JP7523066B2 - Reference Electrode - Google Patents

Description

The present invention relates to a reference electrode.

Conventional comparison electrodes electrically connect the test liquid and the internal electrode by causing the internal liquid to flow out little by little from the liquid junction. This leads to problems such as inaccurate measurement if the liquid junction becomes clogged with dirt, the need to periodically replenish the internal liquid, and contamination of the test liquid by the internal liquid that has flowed out from the liquid junction.
As a reference electrode without a liquid junction, one using a SAM film has been investigated, but the SAM film has a problem in that its physical strength is low and it is difficult to put it into practical use.

International Publication No. 2019/049945 “Drastic Dependence of the pH Sensitivity of Fe2O3-Bi2O3-B2O3 Hydrophobic Glasses with Composition”, Tadanori Hashimoto et al., Materials 2015, 8, 8624-8629

The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a reference electrode that does not have a liquid junction and has sufficient physical strength for practical use.
As a similar technique, for example, as shown in Patent Document 1, an attempt has been made to use a non-pH-responsive sensitive glass produced as a by-product in the process of producing the sensitive glass, in a reference electrode.

The present invention was completed as a result of extensive research by the inventors, who succeeded in creating a glass or ceramic with a composition completely different from the responsive glass described in the aforementioned Patent Document 1, which can electrically connect the test liquid to the internal electrode and is substantially unresponsive to the ions to be measured.

That is, the surface of the comparative electrode according to the present invention that comes into contact with the test liquid is made of glass or ceramics that mainly contains an oxide of an element that can be trivalent or tetravalent, and that has ion conductivity.

With such a comparison electrode, there is no need to provide a liquid junction, so the effect of contamination of the liquid junction on ion concentration measurement can be eliminated. In addition, there is no need to refill the internal liquid of the comparison electrode. Furthermore, contamination of the test liquid caused by leakage of the internal liquid can be eliminated. Furthermore, since the surface of the conductive member is made of glass or ceramics, the physical strength can be significantly improved compared to a comparison electrode using a SAM film.

More specifically, the metal may be at least one selected from the group consisting of tellurium, germanium, and boron.

Specific embodiments of the present invention include those in which the glass or ceramic contains a compound that imparts ionic conductivity to the glass or ceramic, and the compound is an oxide of an element that can be monovalent or divalent. More specifically, the element that can be monovalent or divalent includes at least one selected from the group consisting of silver, lithium, and sodium.

From the viewpoint of stabilizing the reference potential and increasing the accuracy of ion concentration measurement, it is preferable that the sensitivity of the conductive member to ion concentration is 40% or less.

The comparison electrode of the present invention does not require the provision of a liquid junction, and therefore can eliminate the effect of contamination of the liquid junction on ion concentration measurement. In addition, there is no need to refill the internal liquid of the comparison electrode. Furthermore, contamination of the test liquid caused by leakage of the internal liquid can be eliminated.

1 is a schematic diagram showing an ion concentration measuring device according to an embodiment of the present invention; FIG. 3 is a schematic diagram showing a comparison electrode according to the embodiment. FIG. 4 is a schematic cross-sectional view of a conductive member according to another embodiment of the present invention. FIG. 4 is a schematic diagram showing an electrode structure according to another embodiment of the present invention. FIG. 4 is a schematic diagram showing an electrode structure according to another embodiment of the present invention. FIG. 4 is a schematic diagram showing an electrode structure according to another embodiment of the present invention. FIG. 4 is a diagram showing the properties of a conductive member according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1 , the ion concentration measuring device 100 according to this embodiment includes a measurement electrode 1 that detects changes in the concentration of a specific ion contained in a sample liquid S as a change in potential, a comparison electrode 2 that outputs a reference potential for the measurement electrode, a calculation unit 3 that calculates the ion concentration based on output values from the measurement electrode 1 and the comparison electrode 2, and a display unit 4 that displays the ion concentration calculated by the calculation unit 3.

The measurement electrode 1 comprises a working electrode 11 (also called the internal electrode for the measurement electrode) made of, for example, silver/silver chloride, etc., and a cylindrical housing for the measurement electrode 13 that contains the working electrode 11 and the internal liquid for the measurement electrode 12 inside. The portion of the housing for the measurement electrode 13 that comes into contact with the test liquid S is a glass electrode formed of responsive glass 14 that does not respond to the specific ion concentration but responds to the specific ion to be measured.

