JPS6327745A - Apparatus for measuring residual chlorine - Google Patents

Abstract

PURPOSE:To measure residual chlorine simply and accurately without requiring operation, by a method wherein a solution to be inspected is adjusted to pH3-5 by a pH control mechanism and the concn. of hypochlorous acid in the solution to be inspected is measured by an electrode for measuring the concn. of hypochlorous acid. CONSTITUTION:The solution to be inspected flowing through a flow pipe 1 flows in a pH control mechanism 3 to be adjusted to pH3-5 without being substantially diluted. Whereupon, the OCl<-> ion in the solution to be inspected is entirely converted to HOCl. Therefore, by detecting the concn. of HOCl in the solution to be inspected after the adjustment of pH by using an HOCl electrode 4, the total concn. of free available chlorine can be detected. Since the pH of the solution to be inspected is adjusted without substantially diluting said solution, the total concn. of free available chlorine in the solution to be inspected can be directly calculated without requiring operation based on a dilution rate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a residual chlorine measuring device, and more specifically, to a device capable of simply and accurately measuring the total free available chlorine concentration in a test liquid.

Conventionally, free available chlorine (chlorine CQ2, hypochlorous acid HOCfl) in the test liquid
Various means have been proposed for the purpose of measuring hypochlorous acid ion 0CQ-), and for example, a diaphragm-type residual chlorine electrode is used to measure hypochlorous acid. This residual chlorine electrode is equipped with a diaphragm that allows volatile hypochlorous acid to pass through, and is small and easy to make. It also has no driving parts, does not require special reagents, and can be used continuously. It has been widely put into practical use because it has various advantages such as being able to be measured visually.

By the way, the pH of the test solution is usually 6 to 8, and free available chlorine is in equilibrium with hypochlorous acid and hypochlorite ions in the pH range of 6 to 8, and both coexist (as shown in the following formula) (1)
, see (2)).

)-I OCfl H”+○cQ-・-(1) Therefore, when measuring free chlorine in a test liquid with pH 6 to 8 using the residual chlorine electrode, the diaphragm will only allow hypochlorous acid to pass through. However, since it does not permeate hypochlorite ions, the electrode is sensitive only to IM chloric acid, and therefore, depending on the electrode, the total free available chlorine concentration at pH 6 to 8, i.e., hypochlorous acid and hypochlorous acid. It is not possible to directly measure the total concentration of hypochlorous acid and ions.In this case, the equilibrium between hypochlorous acid and hypochlorite ions depends on the pH, so if the pH of the test solution is constant, the hypochlorous acid concentration Although the total free chlorine concentration can be determined by a simple calculation from , it is impossible to use this method in a test liquid where the pH changes because the equilibrium shifts accordingly.

On the other hand, as a means of measuring total free chlorine using a hypochlorous acid electrode, we focused on the fact that the above dissociation equilibrium depends on pH and that its Mt constant is determined once the temperature is known. The hypochlorous acid concentration in the test liquid is measured with an electrode, and at the same time the pH and temperature of the test liquid are detected, and the following formula (
3), that is, [○ CQ-3=K(T)
Q)XIOPII... (3)
It has been proposed to obtain OCQ-) (hypochlorite ion concentration) and thereby detect the total concentration of hypochlorous acid and hypochlorite ions (Japanese Patent Publication No. 59-42693).

However, the method described in the above-mentioned Japanese Patent Publication No. 59-42693 requires a PR and temperature measurement mechanism as well as a calculation mechanism in addition to the electrodes, which makes the device complicated and requires a large number of measurement items. There are various problems in practical use, such as a decrease in the coupling accuracy.

The present invention has been made in view of the above circumstances, and solves the problems of the prior art described above, and measures the total free chlorine concentration in a test liquid simply and accurately using a diaphragm-type hypochlorous acid electrode. The purpose of the present invention is to provide a residual chlorine measuring device that can measure residual chlorine.

Means for Solving the Problems The inventor of the present invention discovered the following matters (1) to (2) while conducting intensive research to achieve the above object.

