JP2004309478A - Current sensing ion-selective electrode, ion measuring system, method of quantifying target ions, and method of fabricating current sensing ion-selective electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current sensing ion-selective electrode which measures a slight quantity of an object to be measured. <P>SOLUTION: The current sensing ion-selective electrode quantifies target ions in a sample solution containing the target ions and chemical species other than the target ions (hereinafter referred to as non-target chemical species). The electrode comprises an electrode main body 1 formed of an electrically conductive substance, a conductive substance which allows the target ions and/or non-target chemical species to pass therethrough, and an ion-sensitive layer 3 into which ionophores having selectivity for the target ions are mixed, wherein the electrode main body is in close contact with the ion-sensitive layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a current detection type ion selective electrode, an ion measurement system, a method for quantifying target ions, and a method for manufacturing a current detection type ion selective electrode.

There is disclosed an electrode composed of an electrode sensitive part made of a composite polymer material and a reference electrode immersed in an internal liquid in contact with the electrode sensitive part (see Patent Document 1). With this electrode, it is possible to analyze alkali metal ions such as ammonium ion and thiosionate ion without using a liquid such as nitrobenzene or dichloroethane as an electrode material.
Further, an electrode is disclosed in which a first electrolyte layer and an ion-sensitive layer are provided on a measurement electrode, and a second electrolyte layer is provided so as to cover the measurement electrode and the counter electrode (see Patent Document 2). In this electrode, the measurement electrode and the counter electrode can be created by screen printing, and the electrode surface area can be made constant. In addition, since the concave portion to which the electrolyte layer or the sensitive layer is applied can be formed by screen printing, the production is easy and the measurement performance can be improved.

However, in the electrode described in Patent Literature 1 or Patent Literature 2, an internal liquid is provided inside the electrode, or the electrode sensitive portion is made of a liquid material. Therefore, when the electrode is inclined, the internal liquid and the electrode sensitive portion are mixed, or the internal liquid evaporates. Therefore, the electrodes described in Patent Literature 1 or 2 cause deterioration of the electrodes such that measurement becomes impossible.
Thus, an electrode is disclosed in which a paste in which conductive particles and an ionophore are mixed is screen-printed and heated and dried to form an ion-sensitive portion (see Patent Document 3). In this electrode, since the internal liquid layer can be omitted, deterioration of the electrode due to the liquid substance can be reduced.
Japanese Patent Publication No. 5-6658 JP-A-6-229973 JP-A-7-31175

However, as described above, since the electrodes of Patent Documents 1 and 2 are provided with the internal liquid, the stability of the electrodes is impaired due to evaporation of the internal liquid and mixing of the internal liquid with the electrode sensitive portion, There is a problem that the handling of the electrode is difficult due to the presence of the internal liquid.
In the measurement of the target substance in the sample solution using the electrodes of Patent Documents 1, 2, and 3, the speed at which the target substance is taken into the electrode sensitive portion is detected as a current value. Therefore, when the amount of the sample solution is small, or when the concentration of the target substance in the sample solution is low, the current value or the amount of electric charge that is taken into the electrode sensitive portion and detected is small. Therefore, there is a problem that it is difficult to measure the concentration of the target substance.

  Furthermore, the electrode described in Patent Document 3 is formed by screen-printing a paste in which conductive particles and ionophore are mixed and then heating and drying the paste. Therefore, the heat resistance of the ionophore in heat drying is required. For example, nonactin, which is an ionophore, is a natural product and is usually stored and used at about 4 ° C., but the properties of nonactin are deteriorated by heating when forming a paste. As described above, there is a problem that the ionophore that can be used is limited in molding the paste, for example, heat resistance is required.

Then, an object of the present invention is to provide a current detection type ion selective electrode which can measure a very small amount of an object to be measured.
Another object of the present invention is to provide a current detection type ion selective electrode which is easy to handle.
Still another object of the present invention is to provide a method for producing a current detection type ion selective electrode which can reduce the deterioration of the ionophore.

  In order to solve the above-described problems, the first invention of the present application is a method for quantifying the target ions in a sample solution containing target ions and a chemical species other than the target ions (hereinafter, referred to as non-target chemical species). A current detection type ion-selective electrode, comprising: an electrode body formed of a conductive material; a conductive material that transmits the target ions and / or the non-target species; and an ionophore having selectivity for the target ions. A current detection type ion-selective electrode in which the electrode body and the ion-sensitive layer are in close contact with each other.

  The ion-sensitive layer includes a conductive material that allows target ions and / or non-target chemical species in the sample solution to pass through the electrode body, and an ionophore that selectively captures target ions from the sample solution. In the electrode body, the presence of target ions and / or non-target species on its surface causes an electrode reaction. Here, the non-target chemical species means a chemical species having an electrochemical reactivity other than the target ion in the solution, such as a molecule or an ion. The electrode reaction due to the target ions and / or non-target species is inhibited by the target ions being captured by the ionophore. The target ions can be quantified by detecting the current generated as a result of the inhibition. Specifically, the detected electrode current value indicates that the target ions and / or non-target species contribute to the electrode reaction through the conductive material, i.e., the ion-sensitive layer, and that the target ions are captured by the ionophore. It has a correlation with inhibiting the electrode reaction. Then, instead of directly quantifying the target ion from the current generated by the electrode reaction of the target ion, the target ion is indirectly determined from the current value of the current generated as a result of the inhibition of the electrode reaction based on the correlation. Therefore, even when the concentration of the target ion is very small, the target ion in the sample solution can be quantified by measuring a current value corresponding to the electrode reaction caused by the target ion and / or the non-target chemical species. .

