Ion-selective electrode and electrolyte concentration measurement device

Abstract

The present disclosure relates to an ion-selective electrode based on an ion exchange membrane having a high-density fixed charge, and proposes an ion-selective electrode for measuring a target ion contained in a sample solution in order to improve ion selectivity and improve stability over time by a simpler method. The ion-selective electrode is provided with an electrode case for accommodating an internal liquid, an internal electrode having a portion in contact with the internal liquid, and an ion-sensing film for isolating the sample liquid from the internal liquid, the ion-sensing film being in contact with the sample liquid on at least a portion of a first surface and in contact with the internal liquid on at least a portion of a second surface different from the first surface. The first surface of the ion-sensing film is covered with an inactive layer that suppresses an ion exchange reaction between the ion-sensing film and the sample liquid (referring to Figure 2).

Description

Technical Field

[0001] The present disclosure relates to an ion selective electrode and an electrolyte concentration measuring device including the ion selective electrode. Background Art

[0002] The potential difference measurement (potentiometric titration) method using an ion selective electrode (ISE) can quickly and easily quantify the concentration of specific ions in a liquid, and is therefore used in a wide range of fields such as water quality analysis and the medical field. In particular, in the medical field, there is a close relationship between the metabolic reaction of an organism and the ion concentration, and by quantifying the specific ions contained in biological samples such as serum and urine, it is used to diagnose hypertension symptoms, kidney disease, neurological disorders, etc. In clinical examinations, it is necessary to continuously analyze multiple specimens, so high-productivity automatic analyzers and electrolyte concentration measuring devices equipped with ion selective electrodes are used daily.

[0003] The main measurement items of the electrolyte concentration measuring device are cations such as sodium ions and potassium ions and anions such as chloride ions. Regarding cations, compounds (ion carriers) that selectively capture specific cations such as crown ethers and valinomycin have been discovered. The ion-sensitive membrane of the cation-selective electrode of sodium, potassium, etc. usually uses a membrane containing these ion carriers and has high ion selectivity.

[0004] On the other hand, regarding anions, there are no ion carriers suitable for ion selective electrodes of automatic analysis devices that require high productivity, rapid responsiveness and long-term stability, and various sensing membranes are used. One of them is a Cl ion sensing membrane based on an ion exchange membrane with a high charge density. For example, Patent Document 1 discloses a chloride ion sensing membrane based on an anion exchange membrane, on the surface of which a condensate of m-phenylenediamine and formaldehyde is coated. In addition, Patent Document 2 discloses an anion selective electrode in which the surface of the anion exchange membrane in contact with the sample solution is coated with an anion responsive epoxyamine resin.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 3812049

[0008] Patent Document 2: Japanese Patent No. 6783704 Summary of the invention

[0009] Problems to be solved by the invention

[0010] In addition to the ions to be measured, the sample sometimes contains a large number of other ions, which become an obstacle when measuring the concentration of the ions to be measured. For example, in serum (sample), which is one of the analytical objects in clinical examinations, as anions, in addition to chloride ions (Cl - ) also contains a large amount of bicarbonate ions (HCO3 - ), the bicarbonate ions become an obstacle when measuring the chloride ion concentration. Therefore, it is important for the chloride ion selective electrode to reduce the selectivity for bicarbonate ions.

[0011] On the other hand, as described above, it is technically difficult to improve the selectivity of anion selective electrodes compared to cation selective electrodes. This is because, unlike cations, no ion carrier suitable for ion selective electrodes has been found in the case of anions.

[0012] When cations are to be measured, an ion-sensitive membrane containing the above-mentioned ion carrier is generally used. However, an ion-sensitive membrane not containing an ion carrier may be used for an ion-selective electrode.

[0013] In view of such circumstances, the present disclosure provides a technology for improving ion selectivity and temporal stability of an ion selective electrode based on an ion exchange membrane having a high density of fixed charges by a simpler method.

[0014] Methods for solving problems

[0015] In order to solve the above-mentioned problems, the present disclosure proposes an ion-selective electrode, which is an ion-selective electrode for measuring target ions contained in a sample solution, comprising: an electrode shell for accommodating an internal liquid, an internal electrode whose portion is in contact with the internal liquid, and an ion-sensitive membrane that isolates the sample liquid from the internal liquid; the ion-sensitive membrane is in contact with the sample liquid at least at a portion of a first surface, and is in contact with the internal liquid at least at a portion of a second surface different from the first surface; the first surface of the ion-sensitive membrane is covered with an inactive layer that inhibits ion exchange reactions between the ion-sensitive membrane and the sample solution.

[0016] Further features related to the present disclosure will become apparent from the description of this specification and the accompanying drawings. In addition, the present disclosure is achieved and realized by the combination of elements and a plurality of elements, the following detailed description and the appended claims.

[0017] The description in this specification is merely a typical example and does not limit the claims or application examples of the present disclosure in any sense.

[0018] Effects of the Invention

[0019] According to the technology disclosed in the present invention, it is possible to improve the ion selectivity and the temporal stability of an ion selective electrode based on an ion exchange membrane having a high density of fixed charges by a simpler method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A It is a front view of the flow-type ion selective electrode 10 .

[0021] Figure 1B Yes means Figure 1A FIG. 1 is a diagram showing a configuration example of the flow-type ion selective electrode 10 at the AA′ cross section.

[0022] Figure 1C 1 is a diagram showing a configuration example of the flow-type ion selective electrode 10 at a BB′ cross section perpendicular to the AA′ cross section.

[0023] Figure 2 Yes Figure 1C The schematic diagram of the enlarged portion of the dashed rectangle 17 - 1 is a diagram showing a characteristic layer structure of the ion-sensitive membrane 17 of the present embodiment.

[0024] Figure 3 It is a diagram showing a configuration example of an electrolyte concentration measuring device (flow type) 100 including the ion selective electrode of the present disclosure.

[0025] Figure 4 This is a flowchart for explaining the operation of the electrolyte concentration measuring device 100 when it is started.

[0026] Figure 5 This is a flowchart for explaining the operation of the electrolyte concentration measuring device 100 during continuous analysis.

[0027] Figure 6 Yes Figure 1C The partially enlarged schematic diagram of the dashed rectangle 17 - 1 is a diagram showing the layer structure of the characteristic ion-sensitive membrane 17 of the present embodiment.

[0028] Figure 7 Yes Figure 1C The enlarged view of the dotted rectangle 17 - 1 is a view showing the layer structure of the ion-sensitive membrane of Comparative Example 1.

[0029] Figure 8 Yes Figure 1C The partially enlarged view of the dotted rectangle 17 - 1 is a view showing the layer structure of the ion-sensitive membrane of Comparative Example 2.

[0030] Fig. 9 It is a diagram showing a cross-sectional configuration example of a rod-type ion selective electrode 20 according to the third embodiment.

[0031] Fig.10 This is a diagram showing the results of comparison of the response behavior of the ion selective electrode 10 of the first embodiment using PVC as the material of the inactive layer 5 and the electrode of Comparative Example 1 to aqueous solutions containing ions of various concentrations and types.

[0032] Fig.11A This is a diagram schematically showing the ion-sensitive membrane of Comparative Example 1 and the ion composition inside the sample solution.

[0033] Fig. 11B It is a diagram schematically showing the ion-sensitive membrane 17 and the ion composition inside the sample solution in the case of the ion-selective electrode 10 including the inactive layer 5 .

[0034] Fig.12 It means in Fig.10 The slope and the potential for chloride ions (Cl - ) is a graph showing the results of the selectivity coefficients of various interfering ions.

[0035] Fig.13 The ion selective electrode of Comparative Example 1 (see Figure 7 ) and the ion selective electrode of the first embodiment (refer to Figure 2 ), for chloride ions (Cl - ) of bicarbonate ions (HCO3 - ) is a graph showing the measurement results of the selection coefficient.

