JP2020003382A - Total effective chlorine measurement device, method for correction of the same, and method for measuring total effective chlorine - Google Patents

Abstract

To provide a total effective chlorine measurement device, a method for correction of the device, and a method for measuring the total effective chlorine which can determine the total effective concentration of chlorine by a two-electrode polarographic method and also can determine an accurate total effective concentration of chlorine including hypobromous acid even in such a sample liquid containing bromine as sea water or a boiler cooling water.SOLUTION: A applied voltage selected from the 750±250-mV range is applied between a metal detection electrode 13 immersed in a sample liquid S and a counter electrode 15 made of platinum, an oxidation-reduction current flowing in the detection electrode and the counter electrode is measured, and the total effective concentration of chlorine in the sample liquid is determined from the obtained oxidation-reduction current.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a total available chlorine measuring device, a calibration method thereof, and a total available chlorine measuring method. More specifically, the present invention relates to a total available chlorine measuring apparatus capable of evaluating the total available chlorine concentration of a sample solution containing bromine such as seawater in a reagentless manner, a calibration method thereof, and a total available chlorine measuring method.

The total available chlorine concentration is the concentration of the entire germicidal halogen-based drug. Specifically, it is represented by the amount of halogen (usually the amount of chlorine) corresponding to the amount of iodine released when potassium iodide is reacted.
Total available chlorine includes bound chlorine such as free chlorine (hypochlorous acid or hypochlorite ion) and chloramine.
When sodium hypochlorite is added to water containing bromine such as seawater, hypobromite is generated by a reaction with bromine, and further reacts with ammonia nitrogen in seawater to form bromoamines (bound bromine). Is generated. The hypobromite, bromoamines, and the like are also included in the total available chlorine because they react with potassium iodide to release iodine.

For continuous measurement of chlorine concentration, a polarographic method for measuring an oxidation-reduction current has been conventionally used. As the apparatus for measuring the chlorine concentration by the polarographic method, there are a reagent type apparatus which requires addition of a reagent and a non-reagent type apparatus which does not use a reagent.
Reagent-free equipment has the advantage of less maintenance work and maintenance costs, but the reagent-free, stable and accurate measurement of chlorine concentration is limited to specific sample liquids such as clean water. This is the current situation (Patent Document 1).
Particularly, in the case of seawater or water containing bromine such as boiler cooling water, the chlorine concentration cannot be measured accurately and stably by the reagentless polarographic method.

Japanese Patent No. 3469962

  In view of the above circumstances, the present invention can determine the total available chlorine concentration by a two-electrode polarographic method without using a reagent, and in a sample solution containing bromine such as seawater or boiler cooling water, hypobromite. An object of the present invention is to provide a total available chlorine measuring device capable of accurately and stably measuring the total available chlorine concentration including an acid and the like, a calibration method thereof, and a total available chlorine measuring method.

In order to achieve the above object, the present invention employs the following configurations.
[1] An apparatus for measuring total available chlorine by a two-electrode polarographic method,
A gold detection electrode immersed in the sample liquid, and a platinum counter electrode,
An applying voltage mechanism for applying an applied voltage selected from a range of 750 ± 250 mV between the detection electrode and the counter electrode;
An ammeter for measuring an oxidation-reduction current flowing between the detection electrode and the counter electrode when the applied voltage mechanism applies the applied voltage.
[2] The total available chlorine measuring apparatus according to [1], further including an arithmetic control unit, wherein the arithmetic control unit obtains a total available chlorine concentration of the sample liquid based on the oxidation-reduction current measured by the ammeter. .
[3] A calibration method for calibrating the total available chlorine measuring apparatus according to [2], wherein a calibration solution containing no halogen other than chlorine and having an electric conductivity of 4 mS / m or more is used. Calibration method.
[4] An applied voltage selected from the range of 750 ± 250 mV is applied between the gold detection electrode immersed in the sample solution and the platinum counter electrode, and an oxidation-reduction current flowing between the detection electrode and the counter electrode is applied. Measuring the total available chlorine concentration of the sample solution from the measured oxidation-reduction current.
[5] The selected applied voltage is applied between the detection electrode and the counter electrode immersed in a calibration solution containing no halogen other than chlorine and having an electric conductivity of 4 mS / m or more, and The oxidation-reduction current flowing between the counter electrode is measured, and a calibration curve based on the correspondence between the obtained oxidation-reduction current and the total available chlorine concentration of the calibration solution is obtained.
The method for measuring total available chlorine according to [4], wherein the total available chlorine concentration of the sample liquid is obtained from the oxidation-reduction current when measuring the sample liquid using the calibration curve.
[6] The method for measuring total available chlorine according to [4] or [5], wherein the sample liquid contains bromine.