The concentration of the target ion is measured, for example, as follows. Using the current-detection-type ion-selective electrode, a reference current value I ₀ in a reference solution containing a non-target chemical species having a concentration similar to that of the non-target chemical species in the sample solution is measured. Further, the current value I ₁ of the sample solution is measured using the current detection type ion selective electrode. Then, by measuring how much the absolute value | I ₁ | of the current value of the sample solution has decreased from the absolute value | I ₀ | of the reference current value, the concentration of the target ion can be measured.

In the above current detection type ion selective electrode, handling is easy because the ion sensitive layer is in a solid state.
In the second invention of the present application, in the first invention of the present application, the non-target chemical species is an ion having the same polarity as the target ion and different from the target ion (hereinafter, referred to as a non-target ion); Provides a current detection type ion-selective electrode, which is an ion-conductive substance that exchanges the target ions and / or the non-target ions.

  The current value of the current detection type ion-selective electrode is based on the fact that target ions and / or non-target ions contribute to the ion conduction of the ion-conductive substance, that is, the ion-sensitive layer. And has a correlation with inhibiting. Based on this correlation, target ions are indirectly quantified by the extracted current value. Therefore, even when the concentration of the target ion is very small, the target ion is trapped by the ionophore, and as a result, the current value corresponding to the electrode reaction caused by the target ion and / or the non-target ion is measured, whereby the sample solution is measured. The target ions in the sample can be quantified.

The third invention of the present application provides the current detection type ion selective electrode according to the first invention of the present application, wherein the inside diameter of the pores of the ionophore is substantially the same as the ion diameter of the target ion.
Since the pore diameter of the ionophore is substantially the same as the ion diameter of the target ion, the selectivity of the target ion by the ionophore can be increased. Therefore, by extracting the current value from the current detection type ion selective electrode, the quantification of target ions can be performed more accurately.

In a fourth aspect of the present invention, in the first aspect of the present invention, the target ion is an ammonium ion, and the ionophore is selected from nonactin, a 19-crown-6 derivative, a 20-crown-6 derivative, and a 21-crown-6 derivative. A current sensing ion selective electrode is provided, which is one or more combinations.
The ionophore described above has the effect of selectively trapping ammonium ions in its vacancies and blocking interfering ions that prevent trapping of ammonium ions in the vacancies. Therefore, the selectivity of the ammonium ion, which is the target ion, is further enhanced. Therefore, by extracting the current having the above-described correlation, the quantification of the target ion can be performed more accurately.

The fifth invention of the present application provides the current detection type ion selective electrode according to the first invention of the present application, wherein a composition ratio of the ionophore to the ion sensitive layer is selected according to the concentration of the target ion.
For example, when the target ion concentration is high, by increasing the composition ratio of the ionophore in the ion-sensitive layer, it is possible to prevent the holes for capturing the target ions from being saturated.

The sixth invention of the present application provides the current detection type ion-selective electrode according to the first invention of the present application, wherein the material of the electrode body is one or a combination of a plurality of glassy carbon, platinum, gold, and silver.
Glassy carbon, platinum, and the like are excellent in electrical properties such as high conductivity and supplying a stable current value, and excellent in properties such as high resistance to a sample solution. Therefore, an accurate current can be extracted from the electrode body.

The seventh invention of the present application relates to a sample cell into which a sample solution containing target ions and a chemical species other than the target ions (hereinafter, referred to as non-target chemical species) is introduced, and a selectivity between a conductive substance and the target ions. Having an ion-sensitive portion in which ionophores are mixed, an electrode provided in the sample cell, a counter electrode of the electrode provided in the sample cell, and a voltage applied between the electrode and the counter electrode. a voltage applying unit for a current value detection unit that detects a current value I ₁ flowing through the electrode resulting from the application of the voltage, the absolute value of the current value according to the increase of the target ion concentration | I ₁ | is reduced based on that, or the absolute value of the current value according to the decrease of the target ion concentration | I ₁ | perform quantification of the based on the increase target ion target To provide an ion measurement system including an ion quantitation section.

An electrode having an ion sensitive portion is immersed in a sample solution in a sample cell containing target ions and non-target species. The ion-sensing section includes a conductive substance that allows target ions and / or non-target chemical species to pass through the electrode body by applying a voltage by a voltage applying section, and an ionophore that selectively captures target ions from a sample solution. Contains. At an electrode, an electrode reaction is caused by the presence of target ions and / or non-target species on the surface. The electrode reaction caused by the target ions and / or non-target species is inhibited by the target ions being captured by the ionophore. Then, the current value detection unit detects a current value I ₁ of the current produced as a result of its inhibition. At this time, the absolute value of the current value in accordance with an increase in target ion concentration | I ₁ | is reduced, or the absolute value of the current value according to the decrease of the target ion concentration | a tendency to increase | I ₁ Have. Therefore, the target ion quantification unit can quantify the target ions in the sample solution based on this tendency.

An eighth invention of the present application is the current detection type ion selective electrode according to the first invention of the present application, a sample cell into which a sample solution containing the target ions and the non-target chemical species is introduced, and a sample cell provided inside the sample cell. A counter electrode of the current detection type ion selective electrode, a voltage application unit for applying a voltage between the current detection type ion selective electrode and the counter electrode, and the current detection type ion selectivity generated by applying the voltage. providing a current value detector for detecting a current value I ₁ flowing through the electrode body of the electrode, the ion measurement system including a target ion quantification section that performs determination of the target ion.

