JPH01262459A - Ion electrode - Google Patents

Abstract

PURPOSE:To provide the ion electrode which has high ion selectivity and excellent durability and can maintain an exact detection characteristic stably over a long period of time by forming an ion sensitive body so as to have a base body consisting of ion selective ceramics and a porous surface layer and holding ionophores on the surface layer. CONSTITUTION:The ion sensitive body is required to have the base body 1 consisting of the ion selective ceramics. The reason thereof lies in that the ion selecting effect is exhibited by the ion selective ceramics itself. The ion sensitive body has the excellent durability such as thermal stability over the entire part thereof. The power to hold the ionophores by a high-polymer supporting film is improved as well by the presence of this base body 1. The ion sensitive body is also required to have the surface layer 2 which is made porous in order to stably holding the ionophores on the layer 2. The surface layer 2 may be constituted of a high-polymer material or ceramics (different from the ceramics of the base body material) and the use of the ion selective ceramics which is the base body material to form the porous surface layer is equally good.

Description

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

[Prior art and issues] An ion electrode or an ion-selective electrode refers to an electrode that detects a potential difference according to the anion and cation activity (thermodynamically corrected concentration) in a solution, and is selective for specific ion species. Based on the state of existence of the ion receptor (membrane) that is sensitive to ions, it is broadly classified into solid membrane type and liquid membrane type.

Examples of solid membrane type ion electrodes include glass electrodes and poorly soluble salt electrodes, but both have insufficient ion selectivity and low 1MJ accuracy. In recent years, a solid membrane type ion electrode using a ceramic solid electrolyte as an ion receptor has been proposed (Japanese Patent Application Publication No. 59-502154), but the ion selectivity cannot be said to be sufficiently satisfactory.

In addition, liquid film type ion electrodes include ion exchange liquid film type electrodes and liquid film type 7! containing neutral carriers. An example is the f-pole, but the liquid film is inconvenient to handle.

Another disadvantage is that the ion permeability is easily affected by stirring or the like. Therefore, as an improvement over the liquid film type, a polymer-supported membrane type ion electrode is generally used in which a porous polymer membrane supports a solution as an ion receptor. However, this type of ion electrode requires an internal electrolyte to be interposed between the polymer support membrane (ion receptor) and the internal electrode, and therefore has the problem that it is difficult to miniaturize the electrode. Furthermore, in consideration of this point, a coated ion electrode is also known in which the surface of the internal electrode is coated with a polymer support membrane ("Surface J Vol. 24. No. 3゜193
G). However, this type of ion electrode does not have sufficient durability because the technology for immobilizing the ion-sensitive substance (solution) has not been completely established. Particularly when using neutral carriers such as io, nophores (ion transport carriers) as ion-sensitive substances.

The difficulty of the immobilization technique has become significant, and the ionophore itself tends to be easily degraded by heat, so it can only be used under limited conditions, and therefore the high ion selectivity of the ionophore cannot be fully utilized.

The present invention aims to solve these problems, that is, it has high ion selectivity and excellent durability.

The purpose of this research is to develop an ion electrode that can stably maintain accurate detection characteristics for a long period of time.

[Means for Solving the Problem] In view of this point of view, the present inventor has developed a solution to the problem. As a result of repeated research, the two inventions were completed.

The present invention solves the above problems by the following means.

The ion receptor consists of a base made of ion-selective ceramics and a porous surface layer, in which ionophores are retained. ion electrode.

[Preferred embodiment and operation] The ion receptor must have a substrate made of ion-selective ceramics. This is because the ion-selective ceramic itself exhibits an ion-selective effect. Moreover, the ion receptor as a whole has excellent durability such as thermal stability. In particular, the presence of this substrate also improves the retention of ionophores by the polymer support membrane. As an ion-selective ceramic.

Examples of the alkali ion conductor include a lithium ion selector, a sodium ion selector, a potassium ion selector, an oxygen ion selector, and the like.

As an alkali ion selector, β-alumina or β
'-Alumina CM-11Affl O:MO,
523 indicates group IA elements such as Na, Li, etc.), and especially Na-β-alumina has high selectivity (k
0.1). As a Na+ selective substance, Na has been in history.
5M514012 (~1 is a group IA element) or the following formula Na
Zr Si P O (0≦1+X
The so-called NAS I C0N (k 0.0
6) etc. The K+ ion selection color is, for example, the following formula: KMgTi! X/2 8-X/201Ei and K A,
Table X with j Ti O (L, S≦X≦2)
8-1 16 Compound having hollandite structure, -β-
Examples include 2O-Fe203 (potassium ferrite) based compounds (kO,02) such as Fe203 or -β'Fe203. The oxygen ion selector is a zirconia solid solution, that is, stabilized (partially stabilized or completely stabilized) zirconia.

