JPS6156464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring the concentration of free residual chlorine, which separates the concentration of free residual chlorine from combined residual chlorine and enables accurate measurement by electrolytic current method.

For example, _Cl2 is commonly used to disinfect water.
Water at 10℃ dissolves approximately 2.7 times the volume of Cl ₂ ,
_Cl2 dissolved in water reacts with water as follows to form HClO
and HCl.

Cl ₂ + H ₂ OHClO + H ⁺ + Cl ^- …(1) The equilibrium constant K _h of this reaction is at 25°C, K _h = [HClO] [H ⁺ ] [Cl ^- ] / [Cl ₂ ] = 4.5×10 ^-4 ( mol/l) ² ...(2). In addition, a portion of HClO dissociates into both ClO ^- and H ⁺ ions.

HClOH ⁺ +ClO ^- ...(3) The equilibrium constant K _i of this reaction at 25°C is K _i = [H ⁺ ] [ClO ^- ] / [HClO] = 2.7×10 ^-8 (mol/l) ...(4) It is. Here, Cl ₂ , HClO, and ClO ^- are collectively referred to as free residual chlorine. Since this free residual chlorine has a strong bactericidal effect, it is necessary to measure its concentration because by knowing its concentration in water, it is possible to determine whether the water is suitable for drinking.

On the other hand, raw river water, swimming pool water, wastewater, etc. that actually require disinfection often contain ammonia compounds and organic nitrogen compounds. Organic nitrogen compounds react with free residual chlorine, and N and Cl combine to form N-Cl bonds, resulting in various organic chloramines. This organic chloramine is hydrolyzed as follows.

RR'NCl + H ₂ OHClO + RR'NH ... (5) The equilibrium constant K _h of this reaction is expressed as K _h = [HClO] [RR'NH] / [RR'NCl] ... (6) depending on the type of
It takes various values from 10 ^-4 to 10 ^-10 (mol/l).

On the other hand, an ammonia compound reacts with free residual chlorine in the following manner to generate inorganic chloramine.

NH ₃ +HOCl→NH ₂ Cl+H ₂ O …(7) NH ₃ +2HOCl→NHCl ₂ +2H ₂ O …(8) NH ₃ +3HOCl→NCl ₃ +3H ₂ O …(9) NH ₂ Cl is monochloramine, NHCl ₂ is dichloride. Lamin, NCl ₃ is called nitrogen trichloride. Since the equilibrium constant of equation (7) is 2.8×10 ⁻¹⁰ , almost all of HOCl is converted to monochloramine.
The existence form of inorganic chloramine changes depending on the pH, and there are two types between monochloramine and dichloramine.
There is an equilibrium relationship as follows.

2NH ₂ Cl + H ⁺ NH ⁻ ₄ +NHCl ₂ …(10) At 25°C, this equilibrium constant K _e is: K _e = [NH ⁺ ₄ ] [NHCl ₂ ] / [H ⁺ ] [NH ₂ Cl] ² = 6.7×10 ⁵ (mol/l) ^-1 ...(11).

Since a large amount of ammonia compounds are expected to be present in raw water from rivers and pool water, it is thought that a large amount of chloramine is present in this chlorinated water. In the presence of such a large amount of chloramine, it was very difficult to selectively detect the free residual chlorine concentration by amperometric measurement.

Conventionally, as a continuous amperometric analyzer for measuring free residual chlorine in chlorinated water containing ammonia, a sample water prepared by adding a buffer solution and KBr to the chlorinated water is passed through a current measurement cell, and the combined chlorine is There is a method in which the potential of the measuring electrode is set to a diffusion current level that is not sensitive to the concentration of free residual chlorine. (Refer to Japanese Patent Application Laid-open No. 50-6397).

However, although the above publication states that free residual chlorine and combined residual chlorine can be separated and detected only by selecting the electrode potential, detailed research has shown that this is not possible. found.
In fact, it was found that separation and detection was possible only under specific conditions determined by the correlation between the pH value of water, Br ^- concentration, and flow rate.