As shown in FIG. 1 or FIG. 2, the comparison electrode 2 includes a comparison electrode 21 (also called an internal electrode for the comparison electrode) made of, for example, silver/silver chloride, and a cylindrical case for the comparison electrode 23 that contains the comparison electrode 21 and the internal liquid for the comparison electrode 22. The portion of the case for the comparison electrode 23 that comes into contact with the test liquid S is formed by a conductive member 24 that electrically connects the test liquid S and the internal liquid for the comparison electrode 22 (i.e., electrically connects the test liquid S and the comparison electrode 21, which is an internal electrode).

The calculation unit 3, for example, calculates the potential difference between the potential output from the measurement electrode 1 and the potential output from the reference electrode 2, and calculates the concentration of the specific ion based on the calculated potential difference and a previously obtained calibration curve, etc. Specifically, it is an information processing circuit that includes a digital circuit composed of a CPU, memory, communication port, etc., an analog circuit equipped with a buffer and amplifier, etc., and an AD converter, DA converter, etc. that mediate between the digital circuit and the analog circuit. The CPU and its peripheral devices work together according to a predetermined program stored in the memory, so that this information processing circuit functions as the calculation unit 3.

The conductive member 24 is made of an insensitive glass that has ion conductivity and is substantially unresponsive to the specific ions.
The definition of "substantially no response" depends on the required accuracy of ion concentration measurement, but it is preferable that the sensitivity to the specific ion is 40% or less, more preferably 30% or less, and particularly preferably 10% or less.
The sensitivity can be calculated using a coefficient that indicates the relationship between the specific ion concentration and the change in potential. For example, when the specific ion is a hydrogen ion, the sensitivity can be calculated based on the following formula 1.

More specifically, the insensitive glass forming the conductive member 24 according to this embodiment is mainly composed of an oxide of an element that can be trivalent or tetravalent.
Here, the glass includes glass-ceramics, which is partially crystallized.
The term "main component" means that the content of the component in the entire insensitive glass is 50 mol % or more.

The insensitive glass contains an oxide of an element that can be trivalent or tetravalent as the main component (main skeleton) of its skeleton. The element that can be trivalent or tetravalent is preferably, for example, an element included in Groups 13 to 16 of the periodic table, and more specifically, it is preferable that the glass contains one or more metals selected from the group consisting of tellurium (Te), germanium (Ge), boron (B), and phosphorus (P).

The content of the oxide of the element that can be trivalent or tetravalent in the insensitive glass is preferably 60 mol% or more and 85 mol% or less, more preferably 70 mol% or more and 85 mol% or less, and particularly preferably 75 mol% or more and 80 mol% or less.

The insensitive glass preferably contains a compound that imparts ionic conductivity to the insensitive glass. Examples of the compound include oxides of elements that can be monovalent or divalent. In order to impart ionic conductivity to the insensitive glass, the compound is preferably an element that generates ions of a size that can easily move around in the glass skeleton, and is preferably an element with an effective ionic radius (at six coordinated positions) defined by Shannon in 1976 in the range of -0.38 Å to 1.20 Å. The element that can be monovalent or divalent is preferably, for example, an alkali metal of Group 1 or a tantalum metal element of Group 11, and more specifically, it is preferably one or more metal elements selected from the group consisting of silver (Ag), lithium (Li), sodium (Na), fluorine (F), hydrogen (H) and copper (Cu).

The content of the oxide of the element capable of taking a valence of one or two in the insensitive glass is preferably 15 mol% or more and 30 mol% or less, more preferably 20 mol% or more and 25 mol% or less. By making it 15 mol% or more, it is possible to impart sufficient ionic conductivity to the insensitive glass, which is preferable. Also, by making it 30 mol% or less, it is possible to make the insensitive glass easier to vitrify, which is preferable.

The ionic conductivity of the insensitive glass is preferably high from the viewpoint of suppressing noise in ion concentration measurement. This ionic conductivity can be evaluated, for example, using resistivity. More specifically, the insensitive glass preferably has a resistivity equivalent to that of the responsive glass used in the measurement electrode. More specifically, the resistivity of the glass is preferably on the order of ×10 ¹² Ωcm or less, more preferably on the order of ×10 ¹⁰ Ωcm or less, and particularly preferably on the order of ×10 ⁸ Ωcm or less.

The above-mentioned insensitive glass can be produced, for example, by the following procedure and method.
An oxide of an element that can be trivalent or tetravalent and an oxide of an element that can be monovalent or divalent are mixed in a predetermined ratio, and the mixture is melted at a high temperature of about 800°C to 1200°C, rapidly cooled and pressurized, and then annealed at a temperature of about 200°C to 500°C to obtain an insensitive glass.