Examples include doria or ceria solid solution. The relative density of the ion-selective ceramic is 95% or more, preferably 99%
% or more, and the average crystal grain size is preferably 10 μm or less, preferably 5 μm or less. This is to maintain precise high strength characteristics even when the film is made thinner or smaller.

The ion receptor must hold ionophores on the surface of the substrate. This is to effectively utilize the high ion selectivity of the ionophore component. In particular, by combining it with an ion-selective ceramic that exhibits selectivity for the same ion, it can contribute to improving the ion selectivity in a complementary manner compared to the case where the ionophore or ceramic is used alone. Ionophore refers to a group of compounds that have a polar inside and a non-polar outside, and are capable of taking up ionic substances and transporting them through a solvent, and are also called ion transport carriers. Ionophores include natural substances, particularly physiologically active substances such as palinomycin, monesin, rhodopsin, mixtures of nonactin and monactin, and synthetic substances such as crown ethers, and may also be acyclic ionophores such as nonylphenoxy polyethanol. Crown ether refers to a group of macrocyclic polyethers, including dicyclohexyl, multicyclic cryptands,
There are various types such as sphiniounds, uranophylls, and pyrophosphatephylls, and here 0 atoms are S
, N, P, etc. are also included in the present invention. The ionophore component should be selected according to the ion species, but if you want to selectively permeate two ion species at the same time, or if you want to selectively permeate a common ion species, mix two or more ionophore components. You may also use it as The ionophore is included in the retention process as an ionophore solution. The use of a solvent facilitates the dispersion and impregnation of the ionophore into the porous surface layer. Furthermore, even when a polymeric material is used, it becomes easy to disperse and impregnate the polymeric material. This solvent may be an aliphatic hydrocarbon as long as it is a breeding solvent that can dissolve the ionophore component.

Aromatic bromide water f: 1 Alicyclic hydrocarbon, heterocyclic carbon I
Regardless of the element, it can be used alone or as a mixture of two or more if desired. Examples of aliphatic hydrocarbon solvents include alkanes, alcohols such as decanol, 7% halides such as dichloroethane and chloroform, and examples of aromatic hydrocarbon solvents include benzene and its derivatives such as n-octyl. -2-nitrophenyl ether, p-nitrocymene, di(Ω-octylphenyl)
Examples of the diphosphonate, nitrobenzene, 0-dichlorobenzene, alicyclic hydrocarbon solvent include cyclohexane, and examples of the heterocyclic hydrocarbon include tetrahydrofuran. Specifically, when one selected ion is sodium ion (Na'') as an ionophore solution, it is preferable to use bis-12-crown-4 (selectivity coefficient klX 10') as the ionophore component and O-dichlorobenzene as the solvent. .The selected ion is potassium ion (K+
), it is preferable to use palinomycin (k2XIO-') as the ionophore component and 0-dichlorobenzene as the solvent. The concentration of the ionophore solution can be appropriately selected depending on the ionophore component and the type of solvent.
In the case of 2-crown-410-dichlorobenzene solution, the range is from 2 mg/ml to 100 mg/ml;
10mg/ml ~ in case of dichlorobenzene solution
A range of 3005g/ml is recommended.

The ion receptor must have a porous surface layer (or at least a portion of the surface layer) together with the substrate. This is to stably hold the ionophore in the surface layer.

The porous surface layer may be composed of a polymeric substance or ceramics (different from the base material), or the ion-selective ceramic that is the base material may be used as a porous material. Polyvinyl chloride (PV) is used as a polymer material.
C) etc. may be used. When ceramics are used as the porous surface layer material, the ionophores may be directly held in the porous ceramic, or the ionophores may be held with a polymeric substance interposed therebetween. As ceramics other than ion-selective ceramics, it is preferable to use materials with excellent corrosion resistance and heat resistance.In particular, in consideration of affinity with polymeric substances, oxide-based ceramics are preferable (for example, SiO, A I!
It may be either glass (vitreous) or crystallized glass. It is preferable that this porous ceramic exists in an open pore state. This is to stably impregnate and retain the ionophore and to prevent the permeation of selected ions from being inhibited by the presence of the ceramic. When the porous surface layer is composed of ion-selective ceramics as the base material.

