JPS6156957A - Residual chlorine meter - Google Patents

Abstract

PURPOSE:To enable accurate measurement of isolated chlorine, by mixing a specified buffer reagent into a solution to be measured at a fixed ratio while a fixed voltage is applied between an indicator pole comprising a rotary platinum electrode and an opposed pole comprising a silver bromide electrode. CONSTITUTION:Feed pumps 2a and 2b are driven, a buffer reagent in a tank 1 and a liquid to be measured in a tank 3 are fed and mixed together at a fixed ratio, for example, 3:100 to be fed to a measuring container 4. When an isolated chlorine such as Cl2 and a bond chlorine such as NH2Cl coexist in the liquid being measured, as potassium bromide KBr is added to the liquid being measured, a reaction is caused according to a specified formula. This reaction will be promoted as the pH value of the reaction liquid is inclined to the acid range to form more Br2. Thus, the pH value of the buffer reagent shall be controlled to about 6.0. When Br2 is reduced with an indicator pole 6 comprising a rotary platinum electrode, a reduction current flows between the indicator pole 6 and an opposed pole 7 comprising a silver bromide and detected with a galvanometer 9 to determine the amount of the isolated chlorine from the current value detected.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a residual chlorine meter that polarographically measures residual chlorine contained in drinking water, etc. in a water treatment plant.

<Prior art> As a conventional example of a residual chlorine meter such as B, an indicator electrode made of a rotating platinum electrode and a counter electrode made of a platinum electrode are immersed in a liquid to be measured, and a DC voltage (for example, -〇, An apparatus is known that measures the residual chlorine concentration in a liquid to be measured by applying a voltage of 35 V) to the liquid to be measured and detecting the magnitude of the diffusion current generated in the liquid to be measured.

In addition, 40 f of potassium bromide (KBr) = 10 t of sodium acetate (CH,C00N&), and acetic acid (C
A reagent containing 10 fml of HgCOOH) with a pH value of 4.5 is used as a buffer.

However, in the conventional example described above, the influence of combined chlorine cannot be ignored, and it is difficult to accurately measure only free chlorine. In other words, residual chlorine is generally dissolved in water, such as chlorine (cz2) and hypochlorous acid (
When the free chlorine concentration is 0 and the combined chlorine concentration is 8 ppm, When the residual chlorine concentration was measured using the above device, it was found to be 2.4 ppm, indicating that the influence of combined chlorine was approximately 30 ppm.
Chi also starts to appear. However, in drinking water at water treatment plants, the concentration of ammonia nitrogen in the raw water increases during the dry season.
When chlorine is injected into raw water, the combined chlorine concentration increases and the free chlorine concentration may drop to zero. Therefore, in order to accurately determine the required amount of chlorine injection, it is necessary to accurately measure free chlorine, which is affected by combined chlorine, and the emergence of a residual chlorine meter that can perform such measurements is strongly desired. It was rare.

<Object of the invention> The present invention was made in view of the above situation, and its object is to reduce residual chlorine so that free chlorine can be accurately measured without being affected by combined chlorine coexisting in the liquid to be measured. The objective is to provide a measurement system.

<Summary of the Invention> The present invention is characterized in that, in a residual chlorine meter, a predetermined buffering reagent is mixed with a liquid to be measured at a constant ratio, and an indicator electrode made of a rotating platinum electrode and a counter electrode made of a silver bromide electrode are used. A constant voltage is applied between these electrodes, and the current flowing between them is detected.

<Example> Hereinafter, the present invention will be described in detail using the drawings. 1st
The figure is an explanatory diagram of the configuration of an embodiment of the present invention, and in the figure, 1/ is, for example, 10F potassium bromide (KBr).

