JPS61209351A - Electrode body for measuring ph and the like - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a silver-silver chloride-based electrode body used as an electrode for measuring pH and the like.

(Prior art) When measuring the pH of a test liquid using a monofunctional or composite pH electrode, the potential E generated on the glass membrane according to the pH,
and the detection potential E hole on the reference electrode side, E&-ER=E
It is well known that the pH of the test liquid can be determined from the electrochemical output of -.

If the glass membrane in the glass electrode is not contaminated, the potential generated on the glass membrane directly corresponds to the pH of the test solution, and the potential of the base reference electrode of the silver-silver chloride thread is determined.

It is desirable for pH measurement electrodes to maintain stability in detection potential over long periods of time, but in actual use, irregular temperature fluctuations are repeatedly applied to the electrodes, and at relatively high temperatures silver chloride Since the solubility product of decreases and silver chloride becomes insufficient in the internal solution, silver chloride at the silver-silver chloride electrode elutes until the solubility equilibrium of silver chloride at the temperature at that time is reached. As described above, silver chloride (Ay(!J)) is eluted into the internal solution as silver ions (A;) and chloride ions (C7-), causing the following problems.

That is, by repeating the elution of silver ions and chloride ions 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. This results in an abnormal shift in the detected potential.

In addition, even before the silver-silver chloride electrode transforms into a mere silver rod due to the elution of silver ions and chlorine ions into the internal solution, the eluted silver ions and chloride ions are converted to silver chloride inside the electrode as the temperature decreases. Or, it may deposit near the liquid junction, causing clogging of the liquid junction, creating an abnormal liquid-to-liquid potential difference between the internal liquid and the test liquid, and making it impossible to determine the correct pH of the test liquid.
This will interfere with measurement.

The phenomenon that leads to clogging of the liquid junction due to the elution of silver ions and chloride ions into the internal solution can occur if reducing agents such as hydrazine or hydroquinone or hydrogen sulfide gas, etc. are present in the test solution. appears even more prominently. That is, when the silver ions eluted into the internal liquid come into contact with the reducing agent in the test liquid at the contact interface of the liquid junction, they turn into silver particles through the reduction reaction A; A), causing clogging of the liquid junction. ,or,
If hydrogen sulfide gas is present in the test liquid, 2A; +
Due to the reaction 5--13r S , poorly soluble precipitates are generated at the liquid junction, resulting in clogging and the like.

Furthermore, when the internal reference electrode of a glass electrode is formed using a silver-silver chloride electrode, the silver ions and chloride ions eluted into the internal solution become silver chloride over a long period of time and are deposited on the inner wall surface of the sensitive glass membrane. However, this causes the potential generated in the glass membrane to deviate from its normal value.

Each of the above phenomena takes the form of dissolution of silver chloride and movement of silver ions and chloride ions. Conventionally, the following measures have been taken to prevent measurement errors caused by such phenomena. There is.

That is, for example, a method has been used in which a complex-forming compound is mixed into the internal solution and reacted with silver ions eluted into the internal solution to form a soluble complex that does not easily precipitate with crystals. However, since it exhibits a certain dissolution equilibrium effect, there is a risk of precipitation if the silver ion concentration becomes high.

Also, a method is used in which a barrier having a structure that makes it difficult for silver ions and chloride ions to reach the liquid junction or glass membrane is provided between the silver-silver chloride electrode and the liquid junction or glass membrane.
Even with this method, it is impossible to completely prevent the movement of eluted silver ions and chloride ions.

The present invention differs from conventional methods that take measures to prevent silver ions and chloride ions eluted into the internal solution from migrating and depositing. The aim is to eliminate the drawbacks of conventional methods and create an electrode with an extremely long lifespan by taking fundamental measures to prevent the elution of particles.

(Means for solving the problem) Cation exchange membranes allow cations to pass through, but under normal conditions they block anions from passing through, and anion exchange membranes allow anions to pass through, but under normal conditions they block anions from passing through. It is well known that ion exchange membranes block the permeation of cations, but the present invention was made by focusing on the properties of such ion exchange membranes. By coating the surface double with an anion exchange membrane and a cation exchange membrane, or by coating only with an anion exchange membrane or a cation exchange membrane, the silver ions and chloride ions dissolved on the surface of the silver chloride membrane can be removed from the outside. In other words, the elution into the internal solution is prevented by an anion exchange membrane and a cation exchange membrane, or at least the elution of silver ions or chloro-complexed silver ions to the outside is prevented. It is composed of

In fact, depending on the concentration difference between the concentration of silver ions and chloride ions held in the microscopic voids 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, it has been found 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 maintained between the silver-silver chloride electrode and the internal liquid without electrical insulation, so there is no risk of adversely affecting the operation of the potential difference detection system. .

(Example) FIG. 1 is a sectional view showing an example of the present invention.
are a silver rod and a silver chloride film forming a silver-silver chloride electrode; for example, by heating a silver rod 1 with an outer diameter of about 3.5 mm and inserting it into a silver chloride crystal, a silver chloride film 2 is formed. 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 to cover the surface portion of the silver chloride membrane 2.