It is preferable to make the surface layer porous. This is because it is sufficient if the ionophore can be retained at least in the surface layer. It is better not to make the surface and base part porous, especially open pores. This is because the internal electrode and the liquid to be measured may come into direct contact with each other, making it impossible to obtain ion selectivity. What does "porous" mean here?

The term also includes a state in which the term is made of ceramic fibers or polymer fibers. When ionophores are directly retained in ceramics (ion-selective or otherwise), the porosity and pore diameter of the porous surface layer must be adjusted appropriately to ensure good ionophore retention. It's good to do that. For example, the average pore diameter is preferably set to IIa11 or less. The thickness in the direction of transmission of selected ions is 50 μl to 2 m+s for the ion receptor, 50 μm to 2 mta for the substrate, and 10 μm for the surface layer.
It is better to set it to ms.

This is to maintain high selectivity without reducing durability. If it is below the lower limit, sufficient selectivity cannot be achieved, while if it is present above the upper limit, it will not exhibit sufficient selectivity.

This is because it does not have much effect on measurement accuracy.

The shape of the ion receptor may be any shape, such as a plate or a cylinder, as long as it can exhibit its highly selective sensing function.

The ion receptor is preferably provided with a porous surface layer (a portion in which the ionophore is held) at the tip of the support, as usual, so as to be located on the front side so that it can come into contact with the M1 constant solution. The support can be made of one of various electrically insulating materials such as polymeric substances such as resins and ceramics. It is preferable to bond the internal electrode directly to the substrate (on the opposite side to the surface layer) made of ion-selective ceramics. This is to maintain high measurement accuracy and to downsize the entire ion electrode.

However, if necessary, an internal solution consisting of an electrolyte solution of selected ions may be interposed. The ion receptor may be attached to the support on two sides.

The ion electrode of the present invention is manufactured, for example, as follows. The base body made of ion-selective ceramics is formed at a predetermined temperature range, e.g.
Bake at 0°C. The surface layer can be formed by applying powder, solution or paste of each material with a brush, dipping, spraying, etc., and then baking it.
Various methods such as thermal spraying may also be used. The retention of ionophore is 5 at the specified concentration! It is preferable to apply a mixture of the ionophore component to be prepared and a solvent to a polymeric material onto the porous surface layer, or to impregnate the porous surface layer with a solution.

The surface layer and ionophores are formed in one step.

In addition to the holding method, a paste made by blending these may be used to form them all at once. A conductive material is attached to one side of the obtained ion sensitive material by printing, plating, sputtering, vapor deposition, etc. to form a conductor part. The ion sensitive body is attached to a predetermined position on the support, and a lead is connected to the conductor portion. Further, the obtained ion electrode and a reference electrode are electrically connected to a potential difference of 3 J- to obtain an ion activity measuring device.

The ion electrode of the present invention can be used for medical and chemical purposes.

Pharmaceutical 1: Suitable for process control in food engineering.

[Example] The present invention will be explained in detail below. Comparative examples will also be described.

Example 1 (Na + selective ion electrode) (a) Production of substrate Nasicon (Na Z "2S12PO12)" prepared in advance
The powder (purity 99%, 42 mesh or less) is press-molded with a die and fired at 1250° C. for 2 hours to obtain a disc (2) of φIOX O, 5II+m made of Nasicon ceramics.

(b) Formation of surface layer and ionophore holding screw (12
-Crown-4) loOsg and polyvinyl chloride 5
A solution prepared by dissolving 0.00@g in 30 ml of tetrahydrofuran was spin-coated on the Nasicon ceramic disk (2) to obtain an ion receptor 1.

Example 2 (Na + selective ion electrode) (a) Production of substrate and formation of surface layer A paste made of Nasicon powder, which is the same as the substrate material, was applied to the surface of the disk (■) of Example 1, and heated at 1200°C for 2 hours. After firing, a disk (1) with one surface made porous is obtained.

(b) Ionophore holding bis(12-crown-4) A solution prepared by dissolving lOQIIlg in 20 ml of tetrahydrofuran is vacuum impregnated into the disk (2) to obtain an ion receptor 2.

Example 3 (K+ selective ion electrode) In Example 1, mono-β-alumina (KO・5.5A n,03) powder (purity 99%, 80 mesh or less) was used instead of Nasicon powder, and .

Ion receptor 3 is obtained by using palinomycin in place of bis(12-crown-4).

Example 4 (K+ selective ion electrode) In Example 2, the above Example 3 was used instead of Nasicon powder.
In the same way as above, mono-β-alumina powder was used, and bis(12
- Crown-4) is replaced with palinomycin to obtain ion receptor 4.

