Ion sensor and ion measurement method

Abstract

To provide an ion sensor having small variation in measurement results among a plurality of ion sensors.SOLUTION: Disclosed is an ion sensor 100 of the present invention, which is a current measuring type ion sensor for measuring a current and performing measurement of a target ion 31, and includes: an organic phase holding layer 13 including an organic phase capable of forming the interface with a sample 30 containing the target ion 31; a first electrode 11 in which the organic phase holding layer 13 is laminated and which includes a first insertion material constituted of an inorganic compound; and a second electrode 12 which is arranged opposite to the organic phase holding layer 13 and comes into contact with the sample 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ion sensor and a method for measuring ions. [Background technology]

[0002] Patent Document 1 discloses an ion sensor including an organic phase retaining layer containing an organic phase capable of forming an interface with a sample containing target ions, an organic phase electrode on which the organic phase retaining layer is laminated, and an aqueous phase electrode in contact with the sample, the organic phase retaining layer and the aqueous phase electrode being arranged to face each other. In the ion sensor of Patent Document 1, a conductive polymer membrane is provided between the organic phase electrode and the organic phase retaining layer in order to fix the electrode potential of the organic phase electrode in the organic phase. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-122883 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional ion sensors such as that disclosed in Patent Document 1, when the same sample is measured using multiple ion sensors, there is a risk of variations in measurement results between the ion sensors. Here, for example, when ion sensors are disposable and replaced each time a measurement is performed, if variations in measurement results occur between the multiple ion sensors, there is a problem in that it becomes difficult to distinguish whether the variations in measurement results are due to variations in the concentration of the ions to be measured in the sample or due to variations in measurement results between the ion sensors.

[0005] An object of the present invention is to provide an ion sensor and a method for measuring ions that minimize variations in measurement results among a plurality of ion sensors. [Means for solving the problem]

[0006] The ion sensor (100, 200) of the present invention is an amperometric ion sensor that measures target ions (31) by measuring current, and includes an organic phase holding layer (13) containing an organic phase capable of forming an interface with a sample (30) containing target ions (31), and the organic phase holding layer (13) is laminated and is made of an inorganic compound, and the organic phase holding layer (13) is formed within the structure by an electrochemical reaction. subject The device comprises a first electrode (11) containing a first insertion material capable of inserting and desorbing ions, and a second electrode (12) arranged opposite the organic phase holding layer (13) and in contact with the sample (30).

[0007] The method for measuring ions of the present invention is a method for measuring ions using an ion sensor (100, 200), and includes the steps of bringing a sample (30) into contact with an organic phase retaining layer (13) and a second electrode (12), applying a voltage between the first electrode (11) and the second electrode (12) to transfer target ions contained in the sample (30) to the organic phase, and measuring the current flowing between the first electrode and the second electrode. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an ion sensor and a method for measuring ions that produce small variations in measurement results among a plurality of ion sensors. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view showing an ion sensor. [Figure 2] FIG. 2 is a perspective view showing the ion sensor before a sample is dropped. [Figure 3] FIG. 2 is a perspective view showing the ion sensor when a sample is dropped. [Figure 4] FIG. 10 is a perspective view showing the ion sensor after a sample has been dropped. [Figure 5] FIG. 2 is a diagram for explaining a method for measuring ions by an ion sensor. [Figure 6]1 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 1 in Measurement Example 1. [Figure 7] 1 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 2 in Measurement Example 1. [Figure 8] 1 is a voltammogram showing the results of current measurement performed using an ion sensor of a comparative example in Measurement Example 1. [Figure 9] 1 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 3 in Measurement Example 1. [Figure 10] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 3 in Measurement Example 2. [Figure 11] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of the comparative example in Measurement Example 2. [Figure 12] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 3 in Measurement Example 3. [Figure 13] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of the comparative example in Measurement Example 3. [Figure 14] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 2 in Measurement Example 3. [Figure 15] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 4 in Measurement Example 4. [Figure 16] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 4 in Measurement Example 5. [Figure 17] 10 is a voltammogram showing the results of current measurement performed using the ion sensor of Example 5 in Measurement Example 5. [Figure 18] FIG. 10 is a plan view showing an ion sensor according to a modified example. [Figure 19] FIG. 10 is a schematic side view showing an ion sensor according to a modified example. [Figure 20]FIG. 19 is a cross-sectional view taken along line 300-300 in FIG. 18. [Figure 21] FIG. 4 is a bottom view showing an insulating substrate on which a second electrode is laminated. [Figure 22] FIG. 22 is a cross-sectional view taken along line 310-310 in FIG. 21. [Figure 23] FIG. 10 is a plan view showing an adhesive layer of an ion sensor according to a modified example. [Figure 24] 1 is a plan view showing an insulating substrate on which a first electrode and an organic phase-retaining layer are laminated. [Figure 25] FIG. 25 is a cross-sectional view taken along line 320-320 in FIG. 24. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an example of an embodiment of an ion sensor and an ion measurement method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments and modifications described below, and design modifications can be made as appropriate within the scope of the present invention. For example, selective combinations of the components of the multiple embodiments and modifications described below are within the scope of the present disclosure.

[0011] (Ion sensor configuration) 1 is a schematic cross-sectional view of an ion sensor 100. As shown in FIG. 1, the ion sensor 100 is an amperometric ion sensor that measures target ions contained in a sample 30 by measuring current.

[0012] The ion sensor 100 includes a first electrode 11, a second electrode 12, an organic phase retaining layer 13, a sheet 14, an insulating substrate 15, and an insulating substrate 16. The first electrode 11 of the ion sensor 100 is connected to a current measuring unit 22 that measures current via a conductor 23. The second electrode 12 is connected to a voltage applying unit 21 that applies voltage via a conductor 24. The current measuring unit 22 includes an ammeter. The voltage applying unit 21 includes a DC power supply device that can vary the applied voltage. The voltage applying unit 21 and the current measuring unit 22 are connected to each other via a conductor 25.

[0013] The first electrode 11 is disposed so as to face the second electrode 12. An organic phase retaining layer 13 is laminated on the second electrode 12 side of the first electrode 11.

[0014] The first electrode 11 functions as an organic phase electrode. The first electrode 11 includes an electrode material and a film of an insertion material (called an insertion coating film) formed by applying the insertion material to the electrode material. The electrode material is formed of, for example, carbon paper. The insertion coating film may be composed of only the insertion material, or may further include at least one of a solid electrolyte, a conductive agent, and a binder.

[0015] The first electrode 11 may contain an insertion material. For example, if the insertion material, which is made of an inorganic compound, itself contains a conductive material and has good conductivity, an electrode material may not be provided. In this case, it is preferable to bind the insertion material with a binder and place it on the insulating substrate 15.

[0016] The electrode material is not particularly limited as long as it contains a conductive material. Examples of conductive materials include metals such as platinum, gold, silver, copper, carbon, palladium, chromium, aluminum, nickel, indium, and tin, alloys containing at least one of these metals, metal halides such as chlorides of these metals, and oxides of these metals (e.g., indium tin oxide). Among these, preferred are platinum, gold, silver, palladium, aluminum, nickel, and carbon. The conductive material may be a single material or a combination of two or more materials.

