JPH0376863B2 - - Google Patents

Description

[Industrial application field]

The present invention relates to a sodium ion sensor, and more particularly to a solid state sodium ion sensor without an internal (standard) solution. [Prior Art and Problems] Conventionally, ion-selective electrodes have been used as ion sensors that measure the ion concentration in a solution based on electrode potential response. This ion-selective electrode has two types of internal structures: (1) an ion-selective membrane, an internal (standard) solution, and an internal reference electrode immersed in the solution (internal solution type); They can be broadly classified into membrane structures in which an ion-selective membrane or an ion-sensitive membrane is directly bonded to a conductive substrate (direct bond type). Among these ion sensors, the sodium ion sensor is an internal solution type that has a glass membrane and measures the sodium ion concentration using the membrane potential difference between the internal solution containing the standard concentration of sodium ions and the test liquid. are commonly used. However, since this type of electrode has an internal solution and an internal liquid chamber, it is difficult to miniaturize the electrode, there is a high risk of glass breakage, and
The disadvantage was that it was necessary to take into account the interference of Ag ⁺ ions. Therefore, in order to eliminate the structural disadvantages of such glass membrane electrodes, we have developed a direct bond type coated wire ion-selective ion electrode.
electrode; hereinafter referred to as CWE) was developed.
Since CWE has a structure in which a polymer sensitive membrane holding a liquid ion exchanger is directly coated on the tip of a conductive substrate, it can be easily miniaturized and easily used. However, since it does not have an internal reference electrode, there is a problem in terms of potential stability.Also, since the conductive substrate and the polymer sensitive membrane are in direct contact with each other, differences in the surface state of the conductive substrate may occur. has a large influence on the measured potential, and tends to cause individual differences in the properties of the resulting electrodes, resulting in practical disadvantages. A CWE with an internal comparison electrode has been proposed to solve this operational drawback of the CWE. That is, an electrode is shown in which a layer of a polystyrene porous membrane impregnated with a solution of KCl and a target ion is provided on the surface of the internal reference electrode, and the electrode is coated with the same sensitive membrane as that used in the above CWE.
However, although this electrode is different in structure from the conventional internal solution type, it can be said that it is similar in terms of functional configuration. In addition, since there is an interface between the impregnated layer and the sensitive membrane, the potential between them may change over time, and the stability may not be satisfactory for long-term use. Ta. Purpose of the Invention Under these circumstances, the present inventor has conducted various studies in order to develop a solid-state sodium ion sensor that does not have an internal solution or an internal liquid chamber, and that does not have the above-mentioned drawbacks of conventional products. However, it has been found that by depositing the sodium ion selective membrane on top of a membrane with a reversible redox function, rather than directly depositing it on the surface of the conductive substrate, the operation is extremely stable and the characteristics are improved. The present invention was completed based on the discovery that it is possible to obtain a sodium ion sensor with excellent sensor characteristics such as no individual differences, miniaturization, and fast response speed. That is, the present invention is a sodium ion sensor that measures the concentration of sodium ions in a solution based on electrode potential response, in which a film having a reversible redox function is deposited on the surface of a conductive substrate, and the surface of the film is The present invention provides a sodium ion sensor comprising a sodium ion selective membrane attached to a sodium ion sensor. The present invention further provides a sodium ion sensor in which the sodium ion selective membrane is a polymeric membrane carrying a sodium ion carrier material. DETAILED DESCRIPTION OF THE INVENTION The conductive substrate used in the sodium ion sensor of the present invention is, for example, basal plain pyrolitic graphite (basal plain pyrolitic graphite).
plane pyrolytic graphite (hereinafter referred to as BPG),
Examples include conductive carbon materials such as glassy carbon, noble metals that undergo redox reactions in solution, and materials whose surfaces are coated with semiconductors such as indium oxide and tin oxide. Among these, conductive carbon materials are preferred, and BPG is particularly preferred. In addition, membranes with reversible redox functions (hereinafter referred to as
A redox film (sometimes referred to as a redox film) refers to an electrode formed by adhering this film to the surface of a conductive substrate, which can generate a constant potential on the conductive substrate through a reversible redox reaction. In particular, it is preferable that the potential does not vary depending on the oxygen gas partial pressure. Examples of such a redox film include, for example, an organic compound film or a polymer film capable of carrying out a quinone-hydroquinone type redox reaction, an organic compound film or a polymer film capable of carrying out an amine-quinoid type redox reaction. Suitable examples include membranes and the like. Here, the quinone-hydroquinone type redox reaction refers to, for example, one expressed by the following reaction formula, taking the case of a polymer as an example. (In the formula, R ¹ and R ² represent, for example, a compound with an aromatic-containing structure.) In addition, the amine-quinoid type redox reaction is the same as above, taking the case of a polymer as an example.
