JP2514067B2 - Ion electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an ion electrode used for detecting ion concentrations in various solutions, particularly alkali metal ion concentrations.

[Prior Art and Problems] An ion electrode or an ion-selective electrode is an electrode for detecting a potential difference according to an anion / cation activity (thermodynamically corrected concentration) in a solution, which is selective for a specific ion species. Depending on the state of existence of the ion-sensitive body (membrane) that is sensitive to, it is roughly classified into solid membrane type and liquid membrane type.

Examples of the solid film type ion electrode include a glass electrode and a sparingly soluble salt electrode, but both have insufficient ion selectivity and low measurement accuracy. In recent years, a fixed membrane type ion electrode using a ceramic solid electrolyte as an ion sensitive material has also been proposed (Japanese Patent Application No. 59-502154), but it cannot be said that the ion selectivity is sufficiently satisfactory.

As the liquid film type ion electrode, there are an ion exchange liquid film type electrode and a liquid film type electrode containing a neutral carrier, but the liquid film is inconvenient to handle and the ion permeability is affected by stirring or the like. It has the drawback of being easy. Therefore, as an improvement of the liquid membrane type, a polymer-supported membrane type ion electrode in which a solution as an ion sensitizer is supported on a porous polymer membrane is generally used. However, this type of ion electrode has a problem in that it is difficult to downsize the electrode because it is necessary to interpose the internal electrolytic solution between the polymer support film (ion sensitive body) and the internal electrode. In consideration of this point, a coated ion electrode in which a polymer supporting film is coated on the surface of the internal electrode is also known (“Surface” vol.24, No.3, 198).
6). However, this type of ion electrode does not have sufficient durability because the technology for immobilizing the ion-sensitive substance (solution) on the polymer membrane has not been fully established. In particular, when an ionophore (ion transport carrier), which is a neutral carrier, is used as the ion-sensitive substance, the immobilization technology becomes extremely difficult, and the ionophore itself is easily thermally deteriorated, so it can be used only under limited conditions. It was not possible to do so, and the high ion selectivity of ionophore could not be fully utilized.

An object of the present invention is to solve such a problem, that is, to develop an ion electrode having high ion selectivity, excellent durability, and capable of maintaining accurate detection characteristics stably for a long period of time.

[Means for Solving the Problems] The inventors of the present invention have completed the present invention as a result of earnest studies in view of such viewpoints, and the present invention solves the above-mentioned problems by the following means.

A first ion-selective ceramics body, a second ion-selective ceramics body, an ionophore solution interposed between the first ion-selective ceramics body and the second ionic ceramics body, and An ion electrode having an electrode disposed on a surface of the ion-selective ceramic body 2 facing the surface on the ionophore solution side, the first ion-selective ceramic body and the second ion-selective ceramic body
An ion electrode, wherein the ion-selective ceramics body and the ionophore solution have ion conductivity with respect to the same ion.

Further, the first ion-selective ceramic body has a vessel shape, the ionophore solution is contained in the vessel-shaped first ion-selective ceramic body, and the second ion-selective ceramic body has the vessel-shaped first ion-selective ceramic body. It is preferable that the ionophore solution is sealed by being bonded to the ion-selective ceramic body through an insulating material.

