JPS6364740B2 - - Google Patents

Description

BACKGROUND TECHNICAL FIELD OF THE INVENTION The present invention relates to an ion selective permeable membrane and an ion sensor, and more particularly to an ion sensor in which a polymer membrane is directly attached to the surface of a conductor, and which detects the concentration of ions in a solution. Concerning what is measured by electrode potential or current response. Prior art and problems Conventionally, hydrogen electrodes and quinhydrone electrodes have been known as electrodes for measuring the concentration of ions such as hydrogen ions in solutions, but today glass electrodes are widely used in terms of their wide range of application and accuracy. It is starting to be used. 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 provide an ion selectively permeable membrane that selectively permeates ions in a solution, and an ion sensor that measures the concentration of ions in the solution, without the need to provide a reference liquid chamber. Therefore, it is an object of the present invention to provide an ion sensor that can be miniaturized. To achieve this objective, the present invention is completely different from the conventional concept of glass electrodes, and utilizes a technique that has rarely been used in the past: chemically modifying the conductor surface with a polymer. This chemical modification technique makes the conductor selectively permeable to dissolved ionic species, prevents surface corrosion and dissolution, and responds to the ion concentration in solution by changes in electrode potential or current. It offers a completely new function. This invention utilizes the responsiveness to ion concentration among the functions of a conductor chemically modified with a polymer. That is, the ion sensor of the present invention contains a nitrogen-containing aromatic compound on the surface of the conductor. In other words, the ion selective separation membrane of the present invention contains aniline, 2-aminobenzotrifluoride, 2-aminopyridine,
A polymer film derived from at least one nitrogen-containing aromatic compound selected from 2,3-diaminopyridine, 4,4'-diaminodiphenyl ether, 4,4'-methylene dianiline and pyrrole, or biscyclo The acid chloride obtained by reacting [2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride with thionyl chloride has 4,
It consists of a polyamide polymer membrane obtained by reacting 4'-diaminodiphenyl ether. Further, the ion sensor of the present invention includes a conductor, aniline, 2
- at least one selected from aminobenzotrifluoride, 2-aminopyridine, 2,3-diaminopyridine, 4,4'-diaminodiphenyl ether, 4,4'-methylene dianiline and pyrrole
Polymeric films derived from species of nitrogen-containing aromatic compounds, or biscyclo[2,2,2]-octo-
A polyamide polymer membrane obtained by reacting 4,4'-diaminodiphenyl ether with an acid chloride obtained by reacting 7-ene-2,3,5,6-tetracarboxylic dianhydride with thionyl chloride. It is characterized by having the following. It is preferable that the impedance of the polymer membrane is reduced, and that the polymer membrane derived from a nitrogen-containing aromatic compound is an electrolytically oxidized polymer membrane. Note that the term polymer used in this specification includes both homopolymers and interpolymers (eg, copolymers, terpolymers, etc.). 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 ion sensor of the present invention has a conductor 11 of arbitrary shape, for example, a rod, whose periphery is coated with an insulator 13 such as polyolefin or polytetrafluoroethylene, and a predetermined polymer film 12 is coated on the disk surface at the tip. It is made by attaching and fixing.
The conductor 11 is made of a conductive material, preferably platinum or the like. The polymer film 12 deposited on the surface of the conductor disk 11 is made of a polymer of a nitrogen-containing aromatic compound. This nitrogen-containing aromatic compound includes aniline,
selected from 2-aminobenzotrifluoride, 2-aminopyridine, 2,3-diaminopyridine, 4,4'-diaminodiphenyl ether, 4,4'-methylene dianiline and pyrrole. In addition, biscyclo[2,
2,2]-oct-7-ene-2,3,5,6-
A polyamide polymer obtained by reacting 4,4'-diaminodiphenyl ether with an acid chloride obtained by reacting tetracarboxylic dianhydride with thionyl chloride (Kobayashi et al., Nikka (12) 1929-32) 1980) can also be used as the polymer membrane 12. In order to deposit the nitrogen-containing aromatic compound polymer film described above on the surface of the conductor 11, the nitrogen-containing aromatic compound is applied to the conductor 11 by electrolytic oxidation polymerization.
A method of polymerizing on the surface, a method of dissolving a pre-synthesized polymer in a solvent and fixing the solution to the conductor surface by dipping/coating and drying, and a method of chemically processing, physically processing or irradiating the polymer film. A method of directly fixing it to the surface of the conductor through treatment can be adopted. The most convenient of the above deposition methods is by electrolytic oxidative polymerization. In this electrolytic oxidative polymerization, a nitrogen-containing aromatic compound is electrolytically oxidized and polymerized in a suitable solvent to deposit a polymer film on the surface of a desired conductor as a working electrode. For example, 1,2
- Electrooxidative polymerization of diaminobenzene, 2-aminobenzotrifluoride and 4,4'-diaminodiphenylmethane in a phosphate buffer solution at pH 7, and polymerization of aniline in an acetonitrile solution containing pyridine and sodium perchlorate. , 4,4'-diaminodiphenyl ether was polymerized in acetonitrile solution containing sodium perchlorate or methanol solution containing sodium hydroxide, and pyrrole was polymerized using tetrabutylammonium hexafluorophosphate (Bu ₄ N (abbreviated as PF ₆ )) in an acetonitrile solution. A polymer film deposited by electrolytic oxidative polymerization has extremely good adhesion stability and a smooth film surface. The thickness of the polymer film is not particularly limited, but approximately 0.01μ to 1μ is appropriate. Specific Functions of the Invention The functions of the coated electrode having the above structure will be explained in detail below. (1) Response as an ion sensor The PH of the sample solution is measured using the ion sensor shown in Figure 1.
