JP7337436B2 - reference electrode - Google Patents

Description

The present invention relates to reference electrodes, and more particularly to reference electrodes used in sensors such as pH sensors.

Potentiometers are known that measure pH values, ion concentrations in solutions, and oxidation-reduction potentials from the potential difference between a reference electrode and a working electrode. In a potentiometric measuring device, a reference electrode (hereinafter also referred to as a reference electrode) exhibits a constant potential, and is used as a potential reference by bringing it into contact with the liquid to be measured together with the working electrode.

The reference electrode is configured by housing an internal liquid as an electrolyte and an electrode immersed in the internal liquid in a container. The container is provided with an opening provided in a portion that comes into contact with the object to be measured, and a liquid junction made up of a moisture-permeable substance filled in the opening. The content liquid maintains electrical connection with the measurement target through the liquid junction.

The liquid junction is usually designed so that the content liquid flows out little by little to the extent that the measurement target does not enter the liquid junction and the internal liquid does not excessively mix into the measurement target and affect the measurement result. .

For example, Patent Document 1 discloses a container in which a liquid junction and a vent hole are formed, a gel-like internal liquid filled in the container, an internal electrode provided so as to be immersed in the internal liquid, and an internal A reference electrode is disclosed which consists of a pressure control layer which is positioned between the liquid and the vent hole, deforms in response to pressure, and is made of a material which is impermeable to water vapor.

JP 2005-77252 A

For example, when a pH sensor using a reference electrode as described above is used to monitor the growing environment of agricultural crops over a long period of time, it may be exposed to a high-temperature environment due to temperature changes. Further, the pH sensor using the reference electrode as described above may be placed in a high temperature environment or a negative pressure environment during transportation or storage.

In this way, when placed in an environment of high temperature or negative pressure, the internal liquid is pushed out by the change in volume of the gas (air) that exists together with the internal liquid in the reference electrode container, and the internal liquid flows out excessively from the liquid junction. However, there was a problem that the internal liquid was depleted and the measurement became impossible. In addition, when the outflow of the content liquid is accelerated by the influence of temperature and pressure as described above, it is difficult to stably use the pH sensor in a system that continuously monitors pH for a long time. was an issue.

The present invention has been made in view of the above points, and is capable of retaining the internal liquid for a long time even in an environment where the pressure and temperature fluctuate greatly, and can continue for a long time regardless of changes in the environment. The object is to provide a usable reference electrode.

The reference electrode of the present invention comprises a container defining an internal space and having a first opening that communicates the internal space with the outside and a second opening that communicates the internal space with the outside; a liquid junction formed by filling the first opening with a porous member; and an air-permeable member provided to cover the second opening and having air permeability. and.

4 is a perspective view showing the outline of the configuration of the reference electrode of Example 1. FIG. 4 is a cross-sectional view showing the internal configuration of the reference electrode of Example 1. FIG. FIG. 10 is a perspective view showing the outline of the configuration of the reference electrode of Example 2; FIG. 8 is a cross-sectional view showing the internal configuration of a reference electrode of Example 2; FIG. 11 is a perspective view showing the outline of the configuration of the reference electrode of Example 3; FIG. 11 is a cross-sectional view showing the internal configuration of a reference electrode of Example 3;

Examples of the present invention will be described in detail below. In the following description and accompanying drawings, substantially the same or equivalent parts are denoted by the same reference numerals.

FIG. 1 is a perspective view showing the structure of the reference electrode 10 of this embodiment. The container 11 is a container made of glass or plastic with a side portion 12, a bottom portion 13 and a lid portion 14 integrally formed to define an internal space.

The side portion 12 has a cylindrical shape with opposed openings, the bottom portion 13 is provided so as to close one opening of the side portion 12, and the lid portion 14 is provided so as to close the other side opening. is provided.

The bottom 13 has a funnel shape extending outwardly of the container along the cylindrical central axis of the side 12 . Specifically, the bottom portion 13 has a tapered portion 13A that forms a wall surface that extends from the end of the side portion 12 along the central axis of the cylindrical shape of the side portion 12 and tapers toward the tip. have

In other words, the tapered portion 13A has a truncated cone shape. Further, the bottom portion 13 has an annular lead-out portion 13B extending from the tip of the tapered portion 13A. In the container 11, the inner space of the container 11 communicates with the outside through the lead-out portion 13B and the first opening 13C at the tip of the lead-out portion 13B.

