JPH0439619B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a reference electrode without internal electrolyte. More specifically, the present invention relates to an improved reference electrode that exhibits a constant potential almost unaffected by changes in electrolyte concentration in a liquid to be measured, and that does not cause deterioration of an ion-selective electrode used in combination with the reference electrode. [Technical background of the invention and its problems] When measuring the concentration of ions using an ion-selective electrode, a reference electrode is used as a reference electrode. The most common reference electrodes include saturated calomel electrodes, silver/silver chloride electrodes, and the like. Among them, the saturated calomel electrode has a saturated KCl solution as the internal electrolyte solution. In addition, the silver/silver chloride electrode
It is usually used by immersing it in a KCl solution or other salt solution at a certain concentration. However, the reference electrode containing an internal electrolyte solution has a complicated structure, which complicates the manufacturing process, and requires special care when handling and maintaining the electrode. In order to solve these problems, recently, reference electrodes with a simpler structure and without an electrolyte solution have been developed, such as polymer membranes containing silver, silver chloride, powdered KCl, etc., and Cl ^- ions at a constant concentration. Silver with a multilayer structure coated with a polymeric protective film in this order to protect the
A silver chloride solid reference electrode has been developed and put into practical use. It has been known from experience that an amine-cured epoxy resin coating is excellent as the polymer protective film for the solid reference electrode. However, since amine-cured epoxy resins contain trace amounts of ammonia or amines generated during curing, if a solid reference electrode using this as a polymer protective film is used together with an ion-selective electrode,
There was a problem in that the ion selective electrode deteriorated due to these ammonia or amines. In order to solve this problem, a solid reference electrode has been proposed in which a polyvinyl chloride film containing a plasticizer such as dioctyl adipate is used as a polymer protective film in place of the amine-cured epoxy resin. However, this type of solid reference electrode has the drawback of being slightly sensitive to Cl ^- ions. For example, if the Cl ^- ion concentration in the solution to be measured increases tenfold, the potential of the reference electrode becomes approximately negative.
It shifts by 10mV. Therefore, when a solid reference electrode using a polyvinyl chloride film as a polymer protective film is used to measure ion concentration, the problem remains that measurement errors become large. Therefore, it has been desired to develop a superior polymeric protective film material for solid reference electrodes to replace amine-cured epoxy resins. [Object of the Invention] An object of the present invention is to provide a solid reference electrode that exhibits a stable potential without deteriorating the ion-selective electrode. [Summary of the Invention] In order to achieve the above object, the present inventors have conducted extensive research and found that when a silicone polymer film is used as a polymer protective film for the reference electrode, the potential of the reference electrode remains at a constant value over a long period of time. The present invention was completed by discovering the fact that That is, the reference electrode of the present invention includes silver to which a lead wire is connected; a silver halide layer formed on at least a portion of the surface of the silver; and an alkali metal halide coated on the surface of the silver halide layer. A polyvinyl chloride resin layer containing the polyvinyl chloride resin layer; and a silicone polymer film covering the surface of the polyvinyl chloride resin layer. In the present invention, silver and silver halide are essential components for forming a monopolar battery X ^- |AgX|Ag (wherein, X represents a halogen element). Silver with a high purity of 99.9% by weight or higher is usually used. If it is less than 99.9% by weight, it will become impossible to obtain a predetermined reference potential. The shape of the silver may be a wire, a bar, or a plate and is not limited in any way. One end of the lead wire is connected to the silver material, and the other end is connected to an electrical signal display device provided outside the electrode. The silver halide fixed on the silver surface is preferably silver chloride, which provides a stable potential. The thickness of the silver halide layer is usually 5 to 100 μm.
shall be. This is because if the layer thickness is less than 5 μm, the reference potential value will not be stable, and if the layer thickness exceeds 100 μm, the electrical resistance will become excessive. The polyvinyl chloride resin layer containing the alkali metal halide used serves to determine the electrode potential of the silver-silver halide electrode reaction AgCl+e=Ag ⁺ +Cl ^- . As alkali metal halides, in particular,
KCl is preferred. This is because the mobilities of K ⁺ and Cl ^- are almost equal, making it difficult for a liquid junction potential difference to occur. Alkali metal halides usually have a particle size of
Uniformly dispersed in polyvinyl chloride resin as a powder of 200 μm or less. As the polyvinyl chloride resin, well-known molding resins can be used. The polyvinyl chloride resin can also contain well-known plasticizers such as dioctyl adipate, dioctyl phthalate, orthonitrophenyl octyl ether, and the like. The content of alkali metal halide in the polyvinyl chloride resin layer is usually 50 to 80% by weight.
This is because if the content deviates from the above range, a predetermined stable potential cannot be obtained. In addition, the thickness of the polyvinyl chloride layer is 30 to 800 μm.
It is preferable that When the layer thickness is less than 30 μm, the mechanical strength of the polyvinyl chloride layer is low and it is easily damaged. On the other hand, when the layer thickness exceeds 800 μm, the electrical resistance becomes too high. In the present invention, the silicone polymer film is a protective film for keeping the Cl ^- ion concentration in the polyvinyl chloride layer constant. The silicone-based polymer used is silicone-based adhesive TSE-385RTV {Toshiba Silicone Co., Ltd.
(manufactured by Shin-Etsu Chemical Co., Ltd.) and KE471 (manufactured by Shin-Etsu Chemical Co., Ltd.) are preferred. The thickness of the silicone polymer film is preferably
The thickness is 20 to 600 μm. When the film thickness is less than 20 μm, the mechanical strength of the polyvinyl chloride layer is low and it is easily damaged. On the other hand, when the film thickness exceeds 600 μm, the electrical resistance becomes too high. Next, the reference electrode of the present invention will be explained with reference to the drawings. The figure is a conceptual cross-sectional view showing a preferred embodiment of the reference electrode of the present invention. In the figure, 1 is a silver bar, one end of which is connected to a lead wire 2, which is a copper wire, through a soldered part 3. 5 is a silver chloride layer formed on the surface of the silver rod 1. This surface is covered by a polyvinyl chloride layer 6 in which KCl powder is dispersed. The outermost part of the silver-silver chloride electrode thus formed is covered with a silicone polymer film 7 as a protective film. Further, the lead wire 2, the soldering portion 3, and a portion of the silver bar 1 are covered with an electrically insulating sheath. Such a reference electrode of the present invention can be obtained, for example, as follows. First, a silver chloride layer is formed on the surface of the silver rod 1 by performing electrolytic treatment in an electrolytic solution containing chloride ions using the silver rod 1 as an anode. Next, after preparing a polyvinyl chloride layer forming solution consisting of a predetermined amount of polyvinyl chloride resin, its plasticizer, potassium chloride powder, and tetrahydrofuran as a solvent, this solution is applied to the surface of the silver chloride layer and dried. , forming a polysilver chloride layer. Next, a liquid silicone polymer is applied to the surface of the polyvinyl chloride layer and dried to form a silicone polymer film, thereby obtaining the reference electrode of the present invention. [Effects of the Invention] Since the reference electrode of the present invention is coated with a silicone polymer protective film on its outermost surface, it exhibits a constant potential almost unaffected by changes in the electrolyte concentration in the liquid to be measured, and furthermore, Since the protective film does not contain ammonia or amines, it has the effect of not deteriorating the ion-selective electrode used together with the reference electrode, and its industrial value is extremely large. [Embodiments of the Invention] Hereinafter, the reference electrode of the present invention will be explained in detail along with Examples. Examples and Comparative Examples First, a copper wire with a diameter of 1 was connected as a lead wire.
10 mm from the tip of a silver rod with mmφ, length 100 mm, and purity 99.9% by weight was immersed in the electrolytic solution shown in the following table, and electrolytic treatment was performed using the silver rod as an anode to form a silver chloride layer on the surface of the silver rod.