To measure PH, as shown in FIG. 2, a sample solution 22 whose pH is to be measured is placed in a tank 21, and an ion sensor 23 of the present invention and a silver-silver chloride electrode as a reference electrode 24 are added to this solution. Immerse calomel electrodes, etc. Then, the potential difference (electromotive force) of the ion sensor 23 with respect to the reference electrode 24 is measured by the potentiometer 26. At this time, the sample solution 22 is mixed with the stirrer 25.
It is best to stir with Then, read the PH of the sample solution using the correlation diagram between electromotive force and PH prepared in advance. Note that when blowing gas, a gas blowing pipe 27 is used. The relationship between the electromotive force and PH by the ion sensor of this invention shows a linear relationship with a slope of 59 mV/PH in a wide range of PH range, 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). However, the sample solution is measured in an open system or in an oxygen stream. Furthermore, when the electromotive force is measured in a hydrogen gas stream, the value changes greatly to a negative potential value, but it still satisfies the Nernst equation for hydrogen ions. (2) Selective membrane permeation and control of ionic species The electrode-coated membrane exhibits selectivity for membrane permeation of ionic species in solution. Convective voltammetry using a rotating disk electrode is effective for this measurement. This is because the amount of mass transport of ionic species onto the electrode can be controlled by the rotational speed of the disc electrode, so the dependence of the critical current value of the voltammogram on the rotational speed can be improved for electrodes with and without a coating film. When examined, the membrane permeability ability for each chemical species can be evaluated. This behavior differs depending on the type of coating membrane and dissolved ionic species, but in general, the thicker the coating membrane, the more the ionic species permeation is inhibited, and the larger the volume of the dissolved ionic species, the more the membrane permeation is suppressed. be done. As for other functionality, it is possible to modify the electrode surface by coating the polymer membrane directly on the electrode surface, which has the potential to contribute to improving the electrode catalytic ability and preventing surface corrosion and dissolution. The coating film also functions as an anchor for introducing appropriate substituents onto the conductor surface. When the electrode surface does not have an appropriate substituent for compounding with an organic substance, etc., the electrode surface is first coated with a polymer having a substituent such as aldehyde or amine. The coated film can be used as a reactive substituent for graft polymerization reactions, etc., and can be used as a substrate for immobilizing a target compound, and can also be used to modify the coated film. If the substituent of the coating film is a ligand such as pyridine, the film has coordination bonding ability, and if the substituent has a charge such as sulfonic acid or quaternized pyridine, the film has It has the properties of a polymer electrolyte and has the ability to accumulate and fix oppositely charged ionic species. Therefore, these coated membrane electrodes have the effect of pre-concentrating trace amounts of dissolved ionic species, and then oxidize or reduce them at the electrode, which can be detected by electric current. It has potential as
Further, by inserting a third chemical species into the coating film, which is an insulator, it is possible to improve the coating film to make it conductive. In addition, by changing the electrode potential, the redox state of reactive active species in the membrane can be changed, and the color of the membrane can change.
Can be colored and bleached. Examples of this invention will be shown below. Example 1 The platinum wire was insulated around it with polytetrafluoroethylene, and the disk surface was pretreated by the following method before electrolysis. First, it is polished and smoothed with silicon carbide paper and alumina powder (0.3 μm), washed with dilute aqua regia, then washed with distilled water, and immersed in a 0.05M acetic acid solution. Next, using a normal three-electrode H-type cell with this electrode as the working electrode, a platinum mesh as the counter electrode, and a saturated calomel electrode as the reference electrode, the voltage applied to the electrode was varied from -0.6V to +1.0V. After activating the electrode surface by moving it back and forth about 10 times, it is washed with distilled water, then with methanol, and then dried. To create the electrode coating film, the working electrode that had been pretreated as described above was immersed in the same electrolytic cell as described above, and an electrolytic oxidation polymerization reaction was carried out on the surface of the platinum disk at 10mM4,
It was carried out in an acetonitrile solvent containing 4'-diaminodiphenyl ether and 0.1 M sodium perchlorate. The electrolyte was sufficiently deoxidized with argon gas before electrolysis. After confirming that the oxidation reaction of the 4,4'-diaminodiphenyl ether monomer was occurring at the platinum electrode, the applied voltage was kept at +1.20 volts (versus the saturated calomel electrode), and constant electrolysis was carried out for 10 minutes. The electrode surface was coated with an oxidized polymer. Thereafter, the electrode surface was washed three times or more with distilled water to produce a polymer-coated chemically modified electrode. Figure 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 (curve a) and the second scanning wave (curve b) is due to the coating on the electrode surface. This is due to film formation. Curves c and d are the third and fourth scan waves. Note that the potential scanning speed is 74mV/
It was hot in seconds. The effect of the prepared coated membrane electrode as a PH sensor was investigated. Total phosphoric acid concentration as a solution for PH measurement
Using a buffer solution containing 50 mM, the pH of the solution was adjusted to a range of 2.00 to 10.00 with sodium hydroxide and perchloric acid. The coated membrane electrode was immersed in this sample solution, and the electromotive force was measured using a saturated calomel electrode as a reference electrode. A plot of this measured electromotive force and the PH value measured with a commercially available glass electrode is shown in FIG. 4 as a straight line a (open system). The slope of this straight line is from 2.0