[0036] Fig.14 The ion selective electrode of Comparative Example 2 (see Figure 8 ) and the ion selective electrode of the second embodiment (refer to Figure 6 ), for chloride ions (Cl - ) of bicarbonate ions (HCO3 - ) is a graph showing the measurement results of the selection coefficient. DETAILED DESCRIPTION

[0037] The present embodiment relates to an ion selective electrode for measuring the ion concentration in a liquid and an electrolyte concentration measuring device having the ion selective electrode. The ion sensitive membrane constituting the ion selective electrode of each embodiment comprises an ion exchange membrane with a high charge density and an inactive layer (a layer composed of a material that does not respond to ions) formed on the surface of the ion exchange membrane on the side in contact with the sample containing the ions to be measured. By adopting such a structure, the ion exchange phenomenon can be suppressed, and the original ion selection characteristics of the ion sensitive membrane can be approached.

[0038] Hereinafter, the embodiments of the present disclosure will be described with reference to the accompanying drawings. In the accompanying drawings, sometimes the same functional elements are shown with the same number. It should be noted that the accompanying drawings show specific embodiments and installation examples that follow the principles of the present disclosure, but these are for understanding the present disclosure and are by no means used to interpret the present disclosure in a limiting manner.

[0039] In the present embodiment, the present disclosure is described in sufficient detail for those skilled in the art to implement the present disclosure, but other installations and methods are also possible, and it is necessary to understand that the composition and structure can be changed and various elements can be replaced without departing from the scope and spirit of the technical idea of ​​the present disclosure. Therefore, the following description is not limited to this and is interpreted.

[0040] (1) First Embodiment

[0041] The first embodiment discloses a flow-type ion selective electrode 10. Here, the embodiment is described by taking a chloride ion selective electrode as an example, but the technology disclosed in the present invention can also be applied to the measurement of other types of ions (e.g., Br - ,I - , CN - 、Cd 2+ , Cu 2+ 、Ag + , S 2- 、F - , K + , Ca 2+ 、NO3 - NH4 + 、Na + Ion selective electrode that can detect concentrations of

[0042] <Structure of flow-type ion selective electrode>

[0043] Figures 1A to 1C It is a diagram showing an overall configuration example of the flow-type ion selective electrode 10 according to the first embodiment. Figure 1A It is a front view of the flow-type ion selective electrode 10 . Figure 1B Yes means Figure 1A FIG. 1 is a diagram showing a configuration example of the flow-type ion selective electrode 10 at the AA′ cross section. Figure 1C 1 is a diagram showing a configuration example of the flow-type ion selective electrode 10 at a BB′ cross section perpendicular to the AA′ cross section.

[0044] The flow-type ion selective electrode 10 includes an electrode case 11 , an internal electrode 13 , a flow path 12 penetrating the electrode case 11 , a gasket 15 , an internal gel housing portion housing an internal gel 16 , an ion sensitive membrane 17 , and a cover 18 .

[0045] The sample solution of the measurement object circulates (flows) in the flow path 12. The ion-sensitive membrane 17 is arranged in a manner that can be in contact with the sample solution. The internal gel (or internal liquid) 16 contains an electrolyte and is stored in a manner that fills the internal gel storage portion in the electrode shell 11. In addition, the internal electrode 13 is arranged in a manner that is in contact with the internal gel 16. Moreover, in order to seal the internal gel 16 in the electrode shell, the cover 18 is bonded to the opening of the electrode shell 11. In addition, the gasket 15 is arranged near the entrance and exit of the flow path 12 of the electrode shell 11 in a manner that can be connected to the flow path of the electrolyte concentration measuring device (electrolyte concentration analysis device) described later or other electrodes. The ion selective electrode 10 having the above structure is mounted on the electrolyte concentration measuring device. During measurement, by connecting the internal electrode 13 to the wiring on the device side, the potential generated according to the concentration of the ions of the measurement object contained in the sample solution can be measured, and the concentration of the ions of the measurement object can be analyzed.

[0046] <Configuration Example of Ion Sensitive Membrane 17>

[0047] Figure 2 Yes Figure 1C The schematic diagram of the enlarged portion of the dotted rectangle 17 - 1 shows the characteristic layer structure of the ion-sensitive membrane 17 of the present embodiment.

[0048] (Electrode manufacturing steps)

[0049] (i) First, the ion-sensitive membrane 17 is based on an anion exchange membrane 1 (in order to measure anions, it is an anion exchange membrane, and in the case of measuring cations, it is a cation exchange membrane) having high-density immobilized cations. The anion exchange membrane 1 has chloride ions (Cl - ) as a counter ion.

[0050] (ii) A solution prepared by dissolving a polymer described later in tetrahydrofuran (THF) as a low boiling point solvent is applied to the surface of the ion-sensitive membrane 17 that contacts the sample solution. Then, the THF is evaporated to form a thin layer of the polymer on the surface of the ion-sensitive membrane 17. This layer is referred to as an inactive layer 5. The method for forming the inactive layer 5 described here is only an example, and other methods may also be used.

[0051] (iii) Thereafter, the anion exchange membrane 1 is bonded to the electrode case 11 so as to close the opening provided in the electrode case 11 .

[0052] (iv) Next, the internal gel storage portion of the electrode case 11 is filled with the internal gel 16 .

[0053] (v) After the filling of the internal gel 16 is completed, the cover 18 is welded to the electrode case 11, and the internal electrode 13 is fixed in contact with the internal gel 16. It should be noted that in order to suppress the evaporation of water in the internal gel 16, the surface of the ion sensitive membrane 17 on the opposite side to the flow path 12 may be coated with a resin or the like.

[0054] (Configuration Example of Anion Exchange Membrane 1)

[0055] As the anion exchange membrane 1 constituting the ion sensitive membrane 17, a membrane using a PVC (polyvinyl chloride) silk fabric as a reinforcement material can be used, which is a highly cross-linked polystyrene-based membrane having quaternary ammonium ions as anion exchange groups.

[0056] However, it is not limited to this membrane, for example, the ion exchange group may be a primary amino group, a secondary amino group, or a tertiary amino group, and the matrix material may not be styrene-based but other hydrocarbon resins such as polyolefins, fluorine resins, etc. In addition, the reinforcing material may be other materials such as other polymer fibers and glass fibers, or may be a membrane without a reinforcing material.

[0057] Furthermore, the counter ions contained in the anion exchange membrane 1 are preferably ions of the same type as the ions to be measured, but may also be other anions. In addition, even if it is not a material used in a general ion exchange membrane, as long as it is a membrane with a high density of fixed charges, the technical effect of the present disclosure can be exerted. Here, high density refers to a charge density of 0.1 to 10 mmol / g.

[0058] It should be noted that as a different type of ion-sensitive membrane from the ion-sensitive membrane 17 of the present disclosure, there is a so-called liquid membrane type membrane. It generally contains an ion carrier that improves ion selectivity by dissolving a lipophilic salt as a fixed charge in a membrane such as soft PVC. In such a liquid membrane type ion-sensitive membrane, the charge density is about 0.001 to 0.1 mmol / g.

[0059] (Configuration Example of Inactive Layer 5)

[0060] The inactive layer 5 has the function of inhibiting the ion exchange reaction between the ion exchange membrane 1 and the sample solution. The inactive layer 5 is characterized in that the charge density is, for example, less than 0.0001 mmol / g and does not respond to ions (is composed of a material that does not respond to ions). That is, the material of the inactive layer 5 is an insulating material such as a general polymer, and is preferably water-insoluble in order not to dissolve in the sample solution. In addition, in order to maintain the close adhesion with the ion exchange membrane, it is preferred to use a material of the same system as the matrix and support material of the membrane, and a material with a close solubility parameter value. Furthermore, in the case of forming the inactive layer 5 using a method such as the present embodiment (as described above, in the case of forming the inactive layer 5 by coating a solution formed by dissolving a polymer in tetrahydrofuran (THF)), it is preferred that the material is easily soluble in a low boiling point solvent.