The insensitive glass manufactured as described above can be used as the conductive member 24 of the reference electrode housing 23 in the same manner as the measurement electrode housing 13, which is manufactured by joining a responsive glass to the tip of a cylindrical support tube glass. To be more specific, the insensitive glass is kept in a molten state, the tip of the cylindrical support tube glass is immersed in the molten glass, and the support tube glass is pulled up at a predetermined speed while being blown to form the insensitive glass into a substantially hemispherical shape.

In the comparative electrode 2 thus constructed, since the conductive member 24 has ion conductivity, there is no need to provide a liquid junction.
As a result, it is possible to eliminate the influence on the ion concentration measurement caused by the liquid junction being clogged with dirt, and it is also possible to prevent the contamination of the test solution S caused by the reference electrode internal liquid 22 leaking from the liquid junction. Furthermore, the effort of refilling the reference electrode internal liquid 22 is not required.

Since the conductive member is substantially unresponsive to the specific ion to be measured, the reference potential output from the reference electrode can be stabilized.
Since the glass can be free of oxides of, for example, silicon (Si), bismuth (Bi), iron (Fe), and the like, which are contained in the sensitive glass, the sensitivity to specific ions, particularly hydrogen ions, can be reduced.

The present invention is not limited to the above-described embodiment.
For example, in the above embodiment, the conductive member is made of insensitive glass, but the conductive member may be made of insensitive ceramics having a similar composition, in which case the insensitive ceramics must be impermeable to liquids.

The insensitive glass or insensitive ceramic may contain additives other than the oxides of the elements that can be trivalent or tetravalent and the oxides of the elements that can be monovalent or divalent. Examples of the additives include alkali salts. Examples of the alkali salts include alkali halides such as silver chloride (AgCl) and silver nitrate (AgNO ₃ ).

The conductive member is not limited to being entirely made of the insensitive glass or insensitive ceramics, and only the surface of the conductive member may be made of the insensitive glass or insensitive ceramics. A conductive member in which only the surface is made of the insensitive glass or insensitive ceramics will be described below.

In this case, the conductive member 24' comprises, for example, a substrate 241' and an insensitive layer 242' formed on the surface of the substrate, as shown in FIG. 3. The substrate 241' may be made of any conductive material, such as a metal such as SUS. The insensitive layer 242' is made of the insensitive glass or insensitive ceramics as described above.

As a method for manufacturing such a conductive member 24', for example, the insensitive glass or insensitive ceramics prepared as described in the above embodiment is crushed, deposited on a substrate 241' made of SUS or the like, and heated at 600°C to 700°C for about 2 hours to form an insensitive layer 242' on the substrate 241'.

Another method is a wet method in which the substrate 241' is immersed or coated in a solution in which the crushed pieces of the insensitive glass described above are dissolved in a mixture of water and polyvinyl alcohol (PVA), dried, and then baked at a temperature of about 600°C to 700°C to form an insensitive layer 242' made of insensitive glass or insensitive ceramics on the substrate 241'. In the case of this wet method, the process of immersing the substrate 241' and drying it may be repeated multiple times. The mixing ratio of water to polyvinyl alcohol can be changed as appropriate depending on the composition of the insensitive glass, the experimental conditions, etc. Also, other water-soluble polymers such as polyvinylpyrrolidone can be used instead of polyvinyl alcohol.

The substrate 241' of the conductive member 24', which comprises a substrate 241' and an insensitive layer 242' formed on the surface of the substrate, may be a single metal plate made of SUS or the like as described above, or may be a metal plate with a layer containing another metal such as silver laminated on the surface. The insensitive layer 242' may be formed on both sides of the substrate 241', or may be formed only on the surface that comes into contact with the test liquid.

In the above embodiment, the measurement electrode and the comparison electrode are described as having an internal liquid, but the internal liquid is not necessarily required, and the internal electrode (working electrode or comparison electrode) may be arranged so as to be in direct contact with the response glass or the conductive member. By not using the internal liquid in this way, it is possible to make the measurement electrode and the comparison electrode smaller than before. In addition, if an ion-responsive membrane made of oxidized SUS is used as the measurement electrode, the physical strength of the measurement electrode and the comparison electrode can be further improved, making it possible to perform stable ion concentration measurement even under high pressure conditions where measurement is difficult with conventional ion concentration measurement devices.

