JP6856867B2 - Reagent-free free residual chlorine measuring device and reagent-free free residual chlorine measuring method - Google Patents

Description

The present invention relates to a residual chlorine measuring device and a residual chlorine measuring method. More specifically, the present invention relates to a residual chlorine measuring device and a residual chlorine measuring method which can determine the residual chlorine concentration by a reagent-free method and can be used even for a sample liquid such as seawater or boiler cooling water where scale is likely to be generated. ..

Residual chlorine is effective chlorine with a disinfecting effect that remains in water as a result of chlorine treatment, and is classified into free residual chlorine such as hypochlorous acid and combined residual chlorine such as chloramine. Both have bactericidal activity by oxidation.
Conventionally, the polarographic method for measuring the redox current is used for measuring the residual chlorine. As the residual chlorine measuring device by the polarographic method, there are a reagent-type device that requires the addition of a reagent and a non-reagent type device that does not use a reagent.

In order to measure free residual chlorine in a sample solution using the polarograph method, especially the reagent-free two-electrode polarograph method, measurement conditions that are sensitive to free residual chlorine and are less affected by combined residual chlorine are required. Must be found.
A reagent-free residual chlorine measuring device that employs measurement conditions that are relatively unaffected by bound residual chlorine is, for example, 0 to 0.3 V between the platinum detection electrode and the silver / silver chloride counter electrode. A device that applies an applied voltage selected from a range is known (Patent Document 1).

The residual chlorine measuring device of Patent Document 1 is used for measuring free residual chlorine in clean water, and exhibits performance without any problem in management of clean water and the like. However, in the case of a sample solution such as seawater or boiler cooling water, which is prone to scale generation, the influence of residual residual chlorine, deterioration of electrodes, deterioration, adhesion of dirt, etc. cannot be ignored, and it is stable for a long period of time. It was also difficult to make the measurements.
Therefore, in the case of sample liquids that easily generate scale, such as seawater and boiler cooling water, follow the DPD method specified in the 2011 edition of the clean water test method "30.3 Diethyl-p-phenylenediamine absorptiometry". There was no choice but to use a residual chlorine measuring device, and costs such as reagent costs and maintenance work costs were incurred on a regular basis.

Japanese Patent No. 3469962

In view of the above circumstances, the present invention is a sample solution in which the free residual chlorine concentration can be determined by a two-electrode polarographic method without using a reagent, and scale is easily generated like seawater or boiler cooling water. It is also possible to provide a residual chlorine measuring device and a residual chlorine measuring method that can be stably used for a long period of time because the influence of the combined residual chlorine is small, the electrode is not easily deteriorated or deteriorated, and cleaning using a chemical solution or the like is possible. Make it an issue.

In order to achieve the above problems, the present invention has adopted the following configuration.
[1] A two-electrode polarographic method for measuring residual chlorine.
A gold detection electrode immersed in the sample liquid and a platinum counter electrode,
A voltage-applying mechanism that applies an applied voltage selected from the range of 500 to 800 mV between the detection electrode and the counter electrode.
A residual chlorine measuring apparatus comprising: an ammeter for measuring a redox current flowing between a detection electrode and a counter electrode when the boosting mechanism applies the applied voltage.
[2] The residual chlorine measuring apparatus according to [1], further comprising an arithmetic control unit, which obtains the free residual chlorine concentration of a sample solution based on the redox current measured by the ammeter.
[3] The residual chlorine measuring apparatus according to [1] or [2], further comprising an automatic cleaning mechanism for cleaning the detection electrode and the counter electrode.
[4] An applied voltage selected from the range of 500 to 800 mV is applied between the gold detection electrode immersed in the sample solution and the platinum counter electrode, and the redox current flowing between the detection electrode and the counter electrode is applied. A method for measuring residual chlorine, which comprises measuring and determining the free residual chlorine concentration from the obtained redox current.
[5] The method for measuring residual chlorine according to [4], wherein the sample liquid is seawater or boiler cooling water.