[0061] As the material of the inactive layer 5, for example, a mixed material of polyvinyl chloride (PVC), ethylene / vinyl acetate copolymer, polyvinyl formal (Poly (vinyl formal)) and a polymer and a plasticizer dioctyl adipate (DOA), i.e., PVC+DOA, ethylene / vinyl acetate copolymer+DOA, polyethyl methacrylate+DOA, polyvinyl acetate+DOA can be used. The specific electrode performance will be described later. These are all materials that exert the technical effects of the present disclosure, but are not limited to the types of these polymer materials and plasticizers. Any material can be used as long as it is an inactive material that does not respond to ions and inhibits the ion exchange reaction between the ion exchange membrane 1 and the sample solution.

[0062] Like this, the material of inactive layer 5 can be a polymer containing carbon and hydrogen as element type. And then, in order to improve the adhesion with ion exchange membrane 1, elements such as chlorine and oxygen can be contained. But, not limited to this, as long as the material that satisfies the above-mentioned conditions (has the effect of suppressing ion exchange reaction, charge density is below 0.0001mmol / g, and does not carry out ion response) is obtained. In addition, not only polymer materials can be used, low molecular materials, inorganic materials, etc. can also be used, and composite materials formed by mixing various materials can also be used. In addition, inactive layer 5 can also be composed of multiple layers.

[0063] As described above, the inactive layer 5 is made of an insulating material, but in order to form a state in which the permeation of ions is completely insulated, it is necessary to form it appropriately thin. Specifically, if the exchange of ions is completely blocked, ion response cannot be performed, so a layer thickness of less than 10 μm is required. On the other hand, in order to obtain the inhibitory effect of the ion exchange reaction, a layer thickness of more than 0.10 μm is required.

[0064] The ion selective electrode 10 of the structure of the present embodiment has an inactive layer 5 on the surface of the ion exchange membrane 1, so that the ion exchange reaction between the ion exchange membrane 1 and the sample solution can be suppressed, and the electrode characteristics in practical use can be close to the original ion selection characteristics of the ion sensitive membrane 17. In addition, in the case of the structure of coating the surface of the ion exchange membrane 1 with the epoxyamine resin disclosed in Patent Document 2, since the epoxyamine resin itself performs ion response, the response characteristics of the epoxyamine resin itself become the electrode characteristics. In the case where the response characteristics of the epoxyamine resin deteriorate over time, the electrode characteristics also deteriorate. Therefore, in order to achieve an ion selective electrode that is stable over time, the epoxyamine resin itself is also required to have a stable response characteristic over time. On the other hand, in the case of the structure of the present embodiment, the inactive layer 5 does not originally have ion responsiveness, so the characteristics are not easily deteriorated. In addition, the inactive layer 5 only has the function of suppressing the ion exchange reaction between the ion exchange membrane 1 and the sample solution. Therefore, as long as the above-mentioned certain conditions are met (having the function of suppressing the ion exchange reaction, the charge density is less than 0.0001mmol / g, and no ion response), the material of the inactive layer 5 can be selected from a wide range of materials. Furthermore, a material that makes it difficult for components contained in the measurement sample to adhere to the membrane surface may be selected.

[0065] It should be noted that, in the present embodiment, the chloride ion selective electrode is described, but the present technology can also be applied to other anion selective electrodes and cation selective electrodes. Of course, it is necessary to use an ion exchange membrane 1 corresponding to the ion to be measured. For example, in a cation selective electrode, it is necessary to use an ion exchange membrane having a fixed charge opposite to that of an anion selective electrode (e.g., sulfonic acid, carboxylic acid group, etc.: - ions are used to fix the ions in the ion exchange membrane, and + ions (as an example, the ions to be measured) are used as counter ions).

[0066] <Configuration Example of Electrolyte Concentration Measuring Device>

[0067] Figure 3 1 is a diagram showing a configuration example of an electrolyte concentration measuring device (flow type) 100 having an ion selective electrode of the present disclosure. The electrolyte concentration measuring device 100 is a device for analyzing the concentrations of three ions, for example, Na, K, and Cl ions. The electrolyte concentration measuring device 100 includes a measuring unit 170, a potential measuring unit 171, a concentration calculating unit 172, an output unit 174, a device control unit 175, and an input unit 176.

[0068] The measuring unit 170 is provided with three electrodes, namely, a chloride (Cl) ion electrode 101, a potassium (K) ion electrode 102, and a sodium (Na) ion electrode 103, as ion selective electrodes, and a reference electrode 104. The dilution tank 110 of the measuring unit 170 is a cup for temporarily storing a sample dispensed from a sample nozzle (not shown) and a diluted sample mixed with a diluent dispensed from a diluent supply nozzle 108, or an internal standard solution dispensed from an internal standard solution supply nozzle 109. When the pipette nozzle 107 is lowered into the dilution tank 110 under the control of the device control unit 175, the diluted sample or internal standard solution in the dilution tank 110 is introduced into the flow path of the ion selective electrodes 101 to 103. In addition, the reference electrode solution is introduced from the reference electrode solution bottle 161 into the flow path of the reference electrode 104 using the pipette syringe pump 133. During this period, the vacuum suction nozzle 106 is moved downward by the control of the device control unit 175 , and the diluted specimen or internal standard solution remaining in the dilution tank 110 is sucked and discharged into the waste liquid tank 111 .

[0069] <Detailed actions of the mechanism>

[0070] The detailed operation of the mechanism when the liquid is introduced into the flow path of the ion selective electrodes 101 to 103 is described. When the liquid in the dilution tank 110 is introduced into the flow path of the ion selective electrodes 101 to 103, the device control unit 175 closes the electromagnetic valve 121 and the electromagnetic valve 125, opens the pinch valve 105 and the electromagnetic valve 122, lowers the pipette nozzle 107 into the dilution tank, and starts the pipette injection pump 133.

[0071] Next, when the reference electrode solution is introduced into the flow path of the reference electrode 104, the device control unit 175 opens the electromagnetic valve 121, closes the pinch valve 105, and starts the pipette syringe pump 133. Thus, the reference electrode solution is introduced from the reference electrode solution bottle 161 into the flow path of the reference electrode 104. In addition, in order to discharge the liquid accumulated in the pipette syringe pump 133, the device control unit 175 closes the electromagnetic valve 122, opens the electromagnetic valve 125, and presses the pipette syringe pump 133.

[0072] The reference electrode solution introduced into the flow path of the reference electrode 104 contacts the liquid introduced into each of the ion selective electrodes 101 to 103 at the liquid junction 120. As a result, each of the ion selective electrodes 101 to 103 and the reference electrode 104 are electrically connected through the liquid. At this time, the electromotive force (potential) between the reference electrode 104 and each of the ion selective electrodes 101 to 103 changes according to the concentration of the ion to be measured in the liquid introduced into the flow path of the ion selective electrodes 101 to 103, etc.

[0073] The potential information is obtained by the potential measuring unit 171. The concentration calculating unit 172 receives the potential measured at a stable time suitable for concentration calculation from the potential measuring unit 171, and calculates the concentration of the ions to be measured. The output unit 174 displays the device operation status received from the device control unit 175 and the calculation results in the concentration calculating unit 172. The operator can input sample information, various parameters, device operation commands, etc. from the input unit 176. The details of the calculation method will be described later.

[0074] <Device startup action>

[0075] Figure 4 This is a flowchart for explaining the operation of the electrolyte concentration measuring device 100 when it is started.

