JPS6313148B2 - - Google Patents

Description

[Detailed Description of the Invention] BACKGROUND OF THE INVENTION Technical Field The present invention relates to a PH sensor, and more particularly to a PH sensor in which a polymer film is directly attached to the surface of a conductor, and which measures hydrogen ion concentration based on electrode potential response. Regarding. Prior art and problems Conventionally, hydrogen electrodes and quinhydrone electrodes have been known as electrodes for measuring hydrogen ion concentration, but today, glass electrodes have become widely used due to their wide range of application and accuracy. ing. The principle of PH measurement using this glass electrode consists of separating two solutions with different hydrogen ion concentrations, one of which is used as a reference solution, by a thin glass membrane, and measuring the potential difference generated on both sides of this glass membrane. That is, with a glass electrode, it is necessary to provide a reference liquid chamber, and therefore miniaturization is difficult. In addition, in solutions containing sticky substances, the sticky substances adhere to the glass membrane, making it difficult to measure the PH.
The reproducibility of electrode potential response may deteriorate. In addition, the resistance of the glass membrane of the glass electrode is 10 to 100MΩ
Therefore, an ordinary potentiometer cannot be used alone to measure PH, and an amplifier with high input impedance is required. Purpose of the Invention Therefore, the purpose of the present invention is to eliminate the need to provide a reference liquid chamber, and thus to achieve miniaturization.
Our goal is to provide PH sensors. In addition, the purpose of this invention is to have a fast potential response speed.
The object of the present invention is to provide a PH sensor capable of measuring a wide range of PH regardless of the type of sample solution to be measured. A further object of the present invention is to provide a PH sensor that does not require the use of a high input impedance amplifier for measurement. The above objects and other objects that will become clear from the following description are, according to the present invention, a PH sensor formed by directly depositing a polymer film derived from a hydroxy aromatic compound on the surface of a conductor. It is achieved by doing so. Preferably, the polymer film has a low impedance and is obtained by electrolytic oxidation polymerization. Hydroxyaromatic compounds have the formula (Here, Ar is an aromatic nucleus, each R is a substituent, and m is the effective valence number of O to Ar). Specific examples include phenol, dimethylphenol, hydroxypyridine, o- and m-
Benzyl alcohol, o-, m- and p-hydroxybenzaldehyde, o- and m-hydroxyacetophenone, o-, m- and p-hydroxypropiophenone, o-, m- and p-
Benzophenol, o-m- and p-hydroxybenzophenone, o-, m- and p-carboxyphenol, diphenylphenol, 2-methyl-8-hydroquinoline, 5-hydroxy-
These include 1,4-naphthoquinone, 4-(p-hydroxyphenyl)-2-butanone, 1,5-dihydroxy-1,2,3,4-tetrahydronaphthalene, bisphenol A, or a mixture thereof.
When viewed as a polymer film, it is polyphenylene oxide or polycarbonate, which is obtained by dissolving the polymer film in a solvent, coating it on the surface and drying it, and specifically, polyphenylene oxide derivatives, polydiphenyl/phenylene oxide, and polydimethylphenylene. Examples include oxides and polycarbonate derivatives. DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings. As shown in FIG. 1, the PH sensor of the present invention is constructed by covering a conductor 11 of arbitrary shape with an insulator 13, and attaching and fixing a predetermined polymer film 12 on the surface of the tip. The conductor 11 is made of a conductive material, preferably platinum or the like. Polymer film 1 adhered to the surface of the conductor 11
2 is made of a polymer of hydroxy aromatic compound.
Such hydroxyaromatic compounds may have, for example, the general formula (Here, Ar is an aromatic nucleus, each R is a substituent, and m is the effective valence number of O to Ar). The aromatic nucleus Ar may be monocyclic (for example, benzene nucleus, pyridine nucleus) or polynuclear (for example, quinoline nucleus, naphthoquinone nucleus, bisphenol nucleus). 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), carboxyl group, aldehyde group, hydroxyl group, etc. Specific examples of such hydroxy aromatic compounds include phenol, dimethylphenol (for example, 2,6- and 3,5-dimethylphenol), 2-, 3- and 4-hydroxypyridine,
o- and m-benzyl alcohol, o-, m-
and p-hydroxybenzaldehyde, o-,
m- and n-hydroxyacetophenone, o
-, m- and p-hydroxypropiophenone, o-, m- and p-benzophenol, o
-m- and p-hydroxybenzophenone, o
-, m- and p-carboxyphenols, diphenylphenols (e.g. 2,6- and 3,
5-diphenylphenol), 2-methyl-8-
Hydroquinoline, 5-hydroxy-1,4-naphthoquinone, 4-(p-hydroxyphenyl)-2
-butanone, 1,5-dihydroxy-1,2,