More generally speaking, the reaction rate of residual chlorine reacting with Br ^- to form Br ₂ depends on the temperature of the test water,
We have newly discovered that PH and Br ^- depend on the concentration, and that this dependence can be used to make the reaction rate different between the free form and the bound form of residual chlorine.

This invention was made based on the above discovery, and it involves adjusting the amount of bromine salt such as KBr added to the test water and the pH of the buffer solution, and adjusting the pH of the buffer solution from the time of adding these reagents to the time of reading the electrolytic current. By setting the time (in the case of flowing water, equal to the ratio of the distance between the reagent addition position and the electrode position to the flow rate), the free residual chlorine concentration can be separated from the bound residual chlorine concentration and measured accurately using the electrolytic current method. It has been made possible.

This invention will be explained in detail below.

FIG. 1 shows the configuration of an electrolytic current measuring device for explaining one embodiment of the present invention, in which 1 is a platinum electrode for measurement, 2 is a silver electrode for comparison, 3 is a saturated calomel electrode, and 4 is a A power source for voltage application, 5 a voltmeter, 6 an ammeter, 7 a tank, and 8 water to be tested.

Now, in the test water 8 that maintains the equilibrium of equation (1), when adding a buffer solution to the test water 8 containing this free residual chlorine to bring its pH to 5, for example,
For an HClO concentration of 3.55 ppm (10 ^-4 mol/l), the
From formula (2), [HClO]/[Cl ₂ ]=4.5×10 ⁵ . Also, from equation (4), [HClO]/[ClO ^- ] = 3.7×10 ² , and almost all of the free residual chlorine is HClO.
It will exist in the form of

The measurement electrode made of a precious metal, that is, the platinum electrode 1, which does not react with HClO and is not attacked by the test water 8, reacts with the component molecules in the test water 8. When the reference electrode, which always maintains a constant potential, i.e., the silver electrode 2, is immersed and the two electrodes are short-circuited, HClO has a strong oxidizing power, so
The following reaction occurs on the measuring electrode.

HClO+H ⁺ +2e→Cl ^- +H ₂ O...(12) The redox potential E ₀ in this case is 1.5V.

Since the reference electrode is the silver electrode 2, the following reaction occurs here.

Ag+Cl ^- →AgCl+e...(13) Therefore, the redox potential E ₀ =0.22V.

Therefore, when HCIO is present in the test water 8, a current flows between the platinum electrode 1 and the silver electrode 2.
Test water 8 with an HClO concentration of 2 ppm and a pH of 5 was stirred at a constant speed, and a platinum electrode 1, a silver electrode 2, and a saturated calomel electrode 3 were placed in a tank 7 to change the potential of the platinum electrode 1. The relationship between the electrolytic current i and the potential v of the platinum electrode 1 at the time is shown by the curve in FIG.

In the curve, when the potential v of the platinum electrode 1 is a high positive potential, the reaction of equation (12) does not occur, but as the potential v becomes lower, the reaction rate of equation (12) progresses monotonically. increases to However, when the potential becomes less than +0.2V, the rate of progress of the reaction of equation (5) on the electrode surface becomes
The current becomes less dependent on the potential because it becomes faster than the diffusion rate of HClO to the electrode surface (diffusion rate-limiting). This region is called the plateau region.
In this plateau region, the electrolytic current i does not depend much on the potential v of the platinum electrode 1 or the activity of the electrode, but is proportional to the HClO concentration, so by setting the potential of the platinum electrode 1 to this value, the value of the electrolytic current i from HClO
You can know the concentration.

When the potential v of the platinum electrode 1 becomes 0.1V or less, the following reaction occurs on the platinum electrode 1 due to dissolved oxygen, so the electrolytic current i further increases and HClO
It is no longer proportional to the concentration.

O ₂ +2H ₂ O+4e→4OH ^- (14) In this case, the redox potential E ₀ =0.4V.