■ The equilibrium of equation (1) above means that the p I-1 of the test solution is 6 to
In the pH range of 8, HOCQ and ○CQ- coexist as mentioned above, and the ratio changes with slight fluctuations in pH, but in the pH range of 3 to 5, ○CQ- is completely replaced by HOCfl.
Therefore, by adjusting the pH of the test liquid to 3 to S, all free chlorine can be detected as HOCQ by the HOCQ electrode.

■ If the pH of the test solution is set to 3 to 5 as shown in ■, I]○
Total free chlorine can be measured with a CQ electrode, and for this reason it is conceivable, for example, to continuously inject a pH 3-5 buffer solution into the flow of the test solution using a pump in continuous measurements; In the H adjustment method, the test solution is diluted with a buffer solution, so the total free available chlorine temperature will be different between the test solution before PII adjustment and the test solution after adjustment, and the concentration to be measured before pH adjustment will be different. cannot be detected directly.

When adopting the pH adjustment method described in Therefore, the device becomes complicated and expensive, making it impractical. Also,
This increases the amount of buffer used and requires more frequent reagent replacement.

■ Therefore, if the pH is adjusted to 3 to 5 without substantially diluting the test solution, the test solution will not be diluted, and the total free available chlorine concentration in the test solution can be directly determined. Since there is no need to use an expensive precision pump and the amount of reagents used can be reduced as much as possible, a practical and simple system for measuring total free available chlorine can be obtained.

That is, by adjusting the pH of the test solution to 3 to 5, the inventor determined that the total free chlorine concentration was converted to the HOCQ concentration by
can be measured using a Q electrode, in which case by adjusting the pH without substantially diluting the test solution;
The inventors have discovered that measurements can be carried out easily and accurately without the need for calculations, leading to the present invention.

Therefore, the present invention provides a diaphragm through which hypochlorous acid permeates, and the detection end of the diaphragm is immersed in a test liquid to detect hypochlorous acid in the test liquid passing through the diaphragm. It is equipped with an electrode for measuring acid concentration and a pH adjustment mechanism that adjusts the pH of the test liquid without substantially diluting the test liquid,
The pH of the test liquid is adjusted to 3 to 5 by the H adjustment mechanism, and the hypochlorous acid concentration in the test liquid is measured by the hypochlorous acid concentration measuring electrode. The purpose is to provide a residual chlorine measuring device.

Function In the device of the present invention, the pH is usually 6 to 8, and HOC
The test solution in which Q and 0CQ- ions coexist is adjusted to pH 3.
Since the pH was adjusted to ~5, all of the 00°C-ions in the test solution are transferred to -(OCQ), and therefore the HOCQfi degree in the test solution after this pH adjustment is detected using the HOC12 electrode. By this, the total free available chlorine concentration can be detected.Also, since the pH of the test solution is adjusted without substantially diluting it, it is possible to directly test the test solution without the need for calculations based on the dilution rate. The total free available chlorine concentration in the liquid can be determined.

In this case, if the pH of the test solution is lower than 3, HOCQ in the solution will shift to CQ2 and the output of the electrode will become unstable, making it impossible to achieve the object of the present invention.

Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples. This shows a continuous measuring device, and numeral 1 in the figure is a test liquid flow pipe through which the test liquid flows at a predetermined flow rate due to the operation of a suction pump 2. Reference numeral 3 denotes a pH adjustment mechanism interposed in the test liquid distribution pipe 1 on the upstream side of the pump 2. The test liquid flowing through the distribution pipe 1 flows into this pH adjustment mechanism 3, and the pH adjustment mechanism 3 allows the test liquid to flow through the flow pipe 1. p without being diluted? (After being adjusted to 3 to 5, it will flow out from here. Furthermore,
4 is a hypochlorite M electrode device installed in the flow pipe 1 on the downstream side of the pH adjustment mechanism 3; The detection end of the electrode is immersed in the test liquid flowing through the flow pipe 1,
Hypochlorous acid tAf: in this test liquid is detected.

When the free available chlorine concentration in a test liquid is continuously measured using the above-described apparatus, the pump 2 is operated to cause the test liquid to flow through the flow pipe 1. This allows the pH adjustment mechanism 3 to
The test solution in the neutral range of pH 6 to 8 is not substantially diluted (continuously adjusted to the acidic range of pH 3 to 5,
After all the free chlorine has been transferred to HOCfl, this H○CΩ
The concentration is detected with an electrode device 4. Therefore, with this device, the free chlorine concentration in the test liquid can be easily and reliably continuously measured.

