distinguish whether the main VFA in the target gas phase is propionic acid or acetic acid. However, in order to estimate its exact concentration, it is necessary to analyze the data obtained from a plurality of sensors equipped with the detection member of the present invention.

[0044] Figure 18 shows the measurement results of near-infrared absorption spectra obtained for an NBR membrane (detection member 101) made using low-nitrile NBR (260S), with the concentration of the VFA aqueous solution being 0.2% and the contact time between the NBR membrane and the gas from the sample solution being 10 minutes. As described above, the low-nitrile NBR (260S) used has higher water resistance than medium-nitrile NBR and has a low water absorption amount. However, even when VFA is present at a low concentration of about 0.2% in the aqueous solution, it can be seen that the detection sensitivity of near-infrared light decreases significantly compared to the case of water. The difference in detection sensitivity near 2100 nm when the sample solution is water and an aqueous butyric acid solution reaches 400 counts (equivalent to 4.2% of the detection count in the case of the aqueous butyric acid solution) even 10 minutes after dropping each sample solution (that is, when the contact time between the NBR membrane and the gas from the sample solution is 10 minutes). When using a detection member having such characteristics, although the difference in detection sensitivity among different types of VFA, that is, acetic acid, propionic acid, butyric acid, etc., is small, it is suitable for use as a total VFA sensor that utilizes the large difference in detection sensitivity between the case of water and the case of a VFA aqueous solution.

Industrial Applicability

[0045] According to the present invention, there are provided a detection member for highly sensitively detecting volatile fatty acids, a method for manufacturing the same, and a small-sized and highly sensitive volatile fatty acid detection device. Further, the device can be placed in a capsule form in the liquid part of a bovine rumen and can also perform on-site and real-time measurement.

[0046] As described in the background art section, VFA is a substance that greatly affects the productivity and quality improvement of dairy farming such as cows, and is also a substance that is highly related to the emission of methane gas through the digestion of food by cows. Therefore, it is considered that if VFA is measured with high precision and the results are fed back, the productivity and quality of dairy farming can be greatly improved, and it can also greatly contribute to the suppression of global warming. In addition, the sensor and device of the present invention for highly sensitive detection of VFA lead to quantitative evaluation of the activity of anaerobic bacteria, and are expected to be widely used in various cases where VFA is generated by microbial decomposition, such as quality control in feed production, monitoring of methane fermentation tanks, operation management of final disposal sites (landfills), and environmental management of paddy fields and lakes.

Explanation of Signs

[0047] 11: Swelling rubber 12: Void 13: Rubber polymer 14: Space 21: Crystal oscillator 22: First electrode 23: Second electrode 51: Swelling rubber 52: QCM device 53: Frequency measurement device 54: Transmitting device 55: Filter (super water-repellent non-woven fabric) 56: Capsule 57: Signal line 58: Signal line 61: Capsule 62: Infrared irradiation device 63: Infrared ray 64: Infrared light receiving device 65: Signal line 66: Signal line 67: Signal control and processing device 68: Signal line 69: Wireless transmitting device 70: Filter (super water-repellent non-woven fabric) 101: VFA detection member 102: Rubber 103: VFA detection device 104: Sensor 105: VFA detection device 106: VFA detection device 107: VFA detection device 108: VFA detection device 109: Infrared reflection plate

Claims

1. A sensing member for a volatile fatty acid detector, which is made of a swelling rubber in a swollen state with dodecane adhered to the portion in contact with the outside air.

2. The sensing member for a volatile fatty acid detector according to Claim 1, wherein the swelling rubber is acrylonitrile-butadiene rubber.

3. A capsule having a filter that is permeable to volatile fatty acids and water-repellent, and disposed on at least a part of the surface in contact with the outside world, A volatile fatty acid detector, wherein the sensing member for a volatile fatty acid detector according to Claim 1 is disposed inside the capsule.

4. The volatile fatty acid detector according to Claim 3, further comprising a weight change measuring device disposed inside the capsule in contact with the sensing member for a volatile fatty acid detector to measure a change in weight.

5. The volatile fatty acid detector according to Claim 3, wherein an infrared irradiation device and an infrared light receiving device are disposed inside the capsule with the sensing member for a volatile fatty acid detector interposed therebetween.

6. The volatile fatty acid detector according to Claim 3, wherein an infrared reflecting plate in contact with the sensing member for a volatile fatty acid detector, an infrared irradiation device, and an infrared light receiving device are disposed on the same side of the sensing member via the infrared reflecting plate inside the capsule.

7. The volatile fatty acid detector according to Claim 4, further comprising a transmitting device disposed inside the capsule to wirelessly transmit the information obtained by the weight change measuring device to the outside of the capsule.

8. The volatile fatty acid detector according to Claim 5, further comprising a transmitting device disposed inside the capsule to wirelessly transmit the information obtained by the infrared light receiving device to the outside of the capsule.

9. The volatile fatty acid detector according to Claim 6, further comprising a transmitting device disposed inside the capsule to wirelessly transmit the information obtained by the infrared light receiving device to the outside of the capsule.

10. Preparing a swelling rubber; Immersing the swelling rubber in a solution containing dodecane and a swelling liquid; A method for manufacturing a sensing member for a volatile fatty acid detector, comprising drying the solution.

11. The method for manufacturing a sensing member for a volatile fatty acid detector according to Claim 10, wherein the swelling liquid is hexane.

12. The method for manufacturing a sensing member for a volatile fatty acid detector according to Claim 10 or 11, wherein the swelling rubber is acrylonitrile-butadiene rubber.

13. When the main volatile fatty acid in the gas phase of the target is either acetic acid or propionic acid, using the volatile fatty acid detection device according to any one of claims 7 to 9, and estimating whether the main volatile fatty acid in the gas phase of the target is acetic acid or propionic acid by utilizing the difference in the temporal change of the detection sensitivity between acetic acid and propionic acid. A method for estimating the main volatile fatty acid in the gas phase.

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