All-solid-state potassium ion-selective electrode and method for manufacturing the all-solid-state potassium ion-selective electrode

Abstract

To provide an all-solid ion selective electrode with which the stability of potentials and the long term stability of detection values have been improved.SOLUTION: An all-solid potassium ion selective electrode 1 comprises a conductor 2, an insertion material 10 which is formed on the surface of the conductor 2, and a potassium ion sensitive film 20 that covers the insertion material 10. The insertion material 10 at least contains a Prussian blue analog expressed by the structural formula KxFe[Fe(CN)6]y-nH2O, where x is a number 0 and over to less than 2, y is a number 0 and over to less than 1, and n is a number 0 or greater.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state ion-selective electrode with an insertion material and a method for making such an all-solid-state ion-selective electrode. [Background technology]

[0002] Ion-selective electrodes are used to measure the concentration of ions in a solution. By contacting the ion-selective electrode and a reference electrode with the solution to be measured (test solution), a potential difference is generated between the ion-selective electrode and the reference electrode, and the concentration of a specific ion in the solution can be measured based on the generated potential difference. Such ion-selective electrodes are used in fields such as the environment, medicine, and agriculture.

[0003] A typical ion-selective electrode consists of an ion-sensitive membrane, an internal liquid, and an internal reference electrode. However, for the purpose of miniaturization, all-solid-state ion-selective electrodes that do not use the internal liquid or the internal reference electrode have been proposed. For example, an ion-selective electrode in which the electrode substrate is directly coated with an ion-sensitive membrane has been proposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 8-23544 [Patent Document 2] Special Publication No. 7-50059 [Patent Document 3] International Publication No. 2017 / 047374 [Patent Document 4] Utility Model Registration No. 2546786 Summary of the Invention [Problem to be solved by the invention]

[0005] Ion-selective electrodes (hereafter referred to as conventional electrodes), which have an ion-sensitive membrane directly coated on the electrode substrate, generally suffer from the problem of low potential stability. When potential stability is low, the detected value fluctuates due to factors such as dark current from the potentiostat and vibrations around the measurement system. Furthermore, conventional electrodes suffer from low long-term stability of the detected value. Even if the electrode is immersed in a test solution of the same concentration, the detected value fluctuates significantly after a few days. Therefore, calibration is required each time such ion-selective electrodes are used.

[0006] Therefore, the present invention provides an all-solid-state potassium ion-selective electrode with improved potential stability and long-term stability of detection values, and further provides a method for producing such an all-solid-state potassium ion-selective electrode. [Means for solving the problem]

[0007] In one embodiment, a conductor, an insertion material formed on the surface of the conductor, and a potassium ion sensitive film covering the insertion material, the insertion material having a structure represented by the formula K x Fe[Fe(CN)6] y Provided is an all-solid-state potassium ion-selective electrode comprising at least a Prussian blue analogue represented by the formula nH2O, where x is a number greater than 0 and less than or equal to 2, y is a number greater than 0 and less than or equal to 1, and n is a number greater than or equal to 0.

[0008] In one aspect, a method for preparing an all-solid-state potassium ion-selective electrode is provided, comprising: x Fe[Fe(CN)6] y a slurry containing Prussian blue represented by the formula (I) is prepared, wherein y is a number greater than 0 and less than 1, x is a number greater than 0 and less than 2, and n is a number greater than 0; the slurry is supplied onto a conductor, and the slurry is dried to form a composite film on the surface of the conductor; and the K of the Prussian blue is +A manufacturing method is provided in which an insertion material is formed on the surface of the conductor by conditioning the ions with a KCl aqueous solution to make them uniform, a potassium ion-sensitive membrane stock solution is supplied to the surface of the insertion material, and the potassium ion-sensitive membrane stock solution is dried to form a potassium ion-sensitive membrane on the surface of the insertion material.

[0009] In one embodiment, the insertion material has the structure K x Fe[Fe(CN)6] y The composition contains at least a Prussian blue analogue represented by nH2O, where x is a number greater than 0 and equal to or less than 2. In one embodiment, the step of preparing the slurry includes a step of mixing the Prussian blue, multi-walled carbon nanotubes (MWCNTs), and polyvinylidene fluoride. [Effects of the Invention]

