Ion concentration measurement method

Abstract

To provide an ion concentration measuring method which reduces an influence of coexistent ions even though coexistent ions are contained in a measuring object liquid, and determines an ion concentration of the measuring object liquid more accurately.SOLUTION: A method for measuring an ion concentration of a measuring object liquid Q uses a measuring device 1 with a measurement unit 2 including: a measuring part 3 retaining the measuring object liquid Q; an ion electrode meter 4 which has a measuring electrode 4E that is disposed by being immersed in the measuring object liquid Q retained by the measuring part 3; and a circulation line 5 for returning the measuring object liquid Q drained from the measuring part 3 to the measuring part 3. The method includes: a measuring step in which a composition of the measuring object liquid Q flowing in the circulation line 5 does not substantially change, and which measures an electric potential of the measuring object liquid Q with the ion electrode meter 4, while the measuring object liquid Q is circulated between the measuring part 3 and the circulation line 5, in order to obtain an electric potential value P for the circulation line 5; and a step for calculating an ion concentration of the measuring object liquid Q from the electric potential value P.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring ion concentrations using an ion electrode meter. [Background technology]

[0002] An ion electrode meter is a device that measures the ion concentration in a solution using an ion selective electrode, and ion concentration measurement using an ion selective electrode is also an official method. For example, Non-Patent Document 1 describes general matters regarding the quantification of ion concentration using an ion selective electrode, including that ion concentration can be determined by measuring potential using an ion selective electrode, that a membrane potential corresponding to ion activity is generated in an ion selective electrode, that activity coefficients fluctuate due to the influence of ionic strength and cause measurement errors, that a high-concentration electrolyte solution is sometimes added as an ionic strength adjusting solution to maintain a constant ionic strength of the solution being measured, and that measurements using an ion selective electrode are affected by coexisting ions, and therefore measures must be taken to avoid this influence. Non-Patent Document 2 describes pretreatment methods and pH conditions during measurement to avoid the influence of coexisting ions in the ion electrode method. Patent Document 1 discloses a method for measuring fluoride ion concentration using an ion electrode meter, which can accurately determine the fluoride ion concentration by suppressing the influence of coexisting ions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 225433 [Non-patent literature]

[0004] [Non-Patent Document 1] Japanese Industrial Standard JIS K 0122-1997 [Non-patent document 2] Japanese Industrial Standard JIS K 0102-2016 Summary of the Invention [Problem to be solved by the invention]

[0005] When measuring ion concentrations using an ion electrode meter, it is desirable to reduce the influence of coexisting ions as much as possible, but even if measures to reduce the influence of coexisting ions are taken as described above, the coexisting ions may still affect the calculated ion concentration. The present invention has been made in consideration of the above circumstances, and its object is to provide an ion concentration measurement method that can reduce the influence of coexisting ions and more accurately determine the ion concentration of a liquid to be measured, even if the liquid to be measured contains coexisting ions. [Means for solving the problem]