In a current-sensing ion-selective electrode, the presence of target ions and / or non-target species on its surface causes an electrode reaction. The electrode reaction is inhibited by the target ion being trapped by the ionophore, and the current value of the current resulting from the inhibition is measured. At this time, the current value tends to decrease as the target ion concentration increases, or the current value tends to increase as the target ion concentration decreases. Based on this tendency, target ions are quantified as follows. First, a reference current value I ₀ in a reference solution containing a non-target chemical species having a concentration similar to that of the non-target chemical species in the sample solution is measured using a current detection type ion selective electrode. Next, the current value I ₁ in the sample solution is measured using the current detection type ion selective electrode. Then, by measuring how much the absolute value | I ₁ | of the current value in the sample solution has decreased from the absolute value | I ₀ | of the reference current value, the concentration of the target ion can be measured. .

A ninth invention of the present application provides the ion measuring system according to the seventh invention of the present application, wherein a reference electrode is further provided inside the sample cell.
By using the reference electrode, the voltage applied to the current detection type ion-selective electrode can be accurately determined, and the current value extracted to the electrode body can be accurately detected by the current value detection unit.

A tenth invention of the present application is a method for quantifying target ions using the current detection type ion-selective electrode according to the first invention of the present application, wherein a sample into which a sample solution containing the target ions and the non-target chemical species is introduced is introduced. An immersion step of immersing the current detection type ion selective electrode and the counter electrode in a cell, a voltage application step of applying a voltage between the current detection type ion selective electrode and the counter electrode, and applying the voltage. A current value detecting step of detecting a current value I ₁ of a current flowing through the electrode body of the current detecting type ion selective electrode, and an absolute value | I ₁ | of the current value decreasing according to an increase in the target ion concentration based on that, or the absolute value of the current value according to the decrease of the target ion concentration | I ₁ | on the basis of the fact that the increased target Io It provides a method of quantifying a target ions including the target ion quantification step for the quantification.

Using the current-detection-type ion-selective electrode according to the _first invention, based on the fact that the absolute value | I ₁ | of the current value decreases as the target ion concentration increases, or based on the decrease in the target ion concentration The amount of the target ion can be determined based on the fact that the absolute value | I ₁ |
According to an eleventh aspect of the present invention, in the ninth aspect of the present invention, in the target ion quantifying step, a reference current value I ₀ at an electrode body of the current detection type ion selective electrode immersed in a reference solution containing the non-target chemical species. When the comparing the detection current value I ₁ detected in step, the absolute value of the reduction current value is a decrease from the reference current value I ₀ of the current value I ₁ | I ₁ -I ₀ | And a method for quantifying the target ion by calculating the target ion.

Quantifying target ions by calculating the absolute value | I ₁ −I ₀ | of the reduced current value in which the current value I ₁ in the sample solution is reduced from the reference current value I ₀ in the reference solution containing no target ion Can be.
A twelfth invention of the present application is a method for manufacturing a current detection type ion selective electrode according to the first invention of the present application,
A mixing step of mixing the conductive substance and the ionophore constituting the ion-sensitive layer in a solution;
A film forming step of applying the mixed solution to one end surface of the electrode main body by a casting method, evaporating the solution, and forming a film so that the ion-sensitive layer is in close contact with the electrode main body,
A method for producing a current detection type ion-selective electrode, comprising:
Effect Since the ion-sensitive layer is formed on the electrode body by the casting method, the current-detection-type ion-selective electrode according to the first invention can be manufactured without deteriorating the conductive material and / or the ionophore.

A thirteenth invention of the present application is an electrode kit provided with at least one electrode pair, wherein the electrode pair includes the current detection type ion selective electrode according to the first invention and the current detection type ion selective electrode. An electrode kit comprising a counter electrode is provided.
By immersing the above-mentioned electrode kit in a sample solution containing target ions and non-target chemical species, and applying a voltage between the electrode pairs, the target ions in the sample solution can be quantified. The quantification of the target ions is performed in the same manner as in the first invention of the present application.

According to the present invention, it is possible to provide a current detection type ion-selective electrode capable of measuring a very small amount of an object to be measured.
Further, according to the present invention, it is possible to provide a current detection type ion selective electrode which is easy to handle.
Further, by using the present invention, it is possible to provide a method for producing a current detection type ion selective electrode which can reduce the deterioration of the ionophore.

<Summary of the Invention>
The current detection type ion selective electrode according to the present invention has an electrode main body and a sensitive portion covering at least a part of the electrode main body. The sensing unit includes a capturing substance that selectively captures a target substance to be measured, and a conductive substance that allows the target substance and / or the non-target substance to pass through the electrode body. Here, the non-target substance refers to a substance other than the target substance contained in the sample.

