JPH0452408B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a reference electrode used to measure the ion concentration of an electrolyte in an aqueous solution. The electrode chemical potentiometric measuring device of the present invention includes various ion meters for measuring ion concentration in aqueous solutions, comparison electrodes for pH measurement, reference electrodes for various electrochemical analyses, comparison electrodes for direct measurement under high temperature and high pressure conditions, and biomedical It can be applied to analytical experimental equipment, etc. Conventionally, in order to measure the ion concentration in an aqueous solution, an ion-selective electrode as an indicator electrode and a reference electrode are inserted into the measurement solution. As a conventional reference electrode, a calomel electrode or a silver-silver chloride electrode is generally used. For example, a silver-silver chloride electrode is a well-known method in which a container made of glass or the like is filled with an electrolyte salt solution, silver coated with silver chloride is immersed in the container, and an electrochemical half cell is formed. A part of the container has a so-called liquid junction. Ion diffusion conduction between the liquid to be measured and the internal electrolyte of the reference electrode is achieved through this liquid junction. Due to the above-mentioned technical configuration, there are essentially the following drawbacks in actual measurement. 1 Ions from the internal electrolyte leak through the liquid junction during measurement. As a result, the liquid to be measured may be contaminated or the true ion concentration may not be measured. 2. The internal electrolyte solution may decrease or the ion concentration may change due to leakage from the liquid junction, which may cause the original reference potential of the reference electrode to fluctuate. 3. Also, the liquid junction may become clogged, and in this case, the electrical continuity described above cannot be obtained, making measurement difficult. 4. In order to obtain smooth electrical conduction at the liquid junction, it is necessary that the internal liquid is at least under a more positive pressure condition than the liquid to be measured. To address the above-mentioned drawbacks, we have tried to reduce leakage as much as possible by making the structure of the liquid junction finer, making the electrolyte gelatinous, etc., in order to prevent deterioration and depletion of the internal electrolyte. Various methods are used, such as arranging a device that pressurizes the liquid. However, essentially, the above-mentioned drawbacks cannot be eliminated with the conventional technology which has an electrolyte and a liquid junction inside to stabilize the potential as a reference electrode. In this way, in the conventional measurement method, when the measuring liquid is under high temperature and high pressure conditions such as primary cooling water of reactor water in a nuclear power plant or boiler water, the conventional reference electrode is difficult to measure, especially at the liquid junction. A problem occurred and there was nothing to be satisfied with. An object of the present invention is to provide a novel electrode chemical potentiometric measuring device that overcomes the drawbacks of the conventional reference electrodes mentioned above. The first purpose is to have no internal electrolytes. The second purpose is to have no so-called liquid junction. The third purpose is that it can be used even if the pressure of the measurement liquid is high. The fourth purpose is that it can be used directly for high temperature measurement liquids. The fifth purpose is to be able to design an extremely compact design.
Its handling becomes simple and easy. The present invention provides an apparatus for measuring an electrochemical potential difference generated between the indicator electrode and the reference electrode using at least one pair of the indicator electrode and the reference electrode, in which the electrode body of the reference electrode in contact with the object to be measured is silver, an alloy of silver and copper, or This is an electrochemical potential difference measuring device characterized by using a comparison electrode made of any material selected from an alloy of silver, nickel, and copper, an oxide of silver, and an oxide of an alloy of silver and copper. An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a comparison electrode 6 of the present invention. Reference numeral 1 denotes a metal electrode body electrically connected to the measurement terminal 4. Reference numeral 2 denotes an insulator, which is tightly fixed to the metal electrode body 1. The metal electrode body 1 and the terminal 4 may be connected to each other through an electric conductor disposed within the insulator 2. The insulator 2 is attached to the mounting bracket 3, and it is desirable that this attachment interface has an airtight structure and is firmly attached. The metal electrode body 1 has a portion at least partially covered with an insulator. This portion is shown as a covering portion 5. The metal electrode body 1 is selected from metals coated with silver, an alloy of silver and copper, an alloy of silver, nickel and copper, a silver oxide, and an oxide of an alloy of silver and copper. The ion concentration in the solution can be measured by immersing the reference electrode and the ion-selective electrode configured in this manner in a measurement solution and measuring the potential difference generated between the two electrodes. FIG. 2 shows an outline of the experimental apparatus used to investigate the characteristics of this comparative electrode. Among the symbols in FIG. 2, the same symbols as those in FIG. 1 indicate the same or similar components. Reference numeral 11 denotes a measuring liquid, and 12 denotes an indicator electrode, and various electrodes can be used depending on the object to be measured. 1 is a metal electrode body and corresponds to the comparison electrode 6 described in the present invention. This metal electrode body 1 is electrically insulated from the test chamber 10 and the like via an insulator 2. An amplifier 15 amplifies the potential difference between the indicator electrode 12 and the metal electrode 1, and its output is measured by a voltmeter 16. Since the indicator electrode 12 generally has a high internal resistance, the amplifier 15 has a high input resistance circuit.
A shield 17 is applied to the lead wire connecting the terminals 5 to 5. Further, the lead wire connecting the metal electrode 1 and the amplifier 15 is also provided with a shield 17 for the purpose of preventing intrusion of electromagnetic induced noise and the like. Chemical tank 20, 2
1 and 22 contain a predetermined chemical solution for changing the ion concentration in the aqueous solution with a measurement number of 11, and 19
Reference numeral 18 indicates a switching branch, and 18 indicates a chemical solution introduction section.By operating the switching branch 19, any chemical solution can be introduced into the measurement liquid. At least a portion of the surface of the metal electrode body 1 is directly immersed in the measurement liquid, and an electrochemical potential is generated in equilibrium depending on the ion concentration in the measurement aqueous solution. In this way, when considering the metal electrode body 1 as a reference electrode, there is no internal electrolyte as seen in the conventional technology,
Therefore, it can be seen that it has a completely new configuration that does not have a liquid junction. Note that, if one or more indicator electrodes 12 are further immersed in the measurement liquid and the potential difference between each indicator electrode 12 and the metal electrode body 1 is measured, the potential difference distribution in the measurement liquid can be measured. Naturally, the potential difference distribution in the measurement liquid can be measured even if a plurality of pairs of the metal electrode body 1 and the indicator electrode 12 are used. The present invention will be explained below with reference to Examples. The measuring device used will be described in more detail with reference to FIG. 2. The test tank 10 has an internal volume of about 1.8 liters and contains about 1.3 liters of pure water as the measuring liquid. In this test chamber 10, a glass electrode was placed as an indicator electrode 12, a metal electrode body 1 was placed as a comparison electrode, and a measuring liquid 11 was placed.
The electrode terminals of both electrodes 12 and 1 are respectively connected to an amplifier 15 having a high input resistance by a coaxial cable coated with Teflon.
The output was measured using a pen recorder. 4.1 to 10 in the chemical liquid tanks 20, 21, and 22, respectively.
% HCl, 4.1-10% NaOH, and about 50-500 c.c. of distilled water or neutral liquid. Example 1 Silver with a diameter of 1 mm and a length of 60 mm was used as a metal electrode body. This electrode body is partially covered with ceramic, and the tip is approximately 25 mm exposed. A glass electrode for pH measurement was used as an indicator electrode. The measurement liquid 11 can be changed from pure water to acidic or alkaline by operating the switching unit 19, and the means for this change is to introduce a predetermined amount of acidic or alkaline liquid in the chemical tank into the measurement liquid. This can be achieved by doing. The potential difference between the indicator electrode 12 and the comparison electrode 6 at this time was measured and recorded, and the results are shown in FIG. Figure 3 shows that the potential difference is +20m when measuring pure water.
V, and by adding 10% HCl solution, the pH of the measurement solution is
When the value becomes 2.2, the potential difference becomes +295 mV.Additionally, 10% NaOH solution is added to this measuring solution, and when the pH value of the measuring solution becomes 12.1, the potential difference becomes -278 mV, and 10% HCl is added again. This shows that the potential difference became +294 mV when the PHH value of the measured solution became 2.2 after adding the solution. Example 2 A silver alloy having a silver to silver mixing ratio of 9 to 1 and having a diameter of 1.2 mm and a length of 50 mm was used as the metal electrode body.
Measurements were carried out by the same means as described in Example 1, except that this silver alloy was used in place of the silver described in Example 1. In this case as well, when the measurement liquid changed from acidic to alkaline to acidic, the potential difference between the glass electrode and the metal electrode body changed. The results were as follows.

