Residual chlorine measuring device, residual chlorine measuring method, and composite sensor for residual chlorine measuring

Abstract

This invention provides a residual chlorine measuring device, a residual chlorine measuring method, and a composite sensor for residual chlorine measurement that can simultaneously quantify free chlorine and combined chlorine. [Solution] A residual chlorine measuring device 1 comprising a flow path 10, a pump 20 for flowing a measurement solution L through the flow path 10, a first measuring unit 30 for measuring the concentration of free chlorine in the measurement solution L, and a second measuring unit 40 provided downstream of the first measuring unit for measuring the concentration of bound chlorine in the measurement solution L. The first measuring unit 30 comprises a first electrolytic cell 31 that reduces all of the free chlorine in the measurement solution L by applying a first voltage, and a first calculation unit 34 that calculates the concentration of free chlorine from its oxidation-reduction current. The second measuring unit 40 comprises a second electrolytic cell 41 that reduces all of the bound chlorine in the measurement solution L by applying a second voltage lower than the first voltage, and a second calculation unit 44 that calculates the concentration of bound chlorine from its oxidation-reduction current.

Description

[Technical Field]

[0001] The present invention relates to a residual chlorine measuring device, a residual chlorine measuring method, and a composite sensor for measuring residual chlorine, for measuring the concentrations of free chlorine and combined chlorine in an aqueous solution. [Background technology]

[0002] Chlorine treatment is a process that kills specific bacteria and microorganisms in water using chlorine. Such chlorine treatment is used for sterilization and disinfection of tap water, swimming pools, public baths, kitchens, and washing water for cut vegetables. The chlorine that remains in the water after chlorine treatment and still has oxidizing power is called residual chlorine. Residual chlorine includes free chlorine (chlorine, hypochlorous acid, hypochlorite ions) which is produced when chlorine reacts with water, and combined chlorine (monochloramine, dichloramine, trichloramine) which is produced when free chlorine combines with nitrogen compounds in the water. It is known that at pH 7-8, free chlorine exists as hypochlorite ions, and combined chlorine exists as trichloramine.

[0003] In chlorine treatment like this, controlling the concentration of residual chlorine in the water is extremely important. For example, the residual chlorine concentration in tap water is 0.1 ppm to 0.4 ppm, in swimming pools it is 0.4 ppm to 1.0 ppm, in public baths it is 0.4 ppm to 1.0 ppm, and in water used to wash cut vegetables it is 200 ppm or less. In particular, in hemodialysis water, the concentration must be less than 0.1 ppm because the presence of bound chlorine can permeate the dialysis membrane and destroy red blood cells, leading to hemolysis. On the other hand, known methods for measuring residual chlorine concentration include iodine titration, colorimetric DPD method, DPD spectrophotometric method, electrostatic titration, and electrochemical method. Among these, the electrochemical method (polarographic method) measures residual chlorine based on the current value at which it is reduced on the electrode surface. Since it can be measured without reagents, it is suitable for continuous measurement. However, it has drawbacks such as the need for calibration curve calibration and temperature correction, and the complicated maintenance of the electrodes.

[0004] As shown in Patent Document 1, the applicant has developed a cartridge-type residual chlorine measuring sensor that does not require calibration curve calibration or temperature correction and has easy electrode maintenance. This residual chlorine measuring sensor consists of a working electrode made of a gold electrode exhibiting a mesh structure, a cation exchange membrane, a porous body impregnated with a solution containing halide ions, and a counter electrode made of a primary electrode, all stacked in that order. Because the working electrode of this residual chlorine measuring sensor has a mesh structure, it has a large specific surface area that reacts with residual chlorine, and can reduce the entire amount of residual chlorine in the measurement solution flowing through the working electrode to measure the residual chlorine concentration. Therefore, calibration curve calibration and temperature correction are not required within a predetermined pH range or temperature. In addition, because it has a large specific surface area, it has the characteristic that the activity of the electrode does not easily decrease. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-31671 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the residual chlorine sensor described in Patent Document 1 measures the total amount of free chlorine and bound chlorine. The applicant has been working on developing a method to quantify free chlorine and bound chlorine simultaneously or continuously as the next challenge. [Means for solving the problem]

[0007] In response to this problem, the applicant diligently investigated the reduction potentials of free chlorine and bound chlorine, and found that the reduction potential of free chlorine is higher than that of bound chlorine. Therefore, by electrolyzing the measurement solution at different reduction potentials, free chlorine and bound chlorine can be reduced separately and quantified. Furthermore, it was found that by measuring free chlorine and bound chlorine in succession, both can be quantified from the measurement solution. This invention is based on these new findings.

[0008] The present invention provides a residual chlorine measuring device for measuring residual chlorine in a measurement solution, comprising: a flow path; a pump for flowing the measurement solution through the flow path; a first measuring unit for measuring the concentration of free chlorine in the measurement solution; and a second measuring unit provided downstream of the first measuring unit for measuring the concentration of bound chlorine in the measurement solution. The first measuring unit comprises a first electrolytic cell that reduces all of the free chlorine in the measurement solution by applying a first voltage, and a first calculation unit that calculates the concentration of free chlorine from the oxidation-reduction current of the first electrolytic cell. The second measuring unit comprises a second electrolytic cell that reduces all of the bound chlorine in the measurement solution by applying a second voltage smaller than the first voltage, and a second calculation unit that calculates the concentration of bound chlorine from the oxidation-reduction current of the second electrolytic cell. Here, "total reduction of free chlorine" and "total reduction of combined chlorine" refer to the substantial removal of free chlorine and combined chlorine from the incoming measurement solution through reduction reactions.