Furthermore, by using a measurement electrode and a comparison electrode that do not have an internal liquid, it is possible to adopt an electrode structure such as that shown in Figures 4 to 6. The electrodes shown in Figures 4 to 6 are described below. The thick arrows in Figures 4 to 6 indicate the side to which the test liquid T is supplied to the measurement electrode or comparison electrode.

The electrode shown in FIG. 4(a) is a composite electrode that includes a cylindrical housing A, a response glass 14 and a conductive member 24 attached to the outer surface of the housing A so as to cover a through hole H formed in the side wall or bottom wall of the housing A, metal wires W that electrically connect the response glass 14 or the conductive member 24 to the calculation unit 3, and a connection member B made of a conductive paste or the like that connects the response glass 14 or the conductive member 24 to each metal wire W. Since the metal wires W are drawn into the inside of the housing through the through holes H, a partition member D is further provided that partitions the space inside the housing A so that the metal wires W do not come into contact with each other inside the housing A.

The material of the housing A is not particularly limited, and may be any material to which the response glass and conductive member can be attached.
Examples of the metal wire W include silver (Ag), copper (Cu), SUS, iron (Fe), platinum (Pt), gold (Au), aluminum (Al), and palladium (Pd).
As the connection member B, for example, a conductive paste is preferably used, and as the conductive paste, for example, glass frit, a paste containing resin and metal, a conductive polymer, or a metal itself can be used. As the resin, for example, polyethylene terephthalate (PET), acrylic, etc. can be mentioned. As the conductive polymer, polyacetylenes, polythiophenes, polyanilines, polypyrroles, etc. can be mentioned. As the metal contained in the conductive paste, it is preferable to use silver (Ag), gold (Au), palladium (Pd), platinum (Pt), carbon (C), copper (Cu), aluminum (Al), SUS, etc.

4A, a partition member D is provided inside the housing A, but instead of this, a cylindrical cover C may be provided to cover each metal wire W. Both the partition member D and the cover C are preferably insulating.
Furthermore, the response glass 14 and the conductive member 24 may be disposed at any position on the outer surface of the housing A as long as they are not in contact with each other and are easily touched by the test liquid T.
The materials of the housing A, the metal wires W, the connecting members B, and the like described with reference to FIG. 4 can also be used in common with FIG. 5 and FIG.

Figure 5 shows a measurement electrode 1' or a comparison electrode 2' that includes a response glass 14 or a conductive member 24 attached to cover a through hole H' formed in the wall of the support S, and a connection member B for electrically connecting the response glass 14 or the conductive member 24 to the calculation unit 3. The response glass 14 or the conductive member 24 can be electrically connected to the calculation unit 3 by applying a conductive paste or the like, which is the connection member B, to the surface of the support S so as to contact the response glass 14 or the conductive member 24 through the through hole H'. This simplifies the manufacturing process of the measurement electrode 1' or the comparison electrode 2' compared to the case where a metal wire W is used as shown in Figure 4. The material of the support S is not particularly limited, as with the housing A described above, and may be any material that can be used to attach the response glass or the conductive member.

FIG. 6( a ) shows a measurement electrode 1 ″ and a comparison electrode 2 ″, which are provided with a response glass 14 or a conductive member 24 attached to the inner surface of a measurement cell E storing a test liquid T therein so as to cover a through hole H ″ formed in a side wall or bottom wall of the measurement cell E, metal wires W electrically connecting the response glass 14 or the conductive member 24 to a calculation unit 3 or the like, and a connection member B made of a conductive paste or the like connecting the response glass 14 or the conductive member 24 to each metal wire W, and the metal wires W are led out to the outside of the measurement cell E via the through hole H ″.
As shown in FIG. 6(a), the measuring cell E may be provided with both a measuring electrode 1'' and a reference electrode 2'', or with only one of them.

Figure 6 (b) shows a measurement electrode 1a" or a comparison electrode 2a" in which the metal wire W is omitted from the components of the measurement electrode 1" or the comparison electrode 2" in Figure 6 (a), and instead of the metal wire W, a connection member B such as a conductive paste is applied to the surface of the measurement cell E to establish electrical continuity with the calculation unit 3, etc.

The insensitive glass or insensitive ceramics described above do not respond to hydrogen ions or various other ions, so a comparison electrode that uses insensitive glass or insensitive ceramics as a conductive member can be applied to various other types of ion concentration measurement devices, not just hydrogen ions.