21 (D acetic acid (CB, COOH), and 54 g of sodium acetate (cIsCOONm) were dissolved in pure water (H2O
) and adjusted the pH value to 1) to be approximately 6.0.
cypress in which a buffering reagent is stored; 2a and 2b are liquid pumps; 3 is a tank in which a liquid to be measured, such as tap water, is stored; and 4 is a liquid pump 2m and 2b. A measuring container in which a liquid 5 containing the above-mentioned buffering reagent and a liquid to be measured is stored, 6 an indicator electrode powered by a rotating platinum (PT) electrode, 7 a silver bromide (silver bromide) whose silver surface is silver bromide 8 is a DC power supply that applies a constant voltage (for example, +〇, 5 V) between the indicator electrode 6 and the counter electrode 7, 9 is a galvanometer, and 10 is discharged from the measuring container 4. This is a waste liquid tank into which the above mixed liquid is introduced. In the embodiment of the present invention based on such a configuration, when the liquid pumps 2a and 2b are driven, the buffer reagent 1 in the tank 1 and the liquid to be measured in the tank 3 are fed at a fixed ratio (for example, 3 :100) and then supplied to the measurement container 4. By the way, when free chlorine (e.g. Ct2) and combined chlorine (e.g. NH2Cl) coexist in the liquid to be measured, and potassium bromide (KBr) is added to the liquid to be measured, the following equation (1) ,
A reaction like +21 occurs.

C1+ 2Br-″ −+ 2C1-+ B r
2 ”...(1) NHCl+2Br-+2H”-
+ NI(4CJ!+Br, “”(21 above formula (2
) reaction is accelerated as the pu value of the reaction solution becomes more acidic, and more nr is produced. Therefore, in order to selectively react only free chlorine with Br-, p of the reaction solution is
It is desirable to keep the H value on the neutral or alkaline side. On the other hand, when the reaction solution becomes alkaline, chlorine (ct2
) is weakened, so the reaction of formula (1) above cannot be carried out quantitatively.

Therefore, while suppressing the reaction of the above formula (2), the reaction of the above formula (1)
) In order to promote the reaction of free chlorine and selectively react with Br-, it is necessary to bring the pu of the reaction solution to around neutrality. Therefore, the pu value of the above buffering reagent is □6.0
~7.5゛, and in the embodiment of the present invention it is 6.0
It has been adjusted. On the other hand, when Br2 generated in the above formula Ill'(1)- is reduced at the indicator electrode 6, the indicator electrode 6
A reduction current flows between the electrode 7 and the counter electrode 7. This reduction current is detected by a galvanometer 9, and the amount of free chlorine is indirectly quantified from the detected current value.

FIGS. 2 and 3 show 20-gram curves created using the conventional example and the embodiment of the present invention. In the figures, the horizontal axis shows the voltage (V) applied between the indicator electrode and the counter electrode. ) is shown, and the vertical axis shows the reduction current detected by the galvanometer as the output (μA). As is clear from the polar quadrature in FIG. 2, in the conventional device, the voltage (about -0.4 V
~-〇, 2 V), it is not possible to remove the influence of combined chlorine. On the other hand, as is clear from the bow 20 g in FIG.
tSV), the effect of combined chlorine is extremely small. Therefore, in the embodiment of the present invention shown in FIG. almost never occurs. Therefore, even if a large amount of combined chlorine coexists in the liquid to be measured, the measured value of free chlorine contains almost no error due to the combined chlorine.

It should be noted that the present invention is not limited to the above-mentioned embodiments and can be modified in various ways. For example, the pH value of the buffering reagent can be varied in a range of 6 to 7.5 other than 6. Furthermore, the composition of this buffering reagent is not limited to an acetic acid-sodium acetate solution, but may also be a phosphate buffer. Furthermore,
Voltage applied to indicator electrode 6 and counter electrode 7, above +〇, 5V
It is not limited to , and can be changed in various ways within the range of +0.4 to +0.6v.

<Effects of the Invention> As explained in detail above, according to the embodiment of the strength-grip invention, even when free chlorine and combined chlorine coexist in the liquid to be measured, free chlorine can be absorbed without being affected by the combined chlorine. Force residual chlorine, so that it can be measured accurately! meter is realized.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the configuration of an embodiment of the present invention, Figs.
The figures are polarograms created using a conventional device and an embodiment of the present invention, respectively.

Claims (2)

[Claims] (1) Mixing a buffering reagent consisting of a potassium bromide solution with a liquid to be measured at a constant ratio, and applying a constant voltage between an indicator electrode consisting of a rotating platinum electrode and a counter electrode consisting of a silver bromide electrode; A residual chlorine meter that measures the residual chlorine concentration in the liquid to be measured by detecting the current flowing between these electrodes. (2) The buffering reagent is 10 g of potassium bromide, 54
The residual chlorine meter according to claim 1, which comprises a solution containing 1 g of sodium acetate and 2 g of acetic acid and having a pH value of about 6.0.