JPS61251764A - Ph sensor - Google Patents

Abstract

PURPOSE:To reduce the size of a pH sensor by depositing a film which develops an oxidation reduction function of a quinone-hydroquinone type on the surface of a conductive base body and depositing a hydrogen ion carrier film which can transport selectively the hydrogen ions in a soln. on the surface of said film. CONSTITUTION:This pH sensor is constituted by coating an insulator 12a around the conductive base body made of a carbon material, platinum, etc. into an optional shape and coating the oxidation reduction film 13 of the quinon- hydroquinone type on the surface at the top end 11a of the body 11. The hydrogen ion carrier film 14 which can transport selectively the hydrogen ion in the soln. is further deposited and fixed on the surface of the film 13. The reduction in the size of the pH meter to the working limit range of the body 11 is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pH sensor, and more particularly to a pH sensor comprising a hydrogen ion carrier film coated on the surface of an electrode substrate.

10 Purpose of the invention [Prior art and problems to be solved by the invention] Conventionally, a small pH measuring device uses a glass membrane electrode,
The outer periphery of the electrode is covered with an insulating material such as a metal or a tube made of polyurethane resin (catheter electrode). However, the glass membrane of the glass membrane electrode is easily damaged and requires frequent cleaning to remove ion obstructions such as proteins attached to the surface of the glass membrane, making it necessary to be careful when using the electrode. Therefore, instead of this glass membrane, a small-sized pH meter was developed that used a so-called hydrogen ion carrier membrane, in which a hydrogen ion transport material was encapsulated in a polymer membrane (US Pat. No. 7549).

However, this pH measuring device using a hydrogen ion carrier membrane has problems such as reproducibility of measurements because carrier membrane components tend to elute. In addition, a liquid film type electrode has been reported as an improved version of this pH measuring device [Analytica
Analytica Chimica
Acta) 131 (1981) 111-1
16]. However, all of them have an internal liquid chamber, and structurally there is a limit to miniaturization.

[Means for solving problems]

The present inventor aims to make the p)I measuring device smaller,
As a result of intensive research on solid-state pH sensors that do not require an internal liquid chamber, we have found that a pH sensor consisting of an electrode with a hydrogen ion carrier film coated on the surface of the electrode base can be made extremely small, and that it can be dissolved in the measurement solution. The present invention was completed based on the discovery that the sensor has excellent sensor properties such as being almost unaffected by oxygen and having a fast response speed.

That is, the present invention is a pH sensor that measures the pH of a solution based on electrode potential response, in which a film expressing a quinone-hydroquinone type redox function is deposited on the surface of a conductive substrate, and then a solution is applied to the surface of the film. The present invention provides a pH sensor coated with a hydrogen ion carrier membrane capable of selectively transporting hydrogen ions therein to its surface.

The present invention further provides a membrane exhibiting a quinone-hydroquinone type redox function, wherein the conductive substrate is selected from the group consisting of a carbon material, a noble metal, and a material whose surface is coated with a semiconductor material. p)1 which is a polymeric membrane derived from hydroxyaromatics
sensor.

A pH sensor in which a membrane expressing a quinone-hydroxy aromatic redox function has a thickness of 1 μm to 0.2 μm.

A membrane that exhibits quinone-hydroquinone type redox function (
A pH sensor with an electrolyte (hereinafter referred to as a redox membrane) impregnated with an electrolyte.

The hydrogen ion carrier membrane is made by supporting a hydrogen ion carrier substance and an electrolyte salt on a polymer compound.p
H sensor.

The hydrogen ion carrier substance has the following formula (wherein 84% avian and avian are the same or different alkyl groups, at least two of which have 8 to 1 carbon atoms)
A pH sensor which is a compound represented by:

A pH sensor in which the electrolyte salt is an alkali metal salt of tetrakis(p-chlorophenyl)boronic acid.

A pH sensor whose polymer compound is divinyl chloride resin.

The polymer compound is at least one selected from the group consisting of dioctyl sebacate, dioctyl adipate, and dioctyl maleate as a plasticizer.
pH sensor containing seeds.

The present invention provides a PH sensor in which the hydrogen ion carrier membrane has a thickness of 200 μm to 10 μm.

