JPH0143904B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to reference electrodes. Prior Art and Problems When measuring the electrode potential of a sensor with respect to a solution, the sensor is combined with a reference electrode to form a battery, and its electromotive force is measured. in this case,
The resulting electrode potential is relative to the reference electrode. Conventionally, hydrogen electrodes,
Calomel electrodes, silver-silver chloride electrodes, etc. have been mainly used. However, in the case of a hydrogen electrode, it is necessary to immerse the platinum electrode to which platinum black is attached in a measurement sample solution, and to use the electrode while blowing hydrogen gas into the vicinity of the platinum black. On the other hand, for calomel electrodes and silver-silver chloride electrodes, a reference solution chamber with a constant chloride ion concentration must be provided. Therefore, the conventionally used reference electrode has a relatively complicated structure and is difficult to miniaturize. Also. A reference electrode provided with a reference liquid chamber has the disadvantage that the reference liquid tends to mix with the measurement sample solution. OBJECT OF THE INVENTION Therefore, an object of the present invention is to provide a reference electrode that has a simple structure and can be miniaturized. Another object of the present invention is to provide a reference electrode that exhibits a constant equilibrium potential value, regardless of measurement conditions, without being affected by the ion species and their concentration in the measurement sample liquid. According to this invention, a conductor, a halide layer containing silver coated on the surface of the conductor, and a polymer film derived from at least one hydroxy aromatic compound directly applied to the surface of the halide layer. A coated reference electrode is provided. Further, according to the present invention, there is provided a reference electrode comprising silver and a polymer film derived from at least one hydroxy aromatic compound directly coated on the surface of the silver. The polymer membrane is preferably an electrolytically oxidized polymer membrane of a hydroxy aromatic compound. The hydroxyaromatic compound used in this invention has the formula (Here, Ar is an aromatic nucleus, each R is a substituent, n is an integer of 1 or more, m is 0 or an integer of 1 or more, and n+m does not exceed the effective valence number of Ar). Examples of such hydroxyaromatic compounds are phenols, 2,6- and 3,5
-xylenol, o-, m- and p-hydroxybenzophenone, o- and m-hydroxybenzyl alcohol, 2,2',4,4'-tetrahydroxybenzophenone, o-, m- and p-hydroxy Propiofenone, o-, m- and p
-Hydroxybenzaldehyde, o-, m- and p-benzophenol, o-, m- and p-
These are hydroxyacetophenone, 4-(p-hydroxyphenyl)-2-butanone, and bisphenol A. The polymer may be synthesized in advance, and such polymers include poly(phenylene oxide), poly(diphenylphenylene oxide),
Includes poly(dimethylphenylene oxide) and polycarbonate. Generally, the conductor surface is made of silver. DETAILED DESCRIPTION AND OPERATIONS OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings. As shown in FIG. 1A, a reference electrode 10 according to one embodiment of the present invention has an arbitrarily shaped conductor 11 covered with an insulating material 13 such as Teflon.
A predetermined polymer film 12 is directly applied and fixed to the exposed tip surface of the holder. The conductor 11 is made of an electrically conductive material, and in particular, its surface is preferably made of silver. Polymer film 1 adhered to the surface of the conductor 11
2 consists of a polymer derived from a hydroxyaromatic compound. Such hydroxyaromatic compounds are aromatic compounds having at least one hydroxyl group directly bonded to an aromatic nucleus, such as those having the formula (Here, Ar is an aromatic nucleus, each R is a substituent, n is an integer of 1 or more, m is 0 or an integer of 1 or more, and n+m does not exceed the effective valence number of Ar). The aromatic nucleus Ar may be a monocyclic type such as a benzene nucleus or a pyridine nucleus, or a polynuclear type. Polynuclear aromatic nucleus includes naphthalene nucleus,
Condensed ring types such as anthracene nuclei, and aromatic nuclei with alkylene,

It includes crosslinked types bonded by a crosslinking group such as [Formula]. Examples of the substituent R include alkyl groups such as methyl groups, aryl groups such as phenyl groups, alkylcarbonyl groups and arylcarbonyl groups.