The current detection type ion selective electrode is immersed in a sample solution containing a target substance and a non-target substance. Then, when a voltage is applied to the current detection type ion selective electrode, the target substance and / or the non-target substance are transmitted to the electrode main body by the conductive substance of the sensitive part, and the target substance and / or the non-target substance transmitted through the electrode main body The resulting electrode reaction occurs. At this time, the target substance is selectively captured by the capture substance constituting the sensitive part, and the electrode reaction is inhibited. The inhibition of the electrode reaction is caused by the reduction of the electrode reaction of the target substance due to the capture of the target substance, and / or the reduction of the transmittance of the non-target substance to the electrode body due to the capture of the target substance, thereby reducing the electrode reaction of the non-target substance. This is due to the decrease. Further, since the inhibition of the electrode reaction is related to the concentration of the target substance, the concentration of the target substance can be determined by measuring the current value of the current flowing through the electrode body immersed in the sample solution.
<First Embodiment>
FIG. 1 is a perspective view of a current detection type ion selective electrode according to a first embodiment of the present invention, FIG. 2 is a sectional view of FIG. 1, and FIG. 3 uses the current detection type ion selective electrode shown in FIG. Ion measurement system. Hereinafter, the configurations of the current detection type ion selective electrode and the ion measurement system according to the first embodiment will be described.
(1) Configuration (1-1) Current Detection Type Ion Selective Electrode The electrode body 1 of the current detection type ion selective electrode 10 covers the side surfaces of the electrode body 1 which is a conductive substance except for both end faces. An insulating material 2 is provided. One of both end surfaces of the electrode body 1 is exposed with a conductive material to apply a voltage, and the ion sensitive layer 3 is adhered to the other end to form a current detection type ion selective electrode 10. The ion-sensitive layer 3 is formed by mixing an ionophore having selectivity for ions to be measured (hereinafter, referred to as target ions) and a conductive substance. The conductive material allows target ions and / or non-target chemical species in the sample solution to permeate the electrode body when a voltage is applied to the electrode body 1 to measure target ions. Here, the non-target chemical species refers to a chemical species having electrochemical reactivity other than target ions in the sample solution 70, and includes, for example, ions, molecules such as dissolved oxygen, radicals, and the like.

Examples of the conductive substance include Nafion and a perfluorocarbon having a sulfone group.
The electrode body 1 is formed of a conductive material. As the conductive material, a material capable of accurately and stably measuring a current value without deterioration, a material having high conductivity, and / or a large resistance to a sample solution. If the substance is harmless to the sample solution, it is preferable because the current of the electrode body 1 can be accurately taken out. For example, one or more combinations selected from glassy carbon, platinum, gold, and silver are preferable.

The shape is not particularly limited, and examples thereof include a rod shape, a tubular shape, and a sheet shape. Preferably, the shape is such that the contact surface with the sample solution is large.
As the ionophore, dibenzo-18-crown-6, dibenzo-30-crown-10, biscrown ethers, nonactin, monactin, valinomycin, or derivatives thereof are appropriately selected according to the target ion. It is preferable to select the ionophore so that the inside diameter of the pores of the ionophore and the ion diameter of the target ion are substantially the same, because the selectivity of the target ion can be enhanced. Further, it is preferable to select according to the molecular structure of the ionophore and the molecular structure of the target ion, because the selectivity of the target ion can be further increased.

  When the target ion is an ammonium ion, the ionophore is selected from one or a combination of nonactin, a 19-crown-6 derivative, a 20-crown-6 derivative and a 21-crown-6 derivative. It is preferable because of high performance. Furthermore, it is preferable to be selected from TD19-crown-6, TD20-crown-6 and TD21-crown-6. The ionophore has the effect of selectively trapping ammonium ions in its vacancies and blocking interfering ions that interfere with the trapping of ammonium ions in the vacancies. Therefore, the selectivity of the ammonium ion as the target ion can be further improved.

When the target ion is a sodium ion, the ionophore is preferably bis-12-crown-4 and dibenzyl-bis-12-crown-4.
When the target ion is a potassium ion or a thallium ion, bis-benzo-15-crown-5 is preferable as the ionophore.
When the target ion is a magnesium ion, the ionophore is preferably C14-K22B5, K22B1B5 and K22B9.

When the target ion is a silver ion, octadecyloxymethylpyridine is preferred as the ionophore.
When the target ion is a lithium ion, preferred ionophores are phosphododecyl-14-crown-4, dibenzyl-14-crown-4, and TTD14-crown-4.

  Further, it is preferable that the composition ratio of the ionophore in the ion-sensitive layer 3 is determined according to the concentration of the target ion. For example, when the target ion concentration is high, by increasing the composition ratio of the ionophore in the ion-sensitive layer 3, it is possible to prevent the holes for capturing the target ions from being saturated. Furthermore, it is preferable to adjust the thickness of the ion-sensitive film 3 according to the concentration of target ions.

In the above-described current detection type ion selective electrode 10, since the ion sensitive layer 3 is in a solid state, mixing and evaporation of the internal liquid do not occur, and the handling is easy.
(1-2) Ion Measurement System FIG. 3 is an ion measurement system using the current detection type ion selective electrode of the present invention. The current detection type ion selective electrode 10 and the counter electrode 20 formed as described above are provided in the sample cell 30. The current detection type ion selective electrode 10 and the counter electrode 20 are connected to the voltage application / current detection system 40 via a connection line 50 such as a conductive wire. The current detection type ion selective electrode 10 and the counter electrode 20 are immersed in the sample solution 70 in the sample cell 30, and a voltage is applied between the current detection type ion selective electrode 10 and the counter electrode 20 by the voltage application / current detection system 40. Apply. At this time, the electrode end of the current detection type ion-selective electrode 10 where the ion-sensitive layer 3 is not adhered is connected to the connection line 50, and the electrode end where the ion-sensitive layer 3 is adhered is immersed in the sample solution 70. You. Then, the value of the current flowing through the electrode main body 1 of the current detection type ion selective electrode 10 caused by the application of the voltage is detected by the voltage application / current detection system 40.

