JPH08327584A - Ion-selective electrode and method for measuring ion concentration - Google Patents

Abstract

PURPOSE: To measure ion concentrations precisely and easily by using an ion- selective electrode that shows stable potential over a long period because it has an oxidation reduction layer and that can be manufactured easily because the oxidation reduction layer is made up of a self-forming monomolecular film. CONSTITUTION: This ion-selective electrode comprises a metallic electrode layer made of gold, silver or copper metal, an oxidation reduction layer composed of a monomolecular film layer made from a ferrocene group coupled via a group that can be coupled with the metallic electrode layer, and an ion-sensitive film layer which reacts selectively to sodiumion ion, potassium ion, chloride ion, with all of the layers stacked one after another in that order. This method for measuring the concentration of ions in a sample solution uses the same.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an ion-selective electrode for measuring the concentration of ions in a solution. Specifically, it is an ion-selective electrode having a simple structure and excellent potential stability, and an ion concentration measuring method using the same.

[0002]

2. Description of the Related Art Recently, attempts have been made to apply ion-selective electrodes for medical purposes to quantify ions dissolved in biological fluids such as blood and urine, such as sodium ions, potassium ions and chlorine ions. Has been done in. This is because, by measuring the specific ion concentration in a biological fluid based on the fact that the specific ion concentration is closely related to the metabolic reaction of the living body, various types of hypertension, heart disease, kidney disease, neuropathy, etc. A diagnosis is made.

In general, an ion-selective electrode is a cylindrical container 1 having an ion-sensitive film 12 as a boundary film provided in a portion (generally a bottom portion) immersed in a sample solution as shown in FIG.
1 is basically configured by providing an internal electrolytic solution 13 and an internal reference electrode 14. A typical structure of an ion measuring device for measuring the concentration of ions in a solution using such an ion selective electrode is shown in FIG. That is, the ion-selective electrode 21 is immersed in the sample solution 23 together with the salt bridge 22, and the other end of the salt bridge is immersed in the saturated potassium chloride solution 26 together with the reference electrode 24. The potential difference between both electrodes is read by the electrometer 25, and the ion concentration of the specific ion species in the sample solution can be determined from the potential difference.

The times are changing from heavy and heavy to light, thin, short and small. This trend also affects the development trend of measuring instruments, and a great deal of effort is put into reducing the size and weight while maintaining the functional performance. The recent launch of highly sensitive and miniaturized analytical instruments is the result of these efforts, and has contributed greatly to saving the space occupied by the instruments in the analytical laboratory. The same applies to the ion-selective electrode, and there is a demand for miniaturization in order to reduce the space occupied by the equipment, the amount of sample, and the amount of waste liquid after measurement.

The above-mentioned ion-selective electrode that has been conventionally used requires an internal electrolytic solution, and when downsizing the ion-selective electrode: Since a liquid is used, a certain amount or more of a container is required.

If the amount is reduced, performance deterioration due to evaporation of the solvent becomes a problem.

It has been pointed out that there are problems such as structural restrictions for ensuring reliable contact between the internal reference electrode / internal electrolyte / ion-sensitive membrane. Further, the ion-selective electrode having the internal electrolyte solution has a problem that the manufacturing process is very complicated and automation of the manufacturing is difficult and the cost is high.

In recent years, in order to solve such problems, there has been proposed an ion-selective electrode having no internal electrolytic solution, that is, having an ion-sensitive membrane in direct contact with an internal reference electrode. Examples of the internal reference electrode of the ion-selective electrode without the internal liquid include (a) metal electrode, (b) silver / silver chloride, (c) electrolytic polymerized film and the like. In (a), since a metal such as gold or platinum is used as it is as an internal reference electrode, the electrode can be easily manufactured. However, the potential of the internal reference electrode is difficult to stabilize, and the stability of the potential for a long time is poor.
When (b) and (c) are used as the internal reference electrode, the potential stability is excellent, but there is a drawback in that the operation during electrode production is complicated. That is, since the electrodes (b) and (c) are formed by passing electricity in an electrolyte solution,
It is known that a special device is required and the reproducibility of the electric potential of the obtained electrode is poor.

[0009]

Therefore, it has been desired to develop an ion-selective electrode which is easy to manufacture, has a simple structure, can be miniaturized, and has a stable electrode potential over a long period of time.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to develop an ion-selective electrode capable of solving such problems. As a result, by using a monomolecular film made of a compound having a ferrocene group having a specific structure as an intermediate layer between a metal electrode and an ion-sensitive film, an ion-selective electrode having easy electrode production and good electrode response can be obtained. This has led to the completion of the present invention.

That is, according to the present invention, (A) a metal electrode layer made of gold, silver, or copper metal, (B) a redox layer, and (C) an ion-sensitive film layer are sequentially laminated, and (B) an oxidation layer. The reduction layer is an ion-selective electrode characterized by comprising a monomolecular film layer of a ferrocene group bonded to the metal electrode layer (A) through a bonding group capable of chemically bonding.

Another invention is characterized in that the ion concentration in the sample solution is quantified by bringing the sample solution into contact with the ion selective electrode and the reference electrode and measuring the potential difference between the two electrodes. Is a measuring method of.