[0076] (i) Overview of operations at startup

[0077] The operator starts the electrolyte concentration measuring device 100, for example, by turning on the power switch (S201). Next, the operator sets (installs) the ion selective electrodes 101 to 103 in the device 100 (S202), and then sets the reagent bottle in the device 100 (S203). In response to the operator's instructions, the device control unit 175 performs reagent filling (replacing and filling each injection pump and flow path with a new reagent) (S204). In addition, in response to the operator's instructions, the device control unit 175 performs continuous measurement of the internal standard solution to confirm that the potential of the electrode is stable (S205). Furthermore, in order to obtain the calibration curve of the ion selective electrodes 101 to 103, the device control unit 175 measures two standard solutions of known concentrations and calculates the slope (S206). Next, the device control unit 175 calculates the concentration of the internal standard solution (S207).

[0078] (ii) Details of S206 and S207

[0079] Here, the specific operations of S206 and S207 are described. After the device control unit 175 uses the dispensing nozzle (not shown) to dispense the known low concentration standard solution into the dilution tank 110, the dilution liquid in the dilution liquid bottle 151 is dispensed into the dilution tank using the dilution liquid injection pump 132 to dilute the known low concentration standard solution at the set ratio D. Next, the device control unit 175 sucks the diluted known low concentration standard solution in the dilution tank from the pipette nozzle 107 and introduces it into the flow path of the ion selective electrodes 101 to 103. Thereafter, the device control unit 175 introduces the reference electrode solution from the reference electrode solution bottle 161 into the flow path of the reference electrode 104. At this time, at the liquid junction 120, the reference electrode solution contacts the diluted known low concentration standard solution.

[0080] The device control unit 175 uses the potential measuring unit 171 to measure the electromotive force between the ion selective electrodes 101 to 103 and the reference electrode 104 from the time when the diluted standard solution is introduced into the electrode flow path until the liquid is stationary. During this period, the device control unit 175 controls the vacuum suction nozzle 106 to suck up the residual liquid in the dilution tank 110, and then dispenses the internal standard solution in the internal standard solution bottle 141 into the dilution tank 110. Furthermore, the device control unit 175 sucks the internal standard solution in the dilution tank 110 from the pipette nozzle 107, fills the flow paths of the ion selective electrodes 101 to 103 with the internal standard solution, and introduces the reference electrode solution from the reference electrode solution bottle 161 into the flow path of the reference electrode 104. Thereafter, the device control unit 175 controls the potential measuring unit 171 to measure the electromotive force of each electrode from the time when the internal standard solution is introduced into the electrode flow path until the liquid is stationary. In addition, during this period, the device control unit 175 uses the vacuum suction nozzle 106 to suck up the residual liquid in the dilution tank 110, and then uses the dispensing nozzle (not shown) to dispense the known high concentration standard solution into the dilution tank 110. After that, the device control unit 175 uses the dilution liquid syringe pump 132 to dispense the dilution liquid in the dilution liquid bottle 151 into the dilution tank 110, and dilutes the known high concentration standard solution at the set ratio D.

[0081] The device control unit 175 sucks the diluted known high concentration standard solution in the dilution tank 110 from the pipette nozzle 107 and introduces it into the flow path of the ion selective electrodes 101 to 103. Then, the device control unit 175 introduces the reference electrode solution from the reference electrode solution bottle 161 into the flow path of the reference electrode 104. At the liquid junction 120, the reference electrode solution contacts the diluted known high concentration standard solution. Then, the device control unit 175 controls the potential measuring unit 171 to measure the electromotive force between the ion selective electrodes 101 to 103 and the reference electrode 104 from the time when the diluted standard solution is introduced into the electrode flow path to the time when the liquid is still. During this period, the device control unit 175 sucks up the residual liquid in the dilution tank using the vacuum suction nozzle, and then dispenses the internal standard solution in the internal standard solution bottle 141 into the dilution tank.

[0082] The device control unit 175 sucks the internal standard solution in the dilution tank 110 from the pipette nozzle 107, fills the flow paths of the ion selective electrodes 101 to 103 with the internal standard solution, and introduces the reference electrode solution from the reference electrode solution bottle 161 into the flow path of the reference electrode 104. Then, the device control unit 175 controls the potential measuring unit 171 to measure the electromotive force of each electrode after the internal standard solution is introduced into the electrode flow path until the liquid is stationary. In addition, the device control unit 175 sucks up the residual liquid in the dilution tank 110 using the vacuum suction nozzle.

[0083] As described above, the electromotive force of the three liquids, the low concentration standard solution, the high concentration standard solution, and the internal standard solution, is obtained by the potential measuring unit 171. The device control unit 175 controls the concentration calculation unit 172 to calculate the slope sensitivity SL corresponding to the calibration curve based on the electromotive force (EMF) received from the potential measuring unit 171 using the following calculation formula.

[0084] (ii-1) Slope sensitivity

[0085] SL=(EMFH-EMFL) / (Log CH-Log CL)·····(1)

[0086] SL: Slope Sensitivity

[0087] EMFH: Electromotive force of known high concentration standard solution

[0088] EMFL: Electromotive force of known low concentration standard solution

[0089] CH: known concentration value of high concentration standard solution

[0090] CL: known concentration value of low concentration standard solution

[0091] The above operation is called calibration. It should be noted that the slope sensitivity SL is equivalent to 2.303×(RT / zF) of the following Nernst equation (2). Although it can be calculated based on the temperature and the valence of the ion to be measured, in order to further improve the analysis accuracy, the slope sensitivity SL inherent to the electrode is obtained by the above calibration in the electrolyte concentration measuring device 100.

[0092] E=E0+2.303×(RT / zF)×log(f×C)·····(2)

[0093] Here, E0: fixed potential determined by the measurement system, z: valence of the ion to be measured, F: Faraday constant, R: gas constant, T: absolute temperature, f: activation coefficient, and C: ion concentration.

[0094] (ii-2) Internal standard solution concentration

[0095] Next, the internal standard solution concentration is calculated based on the slope sensitivity and the electromotive force of the internal standard solution.

[0096] CIS=CL×10 a ·····(3)

[0097] a=(EMFIS-EMFL) / SL·····(4)

[0098] Here, CIS: concentration of internal standard solution, EMFIS: electromotive force of internal standard solution.

[0099] The above describes a specific calibration method, but it is not related to this step. As long as two or more liquids with different ion concentrations can be introduced into the flow path and the electromotive force can be measured, it can also be a different step. In addition, a standard sample with a composition similar to that of a serum sample or a urine sample can be measured to correct the calibration result.

[0100] <Continuous analysis action>

[0101] The electrolyte concentration measuring device 100 analyzes serum, urine, or the like as a sample after calibration. Figure 5 This is a flowchart for explaining the operation of the electrolyte concentration measuring device 100 during continuous analysis.

[0102] (i) Continuous analysis operation overview

[0103] When the device control unit 175 starts the measurement operation (S301), the internal standard solution in the internal standard solution bottle 141 is dispensed into the dilution tank 110. Next, the device control unit 175 sucks the internal standard solution in the dilution tank 110 from the pipette nozzle 107, fills the flow paths of the ion selective electrodes 101 to 103 with the internal standard solution, and introduces the reference electrode solution from the reference electrode solution bottle 161 into the flow path of the reference electrode 104 (S302). Then, the device control unit 175 controls the potential measuring unit 171 to measure the electromotive force of each electrode (S303). During this period, the device control unit 175 sucks up the liquid remaining in the dilution tank 110 using the vacuum suction nozzle 106, and then dispenses the sample into the dilution tank 110 using the dispensing nozzle (not shown). After that, the device control unit 175 dispenses the dilution solution in the dilution solution bottle 151 into the dilution tank using the dilution solution syringe pump 132, and dilutes the sample at the set ratio D. Furthermore, the device control unit 175 sucks the diluted specimen (sample) in the dilution tank 110 from the pipette nozzle 107, fills the flow paths of the ion selective electrodes 101 to 103, and introduces the reference electrode solution from the reference electrode solution bottle 161 into the flow path of the reference electrode 104 (S304). Then, the device control unit 175 controls the potential measuring unit 171 to measure the electromotive force of each electrode (S305). In addition, the device control unit 175 sucks up the liquid remaining in the dilution tank 110 using the vacuum suction nozzle.