[0017] The content of the conductive material is, for example, 70 parts by mass or more and 100 parts by mass or less, preferably 85 parts by mass or more and 100 parts by mass or less, and more preferably 95 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the electrode material.

[0018] The shape of the electrode material is not particularly limited, but is preferably flat. The layer structure of the electrode material is not particularly limited. The electrode material may have a single-layer structure consisting of one layer made of a single composition, or a multi-layer structure consisting of multiple layers made of the same or different compositions. The thickness of the electrode material is not particularly limited as long as the conductivity is not significantly impaired. The thickness of the electrode material is, for example, 1 μm or more and 10 μm or less. From the viewpoints of production efficiency, production costs, etc., the thickness of the electrode material is preferably 1 μm or more and 5 μm or less.

[0019] The insertion material is not particularly limited as long as it is composed of an inorganic compound. Preferably, the insertion material can be an ion-electron conductor capable of inserting and desorbing ions into and from the structure through an electrochemical reaction. That is, the insertion material may be an ion-electron conductor. In this case, the insertion material may be an ion-electron conductor for sodium ions, potassium ions, or lithium ions.

[0020] Examples of insertion materials include metal oxides, oxygen redox materials, and Prussian blue analogs, with metal oxides being preferred. These can be selected appropriately depending on the target ion to be measured.

[0021] As the metal oxide of the insertion material, for example, M x MnO2, M x NiO2, M x CoO2, M x Ni 0.5 Mn 0.5 O2, M x FeO2, M 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, M x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, M x Ni 0.5 Ti 0.5 O2, M x VO2, Mx CrO2, M x FePO4 (where M is independently Na or K for each, and x represents any positive number) and the like can be mentioned. Among these, more preferably, M x MnO2 can be mentioned, and particularly preferably, Na x MnO2 can be mentioned.

[0022] x is usually 0 < x ≤ 1. x is preferably 0.15 or more and 0.66 or less, more preferably 0.2 or more and 0.5 or less, still more preferably 0.22 or more and 0.28 or less, 0.30 or more and 0.36 or less, or 0.41 or more and 0.47 or less, and particularly preferably 0.245 or more and 0.255 or less, 0.325 or more and 0.335 or less, or 0.435 or more and 0.445 or less.

[0023] The crystal structure of the metal oxide of the insertion material is not particularly limited as long as it can be used as the electrode of the ion sensor 100. Examples of the crystal structure include a cubic crystal structure, a tetragonal crystal structure, a trigonal crystal structure, a hexagonal crystal structure, a rhombohedral crystal structure, a triclinic crystal structure, a monoclinic crystal structure, etc. Among these, a cubic crystal structure is preferably mentioned.

[0024] The oxygen redox material of the insertion material is a material that can utilize the oxidation-reduction reaction of not only transition metals but also oxide ions, and is not particularly limited within this range. Examples of the oxygen redox material include Na2Mn3O7, Na 2 / 3 Mg 0.28 Mn 0.72 O2, Na2RuO3, Na 1.3 Nb 0.3 Mn 0.4 O2, Na 0.6 Li 0.2 Mn 0.8 O2 and the like can be mentioned.

[0025] The Prussian blue analogue of the insertion material is a structure in which a cyano group crosslinks a transition metal ion, and is not particularly limited insofar as such structure is concerned. Examples of Prussian blue analogues include Na2Mn[Fe(CN)6], Na y CO[Fe(CN)6] 0.90 2.9H2O (where y is any positive number), K-FeHCF (potassium iron hexacyanoferrate), K-NiHCF (potassium nickel hexacyanoferrate), K-CuHCF (potassium copper hexacyanoferrate), Na-NiHCF (sodium nickel hexacyanoferrate), Ca-NiHCF (calcium nickel hexacyanoferrate), etc.

[0026] The form of the insertion material is not particularly limited, but the insertion material is preferably in the form of particles, which may have any shape, such as scales, columns, spheres, or ellipsoids.

[0027] The average particle size of the particles of the insertion material is preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less, and even more preferably 5 μm or more and 12 μm or less, from the viewpoint of improving adhesion with the solid electrolyte and improving the performance of the electrode of the ion sensor 100. The average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0028] The material and shape of the insertion material may be one type alone or a combination of two or more types.

[0029] The content of the insertion material is, for example, 20 parts by mass or more and 70 parts by mass or less, preferably 25 parts by mass or more and 65 parts by mass or less, and more preferably 30 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the insertion coating film.

[0030] As the solid electrolyte, for example, an ion-conductive ceramic can be used. The ion-conductive ceramic used as the solid electrolyte is not particularly limited as long as it is a solid that can conduct ions. As the ion-conductive ceramic, one that can conduct ions to be measured can be used.

[0031] Examples of the ion conductive ceramics include potassium ion conductive ceramics, sodium ion conductive ceramics, lithium ion conductive ceramics, calcium conductive ceramics, magnesium conductive ceramics, etc. Preferred examples of the ion conductive ceramics include potassium ion conductive ceramics, sodium ion conductive ceramics, and lithium ion conductive ceramics, and particularly preferred examples of the ion conductive ceramics include potassium ion conductive ceramics.

[0032] The ion-conductive ceramic can be appropriately selected depending on the ions to be measured. Examples of the ion-conductive ceramic include oxide-based solid electrolytes such as β" alumina, β alumina, perovskite-type oxides, NASICON-type oxides, and garnet-type oxides; sulfide-based solid electrolytes; stabilized zirconia; and ion exchangers. The ion exchanger is not particularly limited as long as it is a substance that exhibits an ion exchange phenomenon, and examples include zeolite (zeolite can contain cations such as Na ions, K ions, and H ions inside), ion-exchange resin acids, and the like.

[0033] Among the ion-conductive ceramics, β″ alumina, β alumina, zeolite, and the like are particularly preferred, as they have high stability against water and can be suitably used as electrodes of the ion sensor 100.

[0034] β" / β alumina has a layered structure consisting of an ion-conducting layer and a spinel block, and the movement of ions (target ions to be measured) occurs within the ion-conducting layer. β" alumina and β alumina differ in their crystal structures, with β" alumina having a higher sodium ion content within its crystal structure and relatively higher ionic conductivity. β" / β alumina is preferably Na-β" / β alumina, which can conduct sodium ions. Na-β" alumina is typically a substance with the chemical composition Na2O·xAl2O3 (x = 5 to 7). Na-β alumina is typically a substance with the chemical composition Na2O·xAl2O3 (x = 9 to 11).

[0035] The form of the ion-conductive ceramic is not particularly limited, but is preferably particulate. The particles of the ion-conductive ceramic as a solid electrolyte may have any shape, such as scale, columnar, spherical, or ellipsoidal.

[0036] The average particle size of the ion-conductive ceramic particles is preferably 0.02 μm or more and 7 μm or less, more preferably 0.05 μm or more and 5 μm or less, and even more preferably 0.1 μm or more and 3 μm or less, from the viewpoint of improving adhesion with the insertion material and improving the performance of the electrode of the ion sensor 100. The average particle size can be measured with a laser diffraction / scattering particle size distribution analyzer.