The metal electrode layer made of gold, silver, or copper metal used in the present invention stably and firmly holds the redox layer on the electrode surface and has electrical continuity so that the potential of the internal reference electrode can be controlled. Has the role of facilitating measurement. It is preferable that the metal electrode layer is gold, silver, or copper because the adhesion with the redox layer is good and the production is easy. When a metal other than these is used, the adhesion with the redox layer is poor,
Molecules forming the redox layer diffuse into the ion-sensitive membrane,
The stability of the potential may deteriorate.

Among gold, silver and copper metals, the use of gold as the metal electrode layer is particularly preferable because the bond between the electrode and the redox layer becomes stronger and a stable potential can be obtained.

The metal electrode layer may be composed of only the metal, or may be formed as a thin layer on a suitable insulating substrate. The thickness of the metal electrode layer when formed as a thin layer on the substrate is preferably 10 nm to 1 mm. When the thickness is 10 nm or less, the conductivity may be reduced and the potential stability of the ion selective electrode may be deteriorated. Further, when it is 1 mm or more, the step with the substrate is large and the adhesion with the ion-sensitive film may be deteriorated. When the metal electrode layer is composed of only the metal, the layer thickness of the metal electrode layer is preferably 1 mm to 10 mm.
If it is less than 1 mm, the operability is difficult and 10 mm
In the above case, the cost is high.

As the insulating substrate, any known material can be used as long as it is an insulating plate, but in view of easy availability and good workability, glass such as borosilicate glass, quartz glass, polychlorinated or the like. Plastics such as vinyl, polytetrafluoroethylene and polyimide, and ceramics such as alumina and aluminum nitride are preferably used. As a method of forming a metal electrode layer on these insulating substrates, electroless plating,
Sputtering, vapor deposition, etc. may be used without particular limitation.

The redox layer constituting the ion-selective electrode of the present invention is essential for keeping the potential of the internal reference electrode constant, and the potential is the concentration ratio of the oxidant and the reductant contained in the redox layer. Is used to determine the potential of the internal reference electrode. The redox layer of the present invention is basically composed of a monolayer of a ferrocene group, and the ferrocene group is bonded to the metal electrode layer via a bonding group capable of chemically bonding to the metal electrode layer.

The bonding group that can be chemically bonded to the metal electrode layer is not particularly limited, but a bonding group that can bond to the metal mainly by a coordinate bond is preferably used. When a binding group having another binding mode is used, the redox layer may be dissolved in the ion-sensitive membrane layer, and the potential of the resulting ion-selective electrode may become unstable.

The bonding group mainly bonded to the metal by a coordinate bond is usually formed by deriving from a compound having a functional group which can serve as the bonding group. Examples of particularly suitable functional groups include thiol group, disulfide group, and sulfide group. These functional groups form a bonding group and firmly bond with a metal, and the redox layer of the present invention is simple. It is particularly preferable because it can be obtained by various operations. The details of the binding mode between a solid state metal and a binding group derived from and formed by a thiol group, a disulfide group, or a sulfide group have not been fully elucidated at present, but in the case of a thiol group or a disulfide group, the metal -Suspected to form a thiolate bond. In the case of a sulfide group, it is presumed that a coordinate bond is formed between the unshared electron pair on sulfur and the metal.

The ferrocene group in the redox layer of the present invention refers to a group having a structure in which one hydrogen atom of ferrocene is substituted with an appropriate divalent organic group (hereinafter abbreviated as a spacer), and the ferrocene group is It is chemically bonded to the metal electrode layer via the bonding group described above. In the present invention, ferrocene is used to include ferrocene containing divalent iron and ferricinium containing trivalent iron. In the case of ferricinium, it contains an anion known as a counterion.

The spacer in the ferrocene group is carbon,
A main chain having nitrogen and / or oxygen and having 3 to 12 atoms in the main chain is preferably used. If the number of atoms in the main chain is less than 3, the resulting redox layer may become unstable and the potential of the ion selective electrode may become unstable. When the number of atoms in the main chain is larger than 12, the absolute potential of the obtained ion-selective electrode may become unstable.

Specific examples of suitable spacers are as follows. That is,

[0023]

Embedded image

(In the above spacer, the right end binds to the linking group and the left end binds to ferrocene) and the like.

It is essential that the iron ion contained in the ferrocene group of the present invention has an oxidation number of 2 or 3 so that the obtained ion-selective electrode exhibits a stable potential. Here, a ferrocene group (reduced body) containing an iron ion having an oxidation number of 2
Is oxidized into a ferrocene group (oxidized form) containing iron ions with an oxidation number of 3. The ratio of the iron ion of oxidation number 2 and the iron ion of oxidation number 3 is not particularly limited, but the ratio is 0.01 to
When it is in the range of 100, the absolute potential of the obtained ion-selective electrode becomes stable, which is preferable.

The redox layer of the present invention is composed of a monomolecular film layer of a ferrocene group bonded to the above-mentioned metal electrode layer through a bonding group capable of chemically bonding. Since the redox layer is a monomolecular film layer, the amount of ferrocene groups per unit area of the metal electrode is constant, so that the potential of the ion-selective electrode obtained is stable. If it is not a monomolecular layer, the electric resistance of the obtained ion-selective electrode may increase and the potential may become unstable.