A linear relationship that almost satisfied the Nernst equation was obtained in the PH region of 11.0, and its slope was 54 mV/PH.
This measurement was conducted in an open system where the sample solution was left in the air. Oxygen gas in the sample solution,
When measurements were taken while blowing argon gas, the responses shown by straight lines b and c in Figure 4 were obtained, and the slopes of the straight lines were 54 mV/PH and 46 mV/PH, respectively.
It was PH. In addition, in a hydrogen gas flow, the electromotive force value significantly changes to a negative potential value in the PH range from 2.0 to 9.0, but it satisfied the Nernst relation of 59 mV/PH (straight line d). From this, the coated membrane electrode exhibits extremely excellent electrode characteristics for measuring hydrogen ion concentration. The accuracy and stability of the equilibrium electrode potential (electromotive force) response is good, and the potential shows a constant value within 5 to 15 minutes, and then maintains a constant value within ±2 mV even after several hours. Furthermore, even if we examine the electromotive force response to hydrogen ions after immersing this electrode in a phosphate buffer solution with a pH of 7.0 for one week, it satisfies the Nernst equation as shown by the straight line e in Figure 4. The durability of the membrane is extremely good.
Similar measurements were also carried out in the presence of cobalt () ions, nickel () ions, iron () ions, or zinc () ions in the sample solution. The equilibrium potential was not affected by these ionic species and changed only with changes in the hydrogen ion concentration in the solution. A solution containing Felician ions (PH=
Figure 5 shows the measurement results for 4.0). In addition,
Even when alkaline earth metal ions such as calcium (2000) coexisted in the sample solution, the equilibrium potential was not affected by the ions. Example 2 A coating film was formed on the surface of a platinum disk electrode by electrolytic oxidative polymerization reaction of aniline.
Performed in acetonitrile solvent of 20mM pyridine, 0.1M sodium perchlorate. An electrode coating film was created by the same method as in Example 1, that is, the electrolytic oxidation polymerization reaction method. The response of this coated membrane electrode as a PH sensor was investigated.
A linear relationship was obtained with a slope of 52 mV/PH in the region. The electrode potential showed a constant value in 5 to 10 minutes, and then stabilized in the range of ±2 mV for several hours. Although the durability of this coating film is extremely good, when the sample solution contained transition metal ions, the equilibrium potential was affected by the concentration of these ion species. Example 3 Electrolytic polymerization of pyrrole onto the surface of a platinum disk
A coated membrane electrode was prepared in the same manner as in Example 1 in an acetonitrile solution containing 10 mM of the supporting electrolyte Bu ₄ N (PF 6 ) and 50 mM of the supporting electrolyte Bu 4 N (PF ₆ ). The electrolytic oxidative polymerization of pyrrole in this case was carried out by constant voltage electrolysis for 10 minutes at an applied voltage of +0.8 volts (vs. saturated calomel electrode).
This electrode was washed with water and methanol in that order, and dried. The prepared electrode coating film exhibits a purple color. The response of this coated electrode as a sensor was investigated, and a straight line with a slope of 48 mV/PH was obtained in the PH range from 2.0 to 9.0. The electrode potential showed a constant value for 5 to 30 minutes, and after that, it remained stable within the range of ±2 mV for several hours.When measuring while blowing oxygen and argon gas into the sample solution, the potential was 57 mV/PH (2.0 PH10), respectively.
48mV/PH (2.0PH9.0) was obtained, and the potential was 20
A constant value is reached in ~40 minutes, then ±2 mV for several hours
Stable within the range. Next, similar results were obtained when the hydrogen ion concentration was measured after immersing this electrode in a phosphate buffer solution (PH=7.0) for 5 days.
The durability of this coating film is extremely good. Even when the sample solution contained transition metal ions, there was no effect on the equilibrium potential. Example 4 Formation of a coating film of 2-aminopyridine on the surface of a platinum disk electrode was performed using 10mM 2-aminopyridine.
The electrolytic oxidation polymerization was carried out in the same manner as in Example 3 in 50 mM phosphate buffer (PH=7.00).
A linear relationship was satisfied between the equilibrium potential (electromotive force) of this coated membrane electrode and PH, and 48 mV/PH was obtained in the PH range from 2.0 to 11.0. However, the measurement was performed in an open system where the sample solution was left in the air. When measuring while blowing oxygen and argon gas into the sample solution, the values were 48 mV/PH and 59 mV/PH, respectively (however,
The PH range was 2.00PH11.00 and 2.00PH10.5, respectively). Although the electromotive force value in the case of hydrogen gas injection showed a significantly negative potential value, it almost satisfied the Nernst relation of 59 mV/PH. From this, the coated membrane electrode exhibits electrode characteristics that allow measurement of hydrogen ion concentration. The equilibrium potential shows a constant value within 5 to 20 minutes, and remains constant within a range of ±2 mV even after several hours. Furthermore, after immersing this electrode in a phosphate buffer solution with a pH of 7.0 for about 10 days, the electromotive force response to hydrogen ions was examined. As a result, a similar PH response was obtained, indicating that the membrane of the present invention has extremely good durability. Examples 5, 6 2,3-diaminopyridine and 2-aminobenzotrifluoride were prepared in the same manner as in Example 3.
A polymer-coated electrode was fabricated by oxidative polymerization on a platinum surface. Using these coated electrodes, we investigated the hydrogen ion concentration of the measurement solution, the equilibrium potential response, and the effects of gas injection (various gases such as oxygen, argon, hydrogen, etc.) on hydrogen ion concentration measurement, and obtained the following results. Ta.