According to the residual chlorine measuring device and the residual chlorine measuring method of the present invention, the free residual chlorine concentration can be obtained by the two-electrode polarographic method without using a reagent, and scale is generated like seawater or boiler cooling water. Even if the sample solution is easy to use, the influence of bound chlorine is small, the electrode is not easily deteriorated or deteriorated, and it can be washed with a chemical solution or the like, and can be used stably for a long period of time.

It is an overall block diagram of the free residual chlorine measuring apparatus which concerns on 1st Embodiment of this invention. It is sectional drawing of the sensor part in the free residual chlorine measuring apparatus which concerns on 2nd Embodiment of this invention. It is an overall block diagram of the free residual chlorine measuring apparatus which concerns on 3rd Embodiment of this invention. It is sectional drawing of the sensor part in the free residual chlorine measuring apparatus which concerns on 4th Embodiment of this invention. It is a calibration curve of free residual chlorine obtained in the Example of this invention. This is a polarogram showing the relationship between the applied voltage of the free residual chlorine concentration and the redox current, which was obtained by using a sample solution having a low combined residual chlorine concentration. It is a polarogram showing the relationship between the applied voltage and the redox current, which was obtained by using a sample solution containing bound residual chlorine.

<First Embodiment>
[Device configuration]
The free residual chlorine measuring apparatus according to the first embodiment of the present invention will be described with reference to FIG. The free residual chlorine measuring device of the present embodiment is roughly composed of a sensor unit 1 and a main body unit 20.

The sensor unit 1 includes a measurement cell 11 into which the sample liquid S is introduced, a detection pole support 12 in which the lower portion is immersed in the sample liquid S, a detection pole 13 attached to the tip surface of the detection pole support 12, and a sample in the lower portion. Holds the counter electrode support 14 immersed in the liquid S, the counter electrode 15 attached to the outer peripheral surface on the lower end side of the counter electrode support 14, the motor 16 for vibrating the detection electrode 13 in a circular motion, and the detection electrode support 12. The bearing 17 has a large number of beads 18 for cleaning the detection electrode 13 charged in the sample liquid S. The measurement cell 11 is provided with a mesh-shaped partition plate 11a that partitions the detection electrode 13 and the counter electrode 15, so that the beads 18 do not flow out to the counter electrode 15 side.

The main body 20 includes an arithmetic control unit 21, a boosting mechanism 22, an ammeter 23, and a display device 24. The detection electrode 13 and the arithmetic control unit 21 are connected by the wiring L1, the counter electrode 15 and the arithmetic control unit 21 are connected by the wiring L2, and the motor 16 and the arithmetic control unit 21 are connected by the wiring L3. .. The ammeter 23 is provided in the middle of the wiring L1, and the boosting mechanism 22 is provided in the middle of the wiring L2.

The detection electrode 13 is made of gold. The counter electrode 15 is made of platinum.
The detection electrode support 12 is arranged in an inclined state, and a predetermined portion in the intermediate portion in the length direction is held by the bearing 17, and the precession movement can be performed with the holding portion by the bearing 17 as a fulcrum. Further, the base end portion 12a of the detection electrode support 12 and the rotation shaft 16a of the motor 16 are eccentrically engaged with each other. Therefore, by rotating the rotation shaft 16a of the motor 16, the base end portion 12a moves in a circular motion, and the detection pole 13 attached to the tip end portion of the detection pole support 12 also vibrates (circular motion). .. Further, the wiring L1 can be pulled out from the vicinity of the holding portion by the bearing 17 through the detection electrode support 12 without being twisted even if the detection electrode 13 is circularly moved.

A large number of beads 18 are arranged in the vicinity of the detection electrode 13 in a non-fixed state. The beads 18 come into contact with the vibrating (circular motion) detection electrode 13 to polish the detection electrode 13. As the material of the beads 18, ceramic or glass is preferable.