For example, it refers to the reaction represented by the following reaction formula. (-N= ^R3 )= _o1 N-〓〓〓〓〓
〓(−NH−R ⁴ )− _o1 NH− (In the formula, R ³ and R ⁴ represent, for example, a compound having an aromatic-containing structure) Compounds that can form a film having such a reversible redox function include: Examples include the following compounds (a) to (c). (a) (In the formula, Ar ₁ is an aromatic nucleus, each R ⁵ is a substituent, m ₂ is 1 to the effective valence number of Ar ₁ , and n ₂ is 0 to
The aromatic nucleus of Ar ₁ is a monocyclic one such _as a benzene nucleus, anthracene nucleus, pyrene nucleus, chrysene nucleus, It may be a polycyclic nucleus such as a perylene nucleus or a coronene nucleus, and it may be not only a benzene nucleus but also a heterocyclic nucleus. Examples of the substituent R ⁵ include an alkyl group such as a methyl group, an aryl group such as a phenyl group,
and halogen atoms. Specifically, for example, dimethylphenol, phenol,
Hydroxypyridine, o- or m-benzyl alcohol, o-, m- or p-hydroxybenzaldehyde, o- or m-hydroxyacetophenone, o-, m- or p-hydroxypropiophenone, o-, m- or p-
benzophenol, o-, m- or p-hydroxybenzophenone, o-, m- or p-
Carboxyphenol, diphenylphenol, 2-methyl-8-hydroxyquinoline, 5
-Hydroxy-1,4-naphthoquinone, 4-
(p-hydroxyphenyl)2-butanone, 1,
5-dihydroxy-1,2,3,4-tetrahydronaphthalene, bisphenol A, salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8-hydroxyanthraquinone, 5-hydroxy-1,4-naphthoquinone, etc. can be mentioned. (b) The following formula (In the formula, Ar ₂ is an aromatic nucleus, each R ⁶ is a substituent, m ₃ is 1 to the effective valence number of Ar ₂ , and n ₃ is 0 to
The aromatic nucleus of _{Ar 2 and} substituent R ⁶ are the same as Ar ₁ and substituent R ⁵ in compound (a), respectively. be done. Specific examples of amino aromatic compounds include aniline, 1,2-diaminobenzene, aminopyrene, diaminopyrene, aminochrysene, diaminochrysene, 1-aminophenanthrene, 9-aminophenanthrene, 9,10-diamino Phenanthrene, 1-aminoanthraquinone, p-phenoxyaniline, o-phenylenediamine, p-chloroaniline, 3,5-dichloroaniline, 2,4,6-trichloroaniline, N-methylaniline, N- phenyl-p
-phenylenediamine, etc. (c) Quinones such as 1,6-pyrenequinone, 1,2,5,8-tetrahydroxynarizalin, phenanthrenequinone, 1-aminoanthraquinone, purpurin, 1-amino-4-hydroxyanthraquinone, anthralfin, etc. Of these compounds, 2,6-xylenol and 1-aminopyrene are particularly preferred. Further, as compounds capable of forming the redox film according to the present invention, (d) poly(N-methylaniline) [Onuki, Matsuda,
Koyama, Journal of the Chemical Society of Japan, 1801-1809 (1984)], poly(2,6-dimethyl-1,4-phenylene ether), poly(o-phenylene diamine), poly(phenol), polyxylenol; pyrazoquinone series (a) to (c) such as quinone-based vinyl polymer condensation compounds such as vinyl monomer polymers and isoalloxazine-based vinyl monomer polymers;
An organic compound containing the compound of (a) to (c), a low polymerization degree polymer compound (oligomer) of the compound (a) to (c), or (a) to (c) fixed to a polymer compound such as a polyvinyl compound or a polyamide compound. Examples include those having the redox reactivity such as.
