Ion concentration measuring device, ion concentration measuring method, and ion concentration measuring program

Abstract

To provide an ion concentration measuring device that can measure an ion concentration more precisely and with a simpler configuration.SOLUTION: The ion concentration measuring device includes: a work electrode for outputting a measurement potential according to the ion concentration included in a sample liquid; a comparison electrode for outputting a reference potential to the measurement potential output from the work electrode; a resistance value measurement unit for measuring a resistance value of the sample liquid; and a calculation unit for calculating an ion concentration on the basis of a potential difference between the work electrode and the comparison electrode and the resistance value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ion concentration measuring device, an ion concentration measuring method, and an ion concentration measuring program for measuring the concentration of ions contained in a sample liquid. [Background technology]

[0002] In measuring ion concentration, an error in the measured value may occur depending on the electrical conductivity of the sample liquid to be measured. One possible method for reducing the effect of the electrical conductivity of the sample liquid on the measured value is to provide a conductivity meter that measures the conductivity of the sample liquid and correct the ion concentration using the conductivity output from this conductivity meter, as described in Patent Document 1.

[0003] However, this conventional method has the problem that the device configuration is complicated because the conductivity is first measured using a conductivity meter and then the ion concentration is corrected using this conductivity.The problem is that it is difficult to miniaturize the ion concentration measuring device because a complex calculation means is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-27856 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide an ion concentration measuring device that can measure ion concentrations with high accuracy using a simpler configuration. [Means for solving the problem]

[0006] That is, the ion concentration measuring device according to the present invention is characterized by comprising a working electrode that is placed in contact with a sample solution and outputs a measurement potential corresponding to the ion concentration in the sample liquid, a comparison electrode that is placed in contact with the sample liquid and outputs a reference potential, a resistance value measuring unit that measures the resistance value of the sample liquid, and a calculation unit that calculates the ion concentration based on the potential difference between the measurement potential and the reference potential and the resistance value.

[0007] With the ion concentration measuring device configured in this manner, the ion concentration is calculated using the resistance value, so there is no need to calculate the conductivity. Furthermore, the resistance value measuring unit does not need to be a conductivity meter; it only needs to be able to measure the resistance value. Therefore, it is possible to provide an ion concentration measuring device with as simple a configuration as possible while still achieving the desired measurement accuracy.

[0008] If the resistance value measuring unit uses the reference electrode as an electrode for measuring resistance values, the resistance value can be measured using only the parts necessary for measuring the ion concentration.

[0009] In a specific embodiment of the present invention, the calculation unit corrects the potential difference using the resistance value.

[0010] The type of ion to be measured is not particularly limited. However, since the influence of the electrical conductivity of the sample liquid on the ion concentration measurement of calcium ions or ammonium ions is relatively large, the effects of the present invention are significantly exhibited when the working electrode is used to measure calcium ions or ammonium ions.

[0011] When the electrical conductivity of the sample liquid is in the range of 10 mS / cm or more and 25 mS / cm or less, the effects of the present invention are particularly pronounced.

[0012] If dirt adheres to the surface of the resistance measurement electrode for measuring the resistance of the sample liquid, the resistance value measured by the resistance measurement unit may change. Therefore, it is preferable that the device further includes a cleaning mechanism for cleaning the surface of the resistance measurement electrode. [Effects of the Invention]

[0013] According to the present invention, the ion concentration is corrected using the resistance value measured by the resistance value measuring unit, so that the ion concentration can be measured accurately while eliminating the need to convert the resistance value into conductivity. Furthermore, since the ion concentration measuring device includes the resistance value measuring unit, there is no need to prepare a separate conductivity meter. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an overall schematic diagram of an ion concentration measuring device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing the structure of a sensor unit of the ion concentration measuring device according to the embodiment. [Figure 3] FIG. 3 is a flowchart showing a method for calculating an ion concentration in the ion concentration measuring device according to the present embodiment. [Figure 4] FIG. 4 is a schematic diagram showing the structure of a sensor unit of an ion concentration measuring device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] An ion concentration measuring device 100 according to one embodiment of the present invention will be described below with reference to the drawings.

[0016] The ion concentration measuring device 100 according to this embodiment measures, for example, the concentrations of various ions in sample liquids such as industrial wastewater, effluent from water treatment facilities, river water, swamp water, and groundwater.

[0017] As shown in FIG. 1, for example, this ion concentration measuring device 100 includes a working electrode 1, a reference electrode 2, a calculation unit 3 that calculates the ion concentration based on the potential difference between the working electrode 1 and the reference electrode 2, and a display unit 4 that displays the ion concentration calculated by the calculation unit 3.

[0018] The working electrode 1 is disposed in contact with a sample liquid, thereby outputting a measurement potential corresponding to the concentration of a specific ion in the sample liquid. As shown in FIG. 2 , the working electrode 1 according to this embodiment includes a cylindrical resin working electrode housing 11, a measurement internal electrode (not shown) disposed inside the working electrode housing 11, an ion-responsive membrane 12 attached to the tip of the working electrode housing 11 so as to be in contact with the sample liquid, and a measurement internal liquid accommodated inside the working electrode housing 11 and electrically connecting the measurement internal electrode and the ion-responsive membrane 12. The ion-responsive membrane 12 responds to, for example, calcium ions. The measurement internal electrode is, for example, a silver / silver chloride electrode, and the measurement internal liquid is, for example, an aqueous potassium chloride solution.

