JPH0769287B2 - Calibration method for oxidizing gas measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for calibrating an apparatus for measuring an oxidizing gas such as chlorine dioxide or ozone.

[Conventional technology]

Since chlorine dioxide (ClO ₂ ) and ozone (O ₃ ) have a strong oxidizing power, for example, chlorine dioxide is used as a bactericidal agent for bleaching fibers and the like, and recently as a sterilizing agent to replace chlorine. Is also used for deodorizing tap water.

Concentration measurement of oxidizing gases such as chlorine dioxide, ozone, chlorine, etc., has conventionally been carried out by an iodine titration method for dissolved oxidizing gas solutions, but it is not suitable for continuous measurement and the titration operation is complicated. For this reason, recently, an oxidizing gas measuring device using a diaphragm type polarographic electrode method (Japanese Patent Laid-Open No. 54-125095) using a diaphragm that selectively permeates chlorine dioxide, ozone, chlorine and the like has been used. In addition, a diaphragm electrode-type oxidizing gas measuring device that measures the potential with a diaphragm electrode using a similar diaphragm can measure a dissolved oxidizing gas solution or a gas-phase oxidizing gas.

The above-described oxidizing gas measuring device is simple and suitable for continuous measurement because the oxidizing gas concentration can be obtained as an indicated value simply by contacting an electrode equipped with a diaphragm with a sample liquid or a sample gas. Calibration is always required as an electrochemical measurement result.

Conventionally, the calibration of the oxidizing gas measuring device has been performed using the oxidizing gas to be measured, but it is naturally necessary to adjust the oxidizing gas used for calibration to a constant concentration. For example, in order to adjust the dissolved ClO ₂ gas aqueous solution of a constant concentration, ClO ₂ gas is generated by known reduction of chlorate or oxidation of chlorite, and the ClO ₂ gas is collected in pure water. A method of determining the concentration by an iodometric titration method is used, but this adjusting operation is troublesome.

In addition, all the oxidizing gases are unstable, and decomposition progresses during storage for a short period in either a gas phase or a dissolved state, resulting in a decrease in titer or a decrease in concentration. For example, chlorine dioxide (Cl
In the case of a dissolved ClO ₂ gas aqueous solution in which O ₂ ) gas is purely dissolved, as shown by the dotted line in FIG. Even if it is stored in, the concentration of dissolved ClO ₂ gas decreases in a very short period of time. The same applies to ozone gas and chlorine gas.

Therefore, as the standard solution or standard gas for calibration, it is almost impossible to store the oxidizing gas to be measured or its dissolved aqueous solution at a constant concentration for a long period of time. However, since it is necessary to prepare the same as the above, the complicated preparation operation is repeated each time, so that it is extremely complicated and, therefore, it takes a long time to calibrate.

[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 calibrating an oxidizing gas measuring device, which enables accurate calibration in a short time by a simple operation.

[Means for Solving the Problems]

In order to achieve the above object, the calibration method of the oxidizing gas measuring device of the present invention is an acid in which a chlorite salt is dissolved in a chlorite ion aqueous solution and a chloride, or the chlorite ion aqueous solution and an acid. Store chloride or an aqueous solution in which chloride is dissolved in a separate container, and adjust the concentration and pH of chlorite ion and chloride in the mixed solution in advance in a closed container when calibrating the oxidizing gas measuring device. The chlorite ion is quantitatively changed to chlorine dioxide gas by mixing each in a predetermined amount so that the specified conditions are met, and chlorine dioxide gas of a known concentration obtained in a closed container or a known concentration of a mixed aqueous solution is obtained. Dissolved chlorine dioxide gas is measured by the measuring device, and the indicated value is set to the chlorine dioxide concentration or calibrated as a concentration corresponding to the chlorine dioxide concentration of another oxidizing gas.

[Action]

Chlorite ions (ClO ₂ ^-) is chloride ion (Cl ^-) Reducing the pH of the solution in the presence of quantitatively and rapidly changes to chlorine dioxide (ClO ₂₎ in certain pH. Therefore, if the above operation is quantitatively carried out in a closed container, the generated ClO ₂ gas will be in an equilibrium state with the gas phase and the liquid phase, so that the gas phase in the closed container will have a certain concentration of ClO ₂ gas. Cl contained and generated
Even if O ₂ gas is not collected and dissolved in pure water separately, ClO ₂ gas having a constant concentration is dissolved in the liquid phase (mixed aqueous solution).

That is, as shown in Fig. 1, sulfuric acid was added to NaClO ₂ aqueous solutions having different KCl concentrations of 10 ^-3 M in a closed container to adjust pH.
When the pH is decreased, the mixed aqueous solution which is the liquid phase in the closed container becomes an aqueous solution containing a dissolved ClO ₂ gas of a predetermined concentration at an almost constant pH value depending on the KCl concentration. For example, KC
When the l concentration is 10 ^-1 M, ClO at about pH 4 from Fig. 1
₂ ^- changes to ClO _2, the mixed aqueous solution 4.2 mg / of ClO ₂ gas is dissolved.

