JP2514069B2 - 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 solid film type ion electrode using a ceramic solid electrolyte as an ion sensitive material has also been proposed (Table 59-502154), but it cannot be said that the ion selectivity is sufficiently satisfactory.

As the liquid membrane type ion electrode, there are an ion exchange liquid membrane type electrode and a neutral carrier-containing liquid membrane type electrode, but the liquid membrane 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 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. Furthermore,
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, 1986). However, this type of ion electrode does not have a fully established technique for immobilizing an ion-sensitive substance (solution), and its durability is not sufficient. 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.

Ion-selective ceramic body, porous ionophore solution surface layer holding ionophore, which is disposed on one surface of the ion-selective ceramic body, and the porous ionophore solution surface layer of the ion-selective ceramic body An electrode disposed on the surface opposite to the surface, and the ion-selective ceramic body and the porous ionophore solution surface layer have ion conductivity with respect to the same ion. An ion electrode characterized by the above.

Preferred Embodiments and Actions The ion-sensitive part of the ion electrode according to the present invention comprises an ion-selective ceramic body and a porous ionophore solution surface layer. This is because the ion-selective ceramics themselves exert an ion-selective action. In addition, the ion sensitive body as a whole has excellent durability such as thermal stability.
In particular, the presence of this ion-selective ceramic body also improves the ionophore retention by the polymer support membrane. Examples of ion-selective ceramics include alkali ion conductors such as lithium ion selectors, sodium ion selectors, potassium ion selectors, and oxygen ion selectors. There are β-alimina or β ″ -alumina (MO ・ 5-11Al ₂ O ₃ : M is 1A group element such as Na, K, Li, etc.) as an alkali ion selector, especially Na-β-alumina.
It has a high selectivity (k 0.1) for Na ⁺ . As the Na ⁺ selective compound, Na ₅ MSi ₄ O ₁₂ (M is a group 1A element) or the following formula Na
_{1 + x} Zr ₂ Si _x P _3-x O ₁₂ (0 ≦ x ≦ 3)
NASICON (k 0.06) and so on. Examples of K ⁺ ion selectors include the following formulas K _x Mg _{x / 2} Ti _{8-x / 2} O ₁₆ and K _x Al _x Ti _8-x O
A compound having a hollandite structure represented by ₁₆ (1.6 ≦ x ≦ 2), such as K-β-Fe ₂ O ₃ or K-β ″ -Fe ₂ O ₃ .
K ₂ O-Fe ₂ O ₃ (potassium / ferrite) compounds (k 0.0
2) etc. Examples of the oxygen ion selective substance include zirconia solid solution, that is, stabilized (partially stabilized or completely stabilized) zirconia, thoria or ceria solid solution. The relative density of the ion-selective ceramics is 95% or more, preferably 99% or more, and the average crystal grain size is 10 μm or less, preferably 5 μm or less. This is to maintain the dense high-strength characteristics even when the film is thinned or downsized.

The ion sensitive portion of the ion electrode according to the present invention comprises an ion selective ceramic body and a porous ionophore solution surface layer. The porous ionophore solution surface layer means a layer in which an ionophore solution containing an ionophore is held by a polymer substance or a porous substance. This is because the high ion selectivity due to the ionophore component is effectively used. In particular, by combining with an ion-selective ceramic showing selectivity for the same ion, it is possible to complementarily improve the ion selectivity as compared with the case where the ionophore or the ceramic is used alone. 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. Ionophores include natural substances, especially physiologically active substances such as valinomycin,
Monesin, rhodopsin, a mixture of nonactin and monactin, and a synthetic substance such as crown ether may be an acyclic ionophore such as nonylphenoxypolyethanol. Crown ethers are a group of macrocyclic polyethers, including dicyclohexyls, polycyclic cryptands, spherands, uranofils, and pyrophosphates, where O atoms are S, N, P It also includes a modified polyether such as a macrocyclic polysulfide obtained by substituting the same with.
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,
Further, in the case of selectively permeating a common ionic species, two or more ionophore components may be blended and used. The ionophore is subjected to a holding treatment as an ionophore solution. By using the solvent, the ionophore can be easily dispersed and impregnated into the porous surface layer. Further, even when a polymer substance is used, it is easy to disperse and impregnate the polymer substance. This solvent may be an aliphatic hydrocarbon, an aromatic hydrocarbon, an alicyclic hydrocarbon, or a heterocyclic hydrocarbon, as long as it is an organic solvent capable of dissolving the ionophore component, and may be one kind or a mixture of two or more kinds as desired. To use as. 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 solvent as cyclohexane, heterocyclic hydrocarbon as tetrahydrofuran, etc. . Specifically, as the ionophore solution, when the selected ion is sodium ion (Na ⁺ ), bis-12-crown-4 (selection coefficient k 1 × 10 ^-2 ) is used as the ionophore component, and o-dichlorobenzene is used as the solvent. Good to use. 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 ~ It may be in the range of 100 mg / ml, or in the range of 10 mg / ml to 300 mg / ml in the case of a valinomycin / o-dichlorobenzene solution as the K ⁺ selective ion sensitizer.