[Table] Separately, a polyvinyl chloride layer forming solution was prepared by dissolving 1 g of polyvinyl chloride and 3 g of KCl powder with an average particle size of 40 μm in 20 g of tetrahydrofuran. was coated on the surface of the silver chloride layer to form a polyvinyl chloride layer with a layer thickness of 300 μm. Next, 385 g of silicone adhesive TSE manufactured by Toshiba Silicone Co., Ltd. was applied to the surface of this polyvinyl chloride layer and dried to form a protective film with a thickness of 200 μm, thereby obtaining a reference electrode of the present invention. On the other hand, for comparison, a reference electrode for comparison was prepared in the same manner as above except that a protective film was formed from 1 g of polyvinyl chloride and 1.7 g of dioctyl adipate. Next, in order to test the potential stability of the reference electrode of the present invention and the reference electrode for comparison, these electrode parts were
10 ^-1 , 10 ^-2 , 10 ^-3 mol/Immersion in KCl solution,
Potentials were measured with a saturated Amane electrode as a reference. The reference electrode of the present invention was not affected by the concentration of the KCl solution, and the potential change was within the range of ±1 mV. On the other hand, for the reference electrode for comparison, the higher the NaCl concentration of the solution, the lower the indicated potential.
Often -10 mV/decade for Cl ^- concentration change
showed a sensitivity of Furthermore, the potassium ion concentrations of these solutions were continuously measured for 10 hours using a potassium ion selective electrode. In this measurement, when the reference electrode of the present invention was used as a reference, the ion concentration measurement error after 10 hours of continuous measurement was within the range of 1%, but when the reference electrode for comparison was used as a reference, The ion concentration measurement error was 8%.

[Brief explanation of drawings]

The figure is a conceptual cross-sectional view showing a preferred embodiment of the reference electrode of the present invention. 1...Silver bar, 2...Lead wire, 3...Soldering part, 4...Insulating exterior, 5...Silver chloride layer, 6...
Polyvinyl chloride layer in which KCl is dispersed, 7...Silicone polymer film.

Claims (1)

[Scope of Claims] 1 Silver to which a lead wire is connected; a silver halide layer formed on at least a portion of the surface of the silver; and an alkali metal halide containing the surface of the silver halide layer coated. a polyvinyl chloride resin layer;
A reference electrode comprising a silicone polymer film covering the surface of the polyvinyl chloride resin layer. 2. The reference electrode according to claim 1, wherein the silver halide is silver chloride, and the alkali metal halide is potassium chloride. 3 The thickness of the polyvinyl chloride resin layer is 30 to 800μ
The reference electrode according to claim 1, which is m. 4 The thickness of the silicone polymer film is 20~
The reference electrode according to claim 1, which has a diameter of 600 μm.