In the amperometric residual chlorine meter that measures the electrolytic current i of HClO as described above, the plateau region is narrow, and large changes in the potential v or activity of the platinum electrode 1 can easily cause changes in the electrolytic current i. There are drawbacks. Therefore, when a chemical solution that electrolyzes to produce Br ^- is added to water containing HClO, the following reaction occurs and Br ₂ is liberated.

HClO + H ⁺ +2Br ^- →Br ₂ +Cl ^- +H ₂ O...(15) This Br ₂ is hydrolyzed as follows, and a portion becomes hypobromite (HBrO).

Br ₂ + H ₂ OHBrO + H ⁺ + Br ^- (16) The equilibrium constant K _h of this reaction at 25°C is K _h = [HBrO] [H ⁺ ] [Br ^- ] / [Br ₂ ] = 5.8 × 10 ^-9 ( mol/l) ² ...(17) Therefore, for example, if the pH of test water 8 is 4,
When the Br ^- concentration is 10 ^-2 mol/l, when [HBrO] is sufficiently smaller than [Br ^- ], from equation (17), [HBrO] / [Br ₂ ] = 5.8 × 10 ^-3 ... (18 ), and Br ₂ is hardly hydrolyzed. Br ₂ measured using platinum electrode 1 and silver electrode 2 (curve)
The polarogram of and HBrO (curve) is shown in Figure 3. Since the electrolytic current i of Br ₂ has a wider plateau region than that of HBrO or HClO, it has the advantage that it hardly changes due to changes in the potential v or activity of the platinum electrode 1. Therefore, No. (17)
In order to achieve H ⁺ and Br ^- values such that [HBrO]/[Br ₂ ] is sufficiently small in the formula, chemical solutions such as PH
4 acetate buffer solution and KBr to give a Br ^- concentration of 10 ^-2 mol/l to the test water, HCIO reacts with Br ^- to generate an electrolytic current of Br ₂ which is virtually equivalent to HClO. By measuring i with the potential v of the platinum electrode 1 set within the plateau region, the concentration of HClO can be accurately determined even if the potential v of the platinum electrode 1 or activity changes somewhat.

However, when a copper electrode is used as the silver electrode 2, which is the comparison electrode, the added Br ^- reacts as follows.

Cu+Br ^- →CuBr+e...(19) Since this CuBr is poorly soluble in water, as it accumulates on the copper electrode, it forms a resistive film, which causes a potential drop (resistance polarization) when electrolytic current i flows. The potential v of the platinum electrode 1 changes accordingly. In order to eliminate this effect, it is necessary to constantly polish the surface of the copper electrode so that new metallic copper comes into contact with water.

On the other hand, when the reference electrode is silver electrode 2, it reacts with Br ^- as follows.

Ag+Br ^- →AgBr+e...(20) AgBr is poorly soluble like CuBr, but it has the highest photosensitivity among silver halides, exhibiting absorption spectrum characteristics as shown in Figure 4, and photoreduction reaction due to absorbed light. Ag fine particles are precipitated by this method. Therefore, as long as light is irradiated onto the silver electrode 2,
Since Ag fine particles are always present on the surface of the silver electrode 2 and the progress of the reaction of formula (20) is not inhibited, there is an advantage that there is no need for electrode polishing.

As shown above, test water 8 containing only free residual chlorine
In this case, by adding Br ^- to the test water 8 and detecting the diffusion current of the equivalent amount of Br ₂ liberated by the oxidation action of the free residual chlorine using the platinum electrode 1 and the silver electrode 2, Free residual chlorine concentration can be measured accurately. In this case, [Br ₂ ] is changed to [Br ₂ ] +
In order to make [HBrO] more than 95%, for example, from equation (17), [H ⁺ ] [Br ^- ] = 5.8×10 ^-9 · [Br ₂ ]/[HBrO] = 5.8×10 ^-9・95/5 = ~10 ^-7 (mol/l) ² In other words, the hydrogen ion concentration [H ⁺ ] of the test water 8,
The product of bromine ion concentration [Br ^- ] is 10 ^-7 (mol/l) ²
The pH and Br ⁻ concentration of the buffer solution to be added and the amount to be added may be determined so as to achieve the above.