  According to the total available chlorine measuring apparatus, the calibration method thereof, and the total available chlorine measuring method of the present invention, the total available chlorine concentration can be obtained by a two-electrode polarographic method without using a reagent, and seawater or boiler cooling water can be obtained. Even with a sample liquid containing bromine, the total available chlorine concentration including hypobromous acid and the like can be accurately and stably measured. In addition, it can be used to measure low-concentration total available chlorine.

FIG. 1 is an overall configuration diagram of a total available chlorine measuring device according to a first embodiment of the present invention. It is a sectional view of a sensor part in a total available chlorine measuring device concerning a 2nd embodiment of the present invention. It is a whole block diagram of a total available chlorine measuring device according to a third embodiment of the present invention. It is a sectional view of a sensor part in a total available chlorine measuring device concerning a 4th embodiment of the present invention. 4 is a calibration curve obtained in Experimental Example 1 of the present invention. 9 is a polarogram when chlorine is added to seawater obtained in Experimental Example 2 of the present invention. 9 is a polarogram when chlorine is added to the dechlorinated water obtained in Experimental Example 2 of the present invention. 9 is a polarogram of sample liquids A to C obtained in Experimental Example 3 of the present invention. 4 is a calibration curve obtained in Experimental Example 4 of the present invention. It is a measurement result of the total available chlorine concentration of Experimental example 4 of the present invention. It is the result of having measured the seawater which added chlorine of Experimental example 5 of this invention continuously. It is the result of having measured the seawater to which the low concentration chlorine of Experimental example 6 of this invention was added.

<First embodiment>
[Device configuration]
An apparatus for measuring total available chlorine by a two-electrode polarographic method according to the first embodiment of the present invention will be described with reference to FIG. The total available chlorine measuring apparatus according to the present embodiment is schematically configured by 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 electrode support 12 whose lower part is immersed in the sample liquid S, a detection electrode 13 attached to the distal end surface of the detection electrode support 12, and a lower part of the sample. 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 are held. The bearing 17 has a large number of beads 18 for cleaning the detection electrode 13 put in the sample liquid S. The measurement cell 11 is provided with a mesh-shaped partition plate 11a for partitioning between 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 has an arithmetic control unit 21, an applied voltage mechanism 22, an ammeter 23, and a display device 24. The line L1 is connected between the detection electrode 13 and the arithmetic control unit 21, the line L2 is connected between the counter electrode 15 and the arithmetic control unit 21, and the line L3 is connected between the motor 16 and the arithmetic control unit 21. . The ammeter 23 is provided in the middle of the wiring L1, and the applied voltage mechanism 22 is provided in the middle of the wiring L2.

The detection pole 13 is made of gold. The counter electrode 15 is made of platinum.
The sensing pole support 12 is arranged in an inclined state, and a predetermined portion in the middle in the longitudinal direction is held by the bearing 17, and the precession can be performed with the holding location of the bearing 17 as a fulcrum. The base end 12a of the detection pole support 12 and the rotating shaft 16a of the motor 16 are eccentrically engaged. Therefore, by rotating the rotation shaft 16 a of the motor 16, the base end portion 12 a circularly moves, and the detection pole 13 attached to the distal end of the detection pole support 12 also vibrates (circularly moves). . Also, the wiring L1 can be pulled out from the vicinity of the holding position of the bearing 17 through the inside of the detection electrode support 12 without twisting even if the detection electrode 13 is made to circularly move.

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

The detection electrode 13 and the counter electrode 15 can be washed using a chemical solution according to the composition of the dirt component. For example, chemical cleaning using oxalic acid, hydrochloric acid, aqueous hydrogen peroxide, or the like can be performed. Further, ozone cleaning may be performed. Physical cleaning such as brush cleaning may be performed instead of, or in addition to, chemical cleaning.
Further, in order to keep the detection electrode 13 clean, it is preferable to perform electrolytic polishing in addition to mechanical polishing using the beads 18. In the electropolishing, it is sufficient that a current flows between the detection electrode and the counter electrode in a direction opposite to that in the measurement, and a well-known method can be appropriately employed.
The total available chlorine measuring device of the present embodiment may include an automatic cleaning mechanism for cleaning the counter electrode 15 and the detection electrode 13. In that case, periodic cleaning can be performed automatically.

[Measurement of total available chlorine]
In the total available chlorine measuring apparatus of the present embodiment, the voltage applying 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 750 ± 250 mV, preferably from the range of 600 to 900 mV, and more preferably from the range of 700 to 800 mV.
If the applied voltage is around 750 mV, regardless of whether the sample solution contains seawater or not, and since a plateau region can be obtained in the measurement range of the total available chlorine concentration of normal seawater, it does not contain halogens other than chlorine. Using a calibration liquid such as tap water having an electric conductivity of 4 mS / m or more, a calibration curve for measuring the total available chlorine concentration of seawater or a sample liquid containing seawater can be created.
In addition, the same calibration curve can be used regardless of whether the total available chlorine is chlorine or bromine and regardless of the pH.