[0009] The residual chlorine measuring device of the present invention can measure both free and combined chlorine because, in the first measuring unit, the entire amount of free chlorine in the measurement solution flowing through is reduced, and the concentration is measured based on the resulting current; and then, continuously, in the second measuring unit, the entire amount of combined chlorine in the measurement solution flowing through is reduced, and the concentration is measured based on the resulting current. In particular, since the first electrolytic cell of the first measuring unit reduces the entire amount of free chlorine in the measurement solution, and the second electrolytic cell of the second measuring unit reduces the entire amount of combined chlorine, calibration of calibration curves and temperature correction at predetermined pH ranges (especially around pH 7) and predetermined temperatures (especially room temperature) are unnecessary. The residual chlorine measuring device of the present invention, configured in this way, can be miniaturized.

[0010] The present invention provides a residual chlorine measuring device, wherein the first measuring unit comprises: a first electrolytic cell having a mesh structure, a first cation exchange membrane, and a first counter electrode stacked in that order, and the first working electrode being provided with a first supply port for supplying the measuring solution from the flow channel and a first discharge port for discharging the measuring solution into the flow channel; a first voltage applying mechanism for applying a voltage to the first electrolytic cell; a first ammeter for measuring the oxidation-reduction current of the first electrolytic cell; and a first calculation unit. The second measuring unit comprises: a second electrolytic cell having a mesh structure, a second cation exchange membrane, and a second counter electrode stacked in that order, and the second working electrode being provided with a second supply port for supplying the measuring solution from the flow channel and a second discharge port for discharging the measuring solution into the flow channel; a second voltage applying mechanism for applying a voltage to the second electrolytic cell; a second ammeter for measuring the oxidation-reduction current of the second electrolytic cell; and a second calculation unit.

[0011] In this case, since the measurement solution is circulated only within the working electrodes of the first and second electrolytic cells, the concentration of each residual chlorine can be accurately measured. Furthermore, because the first working electrode of the first electrolytic cell and the second working electrode of the second electrolytic cell each exhibit a mesh structure, the specific surface area that reacts with residual chlorine can be increased. Therefore, the entire amount of free chlorine and combined chlorine in the flowing measurement solution can be reacted, and the concentration of residual chlorine in the measurement solution can be accurately measured. In addition, the activity of the electrodes does not easily decrease. In such a residual chlorine measuring device, it is preferable that the first and second counter electrodes are silver electrodes immersed in a solution containing halide ions. In this case, each counter electrode can also be used as a reference electrode.

[0012] The present invention relates to a residual chlorine measuring device having a composite measuring unit including a first measuring unit and a second measuring unit, wherein the composite measuring unit comprises a composite electrolytic cell, a first calculation unit and a second calculation unit, and the composite electrolytic cell is made up of a working electrode having a mesh structure with a supply port for supplying the measurement solution from the flow path and an outlet port from the flow path, a cation exchange membrane and a counter electrode stacked in that order, wherein the working electrode consists of a first working electrode having the supply port and a second working electrode having the outlet port arranged with a gap between it and the first working electrode, and the first electrolytic cell is made up of the first working electrode, the cation exchange membrane and the counter electrode, and the second electrolytic cell is made up of the second working electrode, the cation exchange membrane and the counter electrode. In this case, the concentration of each residual chlorine can be measured by flowing the measurement solution through a combined electrolytic cell. In particular, because a combined electrolytic cell integrating the first and second electrolytic cells is used, the residual chlorine measuring device can be made even more compact. In such a residual chlorine measuring device, it is preferable that the counter electrode is a silver electrode immersed in a solution containing halide ions. In this case, the counter electrode can also be used as a reference electrode.

[0013] In the residual chlorine apparatus of the present invention, it is preferable that the first voltage is 0.4V to 0.8V and the second voltage is 0.2V to 0.4V. In this case, free chlorine can be selectively reduced in the first electrolytic cell, and bound chlorine can be reliably reduced in the second electrolytic cell.

[0014] The present invention relates to a residual chlorine measurement method for measuring residual chlorine in a measurement solution, and is characterized by comprising: a first step of reducing all free chlorine in the measurement solution using a first electrolytic cell to which a first voltage is applied; a second step of calculating the concentration of free chlorine from the oxidation-reduction current of the first electrolytic cell in the first step; a third step of electrolyzing the measurement solution after the first step using a second electrolytic cell to which a second voltage smaller than the first voltage is applied, thereby reducing all bound chlorine in the measurement solution; and a fourth step of calculating the concentration of bound chlorine from the oxidation-reduction current of the electrolysis in the third step. The present invention's residual chlorine measurement method allows for the sequential and total reduction of free chlorine and bound chlorine by continuously electrolyzing the measurement solution at a first potential and a second potential. Therefore, the concentrations of each can be measured. In particular, because free chlorine is selectively reduced and removed in the first electrolytic cell, and then bound chlorine is reduced in the second electrolytic cell, the concentrations can be measured accurately.

[0015] The present invention relates to a method for measuring residual chlorine, wherein the first voltage is preferably 0.4V to 0.8V and the second voltage is preferably 0.2V to 0.4V. In this case, free chlorine can be selectively reduced in the first step, and bound chlorine can be reliably reduced in the third step.

[0016] The present invention relates to a composite sensor for measuring residual chlorine, comprising a mesh-structured electrode, a working electrode, a cation exchange membrane, and a counter electrode stacked in that order, wherein the working electrode is provided with a supply port and an outlet for the measurement solution, and the working electrode consists of a first working electrode having the supply port and a second working electrode having the outlet, and the first working electrode and the second working electrode are arranged with a gap between them. [Effects of the Invention]

[0017] The residual chlorine measuring device and the residual chlorine measuring method of the present invention can measure the concentrations of both free chlorine and combined chlorine in the measurement solution. Also, since all of the residual chlorine in the measurement solution is electrolyzed, it is not necessary to perform correction using a calibration curve for each condition. The composite sensor for measuring residual chlorine of the present invention is a sensor suitable for measuring the concentrations of both free chlorine and combined chlorine.