The lid portion 14 is a disk-shaped portion provided so as to close the opening opposite to the opening in which the bottom portion 13 of the side portion 12 is formed. The lid portion 14 has a second opening 14A penetrating through the plate surface of the disk forming the lid portion 14 . The second opening 14A allows communication between the internal space of the container 11 and the outside. In this manner, the first opening 13C is formed on the bottom 13 side and the second opening 14A is formed on the lid 14 side of the facing openings of the side portion 12 . The second opening 14A may be provided facing the first opening 13C.

The porous member 15 is a member made of a porous material such as porous glass (for example, Vycor glass (manufactured by Corning)), porous ceramics, or porous resin. The porous member 15 is arranged so as to fill the inside of the lead-out portion 13B and block the first opening portion 13C. Moreover, the porous member 15 is provided with a dimension longer than that of the lead-out portion 13B and protrudes into the internal space of the container 11 .

The porous member 16 is a member made of a porous material such as porous glass (for example, Vycor glass (manufactured by Corning)), porous ceramics, or porous resin. The porous member 16 is arranged at a position that closes the first opening 13C.

The heat-shrinkable film 17 is a resin tube, and is provided so as to cover the lead-out portion 13B and the porous member 16 from the outside. The heat-shrinkable film 17 fixes the porous member 16 to a position that contacts the porous member 15 and closes the first opening 13C. In other words, the porous member 16 is attached to the container 11 by the heat shrinkable film 17 .

The liquid junction portion 18 is composed of the lead-out portion 13B, the porous member 15, the porous member 16, and the heat-shrinkable film 17. As shown in FIG. In the liquid junction 18 , the porous member 15 and the porous member 16 hold the internal liquid while permeating it when the container 11 contains the internal liquid. In other words, the container 11 is configured to be able to contain the internal liquid by holding the internal liquid in the liquid junction 18 .

The air-permeable member 19 has a shape corresponding to the shape of the second opening 14A, and is provided so as to cover and block the second opening 14A. The air-permeable member 19 is, for example, shaped to fit into the second opening 14A. The air-permeable member 19 is made of, for example, a hydrophobic porous resin. A material such as a hydrophobic fluorine resin porous film can be used for the air-permeable member 19 . The hydrophobic fluororesin porous film may be made of, for example, PTFE (polytetrafluoroethylene). Note that the material forming the air-permeable member 19 is not limited to the hydrophobic porous resin. The air-permeable member 19 may be air-permeable, impermeable to liquids, and difficult to permeate moisture. In this specification, regarding the air-permeable member 19, the property of being impermeable to liquids and difficult to permeate moisture is referred to as moisture impermeability.

The internal electrode 21 is an electrode inserted into the internal space of the container 11 via the lid portion 14 . One end of the internal electrode 21 is provided so as to be immersed in the internal liquid when the internal liquid is contained in the container 11 . The other end of the internal electrode 21 is connected to the internal electrode (not shown) of the working electrode. The internal electrodes 21 are Ag/AgCl electrodes, for example.

The internal liquid 23 is contained in the internal space of the container 11 . The internal liquid 23 is retained while permeating the porous members 15 and 16 of the liquid junction 18 . The content liquid 23 is an electrolyte solution, such as a KCl aqueous solution or an NaCl aqueous solution. The content liquid 23 is connected to the outside through the liquid junction 18 . Further, as described above, the internal electrode 21 is immersed in the internal liquid 23 .

For example, when measuring the pH of a liquid with a pH meter using the reference electrode 10, the tip of the liquid junction 18 is immersed in the liquid to be measured. The internal liquid 23 is electrically connected to the liquid to be measured via the liquid junction 18 . At the same time, for example, a glass electrode (not shown) provided on the working electrode side is also immersed in the liquid to be measured. In this state, a potential difference is generated between the working electrode and the reference electrode 10 . The potential difference is detected to obtain the pH value of the liquid to be measured.

FIG. 2 is a cross-sectional view schematically showing the structure of the reference electrode 10 of this embodiment. A phenomenon that occurs when the internal liquid 23 is contained in the reference electrode 10 will be described with reference to FIG.

