JPH0375065B2 - - Google Patents

Description

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

[Conventional technology and problems]

Conventionally, so-called liquid film type sensors have been known as electrochemical calcium ion sensors.

However, this type of liquid film sensor has a structure in which an internal liquid containing a certain concentration of calcium ions and an external test liquid are separated by a calcium ion selective membrane, so it is difficult to miniaturize the electrode body. It was hot. Furthermore, when used in vivo, there is a risk of elution or leakage of internal fluids, which limits its use.

In contrast, Etsuchi Fraser (H.
Friiser and Cartral et al. proposed a so-called coated wire electrode (CWE) that eliminates the internal liquid of a liquid film sensor.

However, CWE is made by directly depositing a calcium ion-selective membrane on noble metals such as platinum, silver, or heavy metals such as copper, and has the advantages of being compact, having a simple structure, and being easy to manufacture. However, it cannot be used in vivo or for long-term monitoring due to drawbacks such as large potential drift and large influence by oxygen partial pressure.

Purpose of the Invention Under these circumstances, the present inventor has conducted various studies in order to develop a calcium ion sensor that is a solid-state sensor that does not have an internal liquid chamber, has a small potential drift, and is free from interference due to oxygen partial pressure, etc. However, the above objective can be achieved by depositing a calcium ion-selective membrane on top of a membrane that has a reversible redox function, instead of directly depositing the calcium ion-selective membrane on the surface of the conductive substrate. They discovered this and completed the present invention.

That is, the present invention is a calcium ion sensor that measures the concentration of calcium 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 a film having a reversible redox function is coated on the surface of the film. The present invention provides a calcium ion sensor characterized by being coated with a calcium ion selective membrane.

The present invention further provides a calcium ion sensor in which the calcium ion selective membrane is a polymeric membrane carrying a calcium ion carrier material.

DETAILED DESCRIPTION OF THE INVENTION The conductive substrate used in the calcium 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),
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
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 an organic compound film or a polymer film capable of carrying out a quinone-hydroquinone type redox reaction, and an organic compound film or a polymer film capable of carrying out an amine-quinoid type redox reaction. etc. are mentioned as suitable ones. 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 the above-mentioned polymer, for example, as shown in the following reaction formula. refers to something expressed as

−(N=R ³ −) _o1 N−+H ⁺ ,e ^−——— → ←——— −(NH−R ⁴ −) _o1 NH− (wherein, R ³ and R ⁴ are e.g. Examples of compounds that can form a film having such a reversible redox function include the following compounds (a) to (c).

(a) (where Ar ₁ is aromatic, each R ⁵ is a substituent, m ₂
is 1 or the effective valence number of Ar ₁ , n ₂ is 0 or
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-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
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. 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 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 effect 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 calcium ion-selective membrane deposited over the surface of the redox membrane deposited on the conductive substrate as described above is composed of, for example, a calcium ion carrier material and an electrolyte salt supported on a polymer compound. A membrane is used.

The calcium ion carrier substance is not particularly limited as long as it can selectively transport calcium ions, but examples include calcium bis[di-(n-octylphenyl) phosphate],
(-)-(R,R)-N,N'-bis[11-ethoxycarbonyl)undecyl]-N,N'-4,5-tetramethyl-3,6-dioxaoctane-diamide, calcium bis[ di(n-decyl) phosphate] and the like are preferred.

Examples of electrolyte salts include sodium tetrakis(p-chlorophenyl)borate, potassium tetrakis(p-chlorophenyl)borate, tetraphenylphosphonium salts and compounds of the following formula R ₄ 'NBF ₄ (wherein R' is an alkyl group, preferably a carbon (representing an alkyl group of numbers 2 to 6).

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 sepacic acid ester, dioctyl adipate, dioctyl maleic acid, di-n-octylphenyl phosphonate, and the like. Moreover, tetrahydrofuran is preferably used as the solvent.