[0037] In the insertion coating film layer, the average particle size of the ion-conductive ceramic is preferably smaller than the average particle size of the insertion material. Specifically, the ratio of the average particle size of the ion-conductive ceramic to the average particle size of the insertion material (=average particle size of the ion-conductive ceramic / average particle size of the insertion material) is, for example, 0.001 to 0.3, preferably 0.005 to 0.1, and more preferably 0.01 to 0.05. Alternatively, the ratio of the average particle size of the ion-conductive ceramic to the average particle size of the insertion material (=average particle size of the ion-conductive ceramic / average particle size of the insertion material) is, for example, 0.001 to 0.7, preferably 0.005 to 0.6, and more preferably 0.01 to 0.05.

[0038] The ion-conductive ceramic may be of one material and shape alone or in combination of two or more types.

[0039] The content of the ion conductive ceramics is, for example, 15 parts by mass or more and 70 parts by mass or less, preferably 20 parts by mass or more and 65 parts by mass or less, and more preferably 25 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the insertion coating film.

[0040] The mass ratio of the insertion material to the ion-conductive ceramics in the insertion coating film (insertion material:ion-conductive ceramics) is, for example, 5:1 to 1:5, preferably 2:1 to 1:2, more preferably 1.5:1 to 1:1.5, even more preferably 1.2:1 to 1:1.2, and still more preferably 1.1:1 to 1:1.1.

[0041] Instead of or together with the ion-conductive ceramics, an ion exchanger capable of ion exchange may be used as the solid electrolyte. The ion exchanger may be an inorganic substance such as fluorite, acid clay, or permite, or an organic substance such as a cellulose ion exchanger or alginic acid.

[0042] The insertion coating film preferably further contains a conductive agent, which improves the conductivity of the insertion coating film, improves the buffering effect against volume changes caused by the ingress and egress of ions, and increases the reproducibility of measurements.

[0043] The conductive agent is not particularly limited, and examples thereof include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, carbon powder, and graphite powder; conductive fibers such as metal fibers; metal powders such as carbon fluoride and aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and organic conductive materials such as phenylene derivatives and graphene derivatives.

[0044] The conductive agent may contain one component alone or two or more components in combination.

[0045] The content of the conductive agent is, for example, 0.1 parts by mass or more and 20 parts by mass or less, preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the insertion coating film.

[0046] The mass ratio of the insertion material to the conductive agent in the insertion coating film (insertion material:conductive agent) is, for example, 20:1 to 1:1, preferably 15:1 to 3:1, and more preferably 10:1 to 6:1.

[0047] The mass ratio of the ion conductive ceramic to the conductive agent in the insertion coating film (ion conductive ceramic:conductive agent) is, for example, 20:1 to 1:1, preferably 15:1 to 3:1, and more preferably 10:1 to 6:1.

[0048] The insertion coating film preferably further contains a binder, which allows the components in the insertion coating film to be more firmly bound together.

[0049] The binder is not particularly limited, and examples thereof include polymers such as polyvinylidene fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, acrylic emulsion, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose; similar compounds having a skeleton similar to these polymers; and composites consisting of a plurality of polymers. Among these, (a) polyvinylidene fluoride, (b) a mixture containing styrene butadiene latex and carboxymethyl cellulose, (c) a mixture containing polyamide, polyimide, and carbodiimide, (d) polytetrafluoroethylene, (e) acrylic emulsion, etc. are preferable, and polyvinylidene fluoride is more preferable.

[0050] The binder component may be one type alone or a combination of two or more types.

[0051] The content of the binder is, for example, 0.1 parts by mass or more and 20 parts by mass or less, preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the insertion coating film.

[0052] The mass ratio of the insertion material to the binder in the insertion coating film (insertion material:binder) is, for example, 20:1 to 1:1, preferably 15:1 to 3:1, and more preferably 10:1 to 6:1.

[0053] The mass ratio of the ion conductive ceramic to the binder in the insertion coating film (ion conductive ceramic:binder) is, for example, 20:1 to 1:1, preferably 15:1 to 3:1, and more preferably 10:1 to 6:1.

[0054] The insertion coating film may contain other components in addition to those mentioned above, such as MnCO3, Na2CO3, and Al2O3.

[0055] The total content of the insertion material and ion-conductive ceramics in the insertion coating film (and, if a conductive agent and a binder are further included, the total content including these) is, for example, 70 parts by mass or more and 100 parts by mass or less, preferably 80 parts by mass or more and 100 parts by mass or less, more preferably 90 parts by mass or more and 100 parts by mass or less, even more preferably 95 parts by mass or more and 100 parts by mass or less, and still more preferably 99 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the insertion coating film.

[0056] In the insertion coating film, it is preferable that the components are in a mixed state.

[0057] The layer structure of the insertion coating film is not particularly limited. The insertion coating film may have a single-layer structure consisting of one layer made of a single composition, or a multi-layer structure consisting of multiple layers made of the same or different compositions.

[0058] The thickness of the insertion coating film is not particularly limited as long as the electrical conductivity is not significantly impaired. The thickness of the insertion coating film is, for example, 1 μm or more and 200 μm or less. From the viewpoint of production efficiency, production cost, etc., the thickness of the insertion coating film is preferably 1 μm or more and 100 μm or less, more preferably 1 μm or more and 50 μm or less, and even more preferably 1 μm or more and 20 μm or less.

[0059] The second electrode 12 functions as an aqueous phase electrode. The second electrode 12 is positioned opposite the organic phase retaining layer 13 and is in contact with the sample 30. The second electrode 12 is disposed between the insulating substrate 16 and the sheet 14. An Ag / AgCl plate is used as the second electrode 12 (aqueous phase electrode) because it maintains a constant electrode potential in the sample 30 and immobilizes electrode reactants on the electrode surface. However, the material is not limited to this. Materials such as carbon electrodes modified with redox compounds, carbon paste, platinum, gold, copper, and glass electrodes can also be used instead of Ag / AgCl. If the sample 30 contains a certain concentration of non-target ions, an ion-selective electrode that responds to the non-target ions can also be used. The second electrode 12 may also contain a second insertion material. In this case, the second insertion material may be the same material as the first insertion material, and the second electrode 12 may be formed with the same configuration as the first electrode 11. This allows the ion sensor 100 to be manufactured using a common material for the first electrode 11 and the second electrode 12, thereby preventing the number of types of materials from increasing and improving the mass productivity of the ion sensor 100.

[0060] The organic phase holding layer 13 contains an organic phase capable of forming an interface with the sample 30 containing the ions to be measured. The organic phase contains an organic solvent to which the ionic substance dissolved in the aqueous solvent can migrate from the aqueous solvent, and a supporting electrolyte for the organic phase contained in the organic solvent.

[0061] The organic solvent may be any solvent that forms an interface with the aqueous phase, and examples thereof include halogen-containing solvents such as dichloroethane and trichloromethane, ether solvents such as diethyl ether and tetrahydrofuran, aromatic solvents such as nitrobenzene and toluene, and alkane solvents such as hexane. Alternatively, hydrophobic ionic liquids such as asymmetric alkylammonium bis(nonafluorobutanesulfonyl)imide may be used as the organic solvent.