[Formula] Hydroxyalkyl group (-R″OH), etc. Specific examples of such hydroxy aromatic compounds include phenol, 2,6- and 3,5-
Xylenol, o-, m- and p-hydroxybenzophenone, o- and m-hydroxybenzyl alcohol, 2,2',4,4'-tetrahydroxybenzophenone, o-, m- and p-hydroxypropylene Ofenone, o-, m- and p-
Hydroxybenzaldehyde, o-, m- and p-benzophenol, o-, m- and p-hydroxyacetophenone, 4-(p-hydroxyphenyl)-2-butanone, bisphenol A and two or more of these It is a mixture. In order to directly deposit and fix the film of the polymer derived from the hydroxy aromatic compound described above on the surface of the conductor 11, the hydroxy aromatic compound is applied to the upper surface of the conductor 11 by electrolytic oxidative polymerization. Polymerization method, or dissolving a pre-synthesized polymer (for example, poly(phenylene oxide), poly(diphenylphenylene oxide), poly(dimethylphenylene oxide), polycarbonate, etc.) in a suitable solvent such as benzene, etc. , a method can be adopted in which this solution is applied and adhered to and fixed on the surface of the conductor by dipping/coating and drying. The most preferred method is electrolytic oxidative polymerization. This method consists of electrolytically oxidatively polymerizing a hydroxyaromatic compound in an alkaline solvent such as methanol, and depositing an oxidized polymer film on the surface of the desired conductor as the working electrode. A reference electrode according to another aspect of the invention includes a first B
As shown in the figure, a polymer film 12 formed in the same manner as in FIG. 1A directly covers the halide layer 21 of the conductor 11 supported by the conductor 11. As shown in FIG. In order to form the halide layer 21, the conductor 11 is immersed in an aqueous solution containing a predetermined halogen ion to perform electrolysis. For example, when silver as a conductor is immersed in a 0.1M sodium chloride aqueous solution and electrolyzed for 30 minutes at a current density of 0.25 mA/cm ² , a silver chloride layer is obtained as a halide layer. There is no particular limit to the thickness of the polymer film, but
Approximately 0.01μ to 2.0μ is appropriate. Furthermore, the term polymer used in this specification includes both homopolymers and interpolymers (copolymers, terpolymers, etc.). The polymer membrane used in the reference electrode of this invention exhibits selective ion permeability. For example, a phenol electrolytic oxidation polymer membrane allows hydrogen ions, bromide ions, Fe ²⁺ acoions, etc. to permeate, but Fe
(edta) ^- , Fe(CN) ^3-6 _ions are not transmitted. Among the ionic species that permeate the membrane, if an ionic species that affects the equilibrium potential value of the conductor coexists in the sample solution, the membrane-coated electrode of the present invention cannot be used as a reference electrode. In such cases, the polymer membrane derived from the hydroxyaromatic compound may be coated with another, second membrane. This second membrane has many pores that selectively allow inert dissolved ionic species that do not affect the equilibrium potential value to permeate, and is made of polyacrylamide, polyurethane, polyvinyl chloride, polyamino acid, polyamide, polyethylene. ,
Polypropylene, poly(fluorinated compound), silicone rubber, poly 2-hydroxyethyl methacrylate, cellulose and its derivatives, synthetic rubber,
It can be formed from various polymer materials such as natural polymers (collagen, gelatin, natural rubber, etc.). As the second and third coating films, cationic and anionic polymer electrolytes such as quaternized, highly polymerized polyvinylpyridine and polymers with sulfonic groups such as Nafion (registered trademark) are used. A coating can also be used to prevent dissolved multiply charged ionic species from coming into direct contact with the substrate electrode surface. In addition, these coating films affect the solvent affinity and improve the equilibrium potential reaching speed (responsiveness). In addition, when the equilibrium potential value of the membrane-coated electrode of the present invention is affected by the concentration of dissolved ionic species in the sample solution, a halide layer is formed on the conductor surface,
