JP2001349866A - Apparatus for measuring residual chlorine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a residual chlorine-measuring apparatus, which can accurately measure the concentration of each of a free residual chlorine and a combined residual chlorine in residual chlorine concentration, and can distinctively measure concentrations of monochloramine and dichloramine in the combined residual chlorine. SOLUTION: After a reagent which includes bromide ions are merged with a sample solution, the reagent is introduced to a detecting part 7. In the detecting part 7, a first, a second and a third application voltages are applied between a detection electrode 14 of gold, which moves a circular motion and a counter electrode formed of platinum, and concentrations of the free residual chlorine, the monochlolamine and the dichloramine are calculated separately from each of oxidation-reduction current values obtained then. The first application voltage is selected from a range of -0.2 to -0.4 V, the second application voltage is selected from a range of -0.4 to -0.6 V, and the third application voltage is selected from a range of -0.7 to -1.0 V, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring residual chlorine, and more particularly, it is possible to obtain the concentration of free residual chlorine and the concentration of combined residual chlorine in the residual chlorine concentration. The present invention relates to a residual chlorine measuring apparatus capable of obtaining a concentration of dichloramine and a concentration of dichloramine.

[0002]

2. Description of the Related Art Residual chlorine is available chlorine having a disinfecting action remaining in water as a result of chlorination, and is classified into free residual chlorine such as hypochlorous acid and bound residual chlorine such as chloramine. . All have bactericidal power by oxidation.

[0003] Of these, free residual chlorine is mainly composed of hypochlorite (HClO) generated by the reaction of a chlorine agent with water, hypochlorite ion (ClO-) dissociated therefrom, and molecular chlorine (Cl2). In three forms. The ratio of the three forms depends on the pH. For example, at a pH of 2 or lower, molecular chlorine is mainly present, and in the range of pH 4 to pH 7, it mainly takes the form of hypochlorous acid, and at a pH of 7.4, hypochlorite and hypochlorite ions have almost the same concentration. That is, at ordinary pH such as tap water, most free residual chlorine exists as hypochlorous acid or hypochlorite ion.

[0004] On the other hand, bound residual chlorine is produced by the reaction of free residual chlorine with ammonia, amines and amino acids in water. Monochloramine (NH2Cl), dichloramine (NHCl2) and trichloramine (NCl3) are formed. It takes the form of a kind. These ratios also depend on the pH, with the ratio of monochloramine being maximal in the range of pH 6.5 to pH 8.5. The ratio of dichloramine is pH
It is said to increase in the range of 5.0 to pH 6.5.
Then, at ordinary pH such as tap water, most of the bound residual chlorine is present as monochloramine or dichloramine. Monochloramine and dichloramine have overwhelmingly weak bactericidal activity compared to free residual chlorine.

According to the enforcement regulations of the Water Supply Law of Japan, from the viewpoint of securing sufficient sterilizing power, the water in the hydrant is 0.1 mg / L or more if free residual chlorine and 0.4 mg / L if combined residual chlorine. It specifies that residual chlorine of L or more should be retained. As described above, the concentration of residual chlorine to be retained also differs between the case of free residual chlorine and the case of combined residual chlorine in consideration of the difference in sterilizing power. Therefore, in a water purification plant, it is necessary to distinguish not only the total residual chlorine concentration but also the free residual chlorine concentration and the combined residual chlorine concentration.

In the chlorination treatment, it is necessary to adjust the amount of the chlorine agent to be injected so that the residual chlorine concentration does not become excessive while ensuring sufficient sterilizing power. As described below, in order to properly adjust the amount of the chlorine agent to be injected, it is necessary to distinguish and grasp the free residual chlorine concentration and the combined residual chlorine concentration.