[0006] The ion concentration measuring method of the present invention, which has been able to solve the above problems, is as follows. [1] A method for measuring the ion concentration of a liquid to be measured using a measuring device having a measuring unit including a measuring section in which the liquid to be measured is held, an ion electrode meter having a measuring electrode, the measuring electrode being immersed in the liquid to be measured held in the measuring section, and a circulation line for returning the liquid to be measured that has flowed out of the measuring section, In the circulation line, the composition of the liquid to be measured flowing through the circulation line does not substantially change, a measuring step of measuring the potential of the measurement target liquid with the ion electrode meter while circulating the measurement target liquid between the measurement unit and the circulation line, and obtaining a potential value P; The ion concentration measuring method comprises a step of calculating the ion concentration of the liquid to be measured from the potential value P. [2] A measurement unit including a measurement section in which a liquid to be measured is held, an ion electrode meter having a measurement electrode, the measurement electrode being immersed in the liquid to be measured held in the measurement section, and a circulation line for returning the liquid to be measured that has flowed out of the measurement section to the measurement section; a supply line for introducing a liquid to be measured into the measurement unit; a discharge line for discharging the liquid to be measured from the measurement unit; A method for measuring an ion concentration of a liquid to be measured using a measuring device having the supply line is connected to the measurement unit; In the circulation line, the composition of the liquid to be measured flowing through the circulation line does not substantially change, a measuring step of introducing a liquid to be measured into the measurement unit through the supply line, discharging the liquid to be measured from the measurement unit through the discharge line, and measuring the potential of the liquid to be measured with the ion electrode meter while circulating the liquid to be measured between the measurement unit and the circulation line to obtain a potential value P; The ion concentration measuring method comprises a step of calculating the ion concentration of the liquid to be measured from the potential value P. [3] A measurement unit including a measurement section in which a liquid to be measured is held, an ion electrode meter having a measurement electrode, the measurement electrode being immersed in the liquid to be measured held in the measurement section, and a circulation line for returning the liquid to be measured that has flowed out of the measurement section to the measurement section; a supply line for introducing a liquid to be measured into the measurement unit; a discharge line for discharging the liquid to be measured from the measurement unit; A method for measuring an ion concentration of a liquid to be measured using a measuring device having the supply line is connected to the circulation line; In the circulation line, the composition of the liquid to be measured flowing through the circulation line does not substantially change until the connection with the supply line; a measuring step of introducing a liquid to be measured into the measurement unit through the supply line, discharging the liquid to be measured from the measurement unit through the discharge line, and measuring the potential of the liquid to be measured with the ion electrode meter while circulating the liquid to be measured between the measurement unit and the circulation line to obtain a potential value P; The ion concentration measuring method comprises a step of calculating the ion concentration of the liquid to be measured from the potential value P. [4] The measurement unit has a circulation outflow unit through which the measurement target liquid flows out from the measurement unit to the circulation line, and a discharge unit through which the measurement target liquid is discharged from the measurement unit to the discharge line, The ion concentration measurement method according to [2] or [3], wherein the discharge portion is located at a higher position than the circulation outflow portion. [5] The ion concentration measurement method according to any one of [2] to [4], wherein the flow rate of the measurement target liquid circulating between the measurement section and the circulation line is greater than the flow rate of the measurement target liquid introduced into the measurement unit from the supply line. [6] The ion concentration measurement method according to any one of [1] to [5], wherein in the measuring step, the circulation flow rate of the liquid to be measured calculated based on the following formula is 5 (1 / min) or more. Circulation flow rate (1 / min) = (flow rate of the liquid to be measured circulating between the measuring unit and the circulation line per minute) / (volume of the liquid to be measured held in the measuring unit) [7] The measurement unit has a circulation outflow unit through which the measurement target liquid flows out from the measurement unit to the circulation line, and a circulation return unit through which the measurement target liquid is returned from the circulation line to the measurement unit, The ion concentration measurement method according to any one of [1] to [6], wherein the circulation outflow section is positioned higher than the circulation return section. [8] The measurement unit has a circulation outflow unit through which the measurement target liquid flows out from the measurement unit to the circulation line, and a circulation return unit through which the measurement target liquid returns from the circulation line to the measurement unit, The ion concentration measurement method according to any one of [1] to [7], wherein the measurement electrode is installed in the measurement section between the circulation return section and the circulation outflow section. [9] The ion concentration measurement method according to [8], wherein the measurement electrode is disposed opposite the circulation return section. [Effects of the Invention]

[0007] According to the ion concentration measurement method of the present invention, even if the liquid to be measured contains coexisting ions, the influence of the coexisting ions can be reduced and the ion concentration of the liquid to be measured can be determined more accurately. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows an example of the configuration of a measurement device used in the ion concentration measurement method of the present invention. [Figure 2] 1 shows an example of the configuration of a measurement device used in the ion concentration measurement method of the present invention. [Figure 3] 1 shows an example of the configuration of a measurement device used in the ion concentration measurement method of the present invention. [Figure 4] 1 is a flow diagram illustrating an example of a method for calculating an ion concentration from a potential value P measured by an ion electrode meter. [Figure 5] 1 shows a graph plotting the relationship between the circulation flow rate (SV) and the output value of the copper ion concentration determined in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] Conventionally, a method for measuring the concentration of ions in a solution using an ion electrode meter equipped with an ion selective electrode has been known. The ion electrode meter can rapidly measure the concentration of a specific ion in a solution, i.e., the ion to be measured by the ion electrode meter, and can also automatically measure the concentration of the ion. Therefore, the ion electrode meter can be suitably used for, for example, monitoring the concentration of a specific ion in wastewater or in environments such as rivers and lakes, or for automatically analyzing a large number of samples.

[0010] The ion electrode meter comprises an ion-selective electrode, a reference electrode, and a potentiometer that measures the potential difference between these two electrodes. A calculation unit is preferably electrically connected to the potentiometer, thereby converting the potential difference measured by the potentiometer into an ion concentration and returning a response value. The ion-selective electrode is used to measure the concentration of a specific ion in a measurement target solution. The ion-selective electrode has a sensitive membrane that responds to the specific ion being measured, allowing it to selectively respond to the specific ion. When the ion-selective electrode is immersed in the measurement target solution and the specific ion in the measurement target solution comes into contact with the sensitive membrane, a membrane potential corresponding to the ion activity is generated. The ion-selective electrode is then electrically connected to a reference electrode also immersed in the measurement target solution, and a potentiometer is placed between the two electrodes to measure the potential difference between the ion-selective electrode and the reference electrode. The potential difference thus obtained can be converted into an ion concentration based on the Nernst equation, and the calculation unit returns a response value obtained by converting the potential difference measured by the potentiometer into an ion concentration. However, if the response value is simply a conversion of potential difference to ion concentration based on the Nernst equation, it will represent the specific ion concentration in the measured solution if only the specific ion is present. However, if the measured solution contains coexisting ions other than the specific ion, the response value will deviate from the true specific ion concentration. In other words, if the measured solution contains coexisting ions other than the specific ion, the response value of the ion electrode meter will not accurately represent the specific ion concentration in the measured solution. Therefore, when measuring with an ion electrode meter, measures are usually taken to prevent the influence of coexisting ions, such as adding an ionic strength adjuster. This makes it possible to measure the specific ion concentration in the measured solution even if the measured solution contains coexisting ions. In this case, a correlation equation between the response value of the ion electrode meter and the true specific ion concentration is determined depending on the composition of the measured solution, and the specific ion concentration in the measured solution is calculated based on this correlation equation.