[Measurement of residual chlorine]
In the residual chlorine measuring device of the present embodiment, the boosting mechanism 22 applies an applied voltage between the detection electrode 13 and the counter electrode 15. The applied voltage is selected from the range of 500 to 800 mV, preferably from the range of 550 to 750 mV, and more preferably from the range of 600 to 700 mV.
Further, the ammeter 23 has come to measure the redox current flowing between the detection electrode and the counter electrode when the applying voltage mechanism 22 applies the applied voltage between the detection electrode 13 and the counter electrode 15. There is.
The sample liquid S to be measured is not particularly limited, but the present invention can be particularly preferably applied when the sample liquid S is seawater or boiler cooling water in which scale is likely to be generated.

In the residual chlorine measuring method of the present invention, the arithmetic control unit 21 obtains the free residual chlorine concentration from the redox current obtained by the residual chlorine measuring device of the present invention. The obtained free residual chlorine concentration is given to the display device 24 as a signal D1, and the free residual chlorine concentration is displayed on the display device 24. Further, the value of the free residual chlorine concentration is transmitted as a signal D2 to an external recorder, data logger, memory, printer, computer or the like. The signal D2 may be a digital signal or an analog signal. Further, it may be transmitted by wire or may be transmitted wirelessly.

In order to obtain the free residual chlorine concentration from the redox current, a calibration curve showing the correlation between the redox current and the free residual chlorine concentration obtained in advance using a calibration solution is used for calculation. As the calibration solution, a solution obtained by diluting a sodium hypochlorite solution with desalinated water or actual sample water can be used.
The free residual chlorine concentration of the calibration solution is determined by the following method according to the DPD method defined in the 2011 edition of the clean water test method "30.3 Diamine-p-phenylenediamine absorptiometry".
First, the DPD reagent is prepared by mixing 1.0 g of N, N-diethyl-phenylenediamine sulfate and 24 g of anhydrous sodium sulfate. As for the phosphate buffer solution (pH = 6.5), 35.4 mL of 0.2 mol / L sodium hydroxide solution was added to 100 mL of 0.2 mol / L potassium dihydrogen phosphate, and trans-1,2- Prepared by dissolving 0.13 g of cyclohexanediamine tetraacetic acid-hydrate.

Take 2.5 mL of the prepared phosphate buffer solution into 50 mL of a container with a stopper, add 0.5 g of the prepared DPD reagent, and then add the sample solution and ion-exchanged water to make the total volume 50 mL and mix. Next, about 3 mL of the mixed solution was taken into an absorption cell, the absorbance at a wavelength of 528 nm 10 seconds after mixing was measured using a photoelectric spectrophotometer, and the free residue by the DPD method was measured from the calibration curve prepared in advance. Find the chlorine concentration.

In the residual chlorine measuring device of the present embodiment, it is preferable that the arithmetic control unit 21 stores this calibration curve and obtains the free residual chlorine concentration from the redox current. In this case, the residual chlorine measuring method of the present invention can be carried out by the residual chlorine measuring device of the present embodiment alone.
Further, in the residual chlorine measuring device of the present embodiment, the arithmetic control unit 21 may obtain the total residual chlorine concentration and the combined residual chlorine concentration from the obtained redox current. In order to obtain the total residual chlorine concentration, a calibration curve showing the relationship between the total residual chlorine concentration and the redox current may be prepared in advance in the sample solution containing the combined residual chlorine. Further, in order to obtain the combined residual chlorine concentration, the free residual chlorine concentration may be subtracted from the obtained total residual chlorine concentration.

Further, the arithmetic control unit 21 may output the current value from the ammeter 23 to the external computer as a signal D2. In that case, the method for measuring residual chlorine of the present invention can be carried out by performing an operation of obtaining the free residual chlorine concentration from the redox current in the external computer. The total residual chlorine concentration or the combined residual chlorine concentration may be obtained by the external computer.
Further, the arithmetic control unit 21 may output the current value from the ammeter 23 to the display device 24 as a signal D1. In that case, the residual chlorine measuring method of the present invention can be carried out by obtaining the free residual chlorine concentration from the redox current based on the current value read from the display device 24 and the calibration curve obtained in advance. Further, the total residual chlorine concentration or the combined residual chlorine concentration may be obtained from the redox current based on the current value read by the operator from the display device 24 and the calibration curve obtained in advance.

