Residual chlorine measuring sensor and residual chlorine measuring device using the same

Abstract

To provide a residual chlorine measurement sensor which is less influenced by the conditions of a measurement solution, and a residual chlorine measurement device using the same.SOLUTION: A residual chlorine measurement sensor 10 is provided, comprising a working electrode 11, a cation exchange membrane 12, a porous body 13, and a counter electrode 14 laminated in the described order. The working electrode 11 is provided with a supply port 15 and a discharge port 16 for a measurement solution L. The residual chlorine measurement sensor 10 is configured such that the measurement solution L passes through the working electrode 11 as shown by arrows in Figure 1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a residual chlorine measuring sensor for measuring the residual chlorine concentration in an aqueous solution, and a residual chlorine measuring device using the same. [Background technology]

[0002] Chlorination is a process that uses chlorine to kill certain bacteria and microorganisms in water. Chlorination is used, for example, to sterilize and disinfect tap water, clean kitchens, and disinfect cut vegetables. The oxidizing chlorine remaining in water after chlorination is called residual chlorine. Residual chlorine includes free residual chlorine (hypochlorous acid) that is generated when chlorine reacts with water, and combined residual chlorine (chloramines, etc.) that is generated when the free residual chlorine combines with nitrogen compounds in the water.

[0003] In such chlorination, it is very important to control the concentration of residual chlorine in the water. Methods for measuring residual chlorine concentration include iodometric titration, colorimetric DPD method, DPD spectrophotometric method, amperometric titration, and polarographic method. Among these, the polarographic method measures the current value when residual chlorine is reduced on the electrode surface, and is suitable for continuous measurement.

[0004] For example, Patent Documents 1 and 2 disclose a two-electrode residual chlorine measuring device that includes a detection electrode made of a gold electrode and a counter electrode made of a silver / silver chloride electrode, and applies a predetermined voltage to the detection electrode. By applying a predetermined voltage to the detection electrode of this device, a reduction reaction of residual chlorine occurs at the detection electrode, and an oxidation reaction of silver occurs at the counter electrode, and the residual chlorine concentration in a sample is determined by measuring the current that flows as a result. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-275214 A [Patent Document 2] JP 2015-034741 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the residual chlorine measuring devices of Patent Documents 1 and 2 require the measurement solution to flow relative to the surface of the detection electrode. In order to stably supply the measurement solution, the detection electrode is rotated or vibrated. However, the measurement solution is affected by the temperature, pH, and coexisting substances, which causes errors in the detection sensitivity, and therefore requires correction using a calibration curve. Furthermore, in the residual chlorine measuring devices of Patent Documents 1 and 2, the detecting electrode and the counter electrode are immersed in the measuring solution, making it difficult to reduce the size. The present invention was researched and developed in consideration of these circumstances, and aims to provide a residual chlorine measurement sensor that is less affected by the conditions of the measurement solution, and a residual chlorine measurement device using the same. [Means for solving the problem]

[0007] The applicant of the present invention has made the reaction area of ​​the working electrode sufficiently larger than that of the conventional technology, and has used a mesh-structured gold electrode to measure residual chlorine so that all the residual chlorine in the introduced measurement solution reacts. It has been found that this electrode can measure a stable current value. Furthermore, it has been found that the electrolytic reaction by this electrode is not significantly affected by the concentration of residual chlorine in the measurement solution, the pH of the measurement solution, or the temperature of the measurement solution. The present invention is based on these new findings.

[0008] The residual chlorine measuring sensor of the present invention is characterized in that a working electrode consisting of a gold electrode with a mesh structure, a cation exchange membrane, a porous body impregnated with a solution containing halide ions, and a counter electrode consisting of a silver electrode are laminated in that order, and the working electrode is provided with a supply inlet and a discharge outlet for the measurement solution.