[0007] The residual chlorine concentration typically varies as shown in FIG. 7 according to the amount of the chlorine agent injected. First, in the initial stage of injecting the chlorine agent, the residual chlorine concentration remains almost zero. This is because the injected chlorinating agent is immediately consumed by inorganic and organic substances which are very easily decomposed by chlorine. As the chlorinating agent injection is further continued, the residual chlorine concentration gradually increases with the production of chloramine (mainly monochloramine), but starts decreasing after a certain point. This is because the produced chloramine is finally decomposed into nitrogen and hydrochloric acid by a chlorine agent in excess of the amount of chlorine necessary for producing chloramine.
After the end of the generation and decomposition of chloramine (discontinuous point), the residual chlorine concentration increases in accordance with the subsequent injection amount of the chlorinating agent. After the discontinuous point, since the oxidation of ammoniacal nitrogen and the like has been almost completely completed, the concentration of free residual chlorine mainly increases.

[0008] As described above, since the change in the residual chlorine concentration accompanying the injection of the chlorine agent moves in a complicated manner according to the concentration of ammoniacal nitrogen in the water, etc., in order to optimize the residual chlorine concentration, the total residual chlorine concentration is required. It is necessary to grasp not only the concentration but also the concentration of free residual chlorine and the concentration of residual chlorine residual, and to adjust the amount of the chlorinating agent to be supplied according to these concentrations.

[0009] The residual chlorine concentration has been conventionally measured by various methods. In addition, in the o-tolidine colorimetric method (OT method), the time from the addition of a reagent to the measurement is changed to obtain a diethyl-p-phenylenediamine colorimetric method (DPD).
Method) and polarographic method, it was also possible to separately measure the total residual chlorine concentration and the free residual chlorine concentration by changing the reagent to be added.

For example, in the polarographic method, when a potassium iodide solution is added to a sample solution, iodine is released according to the total residual chlorine concentration. When the released iodine is electrolytically reduced to iodine ions, the total residual chlorine concentration can be obtained by measuring the oxidation-reduction current (diffusion current) flowing between the detection electrode and the counter electrode. The pH at the time of reacting potassium iodide is about pH 3.

When a potassium bromide solution is added in place of potassium iodide, bromine is liberated according to the free residual chlorine concentration. When the released bromine is electrolytically reduced to form bromine ions, the concentration of free residual chlorine can be obtained by measuring the oxidation-reduction current (diffusion current) flowing between the detection electrode and the counter electrode. In addition, p when reacting potassium bromide
H is about pH 4. Then, the combined residual chlorine concentration is obtained from the difference between the total residual chlorine concentration and the free residual chlorine concentration.

As described above, the total residual chlorine concentration and the free residual chlorine concentration can be selectively measured to some extent, and the injection amount of the chlorine agent has been adjusted based on the measurement result. Among various measurement methods, the polarographic method is suitable for continuous measurement and automation, and has been widely used for controlling residual chlorine concentration in water purification plants and the like.

[0013]

As described above, in the apparatus for measuring residual chlorine by the polarographic method or the like, the reagent is changed to provide selectivity. However, when a potassium bromide reagent was reacted with the sample solution, not only free residual chlorine, but also bromine was released due to the residual chlorine, and there was a large positive error due to the influence of the residual chlorine. Therefore, required measurement accuracy could not be obtained.

Further, when a chlorine agent is injected based on the measured total residual chlorine concentration or free residual chlorine concentration, the residual chlorine concentration increases with the passage of time even if the residual chlorine concentration is properly adjusted. The concentration sometimes became too high. It is known that this is because dichloramine is decomposed as time elapses as shown in equation (1) to generate free residual chlorine. This is a phenomenon often seen especially when the water temperature drops in winter. Even if monochloramine is decomposed even with the same combined residual chlorine, free residual chlorine is not generated. 2N HCl2 + OH- → N2 + 2H ++ 3Cl− + HOCl (1)

Therefore, it has been desired that not only the concentration of total residual chlorine and the concentration of free residual chlorine be measured separately but also the concentration of dichloramine among the bound residual chlorine be determined. As a method for measuring dichloramine concentration, Standard Methods in the United States is known. But,
In this method, the reagent must be added to the sample liquid as it is in a powder form, and it has been difficult to apply the method to an automatic measuring device capable of continuous measurement. Therefore, it was practically impossible to adjust the injection amount of the chlorine agent in consideration of the decomposition of dichloramine.