The ion sensitive material has a porous ionophore solution surface layer together with ion selective ceramics. This is to keep the ionophore stable in the surface layer. The porous surface layer may be composed of a polymer substance or ceramics (different from the base material), or the ion-selective ceramics which is the base material may be used as a porous material. Polyvinyl chloride (PVC) or the like may be used as the polymer substance. When ceramics is used as the porous surface layer material, the ionophore may be directly held in the porous ceramics, or the ionophore may be held by interposing a polymer substance. As the ceramics other than the ion-selective ceramics, materials having excellent corrosion resistance and heat resistance may be used. In particular, oxide-based ceramics are preferable in consideration of affinity with polymer materials, such as Si
O ₂ , Al ₂ O ₃ , and ZrO ₂ are listed. Ceramics may be either crystalline or amorphous (glassy), and may be crystallized glass. This porous ceramic is preferably present in an open pore state. This is because the ionophore is stably impregnated and held, and the permeation of selected ions is not hindered by the presence of ceramics. When the porous surface layer is composed of the ion-selective ceramics which is the base material, the surface layer is preferably made porous. This is because it is sufficient that the ionophore can be retained at least in the surface layer. In addition, it is better not to make the base portion porous, especially open pores. This is because the internal electrodes may come into direct contact with the liquid to be measured, and the ion selectivity may not be obtained.
Here, “porous” also includes a state of being composed of ceramic fibers or polymer fibers.
When the ionophore is directly retained on ceramics (one that is ion-selective or other), the porosity and pore diameter of the porous surface layer should be adjusted as appropriate to ensure good retention of the ionophore. Good to do. For example, the average pore size should be less than 1 mm. The thickness of selected ion permeation direction is 50μm for ion-sensitive material.
2mm, 50μm to 2mm for substrate, 10μm to surface layer
1mm is recommended. This is to maintain high selectivity without lowering durability. If it is less than the lower limit, sufficient selectivity cannot be exhibited, while if it exceeds the upper limit, the selectivity,
Therefore, the measurement accuracy is not so affected. The ion sensitive 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 porous surface layer (the portion where the ionophore is held) at the tip of the support so as to be in 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. The internal electrodes may be directly bonded to the substrate (on the side opposite to the surface layer) made of ion-selective ceramics. This is to maintain high measurement accuracy and downsize 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 base made of ion-selective ceramics is fired in a predetermined temperature range, for example, 1250 to 1650 ° C, after the ceramic raw material powder is molded. The surface layer may be formed by various methods such as powder coating, solution or paste of each material, followed by baking, dipping, spraying, etc., or thermal spraying. In order to retain the ionophore, it is preferable to coat the porous surface layer with a mixture of a polymer substance with an ionophore component and a solvent adjusted to a predetermined concentration, or to impregnate the porous surface layer with a solution. The surface layer and the ionophore may be formed and held in a stepwise manner, or may be collectively formed by using a paste or the like prepared by mixing these. 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) Manufacture of Substrate Nasicon (Na ₃ Zr ₂ Si ₂ PO ₁₂ ) Powder (Purity 9
9%, 42 mesh or less) is press-molded in a mold and 2 at 1250 ℃
Φ10 × 0 made of NASICON ceramics after firing for an hour.
Get a 5mm disc.

(B) Formation of surface layer and retention of ionophore 100 mg of bis (12-crown-4) and polyvinyl chloride 5
A solution prepared by dissolving 00 mg in 30 ml of tetrahydrofuran is spin-coated on the NASICON ceramic disk to obtain the ion sensitizer 1.

Example 2 (Na ⁺ Selective Ion Electrode) (a) Production of Substrate and Formation of Surface Layer A paste made of the same Nasicon powder as the substrate material was applied to the surface of the disk of Example 1 and the temperature was 1200 ° C. for 2 hours. Baking is performed to obtain a disk having a porous surface.

(B) Retention of ionophore A solution prepared by dissolving 100 mg of bis (12-crown-4) in 20 ml of tetrahydrofuran is vacuum impregnated into the above disc to obtain an ion sensitizer 2.

Example 3 (K ⁺ selective ion electrode) In Example 1, K-β-alumina (K ₂ O · 5.5Al ₂ O ₃ ) powder (purity 99%, 60 mesh or less) was used in place of the Nasicon powder, and , Bis (12-crown-4) is replaced with valinomycin to obtain the ion sensitive body 3.

Example 4 (K ⁺ Selective Ion Electrode) In Example 2, the same K-β-alumina powder as in Example 3 was used in place of the Nasicon powder, and bis (12
-Using valinomycin instead of crown-4), an ion sensitive body 4 is obtained.

The ion sensitive bodies 1 to 4 thus obtained each have the composition shown in the following table.

In addition, the structure of the obtained ion sensitizer is schematically shown in 1 to 3
Shown in the figure. In each figure, 1 is a substrate, 2 is a surface layer, and 3 is an ion sensitizer.