[0010] Because the all-solid-state ion-selective electrode has an insertion material between the conductor and the potassium ion-sensitive membrane, electron transfer between the conductor and the potassium ion-sensitive membrane occurs via the insertion material. The insertion material improves the electron transfer performance between the conductor and the potassium ion-sensitive membrane, thereby reducing the resistance of the electrode. The insertion material also functions as an internal reference electrode, improving the long-term stability of the detection value. As a result, the all-solid-state potassium ion-selective electrode can improve the stability of the potential and the long-term stability of the detection value. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a plan view showing one embodiment of an all-solid-state ion-selective electrode. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] 1 is a flowchart illustrating one embodiment of a method for manufacturing an all-solid-state potassium ion-selective electrode. [Figure 4]1 is a flowchart illustrating an embodiment of a method for producing a slurry. [Figure 5] 1 is a schematic diagram showing an embodiment of a method for measuring ion concentration in a solution. [Figure 6] FIG. 1 is a schematic diagram showing another application example of an all-solid-state ion-selective electrode. [Figure 7] FIG. 7 is a schematic diagram showing one embodiment of a method for measuring ion concentrations using the all-solid-state ion-selective electrode shown in FIG. 6. [Figure 8] FIG. 1 is a diagram showing a calibration curve obtained by measuring the potential of an all-solid-state potassium ion-selective electrode in an aqueous KCl solution. [Figure 9] This shows the results of evaluation of electrical resistance by chronopotentiometry. [Figure 10] This shows the results of evaluating the resistance of the electrodes by AC impedance measurement. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a plan view showing one embodiment of an all-solid-state potassium ion-selective electrode 1, and Fig. 2 is a cross-sectional view taken along line AA in Fig. 1. Hereinafter, in this specification, the all-solid-state potassium ion-selective electrode 1 may be simply referred to as the electrode 1.

[0013] As shown in Figures 1 and 2, the electrode 1 includes a conductor 2 fixed to an insulating substrate 5, an insertion material 10 formed on the surface of the conductor 2, and an ion-sensitive film 20 formed on the surface of the insertion material 10. The conductor 2 is connected to a conducting wire 7. The insertion material 10 is covered with the ion-sensitive film 20. As an example, the conductor 2 is made of platinum (Pt).

[0014] The ion-sensitive membrane 20 of this embodiment is a membrane that detects potassium ions (K + The insertion material 10 contains a Prussian blue analogue. The structural formula of the Prussian blue analogue in this embodiment is: Kx Fe[Fe(CN)6] y nH2O (1) where x is a number greater than 0 and equal to or less than 2, y is a number greater than 0 and equal to or less than 1, and n is a number greater than or equal to 0. Hereinafter, in this specification, an electrode 1 equipped with a potassium ion-sensitive membrane and a Prussian blue analogue represented by the above structural formula (1) is defined as an all-solid-state potassium ion-selective electrode 1.

[0015] Hereinafter, one embodiment of a method for manufacturing an all-solid-state potassium ion selective electrode 1 will be described with reference to the flowchart shown in FIG. 3. In step 1-1, a slurry containing Prussian blue (details will be described later) is supplied onto a platinum conductor 2 formed on a substrate 5. Specifically, 1 μL of the slurry is dropped onto the conductor 2. The structural formula of Prussian blue in the slurry of this embodiment is: K x Fe[Fe(CN)6] y nH2O (3) where x is a number greater than 0 and less than or equal to 2, and n is a number greater than or equal to 0.

[0016] In step 1-2, the slurry is dried in a room temperature environment to form a mixture film on the surface of the conductor 2. The conductor 2 is covered with the mixture film. In step 1-3, the composite film covering the conductor 2 is immersed in a potassium chloride aqueous solution (first potassium chloride aqueous solution), and the K of the Prussian blue contained in the composite film is + The mixture is made uniform by conditioning. Conditioning is a pretreatment to allow the mixture to exert its inherent functions, and specifically, the mixture film is immersed in a 0.01M potassium chloride aqueous solution (KCl aqueous solution) for 24 hours. In step 1-4, the conductor 2 and the mixture film are taken out of the potassium chloride aqueous solution, and the mixture film is washed with ion-exchanged water.

[0017] In step 1-5, the mixture film is dried. Specifically, the mixture film is dried for 12 hours in a room temperature environment. By steps 1-3 to 1-5, an insertion material 10 made of the mixture film is formed on the surface of the conductor 2. The conductor 2 is covered with the insertion material 10. The insertion material 10 formed by steps 1-3 to 1-5 contains the Prussian blue analogue represented by the structural formula (1) described above.

[0018] In step 1-6, a potassium ion-sensitive membrane stock solution (details will be described later) is supplied to the surface of the insertion material 10. Specifically, 50 μL of the potassium ion-sensitive membrane stock solution is dropped onto the surface of the insertion material 10. In step 1-7, the potassium ion-sensitive membrane stock solution is dried in a room temperature environment to form an ion-sensitive membrane on the surface of the insertion material 10. The insertion material 10 is covered with the ion-sensitive membrane.

