JPH046906B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Field of Application The present invention is directed to silver-based metals used in electrodes for measuring pH, etc.
This invention relates to a silver chloride-based electrode body. Conventional technology The PH of the test liquid is measured using a single-function or composite PH electrode.
When measuring, the difference between the potential E _G generated on the glass membrane depending on the PH and the detected potential E _R on the reference electrode side, E _G −
It is well known that the pH of the test liquid is determined from the electrochemical output E _R = EPH. Problems to be Solved by the Invention If the glass membrane in the glass electrode is not contaminated, the potential generated on the glass membrane will directly increase the pH of the test liquid.
Furthermore, in silver-silver chloride based reference electrodes, a concentrated potassium chloride solution is usually used as the internal solution, so the potential is determined depending on the chloride ion concentration in the internal solution. Therefore, in potassium chloride solution, silver chloride (AgCl) is dissolved under certain conditions such as temperature.
AgClAg ⁺ +Cl ^- , Ag ⁺ +2Cl ^- [AgCl ₂ ] ^- ,
Dissolution proceeds through a complex formation equilibrium process such as Ag ⁺ +3Cl ^- [AgCl ₃ ] ^-- . That is, Ag dissolves in the form of a cation of Ag ⁺ and an anion of a chlorosilver complex. It is desirable that the detection potential of the electrode for PH measurement be maintained over a long period of time, but in actual use, irregular fluctuations in temperature are repeatedly applied to the electrode, and at relatively high temperatures, silver chloride Since the solubility product decreases and silver chloride becomes insufficient in the internal solution, silver chloride at the silver-silver chloride electrode is eluted until the solubility equilibrium of silver chloride at the current temperature is reached. In this way, silver chloride (AgCl) becomes silver ion (Ag ⁺ )
The following problems occur due to the elution into the internal solution as chlorosilver complex ions ([AgCl ₂ ] ^- ). That is, by repeating the elution of silver chloride into the internal solution, the silver chloride at the silver-silver chloride electrode eventually disappears and transforms into a simple silver rod, which senses the redox potential of the internal solution and This results in an abnormal shift in the detection potential. Furthermore, even before the silver-silver chloride electrode transforms into a mere silver rod due to the elution of silver chloride into the internal solution, the eluted silver ions and chlorosilver complex ions change to the electrode as silver chloride as the temperature decreases. Precipitation may occur inside or near the liquid junction, causing clogging of the liquid junction and creating an abnormal liquid-to-liquid potential difference between the internal liquid and the test liquid, making it difficult to accurately measure the pH of the test liquid. It will be a hindrance. The phenomenon of clogging of the liquid junction due to the elution of silver chloride into the internal solution is even more pronounced when a reducing agent such as hydrazine or hydroquinone or hydrogen sulfide gas is present in the test solution. appears in That is, when the silver ions eluted into the internal liquid come into contact with the reducing agent in the test liquid at the liquid junction contact interface,
Ag ⁺ →Ag becomes silver particles through the reduction reaction, clogging the liquid junction, and if hydrogen sulfide gas is present in the test liquid, 2Ag ⁺ +S ^- →Ag ₂ S
Due to this reaction, a hardly soluble precipitate is generated at the liquid junction, causing clogging. Furthermore, when the internal reference electrode of a glass electrode is formed using a silver-silver chloride electrode, the silver ions eluted into the internal solution become silver chloride over a long period of time and deposit on the inner wall surface of the sensitive glass membrane. This causes the potential generated in the membrane to deviate from its normal value. Each of the above phenomena takes the form of silver chloride dissolution and movement as silver ions and chlorosilver complex ions. Conventionally, the following measures have been taken to prevent measurement errors caused by such phenomena. ing. That is, for example, a method has been used in which a complex-forming compound is mixed into the internal solution and reacted with the silver ions eluted into the internal solution to form a soluble complex that does not easily precipitate as a crystal. Since it exhibits a certain dissolution equilibrium effect, there is a risk of precipitation if the silver ion concentration becomes high. Additionally, a method is used in which a barrier is provided between the silver-silver chloride electrode and the liquid junction or glass membrane, with a structure that makes it difficult for silver ions and chlorosilver complex ions to reach the liquid junction or glass membrane. Even with this method, it is impossible to completely prevent the movement of eluted silver ions and chlorosilver complex ions. Means for Solving the Problems The present invention differs from conventional methods that take measures to prevent silver ions and chlorosilver complex ions eluted into the internal solution from migrating and depositing. By taking fundamental measures to prevent the elution of chlorosilver complex ions into the internal solution, the present invention aims to eliminate the conventional drawbacks and realize an electrode with an extremely long life. Cation exchange membranes allow cations to pass through, but