[0062] Examples of supporting electrolytes for the organic phase include hydrophobic salts consisting of hydrophobic cations such as quaternary ammonium, tetraphenylphosphonium, alkylphosphonium, and imidazolium, and hydrophobic anions such as halogenated tetraphenylborates and various sulfonyl imides. Furthermore, ionic liquids such as asymmetric alkylammonium halogenated tetraphenylborates may be used as those that function both as organic solvents and as supporting electrolytes for the organic phase. The concentration of the supporting electrolyte is 10 -3 It can be between M and 0.1M.

[0063] The organic phase is held by a polymer membrane, a porous inorganic insulating material that has an affinity for the organic phase, or the like.

[0064] Examples of polymer membranes include Teflon (registered trademark), polyethylene, polypropylene, and polyvinyl chloride. Examples of porous inorganic insulating materials include porous membranes of alumina and silicon carbide. The polymer membrane may be prepared by permeating an organic phase solvent into a polymer membrane prepared separately, or by mixing the organic phase solvent with a polymer material to integrate the organic phase solvent and polymer membrane. The thickness of the organic phase retaining layer 13 is not limited, but a thinner layer is preferable from the viewpoint of back-extracting ionic substances transferred to the organic phase into the aqueous phase. However, it is necessary to prevent contact between the sample 30 and the first electrode 11 (organic phase electrode). For example, the thickness of the organic phase retaining layer 13 can be 5 μm or more and 1000 μm or less. From a manufacturing standpoint, the thickness of the organic phase retaining layer 13 is preferably 10 μm or more and 200 μm or less.

[0065] The organic phase holding layer 13 may contain an ionophore. This allows the ions to be measured to be separated from other ions and be measured with high accuracy. The ionophore is provided to select cations such as sodium ions and potassium ions, for example.

[0066] Examples of ionophores include valinomycin, monesin, rhodopsin, nonactin, monactin, ionomycin, gramicidin A, nigericin, CCCP (carbonyl cyanide-m-chlorophenylhydrazone), FCCP (carbonyl cyanide-p-trifluoromethoxyphenylhydrazone), crown ethers (a group of macrocyclic polyethers), and also acyclic nonylphenoxypolyethanol, DD16C5, Bis-12Crown-4, 12-Crown-4, 15-Crown-5, 18-Crown-6, and carexarene. Ionophores may be used alone or in combination of two or more.

[0067] The sheet 14 is provided between the organic phase retaining layer 13 and the second electrode 12. The sheet 14 is formed, for example, from a thin plastic plate. As shown in FIG. 2, the sheet 14 has a through hole 141. As shown in FIG. 1, when the sheet 14 is sandwiched between the second electrode 12 and the organic phase retaining layer 13, the through hole 141 forms a space for accommodating the sample 30.

[0068] The first electrode 11 is disposed on the insulating substrate 15. The insulating substrate 15 is formed of, for example, a thin plastic plate.

[0069] The second electrode 12 is disposed on the insulating substrate 16. The insulating substrate 16 is formed of, for example, a thin plastic plate.

[0070] There are no particular limitations on the insulating substrates 15 and 16, as long as they contain an insulating material that does not affect the conductivity of the electrodes. Examples of insulating materials include polyester resins such as polyvinyl alcohol, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate, polyimide, glass epoxy resin, glass, ceramic, and fiber substrates such as paper.

[0071] 2 to 4, a method for setting the sample 30 in the ion sensor 100 will be described. FIG. 2 is a perspective view of the ion sensor 100 before the sample 30 is set. As shown in FIG. 2, a first electrode 11 is arranged on an insulating substrate 15, and an organic phase-retaining layer 13 is placed on the first electrode 11. A second electrode 12 is arranged on an insulating substrate 16. The insulating substrates 15, 16, and the sheet 14 are all rectangular sheets of the same shape, with one short side bonded to each other and capable of being rotated about the short side as a central axis to move away from or contact each other.

[0072] When setting the sample 30 in the ion sensor 100, as shown in Fig. 3, the sheet 14 is rotated to abut against the insulating substrate 15, and the sample 30 is dropped into the space formed by the through-hole 141 of the sheet 14. Then, as shown in Fig. 4, the insulating substrate 16 is rotated to abut against the sheet 14, and the insulating substrate 15, the insulating substrate 16, and the sheet 14 are fixed by pressure bonding. In this way, the ion sensor 100 is assembled. In the assembled ion sensor 100, the first electrode 11 is connected to the conducting wire 23 (see Fig. 1), and the second electrode 12 is connected to the conducting wire 24 (see Fig. 1).

[0073] The ions that are the measurement target of the ion sensor 100 are not particularly limited, but examples thereof include potassium ions, sodium ions, lithium ions, calcium ions, and magnesium ions.

[0074] The ion sensor 100 can preferably be used as a potassium ion sensor. Hyperkalemia patients are at high risk of experiencing fluctuations in cardiac electrical activity, such as electrocardiogram abnormalities, and even fatal arrhythmias, due to behaviors that increase blood potassium, such as excessive intake of high-potassium foods. However, medication, dialysis, or other treatments when blood potassium levels are not high can cause excessive blood potassium levels to drop, resulting in paralysis, muscle spasms, and even death. Because blood potassium levels vary depending on a patient's constitution, pathology, and daily diet, it is desirable for patients to measure their own blood potassium levels and then appropriately adjust medication timing, dosage, diet, and other factors to prevent excessive increases or decreases in blood potassium levels. The ion sensor 100 has reduced potential variation among multiple ion sensors 100, requiring less calibration (even calibration-free), making it particularly suitable as a potassium ion sensor for use in measurements by hyperkalemia patients (which typically require complex and specialized tasks such as calibration).

[0075] The ion sensor 100 can measure target ions using coulometry, a type of measurement method that detects electric current. Coulometry is a method for measuring the quantity of a target ion from the electrical quantity obtained by integrating the detected electric current from the start to the end of the measurement. Because coulometry has high measurement accuracy, it is useful in clinical testing situations where accurate detection of abnormal values ​​that deviate from constant values, such as the composition of body fluids, is required. In addition, because it detects the current derived from the total amount of target ions in a sample, it is a measurement method that allows absolute quantification without the need for a calibration curve, making it suitable for use as a disposable sensor.

[0076] In coulometry, the voltage applied to the ion sensor 100 varies depending on the type of target ion, the sample solvent, and the type of organic solvent in the organic phase support layer, but can generally be between −1.5 V and 1.5 V. Specifically, it is preferable to apply a voltage based on the peak current potential at which a peak current is obtained from a cyclic voltammogram. When measuring by moving cations in the sample, a voltage is applied relative to the first electrode 11 (organic phase electrode) so that the potential of the second electrode 12 (aqueous phase electrode) is at or above the potential at which a positive current peak occurs. When measuring by moving anions, a voltage is applied relative to the first electrode 11 (organic phase electrode) so that the potential of the second electrode 12 (aqueous phase electrode) is at or below the potential at which a negative current peak occurs.