[0019] In step 1-8, the ion-sensitive film covering the insertion material 10 is immersed in a potassium chloride aqueous solution (second potassium chloride aqueous solution). Specifically, the ion-sensitive film is immersed in a 0.01M potassium chloride aqueous solution (KCl aqueous solution) for 24 hours. By the above step 1-8, a potassium ion-sensitive film 20 is formed on the surface of the insertion material 10. The insertion material 10 is covered with the potassium ion-sensitive film 20. The potassium ion-sensitive film 20 formed in step 1-8 is sensitive to potassium ions (K + ) is an ion-sensitive membrane that allows the passage of ions. By the above steps 1-1 to 1-8, an all-solid-state potassium ion-selective electrode 1 is manufactured.

[0020] Next, one embodiment of the method for producing the slurry used to produce the all-solid-state potassium ion-selective electrode will be described with reference to the flowchart shown in FIG. 4. In step 2-1, Prussian blue represented by the structural formula (3) above is prepared. In step 2-2, multi-walled carbon nanotubes (MWCNTs) are mixed with the Prussian blue. The Prussian blue functions as a positive electrode active material, and the MWCNTs function as a conductive material.

[0021] In step 2-3, a solution of polyvinylidene fluoride dispersed in N-methylpyrrolidone is added to the mixture of Prussian blue and MWCNTs, and the mixture is mixed. N-methylpyrrolidone acts as a dispersion medium, and polyvinylidene fluoride acts as a binder.

[0022] The potassium ion-sensitive membrane stock solution is a mixture of an ionophore, an anion rejector, a plasticizer, a membrane matrix, and a dispersion medium. More specifically, the potassium ion-sensitive membrane stock solution is prepared by mixing the ionophore bis(benzo-15-crown-5), the anion rejector potassium tetrakis(4-chlorophenyl)borate, the plasticizer o-nitrophenyl octyl ether, the membrane matrix polyvinyl chloride, and the dispersion medium tetrahydrofuran for two hours. The weight ratio of o-nitrophenyl octyl ether, bis(benzo-15-crown-5), potassium tetrakis(4-chlorophenyl)borate, and polyvinyl chloride is 65.5:0.9:0.3:33.3.

[0023] 5 is a schematic diagram showing one embodiment of a method for measuring ion concentrations in a solution. Electrode 1 and reference electrode 33 are connected to a voltmeter 35. In this state, electrode 1 and reference electrode 33 are brought into contact with a test liquid 30. A potential difference corresponding to the ion concentration of the measurement target in the test liquid 30 is generated between electrode 1 and reference electrode 33. This potential difference is measured by the voltmeter 35 and converted into an ion concentration by an ion concentration converter (not shown).

[0024] In the example shown in Figure 5, the electrode 1 is an all-solid-state potassium ion-selective electrode, and the test liquid 30 is a KCl aqueous solution. The ion-sensitive membrane 20 of the electrode 1 detects the KCl ions in the test liquid 30 and the KCl ions in the insertion material 10. + As a result, a potential difference corresponding to the potassium ion concentration in the test solution 30 is generated between the electrode 1 and the reference electrode 33.

[0025] FIG. 6 is a schematic diagram showing another application example of the all-solid-state ion-selective electrode 1. The configuration of this embodiment, which is not particularly described, is the same as the configuration described with reference to FIGS. 1 and 2, and therefore, redundant description will be omitted. The reference electrode 33 is formed on a substrate 5. The conductive wires 7 and 37 are fixed to the substrate 5 and connected to the conductor 2 of the electrode 1 and the reference electrode 33, respectively. Portions of the conductive wires 7 and 37 are covered with an insulating protective film 39. An example of the protective film 39 is an epoxy coating.

[0026] 7 is a schematic diagram showing one embodiment of a method for measuring ion concentration using the all-solid-state ion-selective electrode 1 shown in FIG. 6. The electrode 1 and the reference electrode 33 are connected to a voltmeter 35. In this state, the electrode 1 and the reference electrode 33 are brought into contact with the test liquid 30. A potential difference corresponding to the concentration of the ion to be measured in the test liquid 30 is generated between the electrode 1 and the reference electrode 33. This potential difference is measured by the voltmeter 35 and converted into an ion concentration by an ion concentration converter (not shown).