Further, as shown in FIG. 4, silver paste (internal electrode 4) was applied to the substrate surface (on the side not holding the ionophore) of each of the ion sensitive bodies 1 to 4 obtained in Examples 1 to 4. After connecting to the copper lead 5, it is attached to the tip of the Teflon support 6 to form the ion electrode 7.

[Test Example] The ion electrode 7 according to Examples 1 and 3 was connected to an electrometer (mV) 9 together with a reference electrode 8 to form an ion activity measuring device (Fig. 5). Using this device, NaCl, KCl The potential change for the solution was examined. 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, as comparative examples, a potential change was similarly examined using the one consisting only of NASICON disk (Na ⁺ ion electrode) and the one consisting of K-β-alumina disk (K ⁺ ion electrode). The results are shown in Figs. 6 and 7, and Fig. 6 shows N
The results are for the a ⁺ ion electrode, and FIG. 7 is the results for the K ⁺ ion electrode. In addition, in FIG.
Is a magnetic stirrer, 11 is a stirrer, and A is a solution to be measured.

As is clear from FIGS. 6 and 7, 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 3 were left at a high temperature of 80 ° C. for 1000 hours, but no abnormality occurred and the initial measurement accuracy was maintained.

Also, when compared with the above-mentioned coated ion electrode in which the inner electrode surface was simply coated with a polymer supporting film using the same ionophore component, the coated ion electrode was 60 ° C, 5 kg / c.
While m ² is the limit, the ion electrode of the present invention 70
It could be used at ℃ and 7kg / cm ² .

The ion electrodes according to Examples 2 and 4 also obtained substantially the same results as in Examples 1 and 3.

[Effect] As described above, according to the present invention, since the ion activity of the liquid to be measured is detected by permeating at least the ionophore component and the ion-selective ceramics, the ionophore and the ceramics having the same ion selectivity are combined. As a result, the non-measurement target ions (interfering ions) are prevented from permeating in a complementary manner, and overall high ion selectivity,
Therefore, it is possible to measure the ion activity with high accuracy. In addition, the composite of the ion-selective ceramic and the ionophore component improves the holding power, and despite the use of the ionophore component, the ion-sensitizer as a whole has excellent durability such as thermal stability. That is, there is little change over time, and the reproducibility of the measured potential is excellent. In particular, compared to conventional ion electrodes that use ionophore components, they can be used at higher temperatures and pressures, thus contributing to the expansion of the range of use. Furthermore, after a certain period of use, the used ionophore component (and polymer substance) is removed by washing and retained again, making it easy to use repeatedly and maintaining highly accurate measurement of ion activity for a long period of time. be able to. Note that the existence of ion-selective ceramics makes the ionophore retention process easy.

Therefore, according to the present invention, the ionophore component and the ion-selective ceramics can be effectively used to measure the activity of a specific ion in a liquid to be measured stably for a long period with high accuracy. It is useful.

[Brief description of drawings]

FIG. 1 is a sectional view of an ion sensitive portion of an ion electrode according to Examples 1 and 3 of the invention, and FIG. 2 is a sectional view of an ion sensitive body showing an example of the ion electrode according to the invention. FIG. 3 is a cross-sectional view of an ion sensitive body showing an example of the ion electrode according to the present invention, in which a porous ionophore solution layer is formed using a porous material different from the ion selective ceramic body. A porous ionophore solution layer is formed by using a porous material of the same material as the ion-selective ceramic body. FIG. 4 is a sectional view showing an example of the ion electrode of the present invention, and FIG. Schematic diagram showing an example of an ion activity measuring device using the ion electrode of the invention, FIGS. 6 and 7 show the amounts of NaCl and KCl solution added in the tests using the ion electrodes of Examples 1 and 3 and corresponding comparative examples. 6 is a graph showing a potential change based on FIG. Shows a Na ⁺ ion electrode (Example 1, corresponding comparative example), and FIG. 7 shows a K ⁺ ion electrode (Example 3, corresponding comparative example). 1 ... Substrate, 2 ... Surface layer 2a ... Ionophore, 7 ... Ion electrode

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hideho Aoki 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Japan Special Ceramics Co., Ltd. (72) Inventor Junichi Tokumoto 14-18 Takatsuji-cho, Mizuho-ku, Aichi No. 14 Specialized Ceramics Co., Ltd. (72) Inventor, Mr. Ando, No. 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Prefecture, Japan (56) References JP-A-57-161544 (JP, A) Sho 61-170645 (JP, A)

Claims (2)

(57) [Claims] 1. An ion-selective ceramic body, a surface layer of a porous ionophore solution for holding an ionophore, which is disposed on one surface of the ion-selective ceramic body, and the porous body of the ion-selective ceramic body. An electrode arranged on the surface facing the surface of the ionophore solution surface layer side,
An ion electrode comprising: the ion-selective ceramics body and the porous ionophore solution surface layer having ion conductivity with respect to the same ion. 2. The ion electrode according to claim 1, wherein the ion-selective ceramic has a flat plate shape.