JPH06249832A - Measurement of chlorous acid ion - Google Patents

Abstract

PURPOSE:To provide a method for invarrably the correct concentration of chlorous acid ions continuously in a simple manner, without being given with the influence of the dissolved dioxidized chlorine, even if the electric coductivity of a sample liquid varies, by using the polarography method. CONSTITUTION:Two electrodes consisting of a working electrode 4 and a counter electrode 5 or three electrodes consisting of the working electrode 4, reference electrode 6 and the counter electrode 5 are immersed in a sample liquid. Relatively moving the working electrode 4 and the sample liquid, the voltage for generating the oxidation electric current of chlorous acid ion is applied on the working electrode 4, having the counter electrode 5 as standard in case of two electrodes, while having the reference electrode 6 as standard in case of three electrodes, and the concentration of the chlorous acid ions in the sample liquid is measured on the basis of the flowing oxidation electric current. then, the chlorous acid ion is measured carrying out compensation according to the electric coductivity of the sample liquid for which the concentration of chlorous acid ion is measured separately.

Description

Detailed Description of the Invention

[0001]

The present invention relates, regardless of the conductivity of the sample solution, chlorite ion in the sample solution ^- relates to a method for accurately measuring the concentration (ClO _2).

[0002]

2. Description of the Related Art Conventionally, chlorine has been used for sterilizing tap water or pool water, but it has been known that chlorine produces carcinogenic trihalomethanes, which has been a problem. Therefore,
It has been considered to sterilize tap water and pool water using chlorine dioxide that does not generate trihalomethane, and recently, it was used to disinfect swimming pool water by disinfecting swimming pool water according to the notification of the director of the Planning Division, Living Health Bureau, Ministry of Health and Welfare. Use of chlorine has been approved.

When chlorine dioxide is used for disinfection of water, chlorine dioxide itself is reduced, but part of it is decomposed to chlorous acid. Since chlorous acid produces chlorine dioxide when it is acidified by light or ultraviolet light and has the potential of oxidizing chlorine dioxide, the concentration of chlorous acid together with chlorine dioxide is used in disinfecting the above water. It is necessary to manage. In addition, since there is a report from an animal experiment that chlorous acid causes hemoglobin disorder and anemia when ingested at a high concentration, chlorous acid concentration in pool water is 1.
It is required to be 2 mg / l or less.

As a method for measuring the concentration of chlorous acid,
Diethyl -p- added to the above "Eki 46th"
Phenylenediamine method (DPD method) and chemical disaster prevention guidelines
The iodometric titration method defined in (7) is known. However, in both methods, sulfuric acid and potassium iodide were added to the sample solution, and after changing potassium iodide to iodine by chlorine dioxide generated from chlorous acid under acidic conditions, the chlorous acid concentration was calculated from the amount of iodine. Method.

That is, in the DPD method, the coloring reagent diethyl-p
-Phenylenediamine is colored with iodine and its absorbance is measured. In the iodine titration method, liberated iodine is subjected to redox titration. Therefore, since any of the methods is affected by dissolved chlorine dioxide, it is necessary to perform an operation to remove the effect, which is extremely complicated and not suitable for continuous monitoring, and sulfuric acid is used as one of the reagents. Since it is used, it has some drawbacks such as being dangerous.

By the way, chlorous acid has a dissociation constant pKa =
With a weak acid of 2.31 (25 ° C), as shown in Fig. 2, almost 100% dissociated into chlorite ions at a pH of about 4 or higher. Therefore, it can be considered that chlorous acid is all chlorite ions in near-neutral water such as tap water or pool water, and the concentration of chlorite ions can be regarded as the concentration of chlorite. it can. That is, even if the concentration of chlorite ion is used to control the concentration of chlorous acid, there is no practical problem.

Based on this fact, a method has been proposed in which the oxidation current generated by electrolysis of chlorite ions is measured to determine the chlorite ion concentration and thus the chlorous acid concentration, which is disclosed in JP-A-2-296145. It is disclosed. According to this method, the chlorite ion concentration can be easily and continuously measured without being affected by dissolved chlorine dioxide.

[0008]

However, since the method disclosed in the above-mentioned Japanese Patent Laid-Open No. 2-296145 is a method using polarography, an error in the measured value may occur when the conductivity of the sample solution changes. It turned out to occur.
In order to avoid the influence of the electric conductivity in the chemical analysis, it is general that an electrolyte irrelevant to the measurement is added to the sample solution in advance to keep the electric conductivity of the sample solution constant and then the measurement is performed. However, this method requires a troublesome operation for adjusting the conductivity of the sample solution with an electrolyte, and it requires time and labor for the operation, and in addition, for adjusting this conductivity, it is necessary to manage tap water or pool water. However, there is a drawback that continuous concentration control is not possible.