Here, when a reference electrode is further provided in the sample cell 30, the voltage applied to the current detection type ion selective electrode 10 is accurately obtained, and the current value taken out to the electrode body 1 is determined by the voltage application / current detection system 40. Can be detected more accurately.
The ion quantification unit 60 quantifies target ions by a target ion quantification method described later.
(2) Method for Quantifying Target Ions Next, a method for quantifying target ions will be described below. A sample solution 70 containing target ions and non-target chemical species is introduced into the sample cell of FIG. The sample solution 70 can be easily measured by using a solution in which the concentration of the non-target species is known in advance, such as a biological sample, but the concentration of the non-target species is adjusted according to the target ion concentration. You may do it.

A voltage is applied between the current detection type ion selective electrode 10 immersed in the sample solution 70 and the counter electrode 20 by the voltage application / current detection system 40. Then, the voltage application / current detecting system 40 detects a current value I ₁ of the current flowing through the electrode body 1 of the current-detection ion-selective electrode 10 caused by application of a voltage.
At this time, the ion-sensitive layer 3 of the current detection type ion-selective electrode 10 includes a conductive substance that allows target ions and / or non-target chemical species in the sample solution 70 to pass through the electrode body 1 and a target substance from the sample solution 70. An ionophore that selectively captures ions. Therefore, in the electrode body 1, the presence of the target ions and / or non-target chemical species on the surface causes an electrode reaction. The electrode reaction caused by the target ions and / or non-target species is inhibited by the target ions being captured by the ionophore. Then, the current generated as a result of the inhibition is extracted by the voltage application / current detection system 40. The detected current value of the electrode indicates that the target ions and / or non-target species contribute to the electrode reaction through the conductive substance, that is, the ion-sensitive layer. It has a correlation with inhibiting. Then, instead of directly quantifying the target ion from the current generated by the electrode reaction of the target ion, the target ion is indirectly determined from the current value of the current generated as a result of the inhibition of the electrode reaction based on the correlation. Therefore, even when the concentration of the target ion is very small, it is possible to quantify the target ion in the sample solution 70 by measuring a current value corresponding to the electrode reaction caused by the target ion and / or the non-target chemical species. it can. That is, since the target ions are continuously captured by the ionophore, the electrode reaction in the electrode body 1 is inhibited. The degree of the inhibition depends on the concentration of the target ion, and the amount of the target ion can be determined by measuring the decrease in the current value due to the inhibition.

At this time, by using the ionophore having higher selectivity for the target ion, more target ions are captured by the ionophore, and as a result, the electrode reaction caused by the target ion and / or the non-target species is more reduced. Strongly inhibits. Therefore, more accurate quantification of target ions can be performed.
The concentration of the target ion is quantified by, for example, the ion quantification unit 60 as described below. First, a reference current value I ₀ is measured from the reference solution containing the non-target species in the same concentration as the non-target species in the sample solution 70 by using the current detection type ion selective electrode 10. Next, the absolute value | I ₁ | of the current value in the sample solution 70 is measured using the current detection type ion selective electrode 10. Then, by measuring how much the absolute value | I ₁ | of the current value in the sample solution 70 has decreased from the absolute value | I ₀ | of the reference current value, the concentration of the target ion can be measured. it can. That is, the absolute value | I ₁ | of the current value decreases as the target ion concentration in the sample solution 70 increases, or the absolute value | I of the current value | I ₁ according to the decrease of the target ion concentration. The amount of the target ion is determined based on the increase of ₁ |. Alternatively, the concentration of the target ion may be determined by calculating the absolute value | I ₁ −I ₀ | of the reduced current value between the reference current value I ₀ and the extracted current value I ₁ .
(3) Manufacturing method of current detection type ion selective electrode Next, a manufacturing method of the current detection type ion selective electrode of the present invention will be described. The ion-sensitive layer 3 is brought into close contact with only one end face of both end faces of the electrode body 1 whose side faces are covered with the insulating material. The ion-sensitive layer 3 is formed by applying a solution in which a conductive substance and an ionophore are mixed in a solvent to one end surface of the electrode body 1. At this time, the ion-sensitive layer 3 is formed by evaporating the mixed solution by a casting method so as to bring the ion-sensitive layer 3 into close contact with the electrode body 1. Therefore, since the ion-sensitive layer 3 is formed on the electrode body 1 without heating by the casting method, the current detection type ion-selective electrode 10 can be manufactured without deteriorating the conductive material and / or the ionophore. In addition, according to this casting method, the ion-sensitive films 3 having different properties in spots can be formed without changing the conductive material, so that various types of electrodes can be easily manufactured. For example, various electrode bodies 1 made of carbon are prepared, and a solution in which a conductive material and an ionophore are mixed according to target ions is applied to the electrode body 1 to form an ion-sensitive film 3. As described above, by changing the ion-sensitive membrane 3 without changing the material of the electrode body 1, the current detection type ion-selective electrode 10 capable of quantifying various target ions can be easily manufactured.
<Example of Second Embodiment>
The current detection type ion selective electrode and the ion measurement system according to the second embodiment of the present invention will be described with reference to FIGS. Since the ion measurement system of the second embodiment is the same as that of the first embodiment, only the current detection type ion selective electrode will be described.
(1) Configuration of Current Detection Type Ion Selective Electrode The electrode body 1 of the current detection type ion selective electrode 10 has an insulating material 2 covering the side surfaces of the electrode body 1 which is a conductive material except for both end faces. Is provided. One of both end surfaces of the electrode body 1 is exposed with a conductive material to apply a voltage, and the ion sensitive layer 3 is adhered to the other end to form a current detection type ion selective electrode 10. The ion sensitive layer 3 is formed by mixing an ionophore having selectivity with respect to a target ion to be measured and an ion conductive substance. When a voltage is applied to the electrode main body 1 to measure target ions, the ion-conductive substance ion-exchanges target ions and / or non-target ions in the sample solution. Here, the non-target ions are ions having the same polarity as the target ions and different from the target ions.