The present invention has been made in view of the above circumstances, and it is possible to accurately measure the concentration of free residual chlorine and the concentration of combined residual chlorine in the concentration of residual chlorine, and to measure the concentration of monochloramine and dichloramine among the combined residual chlorine. It is an object of the present invention to provide a residual chlorine measuring device which can measure the residual chlorine separately.

[0017]

Means for Solving the Problems As a result of studying the above problems, the present inventors have found that even if the polarographic method is used, if specific conditions are selected, different polarograms (applied voltage) may be used depending on the type of residual chlorine. And the measured current) are obtained, and the following invention has been made. Here, the applied voltage is a voltage applied to the detection electrode with reference to the counter electrode.

That is, according to the first aspect of the present invention, there is provided a reagent addition mechanism for adding a reagent containing a halogen ion to a sample liquid, a gold detection electrode, a platinum counter electrode, and a detection electrode between the detection electrode and the counter electrode. And a voltage applying mechanism for applying the first, second, and third applied voltages, and the sample solution to which the reagent is added is caused to relatively flow with respect to the surface of the detection electrode, and between the detection electrode and the counter electrode. A residual chlorine measuring device for measuring a flowing oxidation-reduction current, wherein a first applied voltage ranges from -0.2 to -0.4 V and a second applied voltage ranges from -0.4 to -0.6 V. And a third applied voltage is selected from a range of -0.7 to -1.0 V, respectively.

The oxidation-reduction current measured in the present invention is such that the substance to be reduced is carried to the surface of the detection electrode only by spontaneous diffusion due to a concentration gradient in a layer called a diffusion layer having a constant thickness, and the reduction is performed on the surface. Is the diffusion current that flows when In order to obtain an oxidation-reduction current (diffusion current) corresponding to the concentration of the substance to be reduced, it is necessary to always make the diffusion layer new. If the diffusion layer is constantly refreshed, the substance to be reduced in the sample liquid is supplied to the detection electrode according to the concentration. The diffusion layer can always be refreshed by causing the sample liquid in contact with the sensing electrode to flow relatively to the sensing electrode surface.

In order to cause the sample liquid in contact with the detection electrode to flow relatively to the surface of the detection electrode, the detection electrode is moved by rotating or vibrating the stationary sample liquid, or the detection electrode is kept stationary. Let the sample flow. Alternatively, the sample liquid may be caused to flow while moving the detection electrode.

When a relative flow is obtained only from the flow of the sample liquid, a mechanism for moving the detector is not required, which is suitable for constructing a simple apparatus. However, it is desirable to rotate or vibrate the sensing electrode in order to stably perform accurate measurement for a long period of time. This is because when the measurement is performed using the flow of the sample liquid while the detection electrode is stationary, the polarogram changes depending on the flow rate of the sample liquid.

The detecting electrode used by rotating is called a rotating electrode, and the electrode used by vibrating is called a vibrating electrode. These electrodes rotate and vibrate at a linear velocity much larger than the normal flow rate of the sample liquid. For this reason, a stable diffusion layer can be formed irrespective of the sample liquid flow velocity, and the measurement value is less affected by fluctuations in the sample liquid flow velocity. Further, by performing the rotation and the vibration in the cleaning beads, it is possible to easily prevent the contamination of the detection electrode with dirt.

For the rotating electrode, there are a method of using a mercury contact in order to draw out the lead wire from the rotating detection electrode without cutting, and a method of alternately switching the rotation direction to prevent twisting of the lead wire. As disclosed in Japanese Patent Publication No. Hei 7-4566, it is desirable to use a method in which the detection electrode is circularly moved by moving the support of the detection electrode in a peal shape without rotating.
As for the vibrating electrode, there are various methods such as a method of vibrating the detection electrode with an external vibrator (see Japanese Utility Model Publication No. 62-41240) and a method of using the built-in electromagnet to vibrate (Japanese Utility Model Publication No. 6-765). The known type is known, and any type may be adopted as the detection electrode in the device of the present invention.