[0011] The present invention relates to a method for measuring the ion concentration of a liquid to be measured using an ion electrode meter. The ion concentration of the liquid to be measured is measured using a measuring device having a measurement unit including a measuring section that holds the liquid to be measured, an ion electrode meter having a measuring electrode, the measuring electrode being immersed in the liquid to be measured held in the measuring section, and a circulation line that returns the liquid to the measuring section or to a section upstream of the measuring section. The composition of the liquid to be measured flowing through the circulation line remains substantially unchanged. Alternatively, if a supply line that introduces the liquid to the measuring unit is connected to the circulation line and the liquid to be measured is introduced into the measurement unit through the supply line, the composition of the liquid to be measured flowing through the circulation line remains substantially unchanged from the time it flows from the measuring section to the connection point of the supply line. Furthermore, the ion concentration measuring method of the present invention includes a measuring step in which the potential of the liquid to be measured is measured with the ion electrode meter while the liquid to be measured is circulated between the measuring section and the circulation line to obtain a potential value P, and a step (concentration calculation step) in which the ion concentration of the liquid to be measured is calculated from the potential value P.

[0012] As explained above, when a sample solution contains coexisting ions other than the specific ion, the response value of the ion electrode meter will be affected by the coexisting ions and will not accurately represent the concentration of the specific ion in the sample solution. Therefore, when measuring with an ion electrode meter, measures are usually taken to reduce the influence of the coexisting ions, such as adding an ionic strength adjuster. However, when the inventors incorporated an ion electrode meter into a measurement device to measure the concentration of a specific ion in the sample solution, they found that even with such measures, the resulting potential value P may be lower than the true value. In this case, the potential value P is negatively proportional to the logarithm of the concentration according to the Nernst equation, so the ion concentration calculated from the potential value P will be higher than the true value. To address this issue, it has been found that measuring the potential of the sample solution held in the measurement unit while circulating the sample solution between the measurement unit and the circulation line is an effective solution. By measuring the potential of the sample solution in this manner, the resulting potential value P can be made closer to the true value. The ion concentration method of the present invention is described in detail below.

[0013] 1 to 3 show an example of the configuration of a measurement device used in the ion concentration measurement method of the present invention. The measurement device 1 has a measurement unit 2 including a measurement section 3 that holds a measurement target liquid Q; an ion electrode meter 4 that has a measurement electrode 4E and is immersed in the measurement target liquid Q held in the measurement section 3; and a circulation line 5 that returns the measurement target liquid Q that flows out of the measurement section 3 to the measurement section 3. The measurement section 3 holds the measurement target liquid Q, and the measurement electrode 4E of the ion electrode meter 4 is immersed in the measurement target liquid Q of the measurement section 3. The measurement section 3 may be a water tank (i.e., a measurement tank) that stores the measurement target liquid Q, or it may be a flow path through which the measurement target liquid Q flows. In either case, it is sufficient that the measurement electrode 4E is immersed in the measurement target liquid Q.

[0014] Ions to be measured in the ion concentration measuring method of the present invention include sodium ions, potassium ions, lithium ions, calcium ions, ammonium ions, copper ions, lead ions, cadmium ions, silver ions, fluoride ions, chloride ions, bromide ions, iodide ions, cyanide ions, nitrate ions, and sulfide ions. The measuring electrode 4E of the ion electrode meter 4 has a sensitive membrane that responds to specific ions, allowing it to selectively respond to specific ions.

[0015] The measuring electrode 4E of the ion electrode meter 4 can be a known ion-selective electrode such as a glass membrane electrode, a solid membrane electrode, a liquid membrane electrode, or a diaphragm electrode. The reference electrode of the ion electrode meter 4 can be a known reference electrode such as a single liquid junction electrode or a double liquid junction electrode, and the internal liquid (electrolyte) may be held in a liquid state or a gel state inside the electrode.

[0016] The type of the measurement target liquid Q is not particularly limited, and may or may not contain specific ions. Examples of specific target liquids include wastewater (including treatment process water) from business establishments such as factories, power plants, refineries, mines, hospitals, and laboratories, and environmental water such as river water and lake water. Examples of wastewater from factories include wastewater generated in various factories producing iron and steel, non-ferrous metals, machinery, metal processing, plating, painting, electronic parts, glass, cement, etc.