[0009] The residual chlorine measuring sensor of the present invention has a large specific surface area that reacts with residual chlorine because the working electrode is a gold electrode with a mesh structure. Therefore, when a predetermined voltage is applied to this sensor to reduce the residual chlorine in the measurement solution, unlike the conventional case where the electrode is rotated and only a part of the measurement solution reacts, all the residual chlorine in the introduced solution reacts, so a stable current value can be obtained. In addition, since there is a sufficient area for reaction even when used, the activity of the electrode is not likely to decrease. The residual chlorine measuring sensor of the present invention is capable of accurately measuring the residual chlorine concentration in the measurement solution, since the measurement solution is passed through the working electrode by providing a supply port and a discharge port on the working electrode, and the residual chlorine in the measurement solution is passed only through the working electrode by providing a cation exchange membrane between the working electrode and the counter electrode, and the residual chlorine in the measurement solution is allowed to react completely. In particular, even if the residual chlorine concentration in the measurement solution is high, the residual chlorine in the measurement solution can be adjusted to be completely electrolyzed by appropriately setting the flow rate of the measurement solution and the specific surface area of ​​the gold electrode. In other words, the residual chlorine concentration can be calculated from the current value without correction by a calibration curve according to the measurement conditions. In the residual chlorine measurement sensor of the present invention, the measurement solution, which is the electrolyte solution on the working electrode side, is contained in a mesh-structured working electrode, and the solution containing halide ions, which is the electrolyte solution on the counter electrode side, is impregnated into a porous body.In other words, the size of the sensor is independent of the electrolyte solution, can be made small, and is highly productive.

[0010] In the residual chlorine measuring sensor of the present invention, it is preferable that the mesh structure of the gold electrode has a roughness of 20 mesh or more and 200 mesh or less. In the residual chlorine measuring sensor of the present invention, the thickness of the gold electrode is preferably 80 μm or more and 700 μm or less. In the residual chlorine measuring sensor of the present invention, the solution containing halide ions is preferably a mixed solution of an acid and a halide salt. In the residual chlorine measuring sensor of the present invention, the porous body is preferably filter paper.

[0011] The residual chlorine measuring device of the present invention is a residual chlorine measuring device comprising a residual chlorine measuring sensor of the present invention and a voltage application mechanism for applying a voltage to the sensor, and is characterized in that the voltage application mechanism has a measurement mode in which it applies an applied voltage of 50 mV to 500 mV to the sensor. In the residual chlorine measuring device of the present invention, it is preferable that the voltage application mechanism has an electrode cleaning mode in which a reverse current to the current in the measurement mode flows through the sensor. Effect of the Invention

[0012] The residual chlorine measuring sensor of the present invention can react with the residual chlorine in the measurement solution without being affected by other dissolved substances in the measurement solution by applying a predetermined potential, and can obtain a stable oxidation-reduction current. In particular, under predetermined conditions, the residual chlorine in the measurement solution can be entirely electrolyzed, and an accurate residual chlorine concentration can be calculated from the current value without correction using a calibration curve for each condition. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing an embodiment of a residual chlorine measuring sensor of the present invention. [Diagram 2] 1 is a schematic diagram showing an embodiment of a residual chlorine measuring device of the present invention. [Diagram 3] Figure 3a is a schematic diagram showing the state in which a test solution is continuously measured using a residual chlorine measuring device, and Figures 3b and 3c are each a diagram showing an example of an algorithm for a measurement method using the residual chlorine measuring device of Figure 2. [Figure 4] 1 shows an exploded view of an embodiment of a residual chlorine measuring sensor of the present invention. [Diagram 5] 4 is a graph showing the relationship between time and current value in a measurement mode in which residual chlorine is measured using the residual chlorine measuring device of the present invention. [Figure 6] 6a and 6b are graphs showing the relationship between the measured current value of residual chlorine measured using the residual chlorine measuring device of the present invention and the theoretical current value. [Figure 7]1 is a graph showing the results of measurement using the residual chlorine measuring device of the present invention, illustrating the relationship between the electrolysis potential of residual chlorine and its electrolysis efficiency. [Figure 8] Figure 8a is a graph showing the relationship between the pH of the measurement solution and its electrolysis efficiency, which is a measurement result obtained using the residual chlorine measuring device of the present invention, and Figure 8b is a graph showing the relationship between the temperature of the measurement solution and its electrolysis efficiency, which is a measurement result obtained using the residual chlorine measuring device of the present invention. [Figure 9] 4 is a graph showing the results of measurements using the residual chlorine measuring device of the present invention, illustrating the relationship between the roughness (mesh number) of the working electrode and the electrolysis efficiency. [Figure 10] 1 is a graph showing the measurement results using the residual chlorine measuring device of the present invention, illustrating the relationship between the type of cation in the solution on the counter electrode side and the current value. [Figure 11] This is a graph showing measurement results using the residual chlorine measuring device of the present invention, showing the results of measuring the current value continuously in measurement mode and the results of measuring the current value alternately between measurement mode and electrode cleaning mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment.