However, when Br ^- is added to water containing bound residual chlorine, such as inorganic chloramine, the following reactions occur simultaneously.

NH ₂ Cl + 2Br ^- +2H ⁺ Br ₂ +NH ₄ Cl ... (21) NHCl + 4Br ^- +3H ⁺ 2Br ₂ +NH ₄ Cl + Cl ^- ... (22) When the pH is between 5 and 9.5, monochloramine and dichloramine coexist from equation (11). Therefore, No. (21)
It is thought that the reactions of equation (22) occur simultaneously. In this case, the production rate of Br ₂ is dBr ₂ /dt=k ₁・[NH ₂ Cl] [Br ^- ] ² [H ⁺ ] ² −k ₂ [Br ₂ ], where k ₁ to k ₄ are reaction rate constants. [NH ₄ Cl] ...(23) And, dBr ₂ /dt=k ₃・[NHCl ₂ ][Br ^- ] ⁴ [H ⁺ ] ³ −k ₄ [Br ₂ ] ² [NH ₄ Cl] [Cl ^- ] …(24) becomes. The ratio of [Br ₂ ] and [NH ₂ Cl] in an equilibrium state is given by the following equation.

[NH ₂ Cl] [Br ^- ] ² [H ⁺ ] ² / [Br ₂ ] [NH ₄ Cl] = k ₂ / k ₁ = k ₁₂ ... (25) [NHCl ₂ ] [Br ^- ] ⁴ [H ⁺ ] ³ / [Br ₂ ] ² [NH ₄ Cl] [Cl ^- ] = k ₄ / k ₃ = K ₃₄ ...(26) When the pH of the test water 8 changes, monochloramine changes according to equation (11). Since the abundance ratio of Br and dichloramine changes, the equation for the production rate of total Br ₂ cannot be expressed simply.

Conventionally, this reaction between chloramine and Br ^- was completely ignored, or it was believed that the values of K ₁₂ and K ₃₄ in equations (25) and (26) were sufficiently large; therefore, the reaction between chloramine and Br ^- It was thought that there would be little reaction. For example, in the experimental example in JP-A No. 50-6397 cited above, it is said that the reaction between chloramine and Br ^- does not occur at pH 4, but this happens to be due to the fact that the test water 8 passes through the current measurement cell. The flow rate is sufficiently fast and the reaction time to produce Br ₂ from chloramine and Br ^- is longer than 8
This is thought to be due to the fact that it took a longer time to reach the electrode from the reagent (KBr and buffer) injection point.

This invention deals with chloramine and Br ^- in accumulated water.
As a result of a detailed study of the reaction rate using PH and Br ^- concentration as parameters, we found that this reaction rate is not negligibly small and qualitatively follows equations (23) and (24). This discovery was made based on this discovery. Based on this new fact, in order to selectively measure the free residual chlorine concentration in test water 8 containing a large amount ^of chloramine, it _is necessary to , it is clear that it is necessary to limit the time until the electrolytic current i of Br ₂ is measured. That is, the reaction rate of equation (15) is expressed as dBr ₂ /dt=k ₅ [HClO] [H ⁺ ] [Br ^- ] ² = −k ₆ [Br ₂ ] [Cl ^- ]...(27) However, the reaction rate constants k ₅ and k ₆ are significantly different from those of k ₁ to _{k 4} in equations (25) and (26), and the [H ⁺ ][Br ^- ] dependence is (twenty five)
Using the differences in Equation, Equation (25), and Equation (27), the reaction rate of Br ₂ production from free residual chlorine determined by Equation (27) can be calculated using Equation (25) and Equation (26). ) Br ₂ production reaction rate from combined residual chlorine is determined by the formula, i.e., within a time sufficiently shorter than the fixed time required from the addition of the reagent to the end of the concentration reading, Conditions are satisfied for the normal test water temperature range such that the equivalent Br ₂ production reaction is virtually complete, whereas the Br ₂ production reaction due to the combined residual chlorine has not actually progressed by the time of the reading. The range of H ⁺ and Br ⁻ concentrations can be limited.
It is possible to add a chemical solution that brings the sample water 8 into such a concentration range, and only then can selectively and precisely detect only free residual chlorine in the presence of bound residual chlorine. The measuring method according to the present invention will be explained below based on actual measured values.