As the ion conductive substance, a substance having a property of transmitting a cation or an anion to the electrode body 1 according to the polarity of the target ion, for example, an ion exchange substance is selected. When the target ion is a positive ion, for example, Nafion (Nafion: manufactured by DuPont) having high conductivity of hydrogen ions (H ⁺ ) is used.
The material, shape, and the like of the electrode body 1 are the same as those in the first embodiment. The material and composition ratio of the ionophore are the same as those of the first embodiment.
(2) Method for Quantifying Target Ions Next, a method for quantifying target ions will be described below. A sample solution 70 containing target ions and non-target ions is introduced into the sample cell of FIG. The sample solution can be easily measured by using a solution in which the concentration of the non-target ion is known in advance, such as a biological sample, but the concentration of the non-target ion is adjusted according to the target ion concentration. May be.

A voltage is applied between the current detection type ion selective electrode 10 immersed in the sample solution 70 and the counter electrode 20 by the voltage application / current detection system 40. Then, the voltage application / current detecting system 40 detects a current value I ₁ of the current flowing through the electrode body 1 of the current-detection ion-selective electrode 10 caused by application of a voltage.
At this time, the ion-sensitive layer 3 of the current detection type ion-selective electrode 10 selects an ion conductive substance that exchanges target ions and / or non-target ions in the sample solution 70 and a target ion from the sample solution 70. And an ionophore that selectively captures. Therefore, in the electrode main body 1, the presence of ions on the surface causes an electrode reaction. This electrode reaction is inhibited by the trapping of target ions by the ionophore, and the resulting current is removed by the voltage application / current detection system 40. The detected current value of the electrode indicates that the target ions and / or non-target ions contribute to the ion conduction of the ion-conductive substance, that is, the ion-sensitive layer, and the target ions are trapped by the ionophore and hinder the ion conduction. And have a correlation. Then, instead of directly quantifying the target ion from the current generated by the electrode reaction of the target ion, the target ion is indirectly determined from the current value of the current generated as a result of the inhibition of the electrode reaction based on the correlation. Therefore, even when the concentration of the target ion is very small, the target ion is trapped by the ionophore, and as a result, the current value corresponding to the electrode reaction caused by the target ion and / or the non-target ion is measured, whereby the sample solution is measured. The target ions in 70 can be quantified. That is, since the target ions continue to be captured by the ionophore, the electrode reaction in the electrode body 1 caused by the target ions and / or non-target ions is inhibited. The degree of the inhibition depends on the target ion concentration, and the target ion can be quantified by measuring the decrease in the current value due to the inhibition.

At this time, by using an ionophore having a higher selectivity for the target ions, more target ions are trapped by the ionophore, and as a result, the electrode reaction caused by the target ions and / or non-target ions is stronger. Inhibit. Therefore, more accurate quantification of target ions can be performed.
The concentration of the target ion is quantified by, for example, the ion quantification unit 60 as described below. Using the current-detection-type ion-selective electrode 10, the absolute value I ₀ of the reference current value in a reference solution containing a non-target ion having the same concentration as the non-target ion in the sample solution 70 is measured. Next, the current value I ₁ in the sample solution 70 is measured using the current detection type ion selective electrode 10. Then, by measuring how much the absolute value | I ₁ | of the current value in the sample solution 70 has decreased from the absolute value | I ₀ | of the reference current value, the concentration of the target ion can be measured. . That is, the absolute value | I ₁ | of the current value decreases as the target ion concentration in the sample solution 70 increases, or the absolute value | I of the current value | I ₁ according to the decrease of the target ion concentration. The amount of the target ion is determined based on the increase of ₁ |. Alternatively, the concentration of the target ion may be determined by calculating the absolute value | I ₁ −I ₀ | of the reduced current value between the reference current value I ₀ and the extracted current value I ₁ .
<Third embodiment example>
FIG. 4 is a sectional view of an electrode kit according to the third embodiment of the present invention, and FIG. 5 is a plan view of the electrode kit. Hereinafter, the configuration of the electrode kit according to the third embodiment will be described.
(1) Configuration The electrode kit has an electrode pair 200 formed on a substrate 100. The electrode pair 200 has a current detection type ion selective electrode 10 and a counter electrode 20 of the current detection type ion selective electrode 10. The ion sensing layer 3 is provided in close contact with the current detection type ion selective electrode 10 so as to cover a part of the electrode body 1. As in the first embodiment, the ion-sensitive layer 3 is formed by mixing an ionophore and a conductive substance. The material, operation, and the like of the electrode body 1, the ionophore, and the conductive substance are the same as those in the first embodiment.
(2) Method for Quantifying Target Ions Next, a method for quantifying target ions will be described below. The electrode pair 200 of the electrode kit of FIG. 5 is immersed in a sample solution 70 containing target ions and non-target chemical species. Then, a voltage is applied between the electrode pairs 200. At this time, the portion of the current detection type ion-selective electrode 10 to which the ion-sensitive layer 3 is adhered is immersed in the sample solution 70, and a wire or the like is provided between the electrode body 1 to which the ion-sensitive layer 3 is not adhered and the counter electrode 20. And a voltage is applied. By detecting the current value I ₁ of the current flowing through the electrode body 1 of the current-detection ion-selective electrode 10 caused by the application of voltage, the quantitative target ion. The method of quantifying the target ions is the same as in the first embodiment.
(3) Method for Producing Electrode Kit Next, a method for producing the electrode kit of the present invention will be described. The electrode body 1 and the counter electrode 20 made of, for example, carbon paste are screen-printed on the substrate 100 of FIG. Then, the ion-sensitive layer 3 is formed by a casting method so as to be in close contact with the electrode body 1. As described above, the electrode body 1 and the counter electrode 20 are screen-printed on the substrate 100, and the ion-sensitive layer 3 is formed by using the casting method, whereby an electrode kit can be easily prepared. In addition, since the ion-sensitive layer 3 of the electrode kit is in a solid phase and the electrode kit can be formed relatively small, it is easy to handle and excellent in portability.
<Other embodiments>
As another embodiment of the present invention, various enzymes may be further immobilized on the ion-sensitive layer 3 of the current-detection-type ion-selective electrode 10 of the present invention to produce an electrode that can be used as an enzyme sensor. it can. For example, creatinine deiminase is immobilized on the ion-sensitive layer 3, and creatinine is detected.