Brief Description of Drawings

[0018] [Figure 1] It is a schematic diagram showing an embodiment of the residual chlorine measuring device of the present invention. [Figure 2] FIG. 2a is a schematic diagram showing the first electrolytic cell, and FIG. 2b is a schematic diagram showing the second electrolytic cell. [Figure 3] FIG. 3a is a schematic diagram showing another embodiment of the residual chlorine measuring device of the present invention, and FIG. 3b is a schematic diagram showing a composite measuring unit having the composite electrolytic cell. [Figure 4] It is a graph showing the behavior of LSV of free chlorine and combined chlorine. [Figure 5] FIG. 5a shows an exploded view of the electrolytic cell used in the example, and FIG. 5b is a schematic diagram of the residual chlorine measuring device using the same. [Figure 6] FIGS. 6a and b are graphs showing the behavior of LSV of free chlorine and free combined chlorine, respectively, using the device of FIG. 5b. [Figure 7] FIGS. 7a and b are graphs showing the results of the quantitative test of free chlorine using the device of FIG. 5b, and FIGS. 7c and d are graphs showing the results of the quantitative test of combined chlorine using the device of FIG. 5b.

Embodiments for Carrying Out the Invention

[0019] Next, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments.

[0020] [Residual Chlorine Measuring Device 1] The residual chlorine measuring device 1 shown in Figure 1 comprises a flow path 10, a pump 20 for flowing the measurement solution L through the flow path 10, a first measuring unit 30 provided in the flow path 10, and a second measuring unit 40 provided downstream of the first measuring unit 30. The first measuring unit 30 measures the concentration of free chlorine in the measurement solution, and the second measuring unit 40 measures the concentration of combined chlorine in the measurement solution. In other words, the residual chlorine measuring device 1 is a device that directly measures the concentration of free chlorine and the concentration of combined chlorine in the measurement solution. In Figure 1, the measurement solution L flows from upstream to downstream along the arrow. Reference numeral 50 denotes a display unit that shows the concentrations of free chlorine and bound chlorine.

[0021] [Flow path 10, pump 20] The flow path 10 is made of a flexible tube or the like. Pump 20 controls the flow rate of the measurement solution in the flow path 10. The flow rate depends on the specific surface area of ​​the working electrodes, such as the first working electrode and the second working electrode, which will be described later, and is not particularly limited, but for example, it can be 0.1 ml / min or more and 30 ml / min or less, with a lower limit of 0.5 ml / min or more, particularly 1 ml / min or more, and an upper limit of 20 ml / min or less, 10 ml / min or less, particularly 5 ml / min or less, and most preferably 3 ml / min or less. If the flow rate is less than 0.1 ml / min, the current may not be stable and the sensitivity may decrease, and if the flow rate is greater than 30 ml / min, it is necessary to enlarge the first working electrode and the second working electrode in order to react the entire amount of each residual chlorine, which may be undesirable for miniaturizing the device.

[0022] [First measuring section 30] As shown in Figure 2a, the first measuring unit 30 includes a first electrolytic cell 31, a first voltage-adding mechanism 32, a first ammeter 33, and a first calculation unit 34.

[0023] [First electrolytic cell 31] The first electrolytic cell 31 reduces all free chlorine in the measurement solution at a first potential. Specifically, it consists of a first working electrode 31a exhibiting a mesh structure, a first cation exchange membrane 31b, a first porous body 31c impregnated with a solution containing halide ions, and a first counter electrode 31d made of a silver electrode, all stacked in that order. The first working electrode 31a is also provided with a first supply port 31x for supplying the measurement solution L from the flow path 10 and a first discharge port 31z for discharging the measurement solution L into the flow path 10. The measurement solution L flows in the direction of the arrow in Figure 2.

[0024] The first working electrode 31a is a metal electrode exhibiting a mesh structure, particularly a gold electrode. Examples of gold electrodes include gold mesh and gold-plated base metal mesh. When gold plating is applied, the base metal mesh is not particularly limited as long as it can be completely covered with gold plating, and examples include titanium mesh, steel mesh (especially stainless steel mesh), nickel mesh, and copper mesh. Titanium mesh and stainless steel mesh are particularly preferred due to their stability and excellent corrosion resistance. By using a mesh metal as the first working electrode 31a, a sufficient reaction area with residual chlorine can be ensured. Furthermore, while measurement values ​​become unstable when the electrode surface is contaminated by electrolysis and the reaction sites decrease, the electrode has a sufficient reaction area with respect to residual chlorine, resulting in higher electrode durability compared to general electrodes. Furthermore, in this first electrolytic cell 31, the measurement solution L supplied to the first working electrode 31a acts as the electrolyte solution on the working electrode side, and cations (protons) are transported to the cation exchange membrane 31b. In other words, the mesh structure of the first working electrode 31a also plays a role in limiting the depth of the liquid junction (reaction channel), and even if the solution resistance of the measurement solution L is high, the effect of voltage drop can be minimized without providing a special electrolyte on the working electrode side.

[0025] The coarseness of the mesh structure (mesh size per inch) can range from 20 mesh to 200 mesh. A lower limit of 30 mesh is preferred, with 40 mesh being particularly desirable. An upper limit of 150 mesh or less, 120 mesh or less, 110 mesh or less, and 100 mesh or less is particularly desirable. If the coarseness is less than 20 mesh, i.e., the mesh of the gold electrode is too coarse, the surface area becomes small, making it unsuitable for total electrolysis. On the other hand, if the coarseness is greater than 200 mesh, i.e., the mesh of the gold electrode is too fine, turbulence with the first cation exchange membrane 31b becomes difficult to occur, reducing the probability of contact with the first cation exchange membrane 31b and significantly decreasing the electrolysis efficiency. The thickness of the first working electrode can be appropriately set according to the conditions of the measurement solution, such as the flow rate of the measurement solution L, but is generally between 80 μm and 700 μm. The upper limit of the thickness is preferably 600 μm or less, and particularly preferably 400 μm or less. A thickness greater than 700 μm is undesirable because, for example, a large difference in reaction channel depth occurs between a position away from the first cation exchange membrane 31b and a position in contact with the first cation exchange membrane 31b. On the other hand, a thickness less than 80 μm is not practical.