The ion receptors 1 to 4 thus obtained each have a composition as shown in the table below.

table *1: rPVCJ indicates polyvinyl chloride.

*2: The numbers in parentheses are the solvents used in the retention process.

rTHFJ indicates tetrahydrofuran.

The structure of the obtained ion receptor is schematically shown below.
As shown in FIG. 4, a silver paste (internal electrode 4) is applied to the substrate surface (the side that does not hold the ion receptors 7t7) of each of the ion receptors 1 to 4 prepared in Examples 11 to 4. After connecting to the lead 5, it is attached to the tip of a Teflon support 6 to form an ion electrode 7.

[Test Example] The ion electrode 7 according to Example 1.3 was connected to an electrometer (mV) 9 together with a reference electrode 8 to generate ion activation f.
:L measurement device (Fig. 5), and using this device, NaC
Potential changes for the CKC1 solution were investigated. That is, the ion electrode and the reference electrode are immersed in pure water adjusted to pH 1O, and the NaCJ, KCj7 solution is added dropwise.
The change in potential with respect to ion concentration was investigated. Also, as a comparative example, one consisting only of the Nasicon disk ■ (Na + ion electrode).

Potential changes were investigated in the same manner as in 2 using a K-β-alumina disk (K+ ion electrode). The result is the 6th
, 7, FIG. 6 shows the results for the Na+ ion electrode, and FIG. 7 shows the results for the Na+ ion electrode. In FIG. 5, 10 is a magnetic stirrer, 11 is a stirrer, and A is a liquid to be measured.

As is clear from FIGS. 6 and 7, the ion selectivity of the Na + ion electrode and the Na + ion electrode according to the example was significantly improved compared to the corresponding comparative example.
The ion electrode related to 1 (100
I left it for hours, but no abnormality occurred.

The original measurement accuracy was maintained.

In addition, when compared with the aforementioned coated ion electrode, which uses the same ionophore component and simply coats the internal electrode surface with a polymer support membrane, the coated ion electrode can be used at 60°C and 5k.
Whereas g/c- is the limit.

The ion electrode according to the present invention could be used at 70° C. and at a pressure of 7 kg/c.

It should be noted that the ion electrodes according to Examples 2 and 4 had substantially the same resultant force (j) as in Examples 1 and 3.

[Effect] As described in Section 2, according to the present invention, the ionic activity of the liquid to be measured is detected by passing through at least the ionophore component and the ion-selective ceramics. By combining these, the transmission of ions not to be measured (interfering ions) is complementarily prevented, resulting in high ion selectivity as a whole.
Therefore, highly accurate measurement of ion activity becomes possible. In addition, by combining the ion-selective ceramics and the ionophore component, the retention force is improved, and the ion receptor as a whole has excellent durability such as thermal stability despite the use of the ionophore component. That is, there is little change over time and the reproducibility of the 1M1 constant potential is excellent.

In particular, it can be used at higher temperatures and pressures than conventional ion electrodes using ionophore components, and can therefore contribute to expanding the range of use. Furthermore.

After a certain period of use, the used ionophore components (and polymeric substances) are washed away and freshly retained, making it easy to use repeatedly.

Highly accurate measurement of ion activity can be maintained for a long period of time. Furthermore, due to the presence of ion-selective ceramics,
Ionophore retention treatment is also a component.

Therefore, the present invention effectively utilizes ionophore components and ion-selective ceramics to measure the activity of specific ions in a liquid to be measured with high accuracy over a long period of time.
It is extremely useful in the field of ion electrodes and furthermore in the field of sensors.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the ion receptor of the present invention. 2 and 3 are partially enlarged views of FIG. 1. FIG. 2 shows a porous surface layer formed from a material different from the base material, and FIG. 3 shows a porous surface layer formed from the same material as the base material. FIG. 4 is a sectional view showing an example of the ion electrode of the present invention. FIG. 5 is a schematic diagram showing an example of an ion activity measuring device using the ion electrode of the present invention. Figure 6.7 is a graph showing potential changes based on the amount of NaC1°KC1 solution added in tests using the ion electrodes of Examples 1 and 3 and corresponding comparative examples;
Related to ion electrode (Example 1, corresponding comparative example), No. 7
The figure is I (+ ion 7 + Lh c Example 3. Comparative example)
related to. are shown respectively. 1...Substrate 2...Surface layer λ4 1...Ionophore 7...Ion electrode applicant
NGK Spark Plug Co., Ltd. Agent Patent Attorney Asami Kato (1 other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] An ion electrode in which an ion receptor has a base made of ion-selective ceramics and a porous surface layer, and the surface layer holds an ionophore.