[0017] The measurement target liquid Q preferably contains specific ions, and may further contain ions other than the specific ions. Note that the higher the concentration of ions other than the specific ions in the measurement target liquid Q, the more favorably the effects of the present invention are exhibited, so the measurement target liquid Q preferably contains ions other than the specific ions. More preferably, the measurement target liquid Q contains a larger amount (on a molar basis) of ions other than the specific ions than the specific ions. Note that the type of ions other than the specific ions is not particularly limited.

[0018] As an index representing the total amount of ions contained in the measurement target liquid Q, the measurement target liquid Q preferably has an evaporation residue of 0.05 g / L or more, more preferably 0.1 g / L or more, even more preferably 0.3 g / L or more, and preferably 300 g / L or less, more preferably 200 g / L or less, and even more preferably 100 g / L or less. This allows the effects of the present invention to be more suitably exhibited. The evaporation residue can be determined in accordance with JIS K 0067-1992.

[0019] The measurement unit 3 may be configured so that the measurement target liquid Q flows upward, downward, or sideways. In Figures 2 to 4, the measurement unit 3 is configured so that the measurement target liquid Q flows upward.

[0020] The ion electrode meter 4 (specifically, the portion including the measurement electrode 4E) may be inserted and installed from the top, bottom, or side of the measurement unit 3. For ease of maintenance of the ion electrode meter 4, it is preferable that the ion electrode meter 4 be inserted and installed from the top of the measurement unit 3. This makes it easy to remove the ion electrode meter 4 from the measurement unit 3 while the measurement target liquid Q is held in the measurement unit 3.

[0021] The measurement unit 2 is provided with a circulation line 5 that returns the measurement target liquid Q flowing out from the measurement unit 3 to the measurement unit 3. This allows the measurement target liquid Q to circulate between the measurement unit 3 and the circulation line 5. The circulation line 5 refers to the section from when the measurement target liquid Q leaves the measurement unit 3 to when it returns to the measurement unit 3. Specifically, the measurement unit 3 has a circulation outflow section 6 through which the measurement target liquid Q flows out from the measurement unit 3 to the circulation line 5, and a circulation return section 7 through which the measurement target liquid Q is returned from the circulation line 5 to the measurement unit 3. The circulation line 5 is connected to the circulation outflow section 6 and the circulation return section 7. In the present invention, during the measurement process, the measurement target liquid Q is circulated between the measurement unit 3 and the circulation line 5, and the potential of the measurement target liquid Q held in the measurement unit 3 is measured with the ion electrode meter 4 to obtain a potential value P. By measuring the potential of the measurement target liquid Q in this manner, the obtained potential value P can be made closer to the true value. The effect of circulating the measurement target liquid Q, which allows the potential value P to be made closer to the true value, becomes more pronounced as the coexisting ion concentration increases.

[0022] The method for measuring ion concentration of the present invention includes a batch measurement method and a continuous measurement method. In the case of a batch measurement method, new measurement target liquid Q is not supplied to the measurement unit 2 in the measurement step. In the case of a continuous measurement method, new measurement target liquid Q is supplied to the measurement unit 2 in the measurement step.

[0023] 1 shows an example of the configuration of the measuring device 1 when performing batch-type measurement. When performing batch-type measurement, the composition of the measurement target liquid Q flowing through the circulation line 5 does not change substantially, and in the measurement step, the measurement target liquid Q is circulated between the measurement section 3 and the circulation line 5, while the potential of the measurement target liquid Q held in the measurement section 3 is measured with the ion electrode meter 4. When performing batch-type measurement, the measuring device 1 may be provided with a supply line for introducing the measurement target liquid Q into the measurement unit 2 and a discharge line for discharging the measurement target liquid Q from the measurement unit 2, but during the measurement step, the measurement target liquid Q is not introduced into the measurement unit 2 through the supply line, and the measurement target liquid Q is not discharged from the measurement unit 2 through the discharge line.

[0024] 2 and 3 show an example of the configuration of the measurement device 1 when performing continuous measurement. When performing continuous measurement, the measurement device 1 is provided with a supply line 8 that introduces the measurement target liquid Q into the measurement unit 2 and a discharge line 10 that discharges the measurement target liquid Q from the measurement unit 2. During the measurement process, the measurement target liquid Q is introduced into the measurement unit 2 through the supply line 8 and discharged from the measurement unit 2 through the discharge line 10, and the measurement target liquid Q is circulated between the measurement section 3 and the circulation line 5, while the potential of the measurement target liquid Q held in the measurement section 3 is measured with the ion electrode meter 4.