【table】

[Table] Example 7 Biscyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride was converted into acid chloride by reaction with thionyl chloride, and this A polyamide polymer prepared by reacting 4,4'-diaminodiphenyl ether is dissolved in dimethyl sulfoxide (DMOS) at a concentration of 0.04% by weight, the tip of a platinum electrode is immersed in this, and then the solution is removed. It was taken out and air-dried at room temperature for several hours to produce a coated electrode. The relationship between the equilibrium potential (electromotive force) in the measurement solution and PH satisfies a linear relationship, and within the PH range of 2.00 to 10.00.
46mV/PH was obtained. PH when oxygen gas is blown
It was 46 mV/PH in the range of 2.00 to 7.00, but it was about 25 mV/PH on the alkaline side (7.00 PH 10.00). 2.5PH when argon gas is blown
32mV/PH in the range of 10.0. The electromotive force value in the case of hydrogen gas injection shows a significantly negative potential value,
It almost satisfied the Nernst relation of 57mV/PH (2.0PH9.0). The equilibrium potential shows a constant value within 10 minutes, and then remains constant within a range of ±2 mV even after several hours. In addition, after immersing this electrode in a phosphate buffer solution with a pH of 7.0 for a day and night, we investigated the change in hydrogen ion concentration, which satisfied a linear relationship and showed a slope of 31 mV/PH. Admitted. When 1mM iron() ions coexist in the sample solution, the equilibrium potential is affected by this ion species. Examples 8 and 9 The following examples demonstrate that the electrode coating membrane has a selective membrane permeation function for ionic species in a solution.