In this specification, the term polymer includes both homopolymers and interpolymers such as copolymers. In the present invention, in order to deposit a compound capable of forming the above-mentioned redox film on the surface of a conductive substrate, an amino aromatic compound, a hydroxy aromatic compound, etc. are applied by an electrolytic oxidation polymerization method or an electrolytic deposition method. Therefore, by directly polymerizing on the substrate surface, or by applying electron beam irradiation, light, heat, etc., a pre-synthesized polymer is dissolved in a solvent, and this solution is fixed to the substrate surface by dipping/coating and drying. Alternatively, a method of directly fixing the polymer film to the substrate surface by chemical treatment, physical treatment, or irradiation treatment can be adopted. Among these methods, electrolytic oxidative polymerization is particularly preferred. In the present invention, the electrolytic oxidative polymerization method involves electrolytically oxidizing and polymerizing amino aromatic compounds, hydroxy aromatic compounds, etc. in a solvent in the presence of an appropriate supporting electrolyte to deposit a polymer film on the surface of a conductor. Implemented. Examples of the solvent include acetonitrile, water, dimethylformamide, dimethyl sulfoxide, propylene carbonate, etc., and examples of the supporting electrolyte include sodium perchlorate, sulfuric acid, disodium sulfate, phosphoric acid, boric acid, potassium tetrafluorophosphate, Preferred examples include quaternary ammonium salts. The polymer films deposited in this manner are generally very dense, and even thin films can prevent the permeation of oxygen.
However, in order to achieve the effects of the present invention, the redox film is not particularly limited as long as it has the redox reactivity, and it does not matter how dense the film is. The thickness of the redox film is preferably 0.1 μm to 0.5 mm. If it is thinner than 0.1μm,
If the film is thicker than 0.5 mm, the effect of the present invention will not be sufficiently achieved, and the film resistance will increase, which is not preferable. Further, the redox membrane used in the present invention can be used by impregnating it with an electrolyte. Examples of the electrolyte include phosphoric acid, dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoroborate, and tetraphenylborate. A simple method for impregnating the redox membrane with an electrolyte is to attach the redox membrane to a conductive substrate and then immerse it in an electrolyte solution. The sodium ion-selective membrane deposited over the surface of the redox membrane deposited on the conductive substrate as described above is made by, for example, carrying a sodium ion carrier material and an electrolyte salt on a polymer compound. A membrane is used. The sodium ion carrier material is not particularly limited as long as it can selectively transport sodium ions, but aromatic amides or diamides, aliphatic amides or diamides, crown compounds, e.g. Bis[(12-crown-4)methyl] dodecyl malonate,
N,N,N,N-tetrapropyl-3,6-dioxanate diamide, N,N,N',N'-tetrabenzyl-1,2-ethylenedioxydiacetamide, N,N'-dibenzyl-N, N'-diphenyl-1,2-phenylene diacetamide, N,
N',N''-triheptyl-N,N',N''-trimethyl-4,4',4''-prepyridine tris(3-oxbutylamide), 3-methoxy-N,N,N,
N-tetrapropyl-1,2-phenylenedioxydiacetamide, (-)-(R,R)-4,5-dimethyl-N,N,N,N-tetrapropyl-3,
6-dioxaoctane, diamide, 4-methyl-
N,N,N,N-tetrapropyl-3,6-dioxaoctane diamide, N,N,N,N-tetrapropyl-1,2-phenylenedioxydiacetamide, N,N,N,N- Tetrapropyl
2,3-naphthalenedioxydiacetamide, 4
-t-Butyl-N,N,N,N-tetrapropyl-1,2-cyclohexanedioxy-diacetamide, cis-N,N,N,N-tetrapropyl-
1,2-cyclohexanedioxydiacetamide, trans-N,N,N,N-tetrapropyl-1,2-cyclohexanedioxydiacetamide, etc., among others, bis[(12-crown-4) Methyl] dodecyl malonate is preferably used. Examples of electrolyte salts include sodium tetrakis(p-chlorophenyl)borate, potassium tetrakis(p-chlorophenyl)borate, and the following formula R' ₄ NBF ₄ (wherein R' is an alkyl group, preferably a carbon atom having 2 carbon atoms).