The surface is coated with a polymer of hydroxy aromatic compound, the surface is further coated with a halogenated alkylammonium salt containing a retention agent such as Teflon (registered trademark), and the outside is covered with a thin film such as epoxy. Therefore, it can be used as a reference electrode. The above-described reference electrode of the present invention is connected to a sensor whose electrode potential is to be measured, and is used as a reference for measuring the electrode potential by immersing both in a sample solution. Examples of this invention will be shown below. Example 1 The periphery of the silver wire was insulated with Teflon, and the electrode surface was pretreated by the following method before electrolysis. Polish and smooth with silicone carbide paper and alumina powder (particle size 0.3 μm), wash with distilled water, wash with methanol, and dry. Next, to create the electrode coating film, a normal 3-electrode H-type cell was used as the electrode cell, the above electrode was used as the working electrode, a platinum mesh was used as the counter electrode, and a salt-saturated calomel electrode (SSCE) was used as the reference electrode. . The electrolyte was a methanol solvent containing 10mM phenol and 30mM sodium hydroxide, and was sufficiently deoxidized with argon gas before electrolysis. Applied voltage 1.0
It was stopped with a bolt (vs. SSCE), and constant potential electrolysis was performed for 2 minutes to coat the electrode surface with the oxidized polymer. Thereafter, the electrode surface was washed three times or more with distilled water to produce a polymer membrane-covered electrode. The structure of this reference electrode is shown in Figure 1A. The function of the membrane-coated electrode thus prepared as a reference electrode was investigated. As the measurement solution, a commercially available standard buffer solution and a phosphate buffer solution (a buffer solution containing a total phosphate concentration of 50 mM was used, and the pH of the solution was adjusted with sodium hydroxide and perchloric acid) were used (open system). The electromotive force of the membrane-coated electrode was measured using a saturated salt calomel electrode (SSCE) as a reference electrode. A plot of the measured electromotive force and the PH value (measured using a commercially available glass electrode) is shown in Figure 2 with a circle. From this figure, the electromotive force measured by the electrode of the present invention can be seen over a wide range of PH values (2.0
It is constant at pH8.0) and is not easily affected by hydrogen ion concentration. Furthermore, the response speed is approximately 1 minute, which is very fast. Therefore, it has become clear that this membrane-coated electrode can be used as a reference electrode for a PH sensor in the same way as a saturated calomel electrode under measurement conditions where the PH value of the sample solution is different. On the other hand, silver chloride was attached to the silver surface of the conductor,
A so-called solid state silver-silver chloride electrode was further coated with a polymer membrane in the same manner as above to produce a membrane-covered electrode. The structure of this electrode is shown in Figure 1B. The silver chloride substrate electrode was prepared by immersing the silver electrode in a 0.1M sodium chloride solution at 0.25 mAcm ^-2.
Silver chloride was deposited on the surface of the silver electrode by electrolytic oxidation for 30 minutes at a current density of . When the hydrogen ion concentration in the measurement solution (buffer solution) was changed and the equilibrium potential was measured between this membrane-covered electrode and a commercially available SSCE, the result was as shown by the △ mark in Figure 2.
Regardless of changes in PH value, the equilibrium potential is almost constant in the PH range of 4.0≦PH≦9.0, and the membrane-coated electrode of the present invention
It can be used as a reference electrode in a measurement solution in which a standard buffer solution or similar ionic species coexists. Note that the response speed to reach the equilibrium potential value is 1 to 10
It is a minute. Examples 2 to 5 Silver electrode substrates or silver chloride electrode substrates were produced in the same manner as in Example 1. 3 on the surface of these electrodes,
5-xylenol, o-hydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, and o-hydroxybenzyl alcohol were electrolytically oxidized and polymerized (same as in Example 1) to form the polymer film. Covered electrodes were prepared and the performance of these electrodes as a reference electrode was examined (Table 1).