[0026] [First cation exchange membrane 31b] The first cation exchange membrane 31b completely separates the first working electrode 31a and the first counter electrode 31d. As a result, residual chlorine in the measurement solution is retained on the working electrode side, and halide ions are retained on the counter electrode side. The first cation exchange membrane 31b is not particularly limited, but a fluorine-based sulfonic acid cation exchange membrane is preferred.

[0027] [First porous body 31c] The first porous body 31c is impregnated with a solution containing halide ions. Examples of the first porous body 31c include filter paper, porous membranes or filters made of synthetic resin, with filter paper being particularly preferred.

[0028] As for the halide ions in the solution, fluoride ions (F - ), chloride ions (Cl -) Bromide ion (Br - ) or iodide ion (I - ) may be used. As the cation, although not particularly limited, hydrogen ion (H + ), lithium ion (Li + ), sodium ion (Na + ), potassium ion (K + ), rubidium ion (Rb + ), cesium ion (Cs+) etc. may be mentioned, and hydrogen ion, lithium ion, sodium ion are preferable. Hydrogen ion, lithium ion, sodium ion have a small ionic radius and are easy to move in the cation exchange membrane. If the membrane transfer is slow, the reaction amount may be limited and the measured value may be low. In particular, a mixed solution of an acid and a halide salt is preferably used. In this case, 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, particularly 13% or more. By including hydrochloric acid, the electrolysis efficiency is increased. Note that it is not practical to make the ratio of hydrochloric acid in the total chlorine concentration greater than 50% from the aspects of productivity, handling as a sensor, and safety.

[0029] [First counter electrode 31d] The first counter electrode 31d is a silver electrode and is immersed in a solution containing halide ions impregnated in the first porous body 31c. That is, on the counter electrode side, this solution acts as an electrolyte solution. The first counter electrode 31d becomes silver-silver chloride by reaction with the halide ions contained in the first porous body 31c. Since the electrode potentials of the silver substrate and silver-silver chloride are similar, it functions not only as a counter electrode but also as a reference electrode.

[0030] [Function of the first electrolytic cell 31] Because the first electrolytic cell 31 is configured in this way, when the measurement solution L is supplied into the first working electrode 31a and a predetermined potential is applied between the first working electrode 31a and the first counter electrode 31d so that a reduction reaction occurs at the first working electrode 31a, the supplied measurement solution penetrates into the gap of the first working electrode 31a and a reduction reaction of residual chlorine (hypochlorous acid) occurs. At the same time, an oxidation reaction occurs at the first counter electrode 31d in which silver is converted to silver halide. The first electrolytic cell 30 has a mesh structure first working electrode 31a, and therefore has a large specific surface area for reacting with residual chlorine. As a result, it can react with all of the residual chlorine in the introduced solution. Furthermore, the applicant has found that when this sensor is used, residual chlorine is electrolyzed by a two-electron reaction without being significantly affected by the pH and temperature of the measurement solution. Within a predetermined pH range (for example, around pH 7-8), all of the residual chlorine in the measurement solution within a predetermined range (for example, room temperature) is reduced, allowing for accurate calculation of the residual chlorine concentration from the measurement current value without the need for calibration curve correction for each measurement solution.

[0031] "First voltage-generating mechanism 32" The first voltage-applying mechanism 32 applies a voltage to the first electrolytic cell 31. Specifically, a voltage is applied to the first sensor 31 so that the reduction reaction of free chlorine occurs at the first working electrode 31a. A potentiostat is one example of such a first voltage-applying mechanism 32. The voltage applied to the first electrolytic cell 31 by the first voltage-applying mechanism 32 is 0.4V or more and 0.8V or less, with a lower limit of 0.45V or more, particularly preferably 0.5V or more, and an upper limit of 0.75V or less, particularly preferably 0.7V or less. When the applied voltage to the first electrolytic cell 31 is lowered to below 0.4V, the reduction reaction of bound chlorine in the measurement solution becomes detectable. When the applied voltage to the first electrolytic cell 31 is higher than 0.8V, the electrolysis efficiency of free chlorine decreases.

[0032] "1st ammeter 33" The first ammeter 33 measures the oxidation-reduction current flowing between the first working electrode 31a and the first counter electrode 31d when a voltage is applied to the first sensor by the first voltage-applying mechanism 32.

[0033] “First calculation unit 34” The first calculation unit 40 calculates the concentration of free chlorine from the oxidation-reduction current of the first electrolytic cell. More specifically, it calculates the concentration of free chlorine from the oxidation-reduction current measured by the first ammeter 33. One method for calculating the concentration of free chlorine is to apply a voltage to the first electrolytic cell 31 with the first voltage-applying mechanism 32, then determine the average current value over a predetermined period of time from the point when the current stabilizes, and calculate the concentration from that average current value.

[0034] "Operation of the first measuring unit 30" With this configuration, the first measuring unit 30 electrolyzes the measuring container L sent from the flow path 10 at a first potential to reduce all of the free chlorine, and calculates the concentration of free chlorine from the resulting oxidation-reduction current. Since the reduction reaction occurs only for free chlorine at the first potential, the concentration of free chlorine can be measured accurately.

[0035] "Second measurement section 40" As shown in Figure 2b, the second measuring unit 40 includes a second electrolytic cell 41, a second voltage-adding mechanism 42, a second ammeter 43, and a second calculation unit 44. The second electrolytic cell 41 comprises a second working electrode 41a, a second cation exchange membrane 41b, a second porous body 41c, and a second counter electrode 41d, which correspond to the first working electrode 31a, the first cation exchange membrane 31b, the first porous body 31c, and the first counter electrode 31d, respectively, and has substantially the same structure as the first electrolytic cell 31.