[0015] [Residual chlorine measurement sensor 10] The residual chlorine measuring sensor 10 in Fig. 1 is formed by laminating a working electrode 11, a cation exchange membrane 12, a porous body 13, and a counter electrode 14 in that order. The working electrode 11 is also provided with a supply port 15 and a discharge port 16 for a measurement solution L. In other words, the measurement solution L is configured to pass through the working electrode 11 as shown by the arrow in Fig. 1.

[0016] [Working electrode 11] The working electrode 11 is a gold electrode having a mesh structure. Examples of gold electrodes include gold mesh and a base metal mesh plated with gold. When gold plating is applied, the base metal mesh is not particularly limited as long as it can be covered entirely with gold plating, and examples thereof include titanium mesh, steel mesh (particularly, stainless steel mesh), nickel mesh, and copper mesh. In particular, titanium mesh and stainless steel mesh, which are stable and have excellent corrosion resistance, are preferred. By using a mesh metal as the working electrode 11 in this way, the reaction area with residual chlorine can be made sufficient. In addition, if the electrode surface is contaminated by electrolysis and the reaction sites are reduced, the measured value becomes unstable, but since it has a sufficient reaction area with residual chlorine, it has higher durability as an electrode than a general electrode. In addition, in this sensor 10, the measurement solution L supplied to the working electrode 11 acts as an electrolyte solution, and cations (protons) are transported to the cation exchange membrane 12. In other words, the mesh-structured working electrode 11 also serves to limit the depth of the liquid junction (reaction flow path), and the effect of voltage drop can be minimized even if the solution resistance of the measurement solution L is high, without providing a special electrolyte on the working electrode side.

[0017] The roughness of the mesh structure of the gold electrode (mesh size per inch length) can be 20 mesh or more and 200 mesh or less. The lower limit of the roughness is preferably 30 mesh or more, and particularly preferably 40 mesh or more. The upper limit of the roughness is preferably 150 mesh or less, 120 mesh or less, 110 mesh or less, and particularly preferably 100 mesh or less. If the roughness is less than 20 mesh, that is, if the mesh of the gold electrode is too coarse, the surface area becomes small and it is not suitable for total electrolysis. On the other hand, if the roughness is more than 200 mesh, that is, if the mesh of the gold electrode is too fine, turbulence with the cation exchange membrane 12 is difficult to occur, the probability of contact with the cation exchange membrane 12 decreases, and the electrolysis efficiency decreases significantly. The thickness of the gold electrode can be appropriately set depending on the conditions of the measurement solution, such as the flow rate of the measurement solution L, and may be 80 μm or more and 700 μm or less. The upper limit of the thickness is preferably 600 μm or less, particularly 400 μm or less. If the thickness is more than 700 μm, for example, a large difference in the depth of the reaction channel occurs between a position away from the cation exchange membrane and a position in contact with the cation exchange membrane, which is not preferable. On the other hand, a thickness less than 80 μm is not practical.