A buffer solution was added to the test water 8 containing free residual chlorine or inorganic chloramine to adjust the pH to 4, and KBr was added to this.
Figure 5 shows the results of measuring the time change in the Br _{2 concentration generated from the moment the Br 2} was added. In this figure, the curve shows that test water 8 containing 4 ppm chloramine is
When KBr is added to give a Br ^- concentration of 10 ^-2 mol/l, the curve shows that when KBr is added to test water 8, which also contains 4 ppm chloramine, it is added to give a Br ^- concentration of 3 x 10 ^-3 mol/l. When KBr is added, the curve is 1.5ppm
3×10 ^-3 mol/
This corresponds to the case where KBr is added to give a Br ^- concentration of 1. When comparing the curves, it is clear that even if the pH of the test water 8 is the same 4, the rate at which Br ₂ is liberated by the reaction between chloramine and Br ^- varies significantly depending on the amount of KBr added. It is. On the other hand, when comparing the curves, the rate at which Br ₂ is liberated by the reaction between free residual chlorine and Br ^- is the same as that by the reaction between chloramine and Br ^- when the PH and Br ^- concentration conditions are the same. It is clear that the rate at which Br ₂ is liberated is significantly higher. PH
4. When a chemical solution with a Br ^- concentration of 3 x 10 ^-3 mol/l is added to test water 8, 10 seconds after adding the chemical solution,
The concentration of Br ² liberated by the reaction between 1.5 ppm free residual chlorine and Br - reaches saturation and is equivalent to free residual chlorine (equivalent to 1.5 ppm available chlorine) _. The concentration of Br ₂ liberated by the ^- reaction is sufficiently low at approximately 0.05 ppm (equivalent to available chlorine). It is clear that by measuring the Br ₂ concentration at this time, only the free residual chlorine concentration of the test water 8 in which chloramines coexist can be selectively detected.

Furthermore, in the example of JP-A-50-6397 cited above, when the pH of test water 8 was 4, no Br ₂ released by the reaction between chloramine and Br ^- was observed. happens to have a Br ^- concentration of 3×
10 ^-3 mol/l or less, reagents (KBr and buffer)
This is presumed to be due to the fact that it took less than 10 seconds for the test water 8 to come into contact with the current measuring electrode after the addition of .

FIG. 6 shows the results of measuring the polarograms of the following four types of test water using a Pt measurement electrode and an Ag comparison electrode.

Test water 1: Distilled water with KBr and acetate buffer of PH5 added to give a Br ^- concentration of 10 ^-2 M (curve).

Test water 2: Water containing 2 ppm of free residual chlorine
KBr and PH5 buffer added to give a Br ^- concentration of 10 ^-2 M (curve).

Test water 3: After adding 2 ppm of free residual chlorine to water containing 2 ppm of NH ₄ CI, it was left to stand for 30 minutes to produce chloramines, and a PH5 buffer solution was added to this (curve).

Test water 4: KBr added to test water 3 to give a Br ^- concentration of 10 ^-2 M and left to stand for 5 minutes (curve).

The curve is considered to be a polarogram of dissolved oxygen, and the curve is a composite curve of the polarogram and curve of Br ₂ liberated from Br ^- by the oxidation action of free residual chlorine. The curve is explained as a composite polarogram of chloramine and dissolved oxygen, and the curve is a composite polarogram of _Br2 , chloramine, and dissolved oxygen, which are partially liberated by the oxidation action of chloramine.From this, even if the electrolytic current of chloramine (curve )
The measured electrode potential of Pt should be adjusted so as not to result in (e.g.
0.6V), as long as there is an electrolytic current (included in the curve) for Br ₂ generated from chloramine and Br ^- , it selectively converts Br ₂ generated by the reaction between free residual chlorine and Br ^- . It cannot be detected.
Therefore, the means disclosed in JP-A No. 50-6397 are meaningless in achieving the objective of selectively detecting free residual chlorine, and are not effective in suppressing the reaction between chloramine and Br ^- . The determination of the conditions for the liquid phase reaction is essentially important.