The method for producing the redox layer of the present invention is not particularly limited as long as it satisfies the above conditions, and known production methods can be applied. Typically, a bond capable of being bonded to the metal electrode layer is used. A method in which an organic compound having a functional group capable of forming a group and a ferrocene group in the molecule (hereinafter abbreviated as a binding ferrocene compound) is dissolved in a suitable solvent and the metal electrode layer is immersed in the solution for a certain period of time is preferable. Adopted. By this method, the redox layer of the present invention can be easily produced with good reproducibility.

As the binding ferrocene compound, bis (ferrocenoylamino) cystamine, [bis (2-ferrocenoylamide)] 5,5'-dithiodi-1,3,3.
4-thiadiazole, 4,4'-dithiobis (ferrocenoylamino) aniline, bis (ferrocenecarboxylic acid) -4,4'-dithiodiphenolate, bis (ferrocenecarboxylic acid) -2,2'-dithiodiethi Rad, bis (ferrocenoyloxy) -2,2′-dihydroxydithiodipropane, bis (ferrocenylmethyldimethyl- (4,4′-dibutyrylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyl) Dimethyl- (4,4'-benzylcarboxyamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldimethyl- (5,5'-dipentyrylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldimethyl) -(11,11'-diundecanoylamino) ammonium) cysta Nji bromide, 3,
3'-dithiobis (ferrocenylmethyl) propionate, 11,11'-dithiobis (ferrocenylmethyl)
Undecanoate, 2,2'-dithiobis (ferrocenylmethyl) isopropionate, 4,4'-dithiobis (ferrocenylmethyl) dihydrocinnamic acid ester,
2,2'-dithiotetrakis (ferrocenylmethyl) dibutanedioic acid, 3,3'-dithiobis (ferrocenoylamino) propane, 4,4'-dithiobis (ferrocenoylamino) butane, 5,5'- Dithiobis (ferrocenoylamino) pentane, 6,6′-dithiobis (ferrocenoylamino) hexane, 7,7′-dithiobis (ferrocenoylamino) heptane, 8,8′-dithiobis (ferrocenoylamino) octane , 9,9'-dithiobis (ferrocenoylamino) nonane, 10,10'-
Dithiobis (ferrocenoylamino) decane, 11,1
1'-dithiobis (ferrocenoylamino) undecane, bis (ferrocenecarboxylic acid) -3,3'-dithiodipropionate, bis (ferrocenecarboxylic acid)-
4,4'-dithiodibutyrate, bis (ferrocenecarboxylic acid) -5,5'-dithiodipentylate, bis (ferrocenecarboxylic acid) -6,6'-dithiodihexylate, bis (ferrocenecarboxylic acid)- 7,7′-dithiodiheptylate, bis (ferrocenecarboxylic acid) -8,
8'-dithiodioctylate, bis (ferrocenecarboxylic acid) -9,9'-dithiodinonilate, bis (ferrocenecarboxylic acid) -10,10'-dithiodidecanate, bis (ferrocenecarboxylic acid) -11 , 11'-dithiodiundecanoate, bis (ferrocenylmethyldiethyl- (4,4'-dibutyrylamino) ammonium)
Cystamine dibromide, bis (ferrocenylmethyldimethyl- (5,5'-dipentyrylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldiethyl- (5,5'-dipentyrylamino) ammonium) Cystamine dibromide, bis (ferrocenylmethyldimethyl- (6,6'-dihexylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldiethyl- (6,6'-dihexylamino) ammonium) Cystamine dibromide, bis (ferrocenylmethyldimethyl- (7,7'-diheptyrylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldiethyl- (7,7'-diheptyrylamino) ammonium) Cystamine dibromide,
Bis (ferrocenylmethyldimethyl- (8,8'-dioctylylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldimethyl- (8,8'-
Dioctyrylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldiethyl- (9,
9'-dinonylylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldimethyl- (1
0,10'-didesilylamino) ammonium) cystamine dibromide, bis (ferrocenylmethyldiethyl- (10,10'-didesilylamino) ammonium)
Cystamine dibromide, 4,4'-dithiobis (ferrocenylmethyl) butyrate, 5,5'-dithiobis (ferrocenylmethyl) pentylate, 6,6'-dithiobis (ferrocenylmethyl) hexylate, 7,7 '
-Dithiobis (ferrocenylmethyl) heptylate,
Compounds such as 8,8'-dithiobis (ferrocenylmethyl) octylate, 9,9'-dithiobis (ferrocenylmethyl) nonylate, 10,10'-dithiobis (ferrocenylmethyl) decanoate are particularly preferably used. To be

The binding ferrocene compound can be synthesized by combining generally known methods, but the following method is preferably used because it can be synthesized efficiently. By reacting ferrocenecarboxylic acid with oxalyl chloride, the acid chloride of ferrocenecarboxylic acid is obtained in high yield. A ferrocene group can be easily introduced by reacting this with a disulfide or sulfide having a reactive functional group such as an amino group and a hydroxyl group in the molecule. The product can be identified by proton NMR, and a signal based on the hydrogen of the ferrocene group is observed at 4.3 to 4.8 ppm, and a signal based on the hydrogen of methylene next to the disulfide group is observed at 2.6 to 3.0 ppm.