[0036] The second voltage-applying mechanism 42 is substantially the same as the first pressure-applying mechanism 32, except that the voltage applied to the second electrolytic cell 41 is different. The voltage applied to the second electrolytic cell 41 by the second voltage-applying mechanism 42 is 0.2V or more and 0.4V or less, preferably 0.25V or more as the lower limit and 0.35V or less as the upper limit, and particularly preferably 0.3V or less. When the voltage applied to the second electrolytic cell 41 is lowered to less than 0.2V, the reduction reaction of dissolved oxygen in the measurement solution becomes detectable. When the voltage applied to the second electrolytic cell 41 is higher than 0.4V, the electrolysis efficiency of bound chlorine decreases. The second ammeter 43 is substantially the same as the first ammeter 33, and measures the oxidation-reduction current flowing between the second working electrode 41a and the second counter electrode 41d when a voltage is applied to the second electrolytic cell 41 by the second voltage-applying mechanism 42.

[0037] The second calculation unit 44 calculates the concentration of free chlorine from the oxidation-reduction current of the second electrolytic cell 41. More specifically, it calculates the concentration of combined chlorine from the oxidation-reduction current measured by the second ammeter 43. The method for calculating the concentration of combined chlorine is substantially the same as the method for calculating the concentration of free chlorine in the first calculation unit 34. For example, it may be calculated from the average current value over a predetermined period of time after the current stabilizes following the application of voltage to the second electrolytic cell 41 by the second voltage-applying mechanism 42.

[0038] "Operation of the second measuring unit 40" With this configuration, the second measurement unit 40 electrolyzes the measurement solution L sent from the first measurement unit 30 via the flow path 10 at a second potential to reduce all of the bound chlorine, and calculates the concentration of bound chlorine from the resulting oxidation-reduction current. Since the measurement solution L sent to the second electrolytic cell 41 has had free chlorine removed, only bound chlorine is reduced, and the concentration of bound chlorine can be measured accurately.

[0039] [Operation and Effects of Residual Chlorine Device 1] The residual chlorine measuring device 1 measures the concentration of free chlorine in the measurement solution L by reducing it in the first measuring unit 30, and then continuously measures the concentration of combined chlorine in the measurement solution by reducing it in the second measuring unit 40, so that each concentration can be measured directly. In other words, the concentration of each residual chlorine in the measurement solution can be measured accurately. In particular, since the first electrolytic cell of the first measuring unit reduces the entire amount of free chlorine in the measurement solution and the second electrolytic cell of the second measuring unit reduces the entire amount of combined chlorine, calibration of calibration curves and temperature correction at a predetermined pH range (especially around pH 7 to 8) and a predetermined temperature (especially room temperature) are unnecessary. The residual chlorine measuring device of the present invention, configured in this way, can be miniaturized.

[0040] Next, other embodiments will be described. The residual chlorine measuring device 2 shown in Figure 3 is another embodiment of the residual chlorine measuring device of the present invention. Unlike the residual chlorine measuring device 1 shown in Figure 1, it uses a composite measuring unit that integrates the first measuring unit and the second measuring unit. More specifically, it uses a composite electrolytic cell that integrates the first electrolytic cell and the second electrolytic cell.

[0041] [Residual Chlorine Measuring Device 2] As shown in Figure 3a, the residual chlorine measuring device 2 has a flow path 10, a pump 20 that flows the measurement solution L through the flow path 10, and a combined measuring unit 60 provided in the flow path 10. The combined measuring unit 60 serves as both the first and second measuring units of the residual chlorine measuring device 1 in Figure 1, and simultaneously measures the concentration of free chlorine and the concentration of combined chlorine in the measurement solution. In Figure 3a, the measurement solution L flows from upstream to downstream along the arrow. Note that reference numeral 50 denotes a display unit, similar to the residual chlorine measuring device 1 in Figure 1.

[0042] "Composite measurement section 60" As shown in Figure 3b, the combined measurement unit 60 includes a combined electrolytic cell 61, an accelerating mechanism 62, an ammeter 63, and a calculation unit 64.

[0043] The combined electrolytic cell 61 is an integrated unit in which the first electrolytic cell and the second electrolytic cell in the residual chlorine apparatus 1 shown in Figure 1 are connected in series. Specifically, it consists of a working electrode 61a exhibiting a mesh structure, a cation exchange membrane 61b, a porous body 61c impregnated with a solution containing halide ions, and a counter electrode 61d made of silver, all stacked in that order. The working electrode 61a is provided with a supply port 61x for supplying the measurement solution L from the flow channel 10 and an outlet port 61z for discharging the measurement solution L into the flow channel 10. The structure on the counter electrode side relative to the cation exchange membrane 61b is not particularly limited as long as there is an electrolyte that carries protons from the cation exchange membrane 61b to the counter electrode 61d. The working electrode 61a consists of a first working electrode 61a1 having a supply port 61x, and a second working electrode 61a2 having an outlet 61z provided with a space S between it and the first working electrode 61a1. Specifically, the first working electrode 61a1 is positioned upstream of the second working electrode 61a2, and the two working electrodes 61a1 and 61a2 are positioned apart so that they do not come into contact with each other. Therefore, the first working electrode 61a1 and the counter electrode 61d constitute the first electrolytic cell (hereinafter referred to as the first electrolytic cell 61A) in the residual chlorine apparatus 1 shown in Figure 1, and the second working electrode 61a2 and the counter electrode 61d constitute the second electrolytic cell (hereinafter referred to as the second electrolytic cell 61B) in the residual chlorine apparatus 1 shown in Figure 1. Furthermore, the first working electrode 61a1 and the second working electrode 61a2 have substantially the same mesh structure as the first working electrode 31 of the residual chlorine device 1 in Figure 1. Also, the cation exchange membrane 61b, porous body 61c, and counter electrode 61d are substantially the same as the first cation exchange membrane 31b, first porous body 31c, and first counter electrode 31d of the residual chlorine device 1 in Figure 1.