Buffer solution and test water containing approximately 4 ppm of chloramines.
Figure 7 shows the pH dependence of the time required for 0.1 ppm (available chlorine ppm equivalent) of Br ₂ to be liberated after adding KBr. The Br ₂ concentration was measured by amperometry using a Pt measurement electrode and a silver reference electrode. The curves,, are 3×10 ^-2 M and 3×
Data is shown when KBr was added to give a Br ^- concentration of 10 ⁻³ M and 3×10 ⁻⁴ M. As the Br ^- concentration and hydrogen ion concentration increase, the reaction rate between chloramine and Br ^- increases, and the
It is clear that the results are qualitatively consistent with Equation (24). Based on these results, a method for determining the PH and Br ^- concentration to achieve a selectivity ratio of free residual chlorine to combined residual chlorine of 40:1 or more will be described below.

As mentioned above, when measuring the free residual chlorine concentration of test water containing only free residual chlorine, the product of [H ⁺ ] and [Br ^- ] must be 10 ^-7 or more. 7th
The curve in the figure is [H ⁺ ] [Br ^- ] = 10 ^-7 (mol/l) ²
The lower left side of this curve represents the region where [H ⁺ ] [Br ^- ]>10 ^-7 (mol/l) ² . Therefore, when a chemical solution that achieves [H ⁺ ] and [Br ^- ] corresponding to within this range is added to the test water, Br ₂ equivalent to free residual chlorine is liberated.

Next, when Br ^- is added to the test water containing chloramines, the reaction between chloramines and Br ^- causes
_Br2 concentration increases with time. In a continuous measurement type residual chlorine meter, in which test water is continuously passed through a current measurement cell, a chemical solution (buffer solution and KBr) is added to the test water, and then the test water passes through the current measurement cell. The time required for this is 10 seconds. Alternatively, in an intermittent water sampling residual chlorine meter, in which the test water is measured into a water sampling cup and the electrode is immersed in it to measure the electrolytic current, after adding the chemical solution to the test water, The time required to read the electrolytic current is 10 seconds. The selection of free residual chlorine and combined residual chlorine in such an amperometric residual chlorine meter is as follows:
In order to make it 1 or more, the concentration of Br ₂ liberated by the reaction of chloramine and Br ^- (ppm effective chlorine equivalent)
The buffer solution and Br ^- concentration to be added to the test water must be selected so that the time required for the chloramine concentration to reach 1/40 of the chloramine concentration (ppm available chlorine equivalent) before the start of the reaction is 10 seconds or more. The time region above the dotted line V in FIG. 7 satisfies this condition, and a combination of [H ⁺ ] and [Br ⁻ ] must be selected from within this region.

The area that satisfies the above two conditions at the same time naturally corresponds to the shaded area in Figure 7, so a chemical solution that achieves a combination of [H ⁺ ] and [Br ^- ] within this range is applied to the test water. It can be added to. Tawasi, 7th
The figure shows the measurement results when the temperature of the test water is 17.5℃, and since k ₁ to _{k 4} in equations (23) and (24) naturally depend on the temperature, it depends on the temperature of the test water. curve,
, and move. Therefore, when the upper and lower limits of the temperature of the test water are given, it is natural that the group of curves shown in FIG. 7 should be determined accordingly. Figure 7 illustrates the characteristics at 17.5°C, which is selected as the median of the normal water temperature range.