In the apparatus of the present invention, since a reagent containing a halogen ion is added to the sample solution, the substance to be reduced is
It is a substance obtained by reacting residual chlorine in a sample liquid or a reagent containing residual chlorine with a halogen ion. In the apparatus of the present invention, depending on whether the residual chlorine is free residual chlorine, monochloramine, or dichloramine,
Different polarograms are obtained. It is considered that this is because the substance to be reduced under the conditions of the present apparatus is different for each type of residual chlorine.

Specifically, the first voltage of -0.2 to -0.4 V
Is approximately a function of the free residual chlorine concentration. Further, the current obtained at the second applied voltage of -0.4 to -0.6 V is substantially a function of the concentration of free residual chlorine and the concentration of monochloramine. Also, -0.7 to -1.0
The current obtained at the third applied voltage of V is a function of the free residual chlorine concentration, the monochloramine concentration and the dichloramine concentration. As described above, different polarograms can be obtained depending on the type of residual chlorine, so that the respective concentrations can be calculated from the oxidation-reduction current values at three different applied voltages.

Further, as set forth in claim 2, the first applied voltage ranges from -0.2 to -0.4V and the second applied voltage ranges from -0.4 to -0.5V. When the third applied voltage is selected from the range from -0.7 to -0.9 V, the above functional relationship can be obtained more clearly.

The present inventors have not yet verified the specific chemical species of the substance to be reduced in the apparatus of the present invention, but it is presumed as follows. First, when the residual chlorine is free residual chlorine, it reacts immediately with a halogen ion to release a halogen molecule. Therefore, it is considered that most of the substance to be reduced derived from the free residual chlorine is a halogen molecule. On the other hand, when the residual chlorine is a combined residual chlorine such as monochloramine or dichloramine, the reaction with the halogen ions is less likely to proceed as compared with the free residual chlorine. Therefore, most of monochloramine and dichloramine,
It is considered that the substance is directly reduced.

In the apparatus of the present invention, the smaller the number of halogen molecules released due to the residual chlorine residue, the more clearly the above functional relationship can be obtained. In other words, it is desirable that the reaction between the residual chlorine and the halogen ion does not proceed as much as possible.
However, the conditions of the apparatus of the present invention are not limited to conditions under which no halogen molecules derived from the residual chlorine residue are generated. In this case, it is considered that the functional relationship between the current obtained at the first to third applied voltages and each residual chlorine becomes complicated, the calculation of the concentration of each residual chlorine becomes complicated, and the error increases. Can be In this case, it is necessary to fix the measurement conditions more strictly in order to obtain a measurement result with a little reproducibility. Therefore, as described in claims 3 to 5, it is desirable to select conditions under which the reaction between the residual chlorine and halogen ions does not proceed as much as possible.

First, it is desirable that the halogen ions contained in the reagent be bromide ions. It is also possible to select iodide ions as halogen ions, but bromide ions react more slowly with residual chlorine bound.

It is desirable that the reagent contains a pH adjuster for adjusting the pH of the sample solution after the addition of the reagent to a range of pH 4 to pH 5. This is because by adjusting the pH to a relatively high value, the reaction between halogen ions such as bromide ions and bound residual chlorine can be slowed down.

As described in claim 5, it is desirable to measure the oxidation-reduction current within 3 minutes after the addition of the reagent. This is because if the reaction time is too long, the reaction between halogen ions such as bromide ions and the residual chlorine bound proceeds. The lower limit of the time from the addition to the measurement is not particularly limited, but it is necessary to secure a time for mixing the sample solution and the reagent.

Further, the invention according to claim 6 includes:
From the oxidation-reduction current values at the second and third applied voltages,
An apparatus for measuring residual chlorine according to any one of claims 1 to 5, further comprising an operation mechanism for calculating the concentration of dichloramine. This makes it possible to obtain a dichloramine concentration which has been conventionally the most difficult. Moreover, it can be performed automatically.