[0044] The voltage-applying mechanism 62 applies voltage to the first electrolytic cell 61A and also applies voltage to the second electrolytic cell 61B. The ammeter 63 measures the current between the first working electrode 61a1 and the counter electrode 61d of the first electrolytic cell 61A, and also measures the current between the second working electrode 61a2 and the counter electrode 61d of the second electrolytic cell 61B. The calculation unit 64 calculates the concentration of free chlorine from the current value of the first electrolytic cell 61A and the concentration of combined chlorine from the current value of the second electrolytic cell 61B. In other words, the calculation unit 64 serves as both the first and second calculation unit.

[0045] [Operation and Effects of Residual Chlorine Device 2] In the residual chlorine measuring device 2, the measurement solution passes through the first working electrode 61a1 of the first electrolytic cell 61A of the composite electrolytic cell 61, through the space S between the first working electrode 61a1 and the second working electrode 61a2, and reaches the second working electrode 61a2 of the second electrolytic cell 61B. Therefore, the free chlorine in the measurement solution is completely reduced at the first working electrode 61a1, and the combined chlorine is completely reduced at the second working electrode 61a2. In other words, the concentrations of free chlorine and combined chlorine can be measured simply by passing the measurement solution L through the composite measuring unit 60. In particular, since the residual chlorine measuring device 2 uses a composite electrolytic cell in which two second electrolytic cells are connected in series, further miniaturization is possible.

[0046] "Method for measuring residual chlorine" Next, the method for measuring residual chlorine according to the present invention will be described. The present invention provides a method for measuring residual chlorine in a measurement solution, comprising: a first step of electrolyzing the measurement solution L in a first electrolytic cell; a second step of calculating the concentration of free chlorine from the oxidation-reduction current of the first step; a third step of electrolyzing the measurement solution L after the first step in a second electrolytic cell; and a fourth step of calculating the concentration of bound chlorine from the oxidation-reduction current of the third step. The order of the second and fourth steps is not particularly limited.

[0047] The first step involves electrolyzing the measurement solution L in the first electrolytic cell. Specifically, the measurement solution L is electrolyzed in the first electrolytic cell to which the first voltage is applied, thereby reducing all of the free chlorine in the measurement solution. The first electrolytic cell can be constructed by immersing the working electrode and the counter electrode in the measurement solution L. Examples of such first electrolytic cells include the first electrolytic cell of the residual chlorine measuring device 1 in Figure 1 and the first electrolytic cell of the residual chlorine measuring device 2 in Figure 3, but it is not particularly limited as long as it can reduce all of the free chlorine. For example, in the residual chlorine measuring device 1 in Figure 1 and the residual chlorine measuring device 2 in Figure 4, the reduction reaction of free chlorine is carried out while the measurement solution is flowing, but the measurement solution may also be filled into a container and electrolysis may be performed at the first voltage until the reduction reaction of free chlorine is completely finished. In this case, in step 3, the concentration of free chlorine will be calculated from the total amount of current that flowed during the electrolysis. The first voltage applied to this first electrolytic cell is 0.4V or more and 0.8V or less, with a lower limit of 0.45V or more, particularly preferably 0.5V or more, and an upper limit of 0.75V or less, particularly preferably 0.7V or less.

[0048] The second step involves calculating the concentration of free chlorine from the oxidation-reduction current obtained in the first step. The applicant has found that free chlorine is electrolyzed by a two-electron reaction by applying a predetermined voltage suitable for the measurement solution within a predetermined range of pH and conductivity, and the calculation is based on this finding.

[0049] The third step involves electrolyzing the measurement solution L after the first step, that is, the measurement solution from which free chlorine has been removed, in a second electrolytic cell. More specifically, the measurement solution L is electrolyzed in a second electrolytic cell to which a second voltage is applied to completely reduce the bound chlorine in the measurement solution. The second electrolytic cell can be constructed by immersing the working electrode and the counter electrode in the measurement solution L. Examples of such a second electrolytic cell include the second electrolytic cell of the residual chlorine measuring device 1 shown in Figure 1 and the second electrolytic cell section of the residual chlorine measuring device 2 shown in Figure 4, but it is not particularly limited as long as it can reduce all of the bound chlorine. In the third step, as in the first step, electrolysis may be carried out in a container, for example, until the reduction reaction is completely finished. The second voltage applied to this second electrolytic cell is smaller than the first voltage, between 0.2V and 0.4V, preferably with a lower limit of 0.25V or higher and an upper limit of 0.35V or lower, particularly preferably 0.3V or lower.

[0050] The fourth step involves calculating the concentration of bound chlorine from the oxidation-reduction current obtained in the third step. The applicant has found that bound chlorine is electrolyzed by a two-electron reaction by applying a predetermined voltage suitable for the measurement solution within a predetermined pH and temperature range, and the calculation is based on this finding.