4 is a cation exchange membrane, for example, the inner diameter is approximately 0.9 mm.
It consists of a cation exchange membrane tube, an anion exchange membrane 3
It is provided to cover the surface of the 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. This covers the surface of the part of the silver rod 1 that may come into contact with the metal.

By immersing the electrode body thus formed in a potassium chloride (KO/) solution having the same concentration as the internal solution actually used, the potassium chloride solution passes through the ion exchange membranes 4 and 3 to the silver chloride membrane 2. It infiltrates the surface of the membrane and functions as an inner pole.

Instead of providing the cation exchange membrane 4 on the outside of the anion exchange membrane 6, an anion exchange membrane may be provided on the outermost side, or an anion exchange membrane 6 and a cation exchange membrane 4 may be provided in multiple layers. . 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 introduced into a common single membrane so that an anion exchange function and a cation exchange function can be achieved by a single membrane. The surface of the silver chloride film may be covered with an ion exchange membrane formed to exhibit an ion 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,
Although the effect of inhibiting ion elution is somewhat reduced, the adverse effects caused by ion elution and movement can be suppressed much more effectively than in the past.

FIG. 2 is a cross-sectional view showing an example of a pH measuring electrode constructed using the electrode body of the present invention, and 6 is the electrode body shown in FIG.
7 is a glass tube, 8 is a liquid junction, and 9 is an internal liquid.

(Effects of the present 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 require countermeasures against ions, the negative effects of ions can be removed far more effectively.

Next, the results of an experiment conducted by the present inventor using a prototype of the electrode assembly of the present invention shown in FIG. 1 will be shown.

(Experiment 1) A diameter of Q is 20 m on the surface of a 5 mm silver rod.
In the electrode body to which the silver chloride film was attached over the axial length of m, it was clearly determined by weight measurement that the amount of silver contained in the silver chloride film was approximately 2.6 mg. Inside the body, the surface of the silver chloride membrane was covered with silicone adhesive on the double belly of the anion exchange membrane and cation exchange membrane, and the part of the silver rod to which the silver chloride membrane was not attached was covered with silicone adhesive. The electrode body was soaked in 33 m of 3M potassium chloride solution.
/ into a beaker containing 3M potassium chloride solution as above, and the electrode body, in which only the silver rod part was covered with silicone adhesive without covering the surface of the silver chloride film with an ion exchange membrane, was placed in a 3M potassium chloride solution as above. After boiling both heaters on a hot plate for 7 hours, the concentration of silver ions in the potassium chloride solution in each beaker was measured using an atomic absorption spectrometer. In the exposed electrode body, approximately 20% of the silver contained in the silver chloride film
However, in the electrode body in which the surface of the silver chloride film was covered with an ion exchange membrane, 0.04 mg of silver, equivalent to 1.7%, was eluted in the potassium chloride solution. (Experiment 2) In the same way as above, the surface of the silver chloride film was covered with a double ion exchange membrane and silicone adhesive, and the part of the silver rod was The electrode body covered with silicone adhesive was immersed in a 1M potassium chloride solution and the electrical resistance between the outer surface of the ion exchange membrane and the silver rod was measured. It has become clear that there are no similar problems when used.

(Experiment 3) Figure 6 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 reference electrode are immersed in a 3M potassium chloride solution, and the potential of the conventional reference electrode is referenced. The horizontal axis is the elapsed time T (unit, days), and the vertical axis is the detected potential E (unit, m
As is clear from the figure, the detected potential was kept extremely stable for about one month.

(Experiment 4) The electrode body of the present invention shown in Fig. 1 was used as the inner electrode of a double-junction type comparison electrode to form a 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.

As is clear from the table, there is 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, and the performance of the comparison electrode constructed using the electrode assembly of the present invention is shown. There are some excellent ones.

As is clear from the above description, the electrode body of the present invention covers the surface of the silver chloride film with an anion exchange membrane and a cation exchange membrane to prevent the elution of silver ions and chloride ions into the internal solution. Alternatively, 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 eliminated in the past, can be almost completely suppressed, and the conditions as a reference electrode are sufficiently provided.
Moreover, it has a long lifespan, and in addition to pH, various ion concentrations,
It is extremely effective when used as an electrode for measuring oxidation-reduction potential, oxygen concentration, etc.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG. 2 is a sectional view showing an embodiment of the present invention.
FIG. 6 is a cross-sectional view showing an example of a pH measuring electrode incorporating the electrode body of the present invention, and is a curve diagram showing the characteristics of the electrode body of the present invention.
1: Silver rod, 2: Silver chloride membrane, 6: Anion exchange membrane, 4: @
ion exchange membrane, 5: sealant, 6: electrode body of the present invention, 7: glass tube, 8: liquid junction, 9: internal liquid.

Claims (6)

[Claims] (1) An electrode body for measuring pH, etc., characterized in that the surface of a silver chloride film attached to the surface of a silver rod is covered with an ion exchange membrane. (2) The electrode assembly for measuring pH and the like according to claim 1, wherein the ion exchange membrane is a double membrane in which an anion exchange membrane and a cation exchange membrane are stacked. (3) The electrode assembly for measuring pH and the like 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 assembly for measuring pH and the like as set forth in claim 1, wherein the ion exchange membrane is formed by introducing an anion exchange group and a cation exchange group 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.