3,4-tetrahydronaphthalene, bisphenol A, etc. Note that the term polymer used in this specification includes both homopolymers and interpolymers (eg, copolymers, terpolymers, etc.). Specific examples of the polymer film include polyphenylene oxide or polycarbonate. Specifically, it is as described above. In order to deposit such a polymer film of a hydroxy aromatic compound on the surface of the conductor 11, the hydroxy aromatic compound is coated onto the conductor by an electrolytic oxidation polymerization method, a plasma polymerization method, a thermal polymerization method, a radiation polymerization method, etc. 11 A method of polymerizing on the surface, a method of dissolving a pre-synthesized polymer in a solvent and fixing this solution on the conductor surface by dipping/coating and drying, and a method of polymerizing the polymer film by chemical treatment, physical treatment or A method of directly fixing it to the surface of the conductor by irradiation treatment can be adopted. The most convenient of the above deposition methods is by electrolytic oxidative polymerization. In this method, a hydroxy aromatic compound is electrolytically oxidized and polymerized in an alkaline solvent such as methanol, and a polymer film is deposited on the surface of a desired conductor as a working electrode. There is no particular limit to the thickness of the polymer film, but it is 0.1μ or more.
Approximately 2μ is appropriate. Specific effects of the invention The PH sensor of the above-mentioned configuration is used to determine the PH of a sample solution.
To measure PH, as shown in FIG.
Immerse silver-silver chloride electrodes, calomel electrodes, etc. and the PH sensor 2 relative to the reference electrode 24
3, the potential difference (electromotive force) is measured with a potentiometer 26. At this time, it is preferable to stir the sample solution 22 with a stirrer 25. Then, the PH of the sample solution is determined from the correlation diagram between electromotive force and PH prepared in advance. The relationship between the electromotive force and PH due to the PH sensor of this invention is a linear relationship with a slope of 59 mV/PH in a wide range of PH regions, and is expressed by the formula E=E ₀ −RT/Fln[H ⁺ ] (where E is the electromotive force It satisfies the Nernst equation expressed by power (mV), E ₀ is a constant potential (mV), R is a gas constant, T is an absolute temperature, F is a Faraday constant, and [H ⁺ ] is a hydrogen ion concentration). Examples of this invention will be described below. Example 1 To create an electrode coating film, a normal three-electrode H-type cell was used as an electrolytic cell, a platinum mesh was used as the counter electrode, a saturated calomel electrode was used as the reference electrode,
Platinum wire for coated solid electrode (diameter 1
mm) with the wires insulated with Teflon (registered trademark), and the electrode surface was smoothed with a polishing machine.
After pre-washing with dilute aqua regia, it was washed with distilled water and immersed in electrolyte. The electrolyte was a methanol solvent containing 10mM phenol and 30mM sodium hydroxide;
Before electrolysis, oxygen was sufficiently removed with argon gas. After scanning the applied voltage and confirming that the oxidation reaction of the phenol monomer is occurring on the surface of the platinum electrode, the applied voltage was increased to 0.9 volts (vs. saturated calomel electrode).
The electrode was stopped at a constant electrolytic state for 3 minutes to coat the electrode surface with the oxidized polymer product. After that, soak the electrode surface with distilled water.
After washing several times, a polymer-coated chemically modified electrode (PH sensor) was fabricated. FIG. 3 is a cyclic voltamgram showing the start of the oxidative polymerization reaction, and the difference in peak current between the first scanning oxidation wave and the second scanning wave is due to the formation of a coating film on the electrode surface.
Note that the potential scanning speed was 74 mV/sec. As a sample solution for PH measurement, a buffer solution containing a total phosphoric acid concentration of 0.05M was used, and the pH of the solution was adjusted to a range of 2.00 to 12.00 with sodium hydroxide and perchloric acid. The coated membrane electrode was immersed in this sample solution, and the electromotive force was measured using the silver-silver chloride electrode as a reference electrode. A plot of the measured electromotive force of this coated membrane electrode and the PH value measured with a commercially available glass electrode is shown in FIG. 4 by white circles. The slope of this straight line is 59mV/PH over a wide range of pH ranges, completely satisfying the Nernst relation. Further, Table 1 shows the AC impedance measurement results of the PH sensor obtained in this example. Extremely low impedance with little change in resistance and capacitance components before and after coating with polymer film.
It is acknowledged that the PH sensor was provided. The measurement conditions were as follows: platinum was used as an electrode in a 0.05M phosphate buffer solution with a pH of 7.