In this case, by interposing an electrode device similar to the above in the flow pipe 1 on the upstream side of the pH adjustment mechanism 3, the p.
The HOCfl concentration in the test liquid before pH adjustment is determined, and the HOCfl concentration before pH adjustment is calculated from the HOCR concentration before pH adjustment and the HO(,Q!3 degrees) after PFr adjustment detected as described above. The 0CQ-concentration of the test solution can be determined.

In the present invention, there are no particular limitations on the configuration of the pH adjustment mechanism, such as one in which acidic gas such as hydrochloric acid vapor is bubbled into the test liquid, a silicone membrane or a microporous P
Use a membrane that is impermeable to ions and permeable to acidic reagents, such as a TFE membrane tube.

Although a known mechanism such as one in which an acidic reagent is added to the sample without substantially diluting the sample through this membrane can be adopted, a pH adjustment mechanism using a tube made of a cation exchange membrane can be adopted. It is particularly preferable to use

That is, FIG. 2 shows the p
This figure shows an example of the H adjustment mechanism 3, in which 5 is a reagent container;
6 is an acidic reagent injected into this container 5. A cation exchange membrane tube 7 inserted into the test liquid flow tube 1 is immersed in this reagent 6, and the test liquid is supplied to the tube 7.
While flowing through the reagent 6, hydrogen ions in the reagent 6 pass through the peripheral wall made of a cation exchange membrane of the tube 7 and migrate into the test liquid.
Thereby, the pH of the test solution can be reliably adjusted to 3 to 5 with the minimum amount of reagent used without substantially diluting the test solution.

In this case, the type of acidic reagent 6 is not limited, and any acidic liquid can be used, but it is particularly preferable to use acetic acid, propionic acid, etc., and it is effective to use a highly purified one. It is.

Furthermore, the type of cation exchange membrane tube is not limited either.

Specifically, a fluororesin Najion membrane tube (manufactured by DuPont) having So and H groups as ion exchange groups was used.
However, in this case, the 5o3H group alone has a high affinity for water, and the test solution may slightly flow into the reagent due to the osmotic pressure based on the concentration difference between the test solution and the reagent. There is. For this reason, in the present invention, it is particularly preferable to use a composite cation exchange tube in which a cation exchange membrane having So and H groups is laminated with a cation exchange membrane having C○OH groups with no water affinity. By using a cation exchange membrane in which SO2F groups and COOH groups are arranged in a composite manner as described above, it is possible to reliably prevent the test liquid from flowing into the reagent and diluting the reagent.

In addition, when adjusting the pH of a test solution using a cation exchange membrane tube in this way, in addition to the method of immersing the tube in the reagent solution, it is also effective to use a method of placing the tube in the vapor of the reagent. As a result, water permeation from the test liquid into the reagent can be minimized.

In addition, in the present invention, the configuration of the electrode for measuring hypochlorous acid concentration is not particularly limited. For example, an electrolyte is sealed in the electrode body, seven nodes and a cathode are housed, and the detection end is hypochlorous acid. Known devices equipped with a diaphragm that permeates chloric acid can be suitably used.

Next, the effects of the present invention will be concretely demonstrated through experimental examples.

Daitai Aim 1: Pour the test liquid continuously over a long period of time into the device shown in Figure 1.
The p II-I stability was investigated when H adjustment was performed. In this case, the pH adjustment mechanism shown in FIG. 2 was used. The results are shown in FIGS. 3 and 4.

Figure 3 shows a cation exchange membrane tube with a length of 200 WI.
Using a Najion membrane tube of I, add vinegar W as a reagent.
! This is the result when using (steam). Note that the flow rate of the test liquid was 2.5all/min.

In addition, Figure 4 shows SO, H as a cation exchange membrane tube.
The results were obtained using a composite cation exchange membrane tube with a length of 130 m in which an exchange membrane having groups and an exchange membrane having C○○H groups were laminated, and acetic acid was used as a reagent. Note that the flow rate of the test liquid was 1.1 d/min.