~6 alkyl group). Further, examples of the polymer compound include vinyl chloride resin, vinyl chloride-ethylene copolymer, polyester, polyacrylamide, polyurethane, silicone resin, etc., and those from which plasticizers do not easily elute are used. Examples of such plasticizers include dioctyl sebacate, dioctyl adipate, dioctyl maleate, and the like. Moreover, tetrahydrofuran is preferably used as the solvent. In order to attach a sodium ion selective membrane to the surface of a redox membrane, for example, a polymer compound as a carrier is used.
A base electrode (in this case, a redox membrane) is added to a solution containing 50 to 500 parts by weight of a plasticizer, 0.1 to 50 parts by weight of a sodium ion carrier material, and an electrolyte salt in a solvent (e.g., tetrahydrofuran) per 100 parts by weight. It is preferable to repeat dipping, pulling up, air-drying and drying (80 DEG C., 3 minutes) about 30 times to obtain a carrier film thickness of 50 .mu.m to 3 mm, particularly 0.3 mm to 2 mm. Alternatively, paste vinyl chloride, sodium ion carrier material, plasticizer, electrolyte salt are mixed in the above weight ratio, and then placed on the base electrode to a thickness of 50 μm to 3 mm.
A sodium ion carrier film can also be obtained by heat treatment at 160° C. for 1 minute to form a gel. Traditionally, membranes used for ion-selective electrodes are
Although the sodium ion sensor of the present invention is generally made of a thin film in order to reduce the membrane resistance, it is not necessarily necessary to use a thin film, and as mentioned above, the film can be made as thick as about 1 to 3 mm. This is thought to be based on the unique configuration of the sensor of the present invention, but is surprising. Furthermore, the sodium ion selective membrane used in the present invention can effectively prevent the influence of dissolved oxygen and other coexisting substances in the test liquid. To measure the sodium ion concentration of a test liquid using the sodium ion sensor of the present invention, as shown in FIG. The sodium ion sensor 23 of the present invention and a silver-silver chloride electrode or a calomel electrode as the reference electrode 24 are immersed in the solution. Then, the potential difference (electromotive force) of the sodium ion sensor 23 with respect to the reference electrode 24 is measured by the potentiometer 26. At this time, it is preferable to stir the test liquid 22 with a stirrer 25. The sodium ion concentration of the test liquid is read from a calibration curve of electromotive force and sodium ion concentration prepared in advance. [Example] Next, an example will be given and explained. Example 1 A sodium ion sensor shown in FIG. 1 was produced by the following method. (i) Basal plain pyrolitic graphite (BPG) (manufactured by Union Carbide)
After cutting out a cylinder with a diameter of 5 mm from the plate, conductive adhesive (manufactured by Amicon, Inc.,
C-850-6) to which the lead wire 16 was connected, and a heat-shrinkable tube (manufactured by Alpha Wire Co., Ltd.) so that the top surface 11a of the BPG slightly protrudes.
It was covered and insulated. The protruding tip of the BPG substrate thus prepared was peeled off with a knife blade to expose a new surface. Next, using this as a working electrode, electrode oxidation was performed under the following conditions using a saturated sodium chloride calomel electrode (SSCE) as a reference electrode and a platinum mesh as a counter electrode. Electrolyte: Sodium perchlorate 0.2M as supporting electrolyte
and 2,6-xylenol as reactant
Acetonitrile contained in a proportion of 0.5M. Electrolysis conditions: After sweeping the electrolytic potential from 0 volts to 1.5 volts three times (sweep speed 50 millivolts/second),
Potential electrolysis for 10 minutes at 1.5 volts. In this way, 2,6-
Xylenol electrolytic oxidation polymer membrane (thickness approx. 30μ)
m) was formed. This electrolytically oxidized polymer film was dark blue. (ii) The electrode coated with the electrolytic oxidative polymer membrane prepared in (i) above was washed with water and then dried, then immersed in a solution containing a sodium ion carrier substance with the following composition, dried, and then coated on the electrolytic oxidative polymeric membrane. A sodium ion selective membrane 14 was deposited. The dipping and drying operations were repeated 30 times to form a sodium ion selective membrane with a thickness of about 0.3 mm. Immersion liquid composition: Bis[(12-crown-4)methyl]dodecylmalonate 20.7mg Potassium tetrakis(p-chlorophenyl)borate 4.5mg Polyvinyl chloride (average degree of polymerization 1050) 270.3mg Di(2-ethylhexyl sebacate) 536.9 mg Tetrahydrofuran 10ml The thus prepared sensor was thoroughly dried and then immersed in a 1mM sodium chloride aqueous solution for 2 hours before being used in subsequent experiments. Experimental Example 1 The responsiveness of the sodium ion sensor prepared in Example 1 to sodium ions was evaluated by dipping the sensor into a 8×10 ^-4 to 3×10 ^-1 M sodium chloride solution.