[0025] In FIG. 2, the supply line 8 is directly connected to the measurement unit 3, and therefore the supply line 8 is not connected to the circulation line 5. The measurement device 1 is configured so that new liquid to be measured Q is directly supplied to the measurement unit 3 through the supply line 8; that is, the measurement unit 3 has a supply unit 9 through which new liquid to be measured Q is supplied to the measurement unit 3 from the supply line 8, and the supply line 8 is connected to the supply unit 9 of the measurement unit 3. In FIG. 2, the composition of the liquid to be measured Q flowing through the circulation line 5 does not substantially change. In the measurement step, new liquid to be measured Q is supplied to the measurement unit 3 through the supply line 8, and the liquid to be measured Q is discharged from the measurement unit 3 through the discharge line 10.

[0026] In FIG. 3, the supply line 8 is connected to the circulation line 5, and the measuring device 1 is configured so that new liquid to be measured Q is supplied from the supply line 8 through the circulation line 5 to the measuring unit 3. In this case, the composition of the liquid to be measured Q flowing through the circulation line 5 does not change substantially up to the connection point of the supply line 8 (specifically, in the range of the circulation line 5 from leaving the measuring unit 3 to the connection point of the supply line 8). In the measurement step, new liquid to be measured Q is supplied from the supply line 8 through the circulation line 5 to the measuring unit 3, and the liquid to be measured Q is discharged from the measuring unit 3 through the discharge line 10.

[0027] In the case of continuous measurement, the discharge line 10 may be connected to the measurement unit 3 or to the circulation line 5. In the former case, the measurement target liquid Q held in the measurement unit 3 is directly discharged from the discharge line 10, and in the latter case, the measurement target liquid Q held in the measurement unit 3 is drawn into the discharge line 10 from the middle of the circulation line 5. In Figures 2 and 3, the measurement unit 3 has a discharge unit 11 that discharges the measurement target liquid Q from the measurement unit 3 to the discharge line 10, and the discharge line 10 is connected to the discharge unit 11 of the measurement unit 3.

[0028] The composition of the liquid Q to be measured flowing through the circulation line 5 does not change substantially means that other components are not added to the liquid Q to be measured, components contained in the liquid Q to be measured are not removed, and the liquid Q to be measured is not intentionally concentrated or diluted in the circulation line 5.

[0029] It is preferable that a liquid feed pump is provided in the circulation line 5. As a result, the measurement target liquid Q held in the measurement unit 3 is drawn into the circulation line 5 by the liquid feed pump, and the measurement target liquid Q drawn into the circulation line 5 is sent out by the liquid feed pump and returned to the measurement unit 3.

[0030] In the measurement step, it is preferable to circulate as much of the measurement target liquid Q as possible between the measurement unit 3 and the circulation line 5, thereby making it possible to bring the potential value P closer to the true value. The circulation flow rate of the measurement target liquid Q can be expressed by the following formula. The flow rate of the measurement target liquid Q circulating between the measurement unit 3 and the circulation line 5 can be calculated, for example, from the discharge rate of a liquid feed pump. Circulation flow rate (1 / min) = (flow rate of the measurement object liquid Q circulating between the measurement unit 3 and the circulation line 5 per minute) / (volume of the measurement object liquid Q held in the measurement unit 3)

[0031] The circulation flow rate represented by the above formula is preferably, for example, 5 (1 / min) or more, which makes it easier to optimally demonstrate the effect of circulating the measurement target liquid Q. The circulation flow rate is more preferably 10 (1 / min) or more, even more preferably 15 (1 / min) or more, and particularly preferably 20 (1 / min) or more. On the other hand, there is no particular upper limit to the circulation flow rate, and it may be, for example, 100 (1 / min) or less. However, in order to avoid excessive specifications for the liquid delivery pump and circulation line 5 and taking into consideration the performance and utility costs of the liquid delivery pump, a value of 50 (1 / min) or less is preferred, more preferably 40 (1 / min) or less, and even more preferably 30 (1 / min) or less is preferred.

[0032] When performing continuous measurement, the flow rate of the sample liquid Q circulating between the measurement section 3 and the circulation line 5, i.e., the circulation flow rate, is preferably greater than the flow rate of the sample liquid Q introduced into the measurement unit 2 from the supply line 8. This allows for stable measurement of the potential of the sample liquid Q even if the composition of the sample liquid Q introduced into the measurement unit 2 from the supply line 8 fluctuates slightly. For example, the circulation flow rate is preferably at least twice, and more preferably at least three times, the flow rate of the sample liquid Q introduced into the measurement unit 2 from the supply line 8. There is no particular upper limit to the ratio of the circulation flow rate to the flow rate of the sample liquid Q introduced into the measurement unit 2 from the supply line 8. However, in order to easily ensure the circulation flow rate, the circulation flow rate is preferably no more than 50 times, more preferably no more than 20 times, and even more preferably no more than 10 times the flow rate of the sample liquid Q introduced into the measurement unit 2 from the supply line 8.

