JPH034159A - Method for measuring residual chlorine - Google Patents

Abstract

PURPOSE:To separate bond chlorine and free effective chlorine and to exactly measure the concn. of free effective chlorine by adding a reagent specified in the content of potassium bromide to a liquid to be measured. CONSTITUTION:The reagent 1 having, for example, CH3COOH of 2g/l concn., CH3COOH of 54g/l concn., and KBr of 40g/l concn. and about pH6.0 is added to the liquid 3 to be measured. The liquid is then introduced into a measuring chamber 5. A liquid mixture is subjected to reduction by +0.6V voltage im pressed between a rotary platinum electrode 6 and a silver chloride electrode 7. Current is thereby passed therein and is detected by a polarographic technique in a detecting section 8. The influence by the bond chlorine is substantially eliminated and sufficient linearity is obtd. in this way. The concn. of the free effective chlorine is thus exactly measured.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for measuring residual chlorine during chlorination of water such as rivers, and more specifically, to a method for measuring residual chlorine in water in which free available chlorine and combined chlorine coexist. This invention relates to a residual chlorine measuring method for measuring chlorine concentration while reducing the influence of combined chlorine.

<Prior art> Chlorine is usually injected at water supply stations to sterilize river water, etc., but if ammonia nitrogen is present in the water, this ammonia nitrogen is injected. A compound called combined chlorine is produced by reacting with the chlorine. Therefore, as residual chlorine, free available chlorine such as hypochlorite fiHCQO and combined chlorine such as monochloramine NH2Ce and dichloramine NHCt2 coexist. Because there is a difference in sterilizing power between free available chlorine and combined chlorine,
Residual chlorine meters are required to detect only free available chlorine, which is effective for sterilization.

By the way, methods disclosed in Japanese Patent Publication No. 45-20240 and Japanese Patent Application No. 62-247307 are known as methods for detecting only free available chlorine from a sample liquid in which free available chlorine and combined chlorine coexist. There is. Tokuko Showa 45. −
In the method disclosed in No. 20240, a potassium bromide reagent with a pH of 5.6 or higher is used. In the case of such a reagent, since bound chlorine is hardly replaced with bromine, free available chlorine and bound chlorine can be separated. That is, the pH
is on the acidic side of, for example, 4,5, the combined chlorine reacts with KBr in the reagent according to the following formula (1) to liberate Br. For this reason, current flows even when free available chlorine does not exist, resulting in an error.

NH2Cg±28r-+28” Br2+NH4Cg ・・・ ・・・ ・・・ ・・
... (1) On the other hand, if the pH is in the neutral range (e.g. pH
6,00> or more, bromination substitution of combined chlorine is suppressed, and bromine substitution with free available chlorine shown in the following formula (2) is mainly performed.

CQ2+2KBr-Br2 +2KC1''--(2) Therefore, if the free curve r2 is measured at this time, only the free available chlorine concentration can be measured.

<Problems to be Solved by the Invention> However, in the above conventional example, even when the pH is set to a neutral range, chloramine and potassium bromide react according to the following formula (3) to generate prolamine NH2Br. .

N H2CR ten K Rr - NO3 B r ten KCe - (3) When this prolamin is measured using a polarographic method using a platinum indicator electrode and a platinum comparison electrode, a reduction wave appears, and in the state where prolamin coexists, the current flowing due to prolamin is added. However, when it is not possible to obtain an output that accurately corresponds to the concentration of free available chlorine, that is, at a pH of about 5, electrochemistry is performed using a polarographic method using a reagent such as potassium bromide and a platinum indicator electrode and a platinum reference electrode. The method of directly measuring the free available chlorine concentration has a major drawback in that it is influenced by combined chlorine and causes measurement errors, resulting in the inability to accurately measure free available chlorine.

On the other hand, in the measuring method disclosed in Japanese Patent Application No. 62-247307, a reagent containing potassium bromide is added to the liquid to be measured, and the p of the mixture of the reagent and the liquid to be measured is determined by 6.
Using an indicator electrode made of platinum and a reference electrode made of silver chloride, and applying a voltage of +0.35 V to +0
．． The free available chlorine concentration is measured as a voltage within the range of 65V. However, in this method of measuring free available chlorine, when the applied voltage is around +0.5V, the output current value of the polarogram due to combined chlorine is so large that it cannot be ignored, and it has a considerable negative effect on the indicated value of residual chlorine. There were drawbacks.