Under normal conditions, it blocks the permeation of cations,
It is well known that anion exchange membranes allow anions to permeate, but under normal conditions they block the permeation of cations; however, the present invention was made by focusing on the properties of such ion exchange membranes. With something that
It is constructed so that the surface of the silver chloride film attached to the surface of the silver rod is coated double with an anion exchange membrane and a cation exchange membrane, or only with an anion exchange membrane or a cation exchange membrane. be. Effect By configuring as above, the anion exchange membrane and the cation exchange membrane prevent silver ions and chlorosilver complex ions dissolved on the surface of the silver chloride membrane from being eluted to the outside, that is, to the internal solution. or at least prevent the elution of silver ions or chlorosilver-complexed silver ions to the outside. In reality, there is a difference in concentration between the concentration of silver ions and chlorosilver complex ions held in the microscopic cavities that exist between the silver chloride membrane and the ion exchange membrane, and the ion concentration outside the ion exchange membrane. Although there is a possibility that some ion outflow may occur due to the osmotic pressure generated between the inside and outside of the ion-exchange membrane depending on the temperature, it has been shown that this is negligible in practical terms. In addition, since all types of ion exchange membranes are inherently hydrophilic, by interposing the ion exchange membrane, good electrical continuity can be achieved between the silver-silver chloride electrode and the internal liquid without electrical isolation. Therefore, there is no risk of adversely affecting the operation of the potential difference detection system. Embodiment FIG. 1 is a diagram showing an embodiment of the present invention, in which 1 and 2 are a silver rod and a silver chloride film forming a silver-silver chloride electrode. For example, a silver rod 1 with an outer diameter of approximately 0.5 mm is heated. By inserting it into a silver chloride crystal, the silver chloride film 2 is attached to the surface of the tip of the silver rod 1 in an appropriate axial length range. Incidentally, in order to attach the silver chloride film 2 to the surface of the silver rod 1, in addition to the conventional method described above, any suitable method among conventionally known methods may be used. Reference numeral 3 denotes an anion exchange membrane, for example, a silver rod 1 is inserted into an anion exchange membrane tube having an inner diameter of approximately 0.6 mm, and the surface portion of the silver chloride membrane 2 is covered. 4 is a cation exchange membrane, for example, consisting of a cation exchange membrane tube with an inner diameter of approximately 0.9 mm;
It is provided so as to cover the surface of the anion exchange membrane 3. A sealant 5 is made of silicone adhesive, for example, and seals between the upper end of the cation exchange membrane 4 and the silver rod 1, as well as the lower end of the cation exchange membrane 4, and further seals the internal liquid as necessary. The surface of the silver rod 1 that is likely to come into contact with is covered. By immersing the electrode body thus formed in a potassium chloride (KCl) solution having the same concentration as the internal solution actually used, the potassium chloride solution flows through the ion exchange membranes 4 and 3 to the silver chloride film 2. It penetrates to the surface and functions as an inner pole. Instead of providing the cation exchange membrane 4 on the outside of the anion exchange membrane 3, an anion exchange membrane may be provided on the outermost side, and the anion exchange membrane 3 and the cation exchange membrane 4
may be provided in each multiplex. In this case, anion exchange membranes may be provided in multiple layers, and multiple cation exchange membranes may be provided on the outside or inside of the anion exchange membranes, or anion exchange membranes and cation exchange membranes may be provided alternately. Furthermore, instead of forming an anion exchange membrane and a cation exchange membrane separately, an anion exchange group and a cation exchange group are each introduced in layers into a common single membrane.
The surface of the silver chloride membrane may be covered with an ion exchange membrane formed so that two membranes can exhibit an anion exchange function and a cation exchange function. In addition, the surface of the silver chloride membrane may be covered with only an anion exchange membrane for the purpose of capturing only silver ions, or the surface of the silver chloride membrane may be covered with only a cation exchange membrane for the purpose of capturing chloro-complexed silver ions. In these cases, the effect of inhibiting ion elution is somewhat reduced, but when compared to the conventional method, the adverse effects caused by ion elution and movement can be suppressed much more effectively. FIG. 2 is a sectional view showing an example of an electrode for pH measurement constructed using the electrode body of the present invention, in which 6 is the electrode body shown in FIG. 1, 7 is a glass tube, 8 is a liquid junction, and 9 is a It is an internal fluid. Effects of the Invention In the present invention, the surface of the silver chloride membrane is covered with an ion exchange membrane to prevent the elution of ions into the internal liquid.