[0033] In the measurement step, it is preferable to promote contact between the measurement electrode 4E and the measurement liquid Q flowing through the measurement unit 3. From this perspective, it is preferable that the measurement electrode 4E be installed between the circulation return unit 7 and the circulation outflow unit 6 in the measurement unit 3. Specifically, it is preferable that the measurement electrode 4E be installed in the measurement unit 3, midway between the circulation return unit 7 and the circulation outflow unit 6 as the measurement liquid Q flows. For example, when the measurement liquid Q flows upward or downward in the measurement unit 3, it is preferable that the measurement electrode 4E be installed vertically between the circulation return unit 7 and the circulation outflow unit 6. When the measurement liquid Q flows horizontally in the measurement unit 3, it is preferable that the measurement electrode 4E be installed horizontally between the circulation return unit 7 and the circulation outflow unit 6. Installing the measurement electrode 4E in this manner increases the frequency with which the measurement electrode 4E comes into contact with the measurement liquid Q flowing through the measurement unit 3, making it easier to bring the potential value P obtained by measuring the potential of the measurement liquid Q with the ion electrode meter 4 closer to the true value.

[0034] The measurement electrode 4E is preferably installed facing the circulation return section 7. Installing the ion electrode 4 in this manner promotes contact between the measurement electrode 4E and the measurement liquid Q flowing through the measurement unit 3. Since the measurement electrode 4E is usually provided at the tip of the ion electrode 4, the ion electrode 4 is preferably installed in the measurement unit 3 so that the tip of the ion electrode 4 faces the circulation return section 7. For example, when the measurement liquid Q flows upward in the measurement unit 3, the ion electrode 4 (specifically, the portion of the ion electrode 4 including the measurement electrode 4E) is preferably inserted and installed from the top of the measurement unit 3. When the measurement liquid Q flows downward in the measurement unit 3, the ion electrode 4 is preferably inserted and installed from the bottom of the measurement unit 3. When the measurement liquid Q flows sideways in the measurement unit 3, the ion electrode 4 is preferably inserted and installed from the side of the measurement unit 3, opposite the flow direction of the measurement liquid Q.

[0035] It is preferable that the measurement object liquid Q flows upward in the measurement unit 3. Specifically, it is preferable that the measurement object liquid Q circulating between the measurement unit 3 and the circulation line 5 flows upward in the measurement unit 3. Therefore, it is preferable that the circulation outflow part 6 of the measurement unit 3 is located higher than the circulation return part 7. By providing the circulation outflow part 6 and the circulation return part 7 in this way, it becomes easier to maintain the state in which the measurement electrode 4E is immersed in the measurement object liquid Q, and further promotes contact between the measurement electrode 4E and the measurement object liquid Q.

[0036] When performing continuous measurement, it is preferable that the outlet 11, through which the measurement object liquid Q is discharged from the measurement unit 3 to the discharge line 10, is located higher than the circulation outlet 6, through which the measurement object liquid Q flows out from the measurement unit 3 to the circulation line 5. By providing the outlet 11 and the circulation outlet 6 in this manner, the measurement object liquid Q held in the measurement unit 3 can be reliably extracted from the circulation outlet 6 even if the circulation flow rate is increased. This makes it easy to circulate the measurement object liquid Q between the measurement unit 3 and the circulation line 5.

[0037] 2, when the measurement unit 3 is provided with a supply unit 9 to which new measurement target liquid Q is supplied, it is preferable that the discharge unit 11 is located at a higher position than the circulation outflow unit 6, and the supply unit 9 is located at a lower position than the circulation outflow unit 11. By configuring the measurement unit 3 in this way, the new measurement target liquid Q supplied from the supply unit 9 to the measurement unit 3 can be more easily and quickly mixed with the measurement target liquid Q already held in the measurement unit 3.

[0038] In the measurement step, the potential of the measurement target solution Q is measured using an ion electrode meter 4 to obtain a potential value P. Then, in the concentration calculation step, the ion concentration of the measurement target solution Q is calculated from the potential value P. In the concentration calculation step, a calibration curve corresponding to the composition of the measurement target solution Q is created, and the concentration of a specific ion in the measurement target solution Q is determined based on the calibration curve. That is, the potential value P obtained in the measurement step is converted into the concentration of a specific ion corresponding to the composition of the measurement target solution Q based on the calibration curve. Measurements using an ion electrode meter can be performed in accordance with JIS K 0122-1997. For details on creating a calibration curve and determining ion concentrations, see "6.4 Measurement Methods" in the JIS. To reduce the influence of coexisting ions, for example, an ionic strength adjuster can be added to the standard solution and the measurement target solution Q to ensure equal ionic strengths. If a specific ion forms a complex in the measurement target solution Q, the complex can be dissociated by adding a complex dissociator or adjusting the pH before measurement.