It is preferable to correct the temperature of the redox current used in the calculation. Therefore, the residual chlorine measuring device of the present invention preferably includes a temperature sensor. If the temperature of the sample liquid is kept sufficiently constant, or if the required measurement accuracy is low, the temperature correction may be omitted.
Temperature correction means converting to a redox current at a reference temperature (for example, 25 ° C.) in consideration of the temperature dependence of the redox current measurement. When the reference temperature is 25 ° C., the temperature is specifically corrected by the following formula (1).
I (V) ₂₅ = I (V) _t / (1+ (α × (t-25) / 100)) ・ ・ ・ (1)
t: Sample liquid temperature (° C) at the time of measurement
I (V) _t : Redox current value at voltage V obtained at sample solution temperature t ° C. I (V) ₂₅ : Redox current value at voltage V temperature-corrected at reference temperature 25 ° C. α: 1 ° C. Electrode output change amount (%)

[Washing]
The counter electrode 15 can be washed with a chemical solution according to the composition of the dirt component. For example, chemical cleaning using oxalic acid, hydrochloric acid, hydrogen peroxide solution, or the like can be performed. In addition, ozone cleaning may be performed. Further, physical cleaning such as brush cleaning may be performed instead of chemical cleaning or the like, or together with chemical cleaning or the like.
Further, in order to keep the detection electrode 13 clean, it is preferable to perform electrolytic polishing. In electrolytic polishing, it is sufficient that a current flows between the detection electrode and the counter electrode in the direction opposite to that at the time of measurement, and a well-known method can be appropriately adopted.
The residual chlorine measuring device of the present embodiment is provided with an automatic cleaning mechanism for cleaning the counter electrode 15 and the detection electrode 13, and regularly performs cleaning.

<Second Embodiment>
[Device configuration]
The free residual chlorine measuring device according to the second embodiment of the present invention is the same as the first embodiment except that the sensor unit 1 in FIG. 1 is changed to the sensor unit 2 shown in FIG.

FIG. 2 is a cross-sectional view of the sensor unit 2. The sensor unit 2 shown in FIG. 2 is provided with a substantially cylindrical case 31, and a support base 32 in which a through hole 32a along the axial direction is formed in one opening of the case 31. Is stuck. A pair of upper and lower circular windows 32b, 32b are bored in the substantially central portion of the support base 32 in the axial direction so as to penetrate from one peripheral surface to the opposite peripheral surface at right angles to the axial direction. .. Further, a recess 32c is formed in the circumferential direction near the tip thereof, and a counter electrode 33 is wound around the entire surface of the recess 32c.

Further, below the counter electrode 33, a cap 34 made of a mesh is screwed so as to cover the tip of the support base 32. Further, a large number of beads 36 for polishing and cleaning the detection electrode 35, which will be described later, are housed in the cap 34. An inner net 37 is provided at a position that covers the window 32b from the inside to prevent the beads 36 from flowing out.

A motor 38 is attached to the inside of the case 31, and is fixed to the rotating shaft 38a of the motor 38 on the upper side of the eccentric coupling 41. The eccentric coupling 41 is held by the coupling case 42, and the coupling case 42 is held above the support base 32 by a plurality of columns 43.
A substantially rod-shaped connecting shaft 44 is connected to the lower side of the eccentric coupling 41. The angle formed by the rotating shaft 38a and the connecting shaft 44 is set to about 3 degrees, and the portion of the connecting shaft 44 connected to the coupling case 42 makes a circular motion by driving the motor 38.

A little lower side of the connecting shaft 44 in the axial direction is inserted into the bearing 45. The bearing 45 is composed of a cylindrical tubular portion 45a in the direction of the connecting shaft 44 and a flange portion 45b extending in the radial direction around the lower end side of the tubular portion 45a, and is made of a rubber material. The tubular portion 45a is in close contact with the connecting shaft 44 in a watertight state with high pressure. Further, the outer peripheral surface of the bearing 45 is in watertight contact with the inner peripheral surface of the support substrate 32.