It is preferable that the applied voltage is appropriately selected from the range of 750 ± 250 mV according to the measurement range of the total available chlorine concentration.
Specifically, when the measurement range is 2 mg / L or less, it is preferable to select from the range of 700 ± 200 mV, more preferably to select from the range of 700 ± 100 mV, and to select from the range of 700 ± 50 mV. Is more preferred.
When the measurement range is 2 mg / L or more, it is preferable to select from the range of 800 ± 200 mV, more preferably from the range of 800 ± 100 mV, and even more preferably from the range of 800 ± 50 mV.

Also, the ammeter 23 measures an oxidation-reduction current flowing between the detection electrode and the counter electrode when the applied voltage mechanism 22 applies the applied voltage between the detection electrode 13 and the counter electrode 15. I have.
Although the sample liquid S to be measured is not particularly limited, the present invention is particularly suitable when the sample liquid S is seawater containing bromine (bromine ion or bromate) or when it contains seawater such as boiler cooling water. Applicable to

In the total available chlorine measuring method of the present invention, the arithmetic and control unit 21 obtains the total available chlorine concentration from the oxidation-reduction current obtained by the total available chlorine measuring device of the present invention. The obtained total available chlorine concentration is given to the display device 24 as a signal D1, and the total available chlorine concentration is displayed on the display device 24. The value of the total available chlorine concentration is transmitted as a signal D2 to an external recorder, data logger, memory, printer, computer, or the like. Note that the signal D2 may be a digital signal or an analog signal. Further, the information may be transmitted by wire or wirelessly.
In order to obtain the total available chlorine concentration from the oxidation-reduction current by the arithmetic and control unit 21, the calculation is performed using a calibration curve indicating a correlation between the oxidation-reduction current and the total available chlorine concentration previously obtained using a calibration liquid. The calibration solution and a calibration method using the calibration solution will be described later.

Further, the arithmetic and control unit 21 may output the current value from the ammeter 23 to the external computer as the signal D2. In this case, if the external computer performs an operation for calculating the total available chlorine concentration from the oxidation-reduction current, the total available chlorine measuring method of the present invention can be implemented.
Further, the arithmetic and control unit 21 may output the current value from the ammeter 23 to the display device 24 as the signal D1. In this case, if the operator obtains the total available chlorine concentration from the oxidation-reduction current based on the current value read from the display device 24 and the previously obtained calibration curve, the total available chlorine measuring method of the present invention can be performed. .

The temperature of the oxidation-reduction current used in the calculation is preferably corrected. Therefore, the total available chlorine measuring device of the present invention preferably includes a temperature sensor. When the temperature of the sample liquid is kept sufficiently constant or when the required measurement accuracy is low, the temperature correction may be omitted.
The temperature correction means conversion to an oxidation-reduction current at a reference temperature (for example, 25 ° C.) in consideration of the temperature dependence of the measurement of the oxidation-reduction current. When the reference temperature is 25 ° C., specifically, the temperature is corrected by the following equation (1).
I (V) ₂₅ = I (V) _t / (1+ (α × (t−25) / 100)) (1)
t: Sample liquid temperature during measurement (° C)
I (V) _t : Redox current value at voltage V obtained at sample liquid temperature t ° C. I (V) ₂₅ : Redox current value at voltage V corrected at reference temperature 25 ° C. α: per 1 ° C. Electrode output change (%)

[Proofreading]
In the calibration method for calibrating the total available chlorine measuring device of the present invention, a calibration solution containing no halogen other than chlorine and having an electric conductivity of 4 mS / m or more is used.
When the sample liquid is seawater or the like containing bromine, there is an idea that a calibration liquid to which a known concentration of chlorine is added to seawater or the like should be used.
However, the present inventor considered that seawater contains various components, and since its composition also constantly changes, the effect on the calibration value cannot be predicted, and it was considered unfavorable to use a calibration solution based on seawater. . Then, in the total available chlorine measuring apparatus of the present invention, dechlorinated water, and a solution obtained by adding a known concentration of chlorine to this dechlorinated water, or tried to use tap water as a calibration liquid, stably with high accuracy It has been found that calibration that can be measured is possible.