[0104] Next, the device control unit 175 receives the potential value (electromotive force) from the potential measuring unit 171 (S306), controls the concentration calculating unit 172, and calculates the concentration of the sample using the following calculation formula based on the above-mentioned slope sensitivity and the internal standard solution concentration (S308).

[0105] (ii) Specimen concentration

[0106] C S =CIS×10 b·····(5)

[0107] b=(EMFIS-EMFS) / SL·····(6)

[0108] Here, CS is the sample concentration, and EMFS is the measured electromotive force of the sample.

[0109] It should be noted that the present technology can be used even if the device configuration, the structure of the comparison electrode, the measurement sequence, the concentration calculation method, etc. are different from those of the present embodiment.

[0110] (2) Second Embodiment

[0111] The second embodiment is similar to the first embodiment. Figures 1A to 1C The flow-type chloride ion selective electrode is shown.

[0112] <Configuration Example of Ion Sensitive Membrane 17>

[0113] Figure 6 Yes Figure 1C The partially enlarged schematic diagram of the dashed rectangle 17-1 shows the layer structure of the characteristic ion-sensitive membrane 17 of this embodiment. Figure 6 As shown, the ion-sensitive membrane 17 of the second embodiment includes an anion exchange membrane 1, MPDA condensation layers 2 provided on both upper and lower sides of the anion exchange membrane 1, and an inactive layer 5 provided on the surface of the MPDA condensation layer 2 in contact with the sample solution.

[0114] (Electrode manufacturing steps)

[0115] (i) The ion-sensitive membrane 17 is based on the anion exchange membrane 1 having cations immobilized at a high density. First, the anion exchange membrane 1 is immersed in a solution in which meta-phenylenediamine is dissolved in a solvent.

[0116] (ii) Next, the anion exchange membrane 1 is immersed in a mixed solution of formaldehyde and an inorganic acid to form a condensate of metaphenylenediamine (MPDA) and formaldehyde on the ion exchange membrane. This condensation layer is referred to as an MPDA condensation layer 2 .

[0117] (iii) A solution of PVC dissolved in tetrahydrofuran (THF) as a low boiling point solvent is applied to the surface of the ion exchange membrane 1 having the MPDA condensation layer 2 formed thereon, which surface is in contact with the sample solution, and THF is evaporated to form a thin polymer layer (inactive layer).

[0118] (iv) Thereafter, the anion exchange membrane 1 is bonded to the electrode case 11 so as to close the opening provided in the electrode case 11 .

[0119] (v) Thereafter, the internal gel 16 is filled in the electrode case 11, the cover 18 is welded to the electrode case 11, and the internal electrode 13 is fixed in contact with the internal gel 16. It should be noted that in order to suppress evaporation of water in the internal gel 16, the surface of the ion-sensitive membrane 17 on the opposite side to the flow path may be coated with a resin or the like.

[0120] (Configuration Example of Anion Exchange Membrane 1)

[0121] As in the first embodiment, the anion exchange membrane 1 constituting the ion sensitive membrane 17 of the second embodiment may be a membrane reinforced with a silk fabric made of PVC (polyvinyl chloride), which is a highly cross-linked polystyrene-based membrane having quaternary ammonium ions as anion exchange groups.

[0122] However, it is not limited to this membrane, for example, the ion exchange group may be a primary amino group, a secondary amino group, or a tertiary amino group, and the matrix material may not be styrene-based but other hydrocarbon resins such as polyolefins, fluorine resins, etc. In addition, the reinforcing material may be other materials such as other polymer fibers and glass fibers, or may be a membrane without a reinforcing material.

[0123] Furthermore, the counter ions contained in the anion exchange membrane 1 are preferably ions of the same type as the ions to be measured, but may also be other anions. In addition, even if it is not a material used in a general ion exchange membrane, as long as it is a membrane with a high density of fixed charges, the technical effect of the present disclosure can be exerted. Here, high density refers to a charge density of 0.1 to 10 mmol / g.

[0124] <Configuration Example of Inactive Layer 5>

[0125] Although the inactive layer 5 is made of insulating material, it is appropriately thin, so that the permeation of ions is not completely insulated. In order to obtain the inhibitory effect of ion exchange reaction, a layer thickness of 0.10 μm or more is required. In addition, when the exchange of ions is completely blocked, no ion response is performed, so a layer thickness of less than 10 μm is required.

[0126] Thus, the structure of the ion-sensitive membrane 17 of the second embodiment is a structure in which the MPDA condensation layer 2 is added to the ion-sensitive membrane 17 of the first embodiment. The MPDA condensation layer 2 plays a role in improving the ion selectivity of the ion-sensitive membrane 17 itself. In the second embodiment, by forming the inactive layer 5 on the MPDA condensation layer 2, the ion exchange reaction can be suppressed, and the electrode characteristics in actual use can be made close to the original ion selectivity of the membrane. It should be noted that the specific electrode performance will be described later.

[0127] The material of the ion exchange membrane 1 and the material of the inactive layer 5 used can be selected from various materials as in the first embodiment described above.

[0128] Thus, even if the ion exchange membrane 1 having a high density of fixed charges is treated to improve ion selectivity (forming the MPDA condensation layer 2), the technical effect of the present disclosure can be expected as long as the inactive layer 5 is formed. In addition, the present technology can also be applied to other anion selective electrodes and cation selective electrodes.

[0129] <Configuration Example of Electrolyte Concentration Measuring Device>

[0130] The ion selective electrode 10 of the second embodiment can be used in the electrolyte concentration measuring device 100 (see FIG. 1 ) in the same manner as the ion selective electrode 10 of the first embodiment. Figure 3 ) is used in

[0131] (3) Third Embodiment

[0132] The third embodiment relates to a rod-type ion selective electrode. Fig. 9 It is a diagram showing a cross-sectional configuration example of a rod-type ion selective electrode 20 according to the third embodiment.

[0133] <Configuration Example of Rod-Type Ion Selective Electrode>

[0134] The rod-type ion selective electrode 20 has an opening ( Fig. 9 The rod-type ion selective electrode 20 includes an electrode housing 22 having an opening at the bottom. The rod-type ion selective electrode 20 includes an ion sensitive membrane 17 provided so as to block the opening. The surface of the ion sensitive membrane 17 in contact with the sample solution is covered with an inactive layer 26. Furthermore, an internal gel (internal liquid) 23 containing an electrolyte is provided so as to fill the electrode housing 22. An internal electrode 24 is provided so as to contact the internal liquid 23, and a cover 25 is installed to seal the internal liquid 23 in the electrode housing 22. It should be noted that by mounting the ion selective electrode 20 on the electrolyte concentration measuring device 100 (see Figure 3 ), the internal electrode 24 is connected to the wiring on the device 100 side, so that the potential generated according to the concentration of the ions to be measured contained in the sample solution can be measured, and the concentration of the ions to be measured can be analyzed.

[0135] <Electrode Manufacturing Steps>

[0136] Hereinafter, a method for manufacturing the rod-type ion selective electrode 20 according to the present embodiment will be described.

[0137] (i) First, the ion exchange membrane 21 having a fixed charge is coated with the inactive layer 26. At this time, the entire surface may be coated, or only the surface in contact with the sample may be coated.

[0138] (ii) The electrode case 22 and the ion exchange membrane 21 covered with the inactive layer 26 are bonded to each other so as to close the opening provided in the electrode case 22 .

[0139] (iii) Thereafter, the electrode case 22 is filled with the internal gel (internal liquid) 23 , the cover 25 is attached, and the internal electrode 24 is arranged to be in contact with the internal gel 23 .