The ion concentration measuring device may be a three-electrode type having a pseudo-electrode made of a metal wire made of platinum, silver chloride or the like in addition to the measuring electrode and the reference electrode.
By using a three-electrode ion concentration measuring device having a pseudo electrode, the potential difference between the measurement electrode and the pseudo electrode and the potential difference between the reference electrode and the pseudo electrode can be measured, and the potential difference between the measurement electrode and the reference electrode can be measured by calculating the sum of these two potential differences. As a result, the load on the amplifier that amplifies the electromotive force difference between the measurement electrode and the reference electrode can be reduced.
In addition, since the potential difference between the measurement electrode or comparison electrode and the pseudo electrode is measured, the potential difference between the measurement electrode and the comparison electrode can be stably measured even if the electrical resistance of the response glass or conductive member is large.
Furthermore, since a reverse voltage can be applied only between the measurement electrode and the pseudo electrode, contamination of the measurement electrode can be suppressed without changing the reference potential of the comparison electrode. In addition, various modifications and combinations of the embodiments may be made as long as they are not contrary to the spirit and scope of the present invention.

The comparative electrode according to the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

Example 1
Glass containing Ag ₂ O as a compound that gives ion conductivity to the insensitive glass and TeO ₂ as the main component of the glass was prepared. Specifically, as shown in Table 1, a plurality of types of glass were prepared by varying the contents of Ag ₂ O and TeO ₂ contained in the glass as shown in Table 1 below. The composition of the insensitive glass shown in Table 1 below is, for example, a sample described as 20Ag80Te indicates that the content of Ag ₂ O relative to the entire glass is 20 mol % and the content of TeO ₂ is 80 mol %. These insensitive glasses were prepared using a melt quenching method. The material was melted by heating at 900 ° C for 1 hour, then quenched to 200 ° C, and annealed at 200 ° C for 1 hour. Finally, the surface was polished and adjusted to obtain the insensitive glass.
From the results in Table 1, it was confirmed that all of the insensitive glasses with the compositions prepared this time could be vitrified.

Next, these glasses were used to examine their pH response (sensitivity to ion concentration) and resistivity.
The sensitivity was investigated by repeatedly measuring the potential difference between standard solutions of pH 4, pH 7, and pH 9 using a measurement electrode using these glasses as a response membrane and a double junction type reference electrode (2565A-10T, manufactured by Horiba, Ltd.), which is a conventional reference electrode equipped with a liquid junction, and measuring the potential change with respect to pH. The resistivity was measured using a super insulation meter manufactured by Hioki E.E. Corporation. The measurement results of the sensitivity and resistivity of these glasses are shown in Figure 7.

From the results of Fig. 7, it was found that the sensitivity to pH was significantly reduced for all glasses prepared in this example, and that they could be used as insensitive glasses. When used as a reference electrode in a more accurate ON concentration measuring device, it is preferable that the sensitivity is 30% or less and the resistivity is ×10 ¹⁰ Ωcm or less. Therefore, it is found that, among these insensitive glasses, those with an Ag ₂ O content in the range of 21 mol% to 23 mol% and a TeO ₂ content in the range of 77 mol% to 79 mol% are particularly preferable.
In this Example 1, the melting temperature is 900° C. and the annealing temperature is 200° C. However, the melting temperature and the annealing temperature can be appropriately changed to temperatures that facilitate vitrification depending on the glass composition.

Example 2
In FIG. 7, the pH sensitivity of 25Ag75Te was 39. When the sample was further heated at 250° C. or 275° C. for 24 hours after polishing, the sensitivity between pH 4 and 9 was further reduced, becoming 30% or less in all samples, as shown in Table 2 below.

Example 3
Next, a sample was prepared in which only the surface of the conductive member was made of insensitive glass. Specifically, insensitive glass containing _Ag2O as a compound imparting ionic conductivity and _TeO2 as the main component of the glass was fused onto a SUS substrate to form enamel glass.
In addition, an experiment was also carried out on the case where crushed insensitive glass was fused with AgCl added as an additive, in which 10% by mass of AgCl was added to 90% by mass of the crushed insensitive glass.
The conditions for producing these enamel glasses are as follows:
First, the crushed 25Ag75Te prepared in Example 1 was deposited on a substrate made of SUS, and this was fired at 640° C. or 680° C. for 2 hours to fuse the insensitive glass onto the substrate.
The results are shown in Table 3 below. In Table 3, *1 indicates the case where the firing temperature was 640° C., and *2 indicates the case where the firing temperature was 680° C.