The lower end side of the connecting shaft 44 with respect to the bearing 45 is inserted into the upper end side of the substantially cylindrical detection electrode support 46. As a result, the detection electrode support 46 is connected and fixed to the lower end side of the connecting shaft 44, and hangs down in the through hole 32a of the support base 32. A detection pole 35 is provided at the lower end of the detection pole support 46.
When the portion of the connecting shaft 44 connected to the coupling case 42 makes a circular motion by driving the motor 38, the connecting shaft 44 makes a precession movement with the portion where the flange portion 45b is located as a fulcrum. As a result, the detection pole 35 provided at the lower end of the detection pole support 46 fixed to the connecting shaft 44 also moves in a circular motion.

The lead wire 47 of the detection electrode 35 is finally connected to the arithmetic control unit 21 of the main body 20 via the connector 48. Further, the counter electrode 33 is connected to the arithmetic control unit 21 of the main body unit 20 via the connector 48. The motor 38 is also connected to the arithmetic control unit 21 of the main body 20 via the connector 48.
In FIG. 2, the wiring in the vicinity of the connector 48 of the lead wire 47 is not shown. Further, the wiring from the counter electrode 33 to the connector 48 and the wiring from the motor 38 to the connector 48 are not shown.
Similar to the first embodiment, the detection electrode 35 is made of gold and the counter electrode 33 is made of platinum.

When the lower end of the sensor unit 2 of the present embodiment is immersed in the sample liquid S, the sample liquid S flows in and out from the cap 34 and the window 32b. As a result, the sample liquid S comes into contact with the detection electrode 35 and also with the counter electrode 33 wound around the support substrate 32. That is, the detection electrode 35 and the counter electrode 33 are immersed in the sample liquid S.
The sample liquid S is prevented from entering the case 31 above the bearing 45 by the bearing 45.
The free residual chlorine measuring device according to the second embodiment can measure free residual chlorine and the like in the same manner as the free residual chlorine measuring device according to the first embodiment. Further, the counter electrode 33 and the detection electrode 35 can be cleaned in the same manner as in the free residual chlorine measuring device according to the first embodiment.

<Third Embodiment>
[Device configuration]
The free residual chlorine measuring apparatus according to the third embodiment of the present invention will be described with reference to FIG. In FIG. 3, components similar to those in FIG. 1 are designated by the same reference numerals as those in FIG. 1, and detailed description thereof will be omitted.
The free residual chlorine measuring device of the present embodiment is roughly composed of a sensor unit 3, a main body unit 20, and a liquid feeding unit 50.

The sensor unit 3 is the same as the sensor unit 1 of the first embodiment except that the measurement cell 11 of the first embodiment is changed to the flow cell 19. The flow cell 19 is provided with a mesh-shaped partition plate 19a that partitions the detection electrode 13 and the counter electrode 15, so that the beads 18 do not flow out to the counter electrode 15 side.
The liquid feeding unit 50 has an inflow passage 51 for sending the sample liquid S to the flow cell 19, a discharge passage 52 for discharging the sample liquid S from the flow cell 19, and a pump 53 provided in the inflow passage 51.
The pump 53 and the arithmetic control unit 21 are each connected by wiring L4. The pump 53 operates according to an instruction from the arithmetic control unit 21.
The free residual chlorine measuring device according to the third embodiment may measure free residual chlorine and the like in the same manner as the free residual chlorine measuring device according to the first embodiment, except that the sample liquid S is allowed to flow in the flow cell 19. it can. Further, the counter electrode 15 and the detection electrode 13 can be cleaned in the same manner as in the free residual chlorine measuring apparatus according to the first embodiment.

<Fourth Embodiment>
[Device configuration]
The free residual chlorine measuring device according to the fourth embodiment of the present invention is the same as the third embodiment except that the sensor unit 3 in FIG. 3 is changed to the sensor unit 4 shown in FIG.