This was investigated by immersing the sensor in SSCE and measuring the electromotive force of the sensor. Note that the measurements were performed at 37°C. The results are shown in FIG. As is clear from FIG. 2, the electromotive force showed a good linear relationship at a sodium ion concentration of 8×10 ⁻⁴ to 3×10 ⁻¹ M. Furthermore, in the electromotive force measurement at each concentration, the time it took for the sensor to reach 95% of the equilibrium potential (95% response time) was within 1 minute. Experimental Example 2 In order to investigate the influence of dissolved oxygen on the electromotive force of the sodium ion sensor produced in Example 1, pure nitrogen gas (flow rate of 100 ml/min) was blown into the measurement aqueous solution of Experimental Example 1 for 3 hours. Oxygen gas (flow rate 100
The difference in electromotive force was measured when 5 hours of blowing (milliliter/min) was carried out. Note that, as in Experimental Example 1, the measurement was performed after immersing the sensor and SSCE in the same solution to sufficiently saturate the film with dissolved gas. As a result, it was found that the difference in electromotive force was within ±2 mV, and the sensor of the present invention was able to measure the sodium ion concentration without being affected by dissolved oxygen in the measurement solution. Experimental Example 3 The sodium ion selectivity of the sodium ion sensor produced in Example 1 was evaluated by determining the selectivity coefficient K ^Pet _NaM for the cation species (M) shown in Table 1 below for sodium ions. The measurements were carried out using the so-called mixed method. That is, while keeping the sodium ion concentration at 1mM,
This was done by determining the change in electromotive force when the concentration of the cationic species was changed. Note that the measurements were performed at 25°C. The results are shown in Table 1.

[Table] From Table 1, for example, the concentration of potassium ions in body fluids of normal people is 3 to 4.7×10 ^-3 M, so the sensor of the present invention can selectively measure the concentration of sodium ions in body fluids. I found out. Specific Effects of the Invention The sodium ion sensor of the present invention is (i) solid-state, does not require an internal liquid chamber, can be miniaturized, and can be used for in situ measurements of biological solutions. (ii) It is less susceptible to the effects of various coexisting substances, including dissolved oxygen in the test solution, and can be used regardless of the type of test solution. (iii) 95% response is as short as about 1 minute, allowing for rapid measurement. (iv) It has excellent stability over time and enables measurements with good reproducibility over a long period of time. (v) It has various practical advantages, such as the ability to easily produce multiple sensors with the same characteristics.

[Brief explanation of drawings]

FIG. 1 shows an enlarged cross-sectional explanatory view of the sodium ion sensor of the present invention. FIG. 2 is a drawing showing the relationship between the electromotive force and the sodium ion concentration of the sodium ion sensor of the present invention. FIG. 3 is a schematic diagram showing an example of a method for measuring sodium ion concentration using the sodium ion sensor of the present invention. 11... BPG, 11a... Top surface, 11b...
Bottom part, 12... Insulator, 13... Electrolytic oxidation polymer membrane, 14... Sodium ion selective membrane, 15...
... Conductive adhesive, 16 ... Lead, 21 ... Tank,
22... Test liquid, 23... Sodium ion sensor, 24... Reference electrode, 25... Stirrer, 26
...Potentiometer.

Claims (1)

[Scope of Claims] 1. A sodium ion sensor that measures the concentration of sodium ions in a solution based on electrode potential response, which comprises a film having a reversible redox function deposited on the surface of a conductive substrate, and the film has a reversible redox function. A sodium ion sensor comprising a sodium ion selective membrane adhered to the surface of a sodium ion sensor. 2. The sodium ion sensor according to claim 1, wherein the sodium ion selective membrane is a polymer membrane carrying a sodium ion carrier substance.