JPH0758280B2 - Method for measuring chlorite ion - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for continuously measuring the concentration of chlorite ion (ClO ₂ ⁻ ) in a sample solution.

[Conventional technology]

Conventionally, chlorine has been used for sterilizing tap water and pools, but it has been known that chlorine produces carcinogenic trihalomethanes, which has been a problem.

Therefore, recently, chlorine dioxide (ClO ₂ ) that does not generate trihalomethane has been used to sterilize tap water and pools.

When chlorine dioxide is used as an oxidant in this way, chlorine dioxide itself is reduced and part of it is chlorite ion (Cl
O ₂ ^-) to become. This chlorite ion is decomposed by ultraviolet rays to become chlorine dioxide. In addition, chlorite ion is used for bleaching the fiber, which utilizes the bleaching action by the oxidizing power of chlorine dioxide generated when the chlorite ion is made acidic and activated.

As mentioned above, chlorite ion potentially has the oxidizing ability of chlorine dioxide. Therefore, not only the chlorine dioxide concentration control but also the chlorite ion concentration control should be performed at the same time in the above fields. Only then, the necessary and sufficient control of the oxidizing ability of the sample can be performed.

By the way, the conventional method for measuring chlorine dioxide dissolved in a sample solution is the iodine titration method (Chemical Disaster Prevention Guideline (7)).
And a diaphragm-type polarographic electrode using a diaphragm that selectively permeates chlorine dioxide (Japanese Patent Laid-Open No. 54-125095). Moreover, as a measuring method of chlorite ion,
Only the iodometric titration method (Chemical Disaster Prevention Guideline (7)) is known.

A diaphragm polarographic electrode is composed of a diaphragm provided at one end of a cylindrical support, an electrolytic solution filled inside the cylindrical support that is isolated from the outside by a diaphragm, and an anode and a cathode that are immersed in the electrolytic solution. By applying a voltage that produces a reduction current of chlorine dioxide to the cathode to reduce the chlorine dioxide that has passed through the diaphragm, the reduction current flowing between the anode and the cathode is measured to obtain the chlorine dioxide concentration ( In the present invention as well, the term “diaphragm-type polarographic electrode” is used in this sense). This diaphragm-type polarographic electrode is capable of continuous measurement, but there is no known measurement of chlorite ion by the diaphragm-type polarographic electrode.

On the other hand, the iodometric titration method can be used for measuring both chlorine dioxide and chlorite ion, but it is not suitable for concentration control because continuous measurement cannot be performed, and the titration operation is complicated.

[Problems to be Solved by the Invention]

In view of such conventional circumstances, it is an object of the present invention to provide a method for continuously measuring chlorite ion in a sample solution.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, in the method for measuring chlorite ion of the present invention, an acid is added to a sample solution, and the sample solution is added or dissolved depending on the concentration of chloride already dissolved or separately dissolved in the sample solution. By adjusting the pH value to below the specified value, the chlorite ion contained in the sample solution is quantitatively changed to the corresponding carbon dioxide, and the concentration of this chlorine dioxide is measured by using the diaphragm type polarographic electrode. Then, it is characterized in that the chlorite ion concentration in the sample solution is obtained.

When measuring chlorite ion in a sample solution containing chlorite ion and chlorine dioxide, first measure the chlorine dioxide concentration in the sample solution using a diaphragm-type polarographic electrode, and measure the chlorine dioxide concentration. Acid is added to the sample solution after measurement or the same sample solution as the first prepared separately, and it is already dissolved in the sample solution or separately added and below a predetermined pH value according to the concentration of dissolved chloride. By changing the chlorite ion contained in the sample solution to the corresponding chlorine dioxide quantitatively, the chlorine dioxide concentration is measured again using the diaphragm polarographic electrode. It is possible to determine the chlorite ion concentration in the sample solution from the difference in chlorine dioxide concentration between.