The calibration liquid used for the calibration of the present invention has an appropriate electric conductivity required for the polarographic method. Specifically, it is 4 mS / m or more, and preferably 4 to 5000 mS / m. The dechlorinated water is not pure water, and is a liquid containing an ionic component that does not contain halogen but gives an appropriate electric conductivity.
Since tap water usually contains chlorine and has an appropriate electric conductivity (usually 4 to 40 mS / m), it can be used as it is as a calibration solution in the present invention. Further, if chlorine is removed from tap water, dechlorinated water can be obtained. Tap water is easily available, and it is convenient and preferable to use it as it is as a calibration solution.
The calibration solution used in the present invention can also be prepared by diluting a stock solution containing a known concentration of chlorine with dechlorinated water.

Specifically, the calibration using the calibration solution is performed by applying an applied voltage selected in the range of 750 ± 250 mV (the same as when measuring the sample solution) between the detection electrode immersed in the calibration solution and the counter electrode. And a redox current flowing between the detection electrode and the counter electrode is measured. The arithmetic control unit 21 or the external computer receiving the information from the arithmetic control unit 21 obtains a calibration curve based on the obtained redox current and the total available chlorine concentration of the calibration liquid.
The obtained calibration curve is stored in the arithmetic control unit 21 or an external computer which receives information from the arithmetic control unit 21 and is used when calculating the total available chlorine concentration of the sample solution from the oxidation-reduction current when the sample solution is measured. Is done.

The calibration curve can be obtained by using two or more kinds of calibration solutions having different chlorine concentrations. For example, a calibration curve can be obtained using dechlorinated water and a span solution (a stock solution containing a known concentration of chlorine diluted with dechlorinated water at a dilution rate that takes into account the measurement range of a measuring device, or tap water) as a calibration solution. it can.
Once a calibration curve has been created, a highly accurate calibration curve can be maintained by periodically performing span calibration using the actual sample solution.

<Second embodiment>
[Device configuration]
The total available chlorine measuring apparatus by the two-electrode polarographic method 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. It is.

  FIG. 2 is a 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 having a through hole 32 a formed in one opening of the case 31 in the center along the axial direction. Is fixed. A pair of upper and lower circular windows 32b, 32b are formed in a substantially central portion of the support base 32 in the axial direction so as to penetrate from one peripheral surface to the opposing peripheral surface at right angles to the axial direction. . A recess 32c is formed in the circumferential direction near the tip, and a counter electrode 33 is wound around the entire surface of the recess 32c.

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

A motor 38 is mounted inside the case 31, and is fixed to a rotation shaft 38 a of the motor 38 above the eccentric coupling 41. The eccentric coupling 41 is held by a 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 connection shaft 44 is connected to a lower side of the eccentric coupling 41. The angle formed between the rotation shaft 38a and the connection shaft 44 is set to about 3 degrees, and the portion of the connection shaft 44 connected to the coupling case 42 makes a circular motion by driving the motor 38.

  The connection shaft 44 is inserted into the bearing 45 slightly below the axial center. The bearing 45 is composed of a cylindrical portion 45a having a cylindrical shape in the direction of the connecting shaft 44, and a flange portion 45b extending radially around the lower end of the cylindrical portion 45a, and is formed of a rubber material. The cylindrical 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 water-tight contact with the inner peripheral surface of the support base 32.

The lower end of the connecting shaft 44 from the bearing 45 is inserted into the upper end of a substantially cylindrical sensing electrode support 46. As a result, the detection electrode support 46 is connected and fixed to the lower end of the connection shaft 44, and hangs down in the through hole 32 a of the support base 32. The detection pole 35 is provided at the lower end of the detection pole support 46.
When the portion of the connection shaft 44 connected to the coupling case 42 makes a circular motion by the drive of the motor 38, the connection shaft 44 performs precession with the portion where the flange 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 circularly.

The lead wire 47 of the detection electrode 35 is finally connected to the arithmetic and control unit 21 of the main unit 20 via the connector 48. The counter electrode 33 is connected to the arithmetic and control unit 21 of the main unit 20 via a connector 48. The motor 38 is also connected to the arithmetic and control unit 21 of the main unit 20 via a connector 48.
Note that, in FIG. 2, the illustration of the wiring near the connector 48 of the lead wire 47 is omitted. Also, 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.
As in 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 of the cap 34 and the window 32b. As a result, the sample liquid S comes into contact with the detection electrode 35 and also comes into contact with the counter electrode 33 wound around the support base 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 total available chlorine measuring device according to the second embodiment can measure the total available chlorine and the like in the same manner as the total available chlorine measuring device according to the first embodiment. Further, calibration can be performed in the same manner as in the total available chlorine measuring apparatus according to the first embodiment.

