JPH0362225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ammonium ion sensor, and more particularly to a solid-state ammonium ion sensor having no internal liquid or internal liquid chamber.

[Conventional technology and its problems]

Conventionally, ammonium ion sensors include: (1) those that incorporate an ion-selective membrane, an internal (standard) liquid, and an internal reference electrode immersed in the internal liquid (barrel-type liquid membrane electrode type); and (2) ion sensors. Membrane electrodes (covered wire electrode type) in which a selective membrane is directly adhered to a conductive substrate are known.

As electrodes of type (1), Beckman No. 39626 and No. 39137 electrodes and Philips TS560-NH ₄ ⁺ electrodes are commercially available. Also, Wilhelm. Simon (W.Simon) etc. is the following formula () reported a barrel-type liquid film electrode using nonactin expressed as an ammonium ion carrier [Chimia 24 , 372-374]
(1970)].

However, since the electrode of type (1) has an internal liquid and an internal liquid chamber, it is difficult to miniaturize it, and there is a risk of internal liquid leaking during use.
Its uses were limited.

In addition, type (2) of electrodes has been reported;
The interference caused by K ⁺ and Na ⁺ was significant, and the result was not satisfactory for practical purposes [Review, Roumain et al.
Revue Roumaine de Chimie 20 ,
863 (1975)].

[Means for solving problems]

In order to solve the above-mentioned problems, the present inventor conducted intensive research on the type (2) of electrodes that can be miniaturized, and found that a reversible electrode without directly attaching an ammonium ion-selective membrane to a conductive substrate. The present invention was completed based on the discovery that an electrode formed by adhering a membrane with an oxidation-reduction function has extremely excellent sensor properties such as high ion selectivity and quick response.

That is, the present invention provides an ammonium ion sensor that includes an ammonium ion sensitive part and measures the ammonium ion concentration in a solution by electrode potential response, and the ammonium ion sensitive part includes a conductive substrate and a conductive substrate that covers the conductive substrate. This is an ammonium ion sensor characterized by comprising a coating having a reversible redox function and an ammonium ion selective membrane covering the coating. The ammonium ion selective membrane is a polymeric membrane loaded with an ammonium ion carrier material.

The conductive substrate used in the ammonium ion sensitive portion of the present invention may be rod-shaped, tubular, syringe-needle shaped, or the substrate surface is conductive and there is no internal liquid. For example, basal plain pyrolitic graphite (basal
plane pyrolytic graphite (hereinafter referred to as BPG),
Conductive carbon materials such as glassy carbon; metals such as gold, platinum, copper, silver, and palladium, particularly noble metals, or 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
An oxidation-reduction 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 oxidation-reduction reaction. It is preferable that the potential does not vary depending on the gas partial pressure. Examples of such a redox film include an organic compound film or polymer film capable of performing a quinone-hydroquinone type redox reaction, an organic compound or polymer film capable of performing an amine-quinoid type redox reaction, etc. are preferred.
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, for example, the following reaction formula, taking the case of a polymer as described above. refers to something expressed as

(−N=R ³ =)N−+H ⁺ ,+e ^- ――――――→ ←――――――― (−NH−R ⁴ ))− _o1 NH− (In the formula, R ³ , R ⁴ represents, for example, a compound having an aromatic-containing structure.) Examples of compounds that can form a film having such a reversible redox function include the following compounds (a) to (c).

(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 Ar ₁
(indicating the effective valence number -1) A hydroxy aromatic compound represented by:

The aromatic nucleus of Ar ₁ may be a monocyclic one such as a benzene nucleus, or a polycyclic one such as an anthracene nucleus, a pyrene nucleus, a chrysene nucleus, a perylene nucleus, a coronene nucleus, etc. Moreover, not only a benzene bone nucleus but also a heterocyclic bone nucleus may be used.
Examples of the substituent R ⁵ include an alkyl group such as a methyl group, an aryl group such as a phenyl group, and a halogen atom. 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-benzylphenol, 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- Examples include dihydroxy-1,2,3,4-tetrahydronaphthalene, bisphenol A, salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8-dihydroxyanthraquinone, 5-hydroxy-1,4-naphthoquinone, etc. .

(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 , n ₃ is 0 to
An amino aromatic compound represented by (representing the effective valence number of Ar ₂ -1).

As the aromatic nucleus of Ar ₂ and the substituent R ⁶ , the same ones as Ar ₁ and the substituent R ⁵ in compound (a) are used, respectively. 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. kind.

Among 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. Note that 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 direct polymerization 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 0.1 μm, the effects of the present invention will not be sufficiently achieved, and if it is thicker than 0.5 mm, the membrane 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 ammonium ion-selective membrane deposited over the surface of the redox membrane deposited on the conductive substrate as described above is made of, for example, an ammonium ion carrier material and an electrolyte salt supported on a polymer compound. A membrane is used.

As an ammonium ion carrier material,
There is no particular restriction as long as it is a substance that can selectively transport ammonium ions, such as nonactin shown by the above formula () and the following formula Examples include tetranactin represented by: These can be used alone or in combination of two or more.

Examples of electrolyte salts include sodium tetrakis(p-chlorophenyl)borate, potassium tetrakis(p-chlorophenyl)borate, and compounds of the following formula R ₄ 'NBF ₄ (wherein R' ₄ is an alkyl group, preferably having 2 to 6 carbon atoms). (indicates an 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, di-n-octylphenylphosphonate, and the like. Moreover, tetrahydrofuran is preferably used as the solvent.