The solvent for producing the redox layer is not particularly limited as long as it can dissolve the above-mentioned binding ferrocene compound, and known solvents can be used, but the operability of the washing step and the drying step after the washing can be used. Considering the above, a volatile solvent is preferable. Examples of the solvent that is generally suitably used are as follows. That is, methanol, ethanol, isopropyl alcohol, carbon tetrachloride, chloroform, methylene chloride, acetone, acetonitrile, dioxane, tetrahydrofuran, water and the like are preferably used.

The formation of the redox layer of the present invention can be generally confirmed by measuring a cyclic voltammogram. At this time, if a ferrocene group is present, 300 mV
Peaks corresponding to oxidation and reduction are observed at 600 mV (potential to silver-silver chloride electrode). Furthermore, the amount of ferrocene groups in the redox layer can be determined from the peak area and the sweep rate.

The cyclic voltammogram is measured by a known method [Akira Fujishima, Masuo Aizawa, Tohru Inoue, "Electrochemical measurement method (2)", Gihodo, p442, (1984)]. That is, a voltage-current curve is obtained by applying a predetermined potential to the electrode to be measured and sweeping it using a three-electrode cell that uses the electrode to be measured, the counter electrode, and the reference electrode.

The immersion time during the production of the redox layer has an optimum value depending on the structure of the bondable group capable of coordinate bond and the bondable ferrocene compound having it. It is desirable to reduce the uncoated metal electrode surface as much as possible because an unexpected redox reaction may occur on the uncoated metal electrode surface. Therefore, the binding ferrocene compound having a thiol group is immersed for 10 minutes or longer, preferably 2-3 hours, and the binding ferrocene compound having a disulfide group or a sulfide group is immersed for several hours or longer, preferably 12 hours or longer. As a result, the concentration of ferrocene groups in the redox layer can be increased and the surface of the metal electrode can be almost completely covered.

The ion-sensitive membrane layer used in the present invention is necessary to generate a membrane potential according to a specific ion concentration in the sample solution and to make a sensitive response only to target ions. The ion-sensitive film layer is not particularly limited as long as it is a film that generates a film potential according to the ion concentration, and an ion-sensitive film known in the art can be used.

Generally, (a) a polymer compound, a plasticizer, and an ionophore-type ion-sensitive membrane containing an ionophore as a main component, and (b) a polymer compound into which an ion-exchange group is introduced by a covalent bond as a main component. Two types of ion-exchange type ion-sensitive membranes are preferably used because they have good adhesiveness to the redox layer of the present invention.

Since the ion-selective electrode of the present invention is usually used in an aqueous solution, it is preferable that the polymer compound of the ionophore-type ion-sensitive membrane is insoluble in water. Suitable examples of the polymer compound used for the ionophore-type ion-sensitive membrane include, for example, vinyl halide homopolymers or copolymers such as vinyl chloride, vinyl bromide, vinylidene chloride; siloxane polymers or copolymers. Polymers: fibrin derivatives such as cellulose acetate and cellulose nitrate. In particular, a vinyl halide homopolymer or copolymer, or a siloxic acid polymer or copolymer is suitable because it has a long life when the ion-selective electrode of the present invention is used in a biological fluid.

The plasticizer used for the ionophore-type ion-sensitive membrane is not particularly limited, and known ones can be used.
The following is an example of what can be suitably used.
That is, phthalic acid esters such as dimethyl phthalate, diethyl phthalate and dioctyl phthalate; fatty acid esters such as dioctyl adipate and dioctyl sebacate; ortho nitrophenyl octyl ether, ortho nitrophenyl phenyl ether, 2-fluoro-2 '.
-Ortho nitrophenyl ethers such as nitrophenyl ether. The addition amount of these plasticizers may be appropriately selected according to the purpose of use of the anion-sensitive membrane, but generally, the plasticizer is added in an amount of 30 to 30 parts by weight per 100 parts by weight of the polymer compound.
It is preferable to select in the range of 300 parts by weight.

As the ionophore used for the ionophore-type ion-sensitive membrane, an ionophore for ion-sensitive membrane known in the art can be used. Generally, the ionophore is determined by the ion to be measured, and examples of those that are preferably used are as follows.

Potassium ion selective electrode: valinomycin, bis [(benzo-15-crown-5) -4-methyl] pimelate, 15 crown 5 derivative, sodium ion selective electrode: monensin, bis [(1
2-crown-4) methyl] methyldodecyl malonate, 12 crown 4 derivative, calixarene derivative, chlorion-selective electrode: quaternary ammonium salt derivative,
Porphyrin metal complex, organotin compound, calcium ion selective electrode: di-n-octylphenylphosphonate, lithium ion selective electrode: 6,6-dibenzyl-1,
4,8,11-tetraoxacyclotetradecane and the like.