[0018] [Cation exchange membrane 12] The cation exchange membrane 12 completely separates the working electrode 11 from the counter electrode 14. This allows residual chlorine in the measurement solution to be retained on the working electrode side, and halide ions to be retained on the counter electrode side. The cation exchange membrane 12 is not particularly limited, but is preferably a fluorine-based sulfonic acid cation exchange membrane.

[0019] [Porous body 13] The porous body 13 is impregnated with a solution containing halide ions. Examples of the porous body 13 include filter paper, and porous membranes and filters made of synthetic resins, with filter paper being particularly preferred.

[0020] The halide ions in the solution are fluoride ions (F - ), chloride ion (Cl - ), bromide ion (Br - ), iodide ion (I - The cation is not particularly limited, but may be a hydrogen ion (H + ), lithium ion (Li + ), sodium ion (Na + ), potassium ion (K + ), rubidium ion (Rb + ), Cesium ion (Cs + ), hydrogen ions, lithium ions (Li + ), sodium ion is preferred. Hydrogen ion, lithium ion (Li +) Sodium ions have a small ion diameter and move easily through the cation exchange membrane. If the membrane movement is slow, the reaction volume is limited, and the measured value may be low. In particular, a mixed solution of an acid and a halide salt is preferably used, and in this example, a mixed solution of hydrochloric acid (HCl) and sodium chloride (NaCl) was used. In this case, it is preferable that the ratio of hydrochloric acid in the total chlorine concentration in the mixed solution is 3% or more, 6% or more, 10% or more, and particularly 13% or more. By including hydrochloric acid, the electrolysis efficiency is increased. However, from the viewpoints of productivity, handling as a sensor, and safety, it is not realistic to make the ratio of hydrochloric acid in the total chlorine concentration greater than 50%.

[0021] [Opposite 14] The counter electrode 14 is a silver electrode. It reacts with the halide ions contained in the porous body 13 to form silver-silver chloride, but since the electrode potentials of the silver base and silver-silver chloride are similar, it functions not only as a counter electrode but also as a reference electrode.

[0022] [Action and effect of residual chlorine measuring sensor 10] Since the residual chlorine measuring sensor 10 is configured in this way, when a predetermined potential is applied between the working electrode 11 and the counter electrode 14 so that a reduction reaction occurs at the working electrode 11 while a test solution L is being supplied into the working electrode 11, the supplied test solution penetrates into the gap of the working electrode 11, causing a reduction reaction of the residual chlorine (hypochlorous acid). At the same time, an oxidation reaction occurs at the counter electrode 14, converting silver into silver halide. This residual chlorine measuring sensor 10 has a mesh-structured working electrode 11, and therefore has a large specific surface area that reacts with residual chlorine. Therefore, all the residual chlorine in the introduced solution reacts, and residual chlorine can be electrolyzed stably without rotating the electrodes as in the conventional method. This residual chlorine measuring sensor 10 has a supply port 15 and a discharge port 16 on the working electrode 11, and a cation exchange membrane 12 between the working electrode 11 and the counter electrode 14, so that the measurement solution L passes through the working electrode 11 and the residual chlorine in the measurement solution L is retained in the working electrode 11, and therefore the residual chlorine concentration in the measurement solution can be accurately measured. In particular, by setting predetermined conditions, all of the residual chlorine in the measurement solution can be reduced. The applicant has found that when this sensor is used, the residual chlorine is electrolyzed by a two-electron reaction without being significantly affected by the pH and temperature of the measurement solution. Therefore, for a measurement solution having a pH and a temperature within a predetermined range, it is possible to accurately calculate the residual chlorine concentration from the measured current value without making corrections using a calibration curve for each measurement solution by reducing all of the residual chlorine in the measurement solution. Furthermore, since the measurement solution L, which is the electrolyte solution on the working electrode side of the residual chlorine measurement sensor 10, is contained within the working electrode 11, and the electrolyte solution on the counter electrode side is impregnated into the porous body 13, the residual chlorine measurement sensor 10 can be made smaller and is highly productive.