<Third embodiment>
[Device configuration]
An apparatus for measuring total available chlorine by a two-electrode polarographic method according to a third embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof will be omitted.
The total available chlorine measuring apparatus according to the present embodiment is schematically configured by a sensor unit 3, a main body unit 20, and a liquid sending 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 a flow cell 19. The flow cell 19 is provided with a mesh-like partition plate 19a for partitioning between 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 sending section 50 has an inflow path 51 for sending the sample liquid S to the flow cell 19, a discharge path 52 for discharging the sample liquid S from the flow cell 19, and a pump 53 provided in the inflow path 51.
The pump 53 and the arithmetic and control unit 21 are connected by a wiring L4. The pump 53 operates according to an instruction from the arithmetic and control unit 21.
The total available chlorine measuring apparatus according to the third embodiment can measure the total available chlorine and the like in the same manner as the total available chlorine measuring apparatus according to the first embodiment except that the sample liquid S is caused to flow in the flow cell 19. it can. Further, calibration can be performed in the same manner as in the total available chlorine measuring apparatus according to the first embodiment.

<Fourth embodiment>
[Device configuration]
The total available chlorine measuring apparatus by a two-electrode polarographic method 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. It is.

FIG. 4 is a 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. 4, the same components as those in FIG. 2 are denoted by the same reference numerals as in FIG. 2, and detailed description thereof will be omitted.
The support base 32 is inserted into the flow cell 60. The space between the inner wall on the upper end side of the flow cell 60 and the outer periphery of the support base 32 is fixed in a liquid-tight manner via an O-ring 61.
A sample liquid inflow port 60 a for inflow of a sample liquid is provided at the center of the front end of the flow cell 60, and a sample liquid outflow port 60 b for outflow of the sample liquid is provided on a side wall near the O-ring 61. The inflow path 51 is connected to the sample liquid inlet 60a, and the discharge path 52 is connected to the sample liquid outlet 60b.

  When the sample liquid S flows from the sample liquid inlet 60a of the flow cell 60 of the sensor unit 4 of this embodiment, a part of the sample liquid S enters the cap 34 and flows out of the sample liquid outlet 60b through the window 32b. I do. Thereby, the sample liquid S comes into contact with the detection electrode 35. Further, after a part of the sample liquid S flows in from the sample liquid inlet 60a, it passes outside the support base 32 and flows out from the sample liquid outlet 60b. As a result, the sample liquid S comes into contact with the counter electrode 33 wound around the support base 32. That is, by flowing the sample liquid S from the sample liquid inlet 60a of the flow cell 60, the detection electrode 35 and the counter electrode 33 are immersed in the sample liquid S.

  The total available chlorine measuring device according to the fourth embodiment can measure the total available chlorine and the like in the same manner as the total available chlorine measuring device according to the third embodiment. Further, calibration can be performed in the same manner as in the total available chlorine measuring apparatus according to the third embodiment.

<Other embodiments>
In each of the above embodiments, a method of obtaining the reproducibility of the thickness of the diffusion layer necessary for the polarographic method by a method of positively flowing the sample liquid in contact with the detection electrode to the surface of the detection electrode is employed. A method of obtaining the reproducibility of the thickness of the diffusion layer by a method of suppressing the flow of the sample liquid in a narrow range may be adopted. As an apparatus employing the method, for example, an oxidation-reduction current measuring apparatus described in JP-A-2015-34740 can be mentioned.

Hereinafter, experimental examples for clarifying the effects of the present invention will be described.
[Experimental example 1]
The total available chlorine concentration when a known concentration of chlorine was added to seawater was measured using a total chlorine DPD reagent.
(A) Sample solution The total available chlorine concentration of the following sample solutions was measured.
・ Seawater,
A sample solution obtained by adding a known concentration of sodium hypochlorite solution to seawater so that the amount of chlorine added to 1 L of the sample solution is 0.15 mg;
A sample solution obtained by adding a known concentration of sodium hypochlorite solution to seawater so that the amount of chlorine added to 1 L of the sample solution is 0.25 mg;
A sample liquid obtained by adding a known concentration of sodium hypochlorite solution to seawater so that the amount of chlorine added to 1 L of the sample liquid is 0.65 mg.

(B) Total chlorine reagent As a DPD reagent for measuring total chlorine, a total chlorine reagent (item code: HACH0582) manufactured by HACH and containing the following components was used.
Potassium iodide: 20.0-30.0% by mass,
N, N-diethyl-phenylenediamine salt: 1.0 to 5.0% by mass,
Carboxylates: 40.0 to 50.0% by mass,
Disodium hydrogen phosphate: 20.0 to 30.0% by mass,
Disodium ethylenediaminetetraacetate: less than 1.0% by mass.

(C) Measurement of total available chlorine concentration A fixed amount of the total chlorine reagent and 10 mL to 20 mL of the sample solution was taken in an absorption cell having a cell length of 50 mm, and mixed with a photoelectric spectrophotometer (DR2700 manufactured by HACH). The absorbance at a wavelength of 510 nm after 2 seconds was measured, and the total available chlorine concentration was determined from a previously prepared calibration curve. FIG. 5 shows the results.