From the results shown in FIGS. 3 and 4, it is recognized that the mechanism shown in FIG. 2 allows the pH of the test liquid to be stably adjusted in the range of 3 to S over a long period of time.

In addition, in the case of the Najion tube shown in Figure 3, if the test solution is continuously flowed for a long period of time, water will enter the reagent from the test solution due to osmotic pressure and the reagent will be slightly diluted.
-■ A deviation of about 0.5 occurs, but since PH is within the range of 3 to 5, there is no practical problem.

On the other hand, in the case of the composite cation exchange membrane tube shown in FIG. 4, the pH remained almost unchanged at 3.75 throughout the 10 days. This is thought to be because the ion exchange membrane is complex, which suppresses water permeation and prevents the reagent from being diluted. The amount of acetic acid that leaked into the test solution over 10 days was only 9 mQ, and according to the mechanism shown in Figure 2, the pH could be adjusted to a good level with the minimum amount of reagent without substantially diluting the test solution. It was confirmed that it can be adjusted.

Experimental Example 2 The free available chlorine concentration in the test liquid was measured using the same device as in Experimental Example 1. An example of the calibration curve of the HOCQ electrode at this time is shown in FIG. In addition, the sixth chapter shows how the output of the HOCQ electrode changes depending on the pH of the test liquid.
It is a diagram.

From the results shown in FIG. 5, it is recognized that the residual chlorine concentration can be measured satisfactorily with the above device. Additionally, from the results in Figure 6, when the pH drops below 2, the indication becomes abnormal because chlorine is produced in the reaction from HOCQ to CΩ2, but between pH 3 and 5, all free available chlorine is stable as HOCQ g. Therefore, it can be seen that the instructions are stable.

Furthermore, test solutions with a constant residual chlorine concentration (approximately 2,5 ppi+) and different p I-1 were prepared, and the residual chlorine J quality of these test solutions was measured without adjusting the p ) I. In this case, the electrode output was measured when the pH was adjusted to 3 to 5 using the mechanism shown in FIG. 2, and after the pH was adjusted using a pH 5 buffer. An example of the results is shown in FIG.

In addition, in Fig. 7, A is when the test liquid with pH 9 is measured as it is, B is when the pH of this test liquid is adjusted by the V& structure in Fig. 2, and C is when the pH of the test liquid is adjusted with t1 buffer solution with pH 5. Indicates the case where

From the results shown in Figure 7, the output is small when the pH is 9, but when it is passed through the pH adjustment tube, the pH is adjusted to 3 to 5, and the test solution adjusted with a p I-I 5 buffer solution. Therefore, it is recognized that the total free available chlorine concentration can be stably measured with the above device.6 As described in detail of the invention, the residual chlorine measuring device according to the present invention has the following features:
Total free available chlorine (hypochlorous acid tenth chlorite ion) can be measured simply and accurately.

Since its structure is simple and can be manufactured at low cost, it has extremely great practical value.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a residual chlorine measuring device according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing the mechanism of the pH adjustment on the same side, and Figs. 3 and 4 are respectively A graph showing the state in which the pH of the test liquid is adjusted over a long period of time by the adjustment mechanism, FIG. FIG. 7 is a graph showing the change in electrode output when the residual chlorine concentration is measured while changing the pH of the test liquid. 3...pH adjustment mechanism, 4...Electrode device Applicant: Electrochemical Instrument Co., Ltd. Agent, Patent Attorney Takashi Kojima Figure 2

Claims (1)

[Claims] 1. Hypochlorous acid concentration measurement, which is equipped with a diaphragm through which hypochlorous acid permeates, and whose detection end is immersed in the test liquid to detect hypochlorous acid in the test liquid that passes through the diaphragm. electrode for
and a pH adjustment mechanism that adjusts the pH of the test liquid without substantially diluting the test liquid, and the pH adjustment mechanism adjusts the pH of the test liquid to 3 to 5, and A residual chlorine measuring device, characterized in that the hypochlorous acid concentration in the liquid is measured by the hypochlorous acid concentration measuring electrode.