FIG. 4 is a cross-sectional view of the sensor unit 4. The sensor unit 4 has a configuration in which a flow cell 60 is added to the sensor unit 2 of the second embodiment. In FIG. 4, the same components as those in FIG. 2 are designated by the same reference numerals as those in FIG. 2, and detailed description thereof will be omitted.
The support base 32 is inserted into the flow cell 60. The inner wall on the upper end side of the flow cell 60 and the outer circumference of the support base 32 are liquid-tightly fixed via an O-ring 61.
A sample liquid inflow port 60a for inflowing the sample liquid is provided in the center of the tip of the flow cell 60, and a sample liquid outflow port 60b for outflow of the sample liquid is provided on the side wall near the O-ring 61. An inflow path 51 is connected to the sample liquid inflow port 60a, and an discharge path 52 is connected to the sample liquid outflow port 60b.

When the sample liquid S flows from the sample liquid inlet 60a of the flow cell 60 of the sensor unit 4 of the present embodiment, a part of the sample liquid S invades into the cap 34 and flows out from the sample liquid outlet 60b through the window 32b. To do. As a result, the sample liquid S comes into contact with the detection electrode 35. Further, a part of the sample liquid S flows in from the sample liquid inflow port 60a, passes outside the support substrate 32, and flows out from the sample liquid outflow port 60b. As a result, the sample liquid S comes into contact with the counter electrode 33 wound around the support substrate 32. That is, by flowing the sample liquid S from the sample liquid inflow port 60a of the flow cell 60, the detection electrode 35 and the counter electrode 33 are immersed in the sample liquid S.

The free residual chlorine measuring device according to the fourth embodiment can measure free residual chlorine and the like in the same manner as the free residual chlorine measuring device according to the third embodiment. Further, the counter electrode 33 and the detection electrode 35 can be cleaned in the same manner as in the free residual chlorine measuring device according to the third embodiment.

<Other Embodiments>
In each of the above embodiments, granular abrasives (beads 18 and 36) arranged in a non-fixed state in the vicinity of the detection electrode are used, but for example, they are attached to the tip of a spring urged toward the detection electrode. The detection electrode may be polished using a polishing member such as a sponge or a brush that comes into contact with the detection electrode.
Further, in each of the above embodiments, a method of obtaining the reproducibility of the thickness of the diffusion layer by a method of positively flowing the sample liquid in contact with the detection electrode with respect to the surface of the detection electrode is adopted, but a narrow range in contact with the detection electrode is adopted. A method of obtaining reproducibility of the thickness of the diffusion layer may be adopted by a method of suppressing the flow of the sample liquid. Examples of the device adopting this method include the redox current measuring device described in Japanese Patent Application Laid-Open No. 2015-34740.

Hereinafter, an experimental example for clarifying the effect of the present invention will be shown.
The DPD analysis value in the following experimental example was obtained by the following method according to the DPD method defined in the clean water test method 30.3.
(A) Preparation of DPD reagent 1.0 g of N, N-diethyl-phenylenediamine sulfate and 24 g of anhydrous sodium sulfate were mixed to prepare a DPD (N, N-diethyl-p-phenylenediamine) reagent.
(B) Preparation of phosphate buffer (pH = 6.5) To 100 mL of 0.2 mol / L potassium dihydrogen phosphate, 35.4 mL of 0.2 mol / L sodium hydroxide solution was added, and trans-1,2 and 2 were added thereto. 0.13 g of -cyclohexanediamine tetraacetic acid-hydrate was dissolved to prepare a phosphate buffer solution (pH = 6.5).

(C) Measurement of free residual chlorine concentration Take 2.5 mL of phosphate buffer into 50 mL of a container with a stopper, add 0.5 g of DPD reagent to this, and then add sample solution and ion-exchanged water to make the total volume 50 mL. It was mixed. Next, about 3 mL of the mixed solution was taken into an absorption cell, the absorbance at a wavelength of 528 nm 10 seconds after mixing was measured using a photoelectric spectrophotometer, and the free residual chlorine concentration was determined from the calibration curve prepared in advance. I asked.
(D) Total residual chlorine concentration To 50 mL of the mixed solution obtained in (c) above, about 0.5 g of potassium iodide was added and dissolved. Next, about 3 mL of the solution after adding potassium iodide was taken into an absorption cell, and the absorbance at a wavelength of 528 nm 2 minutes after the addition of potassium iodide was measured using a photoelectric spectrophotometer. The total residual chlorine concentration was determined.
(E) Combined chlorine concentration The combined chlorine concentration was determined by (total chlorine concentration)-(free chlorine concentration).