[0023] [Residual chlorine measuring device 100] Next, a residual chlorine measuring device 100 equipped with this residual chlorine measuring sensor 10 will be described. As shown in FIG. 2, the residual chlorine measuring device 100 includes a residual chlorine measuring sensor 10 and a device main body 110 connected to the sensor 10. The device main body 110 includes a voltage application mechanism 111, an ammeter 112, an arithmetic control unit 113, and a display unit 114. The device main body 110 is configured to be detachably connected to the residual chlorine measuring sensor 10. This allows the residual chlorine measuring sensor 10 to be replaced as a consumable item.

[0024] The voltage application mechanism 111 applies a voltage to the residual chlorine measuring sensor 10. In detail, the voltage application mechanism 11 has a measurement mode in which a voltage is applied to the sensor 10 so that a reduction reaction of residual chlorine occurs at the working electrode 11, an electrode cleaning mode in which a reverse current to the current in the measurement mode is passed through the sensor 10, and a standby mode in which no voltage is applied. The residual chlorine measuring device 100 can reduce all of the residual chlorine in the measurement solution passed through the sensor 10, and therefore periodically operates in the measurement mode to continuously measure the residual chlorine concentration in the measurement solution L. In other words, the standby mode and the measurement mode are alternately performed.

[0025] The applied voltage in the measurement mode may be 50 mV or more and 500 mV or less. The lower limit of the applied voltage in the measurement mode is preferably 100 mV or more, particularly 150 mV or more. On the other hand, the upper limit of the applied voltage in the measurement mode is preferably 450 mV or less, particularly 400 mV or less. If the applied voltage in the measurement mode is less than 50 mV, not only the reduction of residual chlorine but also the reduction reaction of dissolved oxygen will be observed. On the other hand, if the applied voltage in the measurement mode is more than 500 mV, the electrolysis efficiency will decrease.

[0026] In the electrode cleaning mode, a reverse current to the measurement mode current is passed through the sensor 10, causing a silver reduction reaction at the counter electrode 14. This returns the gold electrode of the working electrode 11 and the silver electrode of the counter electrode 14 to their original states. For example, when the electrode cleaning mode is performed immediately after the measurement mode, it is possible to pass a reverse current equal to the amount of reaction clones that flowed in the measurement mode, or a reverse current based on that amount of reaction clones. Alternatively, the amount of reaction clones that flow in the measurement mode may be calculated in advance, and a reverse current based on the calculated amount may be periodically passed. As described above, the standby mode is a state in which no voltage is applied.

[0027] The ammeter 112 measures the oxidation-reduction current that flows between the working electrode 11 and the counter electrode 14 when a voltage is applied to the sensor 10 in the measurement mode of the voltage application mechanism 111 .

[0028] The arithmetic and control unit 113 calculates the residual chlorine concentration from the oxidation-reduction current measured by the ammeter 112. For example, the residual chlorine concentration may be calculated by calculating the average current value from the point in time when the current becomes stable after the start of the measurement mode, and calculating the residual chlorine concentration from the average current value. The arithmetic and control unit 113 also controls the voltage application mechanism 111 to switch between the measurement mode, the electrode cleaning mode, and the standby mode. The mode is switched, for example, according to a predetermined algorithm as described below. The display unit 114 displays the residual chlorine concentration calculated by the control unit 113.