As a method for producing the ionophore type ion sensitive membrane used in the present invention, a conventionally known method is adopted. The following is an example of a typical manufacturing method that is generally suitably used. A method is available in which the ionophore is dissolved in an organic solvent together with a polymer compound and a plasticizer, the solution is applied or poured onto the redox layer, and then the organic solvent is evaporated to form an ion-sensitive film. At this time, a fat-soluble organic salt compound such as potassium tetraphenylborate or potassium tetrakis (trifluoromethylphenyl) borate may be added, if necessary. In addition, an ion-sensitive film produced in the same manner on a substrate such as a glass petri dish in advance,
A method of sticking on the redox layer is also suitably adopted.

As the above-mentioned organic solvent, known solvents can be used without any limitation as long as they dissolve the polymer compound, the plasticizer and the ionophore. Specific examples of generally suitable organic solvents include tetrahydrofuran, dioxane, chloroform, methylene chloride, dimethylformamide, dimethylacetamide, benzene, and toluene.

The ion sensitive film obtained by the above-mentioned method is generally a uniform film. The film thickness of the ion-sensitive film of the present invention can be controlled by adjusting the amounts of constituent components used and the film area, but in the range of 1 μm to 1 mm in consideration of operability when used as an ion-selective electrode. Is desirable. As the polymer compound in which the ionic group used for the ion-exchange type ion-sensitive membrane is covalently introduced, a trimethylammoniomethylstyrene copolymer,
Trimethylammonioethyl methacrylate copolymer,
It is preferable to use a dioctadecylmethylammoniomethylstyrene polymer, a copolymer, or the like because the adhesion to the redox layer is good.

A conventionally known method is adopted as a method for producing the ion-exchange type ion-sensitive membrane. The following is an example of a typical manufacturing method that is generally suitably used. Examples include a method in which the polymer compound in which the ionic group is covalently introduced is dissolved in an organic solvent, and the solution is applied or poured onto the redox layer, and then the organic solvent is evaporated to form an ion-sensitive film. . Further, a method of adhering an ion-sensitive film produced in the same manner on a substrate such as a glass petri dish in advance on the redox layer is also suitably used.

Any known organic solvent can be used without limitation as long as it can dissolve the polymer compound. Specific examples of generally suitable organic solvents include tetrahydrofuran, dioxane, chloroform, methylene chloride, dimethylformamide, dimethylacetamide, benzene, and toluene.

The ion-sensitive film obtained by the above-mentioned method is generally a uniform film. The film thickness of the ion-sensitive film of the present invention can be controlled by adjusting the amounts of constituent components used and the film area, but in the range of 1 μm to 1 mm in consideration of operability when used as an ion-selective electrode. Is desirable.

As shown in FIG. 3, the ion-selective electrode of the present invention is provided with an ion-sensitive film 35 as a boundary film in a portion immersed in a sample solution, and an oxidation-reduction layer is provided between the ion-sensitive film and the metal electrode 33. It is basically configured by providing 34. When the electrode is formed on the insulating substrate 31, a base metal layer 32 is formed between the metal electrode and the insulating substrate, if necessary, in order to improve the adhesiveness between the substrate and the electrode. The method for producing each layer is as described above.

The method of quantifying the ion concentration in the sample solution using the ion-selective electrode of the present invention can be used by a known method. For example, the usage pattern shown in FIG. 4 is typical. That is, the ion-selective electrode 41 is immersed in the sample solution 43 together with the salt bridge 42, and the other end of the salt bridge is immersed in the saturated potassium chloride solution 46 together with the reference electrode 44.
As the above-mentioned comparison electrode, generally known ones are adopted, but examples of suitably used ones include calomel electrodes, silver-silver chloride electrodes, platinum plates, carbon graphite and the like.

A general measuring operation for measuring the ion concentration of a sample with the above apparatus is as follows. That is, the potentials generated between the ion-selective electrode and the reference electrode are measured for two standard solutions having known ion concentrations to be detected and different concentrations, and a calibration curve is prepared in advance. Then
The ion concentration of the sample solution can be obtained by measuring the potential generated between the ion selective electrode and the reference electrode for the sample solution containing the ions of unknown concentration and extrapolating it to the calibration curve.

[0049]

Since the ion-selective electrode of the present invention has the redox layer between the metal electrode layer and the ion-sensitive membrane layer, the electrode potential is stable for a long period of time. Furthermore, since the redox layer is composed of a self-association type monomolecular film, the production of the ion-selective electrode is extremely easy and downsizing is possible. Therefore, the ion concentration in the solution can be measured accurately and easily. From the above points, the industrial value of the ion-selective electrode of the present invention is extremely large.

[0050]

EXAMPLES Examples will be given below to more specifically describe the present invention, but the present invention is not limited to these examples.

In this example, proton NMR was used.
¹ HNMR and tetramethylsilane are abbreviated as TMS.

Production Example 1 1.0 g (4.3 mm) of ferrocenecarboxylic acid in 50 ml
ol) was mixed with 20 ml of dichloromethane, 2 ml of oxalyl chloride was added under ice cooling, and the mixture was stirred for 2.5 hours. Then, the solvent and unreacted oxalyl chloride were distilled off under reduced pressure and used for the next reaction without purification.

0.6 g of cystamine dihydrochloride was extracted with dichloromethane / water (pH ~ 13), the organic layer was separated, and the solvent was distilled off under reduced pressure. The free cystamine 0.
To 28 g (2 mmol) of a solution of dichloromethane / triaetylamine = 2/8 (about 30 ml), 1.0 g (4 mmol) of ferrocenyl chloride obtained above was added, and 1
Stir for 4 hours at room temperature.