The calibration curve for obtaining the total available chlorine concentration (measured value) on the vertical axis in FIG. 5 was created by measuring the following dechlorinated water and a standard sample in the same manner as the sample liquid.
Dechlorinated water: tap water treated with activated carbon to remove chlorine (the same applies to the following experimental examples).
Standard sample: prepared by diluting a sodium hypochlorite solution having an effective chlorine concentration of about 12% with dechlorinated water. The total available chlorine concentration of the prepared standard sample was determined according to the above "(c) Measurement of total available chlorine concentration" (the same applies to the following experimental examples).

As shown in FIG. 5, the slope of the measured value with respect to the added concentration was as small as 0.5409. Although the cause is unknown, it is considered that the added chlorine was consumed due to the influence of the components in the seawater, and the absorbance was lower than in the case where no seawater was contained.
However, a good correlation was obtained between the added concentration and the measured value (R ² = 0.9953).
For this reason, it was confirmed that the total available chlorine concentration obtained by the above calibration curve from the absorbance measured using the total chlorine reagent was effective as an index of the total available chlorine concentration in seawater.

[Experimental example 2]
The polarogram showing the relationship between the applied voltage and the oxidation-reduction current was examined using the total available chlorine measuring apparatus of the fourth embodiment. However, a mechanism capable of continuously changing the voltage was used as the applied voltage mechanism 22, a gold electrode having a diameter of 2 mm was used as the detection electrode 13, and rotation was performed so that a linear velocity of about 100 cm / s was obtained. . The counter electrode 15 was a platinum electrode. As the sample solution, a sample solution obtained by adding chlorine (sodium hypochlorite solution) to seawater and a sample solution obtained by adding chlorine (sodium hypochlorite solution) to dechlorinated water were used.
FIG. 6 shows a polarogram when chlorine is added to seawater, and FIG. 7 shows a polarogram when chlorine is added to dechlorinated water.

  In FIG. 6, the numerical value described after T is the total available chlorine concentration measured using the total chlorine reagent as in Experimental Example 1. For example, the polarogram indicated as “T 0.493 mg / L” is a polarogram of a sample solution (sample solution obtained by adding chlorine to seawater) having a total available chlorine concentration of 0.493 mg / L measured in the same manner as in Experimental Example 1. 2 shows a program.

In FIG. 7, the numerical value described after F is the free chlorine concentration measured in the same manner as in Experimental Example 1 except that the DPD reagent for measuring free chlorine was used. For example, the polarogram shown as "F0.48 mg / L" is a sample solution having a free chlorine concentration of 0.48 mg / L measured in the same manner as in Experimental Example 1 except that a DPD reagent for measuring free chlorine was used. 2 shows a polarogram of a sample solution obtained by adding chlorine to dechlorinated water).
Since the sample solution obtained by adding chlorine (sodium hypochlorite solution) to dechlorinated water does not contain available chlorine other than free chlorine, the value described after F in FIG. It is also the total available chlorine concentration.

As a DPD reagent for measuring free chlorine, a free chlorine reagent (item code: HACH0578) manufactured by HACH and containing the following components was used.
N, N-diethyl-phenylenediamine salt: less than 5.0% by mass,
Carboxylates: 60.0 to 70.0% by mass,
Disodium hydrogen phosphate: 30.0 to 40.0% by mass,
Disodium ethylenediaminetetraacetate: less than 5.0% by mass.

6 and 7, the plateau region (the region where the current hardly changes even if the applied voltage slightly changes) tends to shift to the higher voltage side as the total available chlorine concentration increases. Comparing the polarograms of FIG. 6 and FIG. 7 in which the total available chlorine concentration is almost equal, the plateau regions of both were almost equal.
That is, the plateau of the sample solution having a total available chlorine concentration of 0.493 mg / L in FIG. 6 and the sample solution having a free chlorine concentration (total available chlorine concentration) of 0.48 mg / L in FIG. 7 is around 600 mV. The plateau of the sample solution having a total available chlorine concentration of 1.202 mg / L in FIG. 6 and the sample solution having a free chlorine concentration (total available chlorine concentration) of 1.00 mg / L in FIG. 7 was around 700 mV. .

From this, it was found that the extent to which the sample solution contained seawater did not affect the range of the applied voltage that resulted in a favorable plateau region.
Therefore, it can be seen that a calibration curve for measuring the total available chlorine concentration of seawater or a sample solution containing seawater can be prepared using a calibration solution containing no halogen other than chlorine and having an electric conductivity of 4 mS / m or more. Was.