[0039] In the concentration calculation step, the specific ions can be removed from the measurement target solution Q using an adsorbent, and then a known amount of the specific ions can be added to prepare a reference solution, and a calibration curve can be created based on the measurement of the reference solution to determine the ion concentration, in accordance with the method described in International Publication No. 2019 / 225433. This method also reduces the influence of coexisting ions. In this case, as shown in FIG. 4, the concentration calculation step preferably includes the following steps: bringing the measurement target liquid into contact with an adsorbent that adsorbs the specific ion to be measured by the ion electrode meter to obtain a specific ion-removed liquid (specific ion removal step); adding the specific ion to the specific ion-removed liquid to prepare a first reference liquid with a specific ion concentration C1 (first reference liquid preparation step); preparing a second reference liquid with a specific ion concentration C2 with or without adding the specific ion to the specific ion-removed liquid (second reference liquid preparation step); measuring the potential of the first reference liquid with the ion electrode meter to obtain a potential value P1 (first reference liquid measurement step); measuring the potential of the second reference liquid with the ion electrode meter to obtain a potential value P2 (second reference liquid measurement step); creating a calibration curve showing the correlation between the specific ion concentration and the potential value using the specific ion concentrations C1 and C2 and the potential values ​​P1 and P2 (calibration curve creation step); and calculating the specific ion concentration of the measurement target liquid Q corresponding to the potential value P based on the calibration curve (concentration conversion step).

[0040] In the specific ion removal step, the measurement target liquid is brought into contact with an adsorbent that adsorbs specific ions to obtain a specific ion-removed liquid. The measurement target liquid subjected to the specific ion removal step may be from the same batch as the measurement target liquid introduced into the measurement section or measurement unit in the measurement step, or may be from a different batch. In the former case, for example, a portion of the measurement target liquid collected in one batch is subjected to the measurement step, and the other portion is subjected to the specific ion removal step. Alternatively, the measurement target liquid whose potential has been measured in the measurement step may be subjected to the specific ion removal step.

[0041] The adsorbent may be a known adsorbent capable of adsorbing a specific ion. The liquid to be measured may be contacted with the adsorbent in a tank or by passing the liquid through an adsorption column.

[0042] In the specific ion removal step, the liquid to be measured is brought into contact with an adsorbent to obtain a specific ion-removed liquid in which specific ions have been removed from the liquid to be measured. Note that the specific ion concentration in the specific ion-removed liquid does not have to be completely 0 mg / L. The specific ion concentration in the specific ion-removed liquid is, for example, preferably 3 mg / L or less, more preferably 2 mg / L or less, even more preferably 1 mg / L or less, and particularly preferably 0.5 mg / L or less.

[0043] The specific ion-removed solution obtained in the specific ion removal step is then added in a first reference solution preparation step and a second reference solution preparation step to prepare a first reference solution with a specific ion concentration C1 and a second reference solution with a specific ion concentration C2. In the second reference solution preparation step, the second reference solution may be prepared without adding the specific ion. In the first reference solution preparation step and the second reference solution preparation step, it is preferable to prepare a specific ion solution of a predetermined concentration in advance and adjust the amount of specific ion solution added depending on the specific ion concentration of the first reference solution and the second reference solution. This makes it easy to prepare the first reference solution and the second reference solution with the desired specific ion concentration. It is convenient to use a specific ion standard solution with a known specific ion concentration as such a specific ion solution.

[0044] Following the first and second reference solution preparation steps, the potentials of the first and second reference solutions are measured using an ion electrode meter in the first and second reference solution measurement steps. The ion electrode meter used to measure the first and second reference solutions may be the same as or different from the ion electrode meter used to measure the solution to be measured. In the first reference solution measurement step, a potential value P1 is obtained as the potential of the first reference solution having a specific ion concentration C1. In the second reference solution measurement step, a potential value P2 is obtained as the potential of the second reference solution having a specific ion concentration C2.

[0045] Next, in the calibration curve creation step, a calibration curve showing the correlation between the specific ion concentration and the potential value is created using the specific ion concentrations C1 and C2 and the potential values ​​P1 and P2. To create the calibration curve, the horizontal axis is the potential value and the vertical axis is the logarithm of the specific ion concentration, and the specific ion concentration C1 vs. the potential value P1 of the first reference solution and the specific ion concentration C2 vs. the potential value P2 of the second reference solution are plotted, and the calibration curve can be created by linear approximation.

[0046] Once the calibration curve is obtained in the calibration curve creation step, the concentration of a specific ion in the measurement target liquid Q corresponding to the potential value P is calculated based on the calibration curve in the concentration conversion step. This makes it possible to determine the ion concentration of the measurement target liquid Q. [Example]

[0047] The present invention will be described in more detail below by showing examples, but the scope of the present invention is not limited to these examples.

[0048] (1) Experimental method Using the measurement device shown in Figure 1, the potential of the measurement liquid was measured with an ion electrode meter while the measurement liquid was circulated between the measurement unit and the circulation line. The ion electrode meter was equipped with a measurement electrode for copper ions, and the measurement liquid contained 100 mg / L of copper ions and 0.3 g / L of coexisting ions as evaporation residue. The measurement liquid was circulated at various circulation flow rates. A calibration curve was created according to the method described in International Publication No. 2019 / 225433 using the procedure shown in Figure 4. Based on this calibration curve, the potential value measured with the ion electrode meter was converted to copper ion concentration and calculated as an output value.