【table】

[Table] From the above, it has been found that the membrane-coated electrode of the present invention has a substantially constant mV/PH over a wide PH range, and has the potential to be used as a reference electrode. Examples 6 and 7 Poly2,6-dimethylphenylene oxide (PPO) and polycarbonate were each dissolved in benzene at a concentration of 0.01% by weight, and a substrate coated with silver or silver chloride was immersed in these polymer solutions, and then dried. Then, a water-washable polymer membrane coated electrode was prepared (Table 2).

[Table] As a result, the relationship between the equilibrium potential value (mV) of the membrane electrode and the PH value is almost constant when the electrode of the present invention is used in a standard buffer solution or a measurement solution in which similar ions coexist. used as. Comparative Example 1 A silver electrode insulated around a silver wire with Teflon was used, polished and washed in the same manner as in Example 1, and its function as a reference electrode was examined. A commercially available standard buffer solution and a phosphate buffer solution (prepared in the same manner as in Example 1) were used as measurement sample solutions, and a commercially available standard buffer solution and a phosphate buffer solution (prepared in the same manner as in Example 1) were used as the reference electrode.
The electromotive force between the silver electrode and the silver electrode was measured using SSCE (open system). The electromotive force of this electrode is shown in Figure 3 □
As shown by the mark, it varies greatly depending on the pH of the sample solution and does not show a constant value. Therefore, a silver electrode without a coating film cannot be used as a reference electrode in sample solutions with different PH values. On the other hand, using a silver chloride electrode prepared in the same manner as in Example 1, the equilibrium potential of the electrode was measured with respect to a commercially available saturated calomel electrode while changing the pH value in the standard buffer solution and phosphate buffer solution. When I did,
As indicated by the triangle in FIG. 3, no constant value was obtained in the 2.0PH10.5 region. However, when similar measurements were performed using a buffer solution containing 7mM sodium chloride, the equilibrium potential value hardly changed in the pH range of 2.0 to 9.0, as shown by the circle in FIG.
Therefore, when a trace amount of chlorine ions coexists in the sample solution at a constant concentration, this electrode can be used as a reference electrode in the measurement solution. Example 8 In the same manner as in Example 1, a poly(phenol) film was directly coated on a silver surface by electrolytic oxidation polymerization to produce a film-coated electrode. Fe ²⁺ acoion was allowed to coexist in the sample solution, and the influence of the equilibrium potential value of the membrane-coated electrode between this membrane-coated electrode and a commercially available SSCE was investigated (Figure 4). In a system where Fe ²⁺ acoion coexists, the equilibrium potential of the membrane-covered electrode is affected (line b). Therefore, as a result of similar measurements using a silver/poly(phenol)/Teflon measurement liquid type electrode coated with a ^Teflon membrane as the second membrane, we found that the membrane was The coated electrode had a constant equilibrium potential and was not affected by Fe ²⁺ acoion (line a). However, the measurement was performed at PH=4.00. Other metal species were also investigated and the following results were obtained.

[Table] Example 9 A silver/poly(phenol)/Teflon type electrode prepared in the same manner as in Example 8 was used as a reference electrode, and on the other hand, a polymer membrane-covered electrode prepared by electrolytically oxidatively polymerizing phenol on a platinum electrode was used as a working electrode. of both electrodes.
We investigated its responsiveness as a PH sensor. The equilibrium potential of this electrode was measured with a digital voltmeter (TR6841 model manufactured by Takeda Riken), and the equilibrium potential and PH of the electrode were measured.