In the neutral or weakly alkaline solution, hydrogen ion is added to chlorite ion, and part of it becomes chlorite. Since this is a change in morphology that does not involve charge transfer, chlorite ion and chlorite are not electrochemically distinguished. Therefore, according to the method for measuring chlorite ion of the present invention, such chlorite is also electrolyzed similarly to chlorite ion to generate an oxidation current, and the total of both is the concentration of chlorite ion in the present invention. Is measured as

[Action]

The present invention, when gradually lowering the pH of the solution in the presence of chloride, chlorite ions at a given pH value in accordance with the concentration of chloride (ClO ₂ ^-) quantitative chlorine dioxide (ClO ₂₎ It was made based on this finding by discovering the fact that it changes rapidly and rapidly.

That is, as shown in FIG. 1, when sulfuric acid was added to a 10 ⁻³ M NaClO ₂ aqueous solution containing KCl as a chloride to reduce the pH, ClO ₂ was kept at a substantially constant pH depending on the KCl concentration. ^- is ClO ₂
Quantitatively changes to dissolved in the liquid. For example, KCl concentration of 10 ^-3 A decrease in pH in M or less ClO ₂ ^- is hardly changed ClO _2, KCl concentration ClO ₂ is generated at about pH4 or less in the case of 10 ^-1 M, further It is understood that when the KCl concentration is increased, the pH value at which ClO ₂ ⁻ changes to ClO ₂ gradually increases, and the pH value at which ClO ₂ ⁻ changes to ClO ₂ decreases again at the peak of the KCl concentration of approximately 10 ⁻¹ M. .

Further, in the presence of 10 ^-1 M of KCl, ClO ₂ in pH2.4 adding an acid to the NaClO ₂ standard solution ^- and ClO ₂ concentration, which occurs when NaClO ₂ initial concentration is varied to CIO ₂ The relationship is shown in FIG. From FIG. ₂ , it can be seen that the change of ClO ₂ ⁻ into ClO ₂ is quantitative.

In addition, when the pH of the liquid is raised in reverse, there is a hysteresis, ClO ₂ does not suddenly change to ClO ₂ ⁻ at a certain pH, but gradually changes to ClO ₂ ⁻ as the pH rises. .

Therefore, by performing the above operation in a closed container such as a measuring cell of a diaphragm-type polarographic electrode device, the ClO ₂ gas generated as shown in FIG. 1 is dissolved in the liquid phase in equilibrium with the gas phase. and, ClO ₂ before the change ^- so that the concentration levels ClO ₂ of which quantitatively corresponds to the result of the presence, ClO ₂ under previously constant chloride concentration ^- and pH which is changed to ClO _2, this change quantitative relationships, and if previously obtained proportional relation between the ClO ₂ concentration reduction current, ClO ₂ by a diaphragm-type polarographic electrode method
The reduction current of ClO ₂ of the original sample solution was measured in reverse from this value.
^- it is possible to determine the concentration.

In the measurement of ClO ₂ , C
A stable reduction current can be obtained due to the diffusion control of lO ₂ .

In the case of a sample solution containing chlorite ion and chlorine dioxide, the diaphragm type polarographic electrode is insensitive to ions, so that the ClO ₂ concentration is measured first. Then ClO ₂ contained in the sample solution by more than a predetermined pH value by adding dissolving an acid to the sample solution in the same manner as described above ^- after the changing to ClO _2, total ClO with a septum-type polarographic electrodes again _Two concentrations were measured and the total ClO ₂ concentration of the latter was present first in the former
The concentration of chlorite ion contained in the sample solution can be obtained by subtracting the ClO ₂ concentration. In this case, the same sample solution
One of them is measured, and one of them measures the chlorine dioxide contained from the beginning, and the other one contains chlorine dioxide changed from chlorite ion by adding an acid, etc. The total amount of chlorine dioxide may be measured and the difference may be determined, or the chlorine dioxide may be measured twice on the same sample liquid to determine the difference.

The chloride may be added by dissolving the chloride in an acid, adding the chloride without dissolving it in the acid, and adding it at the same time as the addition of the acid, or by adding it before or after the addition of the acid. Is also good. But,
If chloride is already contained in the sample solution at the required concentration or higher, it is not necessary to add it again.