[Preferred Embodiment and Action] The ionophore solution is a solution composed of an ionophore component and a solvent, and must be used as a component of the ion sensitizer in the solution state. This is because the time and effort for holding the polymer on the polymer support membrane are saved and the difficulty of immobilization, which is the difficulty of the conventional technology, is eliminated. Further, by using it in a solution state, the adverse effect on the selectivity due to the presence of the polymer support is prevented, and the high selectivity of the ionophore itself can be fully utilized. Ionophores are a group of compounds that are polar on the inside and non-polar on the outside and that can take in an ionic substance and transport it in an organic solvent. It is also called an ion transport carrier.
Examples of the ionophore include natural substances, particularly physiologically active substances such as valinomycin, monesin, a mixture of nonactin and monactin, and a synthetic substance such as crown ether, and may be an acyclic ionophore such as nonylphenoxypolyethanol. Crown ethers are a group of macrocyclic polyethers, including dicyclohexyls,
There are various compounds such as polycyclic cryptands, spherands, uranofils, and pyrophosphates. Here, modified polyethers such as macrocyclic polysulfides in which O atoms are replaced by S, N, P, etc. are also included. It shall be included. The ionophore component should be selected according to the ionic species, but if you want to selectively permeate two or more ionic species at the same time, or if you want to selectively permeate a common ionic species, mix two or more ionophore components. May be used.
As the solvent, as long as it is an organic solvent capable of dissolving the ionophore component, regardless of whether it is an aliphatic hydrocarbon, an aromatic hydrocarbon, an alicyclic hydrocarbon, or a heterocyclic hydrocarbon, one kind or a mixture of two or more kinds as desired. use. Aliphatic hydrocarbon solvents include alkanes, alcohols such as decanol, dichloroethane, halides such as chloroform, and the like, and aromatic hydrocarbon solvents include benzene and its derivatives such as n-octyl-2. -Nitrophenyl ether, p-nitrocymene, di- (n-octylphenyl) diphosphonate, nitrobenzene, o-
Dichlorobenzene, cycloaliphatic hydrocarbon-based solvents include cyclohexane, and heterocyclic hydrocarbons include tetrahydrofuran. Specifically, as the ionophore solution, when the selected ion is sodium ion (Na ⁺ ), bis-12-crown-4 is used as the ionophore component.
(Selection coefficient k 1 × 10 ^-2 ) and o-dichlorobenzene should be used as the solvent. When the selected ion is potassium ion (K ⁺ ), it is recommended to use valinomycin (k 2 × 10 ^-4 ) as the ionophore component and o-dichlorobenzene as the solvent. The concentration of the ionophore solution can be appropriately selected depending on the type of ionophore component and solvent, but for example, in the case of the bis-12-crown-4 / o-dichlorobenzene solution as the Na ⁺ selective ion sensitizer, 2 mg / ml ~ 100
In the range of mg / ml, and in the case of the valinomycin / o-dichlorobenzene solution as the K ⁺ selective ion sensitizer, 10 mg / m
It should be in the range of l to 300 mg / ml.

The first ion-selective ceramic body is container-shaped, the ionophore solution is contained in the container-shaped first ion-selective ceramic body, and the second ion-selective ceramic body is the container-shaped first ion-selective body. It is preferable that the ionophore solution is sealed by being adhered to the conductive ceramic body through an insulating material. This is because the ionophore solution is prevented from being directly exposed to the outside world and the ionophore solution is used as an ion sensitive body, and at the same time, it has excellent durability such as thermal stability. Examples of ion-selective ceramics include alkali ion conductors such as lithium ion selectors, sodium ion selectors, potassium ion selectors,
An oxygen ion selective body etc. are mentioned. As an alkali ion selector, β-alumina or β ″ -alumina (MO ・ 5
~ 11Al ₂ O ₃ : M is a group 1A element such as Na, K, Li)),
In particular, Na-β-alumina has a high selectivity for Na ⁺ (k 0.
Have 1). As a Na ⁺ selective substance, Na ₅ MSi ₄ O ₁₂ (M is
1A group element) or the following formula Na _{1 + x} Zr ₂ Si _x P _3-x O ₁₂ (0 ≦ x ≦ 3)
The so-called NASICON (k 0.06) and so on are listed. As a K ⁺ ion selector, for example, the following formula K _x Mg _{x / 2} Ti
A compound having a hollandite structure represented by _{8-x / 2} O ₁₆ and K _x Al _x Ti _8-x O ₁₆ (1.6 ≦ x ≦ 2), K-β-Fe ₂ O ₃ or K-β ″ -Fe _{2 K 2 O-Fe 2 O 3} ( potassium ferrite) compounds such as O ₃ (k 0.02), and the like. oxygen ions as the selected body zirconia solid solution i.e. stabilized (partially stabilized or fully stabilized) zirconia , Thorium or ceria solid solution, etc. The relative density of the ion-selective ceramics should be 95% or more, preferably 99% or more, and the average crystal grain size should be 10 μm or less, preferably 5 μm or less. Even in this case, it is for maintaining the dense high-strength characteristics.

The ion sensitive part of the ion electrode according to the present invention comprises the first
Of ion-selective ceramics, a second ion-selective ceramics, and an ionophore solution interposed between the first ion-selective ceramics and the second ion-selective ceramics. Therefore, the ions to be selected in the liquid to be measured are the ceramic part located on the side of the liquid to be measured (hereinafter referred to as "the liquid side ceramic part"), the ionophore solution and the ceramic part located on the internal electrode side, and "the electrode side ceramics". Part)) to generate a potential difference according to the ion activity. Therefore, at least the presence of the ionophore solution can prevent the permeation of ions other than the selective ions, thus ensuring high ion selectivity. When the ion-selective ceramic body is in the shape of a vessel, it is sufficient that the ion-selective ceramic body is made of ion-selective ceramics at least in the permeation path of the ions to be selected.
Both the liquid-side ceramic part and the electrode-side ceramic part should have a thickness of 0.1 mm to 0.5 mm in the permeation direction of selected ions. This is to maintain high selectivity without deteriorating high strength properties. Also, the volume of the ionophore solution should be 1 μl to 50 μl. This is because if the amount is less than the lower limit, sufficient selectivity cannot be exhibited, while if the amount exceeds the upper limit, the selectivity and therefore the measurement accuracy are not significantly affected. Ceramic fibers such as alumina fibers or glass fibers may be filled with the ionophore solution in the ionophore solution existing portion. This is to maintain the heat insulation or heat retention and suppress the deterioration of the ionophore solution as much as possible. Ion-sensitive material (ionophore solution, first ion-selective ceramics body,
The second ion-selective ceramics body may have any shape such as a plate shape or a cylindrical shape as long as it can exhibit a sensitive function having high selectivity.