(1) Specific structure of the invention The following describes the pH sensor of the invention with reference to FIG. 1, which shows an example of the pH sensor of the invention.

As shown in FIG. 1, the pH sensor of the present invention includes a conductive base 11 of arbitrary shape, an insulator 12JL coated around it, a redox film 13 coated on the surface of the tip 11a of the conductive base, and a redox film 13 coated on the surface of the tip 11a of the conductive base. A hydrogen ion carrier film 14 is applied to the surface.
It is fixed.

As the conductive substrate 11, for example, basal plane,
Carbon materials such as pyrolytic graphite (BPG) and glassy carbon, noble metals such as gold, platinum, silver, and palladium, or indium oxide on the surface of these conductors.
Examples include those coated with a semiconductor such as tin oxide.

Further, the redox film deposited on the surface of the conductive substrate 11 undergoes the following quinone-hydroquinone type redox reaction (in the formula, Otori represents an aromatic nucleus, and Toshi represents a ring structure corresponding to R1). A membrane that can perform this is used.

A compound capable of forming such a redox film is the following formula (% formula %) (In the formula, Ar is an aromatic nucleus, each R3 is a substituent, m is the effective valence number of atomic or Ar, and n is O or A hydroxy aromatic compound represented by the following formula (indicating the effective valence number of Ar -1) is suitable. A
The aromatic nucleus of r may be a monocyclic one such as a benzene nucleus, or a polycyclic one such as an anthracene nucleus, bire/nucleus, chrysene nucleus, perylene nucleus, coronene nucleus, etc. Moreover, not only a benzene bone core but also a heterocyclic bone core may be used.

Specifically, for example, dimethylphenol, phenol,
2-hydroxypyridine, o-1A is m-benzyl alcohol, o-lm- or p-hydroxybenzaldehyde, o- or m-hydroxyacetophenone, o+
, m-4 or p-hydroxypropiophenone, o-l
m-mafc is p-benzophenol, o-lm-also H
p-Hydropal benzophenone% ' -% m-'!
or p-carboxyphenol, diphenylphenol, 2-)f-8-hydroxyquinoline, 5-hydroxy-1,4-naphthoquinone, 4-(p-hydroxyphenyl)2-butanone, 1,5-dihydroxy-1, 2
, 3,4-tetrahydronaphthalene, bisphenol A
Examples include 1 salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, and 1°8-dihydroxyanthraquinone.

The redox membrane used in the present invention may be a homopolymer of these compounds or an interpolymer such as a copolymer containing these compounds.

Furthermore, the redox membrane used in the present invention includes, for example, BoIJ (2,6-dimeteru-1.4-7 dinilene ether), poly(phenol), poly(xylenol);
Organic compounds containing the above-mentioned hydroxyaromatic compounds or corresponding quinone compounds, such as quinone-based vinyl polymer condensation compounds such as hyrazoquinone-based vinyl monomer polymers and inalloxazine-based vinyl monomer polymers; hydroxyaromatic compounds or corresponding quinone compounds; Any substance that has the redox reactivity, such as a low polymerization degree polymer compound (oligomer) of a quinone compound, a polyvinyl compound, a polyamide compound, etc., on which a hydroxy aromatic compound or a corresponding quinone compound is fixed. It can be used if

Further, the redox membrane used in the present invention can be used by impregnating it with an electrolyte. As an electrolyte,
Examples include phosphoric acid, dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoroborate, and tetraphenylborate. To impregnate the redox film with electrolyte, after depositing the redox film on a conductive substrate,
A simple method is to immerse it in an electrolyte solution.

In order to deposit the redox film 13 on the surface of the tip 11a of the conductive substrate, a hydroxy aromatic compound can be directly polymerized on the substrate surface by electrolytic oxidation polymerization or electrolytic deposition, or by electron beam irradiation. , a method of dissolving a pre-synthesized polymer in a solvent by applying light, heat, etc., and fixing this solution to the substrate surface by dipping/coating and drying; A method of directly fixing to the substrate surface by irradiation treatment can be adopted. Among these methods, electrolytic oxidative polymerization is particularly preferred.