[0029] As shown in Fig. 3a, the residual chlorine measuring device 100 operates by supplying the measurement solution L to the sensor 10 with a pump P. This allows continuous measurement of the measurement solution L. The flow rate depends on the residual chlorine concentration of the measurement solution and the specific surface area of ​​the working electrode, etc., and is not particularly limited, but may be, for example, 0.1 ml / min or more and 10 ml / min or less, and is particularly preferably 5 ml / min or less, 2 ml / min or less. When performing such continuous measurements, it is preferable to perform measurements periodically, with one cycle consisting of a measurement mode, an electrode cleaning mode, and a standby mode. Figure 3b shows an example of a measurement method algorithm. One cycle may last, for example, 30 seconds to 1 hour. As shown in Figure 3c, the measurement mode and the standby mode may be alternately performed multiple times (twice each in Figure 3c), and then the electrode cleaning mode may be performed. EXAMPLES

[0030] Next, an embodiment of the residual chlorine measuring sensor of the present invention will be described. As shown in FIG. 4, the sensor 10A of the embodiment is assembled by housing a residual chlorine measuring sensor between end plates 20A and 20B. The working electrode 11 is composed of a gold electrode 21 and a working electrode current collector foil represented by reference numeral 22. The gold electrode 21 was a gold-plated titanium mesh (15 mm×60 mm×200 μm) with a roughness of 100 mesh. As the cation exchange membrane 12, a fluorine-based sulfonic acid cation exchange membrane was used. Filter paper was used as the porous body 13. The solution to be impregnated into the filter paper was a mixed solution of NaCl and HCl with a total chlorine concentration of 3M and a hydrochloric acid concentration of 0.5M. The counter electrode 14 is composed of a silver electrode 23 (15 mm×60 mm×100 μm) and a counter electrode current collector foil represented by the reference numeral 24 . Furthermore, reference numerals 25A, 25B, and 25C denote gaskets, and reference numeral 26 denotes a screw. A first communication hole 20A1 communicating with the supply port 15 of the sensor 10 and a second communication hole 20A2 communicating with the discharge port 16 of the sensor 10 are formed in the end plate 20A (working electrode side). The elements sandwiched between end plates 20A and 20B are compressed and tightly attached to each other and fixed with screws 26. In addition, working electrode current collector foil 22 and counter electrode current collector foil 24 are used to conduct electricity to gold electrode 21 and silver electrode 23, respectively, and are extended to the outside of the end plates.

[0031] [Check the current value] As samples, hypochlorous acid solutions with concentrations of 5 to 50 ppm were prepared. Each sample was passed through the residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and each current value was measured in measurement mode (voltage 300 mV). The time after the voltage application and the current value at that time are shown in FIG. 5. 5, it can be seen that the current stabilizes about 20 seconds after the start of the measurement mode, regardless of the concentration. Therefore, it was found that it is preferable to obtain an average current value from 30 to 60 seconds, for example, and calculate the residual chlorine concentration based on the average current value.

[0032] [Confirmation of residual chlorine reduction reaction] As samples, hypochlorous acid solutions with concentrations of 0 to 50 ppm were prepared. Each sample was passed through the residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and each current value was measured in measurement mode (voltage 300 mV). The concentration, measured current value, and theoretical current value calculated as a two-electron reaction are shown in FIG. 6a. As shown in FIG. 6a, it was confirmed that when the residual chlorine concentration was 0 to 50 ppm, the residual chlorine in the measurement solution was totally electrolyzed by a two-electron reaction. Furthermore, hypochlorous acid solutions with a residual chlorine concentration of 100 to 300 ppm were prepared as samples, and the current value of each sample was measured under the same conditions using the residual chlorine measuring device 100 using the sensor 10A of the embodiment. The results are shown in FIG. 6b. Although the values ​​deviated slightly from the theoretical value due to the high residual chlorine concentration, it was confirmed that total electrolysis was generally performed by a two-electron reaction. From these results, it is presumed that total electrolysis is possible even for high concentrations by reducing the flow rate or further increasing the specific surface area of ​​the working electrode.

[0033] [Residual chlorine reduction potential] A hypochlorous acid solution with a concentration of 50 ppm was prepared as a sample. This sample was passed through a residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and each current value was measured at a potential of -200 mV to 800 mV. The theoretical current value calculated as a two-electron reaction was taken as 100%, and the electrolysis efficiency (%) of each current value was calculated. The results are shown in FIG. As shown in Figure 7, it was found that almost complete electrolysis was possible when the measured potential was in the range of 100 mV to 450 mV. At potentials below 50 mV, not only the reduction reaction of residual chlorine but also the reduction reaction of dissolved oxygen in the solution occurred.