[0140] It should be noted that the ion exchange membrane 21 may be subjected to a treatment for improving ion selectivity as described in the second embodiment (for example, forming an MPDA condensation layer 2). The layer structure of the ion sensitive membrane 17 of this embodiment is the same as that of the first and second embodiments, and therefore the slope sensitivity, ion selectivity, resistance, service life, potential stability, etc. of the ion sensitive membrane 17 are also the same.

[0141] Such a rod-type ion selective electrode 20 is usually immersed in a container containing a sample solution together with a reference electrode, and the sample solution in the container is stirred by a stirrer, and the potential is measured during the process. Compared with the ion selective electrode based on the conventional ion exchange membrane, the structure of this embodiment suppresses the ion exchange reaction between the ion exchange membrane and the sample solution, so it can show ion selectivity close to the original ion sensitive membrane in practical use, and can also perform measurements that are not easily dependent on the flow rate of the sample solution. In addition, the material composition, function, effect, etc. are the same as those of the first and second embodiments.

[0142] (4) Comparative Example

[0143] <Comparative Example 1>

[0144] (i) Configuration example of ion selective electrode

[0145] The schematic front view of the flow-type ion selective electrode of this comparative example 1 is similar to that of the first embodiment. Figure 1A express. Figure 1B Yes means Figure 1A FIG. 1 is a diagram showing an example of the AA' cross-section structure. Figure 1C : is a diagram showing an example of the BB' cross-section configuration. The flow-type ion selective electrode of Comparative Example 1 has a flow path 12 penetrating an electrode housing 11, and a sample solution to be measured passes through the flow path 12. An ion-sensitive membrane is provided in contact with the sample solution, and an internal gel 16 containing an electrolyte is provided in a manner that fills the inside of the electrode housing 11. An internal electrode 13 is provided in contact with the internal gel 16, and a cover 18 is bonded to seal the internal gel in the electrode housing. In addition, near the inlet and outlet of the flow path 12 of the electrode housing, a gasket 15 that can be connected to the flow path of the device or other electrodes is provided.

[0146] Figure 7 Yes Figure 1C The enlarged view of the dashed rectangle 17-1 shows the layer structure of the ion-sensitive membrane of this comparative example. The ion-sensitive membrane of comparative example 1 is composed of an anion exchange membrane 1. Unlike the ion-sensitive membrane 17 of the first and second embodiments, it does not include an inactive layer 5.

[0147] (ii) Preparation steps of ion-selective electrodes

[0148] (ii-1) First, the anion exchange membrane 1 having immobilized cations and the electrode case 11 are welded to each other using tetrahydrofuran (THF) as a low boiling point solvent so as to close the opening provided in the electrode case 11 .

[0149] (ii-2) Thereafter, the internal gel 16 is filled in the electrode case 11 , and the lid 18 is welded and fixed to the internal electrode 13 so as to be in contact with the internal gel 16 .

[0150] In this comparative example 1, as the anion exchange membrane 1, a membrane having a silk fabric made of PVC (polyvinyl chloride) as a reinforcement material was used, which is a highly cross-linked polystyrene-based membrane having a quaternary ammonium group as an anion exchange group.

[0151] The ion selective electrode manufactured by such a method has a structure in which the ion exchange membrane 1 is directly exposed to the sample solution. The specific electrode performance will be described later.

[0152] <Comparative Example 2>

[0153] This comparative example 2 is similar to that described in comparative example 1, and relates to Figures 1A to 1C The flow-type ion-selective electrode is shown. Figure 8 Yes Figure 1C The partially enlarged view of the dotted rectangle 17 - 1 shows the layer structure of the ion-sensitive membrane of Comparative Example 2.

[0154] (i) Preparation steps of ion-selective electrodes

[0155] (i-1) First, the anion exchange membrane 1 having immobilized cations is immersed in a solution of metaphenylenediamine dissolved in a solvent, and then immersed in a mixed solution of formaldehyde and an inorganic acid, thereby forming a condensate of metaphenylenediamine (MPDA) and formaldehyde on the anion exchange membrane 1.

[0156] (i-2) The ion exchange membrane 1 on which the MPDA condensation layer 2 was formed was welded to the electrode case 11 using THF as a low boiling point solvent so as to close the opening provided in the electrode case 11 .

[0157] (i-3) Thereafter, the inner gel 16 is filled in the electrode case 11 , and the cover 18 is welded and fixed to the inner electrode in such a manner as to be in contact with the inner gel 16 .

[0158] In this comparative example 2, as the anion exchange membrane 1, a membrane having a PVC (polyvinyl chloride) silk fabric as a reinforcement material was used, which is a highly cross-linked polystyrene-based membrane having a quaternary ammonium group as an anion exchange group.

[0159] The ion selective electrode manufactured by such a method has a structure in which the ion exchange membrane 1 treated with MPDA condensation is in contact with the sample solution. It should be noted that the specific electrode performance will be described later.

[0160] (5) Measurement Examples (Examples)

[0161] <Measurement Example 1>

[0162] (i) Measurement results

[0163] The response behavior of the ion selective electrode 10 having the structure shown in the first embodiment using PVC as the material of the inactive layer 5 and the electrode of the above-mentioned Comparative Example 1 to aqueous solutions containing ions of various concentrations and types was investigated. Fig.10 is a graph showing the comparison results of the response behavior. Fig.10 In the graph of , the horizontal axis represents time, and the vertical axis represents the acquired potential (EMF: in the case of an anion selective electrode, the slope sensitivity is negative, so a small value indicates a high-sensitivity response).

[0164] The black circles on the thick lines in the upper part of the graph indicate the time when each sample solution was introduced. The liquid was kept still except when the liquid was introduced. As a result, even for the electrode of Comparative Example 1, Fig.10 The potentials of the NaCl aqueous solutions of (a) to (c) with different concentrations when the liquid is at rest are all stable over time.

[0165] However, in Fig.10 In (d), for 10 mM NaHCO3, the potential drops sharply just after the liquid comes to rest, and its change gradually becomes gentle. When the NaHCO3 aqueous solution of the same concentration is introduced again, the same curve is drawn starting from the same potential as the first time. Fig.10 In (e), when 100 mM NaHCO3 is introduced, the potential also changes to the negative direction. Fig.10 In (f), when 10 mM NaBr was introduced, on the contrary, the potential rose sharply just after the liquid came to rest, and the change gradually became gentle. Fig.10In (g), when 10 mM NaSCN was added, a more significant potential change was shown. If the same liquid was introduced again, the phenomenon was reproduced. Fig.10 In (h), when 10 mM NaCl was introduced, the Fig.10 (b) approximately the same potential.

[0166] On the other hand, regarding the ion selective electrode 10 having the structure of the first embodiment, with respect to all liquids ( Fig.10 (a) to (h)) show a relatively stable potential.

[0167] (ii) Reasons why the inactive layer 5 prevents the influence of interfering ions

[0168] Here, in the ion selective electrode of the structure of Comparative Example 1 (refer to Figure 7 ) in the measurement of a sample solution containing interfering ions, the potential changes with time. In the ion selective electrode 10 of the first embodiment (see Figure 2 ) does not occur, and the mechanism is explained.

[0169] Fig.11A Schematically shows the ion composition of the ion sensitive membrane and the sample solution of Comparative Example 1. In Comparative Example 1, the cations (cations) immobilized in the ion exchange membrane 1 of the ion sensitive membrane exist at a high concentration, and chloride ions (Cl - ). Therefore, in the presence of the interfering ion J - When the sample liquid contacts the membrane, the interfering ions J in the sample liquid near the membrane will occur. - With Cl in the membrane - The ion exchange reaction. As time passes after the liquid is still, Fig.11A The state (a) changes to the state (b).