[0051] The present invention's residual chlorine measurement method involves measuring the concentration of free chlorine in a measurement solution L in the first step, removing the free chlorine from the measurement solution L, and then measuring the concentration of combined chlorine in the measurement solution L in the third step. Therefore, it is possible to accurately measure the concentrations of both free and combined chlorine. [Examples]

[0052] "Linear sweep voltammetry (LSV) behavior of free chlorine and bound chlorine" In a 0.1M buffer solution (pH 8) containing 2mM sodium hypochlorite (free chlorine), a gold electrode was inserted as the working electrode, a silver electrode as the counter electrode, and silver / silver chloride (3MKCl) as the reference electrode. When the potential was lowered from 0.9V (vsAg / AgCl) at a sweep rate of 5mV / s, a peak of free chlorine reduction appeared around 500mV (vsAg / AgCl). In a 0.1M buffer solution (pH 8) containing 2mM sodium hypochlorite and 20mM ammonium chloride (bound chlorine), a gold electrode was inserted as the working electrode, a silver electrode as the counter electrode, and silver / silver chloride (3MKCl) as the reference electrode. When the potential was lowered from 0.9V (vsAg / AgCl) at a sweep rate of 5mV / s, a peak of free chlorine reduction appeared around 110mV (vsAg / AgCl). These results are shown in Figure 4. Thus, it was found that the reduction potentials of free chlorine and bound chlorine are different.

[0053] "Assembly of electrode cartridges" As shown in Figure 5a, the electrolytic cell was housed in end plates 101 and 102, and the electrode cartridge 100 was assembled. The working electrode 110 consists of a gold electrode 111 and a working electrode current collector foil represented by reference numeral 112. For the gold electrode 111, a titanium mesh (15 mm × 60 mm × 200 μm) with a coarseness of 100 mesh, plated with gold, was used. A fluorine-based sulfonic acid cation exchange membrane was used as the cation exchange membrane 120. Filter paper was used as the porous material 130. The solution used to impregnate the filter paper was a mixed solution of NaCl and HCl with a total chlorine concentration of 3 M and a hydrochloric acid concentration of 0.5 M. The counter electrode 140 consists of a silver electrode 141 (15 mm × 60 mm × 100 μm) and a counter electrode current collector foil represented by symbol 142. The end plate 101 (working electrode side) has a first communication hole 115 which serves as a supply port for the working electrode 110 and a second communication hole 116 which serves as an outlet for the working electrode 110. Reference numerals 150A, 150B, and 150C indicate gaskets, and reference numeral 160 indicates a screw. Each element held between the end plates 101 and 102 is compressed and tightly fitted together and secured with screws 160. The working electrode current collector foil 112 and the counter electrode current collector foil 142 are for supplying current to the gold electrode 111 and the silver electrode 141, respectively, and are extended to the outside of the end plates.

[0054] "Residual chlorine measuring device" As shown in Figure 5b, the electrode cartridges 100 were connected in series to assemble the residual chlorine measuring device 5. Reference numeral 10 denotes a flow path, reference numeral 20 denotes a pump, and reference numerals 34 and 44 denotes potentiostats.

[0055] "LSV measurement of free chlorine (hypochlorite ions)" A 10 mM buffer solution (pH 8) containing 5 ppm sodium hypochlorite was flowed through the residual chlorine measuring device 5 at a flow rate of 2 ml / min, while voltage was simultaneously applied to the upstream and downstream electrode cartridges at a sweep rate of 1 mV / s (0.9 V to 0.1 V). The results are shown in Figure 6a. In the upstream electrode cartridge, current gradually began to flow from 0.8V, and it was found that the entire amount of hypochlorite ions was reduced at slightly over 0.65V. Furthermore, below 0.2V, the reduction of dissolved oxygen began to occur. This can also be seen from the fact that the downstream electrode cartridge hardly generates any current from a voltage slightly over 0.65V. In other words, it was found that applying a voltage of 0.2V to 0.8V is optimal for measuring free chlorine at pH 8.

[0056] LSV measurement of combined chlorine (trichloramine) A 10 mM buffer solution (pH 8) containing 5 ppm sodium hypochlorite and 5 ppm ammonium chloride was flowed through the residual chlorine measuring device 5 at a flow rate of 2 ml / min, while voltage was simultaneously applied to the upstream and downstream electrode cartridges at a sweep rate of 1 mV / s (0.9 V to 0.1 V). The results are shown in Figure 6b. In the upstream electrode cartridge, current began to flow at slightly over 0.6V, and it was found that about 90% of the trichloramine was reduced at 0.40V. Furthermore, it was found that almost all of it was reduced around 0.4V. Below 0.2V, the reduction of dissolved oxygen began to occur. Similarly, in the downstream electrode cartridge, almost no current was generated at 0.4V. In other words, it was found that applying a voltage of 0.2V to 0.4V is optimal for measuring bound chlorine at pH 8.

[0057] These LSV measurements revealed that applying 0.4V to 0.8V to the upstream electrode cartridge selectively reduces free chlorine without removing bound chlorine. In other words, it was found that applying a voltage of 0.4V to 0.8V, preferably 0.5V to 0.7V, to the upstream electrode cartridge and applying a voltage of 0.2V to 0.4V, preferably 0.2V to 0.3V, to the downstream electrode cartridge is optimal.

[0058] Next, using a residual chlorine measuring device 5 that applied 0.6V to the upstream electrode cartridge and 0.25V to the downstream electrode cartridge, free chlorine and combined chlorine were measured. 10 mM buffer solutions (pH 8) were prepared by adding sodium hypochlorite at concentrations of 0 ppm, 1 ppm, 2 ppm, 3 ppm, 4 ppm, and 5 ppm, respectively, and these were sequentially flowed through the residual chlorine measuring device 5 at a flow rate of 2 ml / min. The results are shown in Figures 7a and 7b. It was found that hypochlorite ions were reduced along the total electrolysis line of hypochlorite ions, which corresponds to the theoretical value. 10 mM buffer solutions (pH 8) were prepared by adding sodium hypochlorite and ammonium chloride (trichloroamine) at concentrations of 0 ppm, 1 ppm, 2 ppm, 3 ppm, 4 ppm, and 5 ppm, respectively, and these were sequentially flowed through the residual chlorine measuring device 5 at a flow rate of 2 ml / min. The results are shown in Figures 7c and 7d. It was found that dichloramine was reduced along the total electrolysis line of dichloramine, which corresponds to the theoretical value. Thus, it was found that the residual chlorine measuring device 5 can selectively quantify free chlorine and combined chlorine. [Explanation of Symbols]

