JPH0493758A - Reference electrode - Google Patents

Abstract

PURPOSE:To facilitate the achievement of a compact configuration and mass production and to omit maintenance control by filling the hole of a porous electrode supporting substrate with inner liquid, and coating electrodes formed on the electrode supporting substrate and the electrode supporting substrate other than a liquid junction part with an insulating films. CONSTITUTION:A porous material having excellent heat resistance, mechanical strength and insulating property is used for an electrode supporting substrate 2. The air hole in the electrode supporting substrate 2 is filled with aqueous solution such as KCl as inner liquid. A silver film 3 is formed on a surface 2b. The surface 2b of the substrate 2 other than a liquid junction part 2a and a connecting part 3a is coated and insulated with an insulating film 5. A rear surface 2c of the substrate 2 is coated and insulated with an insulating film 6. The connecting part 3a to which a lead 4 is electrically connected and cross sections 2d and 2e of the substrate 2 are insulated and sealed with an epoxy resin 7. In this way, the structure is simple, the achievement of the compact configuration and the mass production becomes easy and the inner liquid is held in the solid-state supporting substrate. Therefore, maintenace control is not required. The mechanical strength is excellent, and the excellent measuring accuracy can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a reference electrode in a potentiometric measuring electrode.

(b) Conventional technology Potentiometric measurement electrodes measure the potential difference between a potential detection electrode and a reference electrode to detect the pH, ion concentration, concentration of biologically functional substances, etc. of a test liquid. . For example, to detect a certain ion concentration, a potential detection electrode equipped with an ion-selective membrane that selectively permeates this ion;
A comparison electrode is immersed in the test liquid, and the potential difference between the two is measured.

Conventionally, this reference electrode is a saturation force Romero electrode (SCE).
, silver chloride electrodes, mercury oxide electrodes, etc. have been used. All of these electrodes were made of glass and had an internal liquid and a liquid junction.

(c) Problems to be Solved by the Invention In the above-mentioned conventional reference electrode, the space for storing the internal liquid;
Due to the complex structure of the internal liquid inlet and liquid junction, mass production is difficult and expensive, miniaturization is difficult, the shape is limited, and the internal liquid is stored, making it difficult to use electrodes. There was a problem that the condition was limited. In addition, since it has a liquid junction and a high concentration internal liquid, careful maintenance is required, and since it is made of glass, it has poor mechanical strength and is easily damaged, which requires careful handling. there were.

On the other hand, conventional comparison electrodes have the problem of large variations in characteristics between electrodes, such as temperature characteristics. There was also the problem that substances in the test liquid adhered to the liquid junction, degrading measurement accuracy. Furthermore, in combination with a potential detection electrode, there is a problem in that sufficient consideration must be given to insulation between electrodes in the entire measurement system, including the potential difference measurement circuit.

The present invention was made in view of the above, and aims to provide a comparison electrode that is compact, mass-producible, easy to handle, and has excellent characteristics.

(d) Means and action for solving the problems In order to solve the above problems, the reference electrode of the present invention includes a porous electrode support base material and an internal liquid filled in the pores of this electrode support base material. , an electrode formed on the electrode support base material, and an insulating film covering the electrode and the electrode support base material except for the liquid junction.

Due to the above-mentioned configuration, the reference electrode of the present invention has an extremely simple structure and manufacturing process, which facilitates mass production and low cost. It can also be miniaturized and manufactured into any shape, and the conditions of use are limited. Not done. Furthermore, since the internal liquid is held in the solid electrode support base material, maintenance management is also unnecessary.

On the other hand, since the structure is simple as mentioned above, the electrode characteristics
Eliminates variations in electrode shape. In addition, it has excellent mechanical strength, and substances in the test liquid are less likely to adhere to the liquid junction, making it possible to maintain good measurement accuracy. Furthermore, since the electrode is not a glass electrode, a simple and inexpensive potential difference measuring circuit can be applied without paying attention to electrical resistance.

(e) Examples An embodiment of the present invention will be described below based on the drawings.

FIG. 1(a) and FIG. 1(b) are an external perspective view and a longitudinal cross-sectional view of an example comparative electrode assembly, respectively. 2 is an electrode support substrate, and a porous material with excellent heat resistance, mechanical strength, and insulation properties is used. In this example, the material of the electrode support substrate 2 is porous ceramics (material: aluminumite, composition Aj 2.0376%, 5iOz 23%,
43% porosity) is used.

