JPH0362226B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnesium ion sensor, and more particularly to a solid-state magnesium ion sensor without an internal (standard) solution.

[Conventional technology and its problems]

Conventionally, an ion-selective electrode has been used as a sensor for measuring the magnesium ion concentration in a solution based on electrode potential response. Ion-selective electrodes are classified into two types based on their internal structures: (1) those that incorporate an ion-selective membrane, an internal (standard) solution, and an internal reference electrode immersed in the solution (barrel-type liquid membrane type);
(2) It can be broadly classified into membrane structures in which an ion-selective membrane is directly attached to a conductive substrate (membrane coating type).

Wilhelm. W.Simon et al. (1)
reported on a magnesium ion sensor using a barrel-type liquid membrane type membrane containing a carrier compound that exhibits selectivity for magnesium ions as a magnesium ion-selective membrane [Analytical Chemistry]
Chemistry) 52 , 2400-2402 (1980); Helvetica Himica Acta (Helv.Chim.Acta) 63 ,
2271-2279 (1980)].

However, since the barrel-type liquid film type electrode (1) has an internal liquid and an internal liquid chamber, it has the disadvantage that it is generally difficult to miniaturize. On the other hand, the membrane-coated electrode (2), which is thought to be possible to miniaturize, is unknown as far as magnesium ion sensors are concerned.

[Means for solving problems]

As a result of intensive research on solid-state magnesium ion sensors that do not have an internal liquid or an internal liquid chamber, the present inventors discovered a type (2) in which a magnesium ion selective membrane is directly adhered to the surface of a conductive substrate. In order to obtain the ion selectivity required for practical use, electrodes must have a large film thickness, and are unsatisfactory in terms of slow response speed, susceptibility to the effects of dissolved oxygen in the solution, etc. It became clear. After conducting further research, we found that it is possible to downsize the conductive substrate by coating it with a membrane that has a reversible redox function instead of directly attaching the ion-selective membrane to the conductive substrate. The present invention has been completed based on the discovery that a magnesium sensor with excellent sensor characteristics without any oxidation can be obtained.

That is, the present invention is a magnesium ion sensor that includes a magnesium ion sensitive part and measures the magnesium ion concentration in a solution by electrode potential response, and the magnesium ion sensitive part has a reversible redox function on the surface of a conductive substrate. This is a magnesium ion sensor characterized by comprising a coating having the above-mentioned properties, and further comprising a magnesium ion-selective membrane adhered to the entire surface of the coating and beyond the coating. The magnesium ion selective membrane is a polymer membrane carrying a magnesium ion carrier material.

As the conductive substrate used in the magnesium ion sensor of the present invention, 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 or the effective valence number of Ar ₁ , n ₂ is 0 or
A hydroxy aromatic compound represented by (representing the effective valence number of Ar ₁ -1).

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 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-
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-dihydroxy-1,2,3,4-tetrahydronaphthalene, bisphenol A, salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8-dihydroxyanthraquinone, 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 , 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 oxidative 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 0.1 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 magnesium ion-selective membrane deposited on the surface of the redox membrane deposited on the conductive substrate as described above may be formed by, for example, carrying a magnesium ion carrier material and an electrolyte salt on a polymer compound. A different membrane is used.

As a magnesium ion carrier material,
There is no particular restriction as long as it is a substance that can selectively transport magnesium ions, for example, the following formula N,N'-diheptyl-N,N'-dimethyl-1,4-butanediamide represented by the following formula N,N'-diheptyl-N,N'-dimethylmalonamide, represented by the following formula: 2-ethyl-N,N'-diheptyl-N,N'-dimethylmalonamide, represented by the following formula: (In the formula, R ⁷ and R ⁸ each represent H, Cl, F or Br.) For example, 1,3-diphenyl-1,3-propanediol, 1-phenyl-3
-(p-chlorophenyl)-1,3-propanediol and the like.