[0019] 2, the reference electrode 2 outputs a reference potential relative to the measured potential output from the working electrode 1, and includes, for example, a reference electrode casing 21 made of resin, a reference internal electrode (not shown) housed inside the reference electrode casing 21, a through-hole formed through the reference electrode casing 21 in the thickness direction and opening onto the surface of the reference electrode casing 21 that comes into contact with the sample, a liquid junction 22 made of porous ceramic or the like attached inside the through-hole, and a reference electrode internal liquid housed inside the reference electrode casing 21 and electrically connecting the reference electrode internal electrode and the liquid junction 22. The measurement internal electrode is, for example, a silver / silver chloride electrode, and the measurement internal liquid is, for example, an aqueous potassium chloride solution.

[0020] The calculation unit 3 is, for example, disposed between the working electrode 1 and the reference electrode 2, and calculates the ion concentration based on the potential difference output from an electrometer 5 that detects the potential difference between the working electrode 1 and the reference electrode 2. For example, an information processing circuit including a CPU, a memory, an A / D converter, a D / A converter, etc. is configured to perform its functions by the CPU and peripheral devices working together in accordance with a program stored in a predetermined area of ​​the memory.

[0021] Therefore, the ion concentration measuring device 100 according to this embodiment further includes a resistance value measuring unit 6 that measures the resistance value of the sample liquid, as shown in FIG. The resistance value measuring section 6 includes a resistance value measuring electrode 61 , a ground electrode 62 , and a resistance value output section 63 . The resistance value output unit 63 outputs to the calculation unit 3 the resistance value (e.g., resistance count value) detected between the resistance value measurement electrode 61 immersed in the sample liquid and the earth electrode 62.

[0022] In this embodiment, as shown in FIG. 2, the reference electrode 2 is used as the resistance value measuring electrode 61 . As described above, when calculating the ion concentration based on the potential difference between the working electrode 1 and the reference electrode 2, the calculation unit 3 also refers to the resistance value measured by the resistance value measurement unit 6 to calculate the ion concentration.

[0023] A specific method in which the calculation unit 3 calculates the ion concentration based on the potential difference and the resistance value is, for example, as shown in FIG.

[0024] The potential difference between the working electrode 1 and the reference electrode 2 output from the electrometer 5 and the resistance value output from the resistance value measuring unit 6 are received, and the potential difference is corrected by the resistance value.

[0025] More specifically, a correlation equation is determined in advance to represent the correlation between the electrical conductivity of a sample liquid and the resistance count value measured for the same sample by the resistance value measuring unit 6. Because the correlation between the electrical conductivity and the resistance count value varies relatively little between individual ion concentration measuring devices 100, the previously determined correlation equation may be stored in the ion concentration measuring device 100 before shipping.

[0026] Furthermore, for example, a standard sample solution having a known concentration of the ion to be measured is used, and the potential difference output from the electrometer 5 is measured when the electrical conductivity is changed while the ion concentration is kept constant, and a correlation equation expressing the correlation between the electrical conductivity (electrical conductivity) and the potential difference is determined in advance.

[0027] Using the two correlation equations previously determined by the procedure described above, a correlation equation between the resistance count and the potential difference is created and stored in the ion concentration measuring device.

[0028] Thereafter, the potential difference and the resistance count value are measured for a sample liquid whose ion concentration and electrical conductivity are unknown, and the calculation unit 3, upon receiving these, corrects the potential difference with the resistance count value using a correlation equation between the resistance count value and the potential difference. Based on this corrected potential difference and the Nernst equation, the calculation unit 3 calculates the ion concentration.

[0029] According to the ion concentration measuring device 100 and ion concentration measuring method of this embodiment, the calculation unit 3 corrects the potential difference between the working electrode 1 and the reference electrode 2 using the resistance value measured by the resistance value measuring unit 6, and calculates the ion concentration using this corrected potential difference, thereby making it possible to minimize fluctuations in ion concentration due to changes in the electrical conductivity of the sample liquid.

[0030] Since the calculation unit 3 uses the resistance count value measured by the resistance value measurement unit 6 as is to correct the potential difference, it is possible to omit the device configuration for calculating the electrical conductivity (electrical conductivity) from the resistance count value.

[0031] Since the reference electrode 2 that is always provided in the ion concentration measuring device 100 is used as the resistance value measuring electrode 61, there is no need to increase the number of parts of the ion concentration measuring device 100.

[0032] <Other embodiments of the present invention> The present invention is not limited to the above-described embodiment. If the surface of the resistance measurement electrode becomes dirty, the measured resistance value may fluctuate. Therefore, it is preferable to further provide a cleaning mechanism 7 for cleaning the surface of the resistance measurement electrode.