[Table] Example 3 1mmφ, length 60mm silver wire and 1.2mmφ, length 50
mm silver alloy wires (Ag:Cu=9:1) were immersed in methyl alcohol for 2 hours at room temperature, then washed with pure water for a sufficient period of time, and then heated at 100°C for 30 minutes in a constant temperature bath. Using two types of metal electrode bodies that had been heat-treated at 380°C for 1 hour to give an oxide film treatment to silver and silver alloy, a glass electrode and each metal electrode body were formed by the method described in Example 2 above. The potential difference generated between the two was measured. In this case as well, when the measurement liquid changed from acidic to alkaline to acidic, the potential difference between the glass electrode and the metal electrode body changed. The results were as follows.

[Table] Comparative Experimental Examples Experiments were conducted on other metal materials using the same methods as those described above. FIG. 4 shows an experimental example in which platinum was used as the metal electrode body. In this case, unlike the fist movements explained so far, the generated potential difference changes when the PH value of the measuring solution changes, but the value is not stable and does not show a stable potential difference corresponding to the PH value of the measuring solution. . When comparing FIG. 3 with a silver electrode and FIG. 4 with a platinum electrode, it was found that there was a significant difference, and based on these findings, the present inventors came to confirm the following important fact. That is, in an ionic aqueous solution, certain metals and metal compounds directly serve as reference electrodes while remaining in their solid surface state. FIG. 5 shows the change in potential difference between the glass electrode and the metal electrode body when the pH of an aqueous solution at a liquid temperature of 25° C. is changed. In the figure, A is for the silver electrode of Example 1, B is for the silver alloy electrode of Example 2, C is for the silver oxide of Example 3, and D is for the silver alloy oxide of Example 3. This is the result. E indicated by a broken line is a calculated value line calculated from the Nernst equation. As is clear from these results, it can be seen that the results of the conventional PH measurement method and the results of the present invention and the silver electrode, silver alloy electrode, or oxide electrode thereof show similar trends. Table 3 shows the experimental results of experimental examples conducted in more detail by the present inventor.