[0170] For example, in J - Bicarbonate ion (HCO3 - ) in the case of ion-sensitive membrane than HCO3 - More likely to respond to Cl - Therefore, when HCO3 in the sample solution near the surface of the ion exchange membrane 1 - Replaced by Cl - When the anion selective electrode is used, it will sense (detect) that the ion concentration of the sample solution has increased. Fig.10The potential difference when the ion concentration of the measured object is increased by one digit: for example, the theoretical value of the slope sensitivity when the measured object is changed from 10mM NaCl to 100mM NaCl is about -59mV / decade at room temperature) is negative, so as the J in the sample solution increases, the slope sensitivity increases. - To Cl - As the exchange reaction proceeds, the potential changes in the downward direction (refer to Fig.10 (d) and (e)). Then, when the same sample solution is introduced again, the sample solution is renewed and the same phenomenon occurs again. It should be noted that although HCO3 also flows into the ion exchange membrane 1 side - , but Cl exists at a high density in the ion exchange membrane 1 - , so it is believed that there is little impact on membrane performance.

[0171] For example, after introducing a selectivity ratio of Cl - High Br - 、SCN - In the case of a sample solution containing hydrophobic ions, that is, in J - Br - 、SCN - In the case of - 、SCN - Exchanged for Cl - When the potential changes in the upward direction (refer to Fig.10 (f) and (g)).

[0172] On the other hand, in the case of the ion selective electrode 10 including the inactive layer 5 (the case of the first and second embodiments), it is possible to prevent Fig.11A The phenomenon shown. Fig. 11B This is a diagram schematically showing the ion sensitive membrane 17 and the ion composition inside the sample solution in the case of the ion selective electrode 10 having the inactive layer 5. Since the surface of the ion sensitive membrane 17 is covered with the inactive layer 5, the ion exchange reaction between the ion exchange membrane 1 and the sample solution is suppressed, and the potential change caused by the ion exchange reaction as in Comparative Example 1 is not likely to occur.

[0173] Fig.12 Indicated in Fig.10 The slope and the potential relative to chloride ions (Cl - ) of each interfering ion selectivity coefficient (a numerical value indicating the degree of interfering ion response when chloride ion is set to 1). The numbers in brackets indicate the selectivity calculation results at 100mM ion concentration. Figure 2 The ion selective electrode 10 (first embodiment) having the structure shown in FIG. Figure 7 In the ion selective electrode (Comparative Example 1) of the structure shown in the figure, the slope sensitivity is approximately the same. Regarding the selectivity, in the structure of the first embodiment, HCO3 as a hydrophilic ion is increased compared to Comparative Example 1. - The selectivity is low compared to Br as a hydrophobic ion. - 、SCN - , the selectivity coefficient becomes higher. This is considered to be because, in Comparative Example 1, the ion composition of the sample solution near the membrane changes due to the ion exchange reaction, so the selectivity coefficient can be measured to a value close to that of the original ion-sensitive membrane 17, whereas, according to the structure of the first embodiment, the inactive layer can suppress the ion exchange reaction, so that a value close to the selectivity coefficient of the ion-sensitive membrane 17 can be measured. In addition, the HCO3 at 100mM in Comparative Example 1 and the first embodiment - The selectivities were close to each other. This is probably because the ion concentration of the liquid was high, so the influence of the ion flux was relatively small, and the difference due to the presence or absence of the inactive layer was not easily seen.

[0174] It should be noted that in Comparative Example 1, it is considered that SCN - The selectivity coefficient is lower than 1, which may be due to the SCN - The membrane characteristics may change due to the entry of ions into the ion exchange membrane 1 or the influence of the diffusion potential within the ion exchange membrane 1 .

[0175] As described above, unlike a general liquid membrane type ion-sensitive membrane having a low fixed charge density, a membrane having a high fixed charge density such as the ion exchange membrane 1 of the present embodiment rapidly undergoes an ion exchange reaction with a liquid. As in the embodiment of the present disclosure, by coating the surface of the ion exchange membrane 1 with the inactive layer 5, the ion exchange reaction can be suppressed, and the ion selectivity of the ion-sensitive membrane 17 can be approached.

[0176] <Measurement Example 2>

[0177] For the ion selective electrode of the structure of Comparative Example 1 (refer to Figure 7 ) and the ion selective electrode of the first embodiment (refer to Figure 2 ), measured relative to chloride ions (Cl - ) of bicarbonate ions (HCO3 - )Selection coefficient. Fig.13 : is a graph showing the measurement results. The bicarbonate ion selectivity is evaluated by the so-called mixed solution method using a sample solution of an interfering ion added to a standard solution. As a chloride ion selective electrode, the smaller the selectivity of the bicarbonate ion as an interfering ion, the better. It should be noted that the measuring device uses a high-productivity automatic analyzer. This device dilutes the specimen and performs the analysis.

[0178] exist Fig.13 In the figure, No. 1 represents the bicarbonate ion selectivity of an electrode having an untreated membrane mounted on an ion exchange membrane 1 (electrode structure of Comparative Example 1). No. 2 represents the bicarbonate ion selectivity of an electrode having a membrane formed by coating only THF (containing no polymer) on the surface of the ion exchange membrane 1 and drying it (electrode structure equivalent to Comparative Example 1).

[0179] No. 3 to 9 respectively represent the bicarbonate ion selectivity coefficient of an electrode (structure of the first embodiment) having a membrane formed by coating the membrane surface with a THF solution containing PVC, ethylene / vinyl acetate copolymer, polyvinyl formal, PVC+DOA, ethylene / vinyl acetate copolymer+DOA, polyethyl methacrylate+DOA, and polyvinyl acetate+DOA and drying the membrane surface.

[0180] like Fig.13 As shown, the electrodes No. 3 to No. 9 of the first embodiment have smaller bicarbonate ion selectivity coefficients and improved performance compared to No. 1 and No. 2 of the structure of Comparative Example 1. Thus, by forming the inactive layer 5 on the surface of the ion exchange membrane 1, the ion selectivity close to the original ion sensitive membrane 17 can be exhibited regardless of the type of material of the inactive layer 5.

[0181] Although not shown in the figure, for example, when the ion-sensitive membrane 17 of the structure of the first embodiment is reversed and assembled with the surface covered by the inactive layer 5 facing the inner gel 16 side, the ion selective electrode 10 has a significantly larger selectivity coefficient for bicarbonate ions than the electrode with the surface covered by the inactive layer 5 facing the sample solution side. Therefore, it can be said that forming the inactive layer 5 between the ion exchange membrane 1 and the sample solution is effective.

[0182] <Measurement Example 3>

[0183] For the ion selective electrode of the structure of Comparative Example 2 (refer to Figure 8 ) and the ion selective electrode of the second embodiment (refer to Figure 6 ), measured relative to chloride ions (Cl - ) of bicarbonate ions (HCO3 - )Selection coefficient. Fig.14: is a graph showing the measurement result. The bicarbonate ion selectivity is evaluated by the so-called mixed solution method using a sample solution in which an interfering ion is added to a standard solution. As a chloride ion selective electrode, the smaller the selectivity of the bicarbonate ion as an interfering ion, the better. It should be noted that the measuring device uses a high-productivity automatic analyzer. This device dilutes the specimen and performs the analysis. The material of the inactive layer 5 of the structure of the second embodiment uses PVC, and 5 electrodes are made under the conditions of an average layer thickness of 0.1μm, 1μm, and 10μm. Fig.14 The average values ​​of these bicarbonate ion selectivity coefficients are shown in a bar graph, and the respective maximum and minimum values ​​are shown with error bars.

[0184] Fig.14 In the figure, "blank" is the result of the ion selective electrode having a structure equivalent to Comparative Example 2. That is, a membrane having a condensation layer 2 of MPDA and formaldehyde formed on an anion exchange membrane 1, and no inactive layer formed. The bicarbonate ion selectivity coefficient of this ion selective electrode is about 0.19. No significant difference in the bicarbonate ion selectivity coefficient was observed between the ion sensitive membrane 17 (structure of the second embodiment) having an inactive layer 5 formed on the ion sensitive membrane with an average thickness of 0.1 μm and the ion sensitive membrane not covered with the inactive layer 5 (equivalent to Comparative Example 2).