[0033] The cleaning mechanism 7 may be, for example, as shown in FIG. 4, one that includes a light source 71 that irradiates the surface of the comparison electrode with ultraviolet light, one that includes an antifouling coating having a self-cleaning effect, such as titanium dioxide, formed on the surface of the comparison electrode, or one that includes a cleaning member that physically scrapes off dirt from the surface of the comparison electrode.

[0034] The resistance value measuring electrode is not limited to the reference electrode, but may be any other electrode or component provided in the ion concentration measuring device, such as a temperature sensor, that also serves the function of the reference electrode. Furthermore, instead of providing a separate earth electrode, another electrode may also serve as the earth electrode.

[0035] A temperature sensor for measuring temperature may be further provided, and the ion concentration measurement results may be further corrected based on information about the temperature output from the temperature sensor.

[0036] In the above embodiment, the working electrode outputs a potential corresponding to the calcium ion concentration. However, the working electrode may be responsive to ammonium ions, or may be responsive to other types of ions such as hydrogen ions, potassium ions, or sodium ions.

[0037] In the above-described embodiment, the case where the working electrode and the reference electrode are housed in a single housing has been described as a composite electrode, but the working electrode and the reference electrode may also have housings that are independent of each other. In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention. [Example]

[0038] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0039] In this example, calcium ion concentration was measured using the ion concentration measuring device described in detail in the above embodiment, and it was confirmed that the accuracy of ion concentration measurement was improved by the ion concentration measuring method according to the present invention. The specific experimental procedure was as follows.

[0040] The sample liquid used was an aqueous solution with a calcium ion concentration of 40 mg / L. Potassium chloride was added to this aqueous solution to prepare a number of sample solutions with different electrical conductivities while maintaining a constant calcium ion concentration.

[0041] For the above-mentioned sample solutions with different electrical conductivities, the resistance count value measured between the reference electrode and the earth electrode, the output potential actually measured between the working electrode and the reference electrode, the corrected potential difference corrected using the resistivity count value, and the calcium ion concentration calculated based on the corrected potential difference were each determined.

[0042] The results of the above experiment showed that the output potential for each sample with different electrical conductivity gradually decreased as the electrical conductivity increased, even though the calcium ion concentration was constant. Furthermore, the same experiment showed that the resistance count value also gradually decreased as the electrical conductivity of the sample increased. Evaluation of these results revealed a relatively high correlation between the change in resistance count value and the change in output potential. The corrected potential difference, corrected using this correlation, showed a significantly smaller change than the change in output potential when the electrical conductivity of the sample was changed, demonstrating stability. Furthermore, the calcium ion concentration calculated using this corrected potential difference and the Nernst equation was confirmed to be stable at approximately 40 mg / L. Thus, it was confirmed that the error in the calcium ion concentration calculated using the corrected potential difference was within the acceptable range.

[0043] Furthermore, the results of the above experiments have shown that the correlation between the resistance count value and the output potential is particularly high when the electrical conductivity of the sample liquid is in the range of 10 mS / cm to 25 mS / cm, and therefore it is presumed that the effects of the ion concentration measuring device and ion concentration measuring method according to the present invention will be more pronounced in sample liquids with electrical conductivity within the above range. [Explanation of symbols]

[0044] 100...Ion concentration measuring device 1...Working electrode 2...Reference electrode 3. Calculation section 6 Resistance measurement section 7 Cleaning mechanism

Claims

1. a working electrode that outputs a measurement potential corresponding to the ion concentration contained in the sample liquid; a reference electrode that outputs a reference potential relative to the measured potential output from the working electrode; a resistance value measuring unit for measuring the resistance value of the sample liquid; a calculation unit that calculates an ion concentration based on the potential difference between the working electrode and the reference electrode and the resistance value, The resistance value measuring unit includes a ground electrode, The ion concentration measuring device, characterized in that the resistance value measuring unit measures the resistance value of the sample liquid between the reference electrode and the earth electrode.

2. The ion concentration measuring device according to claim 1 , wherein the calculation unit corrects the potential difference using the resistance value.

3. 3. The ion concentration measuring device according to claim 1, wherein the working electrode is for detecting a calcium ion concentration or an ammonium ion concentration.

4. The ion concentration measuring device according to any one of claims 1 to 3, wherein the sample liquid has an electrical conductivity in the range of 10 mS / cm to 25 mS / cm.

5. 2. The ion concentration measuring device according to claim 1, further comprising a cleaning mechanism for cleaning the surface of the reference electrode.

6. A method for measuring the concentration of ions contained in a sample liquid, comprising: An ion concentration measurement method characterized by using a working electrode, a comparison electrode, and an earth electrode arranged so as to be in contact with the sample liquid, and calculating the concentration of the ions using the potential difference between the working electrode and the comparison electrode and the resistance value of the sample liquid detected between the comparison electrode and the earth electrode.

7. A program for measuring the concentration of ions contained in a sample liquid, An ion concentration measurement program that causes a computer to function as a calculation unit that calculates the concentration of the ions using a working electrode, a comparison electrode, and an earth electrode that are arranged so as to be in contact with the sample liquid, and using the potential difference between the working electrode and the comparison electrode and the resistance value of the sample liquid detected between the comparison electrode and the earth electrode.

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