The muko in the pores of this electrode support substrate 2 contains 4 as an internal liquid.
．． It is filled with 0M potassium chloride (KCI) aqueous solution. Furthermore, a silver film 3 is formed on the surface 2b of the electrode support substrate 2.

On the surface 2b of the electrode support substrate 20, a liquid junction portion 2a1 and a connection portion 3 are provided.
An insulating film 5 is formed except for a. Further, an insulating film 6 is also formed on the back surface 2c of the electrode support substrate 2, and the front surface 2b and back surface 2C of the electrode support substrate 20 are covered and insulated.

A lead 4 is electrically connected to the connecting portion 3a, and the connecting portion 3a and the end faces 2d and 2e of the electrode supporting substrate are insulated and sealed with an epoxy resin 7.

Next, the manufacturing process of Example Comparative Electrode I will be explained with reference to FIG. First, as shown in FIG. 2(a), prepare a porous ceramic plate 2° of an appropriate size (in this example, 50 mm x 50 mm, 2 cylinders thick), and cover the negative side with a band-shaped silver film 3. Form mountain 3. In this example, the film thickness was approximately 1 μm by sputtering using a metal mask.
However, the method for forming the silver film 3 is not limited to this, and can be changed as appropriate, such as a vacuum evaporation method or adhesion of silver foil.

Next, on the surface 2° of the ceramic substrate 2°, there is a liquid junction 2.
An insulating film 5° is formed except for the connecting portion 3a and the connecting portion 3a (second
See figure (b)]. This insulation layer with an angle of 5° was formed by applying a photosensitive polyimide resin on the surface 2°, exposing it to light using a photomask, developing it, and rinsing it to form a pattern (photolithography).

Furthermore, an insulating film 6° is formed over the entire surface of the back surface 2° of the ceramic group 45.2o. This insulating film 6o is also made of photosensitive polyimide resin.

Next, the ceramic substrate 2° is diced and divided into individual electrode support substrates 2. Connection portion 3 of this electrode support substrate 2
A lead wire 4 is connected to a using a suitable means, for example a conductive adhesive. Further, an epoxy resin 7 is applied to the connecting portion 3a and the end surfaces 2d and 2e of the electrode support substrate, and the epoxy resin 7 is cured to insulate and seal the connecting portion 3a and the end surfaces 2c and 2e. Note that this insulation/sealing is not limited to epoxy resin and can be changed as appropriate.

In the electrode thus obtained, the silver film 3 is converted into silver/silver chloride, and the electrode supporting substrate 2 is filled with an internal liquid.

First, this electrode is 1. ON (normal) hydrochloric acid (HCfaq
) and defoamed with voltage to form the liquid junction 2a.
Hydrochloric acid is caused to flow into and fill the electrode support substrate 2. In this state, the platinum (Pt) wire is immersed in the hydrochloric acid, and the electrode is placed between the electrode (silver film 3) and the platinum wire at +0.
A voltage of 5 V is applied to convert the silver film 3 into silver/silver chloride.

Next, the silver/silver chloride electrode is immersed in distilled water and subjected to voltage defoaming two to three times to remove hydrochloric acid and wash it. After drying in a constant temperature bath at 40'C,
This electrode is immersed in an M potassium chloride aqueous solution, defoaming is performed by voltage, and the inside of the electrode support substrate 2 is similarly filled with the potassium chloride aqueous solution.

Incidentally, the silver/silver chloride conversion and the filling of the internal liquid are not limited to those described above, and can be changed as appropriate.

FIG. 5 is a diagram showing an example of a measurement circuit to which this comparison electrode 1 is applied. Ion electrode (same as conventional) 10
and the example comparison electrode 1 are connected to the arithmetic circuit 13 after being subjected to impedance conversion by impedance conversion circuits 12 and 11, respectively.

This arithmetic circuit I3 calculates the difference in detected potentials.

FIG. 6 shows a measurement system 21 used to measure the characteristics of the example comparative electrode 1. 22 is a constant temperature bath, and various pH buffer solutions 23 are stored therein. This buffer? In F123, an electrode 24 for measuring characteristics is immersed together with a comparison electrode 1. Further, this buffer $23 is stirred by a star 25, and 26 is this star 5250 rotor. The reference electrode 1 and the electrode 24 are connected to an electrometer 29 by a lead wire 4.28. The electrometer 29 includes the above-mentioned measurement circuit and the like, and displays the electrode output.