6 and 7, a good plateau region was obtained near the applied voltage of 750 mV. From FIG. 7, it is considered that a plateau region can be obtained at about 900 mV in the case of a sample solution having a total available chlorine concentration of about 3 mg / L.
Considering this result and that the measurement range of the total available chlorine concentration of seawater is usually 2 mg / L or less on the low concentration side and 2 mg / L or more on the high concentration side, the applied voltage is in the range of 750 ± 250 mV. I knew what to do.
In addition, in order to perform particularly accurate measurement, it is necessary to appropriately select an applied voltage in the range of 750 ± 250 mV according to the measurement range (the higher the measurement range of the total available chlorine concentration, the more the applied voltage becomes 750 ± 250 mV). The application voltage on the high voltage side should be selected within the range).

[Experimental example 3]
Polarograms showing the relationship between the applied voltage and the oxidation-reduction current were examined for the following sample solutions A to C using the same apparatus as in Experimental Example 2 and under the same measurement conditions. FIG. 8 shows the results.
Sample liquid A: a sample liquid obtained by adding a known concentration of sodium hypochlorite solution to dechlorinated water so that the free chlorine concentration per 1 L of the sample liquid after addition is 2 mg / L,
Sample liquid B: a sample obtained by adding 0.6 g of potassium bromide to 1 L of sample liquid A,
Sample liquid C: A sample obtained by adding 0.6 g of potassium bromide, 0.2 g of anhydrous sodium acetate, and 0.2 mL of acetic acid to 1 L of sample liquid A.

Sample solution A contains free chlorine (hypochlorous acid). On the other hand, the sample solutions B and C contain hypobromous acid due to the added potassium bromide.
The pH of the sample solution B is about 7.5, while the pH of the sample solution C containing the buffer component is about 4.0.
As shown in FIG. 8, there was no significant difference between the sample liquids A to C in the current value when the applied voltage was around 750 mV.
From this, it was found that, when the applied voltage was around 750 mV, the same calibration curve could be used irrespective of the difference between free chlorine and hypobromite and regardless of the pH. .

[Experimental example 4]
Calibration of the total available chlorine measuring apparatus of the fourth embodiment with an applied voltage of 800 mV was performed using a span solution (containing free chlorine but not other halogens) composed of dechlorinated water and tap water. . A gold electrode having a diameter of 2 mm was used as the detection electrode 13 of the total available chlorine measuring device, and the rotation was applied to a linear velocity of about 100 cm / s. The counter electrode 15 was a platinum electrode. When the span liquid was measured using the total chlorine reagent in the same manner as in Experimental Example 1, the total available chlorine concentration was 0.68 mg / L. The obtained calibration curve is shown in FIG.
The obtained calibration curve of FIG. 9 was stored in the total available chlorine measuring apparatus.

The total available chlorine concentration of the following sample liquids was measured using the above-mentioned total available chlorine measuring device in which the calibration curve of FIG. 9 was stored. The results are shown in Table 1 and FIG.
The “additional concentration” in Table 1 and FIG. 10 is the concentration of chlorine added to seawater or the total available chlorine concentration measured using a total chlorine reagent in tap water. In addition, the oxidation-reduction current in Table 1 is a value obtained by using a total available chlorine measuring apparatus, and the measurement values in Table 1 and FIG. 10 are obtained from the oxidation-reduction current using the calibration curve in FIG. Effective chlorine concentration.

(Sample liquid)
A sample solution obtained by adding a sodium hypochlorite solution of known concentration to seawater so that the amount of chlorine added to 1 L of the sample solution is 0.45 mg;
A sample solution obtained by adding a known concentration of sodium hypochlorite solution to seawater so that the amount of chlorine added to 1 L of the sample solution is 1.04 mg;
A sample liquid obtained by adding a known concentration of sodium hypochlorite solution to seawater so that the amount of chlorine added to 1 L of the sample liquid is 2.75 mg;
-Tap water: Tap water having a total available chlorine concentration of 0.75 mg / L measured in the same manner as in Experimental Example 1.

As shown in Table 1 and FIG. 10, the measured value was in good agreement with the additive concentration, and a good correlation was observed between the additive concentration and the measured value.
Further, in FIG. 10, it was confirmed that the data of tap water and the data of the sample liquid obtained by adding chlorine to seawater were on the same straight line.
From this, the calibration curve obtained using a calibration solution that does not contain halogen other than chlorine such as tap water and has an electric conductivity of 4 mS / m or more can be used for measurement of a sample solution obtained by adding chlorine to seawater. It turned out to be effective.