The reaction mixture was mixed with chloroform / water (pH 1
2), followed by extraction with chloroform / water (pH 2) (all chloroform layers were separated). The solvent was distilled off under reduced pressure, and the residue was treated with a silica gel column (chloroform / methanol = 9/1) to obtain 0.99 g (yield 87%) of a yellow solid.

1H NMR of the purified product (TM in CDCl ₃
Let S be an internal standard (0.0 ppm). ) And IR measurements were performed and the following results were obtained.

¹ HNMR: 6.6 ppm (t; 1H, amide-H), 4.3 to 4.8 ppm (m; 9H, ferrocene-H), 3.7 ppm (q; 2H, N-CH ₂ ),
3.0ppm (t; 2H, S- CH 2) IR: 1628cm -1 (C = O, amide I), 1537
cm ⁻¹ (NH, N—C═O, amide II) Table 1 shows the structure of the disulfide having a ferrocene group at the terminal obtained here.

[0057]

[Table 1]

Production Example 2 Solution of 2 mmol of difunctional disulfide shown in Table 2 in dichloromethane / triaetylamine = 2/8 (about 30 m
l), 1.0 g (4 mmol) of ferrocenyl chloride
Was added and the mixture was stirred for 14 hours at room temperature. The reaction mixture was extracted with chloroform / water (pH 12), and the chloroform layer was separated. The solvent was distilled off under reduced pressure, and the residue was treated with a silica gel column (chloroform / methanol = 9/1) to introduce a ferrocene group into the disulfide compound. The structure of the obtained compound is shown in Table 2.

[0059]

[Table 2]

Production Example 3 (1) 5 g (42 mmol) of thionyl chloride was added to 6.7 g (40 mmol) of 4-bromobutyric acid, and the mixture was stirred at room temperature for 5 hours. After the gas was completely generated, excess thionyl chloride was distilled off under reduced pressure, and 10 ml of methylene chloride was added.

4.5 g of cystamine dihydrochloride (20 mmo
l) was extracted with chloroform / NaOH aqueous solution (pH 12), the solvent was distilled off under reduced pressure, and triethylamine 4 g (40
mmol) and methylene chloride were added. This methylene chloride solution was gradually added dropwise to the methylene chloride solution of the acid chloride obtained above, and the mixture was stirred at room temperature for 72 hours. After completion of the reaction, distilled water was added, and the mixture was stirred at room temperature for 1 hour and then separated, and the organic layer was separated. This was extracted again with distilled water, the organic layer was separated, and the solvent was distilled off under reduced pressure. The residue was treated with a silica gel column (chloroform / methanol = 93/7) to give a pale yellow solid 4.
0 g (yield 40%) was obtained.

¹ HNMR of the purified product (TMS in CDCl ₃
Is the internal standard (0.0 ppm). ) The measurement was performed and the following results were obtained.

1H NMR: 6.8 ppm (s; 1H, amide-H), 4.3 ppm (t; 2H, Br-C)
_{H 2), 3.6ppm (q;} 2H, N-CH 2), 2.8
ppm (t; 2H, S- CH 2), 2.4ppm (m;
_{2H, CO-CH 2),} 2.2ppm (m; 2H, Br
-C-CH ₂₎ (2) bis - (4-bromo-butyryl amino) was dissolved cystamine 4g of (8 mmol) in benzene 50 ml, N,
2.5 g of N-dimethylaminoferrocene (10 mmo
1) was added and the mixture was heated under reflux for 6 hours. The reaction mixture was purified by silica gel column treatment (chloroform / methanol = 4/1) and extraction (hydrochloric acid / water / chloroform) to obtain a yellow solid.

¹ H NMR of purified product (TMS in CDCl ₃
Is the internal standard (0.0 ppm). ) The measurement was performed and the following results were obtained.

¹ HNMR: 6.8 ppm (s; 1H, amide-H), 4.3 to 4.8 ppm (m; 9H, ferrocene-H), 3.2 to 3.7 ppm (m; 10H, N ^{+)
_{-CH 2, N + -CH 3)}} , 2.8ppm (t; 2H, S
_{-CH 2), 2.2~2.4ppm (m;} 4H, CO-
CH ₂ —CH ₂ —) Table 3 shows the structure of the resulting disulfide having a ferrocene group at the terminal.

[0066]

[Table 3]

Production Example 4 A solution of 3 g (20 mmol) of free cystamine dissolved in 4 g (40 mmol) of triethylamine and 10 ml of methylene chloride was gradually added to a methylene chloride solution (40 mmol / 10 ml) of acid chloride of carboxylic acid shown in Table 4. The mixture was added dropwise to and stirred at room temperature for 72 hours. After completion of the reaction, distilled water was added, and the mixture was stirred at room temperature for 1 hour and then separated, and the organic layer was separated. This was extracted again with distilled water, the organic layer was separated, and the solvent was distilled off under reduced pressure. The residue was treated with a silica gel column (chloroform / methanol = 93/7). 8 mmol of this was weighed and dissolved in 50 ml of benzene, 2.5 g (10 mmol) of N, N-dimethylaminoferrocene was added, and the mixture was heated under reflux for 6 hours. The reaction mixture was purified by silica gel column treatment (chloroform / methanol = 4/1) and extraction (hydrochloric acid / water / CHCl3). Table 4 shows the structure of the obtained disulfide having a ferrocene group at the terminal.