[0077] In coulometry, a voltage is applied between the electrodes, the ion migration current accompanying the migration of cations or anions is measured, and the coulomb number (quantity of electricity) can be calculated by integrating the current from the start to the end of the measurement, and the amount of substance (number of moles) of the ion can be calculated from this coulomb number. Note that when the ion migration current approaches 0 A and stops changing, it can be determined that the migration of cations or anions has ended.

[0078] Next, a method for measuring target ions using the ion sensor 100 will be described. As shown in FIG. 5, in the ion sensor 100, the sample 30 is brought into contact with the organic phase holding layer 13 and the second electrode 12. The method for bringing the sample 30 into contact with the organic phase holding layer 13 and the second electrode 12 can be, for example, the method described with reference to FIGS. 2 to 4. Then, by applying a voltage between the first electrode 11 and the second electrode 12, target ions 31 contained in the sample 30 are transferred from the sample 30 (aqueous phase) to the organic phase holding layer 13 (organic phase). Specifically, a constant voltage for transferring the target ions 31 is applied between the first electrode 11 and the second electrode 12 by the voltage application unit 21 (see FIG. 1), thereby transferring the target ions 31 from the sample 30 (aqueous phase) to the organic phase holding layer 13 (organic phase).

[0079] The movement of the target ions 31 causes a charge transfer, resulting in a current flow. The current flowing between the first electrode 11 and the second electrode 12 is measured by the current measurement unit 22 (see FIG. 1). The amount of the target ions is then calculated based on the quantity of electricity (sample current integral) obtained by integrating the measured current value from the start to the end of voltage application. Specifically, the amount of ions (mol) is calculated by Q / n·F, where Q is the measured quantity of electricity (C), n is the charge number of the target ions 31, and F is Faraday's constant (approximately 96485 C / mol). Q is calculated by subtracting the background current integral from the sample current integral described above. The background current integral is the current integral obtained by integrating the current obtained by applying a voltage between the first electrode 11 and the second electrode 12 when the target ions are not contained in the aqueous phase from the start to the end of voltage application.

[0080] (Example) An example of the ion sensor 100 of this embodiment will be described below.

[0081] Example 1 In Example 1, the first electrode 11 (electrode for organic phase) is made of carbon paper with a metal oxide (Na 0.33 MnO2 (rectangular crystal structure, average particle size 7.3 μm, flake-shaped) and solid electrolyte (β" alumina: Na2Al 10.6 O 15.9 The insertion coating film was formed by applying a paste containing cellulose nitrate (average particle size 0.99 μm), a conductive material (acetylene black), and a binder (polyvinylidene fluoride) using a squeegee.

[0082] The second electrode 12 (aqueous phase electrode) was an Ag / AgCl electrode.

[0083] The organic phase holding layer 13 was prepared by impregnating a Teflon porous membrane (thickness: 30 μm) with a solution of nitrophenyl octyl ether (NPOE), an organic solvent, and 0.01 M BTPPATFPB, a supporting electrolyte.

[0084] In the ion sensor 100 of Example 1, an organic phase retaining layer 13 was laminated on the insertion coating film of the first electrode 11, and a sheet 14 (thickness: 100 μm) with a through-hole 141 having a diameter of 5 mm for retaining a sample was laminated thereon. 1 μL of the sample was dropped into the through-hole 141 of the sheet 14 using a micropipette, and then the second electrode 12 was placed over the sheet. Furthermore, three cells were fabricated by assembling the first electrode 11, the organic phase retaining layer 13, the sheet 14 containing the sample, and the second electrode 12 by pressure bonding, and these were used for measurement.

[0085] Example 2 In Example 2, the first electrode 11 (electrode for organic phase) is made of carbon paper with a metal oxide (Na 0.33 A paste containing MnO2 (orthorhombic crystal structure, average particle size 7.3 μm, flake-shaped), a conductive material (acetylene black), and a binder (polyvinylidene fluoride) was applied using a squeegee to form an insertion coating film. That is, the first electrode 11 of Example 2 does not contain a solid electrolyte (β" alumina), unlike Example 1. The other configurations of Example 2 are the same as those of Example 1.

[0086] Example 3 In Example 3, the first electrode 11 (electrode for organic phase) is made of carbon paper with a metal oxide (Na 0.33 MnO2 (rectangular crystal structure, average particle size 7.3 μm, flake-shaped) and solid electrolyte (β" alumina: Na2Al 10.6 O 15.9 The first electrode 11 of Example 3 was fabricated by electrostatically applying a paste containing cellulose nitrate (average particle size 0.99 μm), a conductive material (acetylene black), and a binder (polyvinylidene fluoride) to form an insertion coating film. That is, the first electrode 11 of Example 3 differs from Example 1 in that the first electrode 11 is formed by electrostatically applying an insertion coating film. The other configurations of Example 3 are the same as those of Example 1.

[0087] Example 4 In Example 4, an ionophore (0.01 M Valinomycin) was further added to the organic phase retention layer 13 of Example 1. Other configurations of Example 4 were the same as those of Example 3.

[0088] Example 5 In Example 5, the second electrode 12 (aqueous phase electrode) is made of carbon paper with a metal oxide (Na 0.33 MnO2 (rectangular crystal structure, average particle size 7.3 μm, flake-shaped) and solid electrolyte (β" alumina: Na2Al 10.6 O 15.9 The electrode was fabricated by applying a paste containing cellulose nitrate (average particle size 0.99 μm), a conductive material (acetylene black), and a binder (polyvinylidene fluoride) using a squeegee to form an insertion coating film. That is, in Example 5, the first electrode 11 and the second electrode 12 have the same configuration. The other configurations of Example 5 are the same as those of Example 4.

[0089] Example 6 In Example 6, the first electrode 11 and the second electrode 12 have the same configuration as in Example 2, but an ionophore (0.01 M Valinomycin) is further added to the organic phase retaining layer 13. The other configurations of Example 6 are the same as those of Example 2.

[0090] (Comparative Example) In the comparative example, the first electrode (organic phase electrode) was prepared by applying a PEDOT-PEG:TFPB dispersion methanol solution (3 g / L) to carbon paper and drying it to form a coating film. The other configurations of the comparative example were the same as those of Example 1.

[0091] The configurations of the ion sensors of Examples 1 to 6 and the comparative example are summarized in Table 1 below. [Table 1]

[0092] (Measurement example 1) Measurement Example 1 was carried out to evaluate the reproducibility of measured values ​​between a plurality of ion sensors, that is, the magnitude of variation, for the ion sensors of Examples 1 to 3. In Measurement Example 1, cations contained in a sample were measured using the ion sensors of Examples 1 to 3 and the Comparative Example. In Measurement Example 1, 10 mL of tetraethylammonium chloride containing tetraethylammonium ion (TEA), which is the target ion to be measured, was used as the sample. -4 An aqueous solution containing 0.01M of the supporting electrolyte NaCl was used.