The present invention has been made in view of this situation, and the technical problem to be solved is to provide an applied voltage value such that the polarogram current value of free available chlorine and the free available chlorine concentration exhibit good linearity. The objective is to separate the polarograms of combined chlorine and free available chlorine, thereby making it possible to accurately measure the free available chlorine concentration.

Means for Solving the Problems> A feature of the present invention that solves the problems described above is that in a method for measuring the concentration of free available chlorine in a liquid to be measured, free available chlorine and combined chlorine are determined by a polarographic method. In the method for measuring the concentration of free available chlorine in a liquid to be measured in which potassium bromide coexists, a reagent containing 40 g/1 or more of potassium bromide is added to the liquid to be measured, and a rotating indicator electrode made of platinum and a reference electrode made of silver chloride are used. and with the applied voltage +0.6V,
The objective is to measure the free available chlorine concentration.

<Example> The present invention will be described in detail below with reference to the drawings. 1st
The figure is an explanatory diagram of the configuration of a residual chlorine analyzer used to carry out the method of the present invention.
, and the concentration is 409/(1, a reagent with KBr and a pH value of approximately 6.0, 2 is a reagent pump that delivers reagent 1, 3 is a!j constant solution, and 4 is a reagent pump that delivers sample liquid 3. The sample bottle 1.5 for feeding the liquid is an inlet [15a and a measuring tank having an outlet 5b, 6
7 is a rotating platinum electrode as an indicator electrode, 7 is a silver chloride electrode as a comparison electrode, and 8 is a detection section consisting of a polarograph or a signal processing circuit. In the residual chlorine meter having such a configuration, the reagent 1 and the liquid to be measured 3 are mixed at a constant ratio and introduced into the measurement tank 5. The mixed solution is reduced by a voltage (for example, 0.6 V) applied between the rotating platinum electrode 6 and the silver chloride electrode 7, a current flows, and detection is performed by the detection section 8 using a polar graphics method.

Figure 2 is a polarogram to explain the influence of combined chlorine when the KBr concentration is 10 g/l. In the figure, the horizontal axis represents the applied voltage (V) and the vertical axis represents the detected current (μA). It represents. Curve ■ is a detection curve for combined chlorine at a concentration of 4.43 m9/l, curve ■ is a detection curve for combined chlorine at a concentration of 2.151 FL9/1, and curve ■ is a detection curve for combined chlorine at a concentration of 0.951 rt9/l.
1 represents the detection curve of combined chlorine of 1.

In contrast, Figure 3 shows KBr floating concentration 0 g/1
FIG. 4 is a polarogram for explaining the influence of combined chlorine when the K Hγ concentration is 200 g/l.

In FIGS. 3 and 4, the horizontal axis represents applied voltage (V), and the vertical axis represents detected current (μA). Also, the third
In the figure, the curve ■ indicates a concentration of 4. The curve ■ represents the detection curve of combined chlorine at a concentration of 13m9/1, the curve ■ represents the detection curve for combined chlorine at a concentration of 2.44R9/l, and the curve ■ represents the detection curve for combined chlorine at a concentration of 0.89119/l. , curve ■ is a detection curve for combined chlorine at a concentration of 5.42 m9/l, curve ■ is a detection curve for combined chlorine at a concentration of 3.91 m971, curve ■ is a detection curve for combined chlorine at a concentration of 2.38 m9/l, and curve ■ is a detection curve for combined chlorine at a concentration of 2.38 m9/l. Concentration 1. Figure 3 depicts the detection curve for combined chlorine of OOmfl/1. In addition, each concentration in FIG. 2 to FIG. 4 all shows the value of free available chlorine measured by amperometric titration method (A i'' method).

As is clear from comparing Figures 2 and 3 (and Figure 4), in Figure 2 linearity deteriorates when the applied voltage exceeds +0°5V, but in Figures 3 and 4 [ At 11il, the plateau region of the polarogram expands and linearity is maintained at 61-min when the applied voltage is +0.6V.