In view of such conventional circumstances, the present invention uses the method described in Japanese Patent Application Laid-Open No. 2-296145 to always obtain a correct chlorite ion concentration even when the conductivity of the sample liquid changes. The aim is to provide a method by which the

[0010]

In order to achieve the above object, in the method for measuring chlorite ion provided by the present invention, a working electrode and a counter electrode are provided in a sample liquid, or a working electrode and a reference electrode and a counter electrode. While immersing the three electrodes, the working electrode made of a noble metal or carbon and the sample liquid are relatively moved, the working electrode is divided into two parts by using the counter electrode as a reference and the reference electrode as a reference in the case of three electrodes. A voltage that produces an oxidation current of chlorate ions is applied, the concentration of chlorite ion in the sample solution is measured based on the flowing oxidation current, and the measured value of the concentration of this chlorite ion is measured separately. The feature is that compensation is performed according to the electric conductivity.

One of the specific methods of conducting the conductivity compensation according to the method of the present invention is: (1) Based on the oxidation current of the above method for a plurality of reference solutions of known concentrations of chlorous acid having arbitrary conductivity. The concentration measurement value of each chlorite ion is obtained, and (2) a function having at least the electric conductivity and the chlorite ion concentration corresponding to the electric conductivity as variables from the obtained concentration measurement values, A calculation formula for calculating the correct chlorite ion concentration at the specified conductivity is obtained in advance, and (3) after that, the chlorite ion concentration and the conductivity based on the oxidation current by the above method are measured for the sample solution. (4) A method of calculating the conductivity-compensated chlorite ion concentration of a sample solution by substituting the measured concentration of chlorite ion of the sample solution and the conductivity into the above calculation formula.

As another method of compensating for the conductivity, the conductivity and the sub-correspondence corresponding to the conductivity can be calculated from the respective concentration measurement values corresponding to the conductivity of the plurality of reference solutions obtained in (1) above. A table or figure with the chlorate ion concentration as a variable is prepared in advance, and then the conductivity of the sample solution is measured using either the table or the figure from the measured concentration of chlorite ion and the conductivity measured for the sample solution. The degree-compensated chlorite ion concentration can also be obtained.

[0013]

The present inventors have studied the electric conductivity dependence of the method described in Japanese Patent Application Laid-Open No. 2-296145, and as a result, the measured concentration value is affected by the electric conductivity of the sample liquid, and It was found that the effect can be quantitatively determined, and based on this finding, it is possible to compensate for the effect of the change in conductivity and obtain the correct chlorite ion concentration.

That is, in the method of the present invention, the relationship between the quantitatively changing conductivity and the chlorite ion concentration is obtained in advance, and the relationship is expressed or recorded as a calculation formula, table or figure, and then the actual value is recorded. When measuring the sample solution, measure the chlorite ion concentration of the sample solution and the conductivity of the sample solution with a conductivity meter, and use these values to calculate the correct chlorite ion concentration from the formula. Or read from the table or figure.

However, even though the influence of the electrical conductivity is quantitative, the degree thereof may vary depending on the measuring device used, particularly the structure of the working electrode and the like. It is preferably applied. Moreover, it is preferable to measure the conductivity at the same time as the measurement of the chlorite ion concentration in the same sample solution, but if the fluctuation range of the conductivity is small, increase the measurement interval of the conductivity to make one conductivity. It is also possible to use the degree measurement value to measure the chlorite ion concentration several times.

[0016]

EXAMPLE FIG. 1 shows a concrete example of a measuring apparatus for carrying out the method of the present invention. The electrolysis cell 1 is provided with a sample solution inlet 2 at the bottom and a sample solution outlet 3 at the top, and a working electrode 4 having a sensitive portion made of glassy carbon is arranged at the bottom of the electrolysis cell 1 and a silver / silver chloride electrode. A counter electrode 5 and a reference electrode 6 are arranged above the working electrode 4. The working electrode 4, the counter electrode 5 and the reference electrode 6 are connected to a potentiostat 7, and a voltage of 0.6 to 1.2 V that causes an oxidation current of chlorite ion in the working electrode 4 with reference to the reference electrode 6 is applied. It can be applied.

The potentiostat 7 is connected to the data processing unit 8. The relation between the chlorite ion concentration experimentally obtained and its oxidation current is input to the data processing unit 8, and the input data and the oxidation current of the sample liquid obtained by the potentiostat 7 by actual measurement are input. Based on the above, the data processing unit 8 calculates the concentration measurement value of the chlorite ion in the sample liquid, and this can be displayed or printed on the display / printing unit 9. Further, the electrolysis cell 1 is provided with a conductivity cell 10 for measuring conductivity, and the conductivity cell 10
Is connected to the conductivity meter 11.