According to a seventh aspect of the present invention, there is provided an arithmetic mechanism for calculating a concentration of dichloramine from an oxidation-reduction current value at the second and third applied voltages. The present invention provides a residual chlorine measuring device according to any one of the above. It is clear from experience that under normal conditions where dichloramine is present, there is almost no free residual chlorine.Based on this fact, the dichloramine concentration can be approximately determined only by the current value at two different applied voltages. is there.

When the residual chlorine concentration is adjusted based on the measured value obtained by the residual chlorine measuring device according to any one of claims 1 to 7, the amount of the chlorine agent injected into the water to be sterilized is adjusted. Since the residual chlorine concentration present at that time can be accurately measured for each type, it is possible to accurately control the required residual chlorine concentration prescribed in the Water Supply Law enforcement regulations. In addition, since the concentration of bound residual chlorine, particularly dichloramine, can be measured, it is possible to predict the change in residual chlorine concentration after the injection of the chlorinating agent, and to optimize the injection amount.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a residual chlorine measuring apparatus according to one embodiment of the present invention, in which a sample liquid is interposed in a reagent inflow path 3 by a pump 2 interposed in a sample liquid inflow path 1. Mixing coil 5
Flows into the intervening merging channel 6. Then, the sample liquid and the reagent mixed in the joining channel 6 are introduced into the detecting section 7 and then discharged from the discharge path 8. Reference numeral 9 denotes an arithmetic and control unit that controls the detection unit 7 and calculates a measured value.

The reagent contains a halide such as potassium bromide or potassium iodide, and a pH adjuster. In order to facilitate the addition of tap water to a sample solution, the solution is supplied as a solution instead of a powder. Sample solution and reagents
It is designed to be introduced into the detection unit 7 several seconds to several tens of seconds after the merging.

FIG. 2 shows the structure of the detection unit 7. Reference numeral 11 denotes a flow cell, reference numeral 12 denotes a sample liquid mixed with a reagent introduced into the flow cell 11, and reference numeral 13 denotes a columnar part whose lower part is immersed in the sample liquid 12. , The detection electrode support 14;
Reference numeral 3 is a detection electrode attached to the tip surface, 15 is a cylindrical counter electrode support whose lower part is immersed in the sample solution 12, 16 is a counter electrode attached to the outer peripheral surface of the counter electrode support 15, and 17 is a rotation of the detection electrode. The motor, 18 is a variable applied voltage circuit, and 19 is an ammeter. The sample solution 12 contains glass beads (not shown) for cleaning the detection electrode.

The detection pole 14 is the same as the above-mentioned actual fair 7-4566.
No. 4, pp. 147-64, 1991. The circular motion is performed according to the method described in Japanese Unexamined Patent Publication (Kokai) No. H10-209686. That is, the sensing electrode support 13 is arranged in an inclined state, and a predetermined portion in the lengthwise middle portion is held by the bearing 23. Further, the base end portion 24 of the detection electrode support 13
The rotation shaft 25 of the motor 17 is eccentrically engaged with the rotation shaft 25 of the motor 17.
Numeral 4 is adapted to make a circular motion with the holding point of the bearing 23 as a fulcrum. Then, with the circular movement of the base end 24, the detection pole 14 attached to the distal end of the detection pole support 13 also makes a circular movement. Further, the lead wire 26 connecting between the detection electrode 14 and the ammeter 19 is twisted even when the detection electrode 4 is moved circularly from the vicinity of the holding position of the bearing 23 through the inside of the detection electrode support 3. It can be pulled out without.

In the present embodiment, the detection electrode 14 is made of gold, and the counter electrode 16 is made of platinum. In addition, the applied voltage circuit 18 receives the first applied voltage (−0.2
And a second applied voltage (-0.4 V to -0.6 V, preferably -0.4 V to -0.4 V).
And a third applied voltage (-0.7 V to -1.0 V, preferably -0.7 V to -0.7 V).
(A voltage selected from the range of 0.9 V) can be switched at intervals of about 1 second.