[Table] Regarding the accuracy and stability of the electrode potential (electromotive force) response, the potential reaches a constant value within 3 to 5 minutes and remains stable within a range of ±2 mV for several hours thereafter, making it extremely excellent for measuring hydrogen ion concentration. This is an electrode. Also, the PH range that satisfies the Nernst formula is 3.0PH10.5
It has a measurement pH range similar to that of a glass electrode. Next, after continuing to immerse the corresponding electrode in a phosphate buffer solution with a pH of 7 for 24 hours, the electromotive force was measured. The results are shown in Figure 4 with black circles, and in this case, the Nernst equation was also satisfied. The durability of the coated membrane electrode was proved to be extremely good. Examples 2 to 21 Using the same electrolytic polymerization method as in Example 1, the hydroxy aromatic compounds shown in Table 2 below were polymerized on a platinum electrode to form a coating film, and the functionality of the electrode as a PH sensor was investigated. The results are summarized in Table 2.
Among these, o-hydroxybenzophenone, o-
It has been found that an electrode coated with electrolytic polymerization of hydroxybenzyl alcohol and 3,5-dimethylphenol is particularly excellent as a sensor for measuring hydrogen ion concentration.

【table】

【table】

【table】

[Table] *Note) φ represents a phenyl group.
Example 22 In order to change the ion concentration in the sample solution, the total phosphoric acid concentration was varied from 0.1 M to 5×10 ⁻⁴ M, and the electromotive force response to the hydrogen ion concentration was investigated using the electrode prepared in Example 1. PH range 3.0＜PH＜10.0
The slope of 59mV/PH was satisfied. It was found that the electrode can be used as a PH sensor even in a sample solution containing almost no supporting electrolyte. Example 23 Polyphenylene oxide, poly2,6-dimethylphenylene oxide, and polycarbonate were each dissolved in benzene at a concentration of 0.01% by weight, and the end of a platinum wire was immersed in each of these solutions. After several seconds, each platinum wire was taken out from each solution and dried to obtain a PH sensor having the same function as that of Example 1. The relationship between electromotive force and PH was 54 mV/PH for polycarbonate, and 59 mV/PH for the others. Specific Effects of the Invention As described above, the PH sensor of the present invention has the following effects, unlike conventional glass electrodes. (1) A conductor coated with a polymer film derived from a hydroxyaromatic compound is immersed in a solution, and PH can be measured based on the electrode potential response. Therefore, there is no need to provide a reference liquid chamber, miniaturization can be achieved to a limited range of processing of the conductor, and a small amount of measurement sample liquid is required. Also, the potential response speed is fast. The PH sensor of this invention can also be formed so that it can be inserted into the body. (2) The conductivity of the polymer membrane is extremely good, the membrane resistance is extremely low, and the impedance is low, so there is no need to use a high input impedance amplifier for measurement. (3) In a short time even in solutions containing many types of ionic species.
PH can be measured quantitatively and reliably. In addition, an appropriate coating film treatment can be performed to enable PH measurement even in solution systems containing heterogeneous substances such as suspensions and slurry liquids. (4) There is no reference liquid chamber, and the temperature of the polymer membrane is approximately 200℃.
PH measurement in high temperature liquids is possible. (5) The polymer membrane can be used many times until it wears out. (6) PH measurable range of glass electrode (PH=3 to 10)
PH not only, but also beyond that.
can be measured, making it particularly suitable for PH measurement in the alkaline region.

[Brief explanation of the drawing]

Fig. 1 is an enlarged sectional view of a part of the PH sensor of the present invention, Fig. 2 is a schematic diagram showing the PH measurement method using the PH sensor of the present invention, and Fig. 3 is a cyclic voltamgram during the electrode oxidation reaction of phenol. , 4th
The figure is a graph showing the relationship between the electromotive force and PH of the PH sensor of this invention. 11... Conductor, 12... Polymer film, 23...
PH sensor, 24... reference electrode, 26... potentiometer.

Claims (1)

[Claims] 1. A PH sensor that measures the PH of a solution based on electrode potential response, which is made by directly depositing a polymer film derived from a hydroxy aromatic compound on the surface of a conductor. Characteristic PH sensor. 2. The PH sensor according to claim 1, wherein the polymer film has a low impedance. 3. The PH sensor according to claim 1 or 2, wherein the polymer membrane is an electrolytically oxidized polymer membrane. 4 Hydroxy aromatic compound has the formula (Here, Ar is an aromatic nucleus, each R is a substituent, and m is the effective valence number of O to Ar.) PH sensor according to any one of claims 1 to 3. 5 Hydroxyaromatic compounds include phenol, dimethylphenol, hydroxypyridine, o- and m-benzyl alcohol, o-, m- and p-
-Hydroxybenzaldehyde, o- and m-
Hydroxyacetophenone, o-, m- and p
-Hydroxypropiophenone, o-, m- and p-benzophenol, o-, m- and p-
Hydroxybenzophenone, o-, m- and p
-Carboxyphenol, diphenylphenol, 2-methyl-8-hydroquinoline, 5-hydroxy-1,4-naphthoquinone, 4-(p-hydroxyphenyl)-2-butanone, 1,5-dihydroxy-1,2 , 3,4-tetrahydronaphthalene, and bisphenol A. 6. The PH sensor according to claim 1 or 2, wherein the polymer film is polyphenylene oxide or polycarbonate dissolved in a solvent, coated on the surface and dried. 7. A patent in which the polymer film is selected from the group consisting of at least one of polyphenylene oxide, polyphenylene oxide derivatives, polydiphenylphenylene oxide, polydimethyl phenylene oxide, and polycarbonate derivatives. PH sensor according to any one of claims 1, 2 and 6.