In the present invention, the electrolytic oxidative polymerization method is carried out by electrolytically oxidatively polymerizing a hydroxy compound in a suitable supporting electrolyte solution and depositing a polymer film on the surface of a conductive substrate. Examples of the solvent include acetonitrile, water, dimethylformamide, dimethyl sulfoxide, propylene carbonate, etc., and examples of the supporting electrolyte include perchloric acid, sulfuric acid, disodium sulfate, phosphoric acid,
Preferred examples include boric acid, potassium tetrafluorophosphate, and quaternary ammonium salts. The polymer film deposited in this way is extremely dense and can block oxygen permeation even if it is a thin film.

The thickness of the redox film is preferably 0.1 μm - 0.2 m. If it is thinner than 0.1 μm, the effect of the present invention will not be achieved, and if it is thicker than 0.2 m, the membrane resistance will increase, which is not preferable.

Furthermore, the hydrogen ion carrier film 14 deposited on the surface of the redox film 130 is made of a polymeric hydrogen ion carrier substance and electrolyte salt for selectively transporting hydrogen ions in the solution to the surface of the nuclear redox film. A membrane supported on a compound is used.

As the hydrogen ion carrier substance, amines can be used, such as amines represented by the following formula (wherein R4, Rs and H have the same meanings as above), and amines represented by the following formula (wherein R2 is the carbon number 8 to 18 alkyl groups), and preferred is tri-n-dodecylamine.

Examples of electrolyte salts include sodium tetrakis (p-
chlorophenyl) porate, potassium tetrakis (p-
Chlorophenyl)borate, sodium tetrakis(p
-chlorophenyl) phosphate, potassium tetrakis (p-
chlorophenyl) phosphoric acid, and compounds represented by the following formula % (wherein R' represents an alkyl group, preferably an alkyl group having 2 to 6 carbon atoms).

In order to deposit the hydrogen ion carrier film 14 on the surface of the tip portion 111 of the conductive substrate, for example, a solution of a polymer compound as a carrier, a hydrogen ion carrier substance, and an electrolyte salt may be applied to the surface of the electrode substrate and dried. . Examples of the polymer compound include vinyl chloride resin, vinyl chloride-ethylene copolymer, polyester, polyacrylamide, polyacrylonitrile, polyurethane, and silicone resin, and those from which plasticizers are difficult to elute are used. Examples of such plasticizers include dioctyl sebacate 3, dioctyl adipate,
Examples include dioctyl maleate. Also,
Tetrahydrofuran is preferably used as the solvent.

The thickness of the hydrogen ion carrier membrane is 200 μm to 10 m.
In particular, it is preferable that the thickness be 300 μm to 1 thick.

If it is thinner than 200 μm, the effect of the present invention will not be achieved,
Moreover, if it is thicker than 10 m, the film resistance will increase, which is not preferable.

10 Specific Actions and Effects of the Invention [Effects] The plot of electromotive force against pH (hereinafter referred to as Nernst plot) by the pH sensor of the invention has a wide range of Op.
It shows a linear relationship with a slope of approximately -59 mV/pH (37°C) in the H region. Therefore, the following formula (where E is the electromotive force (
mV), Eo is a constant potential (mV), R is a gas constant, T is a thermodynamic temperature, F is a Faraday constant, and [H] represents a hydrogen ion concentration.

〔effect〕

The pH sensor of the present invention is constructed as described above, and can measure pH based on electrode potential response by immersing it in a solution. Therefore, since an internal reference liquid is not required, the size can be reduced to a limited range of processing of the conductive substrate, and a small amount of measurement sample liquid is required.

In addition, ■It is less susceptible to the effects of dissolved oxygen in the measurement sample solution, ■It has a rapid potential response, can be miniaturized so that it can be inserted into the body, and ■It is a conductor because no electrode reaction occurs on the conductor surface. 1) The observed electromotive force hardly depends on the type of sample solution to be measured, so for example, a calibration curve created using a standard solution can be used as is for pH measurement of blood or serum. It has features such as being able to

■Example of 0 invention Next, the present invention will be explained with reference to Examples.

Example 1 A pH sensor having the shape shown in FIG. 1 was manufactured by the following method.