As shown in Figure 5, the correlation between the values (measured with a commercially available glass electrode) satisfies a good linear relationship over a wide range of PH2.5 to 10.0 at 25°±0.01°C, and the slope of this straight line is 50mV/PH. It was hot. The response speed to reach the equilibrium potential value was about 30 minutes. Therefore, it can be seen that the membrane-coated electrode functions as a reference electrode for the PH sensor. Furthermore, when Fe(edta) ^1- (edta = ethylenediaminetetraacetic acid ion) coexisted, if its concentration was 3mM or less, no effect on the equilibrium potential was observed and it functioned as a reference electrode. The response time was approximately 30 minutes. In addition, Co(), ion, Cu() ion
The same was true when coexisting at 3mM or less. Ru (edta) ^1- influenced. Example 10 In the same manner as in Example 1, a poly(phenol) film was directly coated on the surface of a silver wire base material by electrolytic oxidation polymerization to produce a film-coated electrode. This electrode is made of quaternized polyvinylpyridine (QPVP) (degree of chloride methylation approximately 90%, average degree of polymerization of polyvinylpyridine 7500).
was immersed in a methanol solution for 1 minute, and then covered with a naphion membrane (No. 125, polyfluorosulfonic acid resin manufactured by Dupont) to examine its effectiveness as a reference electrode. Silver of the present invention/poly(phenol)/
When the equilibrium potential value of the electrode made of QPVP/nafion membrane was measured against commercially available SSCE, PH2.0PH
It was found that the electromotive force (equilibrium potential) was constant in the PH range of 10.0, and the electrode of the present invention could be used as a reference electrode. Furthermore, the response speed to reach the equilibrium potential value was about 15 minutes. An electrode prepared under the same electrolytic conditions as in Example 1, in which the surface of the platinum/poly(phenol) membrane was coated with QPVP and then with a naphion membrane, was used as the working electrode, and the electrode of the present invention was used as the reference electrode to measure the sample solution. PH
Measurement was carried out. As a result, as shown in Figure 6,
PH to equilibrium potential value in the range of 2.2PH10.0
The dependence of satisfies a linear relationship, and the slope of this straight line is
It was 50mV/PH (25°±0.01°C). In addition, the response speed to reach the equilibrium potential value is 1 to 15 minutes, and the response speed is faster than that of the electrode of Example 9 (7th
figure). In FIG. 7, lines a, b, c, and d are for PH of 10.02, 6.86, 4.01, and 2.23, respectively, and were measured in this order. Example 11 Trioctylmethylammonium chloride: Lacquer: Methyl ethyl ketone = on the surface of a silver-silver chloride electrode
After coating the melt with a ratio of 1:0.7:0.748
After drying for a while, a membrane-covered electrode was prepared. The potential difference between this electrode and a commercially available SSCE remains constant even when the pH of the sample solution is changed, but the response time is slow at about 30 minutes. However, when the surface of the silver chloride was coated with an electrolytically polymerized poly(phenol) film and a similar film was coated on the outside, the response speed was as fast as about 15 minutes. Example 12 As in Example 9, a Teflon membrane-coated electrode was used as the reference electrode, and a poly(4,4'-diaminodiphenyl ether) membrane-coated electrode (10mM4,
We fabricated a PH electrode using 4′-diaminodiphenyl ether (a polymer film was coated on a platinum electrode by electrolytic oxidation polymerization method in an acetonitrile solvent containing 0.1M sodium perchlorate), and evaluated the performance of this electrode. Examined. The correlation between the equilibrium potential value and the PH value (measured using a commercially available glass electrode) of the electrode of the present invention is shown in FIG. A linear relationship is established over a wide range of pH values from 2.5 to 9.0, and the slope of this straight line is approximately 48 mV/PH.