[0185] On the other hand, in the ion-sensitive membrane 17 in which the inactive layer 5 was formed with an average thickness of 1 μm, the bicarbonate ion selectivity coefficient was significantly improved by about 0.09. Furthermore, the ion-sensitive membrane 17 in which the inactive layer 5 was increased in thickness to 10 μm did not show any ion response because the inactive layer 5 was too thick, and the slope sensitivity showed an irregular value.

[0186] According to the above measurement results, it is considered that when the thickness of the inactive layer is less than 0.1 μm, it is an insufficient thickness for the inactive layer 5 to exert the function of suppressing the ion exchange reaction, and when it is more than 10 μm, the inactive layer 5 is too thick to exhibit the ion response characteristics of the ion exchange membrane 1. Therefore, it is known that in order to improve the ion selectivity, it is preferred to set the thickness of the inactive layer 5 to between 0.1 and 10 μm.

[0187] It should be noted that, although not shown in the figure, the ion-sensitive membrane 17 formed with the inactive layer 5 having an average thickness of 1 μm can exert the effect of the inactive layer 5 without change even after storage, and maintains a low selectivity coefficient compared to the ion-sensitive membrane (comparative example) not covered with the inactive layer 5. In this way, the inactive layer 5 can exert its effect even during long-term storage.

[0188] From the above results, it was confirmed that the effect of the present disclosure, that is, the ion selectivity is improved by forming the inactive layer 5 also on the ion sensitive membrane 17 subjected to the treatment for improving the selectivity of the ion exchange membrane 1 , can be improved.

[0189] (6) Summary

[0190] The ion-sensitive membrane in the ion-selective electrode of each embodiment is in contact with the sample solution at least in a portion of the first surface, and is in contact with the internal gel (internal solution) at least in a portion of the second surface different from the first surface (opposite to the first surface). In addition, the first surface of the ion-sensitive membrane is covered with an inactive layer that inhibits ion exchange reaction between the ion-sensitive membrane and the sample solution. Here, the ions to be measured contained in the sample solution are various anions and various cations. For example, Br - ,I - , CN - 、Cd 2+ , Cu 2+ 、Ag + , S 2- 、F - , K + , Ca 2+ 、NO3 - NH4 + 、Na + As a measurement object. Thus, in an ion selective electrode based on an ion exchange membrane (ion exchange resin) 1 having a high-density fixed charge, by adding a structure (inactive layer) that can be manufactured by a simple process, it is possible to achieve an improvement in ion selectivity and an improvement in stability over time. An ion selective electrode having such a structure is also suitable for an automatic analysis device that performs continuous measurement with high productivity, and can further improve the analytical accuracy and reliability of ion concentration measurement.

[0191] The ion selective electrode is based on an ion exchange membrane (ion exchange resin) 1 having a high-density fixed charge. In this case, the charge density of the fixed charge can be set to 0.1 mmol / g or more.

[0192] On the other hand, when the ion concentration in the sample solution is low, even a small ion exchange phenomenon between the ion exchange membrane and the sample solution will affect the measured value, so the charge density of the ion-sensitive membrane is not as high as described above, and even in the case of a medium charge density such as a liquid membrane type ion-sensitive membrane, it will have an effect. However, in such a system, the effect of the present invention can be exerted by providing an inactive layer.

[0193] The inactive layer can be composed of a material that does not respond to ions. As an example of a material that does not respond to ions, an insulating material can be cited. As an example of the insulating material, a polymer material (a polymer containing carbon and hydrogen, a material containing at least one element of chlorine and oxygen) can be cited. In addition, the charge density of the inactive layer can be set to less than 0.001 mmol / g. Furthermore, the inactive layer has a portion with a thickness of more than 0.10 μm and less than 10 μm. By setting the thickness of the inactive layer to this range, ion response can be reliably achieved and ion exchange reaction can be suppressed.

[0194] In addition, the ion-sensitive membrane may be composed of an ion exchange membrane 1, a treatment layer (for example, an MPDA condensation layer) 2 formed on both surfaces (the first surface is the sample side, and the second surface is the internal liquid side) of the ion exchange membrane 1 for improving ion selectivity, and an inactive layer 5 formed on the condensation layer on the first surface side (second embodiment). In this way, the ion selectivity of the ion-sensitive membrane 17 itself can be further improved.

[0195] Explanation of symbols

[0196] 1, 21: ion exchange membrane; 2: MPDA condensation layer; 5, 26: inactive layer; 11, 22: electrode shell; 12: flow path; 13, 24: internal electrode; 15: gasket; 16, 23: internal gel; 17: ion sensing membrane; 18, 25: cover; 100: electrolyte concentration measuring device; 101: chloride ion electrode; 102: potassium ion electrode; 103: sodium ion electrode; 104: reference electrode; 105: pinch valve; 106: vacuum suction nozzle; 107: pipette nozzle; 108: diluent supply nozzle; 109 : Internal standard solution supply nozzle; 110: Dilution tank; 111: Waste liquid tank; 112: Vacuum pump; 120: Liquid joint; 121, 122, 123, 124, 125, 126, 127: Solenoid valve; 131: Syringe pump for internal standard solution; 132: Syringe pump for diluent; 133: Pipette syringe pump; 141: Internal standard solution bottle; 151: Dilution solution bottle; 161: Reference electrode solution bottle; 171: Potential measurement section; 172: Concentration calculation section; 174: Output section; 175: Device control section; 176: Input section.

Claims

1. An ion selective electrode for measuring target ions contained in a sample solution, comprising: The electrode housing that holds the internal liquid, an internal electrode having a portion in contact with the internal liquid, and an ion-sensitive membrane isolating the sample liquid from the internal liquid, The ion-sensitive membrane is in contact with the sample solution at least partially on a first surface, and is in contact with the internal solution at least partially on a second surface different from the first surface. The first surface of the ion-sensitive membrane is covered with an inactive layer that suppresses an ion exchange reaction between the ion-sensitive membrane and the sample solution.

2. The ion selective electrode according to claim 1, wherein The charge density of the ion-sensitive membrane is greater than 0.1 mmol / g.

3. The ion selective electrode according to claim 1, wherein The ion-sensitive membrane comprises an ion exchange resin.

4. The ion selective electrode according to claim 3, wherein The ion-sensitive membrane has a treatment layer for improving ion selectivity at least in a portion of the first surface that contacts a sample, and the inactive layer is formed on the treatment layer on the first surface side.

5. The ion selective electrode according to claim 1, wherein The inactive layer is composed of a material that does not respond to ions.

6. The ion selective electrode according to claim 1, wherein The charge density of the inactive layer is 0.001 mmol / g or less.

7. The ion selective electrode according to claim 1, wherein The inactive layer is made of an insulating material.

8. The ion selective electrode according to claim 1, wherein The inactive layer comprises a polymer material.

9. The ion selective electrode according to claim 8, wherein The polymer material is a polymer containing carbon and hydrogen.

10. The ion selective electrode according to claim 8, wherein The polymer material contains at least one element of chlorine and oxygen.

11. The ion selective electrode according to claim 1, wherein The inactive layer has a portion having a thickness of 0.10 μm or more and 10 μm or less.

12. The ion selective electrode according to claim 1, wherein The target ion is an anion.

13. The ion selective electrode according to claim 12, wherein The target ion is a chloride ion.

14. The ion selective electrode according to claim 1, wherein The target ions are cations.

15. An electrolyte concentration measuring device comprising the ion selective electrode according to claim 1 and a concentration calculation unit, The concentration calculation unit calculates the concentration of the target ion based on potential information measured using the ion selective electrode.

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