[0093] In Measurement Example 1, a predetermined negative voltage was applied between first electrode 11 and second electrode 12 by voltage application unit 21 (see FIG. 1 ), and the applied voltage value was changed in a positive direction in steps of 20 mV per second until a predetermined positive voltage value was reached. After reaching the predetermined positive voltage value, the applied voltage value was changed in a negative direction in steps of 20 mV per second until the predetermined negative voltage value was reached. Note that, here, a positive voltage value is defined as a case where the potential of second electrode 12 is higher than the potential of first electrode 11, and a negative voltage value is defined as a case where the potential of second electrode 12 is lower than the potential of first electrode 11. In addition, a current value at each voltage value was measured by current measurement unit 22 (see FIG. 1 ), and a cyclic voltammogram (current / voltage characteristic waveform, hereinafter referred to as a voltammogram) was created based on the measured current values.

[0094] In Measurement Example 1, the ion sensors of Examples 1, 2, and 3, and the ion sensor of the comparative example were measured using three cells (Cell 1 to Cell 3), and a voltammogram was created for each cell.

[0095] FIG. 6 is a voltammogram using the ion sensor of Example 1, FIG. 7 is a voltammogram using the ion sensor of Example 2, FIG. 8 is a voltammogram using the ion sensor of the comparative example, and FIG. 9 is a voltammogram using the ion sensor of Example 3. When comparing the voltammograms using the ion sensors of Examples 1 to 3 with the voltammogram using the ion sensor of the comparative example, the voltammograms of Examples 1 to 3 show that the voltammograms of the three cells (Cell 1 to Cell 3) almost overlap, while the voltammogram of the comparative example shows that the voltammograms of the three cells (Cell 1 to Cell 3) do not overlap. Therefore, it can be seen that the ion sensors of Examples 1 to 3 have less variation in the measured values among multiple ion sensors than the ion sensor of the comparative example.

[0096] In a voltammogram, the voltage value indicating the current peak corresponding to the target ion is the voltage value that most efficiently moves the target ion, and the small variation in the current peak among multiple ion sensors also indicates the small variation in the measured values of the target ion among multiple ion sensors. As shown in FIG. 6, in the ion sensor of Example 1, the variation between cells in the voltage value at the peak of the positive current is V1. As shown in FIG. 7, in the ion sensor of Example 2, the variation between cells in the voltage value at the peak of the positive current is V2. As shown in FIG. 8, in the ion sensor of the comparative example, the variation between cells in the voltage value at the peak of the positive current is V3. As shown in FIGS. 6 to 8, the variation between cells in the voltage value is V1 < V2 < V3. When comparing the ion sensor of Example 1 with the ion sensor of the comparative example, since the ion sensor of Example 1 has less variation between cells in the voltage value, it can be seen that the variation in the measured values among multiple ion sensors is smaller than that of the ion sensor of the comparative example. Similarly, when comparing the ion sensor of Example 2 with the ion sensor of the comparative example, since the ion sensor of Example 2 has less variation between cells in the voltage value, it can be seen that the variation in the measured values among multiple ion sensors is smaller than that of the ion sensor of the comparative example.

[0097] Comparing the ion sensor of Example 1 with the ion sensor of Example 2, it is found that the ion sensor of Example 1 has smaller variations in voltage values ​​between cells, and therefore has smaller variations in measured values ​​between multiple ion sensors than the ion sensor of Example 2. This shows that by including a solid electrolyte (β″ alumina) in the first electrode 11, it is possible to further reduce variations in measured values ​​between multiple ion sensors.

[0098] (Measurement example 2) Measurement Example 2 was carried out to evaluate the influence of changes over time on the ion sensor of Example 3. As in Measurement Example 1, 10 mL of tetraethylammonium chloride containing the target ion, TEA ion, was used as a sample. -4 An aqueous solution containing 0.01M of the supporting electrolyte NaCl was used. In Measurement Example 2, current measurements were performed on the same cell in the same manner as in Measurement Example 1 on the 1st, 2nd, 3rd, 5th, and 7th days after assembly, and voltammograms were created.

[0099] FIG. 10 shows a voltammogram using the ion sensor of Example 3, and FIG. 11 shows a voltammogram using the ion sensor of the comparative example. For the ion sensor of Example 3, measurements were taken on the 1st, 2nd, 3rd, 5th, and 7th days. For the ion sensor of the comparative example, measurements were taken on the 1st, 3rd, 5th, 7th, and 9th days. In Measurement Example 2, multiple measurements were taken using the same cell, so after each measurement, all target ions were transferred (back-extracted) from the organic phase to the aqueous phase (sample) so that no target ions remained in the organic phase. The sample was then removed and the electrode was stored in a dry state.

[0100] Comparing Example 3 with the Comparative Example, the voltammograms for the ion sensor of Example 3 shown in Fig. 10 are plotted at approximately the same position for each measurement, whereas the voltammograms for the ion sensor of the Comparative Example shown in Fig. 11 are plotted at different positions depending on the measurement date. This shows that the ion sensor of Example 3 has better reproducibility over time than the ion sensor of the Comparative Example.

[0101] (Measurement example 3) Measurement Example 3 was performed to evaluate the influence of repeated anion measurements on the ion sensors of Examples 1 and 2. In Measurement Example 3, anions contained in a sample were measured using the ion sensors of Examples 1 and 2 and the Comparative Example. In Measurement Example 3, the sample used was an aqueous solution containing 10 mM NaCl as a supporting electrolyte and 0.1 mM sodium picrate, a salt of the picrate ion to be measured. In the Comparative Example, the sample used was an aqueous solution containing 10 mM MgCl as a supporting electrolyte and 0.1 mM sodium picrate, a salt of the picrate ion to be measured. In Measurement Example 3, one ion sensor each of Examples 1, 2, and the Comparative Example was used. As in Measurement Example 1, the applied voltage was changed three or four times from a predetermined negative voltage to a predetermined positive voltage and then back to the predetermined negative voltage. Current measurements were performed at each voltage value, and a voltammogram was created.

[0102] FIG. 12 is a voltammogram using the ion sensor of Example 3, FIG. 13 is a voltammogram using the ion sensor of the comparative example, and FIG. 14 is a voltammogram using the ion sensor of Example 2.

[0103] In the ion sensor of Example 3, the current peak for picrate ions was when the applied voltage was −0.15 V. In FIG. 11 indicates the current value when a voltage of -0.15 V is applied for the first time, and the current value a 12 indicates the current value when a voltage of -0.15 V is applied for the second time, and the current value a 13 indicates the current value when a voltage of −0.15 V was applied for the third time.

[0104] In the ion sensor of the comparative example, the current peak for picrate ions was when the applied voltage was −0.3 V. In FIG. c1 indicates the current value when a voltage of -0.3 V is applied for the first time, and the current value a c2indicates the current value when a voltage of -0.3 V is applied for the second time, and the current value a c3 indicates the current value when a voltage of -0.3 V was applied for the third time. When Example 3 is compared with the comparative example, the ion sensor of Example 3 has a current value a 11 From the current value a 13 The change in the current value up to a c1 From the current value a c3 Therefore, it is clear that the ion sensor of Example 3 is less susceptible to the effects of repeated measurements than the ion sensor of Comparative Example.