〔Example〕

Example 1 A chlorine dioxide measuring device (CLO-20 type manufactured by Toa Denpa Kogyo Co., Ltd.) using a diaphragm-type polarographic electrode was used, and the concentration was 5 × 10 ⁻⁴ M and 2.5 × 10 ⁻⁴ M in the measuring cell. Two kinds of NaC
lO ₂ solution (pH about 6.0) was sequentially introduced, and 5 × 10 ^-2 M of each was introduced.
ClO ₂ ⁻ was changed to ClO ₂ by dissolving KCl and then dropping hydrochloric acid to lower the pH to about 2.5.

After that, when the generated current was measured for each solution while changing the applied voltage, the graph of applied voltage-current characteristics shown in FIG. 3 was obtained. From the result of Figure 3, 0-500mV
By measuring the reduction current generated under a given applied voltage within the range of, a reduction current corresponding to ClO ₂ can be obtained, and this
Reduction current value of the ClO ₂ is ClO ₂ was initially present in the sample solution ^- seen to be proportional to the concentration.

Example 2 Using the same equipment as in Example 1, 7.4 mg / l ClO ₂ and 1.7 x 10
^-4 M ClO of ₂ ^- C from the reduction current corresponding to the ClO ₂ in a mixed solution of
The lO ₂ concentration was measured. Next, 10 ^-1 M KCl was added to this mixed solution.
After adjusting to 2.6 pH by the addition of hydrochloric acid and was measured ClO ₂ concentration from the reduction current corresponding to the ClO ₂ again.

From the results shown in FIG. 4, the difference between the ClO ₂ concentration of the latter (a) and the ClO ₂ concentration of the former (b) was determined as the concentration of ClO ₂ ⁻ contained in the first mixed solution of 1.7 × 10 ^−4. It is found that M corresponds to 6.4 mg / l ClO ₂ .

〔The invention's effect〕

According to the present invention, it is possible to continuously measure chlorite ion in a sample liquid by using a diaphragm type polarographic electrode instead of the conventional titration method, and it is extremely effective in controlling the concentration thereof.

[Brief description of drawings]

Fig. 1 is a graph showing the relationship between the pH and the concentration of dissolved ClO ₂ when acidifying a constant concentration of NaClO ₂ aqueous solution under different KCl concentrations. Fig. 2 shows the initial concentration of NaClO ₂ and 10 ^-1 M FIG. 3 is a graph showing the relationship with the ClO ₂ concentration generated by the pH decrease in the presence of KCl, and FIG. 3 is the applied voltage current obtained for the ClO ₂ solution changed from ClO ₂ ⁻ by the pH decrease in Example 1. FIG. 4 is a graph showing the characteristics, and FIG. 4 shows ClO ₂ ⁻ and ClO obtained in Example 2.
₂ is a graph showing the applied voltage-current characteristics of the mixed solution (b) of No. ₂ and the solution (a) after changing ClO ₂ ^{− of the} mixed solution to ClO ₂ .

Claims (2)

[Claims] 1. A sample solution is prepared by adding an acid to the sample solution so that the pH value is not more than a predetermined pH value depending on the concentration of chloride already dissolved in the sample solution or separately added and dissolved. The chlorite ion concentration in the sample solution is determined by converting the chlorite ion to be converted into chlorine dioxide that corresponds quantitatively and measuring the concentration of this chlorine dioxide using a diaphragm-type polarographic electrode. Method for measuring chlorite ion. 2. A sample solution containing chlorite ion and chlorine dioxide, the concentration of chlorine dioxide in the sample solution is measured by using a diaphragm type polarographic electrode, and the sample solution after the chlorine dioxide concentration is measured or prepared separately. The acid is added to the same sample solution as in the first step, and the sample solution is added to the sample solution by adjusting the pH value to below the specified pH value depending on the concentration of chloride already dissolved in the sample solution or dissolved separately. After changing the contained chlorite ion into the corresponding chlorine dioxide quantitatively, the concentration of chlorine dioxide in the sample solution was measured using a diaphragm-type polarographic electrode, and the chlorine dioxide concentration of the latter and that of the former were measured. A method for measuring chlorite ion, characterized in that the chlorite ion concentration in a sample solution containing the chlorite ion and chlorine dioxide is determined from the difference in chlorine concentration.