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 a magnesium 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 redox film-covered electrode) is immersed in a solution containing electrolyte salt, etc. dissolved in a solvent (e.g., tetrahydrofuran), pulled up, air-dried, and dried repeatedly to obtain a carrier film thickness of 50 μm or more.
The thickness is preferably 3 mm, particularly 0.3 mm to 2 mm. Alternatively, after mixing the paste vinyl chloride, magnesium ion carrier material plasticizer electrolyte salt in the above weight ratio, apply a thick layer onto the base electrode.
A magnesium ion carrier film can also be obtained by placing the film to a thickness of 50 μm to 3 mm and heating it at 150° C. for 1 minute to gel.

〔Effect of the invention〕

As described above, the present invention is a magnesium ion sensor composed of two layers in which a magnesium ion selective membrane is coated on the surface of a redox membrane. Compared to 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 high potential responsiveness. The electrode potential is stable and the magnesium ion concentration can be measured with high accuracy.

(ii) In addition, compared to a coated wire type magnesium ion sensor with an ion-selective membrane directly attached, it is less susceptible to the effects of various coexisting substances such as dissolved oxygen in the sample solution, has good magnesium ion selectivity, and It can be used regardless of the type of liquid, has a fast response speed, and has excellent stability over time.

Furthermore, (iii) the structure of the electrode is simple, so it can be manufactured in large quantities.

It has various features such as

〔Example〕

Next, examples and test examples will be given and explained.

Example 1 A magnesium 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 Pyrolithic Graphite (BPG, manufactured by Union Carbide), conductive adhesive (C-850-6 manufactured by Amicon) was applied to the bottom surface 11a. ) 18 using lead wire 12
(Teflon-coated copper wire) and connect it to a cylindrical shape using 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.
The surrounding area was covered and insulated so that 1.5 mm of BPG11 was exposed. Furthermore, the exposed tip portion 11b of the BPG 11
was cut into a hemispherical shape, and the hemispherical surface and the side surface of the BPG cylinder were polished with sandpaper (#2000).

A three-electrode cell was constructed with the thus prepared BPG electrode as the working electrode, a saturated sodium chloride calomel electrode (SSCE) as the reference electrode, and a platinum cell as the 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, dried, and further coated with a magnesium ion carrier film 16. The magnesium ion carrier film 16 was formed by repeating dipping and drying three times using a constant speed elevator.
The film thickness is 0.3 mm at the tip part 11b of the electrode, and the film thickness at the side part 1
A 0.5 mm film was formed using 1c.

(Immersion liquid composition) N,N'-diheptyl-N,N'-dimethyl-1,
4-Butanediamide (manufactured by Fluka) 25mg Potassium tetrakis(p-chlorophenyl)borate 5mg Polyvinyl chloride (average degree of polymerization 1050) 323mg Dioctyl sebacate 647mg Tetrahydrofuran (solvent) 4ml The magnesium ion sensor thus prepared was thoroughly dried. Thereafter, it was immersed in a 1mM magnesium chloride (MgCl ₂ .6H ₂ O) solution for about 12 hours, and then used in the next experiment.

Test Example 1 The magnesium ion sensor of the present invention prepared in Example 1 and SSCE as a reference electrode were immersed in a 1mM magnesium chloride solution, and 1M magnesium chloride solution was added to increase the magnesium ion concentration. Power measurements were made at a temperature of 36.8°C. The measurement results are shown in Figure 2. The relationship between the measured electromotive force and the magnesium ion concentration shows a linear relationship in the range of 10 ^-3 to 10 ^-1 , and the slope is 29.8 mV/log [MG ₂ ⁺ ],
A response according to the Nernst equation was obtained.

Next, the influence of selectivity with cations was investigated. The value obtained by taking the common logarithm of the selection coefficient is logK ^pot _Mg for potassium ion.

Claims (1)

[Scope of Claims] 1. A magnesium ion sensor that includes a magnesium ion sensitive part and measures the magnesium ion concentration in a solution by electrode potential response, wherein the magnesium ion sensitive part has a reversible oxidation-reduction effect on the surface of a conductive substrate. A magnesium ion sensor comprising a functional coating and further comprising a magnesium ion selective membrane on the entire surface of the coating and over the coating. 2. The magnesium ion sensor according to claim 1, wherein the magnesium ion selective membrane is a polymer membrane supporting a magnesium ion carrier material.