Basal Plain Pyrolitics Graphite (
BPG) (manufactured by Union Carbide) with a diameter of 1.
After cutting out a cylinder of 3 mu, a lead wire 17 was connected to the bottom part 11b using a conductive adhesive (manufactured by Amicon, C-850-6), and a Teflon tube 12b with a diameter of 1.7 tx was attached. and filled with an insulating material (manufactured by Three Bond, TB2067) to electrically insulate. The tip part 111 of the electrode of the BPG substrate 11 prepared in this way was peeled off with a knife blade to expose the new basal surface, and the working electrode was used as the working electrode, the saturated sodium chloride calomel electrode (5SCE) was used as the reference electrode, and the platinum mesh was used as the working electrode. As a counter electrode, electrolytic oxidation is performed under the following conditions, and the tip of the base 11&
A redox polymer film 13 was formed on the surface.

The electrolytic solution used was an acetonitrile solution containing 0.2 mol/liter of perchloric acid as a supporting electrolyte and 0.5 mol/liter of 2,6-dimethylphenol as a monomer. Electrolytic oxidation was performed by scanning the electrolytic voltage from 0 volts (vs. 5SCE, hereinafter the same) to 1.5 volts three times at a sweep rate of 50 millivolts/second, and then performing constant potential electrolysis at 1.5 volts for 10 minutes.

The membrane prepared in this way (clear blue when dry) was washed with methanol (the color of the membrane changed to orange) and then immersed in a phosphate buffer solution of pH 7.4 to stabilize the potential of the redox membrane. .

Next, this redox membrane electrode was washed with water, dried, and coated with a hydrogen ion carrier membrane using the method described below.

First, tIJ-n-dodecylamine:y (TDDA) 25.51n9 as a hydrogen ion carrier, potassium tetrakis(p-chlorophenyl)borate (KT, C1PB) 5.7~ as an electrolyte salt, and vinyl chloride (bor) as a polymer. (PVC, Kanebuchi Chemical, PS
L-10, average degree of polymerization n = 1050) 367mg
, dioctyl sepacate (DO8) 732 as a plasticizer
A coating solution A prepared by dissolving # in 10% of tetrahydrofuran (THF) was applied to the surface of the oxidation-reduction membrane to a thickness of 2μ to reinforce the oxidation-reduction membrane. Next, the electrode is inserted into a t-pvc tube, and after filling it with a paste resin solution having the following composition,
The mixture was heated separately at 140° C. for 1 minute to form a gel, thereby forming a hydrogen ion carrier film 14 having a thickness of about 1 fl. This electrode was further dipped in coating solution A several times in order to close the gap caused by volume reduction during gelation, dried, and then subjected to the following test.

Base resin liquid composition: TDDA 0.3 P KTp (4PB O, t8 f-D, O819,
68f-PVC9,84? Test Example 1 Standard phosphate buffer solution (
pH4,54,5,32,6,47,7,45,8,1
The electromotive force in 01 was measured using a bipolar cell. Note that a saturated chloride (IJ) calomel electrode (5SCE) was used as the reference electrode, and the measurement was performed at 37±0.1°C. The results are shown in Figure 2. In addition, in the same figure, standard serum [Persatol A (Ve
rsatol Al, Warner Lumber) (W
(manufactured by Erner Lambert) are also shown.

As is clear from Fig. 2, the electromotive force E and pI (showing a good linear relationship, the slope of the straight line is -60 mV/pH, the value predicted from the Nernst equation -a 1.2
Almost consistent with mV/pH, 7'c.

In addition, immediately after pH sensor production, 9 days later, 15 days later, 27 days later,
Days later, the electromotive force was measured in the same manner as above, and the stability of the Nernst plot over time was examined. The results are shown in FIGS. 3 and 4.

As is clear from Figures 3 and 4, the slope of the Nernst plot drops to -60 mV/pH after 10 days of production.
is the ideal value, and E. also converges to 500mV vs. sscg. Therefore, a Nernst plot created 10 days after the pH sensor was created can be used as a calibration curve.

Note that the pH response time of the electrode prepared in Example 1 was 95
% response was within 5 seconds, which was an extremely short time.