[Experimental example 5]
A sample liquid in which a known concentration of sodium hypochlorite solution was added to seawater so that the amount of chlorine added to 1 L of seawater was 0.5 mg, and the total available chlorine measurement of the fourth embodiment was calibrated by Experimental Example 4. The measurement was performed using an apparatus, and the change over time in the measurement results was examined. The results are shown in FIG.
As shown in FIG. 11, the measured value decreased with the passage of time, but the state of the decrease was along a gentle curve.
This is because hypobromite and bromoamines generated by the reaction of added sodium hypochlorite with bromine and ammoniacal nitrogen in seawater are consumed or decomposed by components in seawater and reduced. It is thought that the situation that goes is correctly caught.

[Experimental example 6]
While continuously measuring seawater with the total available chlorine measuring device calibrated in Experimental Example 4, a fixed amount of sodium hypochlorite solution of known concentration was sequentially added, and the change in the measured value was examined. The results are shown in Table 2 and FIG.
In Table 2 and FIG. 1 to 4 indicate that the measurement was performed at the following times.
The DPD values in Table 2 and FIG. 12 are the total available chlorine concentrations measured using the total chlorine reagent in the same manner as in Experimental Example 1, and the measured values are values obtained by the total available chlorine measuring device.

NO. 1: Before adding the sodium hypochlorite solution.
NO. 2: The time when sodium hypochlorite solution was added for the first time so that the amount of chlorine added to 1 L of seawater was 0.02 mg.
NO. 3: The time when the sodium hypochlorite solution was added for the second time so that the amount of chlorine added to 1 L of seawater was 0.02 mg.
NO. 4: The time when the sodium hypochlorite solution was added for the third time so that the amount of chlorine added to 1 L of seawater was 0.02 mg.

  As shown in Table 2 and FIG. 12, a good correlation was obtained between the DPD value and the measured value even though the total available chlorine concentration was extremely low. In addition, for example, NO. It was also found that if the zero point of the calibration curve obtained by the calibration of Experimental Example 4 was corrected based on the measurement result at the time point 1, the DPD value and the measured value could be matched with higher accuracy.

[Experimental example 7]
A low-concentration sample in which dechlorinated water and a sodium hypochlorite solution having an amount of chlorine added to dechlorinated water of 0.03 mg were added to the dechlorinated water by the total available chlorine measuring device of the fourth embodiment calibrated in Experimental Example 4. The liquid and the liquid were alternately measured, and the reproducibility of the measurement results of the low-concentration sample liquid from the first time to the fourth time was examined. Table 3 shows the results.
As shown in Table 3, high reproducibility was obtained with the total available chlorine measuring device, even though the total available chlorine concentration was extremely low.

1-4 sensor part, 11 measurement cell, 12 detection electrode support, 13, 35 detection electrode,
14 ... counter electrode support, 15, 33 ... counter electrode, 16, 38 ... motor, 17, 45 ... bearing,
18, 36: beads, 19, 60: flow cell, 20: body,
21: arithmetic control unit, 22: applied voltage mechanism, 23: ammeter, 24: display device,
50: liquid sending section, 53: pump, S: sample liquid

Claims (6)

An apparatus for measuring total available chlorine by a two-electrode polarographic method,
A gold detection electrode immersed in the sample liquid, and a platinum counter electrode,
An applying voltage mechanism for applying an applied voltage selected from a range of 750 ± 250 mV between the detection electrode and the counter electrode;
An ammeter for measuring an oxidation-reduction current flowing between the detection electrode and the counter electrode when the applied voltage mechanism applies the applied voltage.   The total available chlorine measuring apparatus according to claim 1, further comprising an arithmetic control unit, wherein the arithmetic control unit obtains a total available chlorine concentration of the sample liquid based on the oxidation-reduction current measured by the ammeter.   3. A calibration method for calibrating an apparatus for measuring total available chlorine according to claim 2, wherein a calibration liquid containing no halogen other than chlorine and having an electric conductivity of 4 mS / m or more is used.   An applied voltage selected from the range of 750 ± 250 mV is applied between the gold detection electrode immersed in the sample solution and the platinum counter electrode, and an oxidation-reduction current flowing between the detection electrode and the counter electrode is measured. A method for measuring the total available chlorine, wherein the total available chlorine concentration of the sample liquid is obtained from the obtained oxidation-reduction current. Applying the selected applied voltage between the detection electrode and the counter electrode immersed in a calibration solution containing no halogen other than chlorine and having an electric conductivity of 4 mS / m or more, Measure the oxidation-reduction current flowing between, to obtain a calibration curve based on the correspondence between the obtained oxidation-reduction current and the total available chlorine concentration of the calibration solution,
The total available chlorine measuring method according to claim 4, wherein the total available chlorine concentration of the sample liquid is obtained from the oxidation-reduction current when the sample liquid is measured using the calibration curve.   The total available chlorine measuring method according to claim 4 or 5, wherein the sample liquid contains bromine.

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