In the state where the reference electrode 10 is upright, that is, in the vertical direction, the liquid junction portion is on the lower side and the lid portion 14 is on the upper side. It is a space surrounded by the inner wall of the container 11 between. The air space 25 is filled with gas. In addition, the gas layer space 25 faces the air-permeable member 19 in the upright state of the reference electrode 10 .

The tank space 26 is a space that holds liquid when the reference electrode 10 is upright. In other words, the content liquid 23 is contained in the tank space 26 of the internal space of the container 11 .

When the pressure inside the container 11 rises above the outside pressure, part of the gas in the air layer space 25 is discharged to the outside through the air-permeable member 19 . Also, when the pressure inside the container 11 becomes lower than the outside pressure, outside air flows into the air layer space 25 through the air-permeable member 19 .

For example, when the temperature around the reference electrode 10 rises, the volume of the gas in the gas layer space 25 increases and the pressure inside the container 11 rises to become higher than the outside pressure. In this case, since the air-permeable member 19 has air-permeability, the difference between the pressure inside the container 11 and the pressure outside the container 11 is such that part of the gas in the air space 25 is released to the outside through the air-permeable member 19 . Pressure is adjusted by being relieved by being discharged. Then, the external pressure becomes equal to the internal pressure, and it is possible to prevent the content liquid 23 from flowing out from the liquid junction 18 due to an increase in the internal pressure of the container 11 .

For example, when the temperature around the reference electrode 10 drops, the volume of the gas in the gas layer space 25 will decrease, and the pressure inside the container 11 will drop and become lower than the external pressure. The pressure drop is adjusted by the outside air flowing into the air layer space 25 via the air-permeable member 19 . Therefore, it is possible to prevent external liquid such as outside air or liquid to be measured from flowing in from the liquid junction 18 .

Further, for example, when there is a difference between the atmospheric pressure outside the reference electrode 10 and the atmospheric pressure inside, part of the gas in the gas layer space 25 flows in or out through the air-permeable member 19, thereby pressure difference is relaxed. By adjusting the pressure in this way, it is possible to prevent the content liquid 23 from flowing out from the liquid junction 18 due to the pressure difference between the reference electrode 10 and the outside.

The air-permeable member 19 is impermeable to liquids and difficult to permeate moisture, so it is possible to suppress the reduction of the content liquid.

Since the reference electrode 10 has the structure described above, the internal liquid 23 can be retained in the container 11 for a long time.

Furthermore, even if the pressure is repeatedly adjusted by entering and exiting the gas layer space 25 due to changes in temperature and atmospheric pressure, the constituent members of the reference electrode 10 do not deform, and since the constituent members do not have any moving parts, the reference electrode 10 is durable. It can be said that the quality is high.

As described above, according to the reference electrode 10 of Example 1, when there is a difference between the pressure inside the container 11 and the pressure outside due to the influence of the temperature or air pressure around the reference electrode 10, the gas permeability is reduced. The gas in the air layer space 25 can enter and leave the outside through the member 19 . As a result, the pressure difference with the surroundings is eliminated, and the outflow of the internal liquid 23 and the inflow of external air or liquid through the liquid junction 18 due to the pressure difference can be prevented. Therefore, for example, continuous measurement over a long period of time can be prevented from being interrupted due to depletion of the internal liquid. In addition, for example, it is possible to prevent problems such as deterioration of measurement accuracy due to inflow of outside air or outside liquid.

Therefore, it is possible to retain the internal liquid for a long time even in an environment where the pressure and temperature fluctuate greatly, and it is possible to provide a reference electrode that can be used continuously for a long time regardless of changes in the environment.

FIG. 3 is a perspective view showing the configuration of the reference electrode 30 of this embodiment. In FIG. 3, portions that are substantially the same as or equivalent to the reference electrode 10 of Example 1 are denoted by the same reference numerals.

The reference electrode 30 is different from the reference electrode 10 in that it has a partition plate 31, and is configured similarly to the reference electrode 10 in other respects.

The partition plate 31 is a plate-like member having a circular shape corresponding to the cross section of the side portion 12 of the container 11 . The partition plate 31 divides the internal space of the container 11 into an air layer space 25 on the side where the air-permeable member 19 is provided and a space on the side where the liquid junction 18 is provided, and holds the liquid. It is provided so as to partition into two spaces, a tank space 26 which is a space.

The pore 32 is at least one pore penetrating from one main surface of the partition plate 31 to the other main surface. FIG. 3 shows an example in which the partition plate 31 is provided with five holes 32 .