When measuring the residual chlorine concentration of the sample liquid using the residual chlorine measuring apparatus of this embodiment, the sample liquid and the reagent
After being mixed in the merging channel 6, it is introduced into the detection unit 7. Since the free residual chlorine in the sample solution reacts instantaneously with the halogen ions in the reagent, it is almost completely replaced by halogen molecules when the sample solution is introduced into the detection section. On the other hand, the bound residual chlorine is introduced into the detection section 7 with little or no reaction with the halogen ions.

In the detecting section 7, the operation of the motor 17 causes the detection pole support 13 to make a circular motion about the bearing 23, thereby causing the detection pole 14 to make a circular motion. Then, a measurement voltage is applied between the detection electrode 14 and the counter electrode 16 by the applied voltage circuit 18, and a measurement current flowing between the detection electrode 14 and the counter electrode 16 at this time is detected by the ammeter 19.

At this time, the applied voltage by the applied voltage circuit 18 is switched in time series from the first to the third applied voltage. Then, the current value at each applied voltage is
9 and using these values, the arithmetic and control unit 9 calculates the concentrations of free residual chlorine, monochloramine and dichloramine.

In this embodiment, the mechanism for adding the reagent is as follows.
Since the system is combined before being introduced into the detection unit, the replacement of the sample liquid in the detection unit 7 is good, and an unstable component called residual chlorine can be accurately measured. In addition,
The reagent solution may be directly added to the detection unit 7, but in this case, it is necessary to take in the measured current value after the time when it is determined that the time required for mixing has elapsed.

In this embodiment, one applied voltage circuit is switched in time series to obtain three kinds of applied voltages. However, a plurality of applied voltage circuits each providing a single applied voltage are provided with a plurality of applied voltages. A pair of detection electrodes and counter electrodes may be connected to each other so that current values at three types of applied voltages can be obtained simultaneously. Further, although the detection electrode is a rotating electrode, it may be a vibrating electrode or a stationary electrode (an electrode utilizing the flow rate of the sample liquid).

[0045]

FIG. 3 shows a polarogram showing the relationship between the measured voltage (voltage applied to the detection electrode with reference to the counter electrode) and the measured current for each type of residual chlorine using the residual chlorine measuring apparatus shown in FIG. It is a thing. However, a circuit capable of continuously changing the voltage was used as the applied voltage circuit 18, and the voltage was swept at a sweep speed of 100 mV / min. As the detection electrode, a gold electrode having a diameter of 2 mm is used and the linear velocity is 30 to 50 c.
The rotation was given such that m / s was obtained. The counter electrode is a platinum electrode as described above.

As sample liquids, a sample α in which most of residual chlorine is free residual chlorine, a sample β in which most of residual chlorine is monochloramine, a sample γ in which most of residual chlorine is dichloramine, and A sample δ containing almost no sample was prepared. As a reagent, potassium bromide 30 g
And 10 g of sodium acetate as a pH adjuster and 10 mL of acetic acid were adjusted to 1 L with pure water. The flow rate of the sample solution is 50 mL / min, and the flow rate of the reagent is about 1.1 mL
/ Min, and introduced into the detection unit 7 about 30 seconds after the merging.

The reference value of the concentration of each component in each sample solution was determined by the following manual analysis method according to the United States Standard Methods. First, 1 mL of a DPD (diethyl-p-phenylenediamine) solution reagent and a buffer (0.2 mol)
1 / L KH2PO4 300mL, 0.2mol /
L NaOH 106 mL, and 1,9 cyclohexanediaminetetraacetic acid 0.39 g was dissolved) 1 m
L was placed in a 25 mL colorimetric tube with a stopper. Then, 20 mL of the sample solution was added thereto, and the absorbance at 552 nm was measured.
From this value, the free residual chlorine concentration was obtained.