FIG. 7 shows the potential of the Example Comparative Electrode 1 in various pH standard solutions with respect to the conventional commercially available comparative electrode when the pH electrode of a commercially available pH meter was replaced with the Example Comparative Electrode 1. Even if the pH changes significantly, there is no difference in output compared to the commercially available comparison electrode, indicating that the Example Comparison Electrode 1 has no problems as a comparison electrode. Although not shown, even if the ion concentration was changed, there was no effect.

In FIG. 8, the broken line indicates the electrode output of a commercially available pH meter for various pH standard solutions.

On the other hand, the solid line in the figure is the electrode output for various pH standard solutions when the reference electrode of the pH meter is replaced with Example Comparative Electrode I, that is, the electrode output between the commercially available pH electrode and Example Comparative Electrode 1. be. There is no difference between the two, and it can be confirmed that Example Comparative Electrode 1 functions sufficiently as a comparative electrode.

FIG. 3 and FIG. 4 respectively show a comparative electrode 1 according to a modified example.
In FIGS. 3(a) and 3(b), the end surface 2d of the electrode support substrate 2 is exposed as a liquid junction.Other points are the same as the comparison electrode 1 in FIG. The same is true.

On the other hand, the comparative electrode 1° according to the modified example has a structure in which not only the connecting portion 3a but also the rear end portion of the electrode support substrate 2 are exposed so that it can be directly inserted into the connector 8.
(see Figures (a), (b), and (C))]. When inserted into the connector 8, a connector contact (not shown) comes into pressure contact with the connecting portion 3a, and conduction is established. Further, in this comparative electrode 1'', a liquid junction 2a is provided on the back surface 2c of the electrode support substrate, and the silver film 3 is formed over almost the entire surface of the electrode support substrate surface 2b.

The other points are the same as the comparison electrode 1 in FIG.

(f) As described in detail, the reference electrode of the present invention includes a porous electrode support base material, an internal liquid filled in the pores of the electrode support base material, and a porous electrode support base material. Since it includes an electrode to be formed and an insulating film that covers the electrode and the electrode supporting base material except for the liquid junction, it has the following advantages.

1: The structure and manufacturing process are extremely simple, and miniaturization, mass production, and cost reduction are easy.

ii: It can be manufactured into any shape, and the conditions of use are not limited.

ij: Since the internal liquid is retained in the solid electrode support base material, no maintenance is required.

i■: Since the price can be reduced, it can also be disposable.

V: Since it has a simple structure and can be mass-produced, variations in characteristics and shape between comparison electrodes can be resolved.

vi: Excellent mechanical strength, substances in the test liquid are less likely to adhere to the liquid junction, and good measurement accuracy can be maintained.

Since it is not a vi mini glass mirror, a simple and inexpensive potential measuring circuit can be applied without paying attention to the electrical resistance of the electrode.

viii: It is possible to use it by directly inserting it into a connector without providing a lead wire part.

iX: A small potentiometric sensor can be provided by combining with a small potential detection electrode (similarly having a structure in which a membrane electrode is formed on an electrode support base material).

[Brief explanation of the drawing]

FIG. 1(a) is an external perspective view of a comparison electrode according to an embodiment of the present invention, FIG. 1(b) is a longitudinal cross-sectional view of the comparison electrode,
2(a) and 2(b) are diagrams explaining the manufacturing process of the comparative electrode in order, respectively, FIG. 3(a) is an external perspective view of the comparative electrode according to a modified example, and FIG. 4(b) is a longitudinal sectional view of the same comparative electrode, FIG. 4(a) is an external perspective view of another modified comparative electrode seen from above, and FIG. 4(b) is a longitudinal sectional view of the same modified comparative electrode. Fig. 4 (C) is a perspective view of the exterior seen from below.
5 is a diagram showing an example of the measurement circuit applied to the comparison electrode of the example, and FIG. 6 is a diagram illustrating the measurement system applied to measure the characteristics of the comparison electrode of the same modification. figure to do,
FIG. 7 and FIG. 8 are diagrams each explaining the characteristics of the comparison electrode. 2: electrode support substrate, 2a: liquid junction, 3: silver film,
5/6: Insulating film, 7: Epoxy resin. Patent Applicant Omron Corporation Agent Patent Attorney Shigeru Nakamura Figure 1 (a) Figure 2 (a) Figure 1 (b) 7: Loss of Efficiency Figure 2 (b) C Figure ( a) Figure (b) Figure Figure Figure Figure

Claims (1)

[Claims] (1) A porous electrode support base material, an internal liquid filled in the pores of this electrode support base material, an electrode formed on this electrode support base material, and the electrode and A reference electrode comprising an insulating film covering an electrode support base material.