The pores 32 are formed with a size that allows gas to pass through between the gas layer space 25 and the tank space 26 but does not allow liquid to pass through. For example, the pores 32 are formed with a size that can prevent passage of the content liquid used in the reference electrode 30 by surface tension. The pores 32 may be provided with a size of 1 mm or less in diameter and 3 mm or more in length, for example. Also, the size of the pores 32 may be optimized according to properties such as the viscosity of the content liquid to be used.

FIG. 4 is a cross-sectional view schematically showing the internal configuration of the reference electrode 30. As shown in FIG. A phenomenon that occurs when the reference electrode 30 is filled with the internal liquid 23 will be described with reference to FIG.

As shown in FIG. 4 , the internal space of the container 11 is partitioned into two spaces, an air layer space 25 and a tank space 26 , by a partition plate 31 . In a state in which the reference electrode 30 is upright, that is, in a posture in which the liquid junction portion 18 is on the lower side and the lid portion 14 is on the upper side in the vertical direction, the gas layer space 25 is filled with gas. Also, the air space 25 faces the air-permeable member 19 . The tank space 26 contains the internal liquid 23 . Moreover, the partition plate 31 is provided parallel to the liquid surface 23A of the content liquid 23 .

As in the case of the reference electrode 10, when the reference electrode 30 is placed in a high-temperature or low-pressure environment, when a pressure difference occurs between the inside and outside of the container 11, the gas in the air space 25 becomes breathable. Entry and exit via member 19 . Thereby, the internal pressure of the air space 25 is adjusted.

In addition, the internal pressure of the tank space 26 is adjusted by the gas existing in the air layer space 25 and the tank space 26 entering and exiting through the pores 32 .

Thus, in the reference electrode 30 , the pressure inside the container 11 is adjusted by the inflow and outflow of the gas through the air-permeable member 19 and the pores 32 .

Here, even if the reference electrode 30 is tilted from the upright posture, the content liquid 23 is separated from the air space 25 by the partition plate 31 and therefore does not reach the air-permeable member 19 . In addition, since the pores 32 do not allow liquid to pass therethrough, the internal liquid 23 is retained in the space on the side where the liquid junction 18 is provided and does not flow into the gas layer space 25 .

Accordingly, in the reference electrode 30 , the state in which the air-permeable member 19 is in contact with the air space 25 is maintained regardless of the orientation of the reference electrode 30 . For example, the reference electrode 30 allows gas to enter and exit the gas layer space 25 via the communicative member 19 regardless of the position of the reference electrode 30, such as when the temperature of the surrounding environment is high or low. and the internal pressure can be adjusted.

Therefore, it is possible to retain the internal liquid for a long time regardless of the orientation of the reference electrode even in an environment where the pressure and temperature fluctuate greatly, and to provide a reference electrode that can be used continuously for a long time. can.

FIG. 5 is a perspective view showing the configuration of the reference electrode 40 of this embodiment. In FIG. 5, portions substantially the same as or equivalent to the reference electrode 10 of Example 1 are denoted by the same reference numerals.

The reference electrode 40 differs from the reference electrode 10 in that it has a partition film 41, and is configured similarly to the reference electrode 10 in other respects.

The partition membrane 41 is a membrane member having a circular shape corresponding to the cross section of the side portion 12 of the container 11 . The partition membrane 41 includes an air layer space 25 which is a space on the side where the air-permeable member 19 is provided, and a tank space 26 which is a space on the side where the liquid junction part 18 is provided and holds liquid. , and are provided so as to be partitioned into two spaces.

The partition membrane 41 is a porous membrane having a hydrophobic surface. For example, the partition membrane 41 is made of a porous resin membrane. The partition membrane 41 has pores of a size impermeable to liquid. For example, the partition membrane 41 can be a polyethylene porous membrane.

FIG. 6 is a cross-sectional view schematically showing the internal configuration of the reference electrode 40. As shown in FIG. A phenomenon that occurs when the internal liquid 23 is contained in the reference electrode 40 will be described with reference to FIG.