[Table] Table 3 shows the results of experiments in which the aforementioned glass electrode was used as the indicator electrode and various metal materials were used as the metal electrode body. As is well known, the glass electrode for PH measurement is used to measure the PH of an aqueous solution.
(JISZ8805), the potential difference shown in this table is based on the stability of the potential balance on the surface of the metal electrode itself in the aqueous solution used as the counter electrode of this glass electrode. As a result, it was found that a certain metal or metal compound can serve as a comparison electrode corresponding to the indicator electrode of the measuring liquid. Among certain metals or metal compounds, silver, silver alloys,
Examples include oxides of silver and silver alloys, and substances consisting of combinations thereof. In this example, a case was explained in which a glass electrode for PH measurement was used as an indicator electrode, but this metal electrode also operated extremely effectively in combination with other indicator electrodes, such as various ion concentration electrodes in an aqueous solution. Example 4 Glass electrodes were used as the reference electrode and indicator electrode as explained in Example 1, and the PH value of the measuring solution was changed using "10% sulfuric acid aqueous solution" and "10% caustic potassium aqueous solution" in a similar device. I experimented. Change the measurement solution from “acidic” → “alkaline” → “acidic”
When the voltage was changed, the potential difference between the indicator electrode and the reference electrode changed. The results were as follows.

[Table] As shown in Table 4, even when using a 10% sulfuric acid solution and a 10% caustic potassium aqueous solution, it is possible to obtain a potential difference that is almost equal to Nernst's calculated value, and the stability over time is also 10% compared to a 10% HCl aqueous solution. The saturation value was reached and stabilized in a short period of time, almost the same as when using an aqueous NaOH solution. As described above, the reference electrode of the present invention has the above-mentioned configuration and is structurally simple using a stable solid, so it can be applied to a reference electrode for measuring the concentration of electrolyte in an ionic solution. As described below, it exhibits extremely excellent characteristics and effects. 1 Does not have an internal electrolyte and therefore does not have an internal electrolyte junction. 2. Can measure the original potential of the measurement solution without contaminating the measurement solution. 3 Can be used in high temperature liquids. 4 Can be used under high pressure conditions. 5. Extremely compact design makes handling simple and easy. 6. Eliminate essential defects in the liquid junction. 7. When output fluctuations occur during use, the characteristics can be easily restored by polishing or cleaning the surface of the metal electrode body, and the life span can be improved. As explained above, the electrochemical potentiometric measuring device equipped with the reference electrode of the present invention can be used as a reference electrode for various ion meters and PH meters for measuring ion concentration in aqueous solutions, or as a reference electrode for various electrochemical analyses.
It is industrially useful as it can be used as a comparison electrode for direct measurement under high pressure conditions, a biomedical analysis experiment device, etc.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of an electrochemical potentiometric measuring device equipped with a reference electrode of the present invention, and FIG. 2 is a schematic diagram showing an experimental apparatus used to investigate the characteristics of the reference electrode of the present invention. Figure 3 is a chart showing the relationship between the potential difference and measurement time measured by combining a glass electrode and silver as a metal electrode body and changing the measurement liquid from acidic to alkaline to acidic over time. , a chart showing the relationship between the potential difference and measurement time measured by combining a glass electrode and platinum as a metal electrode body, and Figure 5 shows the potential difference between the glass electrode for PH measurement and the metal electrode body used as a comparison electrode and an aqueous solution. FIG. 2 is a characteristic diagram showing the relationship between PH value and DESCRIPTION OF SYMBOLS 1... Metal electrode body, 2... Insulator, 3... Mounting bracket, 4... Measurement terminal, 5... Covering part, 6... Reference electrode, 10... Test tank, 11... Measurement liquid, 12
... Indicator electrode, 15 ... Magnifier, 16 ... Voltmeter, 17 ... Shield, 18 ... Chemical solution introduction part, 1
9...Switching (branching) part, 20, 21, 22... Chemical liquid tank.

Claims (1)

[Claims] 1. In an apparatus for measuring an electrochemical potential difference generated between the indicator electrode and the reference electrode using at least one pair of the electrodes, the electrode body of the reference electrode in contact with the object to be measured is made of silver, an alloy of silver and copper, or silver and nickel. An electrochemical potential difference measuring device characterized in that a reference electrode is made of a material selected from an alloy of copper and copper, an oxide of silver, and an oxide of an alloy of silver and copper.