In order to deposit a calcium ion selective membrane on 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 calcium 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° C., 3 minutes) about 30 times to obtain a carrier film thickness of 50 μm to 3 mm, particularly 0.3 mm to 2 mm. Alternatively, paste vinyl chloride, calcium 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 calcium ion carrier film can also be obtained by heat treatment at 160° C. for 1 minute to form a gel.

Conventionally, membranes used in ion-selective electrodes have generally been thin in order to reduce membrane resistance, but the calcium ion-selective membrane used in the present invention does not necessarily have to be thin; The film can be made as thick as about 1 to 3 mm. This is believed to be based on the unique configuration of the sensor of the present invention. Furthermore, the calcium ion selective membrane used in the present invention has a property that it is not easily affected by dissolved oxygen and other coexisting substances in the test liquid.

〔Example〕

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

(i) After cutting out a cylinder 11 with a diameter of 5 mm from a sheet of basal plain pyrolithic graphite (BPG) (manufactured by Union Carbide), conductive adhesive (manufactured by Amicon, C- 850-6) 15 to connect the Teflon-coated copper wire lead wire 16, and then connect the BPG with a heat shrink tube (manufactured by Alpha Wire).
After coating and insulating it so that the tip surface 11a of was slightly exposed, the exposed tip portion was peeled off with a knife blade to expose a new surface. Electrolytic oxidation was carried out under the conditions shown below using the BPG substrate electrode thus prepared as a working electrode, a saturated sodium chloride electrolyte (SSCE) as a reference electrode, and a platinum mesh as a counter electrode.

(Electrolyte) Supporting electrolyte: 0.2M sodium perchlorate Reactive substance: 10mM 1-aminopyrene 10mM pyridine Solvent: acetonitrile (electrolytic conditions) Working electrode potential was swept from 0V to 1V 3 times (50mV/sec) with respect to SSCE After that, at 1V vs. SSCE
Potential electrolysis was carried out for 10 minutes.

In this way, an electrolytically oxidized polymer film (about 30 μm thick) of 1-aminopyrene was coated on the exposed surface of the BPG substrate.
13 was formed. This membrane generates a constant potential by an amine-quinoid type redox reaction [a constant potential of 50 mV vs. SSCE is generated in a solution of 0.1M potassium tetrakis(p-chlorophenyl)borate (KTpClPB) in dioctyl sebacic acid (DOS). did〕.

(ii) The electrode body prepared in (i) is immersed in an immersion liquid containing a calcium ion carrier material and having the composition shown below, and then dried to form an electrolytically oxidized polymer film 13.
A calcium ion selective membrane 14 was deposited thereon. In addition, the dipping and drying operations are repeated.
A calcium ion carrier film with a thickness of about 0.3 mm was formed.

(Immersion liquid) Calcium bis[di-(n-octylphenyl) phosphate] 22.5mg (HDOPP-Ca) KTpClPB 8.6mg DOS 493.8mg Polyvinyl chloride 251.1mg Tetrahydrofuran 5ml Example 2 Calcium of the sensor prepared in Example 1 In order to investigate the responsiveness to ions, the sensor and SSCE were immersed in a 10 ^-3 to 10 ^-1 M calcium chloride aqueous solution, and the electromotive force of the sensor of the present invention was measured using an electrometer (TR8652 manufactured by Takeda Riken Co., Ltd.) (temperature 25℃). The results are shown in FIG.

As is clear from Figure 2, the electromotive force (vs.
SSCE) and calcium ion concentration showed a good linear relationship.

Example 3 After producing a BPG base electrode in the same manner as in Example 1, an electrolytic polymerization reaction was performed using the following electrolytic solution and conditions to coat it with a 2,6-dimethylphenol polymer film.

