JPH0517501B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electrode body in which an internal electrode is immersed in an internal liquid, particularly an electrode for pH measurement. The present invention relates to an electrode body. Problems to be Solved by the Prior Art and the Invention When measuring the PH of a sample liquid using a single-function or composite PH electrode immersed in an internal liquid using a silver-silver chloride electrode as an internal reference electrode. , the electrochemical output EPH, which generally corresponds to the PH in the test liquid, is
The difference between the potential EG generated in the PH-sensitive glass film depending on the _PH and the potential _ER of the comparison electrode can be expressed as EPH=E _{G -ER} . If the glass membrane is clean, the potential developed by the glass membrane is immediately determined. Further, the potential of the reference electrode is determined by the potential due to the dissolution equilibrium of Ag ⁺ +Cl ^- AgCl under conditions such as a constant temperature. In this case, during actual use, temperature changes are applied to the electrode many times, but at high temperatures the solubility product decreases, resulting in a shortage of silver chloride in the internal solution. The silver chloride in the electrode begins to dissolve until the solubility equilibrium of silver chloride at that temperature is reached, and the elution of this Ag ⁺ ion causes the following ~
The problem arises. In other words, the problem with the reference electrode is that the eluted Ag ⁺ ions become AgCl as the temperature decreases.
This causes clogging of the liquid junction of the reference electrode, and as a result, a liquid junction potential is generated between the internal liquid and the test liquid, causing a deviation in the reference electrode potential. In particular, if a reducing agent such as hydrazine or hydroquinone or hydrogen sulfide is present in the test solution, the eluted Ag ⁺ ions will have a more dramatic effect on the electrode. In other words, when Ag ⁺ ions come into contact with the reducing agent at the contact interface of the liquid junction, they turn into silver particles through the reaction Ag ⁺ →Ag and clog the liquid junction. In addition, when gases such as H ₂ S come into contact with each other, a poorly soluble precipitate is formed through the reaction 2Ag ⁺ +S ^- →Ag ₂ S, which also instantly clogs the liquid junction, causing changes in potential and slow response speed. cause Problems with glass electrodes: The eluted Ag ⁺ ions deposit as AgCl on the glass inner surface of the glass electrode, staining the glass membrane and causing a shift in the potential generated on the glass membrane. Further, due to repeated elution of silver chloride, the silver chloride in the silver-silver chloride electrode disappears and becomes a mere silver rod, which cannot function as an internal reference electrode. In this case, the oxidation-reduction potential of the internal fluid is sensed and an abnormal shift in potential occurs. The fundamental solution to the problems mentioned above is:
The goal is to prevent the silver chloride of the silver-silver chloride electrode from dissolving into the internal liquid, but this is a highly technical challenge. Therefore, as a second-best method, in order to prevent the eluted Ag ⁺ ions from having the adverse effects described above and in the electrodes, conventional methods have been used to easily form soluble complexes with Ag ⁺ ions in the internal solution. A method is to add a reagent that prevents precipitation as crystals, or a method is to provide a structural barrier between the silver-silver chloride electrode and the liquid junction or glass membrane to prevent Ag ⁺ ions from migrating. 1986-194352) have been proposed. However, the former method has the drawback that even soluble complexes have a solubility product, so if the Ag ⁺ ion concentration becomes too high, precipitation will occur, and the latter method also completely prevents the movement of Ag ⁺ ions to the liquid junction. There is a problem that it is difficult to prevent, and with either method, the precipitated AgCl may cause clogging of the liquid junction of the reference electrode.
It has been difficult to completely prevent deposition on the glass inner surface of the glass electrode. The present invention was developed in view of the above circumstances, and it is possible that Ag ⁺ ions eluted from the silver-silver chloride electrode become precipitates and clog the liquid junction of the reference electrode or adhere to the PH-sensitive glass membrane. Therefore, even if temperature fluctuations are applied to the electrode many times during measurement or the test liquid contains reducing agents, hydrogen sulfide, etc., temperature resistance caused by Ag ⁺ ions can be avoided. The object of the present invention is to provide an electrode body that is unlikely to suffer from deterioration in performance, response speed, reproducibility, etc., and can perform measurements stably over a long period of time. Means and operation for solving the problems In order to achieve the above object, the electrode body of the present invention has the following features:
In an electrode in which an internal electrode is immersed in an internal liquid and a chelate resin is added to the internal liquid, the chelate resin is a chelate resin treated to form the same cation form as the cations constituting the internal liquid, that is, a chelate resin. A chelate resin is used in which the cation species bonded to the ion exchange chelate group is the same as the cation species constituting the internal solution.