In order to deposit an ammonium ion selective membrane on the surface of a redox membrane, for example, 50 to 500 parts by weight of a plasticizer and 0.1 to 50 parts by weight of an ammonium ion carrier material are added to 100 parts by weight of a polymer compound as a carrier. The base electrode (in this case, the electrode coated with the redox film) is immersed in a solution containing electrolyte salt and the like dissolved in a solvent (e.g., tetrahydrofuran), pulled up, air-dried, and dried repeatedly to form an ammonium ion carrier film with a thickness of 50 μm to 3 mm, especially It is preferable that the thickness be 0.3 mm to 2 mm. Alternatively, paste vinyl chloride, ammonium 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.
An ammonium ion carrier film can also be obtained by heat treatment at 150° C. for 1 minute to form a gel. For example, when the ammonium ion selective membrane deposited in this way has a thickness of 1 mm, at 25°C,
It has a resistance of 10 ³ to 10 ⁶ Ω/cm ² . In addition, the influence of dissolved oxygen and other coexisting substances in the test liquid can be effectively prevented.

〔Effect of the invention〕

As described above, the present invention is a solid-state ammonium ion sensor composed of two layers in which an ammonium ion selective membrane is coated on the surface of a redox membrane. Compared to ammonium ion sensors, the redox membrane acts as an internal liquid and a reference electrode, so it does not require an internal liquid, so it can be made smaller, is safe without liquid leakage or damage, and has a potential response. (ii) In addition, compared to a coated wire type ammonium ion sensor with an ion-selective membrane directly attached, it is possible to measure ammonium ion concentration with high accuracy, with a stable electrode potential. It is less affected by coexisting substances, has good ammonium ion selectivity, can be used regardless of the type of test liquid, has a fast response speed, and has excellent stability over time. It has various features such as a simple structure and the ability to manufacture in large quantities.

〔Example〕

Next, an example will be given and explained.

Example 1 The ammonium ion sensor shown in FIG. 1 was produced by the following method.

After cutting out a cylindrical BPG11 with a diameter of 1.1 mm from a board of Basal Plain Pyrolitic Graphite (BPG, manufactured by Union Carbide), conductive adhesive (C850-6, manufactured by Amicon) was applied to the bottom surface 11a. 18 using the lead wire 12
(Teflon-coated copper wire) and connect it with a Teflon tube (inner diameter 1.7 mm, outer diameter 2.1 mm) 13 and a heat shrink tube (manufactured by Alpha Wire Co., Ltd.) 14 so that the cylindrical BPG 11 is exposed by 1.5 mm. Covered and insulated. In order to produce an ammonium ion sensitive part, the exposed tip 11b of the BPG 11 was shaved into a hemispherical shape, and the hemispherical surface and the side surface of the BPG cylinder were polished with #2000 sandpaper. Made like this
A three-electrode cell was constructed with a BPG electrode as a working electrode, a saturated sodium chloride calomel electrode (SSCE) as a reference electrode, and a platinum cell as a counter electrode, and an electrolytic oxidative polymerization reaction was carried out under the conditions shown below.

(Electrolyte) 0.5M 2,6-xylenol 0.2M Sodium perchlorate Solvent: Acetonitrile (Electrolytic conditions) After sweeping the potential of the working electrode from 0V to 1.5V three times (50mV/sec) with respect to SSCE, 1.5V vs. SSCE
Potential electrolysis was carried out for 10 minutes.

In this way, 2,6
- An oxidized polymer film 15 of xylenol was coated to a thickness of about 30 μm. This membrane electrode was washed with acetonitrile solvent to remove unreacted 2,6-xylenol, washed with water and dried, and then an ammonium ion carrier film 16 was coated thereon. The ammonium ion carrier film 16 was deposited by dipping the membrane at a constant speed using an elevator into an immersion solution containing an ammonium ion carrier material and having the composition shown below, followed by drying. The dipping and drying operations were repeated three times, and the film thickness was 0.3 mm at the tip portion 11b and 0.3 mm at the side portion 11b.
A 0.5 mm film was formed using c.

(Immersion liquid composition) Nonactin (25% monactin content) 6.25mg/ml Potassium tetrakis(p-chlorophenyl)borate 1.25mg/ml Polyvinyl chloride (average degree of polymerization 1050) 80.8mg/ml Dioctyl sebacate 161.8mg/ml Tetrahydrofuran (Solvent) The ammonium ion sensitive part thus prepared was thoroughly dried and then immersed in a 1mM ammonium chloride solution for about 12 hours before being used in the next experiment.

Test Example 1 The ammonium ion sensor of the present invention prepared in Example 1 and SSCE as a reference electrode were immersed in a 1mM ammonium chloride solution, and 1M ammonium chloride solution was added to increase the electromotive force while increasing the ammonium ion concentration. The measurements were carried out at a temperature of 36.8°C. The measurement results are shown in Figure 2.

The relationship between the measured electromotive force E (mV) and ammonium ion concentration shows a linear relationship in the range of 10 ^-3 to 10 ^-1 , and the slope is 60.0 mV/log [NH ₄ ⁺ ]
A response according to Nernst's equation was obtained (E=638.4+60.0lcg [NH ₄ ⁺ ]).

Next, selectivity for cations was investigated. The selectivity coefficient for sodium ion is K ^Pot _NH4

Claims (1)

[Scope of Claims] 1. An ammonium ion sensor comprising an ammonium ion sensitive part and measuring the ammonium ion concentration in a solution by electrode potential response, the ammonium ion sensitive part comprising a conductive substrate and a conductive substrate. An ammonium ion sensor comprising a coating having a reversible redox function and an ammonium ion selective membrane covering the coating. 2. The ammonium ion sensor according to claim 1, wherein the ammonium ion selective membrane is a polymer membrane carrying an ammonium ion carrier substance.