[0034] [Relationship between pH and electrolysis efficiency] As samples, 50 ppm hypochlorous acid solutions adjusted to pH 3.5 to pH 12 were prepared. Each sample was passed through a residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and each current value was measured in measurement mode (voltage 300 mV). The theoretical current value calculated as a two-electron reaction was taken as 100%, and the electrolysis efficiency (%) of each current value was calculated. The results are shown in FIG. 8a. As shown in Fig. 8a, it was found that when the pH is 11 or less, the measurement can be performed with an electrolysis efficiency of 90% or more. In particular, it was found that for pH 3.5 to pH 10.5, the error range from the theoretical value was within 5%. Thus, it was found that the residual chlorine measuring device 100 can accurately measure the residual chlorine concentration in the range of pH 3.5 to pH 11.

[0035] [Relationship between temperature and electrolysis efficiency] As samples, 50 ppm hypochlorous acid solutions were prepared with the temperature adjusted to 5°C to 50°C. Each sample was passed through the residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and each current value was measured in measurement mode (voltage 300 mV). The theoretical current value calculated as a two-electron reaction was set to 100%, and the electrolysis efficiency (%) of each current value was calculated. The results are shown in Figure 8b. As shown in Fig. 8b, it was found that the error of all samples was within 5% of the theoretical value. Thus, it was found that the residual chlorine measuring device 100 can accurately measure the residual chlorine concentration regardless of the temperature of the measurement solution.

[0036] [Relationship between mesh coarseness and electrolysis efficiency] Sensors of Examples 2A to 2F were produced in the same manner as Example 1, except that a mesh shown in Table 1 below was used as the working electrode 11.

[0037] [Table 1]

[0038] As a sample, a 50 ppm hypochlorous acid solution was prepared. The sample was passed through the residual chlorine measuring device 100 using the sensor of Examples 2A to 2F at a flow rate of 1 mL / min, and each current value was measured in measurement mode (voltage 300 mV). The theoretical current value calculated as a two-electron reaction was taken as 100%, and the electrolysis efficiency (%) of each current value was calculated. The results are shown in FIG. In all of the examples, an electrolysis efficiency of 80% or more was obtained. In particular, the sensors of Examples 2B, 2C, and 2D achieved an electrolysis efficiency of 95% or more.

[0039] [Relationship with halide ions] The cations were hydrogen ions (H+), sodium ions (Na+), potassium ions (K+), and cesium ions (Cs+), and solutions were prepared with a standard concentration of 3 M. Except for impregnating filter paper (porous body 13) with these, sensors of Examples 3A to 3D were produced that were the same as Example 1. As a sample, a 250 ppm (pH 9) hypochlorous acid solution was prepared. The sample was passed through the residual chlorine measuring device 100 using the sensors of Examples 3A to 3D at a flow rate of 1 mL / min, and each current value was measured in the measurement mode (voltage 300 mV). The results are shown in FIG. As shown in Fig. 10, a current flowed in the sensors of Examples 3A to 3D. In particular, when hydrogen ions and sodium ions were used as cations, a stable current value was obtained. This is thought to be due to the dependence on the cation exchange membrane used.

[0040] [Relationship with hydrochloric acid concentration] A mixed solution of NaCl and HCl with a total chlorine concentration of 3 M and a hydrochloric acid concentration of 0 M to 0.4 M was prepared, and this was impregnated into filter paper (porous body 13). Except for this, sensors of Examples 4A to 4E were created which were the same as Example 1. As a sample, a 500 ppm (pH 9) hypochlorous acid solution was prepared. The sample was passed through the residual chlorine measuring device 100 using the sensors of Examples 4A to 4E at a flow rate of 1 mL / min, and each current value was measured in the measurement mode (voltage 300 mV). The results are shown in Table 2.