[0068]

[Table 4]

Production Example 5 Ferrocenemethanol 2 g (9.3 mmol) and 3,
0.9 g of 3'-dithiodipropionic acid (4.3 mmo
l) is dissolved in 50 ml of tetrahydrofuran and concentrated sulfuric acid 2
ml was added and the mixture was heated under reflux for 24 hours. After allowing to cool to room temperature, the mixture was extracted with chloroform / water (pH 7 to 8) to separate the organic layer. The solvent was distilled off under reduced pressure and the residue was treated with a silica gel column (chloroform / methanol = 95/5) to obtain 1.5 g of a yellow solid (yield 55%).

¹ HNMR of the purified product (TMS in CDCl ₃
Is the internal standard (0.0 ppm). ) The measurement was performed and the following results were obtained.

¹ HNMR: 4.3 to 4.8 ppm (m;
9H, ferrocene-H), 3.8 ppm (m; 2H, C
OO-CH ₂ - ferrocene), 2.8ppm (m; 4
H, OCO—CH ₂ —CH ₂ —) The structure of the obtained compound is shown in Table 5.

[0072]

[Table 5]

Production Example 6 2 g (9.3 mmol) of ferrocenemethanol and 4.3 mmol of the carboxylic acid shown in Table 6 were added to 5 parts of tetrahydrofuran.
It was dissolved in 0 ml, 2 ml of concentrated sulfuric acid was added, and the mixture was heated under reflux for 24 hours. After cooling to room temperature, chloroform / water (pH 7-
The organic layer was separated by extraction in 8). The solvent was distilled off under reduced pressure, and the residue was treated with a silica gel column (chloroform / methanol =
95/5) to obtain a disulfide compound having a ferrocene group introduced therein. Table 6 shows the structure of the obtained disulfide having a ferrocene group at the terminal.

[0074]

[Table 6]

Example 1 As shown in FIG. 3, a glass substrate was masked with a masking tape in a predetermined shape, and platinum was sputtered and subsequently gold was sputtered to obtain a gold electrode having a thickness of 60 nm. The gold electrode was immersed in a chloroform solution (10 mM) of the compound (Production No. 1) obtained in Production Example 1 for 24 hours at room temperature to form a monomolecular film of the compound obtained in Production Example 1 on the surface of the gold electrode. Let After thoroughly washing with chloroform, the solvent was dried.

When the cyclic voltammogram of the obtained electrode was measured by the above-mentioned operation, it was revealed from the peak area of the voltammogram and the sweep rate that 0.1 nmol of ferrocene group was present on the electrode surface per cm ² of the electrode. . This value is almost the same as the value when it is considered that the above compounds are densely packed in the form of a monomolecular film on the gold surface, and therefore the layer thickness of the redox layer is at the monomolecular film level. It is suggested that a monomolecular film with few defects is formed.

A potassium ion sensitive membrane solution was cast on this electrode and the solvent was dried to obtain a potassium ion selective electrode. The potassium ion sensitive membrane solution contained 200 mg of polyvinyl chloride as a polymer compound, 400 mg of p-nitrophenyl octyl ether as a plasticizer, and bis [(12-crown-4) as a potassium ionophore.
A solution prepared by dissolving 40 mg of methyl] methyldodecyl malonate in 20 ml of tetrahydrofuran was used.

Table 7 shows the results of measuring the potassium ion concentration using the obtained potassium ion-selective electrode by the following procedure. The measurement was performed using the apparatus shown in FIG. 4 according to the following procedure. 10 ^-3 M potassium chloride solution 43
The potential difference between the potassium ion selective electrode and the reference electrode was measured. Next, the same measurement was carried out for a 10 ⁻² M potassium chloride solution, and the potential was plotted against the potassium chloride concentration to obtain a slope of 10 ⁻³ M to 10 ⁻² M and a calibration curve. Further, the potentiometric measurement was repeated 10 times for a 10 ^-2 M potassium chloride solution, and the potassium ion concentration was calculated from the previously obtained calibration curve.
The coefficient of variation (hereinafter abbreviated as CV) for each measurement was obtained. The potential for the silver / silver chloride electrode in the table is 10 ^-4 M potassium chloride solution (hereinafter referred to as 10 ^-4 MKCl) as a sample solution.
(Abbreviated as)), the average value and standard deviation of 10 electrodes are calculated.

[0079]

[Table 7]

Comparative Example 1 The results for the potassium ion selective electrode obtained by casting the potassium ion sensitive membrane solution directly on the gold electrode without using the compound obtained in Production Example 1 and drying the solvent are shown in Table 7. Shown together.

As can be seen from Table 7, 1 out of 10 electrodes
The standard deviation of the absolute potential in 0 ⁻⁴ MKCl is better with the redox layer, and the effectiveness of the present invention is clear.
Regarding the slope, the larger the redox layer is, the larger the value. When the slope is large, the sample concentration obtained from the calibration curve can be measured with high accuracy, which is useful. Further, the CV is smaller with the redox layer. C
V is an index showing the simultaneous reproducibility of measurement, and it is clear that the ion-selective electrode of the present invention enables highly reproducible measurement.