[0105] In the ion sensor of Example 2, the current peak for picrate ions was when the applied voltage was −0.35 V. In FIG. 21 indicates the current value when a voltage of -0.35 V is applied for the first time, and the current value a 22 indicates the current value when a voltage of -0.35 V is applied for the second time, and the current value a 33 indicates the current value when a voltage of -0.35 V was applied for the third time. When comparing Example 2 with the comparative example, the ion sensor of Example 2 had a current value a 21 From the current value a 23 The change in the current value up to a c1 From the current value a c3 Therefore, it can be seen that the ion sensor of Example 2 is less susceptible to the effects of repeated measurements than the ion sensor of the comparative example. On the other hand, when Example 2 is compared with Example 1, the ion sensor of Example 2 shows a large change in the current value a 21 From the current value a 23 In contrast, in the ion sensor of Example 1, the change in the current value is large up to the current value a 11 From the current value a 13The change in the current value is small up to the point where the measurement is repeated. Therefore, it can be seen that the ion sensor of Example 1 is more suppressed in the influence of repeated measurements than the ion sensor of Example 2. That is, it can be seen that the influence of repeated measurements is more suppressed in Example 1, in which the first electrode 11 contains a solid electrolyte (β" alumina), than in Example 2, in which the first electrode 11 does not contain a solid electrolyte (β" alumina). From this, it can be said that when anion measurements are performed repeatedly, it is preferable that the first electrode 11 contains a solid electrolyte (β" alumina).

[0106] (Measurement example 4) Measurement Example 4 was carried out to evaluate the influence of repeated measurements of cations on the ion sensor of Example 4. In Measurement Example 4, an aqueous solution containing 14 mM NaCl, which contained Na ions as the ions to be measured, was used as the sample. In Measurement Example 4, one ion sensor of Example 4 was used, and, as in Measurement Example 1, the applied voltage was changed three to four times from a predetermined negative voltage value to a predetermined positive voltage value and then back to the predetermined negative voltage value, and current was measured at each voltage value to create a voltammogram.

[0107] FIG. 15 is a voltammogram obtained using the ion sensor of Example 4.

[0108] In the ion sensor of Example 4, the current peak for Na ions occurred when the applied voltage was 0.4 V. In FIG. 15, the current value when the applied voltage was 0.4 V hardly changed from the first to the third measurements. Therefore, in the ion sensor of Example 4, it can be seen that Na ions that migrated from the aqueous sample to the organic phase returned from the organic phase to the aqueous phase. Furthermore, it can be seen that the ionophore valinomycin did not affect repeated measurements of Na ions in the ion sensor of Example 4. Therefore, it can be seen that the ion sensor of Example 4 is capable of repeated measurements of Na ions.

[0109] (Measurement example 5) Measurement Example 5 was performed to evaluate the feasibility of measuring a sample containing two types of cations using the ion sensors of Examples 4 and 5. In Measurement Example 5, an aqueous solution containing 14 mM NaCl and 0.4 mM KCl was used as a first sample containing target ions Na ions and K ions; an aqueous solution containing 14 mM NaCl and 1.0 mM KCl was used as a second sample containing target ions Na ions and K ions; and an aqueous solution containing 14 mM NaCl was used as a third sample containing target ions Na ions. In Measurement Example 5, one ion sensor each from Examples 4 and 5 was used, and current measurements were performed on each of the first and second samples while changing the voltage, as in Measurement Example 1, to create voltammograms.

[0110] Fig. 16 is a voltammogram using the ion sensor of Example 4. Fig. 17 is a voltammogram using the ion sensor of Example 5.

[0111] When the ion sensor of Example 4 was used to measure the first sample, the current peak for Na ions was detected when the applied voltage was 0.4 V. When the ion sensor of Example 4 was used to measure the third sample, the current peak for Na ions was detected when the applied voltage was 0.4 V. When the ion sensor of Example 4 was used to measure the first sample, the current peak for Na ions was the same for the first and third samples. When the ion sensor of Example 4 was used to measure the first sample, the current peak for K ions was detected when the applied voltage was 0.1 V. This shows that the ion sensor of Example 4 can measure target ions even in samples containing multiple types of ions.

[0112] When the ion sensor of Example 5 was used to measure the second sample, the current peak for Na ions was observed when the applied voltage was 0.3 V. When the ion sensor of Example 5 was used to measure the third sample, the current peak for Na ions was observed when the applied voltage was 0.3 V. When the ion sensor of Example 5 was used to measure the third sample, the current peak for Na ions was the same for the second and third samples. When the ion sensor of Example 5 was used to measure the second sample, the current peak for K ions was detected when the applied voltage was 0 V. This shows that the ion sensor of Example 5 can measure target ions even in samples containing multiple types of ions. It also shows that the ion sensor of Example 5 can measure Na ions and K ions even when an insertion material is included in the second electrode 12 (see FIG. 1 ), which is the aqueous phase electrode.

[0113] (Measurement example 6) Measurement Example 6 was conducted to evaluate the accuracy of the quantity of electricity (the aforementioned quantity of electricity Q) measured by coulometry for the ion sensors of Examples 4 and 6. In Measurement Example 6 using the ion sensor of Example 4, an aqueous solution containing 0.2 mM KCl, an aqueous solution containing 0.4 mM KCl, and an aqueous solution containing 0.8 mM KCl were used as samples containing K ions, the ions to be measured. Each aqueous solution further contained 14 mM NaCl as a supporting electrolyte. One ion sensor of Example 4 was used for each concentration, and a voltage of 0.1 V, which is the voltage at which the peak current of K ions is obtained, was applied, the current was measured, and the quantity of electricity Q was calculated using the method described above. Measurements were performed five times for each concentration, and the average and standard deviation of the quantity of electricity Q calculated for each measurement were obtained. In addition, the theoretical quantity of electricity was calculated for each aqueous solution, and the electrolysis efficiency was calculated from the theoretical quantity of electricity and the average and standard deviation of the quantity of electricity Q calculated for each measurement.

[0114] The results are shown in Table 2 below. [Table 2] From this result, it is understood that the electrolysis efficiency is close to 100%, and the ion sensor of Example 4 can measure K ions with high accuracy.

[0115] In Measurement Example 6 using the ion sensor of Example 6, an aqueous solution containing 0.4 mM KCl and an aqueous solution containing 0.8 mM KCl were used as samples containing K ions, the ions to be measured. Each aqueous solution further contained 14 mM NaCl as a supporting electrolyte. Two ion sensors (cells) of Example 6 were used for each concentration, and a voltage of 0.1 V, which is the voltage at which the peak current of K ions is obtained, was applied to measure the current, and the quantity of electricity Q was calculated using the method described above. Measurements were performed once for each cell (two times in total) for each concentration, and the quantity of electricity Q was calculated for each measurement. In addition, the theoretical quantity of electricity was calculated for each aqueous solution, and the electrolysis efficiency was calculated from the theoretical quantity of electricity and the quantity of electricity Q calculated for each measurement.