On the other hand, Fig. 5 shows that combined chlorine such as dichloramine or monochloramine (i.e.,
This is a polarogram when only the ATT method (onoiff) was measured; in the figure, the curve ■ is the detection curve for combined chlorine at a concentration of 1°85 m9/l, the curve ■ is the detection curve for combined chlorine at a concentration of 1.82119/l, Curve ■ is a detection curve for combined chlorine at a concentration of 1.77 mR//.

Curve ■ is a detection curve for combined chlorine at a concentration of 1.84 rrt9/l, curve ■ is a detection curve for combined chlorine at a concentration of 1.11119/l, curve ■ is a detection curve for combined chlorine at a concentration of 1.882 m9/l, curve ■ represents a detection curve for combined chlorine at a concentration of 4.16 Jlj/l. As is clear from this figure, when the applied voltage is +0.6V, the detected S flow value of combined chlorine is approximately 0.
(μA). Therefore, the applied voltage is +0
．． When the voltage is 6V, the effect of combined chlorine hardly appears, and if the K IIγ drift is shifted to 40 g/1 or more, sufficient linearity can be obtained as shown in Figures 3 and 4, and as a result, Free available chlorine concentration can be measured accurately with almost no influence from combined chlorine.

Incidentally, according to the experiments conducted by the present inventors, the pH value of the liquid in which the reagent and the liquid to be measured were mixed was determined to be within a certain range (5°0 to 8.6).
), the effect of combined chlorine is approximately 5% of the combined chlorine concentration.
As a result, free chlorine concentration could be accurately measured with almost no influence from combined chlorine. FIG. 6 is a diagram showing the results obtained by the present inventors on hydrochloric acid. In the figure, the horizontal axis is the amperometric titration method (A 'l'
The value of free available chlorine measured by the method (unit: IrL)
g/l), the left vertical axis shows the indicated value of free available chlorine (unit: R9/1) measured with the residual chlorine meter shown in Figure 1, and the right vertical axis shows the value of the free available chlorine measured using the residual chlorine meter shown in Fig. The combined chlorine concentration was measured using fI!i (unit: m9/l). Also, the X mark represents the combined chlorine, and the O mark represents the free available chlorine measured by the AT method and the residual chlorine meter. From Figure 6, it can be seen that even when measuring a liquid containing a high concentration of combined chlorine, the value indicating the concentration of free available chlorine is the same as the straight line A (the calibration curve created by measuring a liquid containing only free available chlorine). ). This indicates that when measuring the free available chlorine Jx, there is almost no effect of the combined chlorine and sufficient linearity can be obtained.

Note that the device used to carry out the measuring method of the present invention is not limited to the configuration example of the residual chlorine meter shown in FIG. 1, and can be modified in various ways. The liquid to be measured flows from the aperture at a constant speed into the indicator type [!
It is also possible to use a configuration in which the liquid is injected at the tip of 6.

<Effects of the Invention> According to the present invention as described in detail above, the effect of combined chlorine hardly appears, sufficient linearity is obtained, and the free available chlorine concentration can be measured accurately.

[Brief explanation of drawings]

Figure 1 is a block diagram of the residual chlorine meter used to carry out the method of the present invention, Figures 2 to 5 are polarograms, and Figure 6 is a polarogram.
The figure shows the experimental results of the present inventors. 1...Reagent, 3...Measurement liquid, 5...Measurement tank, 6
... Rotating platinum electrode as an indicator electrode, 7... Silver chloride electrode as a counter electrode, 8... Detection section -gte, 歂ε (JAll) 1st ward 74 8, j on the coarse side υ, 5=tlft 禮mu・1showηi
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Claims (1)

[Claims] In a method of measuring the concentration of free available chlorine in a liquid to be measured in which free available chlorine and combined chlorine coexist by polarographic method, a reagent containing 40 g/l or more of potassium bromide is added to the liquid to be measured, and a reagent made of platinum is added to the liquid to be measured. A method for measuring residual chlorine, characterized in that the free available chlorine concentration is measured using a rotating indicator electrode and a comparison electrode made of silver chloride, and with an applied voltage of +0.6V.