Example 2 Compounds obtained in Production Examples 2 to 6 (Production Nos. 2 to 15)
Was adsorbed on the surface of the gold electrode in the same manner as in Example 1, and the same experiment as in Example 1 was performed. The results are summarized in Table 8.

[0083]

[Table 8]

Comparative Example 2 The same experiment as in Example 1 was conducted by using each chloroform solution of 3,3′-dibutyl disulfide and ferrocene. The results are also shown in Table 8.

As can be seen from Table 8, regardless of the structure between the ferrocene group and the thiol group or disulfide group,
It can be seen that the use of these substances gives a stable potential as compared with the case of using 3,3′-dibutyl disulfide and ferrocene.

Example 3 Using gold, silver and copper as the metal electrode, the compound (Production No. 1) obtained in Production Example 1 was adsorbed on the surface of the metal electrode in exactly the same manner as in Example 1, The same experiment as in 1 was performed. The results are summarized in Table 9.

[0087]

[Table 9]

Comparative Example 3 The same experiment as in Example 1 was conducted using iron and platinum. The results are also shown in Table 9. As can be seen from Table 9, the potentials of gold, silver, and copper are stable, whereas in the comparative example, the potentials vary depending on the electrodes.

Example 4 In exactly the same manner as in Example 1, the compound obtained in Production Example 1 (Production No. 1) was adsorbed on the surface of the gold electrode, and a potassium-sensitive film, a sodium-sensitive film and a chlor-sensitive film were used. The same experiment as in Example 1 was performed. In addition, as the ionophore of the potassium sensitive film, sodium sensitive film, and chlor sensitive film,
Bis [(benzo-15-
Crown-5) -4-methyl] pimelate (abbreviated as 15c5), bis [(12
-Crown-4) Methyl] methyldodecyl malonate (abbreviated as 12c4), and a tetraphenylporphyrin / Mn complex (abbreviated as TPP-Mn) was used for a chloride ion selective electrode. The composition of the solution and the results are shown in Table 10.

[0090]

[Table 10]

Example 5 In exactly the same manner as in Example 1, the compound obtained in Production Example 1 (Production No. 1) was adsorbed on the surface of the gold electrode, and the same experiment as in Example 1 was carried out using a chloro-sensitive film. I did. In addition, a dioctadecylmethylammoniomethylstyrene polymer was used for the chlor sensitive film. The results are also shown in Table 10.

Example 6 In the same manner as in Example 1, the compound shown in Production Example 1 (Production N
o. 1) was adsorbed to obtain a gold electrode having a shape shown in FIG.
The sensitive film was covered with epoxy resin 53, leaving 1 mm ² for pouring and a part for taking leads. A potassium ion sensitive membrane solution was poured into the uncoated portion of this electrode, the solvent was dried, and the electrode was coated with the potassium ion sensitive membrane 54 to obtain a potassium ion selective electrode. The shape of the obtained electrode is shown in FIG. The potassium ion concentration was measured using the apparatus shown in FIG. FIG. 6 shows the results.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an example of a general ion-selective electrode using an internal liquid.

FIG. 2 is an explanatory view of an apparatus for measuring a potential difference using the ion selective electrode of FIG.

FIG. 3 is an exploded view showing the configuration of an example of an ion-selective electrode that does not use an internal solution of the present invention.

4 is an explanatory view of an apparatus for measuring a potential difference using the ion selective electrode of FIG.

FIG. 5 is an explanatory diagram of an ion-selective electrode that is made compact by using the present invention.

6 is an ion concentration response measured using the ion-selective electrode of FIG.

[Explanation of symbols]

 11 Electrode Cylinder 12 Ion Sensitive Membrane 13 Internal Electrolyte 14 Internal Reference Electrode 15 O-ring 21 Ion Selective Electrode 22 Salt Bridge 23 Sample Solution 24 Reference Electrode 25 Electrometer 26 Saturated Potassium Chloride Aqueous Solution 27 Recorder 31 Insulating Substrate 32 Base Metal 33 Metal Electrode 34 Redox Layer 35 Ion Sensitive Membrane 41 Ion Selective Electrode 42 Salt Bridge 43 Sample Solution 44 Reference Electrode 45 Electrometer 46 Saturated Potassium Chloride Aqueous Solution 47 Recorder 51 Metal Electrode 52 Insulating Substrate 53 Epoxy Resin 54 Potassium Ion Sensitive membrane

Claims (2)

[Claims] 1. A metal electrode layer of (A) gold, silver, or copper metal, (B) a redox layer, and (C) an ion-sensitive membrane layer are laminated in this order, and (B) a redox layer comprises: An ion-selective electrode comprising a ferrocene group monomolecular film layer (A) bonded to a metal electrode layer through a chemically bondable bonding group. 2. An ion characterized in that the ion concentration in the sample solution is quantified by bringing the sample solution into contact with the ion-selective electrode and the reference electrode according to claim 1 and measuring the potential difference between the two electrodes. How to measure concentration.