It is preferable that the ion sensitive body is provided with the liquid-side ceramic portion at the tip side of the support so as to come into contact with the liquid to be measured as usual. The support may be made of various electrically insulating materials such as polymer materials such as resin and ceramics. It is preferable to directly connect the internal electrodes to the electrode-side ceramic portion. This is for maintaining high measurement accuracy and downsizing the entire ion electrode. However, if necessary, an internal solution composed of an electrolytic solution of selected ions may be interposed. Two or more ion sensitive bodies may be attached to the support.

The ion electrode of the present invention is manufactured, for example, as follows.
The container made of ion-selective ceramics is formed into a main body part and a lid part by molding the ceramic raw material powder and firing it in a predetermined temperature range, for example, 1250 to 1650 ° C. Raw powder particle size is 1μ
It is better to set it to m or less. The inside of the main body is filled with an ionophore component and a solvent adjusted to a predetermined concentration together with ceramic fibers as the case may be, the cover is covered, an appropriate spacer is present, and the main body and the cover are bonded together by adhesion or the like. Is enclosed. A conductive material is applied to one surface side of the obtained ion sensitive body by printing, plating, sputtering, vapor deposition or the like to form a conductor portion. Attach the ion sensitizer at a predetermined position on the support and connect the lead to the conductor.
Further, the obtained ion electrode is electrically connected to a potentiometer together with a reference electrode to obtain an ion activity measuring device.

The ion electrode of the present invention is used for medical purposes, chemical, pharmaceutical,
It is suitable for process control in food engineering.

Examples Examples of the present invention will be described below. A comparative example will also be described.

Example 1 (Na ⁺ Selective Ion Electrode) (a) Production of Ion Selective Ceramic Container 91 g of SiO _{2 having} a purity of 99.9%, 186 g of ZrO ₂ having a purity of 99.9%, a purity of 99.
286 g of 7% trisodium phosphate and 350 ml of tert-butyl alcohol are ground and mixed in a ball mill for 24 hours, and the resulting slurry is freeze-dried to obtain a powder of 42 mesh or less. The powder is calcined at 1200 ℃ for 12 hours to obtain NASICON.

Next, 300 g of NASICON powder, 6 g of polyvinyl butyral with a purity of 99.6% and 150 ml of tert-butyl alcohol were ground again for 15 hours in a ball mill, and the resulting slurry was freeze-dried to obtain a powder of 42 mesh or less. And

Next, the base body is molded by die press molding into the main body and the lid shown in FIGS. 1A and 1B, which are fired at 1250 ° C. for 2 hours to obtain a container made of NASICON ceramics.

(B) Encapsulation of ionophore solution A solution of 500 mg of bis-12-crown-4 dissolved in 10 ml of o-dichlorobenzene was filled into the main body of the NASICON ceramics, and further 5 mg of alumina fiber was filled,
The lid is covered, and the main body and the lid are adhered to each other with a silicone adhesive to enclose the ionophore solution in the container (second
Figure). The thickness in the transmission path direction (vertical direction in FIG. 2) is 0.5 mm for the ceramic part (each of the lid part and the main body part) and 0.3 mm for the solution existing part. The outer diameter of the main body is 5 mm, the inner diameter is 3 mm, and the diameter of the lid (the diameter of the corresponding fitting portion of the main body) is 4 mm.

In this way, a Na ⁺ ion sensitizer having a NASICON ion-selective ceramic and a bis-12-crown-4 ionophore is obtained.

Example 2 (K ⁺ Selective Ion Electrode) (a) Production of Ion Selective Ceramics Container A previously prepared Na-β-alumina ceramics container (the shape and dimensions are the same as those in Example 1) was heated at 1000 ° C. It is immersed in potassium molten salt for 30 hours, and Na and K are ion-exchanged to obtain a K-β-alumina ceramics container.

(B) Encapsulation of ionophore solution A solution prepared by dissolving 200 mg of valinomycin in 10 ml of o-dichlorobenzene is encapsulated in a K-β-alumina ceramics container in the same manner as in Example 1 above.