Specifically, the ionic form of the chelate resin is processed into the cation form that constitutes the internal solution, for example, if the internal solution is potassium chloride, it is processed into the potassium ion form, and the cation bonded to the cation exchange chelate group is converted into potassium ion form. ion. That is, in order to prevent Ag ⁺ ions from clogging or adhering to liquid junctions and glass membranes as precipitates, the present inventor developed a solid that removes Ag ⁺ ions in the internal liquid from this liquid phase. We considered using an adsorbent. Ion exchange resins are common as solid adsorbents, but since the internal solution is usually 3M or saturated KCl, there are a large amount of K ⁺ ions in the internal solution, and therefore ordinary ion exchange resins cannot be used. Then, a trace amount
Ag ⁺ ions are difficult to capture. As a result of various studies, we came up with the idea of using a chelate resin that has been treated to form the same cations as the cations constituting the internal liquid as a solid adsorbent, leading to the present invention. In the present invention, by using a chelate resin treated as a solid adsorbent in the same cation form as the cations constituting the internal liquid, metal ions such as Ag ⁺ ions that are present in trace amounts in the internal liquid are reliably adsorbed.・In addition to being able to capture ions, the cations that make up the internal solution are liberated from the internal solution when ion-exchanged with metal ions such as Ag ⁺ ions, so the internal solution does not change in quality. In this case, most of the commonly used chelate resins have iminodiacetic acid groups, but in order to capture Ag ⁺ ions in 3M or nearly saturated KCl solutions, the nitrogen skeleton chelate resin must have polyamine groups or iminopropion groups. The effect is especially noticeable for those who have it. Furthermore, those with chelate groups such as dithiocarbamate groups and thiol groups in the sulfur skeleton are less susceptible to the effects of large amounts of K ⁺ ions.
Better in capture performance of Ag ⁺ ions. The present invention will be explained in more detail below. The electrode body of the present invention is an electrode in which the internal electrode is immersed in an internal liquid, and a chelate resin treated to form the same cation form as the cations constituting the internal liquid is added as a solid adsorbent to the internal liquid. It is something. In this case, the type of chelate group is not particularly limited and various types can be selected, but those having a dithiocarbamate group, a thiol group, a polyamine group, or an iminopropion group as a chelate group can be particularly preferably used. In addition, the chelate resin used is one that has been treated to form the same cations as the cations that make up the internal solution.
For example, when the internal solution is a KCl solution, a chelate resin in which potassium is introduced into the terminal group is used. In addition, the particle size of the chelate resin is 0.1 to 1 mm, especially 0.1 mm.
Preferably, it is formed into a spherical shape of about 0.3 mm. Furthermore, when adding chelate resin to the internal solution,
There is no limit to the amount or form, but 10 to 100 of the internal liquid
It is preferable to add the chelate resin in an amount of about 30 to 50% by volume, and if the amount of the chelate resin is too small, the effect of trapping metal ions such as Ag ⁺ ions may not be sufficiently exerted. In this case, the chelate resin may be dispersed throughout the internal liquid, or may be precipitated or suspended in the internal liquid. Further, in the case of an electrode for pH measurement, the chelate resin is preferably added to both the internal solution of the reference electrode and the internal solution of the glass electrode. Here, we show by experimental examples that chelating resins successfully capture Ag ⁺ ions in concentrated KCl solutions. Experimental example 1 Figure 1 shows that when 25 ml of 3M KCl solution is saturated with AgCl dissolved in a beaker and 5 g of various chelate resins are added into this solution, Ag ⁺ ions are adsorbed to the chelate resin. This is the result of investigating how the Ag ⁺ ion concentration gradually decreases with a silver ion-selective electrode. In Fig. 1, a indicates the case where a chelate resin having a dithiocarbamate group is used as a chelate group, b indicates a case where a chelate resin having a thiol group is used, c indicates a case where a resin having a polyamine group is used, and d indicates an imino group. The results are shown when using one having a propion group. From the results shown in FIG. 1, it was confirmed that these resins adsorbed Ag ⁺ ions to (AgCl ₂ ) ^- ions well in 3M KCl. We also confirmed that adsorption of Ag ⁺ ions by these chelate resins was possible even when the temperature of the 3M KCl solution was raised to 80°C. Therefore, by adding these chelate resins to the internal solution in which the silver-silver chloride electrode is immersed, it becomes possible to capture silver ions eluted even at high temperatures. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the Examples below. Example A chelate resin was added to the internal liquid of the electrode assembly for pH measurement shown in FIG. The electrode body shown in Fig. 2 is a composite type in which a reference electrode and a glass electrode are integrated. 3 is a liquid junction, 4 is a reference electrode, 5 is a tubular body such as a glass tube, 6 is an internal liquid, 7 is a silver rod, 8 is molten silver chloride at the tip of the silver rod 7, 9 is a liquid junction, 10 is a A glass electrode disposed inside the outer cylinder 1, 11 is a PH sensitive glass membrane, 12 is an internal liquid, 13
is a silver bar, and 14 is molten silver chloride at the tip of the silver bar 13. Reference numeral 15 denotes a tubular body such as a glass tube disposed within the outer cylinder 1, and a temperature compensating electrode 16 is provided within the tubular body 15. Note that 17 is an internal liquid replenishment port, and 18 is an O-ring. This electrode body is
In order to minimize the influence of thermal convection during high-temperature use and to quickly achieve temperature-dependent dissolution equilibrium near the silver-silver chloride electrode in response to temperature changes,
A silver-silver chloride electrode, which serves as a reference electrode, is placed inside an elongated glass tubular body filled with chelate resin.