(Measurement temperature 25°±0.01°C). The response speed to reach the equilibrium potential value was about 30 minutes. Next, we investigated the influence of coexisting ionic species on hydrogen ion concentration measurements at PH4.0 (Figure 9). Fe
Hydrogen ion concentration can be measured even when ion species such as (edta) ^-1 and Cu ⁽ 〓 ⁾ ions coexist. on the other hand,
When Co ⁽ 〓 ⁾ ions, Ru (edta) ^-1 , and Fe ⁽ 〓 ⁾ (aco) ions coexist, the hydrogen ion concentration cannot be measured accurately. Note that the response speed to reach the equilibrium potential value was 1 minute to 5 minutes. In Figure 9, line a is
CuSO ₄ , line b is Fe(edta) ^1- , line c is FeSO ₄
, line d shows the case where Ru(edta) coexists, and line e shows the case where CoCl ₂ coexists. Specific Effects of the Invention The reference electrode of the invention described above has the following effects. (1) The reference electrode of the present invention has a structure in which a predetermined polymer film is directly deposited on the surface of a halide layer supported on silver or a conductor, and there is no need to provide a reference liquid chamber. Therefore, it is possible to miniaturize the conductor to the processing limit, and only a small amount of the measurement sample solution is required. (2) Since the reference electrode of the present invention does not require a reference liquid chamber, the reference liquid may not mix with the measurement solution or be easily affected by temperature, unlike in conventional reference electrodes. No inconvenience will occur. (3) Even in a solution system where multiple types of ions coexist, the equilibrium potential can be devised to be constant. (4) It can also be used in heterogeneous solution systems such as suspensions, slurries, and gels. (5) There is no reference liquid chamber, and the temperature of the polymer membrane is approximately 200℃.
It can be used even in high temperature liquids. (6) Can be used repeatedly until the polymer membrane is worn out.

[Brief explanation of drawings]

1A and 1B are cross-sectional views of reference electrodes according to different embodiments of the present invention, FIG. 2 and FIGS. 4 to 9 are graphs showing the characteristics of the reference electrode of the present invention, and FIG. 3 is a comparative example. Graph showing electrode characteristics. 11... Conductor, 22... Polymer film, 13...
Insulating film, 21... halide layer.

Claims (1)

[Scope of Claims] 1 A conductor, a halide layer containing silver coated on the surface of the conductor, and a polymer film derived from at least one hydroxy aromatic compound on the surface of the halide layer. A reference electrode that is directly coated. 2. The reference electrode according to claim 1, wherein the polymer film is an electrolytically oxidized polymer film. 3 Hydroxy aromatic compound has the formula (Here, Ar is an aromatic nucleus, each R is a substituent, n is an integer of 1 or more, m is 0 or an integer of 1 or more, and m+n does not exceed the effective valence of Ar). The reference electrode according to range 1 or 2. 4 The hydroxy aromatic compound is phenol, 2,
6- and 3,5-xylenol, o-xylenol, o-, m- and p-hydroxybenzophenone, o- and m-hydroxybenzyl alcohol, 2,2,4,4'-tetrahydroxybenzophenone, o-, m- and p-hydroxybenzaldehyde, o-, m- and p-benzophenol, o-, m- and p-hydroxyacetophenone, 4-(p-hydroxyphenyl)-
The reference electrode according to claim 3, which is selected from the group consisting of 2-butanone and bisphenol A. 5. The reference electrode according to claim 1, wherein the polymer film is poly(phenylene oxide), poly(diphenylene oxide), or polycarbonate. 6. The reference electrode according to claim 1, wherein the conductor is made of silver. 7. A reference electrode comprising silver and a polymer film derived from at least one hydroxy aromatic compound directly coated on the surface of the silver. 8. The reference electrode according to claim 7, wherein the polymer film is an electrolytically oxidized polymer film. 9 Hydroxy aromatic compound has the formula (Here, Ar is an aromatic nucleus, each R is a substituent, n is an integer of 1 or more, m is 0 or an integer of 1 or more, and m+n does not exceed the effective valence of Ar). The reference electrode according to range 7 or 8. 10 Hydroxy aromatic compound is phenol,
2,6- and 3,5-xylenol, o-xylenol, o-, m- and p-hydroxybenzophenone, o- and m-hydroxybenzyl alcohol, 2,2,4,4'-tetrahydroxybenzophenone Non-, o-, m- and p-hydroxybenzaldehyde, o-, m- and p-benzophenol, o-, m- and p-hydroxyacetophenone, 4-(p-hydroxyphenyl)-2-butanone , and bisphenol A. 11. The reference electrode according to claim 7, wherein the polymer film is poly(phenylene oxide), poly(diphenylene oxide), or polycarbonate.