Compared to conventional methods that take measures against ions eluted into the internal liquid, the adverse effects of ions can be removed far more effectively. Next, the results of experiments conducted by the present inventor using the prototype electrode assembly of the present invention shown in FIG. 1 will be shown. Experiment 1 In an electrode body in which a silver chloride film was attached to the surface of a silver rod with a diameter of approximately 0.5 mm over an axial length of approximately 20 mm, the amount of silver contained in the silver chloride film was approximately 2.3 mg. This was clearly achieved by weight measurement, but in this electrode body, the surface of the silver chloride membrane was covered with a double membrane of an anion exchange membrane and a cation exchange membrane, as well as a silicone adhesive, and the silver chloride membrane was covered with a silicone adhesive. The electrode body, in which the part of the silver rod that is not attached is covered with silicone adhesive, is placed in a beaker containing 30 ml of 3M potassium chloride solution, and the surface of the silver chloride film is not covered with an anion exchange membrane. , put the electrode body with only the silver rod part covered with silicone adhesive into a beaker containing 30ml of 3M potassium chloride solution as above,
After boiling both beakers on a hot plate for 7 hours, the silver ion concentration in the potassium chloride solution in each beaker was measured using an atomic absorption spectrometer. 0.47mg of silver, which is approximately 20% of the silver contained in the solution, was eluted into the potassium chloride solution, but in the electrode body in which the surface of the silver chloride film was covered with an ion exchange membrane, 0.04mg of silver, which is approximately 1.7%, was eluted into the potassium chloride solution. only eluted,
This shows that the effects of the present invention are great. Experiment 2 In the same way as above, the surface of the silver chloride membrane was covered with a double ion exchange membrane and silicone adhesive, and the electrode body, in which the silver rod was covered with silicone adhesive, was immersed in a 1M potassium chloride solution, and ions were removed. As a result of measuring the electrical resistance between the outer surface of the exchange membrane and the silver rod, it was found that there was no problem at all even if the electrode body of the present invention was used in a potentiometric measurement system at 600Ω/cm. Experiment 3 Figure 3 shows that the electrode shown in Figure 2, in which the electrode body of the present invention is housed in a glass tube, and a conventional double junction type reference electrode are immersed in a 3M potassium chloride solution.
It shows the results of potential measurement based on the conventional comparison electrode potential, and the horizontal axis is the elapsed time T (unit:
The vertical axis is the detection potential E (unit: mV), and as is clear from the figure, the detection potential was kept extremely stable for almost one month. Experiment 4 The electrode body of the present invention shown in Fig. 1 was used as an inner electrode in a double-junction type comparison electrode, and the potentials of various sample liquids were measured using the conventional double-junction type comparison electrode as a reference. The results are shown in the table below.

[Table] As is clear from the table, there was almost no change in the detection potential not only for tap water and various PH standard solutions, but also for highly alkaline and highly acidic solutions, compared to the electrode assembly constructed using the electrode assembly of the present invention. Some electrodes have excellent performance. As is clear from the above description, the electrode body of the present invention covers the surface of the silver chloride membrane with an anion exchange membrane and a cation exchange membrane to prevent silver ions and chlorosilver complex ions from elution into the internal solution. or the surface of the silver chloride membrane is covered with only an anion exchange membrane or only a cation exchange membrane to prevent only the elution of silver ions, or to prevent only the elution of chloro-complexed silver ions. In either case, the negative effects caused by the elution and movement of ions, which could not be removed in the past, can be almost completely suppressed, and the electrode also satisfies the requirements for a reference electrode and has a long life. It is extremely effective when used as an electrode for measuring various ion concentrations, oxidation-reduction potential, oxygen concentration, etc. in addition to pH.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing an example of an electrode for pH measurement incorporating the electrode body of the present invention, and FIG. 3 is a characteristic of the electrode body of the present invention. A curve diagram showing 1... silver rod, 2... silver chloride membrane, 3... anion exchange membrane, 4... cation exchange membrane, 5... sealant, 6... electrode body of the present invention, 7 ……
Glass tube, 8...liquid junction, 9...internal liquid.

Claims (1)

[Claims] 1. An electrode body for measuring pH, etc., characterized in that the surface of a silver chloride film adhered to the surface of a silver rod is covered with an ion exchange membrane. 2. The electrode assembly for measuring PH, etc. according to claim 1, wherein the ion exchange membrane is a double membrane consisting of an anion exchange membrane and a cation exchange membrane stacked together. 3. The electrode assembly for measuring PH, etc. as set forth in claim 1, wherein the ion exchange membrane is a multilayer membrane in which an anion exchange membrane and a cation exchange membrane are stacked three or more times. 4. The electrode body for measuring PH, etc. according to claim 1, wherein the ion exchange membrane is formed by introducing an anion exchange group and a cation exchange group in layers into a common single membrane. 5. The electrode assembly for measuring pH, etc. according to claim 1, wherein the ion exchange membrane is an anion exchange membrane. 6. The electrode assembly for measuring pH, etc. according to claim 1, wherein the ion exchange membrane is a cation exchange membrane.