Next, the sample liquid after the measurement of free residual chlorine is
0.1 mL of a 0.1% potassium iodide solution was added, and the absorbance at 552 nm was measured immediately. From this value, the sum of the free residual chlorine concentration and the monochloramine concentration was determined. Further, 0.2 g of potassium iodide crystal was added to the sample after measuring the total value of the free residual chlorine concentration and the monochloramine concentration,
After dissolution, the mixture was allowed to stand for 5 minutes, and the absorbance at 552 nm was measured. From these values, the total of the concentrations of free residual chlorine, monochloramine, and dichloramine was determined. As a result, the hand analysis values shown in Table 1 were obtained for each of the sample liquids α, β, γ, and δ.

[0049]

[Table 1]

As shown in FIG. 3, the sample liquids α, β, γ, δ
, Different polarograms were obtained. First, in sample α, which is mostly free residual chlorine, −0.0.
At 2 to -1.0 V, a plateau flow region (a region where the current hardly changes even if the applied voltage is slightly shifted) was obtained. In the sample β, which is mostly monochloramine, −0.4 to −0.6 V (particularly −0.4 to −0.5 V).
V), and -0.7 to -1.0 V (particularly -0.7 to-
At 0.9 V), a plateau region was obtained. Also,
In sample γ, which is mostly dichloramine, -0.7 to
At -1.0 V, a plateau region was obtained. Also,
In sample δ containing almost no residual chlorine, the current of −1.0 V or less was negligible.

Since each polarogram is obtained by sweeping the applied voltage, the current rises slightly earlier than when the applied voltage is fixed. Therefore, the current value of the sample β at −0.2 to −0.4 V, −
Current value of sample γ at 0.4 to −0.6 V, −0.9
The current value of the sample δ at -1.0 V is smaller when a fixed applied voltage is applied without sweeping, and there is almost no problem in measurement.

From the above, the first region (−0.2 to
The area current of -0.4 V) is approximately a function of the free residual chlorine concentration. In addition, the second applied voltage (−0.4 to −0.6)
V (preferably -0.4 to -0.5 V) is approximately a function of the free residual chlorine concentration and the monochloramine concentration. In addition, the third applied voltage (−0.7 to −1.0 V)
Desirably, the current obtained at -0.7 to -0.9 V) is
It is a function of the concentration of free residual chlorine, monochloramine and dichloramine.

Therefore, it is possible to calculate the concentration of free residual chlorine, the concentration of monochloramine, and the concentration of dichloramine from the oxidation-reduction current values at three different applied voltages. It should be noted that, under the condition where bound residual chlorine is present, since almost no free residual chlorine is present, the concentration of monochloramine can be approximately obtained only from the current at the second applied voltage. Further, the concentration of dichloramine can be approximately obtained only from the current at the second applied voltage and the current at the third applied voltage.

FIG. 4 to FIG. 6 show various conditions under the same conditions as FIG. 3 except that the applied voltage is switched about every one minute so that the first, second, and third applied voltages are discrete. It is the result of measuring the sample liquid. Note that the first applied voltage is -0.0.
3 V, -0.6 V as the second applied voltage, and -0.8 V as the third applied voltage. Each horizontal axis is
The hand analysis value according to the above-mentioned US Standard Methods, and the vertical axis is the oxidation-reduction current value obtained as the electrode output.

FIG. 4 is a graph showing the relationship between the free residual chlorine concentration and the electrode output at the first applied voltage (-0.3 V). y = 0.492x-0.018
A very good correlation of 8, R2 = 0.9747 was obtained. FIG. 5 is a graph showing the relationship between the monochloramine concentration and the electrode output at the second applied voltage (-0.6 V). y = 0.3692x + 0.251, R
A very good correlation of 2 = 0.9337 was obtained. FIG. 6 is a graph showing the relationship between dichloramine concentration and a value obtained by subtracting the electrode output at the second applied voltage (-0.6 V) from the electrode output at the third applied voltage (-0.8 V). is there. y = 0.368x + 0.34
A very good correlation of 21, R2 = 0.9211 was obtained.