Further, an electrode in which polypyrrole is further subjected to electric field polymerization on the ion-sensitive layer 3 of the current detection type ion-selective electrode 10 of the present invention can be produced. It is considered that by providing polypyrrole, an amplified response current can be obtained by utilizing the property that pyrrole accumulates electric charge.
Further, as shown in FIG. 6, an electrode kit capable of simultaneously measuring a plurality of target ions can be prepared. In the electrode kit shown in FIG. 6, a plurality of electrode pairs 200a, 200b, 200c,... Are provided, and the ion-sensitive layer 3 according to the type of target ion is formed so as to adhere to each electrode body 1. For example, an electrode is manufactured by changing the type of the ion-sensitive layer 3 so that the concentration of ammonium ion, the concentration of sodium ion, and the concentration of potassium ion can be simultaneously measured in pure coexisting with ammonium chloride, sodium chloride or potassium chloride.
<Experimental example 1>
A 5% Nafion solution in which 5% nonactin was turbid was dropped on a 5 mm diameter glassy carbon electrode covered with a 3 mm diameter epoxy resin cylinder, and dried at room temperature to prepare an ion-selective electrode.

  A three-electrode system was assembled using this electrode as a working electrode, a platinum wire electrode as a counter electrode, and a saturated calomel electrode (SCE) as a reference electrode. Each of these three electrodes was placed in a phosphate buffer solution (PBS) for measurement. Here, as for the potential, the instantaneous value of the current response when a sweep was performed at a sweep speed of 0.10 V per second in the range of 0.7 V to −1.0 V based on the SCE was measured. Here, the PBS contains sodium and potassium in the same concentration as the sodium and potassium in the blood, and the pH of the solution is adjusted to the same value as the pH of the blood. Therefore, this measurement simulates a measurement system in which blood is analyzed as it is.

Similarly, the same measurement was performed for a solution in which 1 mM to 4 mM ammonium chloride was dissolved in PBS.
FIG. 7 shows the above measurement results. FIG. 7 shows the amount of change (I ₁ −I ₀ ) from the reduction current value I ₀ in the PBS solution (ammonium ion concentration 0 mM) of the reduction current value I ₁ in the solution of each ammonium ion concentration, and the ammonium ion concentration. It is the figure plotted for every electric potential.

In the cyclic voltametry measurement of a solution in which ammonium chloride is dissolved in PBS, the reduction current value at each potential has a certain tendency to decrease as the ammonium ion concentration increases. The ion concentration can be determined.
<Experimental example 2>
A solution in which 5% Nafion solution was turbidized with 1% nonactin was dropped on a 5 mm diameter glassy carbon electrode covered with a 3 mm diameter epoxy resin cylinder, and dried at room temperature to prepare an ion-selective electrode. A three-electrode system was assembled using this electrode as a working electrode, a platinum wire electrode as a counter electrode, and a saturated calomel electrode (SCE) as a reference electrode. Each of these three electrodes was placed in a phosphate buffer solution (PBS) for measurement. Here, the potential was left at −0.6 V for 30 seconds with reference to the SCE, then changed to −1.0 V stepwise, and the instantaneous value of the response current after 0.1 second was measured. In the same manner, the same measurement was performed for a solution in which ammonium chloride having a concentration of 10 μM to 80 μM was dissolved in PBS.

  The above measurement results are shown in FIG. 8 with the ammonium chloride concentration on the horizontal axis and the measured reduction current value on the vertical axis. The ammonium chloride concentration on the horizontal axis in FIG. 8 is the concentration of ammonium chloride dissolved in the phosphate buffer. As shown in FIG. 8, a substantially linear calibration curve can be obtained in the concentration range of 0 μM to 60 μM. Therefore, the concentration of ammonium ions can be quantified by comparing the obtained calibration curve with actual measured values. In the second embodiment, the response current is measured using chronoamperometry that changes the potential in a stepwise manner, so that the response current value can be stabilized.

  By setting the final applied potential to -1.0 V, ammonium ion as a target ion is captured by nonactin, and the response current value in a state where it is not present in the solution is measured. That is, the response current in a state where all the target ions present in the solution are captured by nonactin is measured. Therefore, it is possible to more accurately measure the decrease in the current value due to the inhibition of the electrode reaction caused by the capture of the target ions.