[Table]
Example 10 The results of PH measurement in a gel-like liquid will be described. 4,4'- was applied to the surface of the platinum disk in the same manner as in Example 1.
A coated electrode was prepared by depositing diaminodiphenyl ether. Using this electrode, we measured the hydrogen ion concentration in a gel prepared by dissolving 0.1% by weight of Carbopol #K40 (manufactured by Gutudoritsu), a polyacrylic acid-based thickener, in a 5% by weight sodium hydroxide solution. , an electrode equilibrium potential (electromotive force) of approximately 140 mV versus a saturated calomel electrode was obtained. This value corresponds to approximately PH=10.5 from the relationship between the electromotive force and PH of the open system shown in FIG. Similar measurements were made using a glass electrode, but no equilibrium potential response was obtained and PH could not be measured. Example 11 Electrolytic oxidation polymerization reaction of 4,4'-diaminodiphenyl ether onto the surface of a platinum disk electrode in Example 1
Electrolysis was carried out under different conditions, namely in a methanol solution containing 10 mM 4,4'-diaminodiphenyl ether and 30 mM sodium hydroxide. In this case, a stable golden coating was obtained. The response of this coated membrane electrode as a PH sensor was good. Specific Effects of the Invention The ion sensor of the invention described above has the effects listed below. (1) A conductor coated with a polymer film derived from a nitrogen-containing aromatic 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, the conductor can be miniaturized to a limited range of processing, and only a small amount of measurement sample liquid is required. Also, the potential response speed is fast. Furthermore, the PH sensor of the present 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 a high input impedance amplifier is not required for measurement. (3) PH can be measured quantitatively and accurately in a short time even in solutions containing many types of ions, especially transition metal ions. It also works as a PH sensor in solution systems containing heterogeneous substances, such as suspensions and slurry liquids. (4) Even when oxygen gas, argon gas, or hydrogen gas is blown into the sample liquid, a linear relationship that satisfies Nernst's equation is established, and the pH of the sample liquid can be measured. (5) The coated membrane has the functions of partially permeating hydrogen ions and bromide ions, selectively permeating only hydrogen ions, and not permeating transition metal ions and their complexes, so that they do not allow ions and molecules to pass through. Can be used as a selectively permeable membrane. (6) Since the coating film has a low impedance, it can be used even in solutions with low electrical conductivity such as rainwater.
Operates as a PH sensor.

[Brief explanation of drawings]

Fig. 1 is an enlarged cross-sectional view of a part of the ion sensor of the present invention, Fig. 2 is a schematic diagram showing a pH measurement method using the ion sensor of the present invention, and Fig. 3 is a 4,4'-
Cyclic voltammograms during electrode oxidation reaction of diaminodiphenyl ether, Figures 4 and 5
The figure shows the electromotive force of different ion sensors of this invention.
Graph showing the relationship with PH. 11... Conductor, 12... Polymer film, 23...
PH sensor, 24... reference electrode, 26... potentiometer.

Claims (1)

[Scope of Claims] 1. A membrane that selectively permeates ions in a solution, which contains aniline, 2-aminobenzotrifluoride, 2-aminopyridine, 2,3-diaminopyridine, 4,4'-diaminodiphrolide. enyl ether,
A polymer film derived from at least one nitrogen-containing aromatic compound selected from 4,4'-methylene dianiline and pyrrole, or biscyclo[2,2,2]-oct-7-ene-2,3 ,5,
An ion selective permeable membrane made of a polyamide polymer obtained by reacting 4,4'-diaminodiphenyl ether with an acid chloride obtained by reacting 6-tetracarboxylic dianhydride with thionyl chloride. 2. The ion selectively permeable membrane according to claim 1, which is an electrolytically oxidized polymerized membrane of a nitrogen-containing aromatic compound. 3. An ion sensor that measures ion concentration in a solution using electrode potential or current response, comprising a conductor, aniline, 2.
- at least one selected from aminobenzotrifluoride, 2-aminopyridine, 2,3-diaminopyridine, 4,4'-diaminodiphenyl ether, 4,4'-methylene dianiline and pyrrole
Polymeric films derived from species of nitrogen-containing aromatic compounds, or biscyclo[2,2,2]-octo-
A polyamide polymer membrane obtained by reacting 4,4'-diaminodiphenyl ether with an acid chloride obtained by reacting 7-ene-2,3,5,6-tetracarboxylic dianhydride with thionyl chloride. An ion sensor characterized by comprising: 4. The ion sensor according to claim 3, wherein the polymer membrane has a low impedance. 5. The ion sensor according to claim 3 or 4, wherein the polymer membrane is an electrolytically oxidized polymer membrane of a nitrogen-containing aromatic compound. 6. The ion sensor according to any one of claims 3 to 5, which is a PH sensor.