[0027] Figure 8 shows the calibration curves obtained by measuring the potential of the all-solid-state potassium ion-selective electrode 1 in KCl aqueous solutions of different concentrations. In Figure 8 and subsequent figures, the ion-sensitive membrane made of platinum / MWCNT-Prussian blue (Pt / MWCNT-KFeFe / K + The data obtained by the ion-sensitive membrane (Pt / AB-KFeFe / K) was used as a reference. + As shown in FIG. 8, the all-solid-state potassium ion-selective electrode 1 exhibited a 10 -5 ~10-1 K of M + The all-solid-state potassium ion-selective electrode 1 exhibited good linearity in the concentration range, and a slope close to the theoretical value of 59.2 mV / decade obtained by the Nernst equation was obtained. + It was confirmed that the device exhibited a good electrochemical response to the

[0028] Figure 9 shows the results of evaluation of the electrode resistance by chronopotentiometry. + The Pt / MWCNT-KFeFe / K electrode exhibits polarization of more than ±5 mV upon application of a small current. + The resistance of the Pt / AB-KFeFe / K electrode is suppressed to ±1 mV or less. It is clear that the use of MWCNTs has significantly reduced the electrode resistance. Figure 10 shows the results of evaluating the electrode resistance by AC impedance measurement. + -Compared to the ISM electrode, Pt / MWCNT-KFeFe / K + In the -ISM ​​electrode, the diameter of the capacitive semicircle was reduced, and a significant reduction in electrode resistance was confirmed. By using MWCNTs, which have higher conductivity than acetylene black (AB), as the conductive material, the electronic conductivity of the composite electrode layer was improved, facilitating the transfer of electrons based on the oxidation-reduction of Prussian blue (KFeFe), which is thought to have significantly reduced interfacial resistance and greatly improved potential stability. From the above, it was confirmed that the use of MWCNTs as the conductive material in the insertion material improved potential stability.

[0029] The all-solid-state ion-selective electrode 1 in each of the above-described embodiments includes an insertion material 10 between the conductor 2 and the ion-sensitive membrane 20, and thus electrons are transferred between the conductor 2 and the ion-sensitive membrane 20 via the insertion material 10. The insertion material 10 can improve the electron transfer performance between the conductor 2 and the ion-sensitive membrane 20, thereby reducing the resistance of the electrode 1. As a result, the electrode 1 can improve the potential stability. In other words, the detection value of the electrode 1 is less susceptible to the effects of dark current flowing from the potentiostat, vibrations around the measurement system, and the like.

[0030] Furthermore, the all-solid-state ion-selective electrode 1 in each of the above-described embodiments can improve the long-term stability of the detection value. That is, even when immersed in a test solution of the same concentration, there is little fluctuation in the detection value over several days. In an evaluation of long-term stability, a potential fluctuation of approximately 15 mV was observed over 7 days. The all-solid-state ion-selective electrode using the insertion material has excellent long-term stability because Prussian blue serves as an internal reference electrode.

[0031] Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above embodiment and may be embodied in various different forms within the scope of the technical concept thereof.

Claims

1. A conductor; an insertion material formed on the surface of the conductor; a potassium ion sensitive membrane covering the insertion material; The insertion material has the structural formula K ｘ Fe[Fe(CN) ６ ] ｙ ・nH ２ The composition contains at least a Prussian blue analogue represented by O, An all-solid-state potassium ion-selective electrode, wherein x is a number greater than 0 and equal to or less than 2, y is a number greater than 0 and equal to or less than 1, and n is a number greater than or equal to 0.

2. A method for producing an all-solid-state potassium ion-selective electrode, comprising: Structural formula K ｘ Fe[Fe(CN) ６ ] ｙ ・nH ２ A slurry containing Prussian blue represented by the formula (I) is prepared, wherein y is a number greater than 0 and equal to or less than 1, x is a number greater than 0 and equal to or less than 2, and n is a number greater than or equal to 0; supplying the slurry onto a conductor and drying the slurry to form a mixture film on the surface of the conductor; The mixture film is immersed in a first potassium chloride aqueous solution, and the K of the Prussian blue is ＋ forming an insertion material on the surface of the conductor by uniformly supplying a potassium ion-sensitive membrane stock solution to the surface of the insertion material, and drying the potassium ion-sensitive membrane stock solution to form an ion-sensitive membrane on the surface of the insertion material; The manufacturing method includes immersing the ion-sensitive original membrane in a second potassium chloride aqueous solution to form a potassium ion-sensitive membrane on the surface of the insertion material.

3. The insertion material has the structural formula K ｘ Fe[Fe(CN) ６ ] ｙ ・nH ２ The composition contains at least a Prussian blue analogue represented by O, The method according to claim 2 , wherein x is a number greater than 0 and equal to or less than 2.

4. The manufacturing method according to claim 2 or 3, wherein the step of producing the slurry includes a step of mixing the Prussian blue, multi-walled carbon nanotubes, and polyvinylidene fluoride.

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