Test Example 2 The electromotive force E in a standard serum Persatol (manufactured by Warner Lambard) solution was measured using the pH sensor prepared in Example 1. In addition, the OpH of this solution was measured using a commercially available glass electrode (91-02, manufactured by ORION 1).The electromotive force E that the electrode of the present invention should exhibit at that pH value was determined from the calibration curve (Figure 2). Figure 5 shows the difference in electromotive force between these electrodes (ΔE=E, -E, l) plotted against the number of days after the pH sensor was fabricated. The calibration m obtained in Test Example 1 was used.

As is clear from Figure 5, after fabricating the pH sensor, 10
There was almost no difference in the pH measurement values after 1 day, indicating that the sensor of the present invention had sufficient accuracy after its operation stabilized.

Furthermore, when pH measurements using the sensor of the present invention were continued, no fluctuations were observed in the pH measurements even after 2 to 3 months.

This shows that the sensor of the present invention has excellent durability.

Next, when the pEI was measured using the sensor of the present invention while varying the PO2f in the standard sap from O to 740 mmHf, the electromotive force showed a constant value with a deviation of ±1 mV. This shows that the sensor of the present invention is hardly affected by dissolved oxygen in the sample.

[Brief explanation of the drawing]

Fig. 1 is an enlarged longitudinal cross-sectional view of an example of the p'a sensor of the present invention, Fig. 2 is a drawing showing the Nernst plot of the pH sensor produced in Example 1, and Fig. 3 is a diagram showing the Nernst plot of the pH sensor produced in Example 1. A drawing showing the stability over time of the slope of the obtained Nernst plot, FIG. 4 is the intercept E of the same Nernst plot. Figure 5 is a diagram showing the stability over time of the difference between the electromotive force of the pH sensor of the present invention during standard dissolution and the electromotive force of the glass electrode. DESCRIPTION OF SYMBOLS 11--Conductive base 11 m--Tip portion 1 l b--Bottom portion 12&--Insulator 12 b--Teflon tube 13--M-Redox membrane 14--Hydrogen ion carrier Membrane 15 --- Conductive adhesive 16--, more than polyvinyl chloride tube

Claims (1)

[Scope of Claims] 1. A pH sensor that measures the pH of a solution based on electrode potential response, in which a film exhibiting a quinone-hydroquinone type redox function is deposited on the surface of a conductive substrate, and then the film is coated on the surface of a conductive substrate. A pH sensor comprising a hydrogen ion carrier film that can selectively transport hydrogen ions in a solution to the surface of the pH sensor. 2. The pH sensor according to claim 1, wherein the conductive substrate is selected from the group consisting of carbon materials, noble metals, and materials whose surfaces are coated with semiconductor materials. 3. The pH sensor according to claim 1, wherein the membrane expressing a quinone-hydroquinone type redox function is a polymer membrane derived from a hydroxyaromatic. 4. The pH sensor according to claim 1 or 3, wherein the membrane exhibiting a quinone-hydroquinone type redox function has a thickness of 1 μm to 0.2 mm. 5. The pH sensor according to claim 1, 3 or 4, wherein the membrane exhibiting a quinone-hydroquinone type redox function is impregnated with an electrolyte. 6. The pH sensor according to claim 1, wherein the hydrogen ion carrier membrane has a hydrogen ion carrier substance and an electrolyte salt supported on a polymer compound. 7. The hydrogen ion carrier substance has the following formula ▲ Numerical formula, chemical formula, table, etc. The pH sensor according to claim 6, which is a compound represented by the following formula. 8. The pH sensor according to claim 6, wherein the electrolyte salt is an alkali metal salt of tetrakis(p-chlorophenyl)boronic acid. 9. The pH sensor according to claim 6, wherein the polymer compound is a vinyl chloride resin. 10. Claim 6 or 9, wherein the polymer compound contains at least one selected from the group consisting of dioctyl sebacate, dioctyl adipate, and dioctyl maleate as a plasticizer. The pH sensor described. 11. The hydrogen ion carrier film has a thickness of 200 μm to 10
The pH sensor according to claim 1, 6 or 7, which is a pH sensor of n.