(Electrolyte) Supporting electrolyte: 0.2M sodium perchlorate Reactive substance: 0.5M 2,6-dimethylphenol Solvent: acetonitrile (electrolytic conditions) The potential of the working electrode was adjusted from 0V to 1.5V with respect to SSCE.
After multiple sweeps (50mV/sec), at 1.5V vs. SSCE
Potential electrolysis was carried out for 10 minutes.

A calcium ion carrier film (thickness: about 0.4 mm) was formed on the surface of the redox film electrode thus prepared in the same manner as in (ii) of Example 1.

Example 4 As a result of investigating the calcium ion concentration dependence of the electromotive force of the sensor produced in Example 3 in the same manner as in Example 2, it was found that there was a linear relationship between the electromotive force and the calcium ion concentration, as shown in FIG. Obtained. Also,
The response speed (time required for 95% potential response) was 1 to 2 minutes as shown in FIG. Moreover, no drift was observed in the electromotive force after that.

Example 5 The electromotive force of the sensor produced in Example 3 was measured in a solution where calcium ions and magnesium ions coexisted (25±0.1°C), and the ion selectivity coefficient for magnesium ions was determined: logK ^Pot _CaMg = -3.33 (Figure 5).

In conventional calcium ion sensors -
Considering that it was 1.9 to -2.0, it can be seen that the sensor of the present invention has excellent selectivity.

Example 6 The electromotive force of the sensor produced in Example 3 was measured in a solution where calcium ions and sodium ions coexisted (25 ± 0.1°C), and the ion selectivity coefficient for sodium ions was determined as logK ^Pot _CaNa =
It was -3.12.

This shows that the sensor of the present invention can quantify calcium ions at low concentrations even when sodium ions coexist.

Example 7 A redox membrane electrode of 2,6-dimethylphenol was prepared in the same manner as in Example 3.

Next, this electrode body was immersed in an immersion liquid containing a calcium ion carrier material and having the composition shown below in the same manner as in (ii) of Example 1, and then dried to form a calcium ion selective membrane on the electrolytically oxidized polymer membrane. (film thickness approx. 0.4mm).

(Immersion liquid) HDOPP-Ca 80mg DOS 360mg D-n-octylphenyl phosphonate 360mg Polyvinyl chloride 340mg Tetrahydrofuran 10ml The sensor prepared in this way has 10 ^-1 ~
It was found that calcium ion concentration could be measured without being affected by magnesium ions even if magnesium ions coexisted at a concentration of 10 ^-2 M.

The measurable calcium ion concentration of the sensor of the present invention is 10 ^-4 to 10 ^-1 M (the detection limit is approximately
10 ^-5 M).

Specific Effects of the Invention Since the present invention is a calcium ion sensor configured as described above, (i) it can be miniaturized and can be used for in situ measurement of in vivo solutions, and (ii) it has an internal liquid chamber. (iii) It is not affected by various coexisting substances such as dissolved oxygen in the test solution, and is not limited by the type of test solution. Can be used.

(iv) It has various features not found in conventional sensors, such as fast response speed and excellent stability over time.

[Brief explanation of drawings]

FIG. 1 shows an enlarged sectional view of the calcium ion sensor of the present invention. FIG. 2 is a diagram showing the relationship between the electromotive force and calcium ion concentration of the sensor of the present invention produced in Example 1. Figure 3 shows Example 3
FIG. 3 is a diagram showing the relationship between the electromotive force and calcium ion concentration of the sensor of the present invention produced in FIG. FIG. 4 is a diagram showing the potential response of the sensor. FIG. 5 is a diagram showing the relationship between the electromotive force and the magnesium ion concentration when the electromotive force of the same sensor was measured in the coexistence of calcium ions and magnesium ions. DESCRIPTION OF SYMBOLS 11... BPG, 11a... Top surface, 11b... Bottom surface part, 13... Electrolytic oxidation polymer membrane, 14... Calcium ion selective membrane, 15... Conductive adhesive, 16... Lead wire.

Claims (1)

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