FIG. 8 is a partially cutaway side sectional view showing the structure of one embodiment of the device of the present invention. In this figure, 10 is a cylindrical transparent water tank made of glass or plastic for collecting and storing a predetermined amount of test water whose chlorine concentration is to be measured. It has holes 11 for injecting and discharging, and has a hole at the top through which a stirring rod 12 passes. The stirring rod 12 is a cylindrical rod made of an electrical insulator such as baking material, and has a sealed tip and an opening 13 having a larger diameter than the center at the other end. The stirring rod 12 is housed near the central axis of the water tank 10 except for the opening 14 and a small portion adjacent thereto, and a member 14 made of a bendable material such as rubber is attached to the top of the water tank 10. It is fixed so as to surround the stirring rod 12.

Two electrodes, a platinum electrode 15 as a measurement electrode and a silver electrode 16 as a comparison electrode, are independently provided near the tip of the stirring rod 12 housed in the water tank 10. Lead wires 15A and 16A leading to the stirring rod 12 are led out of the water tank 10 through the inside of the stirring rod 12. silver electrode 1
6 is for detecting free residual chlorine and total residual chlorine in the test water. The platinum electrode 15 is used in the above detection, and may be made of not only platinum but also a noble metal such as gold, which has a lower ionization tendency than silver, or carbon.

A motor 18 is fixed inside the outer box 17 attached to the top surface of the aquarium 10, and the outer box 1
7 to the inside of the water tank 10 is the reagent injection nozzle 1.
9 is provided to pass through. This reagent injection nozzle 19 is connected to a reagent tank 21 via a manual pump 20.
A certain amount of reagent is injected into the water tank 10 each time the handle 22 is operated. Further, the stroke of the handle 22 can be changed by adjusting a cylinder having a thread on its outer periphery.

A ball 23 having a shaft at the center is fitted into the opening 13 of the stirring rod 12 so as to be in contact with the inner wall thereof. The shaft of the ball 23 and the rotating shaft of the motor 18 are connected through an eccentric cam 24. Therefore, when the motor 18 rotates, the ball 23 rotates with a radius equal to the eccentricity of the eccentric cam 24. A meter 25 such as an ammeter is provided outside the outer box 17 to indicate the amount of chlorine. The switch 26 is a switch that starts the motor 18. Note that the reagent tank 21 is provided with a valve 27, which is designed to allow the inflow of air necessary for liquid injection, but to prevent the liquid from overflowing. 28 is a gripping part, and 29 is test water.

FIG. 9 is a circuit diagram for measuring residual chlorine used in the embodiment shown in FIG. 8 above. 30 is a power source for applying a voltage between the platinum electrode 15 and the silver electrode 16, and 31 is a potentiometer for adjusting the voltage.

When measuring the residual chlorine concentration, switch 2
6, the motor 18 is started, and the stirring rod 12 is rotated to stir the test water 29. When the motor 18 rotates, the ball 23 rotates with a radius equal to the amount of eccentricity of the eccentric cam 24. Since the ball 23 is in contact with the inner wall of the opening 13 of the stirring rod 12, the stirring rod 1
It attempts to perform the same rotational movement as the ball 23 in No. 2. However, the stirring rod 12 is not connected to the water tank 1 by the member 14.
Since the stirring rod 12 is fixed to the upper surface of the stirrer 0, the stirring rod 12 makes a conical movement with the fixed portion as the apex and the opening 13 drawing the circumference. As a result, the stirring rod 1 in the water tank 10
Similarly, the fixed part is the apex of the part 2, and the stirring bar 12
The test water 29 in the water tank 10 is stirred by a conical motion with the generatrix.

In this way, the handle 22 is reciprocated while stirring the stirring rod 12 in the water tank 10, and the reagent in the reagent tank 21 is injected into the quantitative water tank 10 by the action of the pump. The needle of the meter 25 moves due to this injection, but it stabilizes after a few seconds, and by reading the reading at that time, the residual chlorine concentration can be determined.