[0041] [Table 2] * Indicates the percentage of hydrochloric acid in the total chlorine concentration in the mixed solution.

[0042] From Table 2, it can be seen that in the case of a mixed solution, the electrolysis efficiency improves by increasing the hydrochloric acid concentration. In particular, the electrolysis efficiency was 90% or more at 0.3M or more, and 95% or more at 0.4M or more.

[0043] [Electrode cleaning] As a sample, a hypochlorous acid solution with a concentration of 50 ppm was prepared. A sample was passed through the residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and the current value was measured continuously for 18 hours in the measurement mode (voltage 300 mV). On the other hand, a sample was passed through the residual chlorine measuring device 100 using the sensor 10A of the embodiment at a flow rate of 1 mL / min, and the current value was measured for 18 hours by alternately switching between the measurement mode (voltage 300 mV) for 30 minutes and the electrode cleaning mode (reverse current 10 mA). The results are shown in FIG. 11. It was found from Figure 11 that the current value decreases when the measurement mode is performed continuously. This is presumably due to (1) the silver on the counter electrode 14 being oxidized to silver chloride, decreasing the reaction sites, (2) the activity of the gold electrode on the working electrode 11 decreasing, and (3) the cations on the functional end of the cation exchange membrane being replaced. On the other hand, when the measurement mode and the electrode cleaning mode were alternately performed, the decrease in the current value could be suppressed. This is presumably because, by periodically passing a reverse current, the silver chloride of the counter electrode 14 was reduced to silver, the working electrode 11 was activated by electrolytic polishing through oxidation, and hydrogen ions generated by the decomposition of water at the working electrode 11 were supplied to and replaced within the cation exchange membrane, returning the cation exchange membrane to its original state. It was found that by appropriately using the electrode cleaning mode in this manner, the durability of the residual chlorine measuring sensor can be further improved. [Explanation of symbols]

[0044] L Measuring solution P-Pump 10 Residual chlorine measurement sensor 11 Working electrode 12 Cation exchange membrane 13 Porous bodies 14 Opposite 15 Supply port 16 Outlet 20A, 20B End Plates 20A1 1st communication hole 20A2 2nd communication hole 21 Gold electrode 22 Working electrode current collector foil 23 Silver electrode 24 Counter electrode current collector foil 25A, 25B, 25C Gaskets 26 Screws 100 Residual chlorine measuring device 110 Device body 111 Voltage application mechanism 112 Ammeter 113 Control Unit 114 Display section

Claims

1. A working electrode consisting of a gold electrode having a mesh structure; A cation exchange membrane; A porous body impregnated with a solution containing halide ions; A counter electrode made of a silver electrode is laminated in this order. The working electrode is provided with a supply port and a discharge port for a measurement solution. Sensor for measuring residual chlorine.

2. The mesh structure of the gold electrode has a roughness of 20 mesh or more and 200 mesh or less.

2. The residual chlorine measuring sensor according to claim 1.

3. The thickness of the gold electrode is 80 μm or more and 700 μm or less.

2. The residual chlorine measuring sensor according to claim 1.

4. The solution containing halide ions is a mixed solution of an acid and a halide salt.

2. The residual chlorine measuring sensor according to claim 1.

5. The porous body is filter paper.

2. The residual chlorine measuring sensor according to claim 1.

6. A residual chlorine measuring device comprising a residual chlorine measuring sensor according to any one of claims 1 to 5 and a voltage applying mechanism for applying a voltage to the sensor, The voltage application mechanism has a measurement mode in which a voltage of 50 mV to 500 mV is applied to the sensor. Device for measuring residual chlorine.

7. The voltage application mechanism has an electrode cleaning mode in which a reverse current to the current in the measurement mode flows through the sensor.

7. The residual chlorine measuring device according to claim 6.

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