A liquid junction (ceramic junction) is arranged at the tip of this tubular body to establish electrical communication with the outer cylinder.
Further, the glass electrode portion also has a thin tube structure with a height difference between the glass sensitive membrane and the internal reference electrode (see Japanese Patent Laid-Open No. 194352/1983). In the electrode body, the chelate resin is poured into the tubular body of the reference electrode (A in Figure 2), the outer cylinder where the external liquid junction of the reference electrode is located (B in Figure 2), and the inside of the glass electrode. One, two, or all locations within the cylinder (C in Figure 2). In this case, the chelate resin used has a particle size of about 0.1 mm and has an iminopropion group, and since the internal solution of the PH electrode is usually a concentrated KCl solution, the terminal cation of the chelate resin is prepared using a KOH solution, etc. Process to form K type. It is effective to circulate and blend the KCl internal solution after washing thoroughly with water. Here, since the eluted Ag ⁺ is immediately captured when added to Part A, the dissolution equilibrium system is not apparently disturbed, which helps to improve the reaction rate. When placed in part B, only the Ag ⁺ eluted from the double tube is captured, so the trapping life of the chelate resin can be extended. When added to part C, long-term stabilization of the glass film can be expected. When placed in multiple locations, multiple effects can be expected, but the basic idea is to trap Ag ⁺ ions and remove them from the liquid phase. Therefore, having the electrode structure as shown in FIG. 2 is only one example of its implementation.
Regardless of the structure of the electrode, the effect can be achieved by filling the chelate resin into the KCl solution in which the silver-silver chloride internal electrode is immersed. Table 1 compares the effects of a composite PH electrode in which the part B of the electrode in FIG. 2 is filled with chelate resin. In this case, the time required for a composite PH electrode to become unusable due to a significant deviation in potential during continuous use in a sample liquid containing about 100 ppm of hydrogen sulfide gas is shown.

[Table] In this way, chelate resin is dissolved in 3M KCl internal solution.
It captures Ag ⁺ ions and prevents the Ag ⁺ ions eluted from the silver-silver chloride electrode from flowing into the junction section and clogging it. Further, the chelate group introduced into the chelate resin is not limited to that used in this example, and there may be a chelate group that has better coordination ability with silver ions. Finally, by using a chelate resin in which the cation species bonded to the cation exchange chelate group are the same as the cation species constituting the internal solution, the internal solution of the electrode body can be stabilized without altering its quality. An experimental example shows that a potential can be obtained. Experimental Example 2 An experiment was conducted using the apparatus shown in FIG. Third
In the figure, 20 is a beaker, 21 is a reference comparison electrode, 22 is a silver rod, 23 is a silver chloride layer, 24 is a liquid junction (ceramic junction), 25 is a reference electrode internal solution (3M KCl), and 26 is a stopper. , 27 is a reference electrode for testing, 28 is a silver rod, 29 is a silver chloride layer, 30 is a liquid junction (ceramic junction), 31 is a reference electrode internal solution (3M KCl), 32 is a stopper, 33 is a chelate for testing Resin, 34 is lead wire, 35 is mV
Meter 36 indicates the test solution (3M KCl). First, the reference comparison electrode 21 and the test comparison electrode 2
I prepared 7. These reference electrodes 21 and 27 have liquid junction portions 24 and 30 at their lower ends, respectively, and have an outer diameter of 2 mm.
The lower portions of the silver rods 22 and 28 have internal electrodes coated with silver chloride layers 23 and 29 to a thickness of about 3 mm using a melting method. As the internal liquids 25 and 31, a 3M potassium chloride solution is used as the silver chloride layer 23 and 2 of the internal electrode.