[Experimental Example 1]
Using the residual chlorine measuring device of FIG. 4, the relationship between the free residual chlorine concentration obtained by the DPD method and the redox current was investigated for the calibration solution, and a calibration curve was prepared. As the calibration solution, an aqueous solution of sodium hypochlorite having an effective chlorine concentration of about 12% diluted at various dilution rates was used.
In the boosting mechanism 22, a voltage of 600 mV was applied. As the detection electrode 13, a gold electrode having a diameter of 2 mm was used, and rotation was given to such that a linear velocity of about 1500 cm / s could be obtained. The counter electrode 15 was a platinum electrode.
The results are shown in FIG. As shown in FIG. 5, a calibration curve having good linearity was obtained between the free residual chlorine concentration obtained by the DPD method and the redox current.

[Experimental Example 2]
Using the residual chlorine measuring device of FIG. 4, a polarogram showing the relationship between the applied voltage of free residual chlorine and the redox current was investigated. However, as the boosting mechanism 22, a mechanism capable of continuously changing the voltage was used, and as the detection electrode 13, a gold electrode having a diameter of 2 mm was used, and rotation was provided to such an extent that a linear velocity of about 100 cm / s could be obtained. .. The counter electrode 15 was a platinum electrode. Tap water was used as the sample solution.

The results are shown in FIG. In FIG. 6 and FIG. 7 described later, F indicates the free residual chlorine concentration (mg / L) determined by the DPD method, and T indicates the total residual chlorine concentration (mg / L) determined by the DPD method. For example, "F0.01 T0.02" is a sample solution having a free residual chlorine concentration of 0.01 mg / L and a total residual chlorine concentration of 0.02 mg / L determined by the DPD method.
From the results of FIG. 6, in the range of 500 to 800 mV, a good plateau region (a region in which the current hardly changes even if the applied voltage changes slightly) was obtained in relation to the free residual chlorine concentration.

[Experimental Example 3]
Using the same equipment as in Experimental Example 2, under the same measurement conditions, a polarogram showing the relationship between the applied voltage and the redox current was investigated for the sample solution containing the combined residual chlorine. Tap water was used as the sample solution. The results are shown in FIG. 7 and Table 1.

In Table 1, the measured value of the free residual chlorine concentration is a value obtained by converting the redox current at the applied voltage of 600 mV in FIG. 7 into the free residual chlorine concentration based on the calibration curve obtained in FIG. For the error per 1 mg / L of the combined residual chlorine concentration, the difference between the measured value of the free residual chlorine concentration and the value obtained by the DPD method is subtracted from the combined residual chlorine concentration (the total residual chlorine concentration obtained by the DPD method minus the free residual chlorine concentration). It is the value divided by the concentration).

[Experimental Example 4]
The free residual chlorine of the sample solution containing the combined residual chlorine was measured using a CLF-1610 type reagent-free free chlorine meter manufactured by DKK-TOA CORPORATION. The applied voltage of the CLF-1610 type is 100 mV, and the detection electrode is a gold electrode with a diameter of 2 mm, which gives a rotation of about 750 cm / s at a linear velocity. The counter electrode is a silver / silver chloride electrode. Tap water was used as the sample solution.
Prior to the measurement of the sample solution containing the bound residual chlorine, the device was calibrated with an aqueous solution of sodium hypochlorite. The results are shown in Table 2.

In Table 2, the measured values of free residual chlorine concentration are the indicated values of CLF-1610 type. For the error per 1 mg / L of the combined residual chlorine concentration, the difference between the measured value of the free residual chlorine concentration and the value obtained by the DPD method is subtracted from the combined residual chlorine concentration (the total residual chlorine concentration obtained by the DPD method minus the free residual chlorine concentration). It is the value divided by the concentration).