[0116] The results are shown in Tables 3 and 4 below. Table 3 shows the results for a 0.4 mM KCl solution, and Table 4 shows the results for a 0.8 mM KCl solution. [Table 3] [Table 4] From this result, it is seen that the electrolysis efficiency is close to 100%, and the ion sensor of Example 6 can measure K ions with high accuracy. Therefore, it is seen that coulometric measurement is possible even if the first electrode 11 does not contain a solid electrolyte (β" alumina).

[0117] (Variation) It should be noted that the embodiments (and examples) disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims rather than the description of the above embodiments (and examples), and further includes all modifications (variations) within the meaning and scope equivalent to the claims.

[0118] In the above embodiment, an example of the ion sensor 100 is shown in which the sample is dropped into the through-hole 141 of the sheet 14 and then covered with the second electrode 12, but the present invention is not limited to this. As shown in Figures 18 to 25, a modified ion sensor 200 may be configured such that the first electrode 11 and the second electrode 12 are arranged to face each other, and the sample 30 is supplied between the second electrode 12 and the organic phase retaining layer 13. In this case, the sample 30 may be drawn into the space between the second electrode 12 and the organic phase retaining layer 13 from the side of the ion sensor by capillary force.

[0119] FIG. 18 shows a plan view of a modified ion sensor 200. FIG. 19 shows a schematic side view of the ion sensor 200. FIG. 20 is a schematic cross-sectional view taken along line 300-300 in FIG. 18. FIGS. 21 to 25 are exploded views of the ion sensor 200. FIG. 21 is a bottom view of an insulating substrate 16 on which a second electrode 12 is laminated, and FIG. 22 is a schematic cross-sectional view taken along line 310-310 in FIG. 21. FIG. 23 is a plan view of an adhesive layer 17. FIG. 24 is a plan view of an insulating substrate 15 on which a first electrode 11 and an organic phase retaining layer 13 are laminated, and FIG. 25 is a schematic cross-sectional view taken along line 320-320 in FIG. 24.

[0120] 18, 19, and 20, the ion sensor 200 includes a first electrode 11, a second electrode 12, an organic phase retaining layer 13, an insulating substrate 15, an insulating substrate 16, and an adhesive layer 17. The first electrode 11 of the ion sensor 200 is connected to a current measuring unit 22 that measures a current via a conductor 23. The second electrode 12 is connected to a voltage applying unit 21 that applies a voltage via a conductor 24. The voltage applying unit 21 and the current measuring unit 22 are connected to each other via a conductor 25.

[0121] The ion sensor 200 is assembled by placing an adhesive layer 17 on an insulating substrate 15 (see FIGS. 24 and 25 ) on which a first electrode 11 and an organic phase retaining layer 13 are laminated, except for the organic phase retaining layer 13, and then placing an insulating substrate 16 (see FIGS. 21 and 22 ) on which a second electrode 12 is laminated, with the second electrode 12 facing downward. As shown in FIGS. 18 , 19 , and 20 , the assembled ion sensor 200 has the organic phase retaining layer 13 laminated on the first electrode 11, and the second electrode 12 faces the organic phase retaining layer 13 across a space 34 into which a sample is drawn. Openings 35 and 36 are provided on the side of the ion sensor 200, and the space 34 is an open space. When a user of the ion sensor 200 brings a sample 30 into contact with the opening 35 or 36, the sample 30 is drawn into the space 34 by capillary force. The target ions contained in the sample 30 are measured in the same manner as in the ion sensor 100 . [Explanation of symbols]

[0122] 11: first electrode, 12: second electrode, 13: organic phase retaining layer, 14: sheet, 15: insulating substrate, 16: insulating substrate, 21: voltage application unit, 22: current measurement unit, 30: sample, 31: target ion, 100, 200: ion sensor

Claims

1. An amperometric ion sensor that measures target ions by measuring current, an organic phase support layer including an organic phase capable of forming an interface with a sample containing the target ions; a first electrode on which the organic phase-retaining layer is laminated, the first electrode being made of an inorganic compound and containing a first insertion material capable of inserting and desorbing the target ions within the structure by an electrochemical reaction; a second electrode disposed opposite the organic phase supporting layer and in contact with the sample.

2. The ion sensor according to claim 1 , wherein the first electrode further includes an electrode material, and an insertion coating film including the first insertion material is provided on the electrode material.

3. The ion sensor according to claim 2 , wherein the insertion coating film of the first electrode further contains a binder and a conductive agent.

4. 4. The ion sensor according to claim 1, wherein the first insertion material is a metal oxide, an oxygen redox material, or a Prussian blue analogue.

5. 5. The ion sensor according to claim 1, wherein the first insertion material is an ion-electron conductor for sodium ions, potassium ions, or lithium ions.

6. the first insertion material is a metal oxide; The metal oxide is M ｘ MnO ２ 6. The ion sensor according to claim 1, wherein M represents Na or K, and x represents any positive number.

7. The ion sensor according to claim 6 , wherein the x is equal to or greater than 0.2 and equal to or less than 0.

5.

8. 8. The ion sensor according to claim 1, wherein the first electrode further includes a solid electrolyte.

9. 9. The ion sensor according to claim 8, wherein the solid electrolyte is an ion-conductive ceramic.

10. 10. The ion sensor according to claim 9, wherein the solid electrolyte is a sodium ion conductive ceramic, a potassium ion conductive ceramic, or a lithium ion conductive ceramic.

11. 11. The ion sensor according to claim 9, wherein the solid electrolyte is β″ alumina or β alumina.

12. 12. The ion sensor according to claim 8, wherein the first insertion material and the solid electrolyte are particles.

13. The ion sensor according to claim 12 , wherein the average particle size of the solid electrolyte particles is smaller than the average particle size of the first insertion material particles.

14. 14. The ion sensor according to claim 12, wherein the first insertion material has a mass that is 0.5 times or more and 2 times or less than that of the solid electrolyte.

15. The binder is (a) polyvinylidene fluoride, (b) an admixture containing styrene butadiene latex and carboxymethyl cellulose; (c) a mixture containing a polyamide, a polyimide, and a carbodiimide; (d) polytetrafluoroethylene, or (e) Acrylic emulsion The ion sensor according to claim 3, wherein

16. The ion sensor according to claim 3 , wherein the conductive agent is carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, carbon powder, or graphite powder.

17. The ion sensor according to any one of claims 1 to 16, wherein the organic phase supporting layer comprises an ionophore.

18. The ion sensor according to any one of claims 1 to 16, wherein the second electrode includes a second insertion material made of an inorganic compound and capable of inserting and desorbing the target ions within the structure through an electrochemical reaction.

19. the second insertion material is the same material as the first insertion material; 19. The ion sensor according to claim 18, wherein the second electrode is formed to have the same configuration as the first electrode.

20. A method for measuring ions using the ion sensor according to any one of claims 1 to 19, contacting the organic phase-retaining layer and the second electrode with a sample; applying a voltage between the first electrode and the second electrode to move the target ions contained in the sample to the organic phase; measuring a current flowing between the first electrode and the second electrode.

21. transferring the target ions to the organic phase by applying a voltage; The ion measurement method according to claim 20, further comprising a step of determining an amount of the target ion based on an electrical quantity obtained by integrating the current value obtained in the step of measuring the current over a voltage application time.

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