From the results in Table 3, it was confirmed that the sensitivity between pH 4 and 9 was lower than that of the insensitive glass alone in any of the enamel glasses produced in Example 3. In addition, depending on the firing temperature, it was possible to obtain a glass having a lower sensitivity between pH 7 and 9 than the Ag plate.
In this Example 3, the thickness of the insensitive glass fused onto the SUS substrate was set to about 0.7 mm, but it has been confirmed that even if the thickness is reduced to about 0.01 mm, the sensitivity between pH 4 and 9 can be suppressed to about 20% to 30%.
Furthermore, it was found that the sensitivity could be further reduced by adding AgCl as an additive to the insensitive glass.
It has been observed that in some of these enamel glasses, silver precipitates after firing.

Example 4
In Example 3, the conductive member was prepared by depositing crushed insensitive glass on a substrate and fusing it, whereas in Example 4, the conductive member was prepared by applying a solution of dissolved insensitive glass onto a substrate, drying it, and then firing it.
The specific experimental method is as follows.
A solution (slurry) was prepared by dissolving 0.1 g of insensitive glass powder, which had been crushed and classified to 53 μm or less, in a mixture of 3.5 ml of ion-exchanged water and 0.5 g of polyvinyl alcohol, and 0.4 ml of this solution was measured out with an electric pipetter and dropped onto a substrate made of SUS. The solution was then dried at 60° C. for 1 hour and baked to form an insensitive layer on the substrate using a wet method. The baking was performed at 640° C. or 680° C. for 2 hours.
The sensitivity and resistivity of the conductive member thus prepared were measured, and the results are shown in Table 4 below.

From the results in Table 4, it was confirmed that the sensitivity of the conductive member prepared by the wet method was suppressed to 40% or less, and that the conductive member was sufficiently usable as a conductive member for a comparison electrode.
All of the conductive members made by this wet method were enamel glass, but some were observed to have Ag crystals precipitated on the surface, which may have crystallized into glass. Normally, silver is a cubic crystal, but conductive members in which hexagonal crystals were precipitated as silver crystals tended to have lower sensitivity than conductive members in which cubic crystals were precipitated.

Example 5
Insensitive glasses with various compositions were prepared as shown in Table 5. The compositions of the insensitive glasses shown in Table 5 are the same as those in Table 1. For example, a sample described as 20Ag80Te indicates that the content of _Ag2O in the entire glass is 20 mol % and the content of _TeO2 is 80 mol %.

From the results in Table 5, it was confirmed that in addition to the combination of Ag ₂ O and TeO ₂ , insensitive glass with low sensitivity and low resistivity can be prepared even when oxides of elements that can be trivalent or tetravalent and oxides of elements that can be monovalent or divalent are variously combined.
In particular, it was confirmed that glasses combining Li ₂ O and TeO ₂ , Ag ₂ O and B ₂ O ₃ , or CuO and TeO ₂ exhibit sensitivity equivalent to or less than that of the enamel glasses shown in Examples 3 and 4, when used alone as insensitive glasses.

100: Ion concentration measuring device 1: Measuring electrode 2: Reference electrode 24: Conductive member

Claims (7)

a conductive member electrically connecting the internal electrode and the test liquid;
a surface of the conductive member in contact with the test liquid is made of glass or ceramics containing as a main component an oxide of an element that can be trivalent or tetravalent and has ion conductivity ;
the glass or the ceramic contains a compound that imparts ionic conductivity to the glass or the ceramic;
A reference electrode , wherein the compound is an oxide of an element which can be monovalent or divalent . The comparative electrode according to claim 1, wherein the element capable of assuming a valence of three or four includes at least one selected from the group consisting of tellurium, germanium, and boron. 2. The comparative electrode according to claim 1 , wherein the element capable of being monovalent or divalent includes at least one element selected from the group consisting of silver, lithium, and sodium. 4. The comparative electrode according to claim 1, wherein the sensitivity of the conductive member to hydrogen ion concentration is 40% or less. A composite electrode comprising the reference electrode according to any one of claims 1 to 4 . An ion concentration measuring device comprising the reference electrode or the composite electrode according to any one of claims 1 to 5 . a conductive member electrically connecting the internal electrode and the test liquid;
a surface of the conductive member in contact with the test liquid is made of glass or ceramics not mainly composed of silicon dioxide and has ion conductivity ;
the glass or the ceramic contains a compound that imparts ionic conductivity to the glass or the ceramic;
A reference electrode , wherein the compound is an oxide of an element which can be monovalent or divalent .