From the results of FIG. 4 to FIG. 6, not only three kinds of residual chlorine can be accurately obtained from the oxidation-reduction current values at three kinds of applied voltages, but also free residual chlorine can be obtained from the current value at the first applied voltage. It was also confirmed that monochloramine could be easily calculated from the current value at the second applied voltage, and dichloramine could be easily calculated from the difference between the current value at the third and the current value at the second applied voltage.

[0057]

According to the apparatus for measuring residual chlorine of the present invention, the concentration of free residual chlorine and the concentration of combined residual chlorine in the concentration of residual chlorine can be accurately measured, respectively.
Monochloramine and dichloramine concentration can be measured separately. In addition, each concentration can be obtained by an approximately simple calculation. Further, by using the residual chlorine measuring device of the present invention, in chlorination of clean water and the like, it is possible to appropriately control the residual chlorine concentration, and to prevent the injection of an excessive chlorine agent while securing a sufficient sterilizing power. be able to.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a detection unit 7 of FIG.

FIG. 3 is a polarogram showing a relationship between a measured voltage and a measured current in one embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the concentration of free residual chlorine and the output of an electrode in another example of the present invention.

FIG. 5 is a graph showing the relationship between monochloramine concentration and electrode output in another example of the present invention.

FIG. 6 is a graph showing the relationship between dichloramine concentration and electrode output in another example of the present invention.

FIG. 7 is a graph showing the relationship between the amount of injected chlorine and the concentration of total residual chlorine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample inflow path 2, 4 Pump 3 Reagent inflow path 5 Mixing coil 6 Merging path 7 Detector 8 Discharge path 9 Arithmetic controller 14 Detecting pole 16 Counter electrode 18 Applied voltage circuit 19 Ammeter

Claims (7)

[Claims] 1. A reagent addition mechanism for adding a reagent containing a halogen ion to a sample liquid, a gold detection electrode, a platinum counter electrode, and first, second, and third electrodes between the detection electrode and the counter electrode. A voltage applying mechanism for applying an applied voltage of 3 to measure the oxidation-reduction current flowing between the detection electrode and the counter electrode while causing the sample liquid to which the reagent is added to flow relatively to the detection electrode surface. A chlorine measuring apparatus, wherein the first applied voltage is -0.2 to-
From the range of 0.4 V, the second applied voltage is -0.4 to-
From the range of 0.6 V, the third applied voltage is -0.7 to-
An apparatus for measuring residual chlorine, which is selected from a range of 1.0 V. 2. A reagent addition mechanism for adding a reagent containing a halogen ion to a sample solution, a gold detection electrode, a platinum counter electrode, and first, second, and third electrodes between the detection electrode and the counter electrode. A voltage applying mechanism for applying an applied voltage of 3 to measure the oxidation-reduction current flowing between the detection electrode and the counter electrode while causing the sample liquid to which the reagent is added to flow relatively to the surface of the detection electrode. A chlorine measuring apparatus, wherein the first applied voltage is -0.2 to-
From the range of 0.4 V, the second applied voltage is -0.4 to-
From the range of 0.5 V, the third applied voltage is -0.7 to-
An apparatus for measuring residual chlorine, which is selected from a range of 0.9 V. 3. The method according to claim 1, wherein the halogen ions contained in the reagent are bromide ions.
The residual chlorine measuring device according to 1. 4. The method according to claim 1, wherein the reagent is p
The residual chlorine measuring device according to any one of claims 1 to 3, further comprising a pH adjuster for adjusting H to a range of pH 4 to pH 5. 5. The residual chlorine measuring device according to claim 1, wherein the measurement of the oxidation-reduction current is performed within 3 minutes after the addition of the reagent. 6. The apparatus according to claim 1, further comprising an arithmetic mechanism for calculating a concentration of dichloramine from an oxidation-reduction current value at the first, second, and third applied voltages.
The residual chlorine measuring device according to any one of the above. 7. The residual chlorine according to claim 1, further comprising an arithmetic mechanism for calculating the concentration of dichloramine from the oxidation-reduction current value at the second and third applied voltages. measuring device.