9 was injected to the extent that it was immersed. Two comparison electrodes 21 and 27 were placed in a beaker containing a test liquid 36, and the potential difference between both comparison electrodes 21 and 27 was read via a lead wire 34 with an mV meter 35. Before adding the chelate resin 33 to the internal liquid 31 of the test comparison electrode 27, both comparison electrodes 2
1 and 27 are exactly the same, and both comparison electrodes 2
The potential difference between 1 and 27 was almost zero. Next, the chelate resin 33 was added to the internal liquid 31 of the comparison electrode 27 for testing. Two types of chelate resins were used. That is, Eporus Z-7 (chelate resin having an iminopropion group in the chelate group) and Eporus MX-8 manufactured by Miyoshi Resin Co., Ltd.
(Chelate resin having a thiol group in the chelate group)
It is. Approximately 3 ml of the chelate resin, which is approximately the same amount as the internal liquid 31 in the test comparison electrode 27, was added. In this case, the chelate resin was used by treating the terminal cation form with a potassium hydroxide solution, potassium chloride solution, hydrochloric acid solution, etc. into a potassium form, and then thoroughly washing it with water (this was used as the treated chelate resin). (called resin). On the other hand, for comparison, a similar experiment was carried out using each chelate resin in its untreated ionic form (proton form for Eporus Z-7, sodium form for Eporus MX-8, called untreated chelate resin). I went. The potential difference and stability of the comparison electrode for testing when each treated chelate resin and each untreated chelate resin were added are shown in FIG. 4 (using Eporus MX-8) and FIG. 5 (using Eporus Z-7). In the case of Eporus MX-8, when the treated chelate resin was introduced, the test comparison electrode 27 showed approximately the same potential as the reference comparison electrode 21 within 2 to 3 minutes.
On the other hand, when the untreated chelate resin was added, the potential difference with the reference comparison electrode 21 fluctuated irregularly and greatly. In the case of Eporus Z-7, when the treated chelate resin was added, the potential reached almost the reference potential in 2 to 3 minutes and became stable. On the other hand, when untreated chelate resin was added, there were no large fluctuations or potential differences as in the case of Eporus MX-8, but the fifth
As shown in the figure, the potential difference gradually changed from negative to positive, and this change continued even after one day, resulting in a potential difference of nearly 10 mV. moreover,
In the case of Eporus Z-7, there was a problem in that when untreated chelate resin (proton type) was introduced, the resin did not mix with the internal liquid and floated to the surface. From the results of this experiment, it was found that before introducing the chelate resin into the internal solution, by treating the chelate resin in advance into the same cation form as the cations (potassium ions) that make up the internal solution, It can be seen that not only can a stable reference potential be obtained in a short time without any influence on the composition of the liquid, but also the compatibility with the internal liquid is improved, making it more suitable for capturing silver ions. That is, when the treated chelate resin is added to the internal solution of the comparison electrode in the electrode body of the present invention, it is seen that not only does the treated chelate resin capture silver ions, but also that the comparison electrode exhibits a stable potential as a reference electrode. Effects of the Invention As explained above, the electrode body of the present invention uses a chelate resin added to the internal liquid that has been treated to form the same cation form as the cations constituting the internal liquid. It is possible to reliably adsorb and capture metal ions, and when ion exchange with metal ions occurs, the cations constituting the internal liquid are liberated, so that the internal liquid does not change in quality. Therefore, a stable potential can be obtained without altering the internal liquid of the electrode body. Therefore, the electrode body of the present invention has good resistance to, for example, metal ions eluted from the internal electrode becoming precipitates and clogging the liquid junction of the reference electrode or adhering to the PH-sensitive glass membrane. Because of this, it is excellent in various performances such as temperature durability, response speed, and reproducibility, and can perform stable measurements over a long period of time.

[Brief explanation of the drawing]

Figure 1 is a graph examining adsorption of Ag ⁺ ions in 3M KCl by chelate groups in Experimental Example 1, Figure 2 is a partial cross-sectional view showing an electrode according to an example of the present invention, and Figure 3 is an experimental graph. A schematic diagram showing the experimental apparatus used in Example 2, and Figures 4 and 5 are the standard reference electrode and test reference electrode when treated and untreated chelate resins were added to the internal solution in Experimental Example 2, respectively. 3 is a graph showing changes over time in the potential difference between 2, 6, 12... Internal liquid, 7, 13... Silver bar,
8,14...Silver chloride.

Claims (1)

[Scope of Claims] 1. In an electrode in which an internal electrode is immersed in an internal liquid and a chelate resin is added to the internal liquid, the chelate resin is a cationic species bonded to a cation exchange chelate group. An electrode body characterized by using a chelate resin having the same cation species as the cations constituting the internal liquid. 2. The electrode body according to claim 1, wherein the chelate resin has a dithiocarbamate group, a thiol group, a polyamine group, or an iminopropion group.