As shown in FIG. 6, the internal space of the container 11 is partitioned into two spaces, an air layer space 25 and a tank space 26, by a partition membrane 41. As shown in FIG. In a state in which the reference electrode 40 is upright, that is, in a posture in which the liquid junction portion 18 is on the lower side and the lid portion 14 is on the upper side in the vertical direction, the air space 25 is filled with gas. Also, the air space 25 faces the air-permeable member 19 . The tank space 26 contains the internal liquid 23 . Moreover, the partition membrane 41 is provided parallel to the liquid surface 23A of the content liquid 23 .

As in the case of the reference electrode 10, when the reference electrode 30 is placed in a high-temperature or low-pressure environment, when a pressure difference occurs between the inside and outside of the container 11, the gas in the air space 25 becomes breathable. Entry and exit via member 19 . Thereby, the internal pressure of the air space 25 is adjusted.

In addition, since the partition membrane 41 is porous, it allows the gas existing in the gas layer space 25 and the tank space 26 to pass through. When a pressure difference occurs between the inside and the outside of the container 11, the internal pressure of the tank space 26 is adjusted by the gas entering and exiting between the gas layer space 25 and the tank space 26 via the partition membrane 41. be.

Thus, in the reference electrode 40 , the pressure inside the container 11 is adjusted by the gas entering and exiting through the gas-permeable member 19 and the partition membrane 41 .

Even if the reference electrode 40 is tilted from the upright posture, the content liquid 23 is separated from the gas layer space 25 by the partition membrane 41 and therefore does not reach the air-permeable member 19 . In addition, since the partition membrane 41 does not allow liquid to permeate, the internal liquid 23 is retained in the tank space 26 and does not flow into the gas layer space 25 . Therefore, leakage of the internal liquid 23 from the liquid junction 18 due to the pressure difference is prevented.

Therefore, according to the reference electrode 40 of the present embodiment, even when the reference electrode 40 is tilted or when the content liquid 23 is replenished, the content liquid 23 is reliably prevented from entering the gas layer space 25. be able to.

Therefore, even in an environment where the pressure and temperature fluctuate greatly, there is little loss of the content liquid due to installation conditions or replenishment of the content liquid, it is possible to retain the internal liquid for a long time, and it can be used continuously for a long time. A reference electrode can be provided.

In the above embodiment, an example in which the container 11 is a glass container has been described, but the container 11 is not limited to this. For example, the container 11 may be made of resin. The material forming the container 11 can be appropriately selected according to the properties of the internal solution and the object to be measured, such as chemical resistance.

Also, in the above embodiment, an example of the configuration of the liquid junction 18 using the replaceable porous member 16 has been described, but the configuration is not limited to this. The liquid junction 18 may be configured without the porous member 16 and the heat-shrinkable film 17 . The liquid junction 18 may be formed so that the internal liquid 23 is electrically connected to the object to be measured. Although an example in which the internal electrode 21 is an Ag/AgCl electrode has been described, the present invention is not limited to this. For example, any electrode may be used as long as it exhibits a constant potential and can be used as a potential reference when measuring a potential difference.

The configurations in the above-described embodiments are merely examples, and can be changed as appropriate according to the application.

10 reference electrode 11 container 12 side portion 13 bottom portion 13A tapered portion 13B outlet portion 13C first opening portion 14 lid portion 14A second opening portion 15 porous member 16 porous member 17 heat shrink film 18 liquid junction portion 21 internal electrode 23 internal liquid 25 gas layer 31 partition plate 32 pore 41 partition membrane

Claims (5)

a container defining an internal space and having a first opening that communicates the internal space with the outside and a second opening that communicates the internal space with the outside;
an internal electrode inserted into the internal space;
a liquid junction formed by filling the first opening with a porous member;
a breathable member provided to cover the second opening and having breathability;
a partition plate provided inside the container for partitioning the internal space into a space containing the liquid junction and a space containing the air-permeable member;
The partition plate has at least one pore penetrating from one main surface to the other main surface,
The reference electrode, wherein the fine pores have a length larger than a diameter and are formed in a size that allows gas to pass through but does not allow liquid to pass between the two spaces partitioned by the partition plate. 2. The reference electrode according to claim 1, wherein said first opening and said second opening are provided facing each other. 3. The reference electrode according to claim 1 , wherein the air-permeable member is impermeable to moisture. 4. The reference electrode according to any one of claims 1 to 3 , wherein the air-permeable member is made of porous resin. 5. The reference electrode according to claim 1, wherein said air-permeable member is made of fluororesin.

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