Thus, a K ⁺ ion sensitizer having an ion-selective ceramic of K-β-alumina and an ionophore of valinomycin is obtained.

Further, a silver paste (internal electrode) was applied to one surface side of each of the Na ⁺ ion sensitive material and the K ⁺ ion sensitive material obtained in Examples 1 and 2 and connected to a copper lead. As shown in FIG. 2, it is attached to the tip of a resin support to form an ion electrode.

[Test Example] The ion electrode according to Examples 1 and 2 was connected to a potentiometer together with a reference electrode to form an ion activity measuring device (Fig. 3),
This equipment was used to investigate the potential changes for NaCl and KCl solutions. That is, the ion electrode and the reference electrode were immersed in pure water adjusted to pH 10, and the potential changes with respect to Na ⁺ and K ⁺ ion concentrations were examined while dropping NaCl and KCl solutions. In addition, the ion electrode consisting only of NASICON (Na ⁺ ion electrode), K-β-
Using only alumina (K ⁺ ion electrode),
Similarly, the change in potential was examined. The results are shown in FIGS. 4 and 5, FIG. 4 shows the results for the Na ⁺ ion electrode, and FIG. 5 shows the results for the K ⁺ ion electrode. still,
In Figures 1-3, 1 is the ion electrode, 2 is the ion sensitizer, and 3
Is an ion selective ceramic container, 3a is a main body, 3b is a lid, 4 is an ionophore solution, 5 is a spacer, 7 is a potentiometer, 8 is a stirrer, and A is a solution to be measured.

As is apparent from FIGS. 4 and 5, the Na ⁺ ion electrode and the K ⁺ ion electrode according to the example have significantly improved ion selectivity as compared with the corresponding comparative example. Further, the ion electrodes according to Examples 1 and 2 were left at a high temperature of 80 ° C. for 1000 hours, but no abnormality occurred and the initial measurement accuracy was maintained.

[Effects] As described above, according to the present invention, since the ionophore solution can be allowed to exist in the solution state without being supported by the polymer membrane, a wide range of use conditions can be set, and high ionophore component selectivity can be achieved. It can be used effectively. In addition, no troublesome processing is required to support the polymer membrane. Since the ion activity of the solution to be measured is detected by permeating at least the ionophore solution, the permeation of non-measurement target ions is reliably prevented, and overall high ion selectivity and, therefore, highly accurate measurement of ion activity are possible. It will be possible. Furthermore, when the ionophore solution is hermetically sealed with the ceramic body as a container, it is not directly exposed to the external environment and has excellent durability despite the use of the ionophore component. In particular, if necessary, a cooling means may be used in combination from the rear side of the ion electrode, which contributes to improvement of durability and further expansion of use conditions.

Accordingly, the present invention can effectively measure the activity of a specific ion in a liquid to be measured for a long period of time with high accuracy by effectively utilizing an ionophore component having high ion selectivity. It is useful.

[Brief description of drawings]

FIG. 1 is a front view and a plan view showing an ion-selective ceramic container according to an embodiment of the present invention, wherein FIG. 1A relates to a main body portion, FIG. 1B relates to a lid portion, FIG. 2 is a front sectional view showing an ion sensitive body in the above embodiment, FIG. 3 is an ion activity measuring device using an ion electrode in the above embodiment, and FIGS. [Fig. 4] Fig. 4 is a graph showing the potential change based on the amount of NaCl and KCl solution added in the test using an ion electrode. Fig. 4 relates to the Na ⁺ ion electrode and Fig. 5 relates to the K ⁺ ion electrode. Show each. 1 ... Ion electrode, 2 ... Ion sensor 3 ... Container, 4 ... Ionophore solution

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hideho Aoki 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Japan Special Ceramics Co., Ltd. (72) Inventor, Mr. Ando, No. 14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture

Claims (2)

(57) [Claims] 1. A first ion-selective ceramic body, a second ion-selective ceramic body, and an ionophore interposed between the first ion-selective ceramic body and the second ionic ceramic body. An ion electrode having a solution and an electrode disposed on a surface of the second ion-selective ceramics body facing the surface on the ionophore solution side, the first ion-selective ceramics body comprising: An ion electrode, wherein the second ion-selective ceramics body and the ionophore solution have ion conductivity with respect to the same ion. 2. A first ion-selective ceramic body is in the shape of a vessel, the ionophore solution is contained in the vessel-shaped first ion-selective ceramic body, and a second ion-selective ceramic body is in the shape of a vessel. The ion electrode according to claim 1, wherein the ion electrode is adhered to the first ion-selective ceramics body through an insulating material to seal the ionophore solution.