As explained in detail above, the method for measuring residual chlorine concentration of the present invention is such that the amount of bromine salt added to the test water satisfies [H ⁺ ] [Br ^- ] 10 ^-7 (mol/l) ² . The concentration of free residual chlorine is measured by measuring the rate-determining diffusion electrolytic current of _Br2 generated when a bromine salt and a buffer solution with the pH of the buffer solution in the range of 2 to 6 are added to the test water. Therefore, the pH of the buffer, the amount of bromine salt, and the Br ₂
By controlling the time until measurement of the rate-determining diffusion electrolytic current, the free residual chlorine concentration can be separated from the bound residual chlorine concentration and measured with high accuracy. Furthermore, since the free residual chlorine concentration measuring device of the present invention uses silver for the anode, fine silver particles are always precipitated simply by irradiating the anode with light, so accurate measurements can be made without polishing the anode. There are many advantages.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the configuration of an electrolytic current measuring device for explaining an embodiment of the present invention, Fig. 2 is a polarogram of HClO, Fig. 3 is a polarogram of Br ₂ and HBrO, and Fig. 4 is a polarogram of AgBr. Absorption spectrum characteristic diagram, Figure 5 shows the relationship between Br ₂ and the elapsed time after Br ^- addition.
Concentration relationship diagram, Figure 6 is a polarogram of various test waters, and Figure 7 is the pH of the time required for Br ₂ equivalent to 0.1 ppm available chlorine to be liberated after adding the buffer solution and KBr to the test water. FIG. 8 is a partially cutaway side sectional view showing an embodiment of the apparatus of the present invention, and FIG. 9 is a residual chlorine measuring circuit used in the embodiment of FIG. 8. In the figure, 1 is a platinum electrode, 2 is a silver electrode, 3 is a saturated calomel electrode, 4 is a power source, 5 is a voltmeter, 6 is an ammeter, 7 is a tank, 8 is test water, 10 is a water tank, and 12 is stirring rod, 15 is a platinum electrode, 16 is a silver electrode, 17 is an outer box, 18 is a motor, 19 is a reagent injection nozzle, 20
is a manual pump, 21 is a reagent tank, 24 is an eccentric cam, and 25 is a meter.

Claims (1)

[Claims] 1. In an amperometric residual chlorine concentration meter equipped with an anode and a noble metal cathode, the cathode is set to a potential that provides a diffusion-controlled electrolytic current of Br ₂ and at the same time does not generate an electrolytic current of dissolved oxygen. The potential is set, and in the reaction between free residual chlorine and Br ^-, Br ₂ equivalent to the free residual chlorine is instantaneously generated, so [H ⁺ ] [Br ^- ] 10 ^-7 (mol/1) ² is set, In addition, in the reaction between combined residual chlorine and Br ^-, a buffer solution and bromine that realize test water with a PH of 2 to 6 and a Br ^- concentration that produces only Br ₂ which is sufficiently small compared to the above-mentioned Br ₂ concentration in a short time. A method for measuring free residual chlorine concentration, comprising administering an aqueous solution of salt to test water, measuring the diffusion-controlled electrolytic current of Br ₂ after a predetermined period of time has elapsed from the point of administration, and obtaining the free residual chlorine concentration from that value. . 2. A silver anode and a noble metal cathode are installed in the tank containing the test water, and in the reaction between free residual chlorine and Br ^- , Br ₂ equivalent to the free residual chlorine is instantly generated, so that [H ⁺ ][Br ^- ] 10 ^-7 (mol/1) ² , and in the reaction between combined residual chlorine and Br ^-, the concentration is sufficiently lower than the concentration of Br ₂ in a short time.
When an aqueous solution of a buffer solution and a bromine salt that realizes a test water with a pH of ₂ to 6 and a Br ^- concentration that produces only Br ₂ is administered to the test water, a diffusion-controlled electrolytic current of Br 2 is obtained. An apparatus for measuring free residual chlorine concentration, comprising: means for setting the potential of the cathode to a potential that does not generate an electrolytic current of dissolved oxygen; and means for measuring the diffusion-controlled electrolytic current of Br ₂ .