According to the present invention, it is possible to provide a current detection type ion-selective electrode capable of measuring a very small amount of an object to be measured.
Further, according to the present invention, it is possible to provide a current detection type ion selective electrode which is easy to handle.
Further, by using the present invention, it is possible to provide a method for producing a current detection type ion selective electrode which can reduce the deterioration of the ionophore.

FIG. 2 is a perspective view of a current detection type ion selective electrode according to the first embodiment of the present invention. Sectional drawing of FIG. An ion measurement system using the current detection type ion selective electrode shown in FIG. Sectional drawing of the electrode kit which concerns on 2nd Embodiment of this invention. The top view of an electrode kit. An electrode kit for measuring multiple target ions simultaneously. FIG. 4 is a graph showing a relationship between a change amount (I ₁ −I ₀ ) and an ammonium ion concentration. FIG. 4 is a graph showing the relationship between the concentration of ammonium chloride and a measured reduction current value.

Explanation of reference numerals

1: Electrode body
3: Ion sensitive layer
10: Current detection type ion selective electrode
20: Counter electrode
30: sample cell
40: Voltage application / current detection system
60 ion quantification unit
70: Sample solution
100: substrate
200: electrode pair

Claims (13)

A current detection type ion-selective electrode for quantifying the target ions in a sample solution containing target ions and a chemical species other than the target ions (hereinafter, referred to as non-target chemical species),
An electrode body formed of a conductive material,
A conductive material that transmits the target ions and / or the non-target species, and an ion-sensitive layer in which ionophores having selectivity for the target ions are mixed,
A current detection type ion selective electrode, wherein the electrode body and the ion sensitive layer are in close contact with each other. The non-target chemical species is an ion having the same polarity as the target ion and different from the target ion (hereinafter, referred to as a non-target ion);
The current detection type ion selective electrode according to claim 1, wherein the conductive material is an ion conductive material that exchanges the target ions and / or the non-target ions.   The current detection type ion selective electrode according to claim 1, wherein the inside diameter of the pores of the ionophore is substantially the same size as the ion diameter of the target ion.   The method according to claim 1, wherein the target ion is an ammonium ion, and the ionophore is one or a combination of nonactin, a 19-crown-6 derivative, a 20-crown-6 derivative and a 21-crown-6 derivative. A current detection type ion selective electrode according to the above.   The current detection type ion selective electrode according to claim 1, wherein a composition ratio of the ionophore to the ion sensitive layer is selected according to a concentration of the target ion.   The current detection type ion selective electrode according to claim 1, wherein the material of the electrode body is one or a combination of glassy carbon, platinum, gold, and silver. A sample cell into which a sample solution containing target ions and a chemical species other than the target ions (hereinafter, referred to as non-target chemical species) is introduced;
An ion-sensitive portion in which a conductive substance and an ionophore having selectivity for the target ion are mixed, and an electrode provided in the sample cell,
A counter electrode of the electrode provided in the sample cell;
A voltage application unit that applies a voltage between the electrode and the counter electrode,
A current value detector for detecting a current value I ₁ flowing through the electrode resulting from the application of the voltage,
The absolute value | I ₁ | of the current value increases based on the fact that the absolute value | I ₁ | of the current value decreases as the target ion concentration increases or as the target ion concentration decreases. A target ion quantification unit that quantifies the target ion based on the
An ion measurement system including: A current detection type ion selective electrode according to claim 1,
A sample cell into which a sample solution containing the target ions and the non-target species is introduced,
A counter electrode of the current detection type ion selective electrode provided in the sample cell,
A voltage application unit that applies a voltage between the current detection type ion selective electrode and the counter electrode,
A current value detector for detecting a current value I ₁ flowing through the electrode body of the current detection type ion-selective electrodes caused by application of the voltage,
A target ion quantification unit for quantifying the target ion,
An ion measurement system including:   The ion measurement system according to claim 7, wherein a reference electrode is further provided inside the sample cell. A method for quantifying target ions using the current detection type ion selective electrode according to claim 1,
An immersion step of immersing the current detection type ion-selective electrode and the counter electrode in a sample cell into which a sample solution containing the target ions and the non-target chemical species has been introduced,
A voltage applying step of applying a voltage between the current detection type ion selective electrode and the counter electrode,
A current value detection step of detecting a current value I ₁ of the current flowing through the electrode body of the current detection type ion-selective electrodes caused by application of the voltage,
The absolute value | I ₁ | of the current value increases based on the fact that the absolute value | I ₁ | of the current value decreases as the target ion concentration increases or as the target ion concentration decreases. A target ion quantification step of quantifying the target ion based on the
And a method for quantifying a target ion. In the target ion quantification step, the reference current value I _{0 in} the electrode body of the current detection type ion selective electrode immersed in the reference solution containing the non-target species, and the current value detected in the current detection step comparing the I _1, the absolute value of the reduction current value is a decrease from the reference current value I ₀ of the current value I ₁ | perform quantification of the target ion by calculating | I ₁ -I ₀ The method for quantifying a target ion according to claim 9. It is a manufacturing method of the current detection type ion selective electrode according to claim 1,
A mixing step of mixing the conductive substance and the ionophore constituting the ion-sensitive layer in a solution;
A film forming step of applying the mixed solution to one end surface of the electrode main body by a casting method, evaporating the solution, and forming a film so that the ion-sensitive layer is in close contact with the electrode main body,
A method for producing a current detection type ion-selective electrode, comprising: An electrode kit provided with at least one electrode pair,
An electrode kit, wherein the electrode pair comprises the current detection type ion selective electrode according to claim 1 and a counter electrode of the current detection type ion selective electrode.

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