Accordance connexion, under advance certain KCl concentration, ClO ₂ ^- if seeking a quantitative relationship ClO _2, ^- the pH and ClO ₂ changes ClO ₂
Under certain defined conditions, ClO ₂ gas and ClO ₂ solution of known concentration can be obtained in a closed container, which can be used as it is for calibration. Incidentally, the closed container does not have to be a completely closed state in which gas does not flow at all, and may be a closed state container in which ClO ₂ gas hardly escapes to the outside until reaching a gas-liquid equilibrium state, For example, a pinhole-shaped small hole may be present.

Moreover, it is used to generate ClO ₂ for standard solution or standard gas.
ClO ₂ ⁻ is extremely stable in the liquid as shown by the solid line in FIG. 4, and the concentration does not change even after long-term storage. From solution, ^- accordance connexion, ClO ₂ of known concentrations that are stored
Easy to use ClO ₂ solution or Cl of known concentration whenever needed
O ₂ gas is obtained, and the dissolved or gas phase ClO ₂ gas measuring device can be easily and accurately calibrated using this as a standard solution or standard gas.

Also, for other oxidizing gas measuring devices such as O ₃ gas and chlorine gas, if the relationship of sensitivity between the oxidizing gas and ClO ₂ gas is obtained in advance, ClO ₂ gas is used according to the above method. It is possible to calibrate.

〔Example〕

Example 1 An aqueous NaClO ₂ solution having a concentration of 1.30 × 10 ⁻⁴ M and a sulfuric acid solution (pH 2.4) containing KCl having a concentration of 0.1 M were placed in separate containers and stored at room temperature for 100 days. Next, the NaClO
50 ml of a ₂ aqueous solution and 50 ml of a sulfuric acid solution containing 0.1 M KCl were mixed to adjust the pH of the mixed aqueous solution to 2.7. From the relationship between ClO ₂ ⁻ and ClO ₂ obtained in advance, ClO ₂ gas was 6.2 mg / g as a liquid phase under the above conditions.
It has been found that a dissolved mixed aqueous solution can be obtained.

A ClO ₂ gas measuring device (CLO-20 type manufactured by Toa Denpa Kogyo KK) using a diaphragm polarographic electrode was calibrated to 6.2 mg / using the mixed aqueous solution obtained by the above operation as a standard solution. next,
After the calibration, the ClO ₂ gas measuring device was used to continuously measure a plurality of solutions prepared so that the dissolved ClO ₂ gas concentration was 11.4 mg /, and the response curve shown in Fig. 2 was obtained. It turned out that a response was obtained.

Example 2 By the same operation as in Example 1 above, a concentration of 6.2 mg / as a gaseous phase in a closed container was obtained from a sulfuric acid solution containing NaClO ₂ aqueous solution and KCl.
ClO ₂ gas was obtained. Regarding the prototype diaphragm electrode type O ₃ gas measuring device, the sensitivity relationship between ClO ₂ gas and O ₃ gas was obtained in advance, and the same O ₃ gas was used using the above-mentioned 6.2 mg / ClO ₂ gas from this relationship of sensitivity.
The gas measuring device was calibrated to 15.5 mg /.

Next, using the above-mentioned O ₃ gas measuring device after calibration, 0.4 mg /
When the air containing O ₃ was continuously measured, the response curve of FIG. 3 was obtained, and it was found that a good response was obtained.

Note that the diaphragm electrode type chlorine gas measuring device can also be calibrated using ClO ₂ gas by obtaining the relationship between the sensitivities of ClO ₂ gas and Cl ₂ gas as in the case of O ₃ gas. I can.

〔The invention's effect〕

According to the present invention, chlorine dioxide dissolved in a gas phase or in a liquid phase having a known concentration can be obtained from a plurality of liquids which can be stored for a long period of time by a simple mixing operation, and therefore this is used as the standard gas or standard liquid. It is possible to calibrate an oxidizing gas measuring device for chlorine dioxide, ozone, chlorine, etc. easily and accurately.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the pH and the dissolved ClO ₂ concentration when a constant concentration of NaClO ₂ aqueous solution having different KCl concentrations was acidified with sulfuric acid, and FIG. 2 is a diaphragm type polarographic electrode calibrated by the method of the present invention. Fig. 3 is a response curve of a chlorine dioxide gas measuring device, Fig. 3 is a response curve of a diaphragm electrode type ozone gas measuring device calibrated by the method of the present invention, and Fig. 4 is a dissolved Cl
3 is a graph showing changes in concentration of O ₂ aqueous solution and dissolved ClO ₂ ⁻ solution with changes in storage time.

Claims (1)

[Claims] 1. A chlorite ion aqueous solution in which chlorite is dissolved and an acid in which chloride is dissolved, or an aqueous solution of chlorite ion and an acid and an aqueous solution in which chloride or chloride is dissolved are stored in separate containers. Then, by mixing each of the liquids in a closed container at the time of calibration of the oxidizing gas measuring device by a predetermined amount so that the concentration and pH of the chlorite ion and chloride in the mixed liquid are predetermined conditions, Chlorite ion is quantitatively changed to chlorine dioxide gas, chlorine dioxide gas of known concentration obtained in a closed container or dissolved chlorine dioxide gas of known concentration in the mixed aqueous solution is measured by the above-mentioned measuring device, and the instruction is given. A method for calibrating an oxidizing gas measuring device, wherein the value is set to the chlorine dioxide concentration or is calibrated as a concentration corresponding to the chlorine dioxide concentration of another oxidizing gas.