[0049] (2) Results Figure 5 shows a plot of the relationship between the circulation flow rate (SV) and the output value of copper ion concentration. As shown in Figure 5, the output value approached the true copper ion concentration of 100 mg / L as the circulation flow rate increased. In Figure 5, the output value became almost the same as the true value when the circulation flow rate exceeded 20 (1 / min), but even at a circulation flow rate of 6 (1 / min), the difference between the output value and the true value was halved compared to when there was no circulation, confirming the effectiveness of circulation. Since the difference between the output value and the true value increases as the coexisting ion concentration increases, when the coexisting ion concentration is low, the output value can be brought closer to the true value with a lower circulation flow rate. [Industrial Applicability]

[0050] The present invention can be used in wastewater treatment and environmental water measurements. [Explanation of symbols]

[0051] 1: Measuring equipment 2: Measurement unit 3: Measurement section 4: Ion electrode meter, 4E: Measuring electrode 5: Circulation Line 6: Circulation outflow section 7: Circulation return section 8: Supply line 9: Supply section 10: Discharge line 11: Discharge section Q: What liquid is being measured?

Claims

1. a measurement unit including a measurement section in which a liquid to be measured is held, an ion electrode meter having a measurement electrode, the measurement electrode being immersed in the liquid to be measured held in the measurement section, and a circulation line for returning the liquid to be measured that has flowed out of the measurement section to the measurement section; a supply line for introducing a liquid to be measured into the measurement unit; a discharge line for discharging the liquid to be measured from the measurement unit; A method for measuring an ion concentration of a liquid to be measured using a measuring device having the supply line is connected to the measurement unit; In the circulation line, the composition of the liquid to be measured flowing through the circulation line does not substantially change, a measuring step of introducing a liquid to be measured into the measuring unit through the supply line, discharging the liquid to be measured from the measuring unit through the discharge line, and measuring the potential of the liquid to be measured with the ion electrode meter while circulating the liquid to be measured between the measuring unit and the circulation line to obtain a potential value P; The ion concentration measuring method further comprises a step of calculating the ion concentration of the liquid to be measured from the potential value P.

2. a measurement unit including a measurement section in which a liquid to be measured is held, an ion electrode meter having a measurement electrode, the measurement electrode being immersed in the liquid to be measured held in the measurement section, and a circulation line for returning the liquid to be measured that has flowed out of the measurement section to the measurement section; a supply line for introducing a liquid to be measured into the measurement unit; a discharge line for discharging the liquid to be measured from the measurement unit; A method for measuring an ion concentration of a liquid to be measured using a measuring device having the supply line is connected to the circulation line; In the circulation line, the composition of the liquid to be measured flowing through the circulation line does not substantially change until the connection with the supply line; a measuring step of introducing a liquid to be measured into the measuring unit through the supply line, discharging the liquid to be measured from the measuring unit through the discharge line, and measuring the potential of the liquid to be measured with the ion electrode meter while circulating the liquid to be measured between the measuring unit and the circulation line to obtain a potential value P; The ion concentration measuring method further comprises a step of calculating the ion concentration of the liquid to be measured from the potential value P.

3. the measurement unit has a circulation outflow unit through which the measurement target liquid flows out from the measurement unit to the circulation line, and a discharge unit through which the measurement target liquid is discharged from the measurement unit to the discharge line, The ion concentration measuring method according to claim 1 or 2, wherein the outlet portion is located higher than the circulation outlet portion.

4. 3. The ion concentration measuring method according to claim 1, wherein a flow rate of the measurement target liquid circulating between the measuring section and the circulation line is greater than a flow rate of the measurement target liquid introduced into the measurement unit from the supply line.

5. 3. The ion concentration measuring method according to claim 1, wherein in the measuring step, the circulation flow rate of the liquid to be measured calculated based on the following formula is 5 (1 / min) or more. Circulation flow rate (1 / min) = (flow rate of the liquid to be measured circulating between the measuring unit and the circulation line per minute) / (volume of the liquid to be measured held in the measuring unit)

6. the measuring unit has a circulation outflow unit through which the liquid to be measured flows out from the measuring unit to the circulation line, and a circulation return unit through which the liquid to be measured is returned from the circulation line to the measuring unit, The ion concentration measuring method according to claim 1 or 2, wherein the circulation outflow section is located at a higher position than the circulation return section.

7. the measuring unit has a circulation outflow unit through which the liquid to be measured flows out from the measuring unit to the circulation line, and a circulation return unit through which the liquid to be measured is returned from the circulation line to the measuring unit, The ion concentration measuring method according to claim 1 or 2, wherein the measuring electrode is installed in the measuring section between the circulation return section and the circulation outflow section.

8. The ion concentration measuring method according to claim 7 , wherein the measuring electrode is disposed opposite the circulation return section.

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