[Experimental Example 5]
The free residual chlorine concentration in seawater was continuously measured using the apparatus configuration shown in FIG. However, the applied voltage was 0 mV, the detection electrode was a gold electrode with a diameter of 2 mm, and the rotation was such that a linear velocity of about 1500 cm / s could be obtained. The counter electrode was a silver / silver chloride electrode.
As a result, it became impossible to obtain a stable indicated value in only 1 to 2 days.
Since the counter electrode is a silver / silver chloride electrode, it was not possible to perform cleaning that damages the material, such as chemical cleaning and brush cleaning.

[Experimental Example 6]
The free residual chlorine concentration in seawater was continuously measured using the apparatus configuration shown in FIG. However, the applied voltage was 600 mV, the detection electrode was a gold electrode with a diameter of 2 mm, and the rotation was such that a linear velocity of about 1500 cm / s could be obtained. The counter electrode was a silver / silver chloride electrode.
As a result, at the time 5 days after the start of the measurement, the indicated value was stable without any problem.
After 6 days, the indicated value became unstable, and when the electrodes were observed, stains and scales were found. Then, 10 days later, when the chemical solution was washed with an oxalic acid solution having a concentration of about 5%, the situation was restored to a stable reading value as at the start of the measurement.

[Discussion]
According to the residual chlorine measuring device and the residual chlorine measuring method of the present invention, it is possible to stably measure the free residual chlorine concentration for a long period of time even for a sample liquid such as seawater or boiler cooling water where scale is likely to be generated. I found it possible. In particular, it was found that continuous measurement is possible by performing regular cleaning.
Further, as is clear from the comparison of the results in Tables 1 and 2, the influence of the combined residual chlorine concentration was reduced by about 30% as compared with the conventional apparatus (CLF-1610 type).
From the above, according to the residual chlorine measuring device and the residual chlorine measuring method of the present invention, the free residual chlorine concentration can be obtained without using a reagent, and scale is generated like seawater or boiler cooling water. It was found that even an easy sample solution is less affected by the residual chlorine bound and can be used stably for a long period of time.

1-4 ... sensor unit, 11 ... measurement cell, 12 ... detection pole support, 13, 35 ... detection pole,
14 ... counter electrode support, 15, 33 ... counter electrode, 16, 38 ... motor, 17, 45 ... bearing,
18, 36 ... beads, 19, 60 ... flow cell, 20 ... main body,
21 ... Computational control unit, 22 ... Voltage mechanism, 23 ... Ammeter, 24 ... Display device,
50 ... Liquid feeding unit, 53 ... Pump, S ... Sample liquid

Claims (5)

Ri by a two-electrode polarography, a free reagent type free residual chlorine measuring device for measuring the free residual chlorine without reagents,
A gold detection electrode and a platinum counter electrode that are directly immersed in the sample solution,
Between the counter electrode and the sensing electrode, said sensing electrode side negative, the counter electrode side as the positive, and the applied voltage mechanism that gives an applied voltage selected from the range of 500 to 700 mV,
A reagent-free free residual chlorine measuring apparatus comprising: an ammeter for measuring a redox current flowing between a detection electrode and a counter electrode when the applied voltage is applied by the applying voltage mechanism. The reagent-free free residual chlorine measuring device according to claim 1, further comprising an arithmetic control unit, which obtains the free residual chlorine concentration of the sample liquid based on the redox current measured by the ammeter. The reagent-free free residual chlorine measuring apparatus according to claim 1 or 2, further comprising an automatic cleaning mechanism for cleaning the detection electrode and the counter electrode. This is a reagent-free free residual chlorine measurement method that measures free residual chlorine without using reagents.
An applied voltage selected from the range of 500 to 700 mV is applied between the gold detection electrode and the platinum counter electrode directly immersed in the sample solution, with the detection electrode side as minus and the counter electrode side as plus. A reagent-free free residual chlorine measuring method, characterized in that the redox current flowing between the detection electrode and the counter electrode is measured, and the free residual chlorine concentration is obtained from the obtained redox current. The reagent-free free residual chlorine measuring method according to claim 4, wherein the sample liquid is seawater or boiler cooling water.

Images