[0059] 1, 2, 5 Residual chlorine measuring device 10 channels 20 pumps 30 1st measurement section 31. First electrolytic cell 31a 1st working electrode 31b First cation exchange membrane 31c First porous body 31d First Opposite 31x 1st supply port 31z 1st outlet 32. First Booster Mechanism 33 1st ammeter 34 1st calculation section 40 Second measuring section 41. Second electrolytic cell 41a 2nd working electrode 41b Second cation exchange membrane 41c Second porous body 41d Second opposite pole 41x 2nd supply port 41z 2nd outlet 42. Second voltage boosting mechanism 43 Second ammeter 44 2nd calculation section 50 Display 60 Composite measurement section 61 Combined electrolytic cell 61A First Electrolytic Cell 61B Second Electrolytic Cell 61a Working electrode 61a1 1st working electrode 61a2 2nd working electrode 61b Cation exchange membrane 61c Porous material 61d Opposite 61x supply port 61z outlet 62. Voltage-Boosting Mechanism 63 Ammeter 64 Arithmetic section 100 electrode cartridges 101, 102 End Plates 110 Working electrode 111 Metal pole 112 Working electrode current collector foil 115 1st communication hole (supply port) 116 2nd communication hole (discharge port) 120 Cation exchange membrane 130 Porous material 140 opposite poles 141 Silver electrode 142 Counter electrode current collector foil 150A, 150B, 150C gaskets 160 screws S Gap S1 space

Claims

1. A residual chlorine measuring device for measuring residual chlorine in a measurement solution, Flow channels and A pump that flows the measurement solution through the aforementioned flow path, A first measuring unit for measuring the concentration of free chlorine in the aforementioned measurement solution, It has a second measuring unit provided downstream of the first measuring unit, which measures the concentration of bound chlorine in the measurement solution, The first measuring unit comprises a first electrolytic cell that reduces all of the free chlorine in the measurement solution by applying a first voltage, and a first calculation unit that calculates the concentration of free chlorine from the oxidation-reduction current of the first electrolytic cell. The second measuring unit comprises a second electrolytic cell that reduces all of the bound chlorine in the measurement solution by applying a second voltage smaller than the first voltage, and a second calculation unit that calculates the concentration of bound chlorine from the oxidation-reduction current of the second electrolytic cell. Residual chlorine measuring device.

2. The first measuring unit comprises: a first electrolytic cell having a mesh structure in which a first working electrode, a first cation exchange membrane, and a first counter electrode are stacked in that order, and the first working electrode is provided with a first supply port for supplying the measuring solution from the flow channel and a first discharge port for discharging the measuring solution into the flow channel; a first voltage application mechanism for applying a voltage to the first electrolytic cell; a first ammeter for measuring the oxidation-reduction current of the first electrolytic cell; and a first calculation unit. The second measuring unit comprises: a second electrolytic cell having a mesh structure in which a second working electrode, a second cation exchange membrane, and a second counter electrode are stacked in that order, and a second supply port for supplying the measurement solution from the flow channel to the second working electrode and a second discharge port for discharging the measurement solution into the flow channel; a second voltage application mechanism for applying a voltage to the second electrolytic cell; a second ammeter for measuring the oxidation-reduction current of the second electrolytic cell; and a second calculation unit. The residual chlorine measuring device according to claim 1.

3. The first and second counter electrodes are silver electrodes immersed in a solution containing halide ions. The residual chlorine measuring device according to claim 2.

4. It has a composite measuring unit including the first measuring unit and the second measuring unit, The composite measurement unit comprises a composite electrolytic cell, the first calculation unit, and the second calculation unit. The aforementioned composite electrolytic cell consists of a working electrode, which is a mesh structure electrode with a supply port for supplying the measurement solution from the flow path and an outlet port for supplying the measurement solution from the flow path; a cation exchange membrane; and a counter electrode, which are stacked in that order. The working electrode comprises a first working electrode having the supply port and a second working electrode having the discharge port, which is positioned with a gap between it and the first working electrode. The first working electrode, the cation exchange membrane, and the counter electrode constitute the first electrolytic cell. The second electrolytic cell is composed of the second working electrode, the cation exchange membrane, and the counter electrode. The residual chlorine measuring device according to claim 1.

5. The counter electrode is a silver electrode immersed in a solution containing halide ions. The residual chlorine measuring device according to claim 4.

6. The first voltage is 0.4V to 0.8V, The second voltage is 0.2V to 0.4V. A residual chlorine measuring device according to any one of claims 1 to 5.

7. A method for measuring residual chlorine in a measurement solution, The first step involves reducing the entire amount of free chlorine in the measurement solution using a first electrolytic cell to which a first voltage is applied. A second step involves calculating the concentration of free chlorine from the oxidation-reduction current of the first electrolytic cell in the first step, A third step involves electrolyzing the measurement solution after the first step in a second electrolytic cell to which a second voltage smaller than the first voltage is applied, thereby reducing all of the bound chlorine in the measurement solution. The process includes a fourth step of calculating the concentration of bound chlorine from the oxidation-reduction current of the electrolysis in the third step, Method for measuring residual chlorine.

8. The first voltage is 0.4V to 0.8V, The second voltage is 0.2V to 0.4V. The method for measuring residual chlorine according to claim 7.

9. A residual chlorine measuring sensor is provided, comprising a mesh-structured electrode with a working electrode, a cation exchange membrane, and a counter electrode stacked in that order, and the working electrode having a supply port and an outlet for the measurement solution. The working electrode consists of a first working electrode having the supply port and a second working electrode having the discharge port. The first working electrode and the second working electrode are arranged with a gap between them. A composite sensor for measuring residual chlorine.

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