The chlorite ion concentration of the sample liquid was measured as follows using the measuring apparatus shown in FIG. First, in the calibration operation, the chlorite ion concentration was 0 mg / l and 2.5 mg.
The conductivity of each of the two types of calibration solutions of 1 / l was adjusted to 350 μS / cm using sodium salt, and two-point calibration was performed using these two types of calibration solutions. Measurements were performed on five types of sample liquids (each having an electrical conductivity of 350 μS / cm) having different chlorite ion concentrations by using the measuring device after calibration, and the known chlorite ion concentration and its measured value are shown in FIG. As shown, it showed good linearity.

Next, using a calibrated measuring device, the chlorite ion concentration was 1.0 mg / l (constant) and the conductivity was 2
8 kinds of sample liquids between 22 and 731 μS / cm
For the above, the measured concentration of chlorite ion and the electric conductivity were measured at the same time, and the results are shown in Table 1 below. As can be seen from the conductivity and the concentration measurement value in Table 1 and FIG. 4 (○ in the figure) which is a graph of the conductivity measurement value, the concentration measurement value without the conductivity compensation is the conductivity of the used calibration solution of 350 μS / cm. Although it is almost the same as the actual chlorite ion concentration in the higher conductivity region,
In the low conductivity region, the concentration is lower than the actual concentration, and it is clear that the conductivity is affected by the sample liquid.

[0020]

[Table 1] Sample liquid                Conductivity of sample solution (μS / cm) 222 283 374 433 489 561 609 731 Concentration measurement value (mg / l) 0.91 0.94 0.97 0.97 0.97 1.01 1.01 1.01

Therefore, from the measured values of the chlorite ion concentration shown in Table 1 and FIG. 4 obtained by the measurement of the reference liquid and the electric conductivity of the sample liquid, a function having the chlorite ion concentration and the electric conductivity as variables is used. Then, when the calculation formula for calculating the correct chlorite ion concentration at the arbitrarily specified conductivity is obtained, the following formula 1 is obtained.
The following formula was obtained:

[Formula 1] Chlorite ion concentration value = concentration measurement value / {1 + 0.
0002 (conductivity of sample liquid −350)} + 0.0002 × (conductivity of sample liquid −350)

Therefore, in the data processing section 8 of the measuring apparatus, the equation 1
The calculation formula is stored, the conductivity compensation concentration value is calculated by the data processor 8 according to the formula 1 from the measured value of the concentration of chlorite ion and the conductivity, and this is displayed. / Displayed or printed on the printing unit 9. Then, the concentration values of the conductivity-compensated chlorite ions obtained by measuring the same sample liquids again are shown in Table 2 together with the concentration measurement values before compensation.

[0023]

[Table 2] Sample liquid                Concentration measurement value (mg / l) 0.91 0.94 0.97 0.97 0.97 1.01 1.01 1.01 Conductivity compensation concentration value (mg / l) 0.96 0.97 0.97 0.97 0.97 1.01 1.01 1.01

As can be seen from the above Table 2 and the graph of FIG. 4 (● in the figure), the concentration value of the chlorite ion after the conductivity compensation by the method of the present invention is the variation of the conductivity of the sample solution. Regardless of, the actual chlorite ion concentration is always 1.
It can be seen that it shows a value approximately equal to 0 mg / l. Therefore,
By using this measuring device, it is possible to always know the correct chlorite ion concentration at an electric conductivity of 350 μS / cm, irrespective of the subsequent measurement of the sample liquid of any electric conductivity. When a conductivity other than 350 μS / cm is selected as a meaningful arbitrary conductivity when obtaining the above-mentioned calculation formula, a calculation formula for calculating a correct conductivity compensation concentration value at the arbitrary conductivity can be obtained. It is possible.

Next, the relationship between the electric conductivity and the chlorite ion concentration was summarized in a table or a diagram, and a method for compensating the measured value of the chlorite ion concentration with the electric conductivity was carried out using this table or the diagram. First, using the measuring device of FIG. 1 before storing the above calculation formula, the conductivity was changed in the range of 150 to 550 μS / cm with each reference liquid having a chlorite ion concentration of 0.1 to 3.0 mg / l. For a large number of reference liquids, the concentration and conductivity of chlorite ions were measured at the same time, and the results were taken as the vertical and horizontal columns of the correct chlorite ion concentration and each conductivity, respectively. The measured values of chlorite ion concentration were entered at the intersecting positions of both columns and arranged in a table. In addition, the results organized in this table are shown in a diagram in which the horizontal axis represents the conductivity and the left and right vertical axes represent the measured concentration of chlorite ion and the correct concentration value.

After that, the same measuring device was used to measure the chlorite ion concentration and the conductivity of the sample liquid. By applying the obtained measured value of chlorite ion concentration and the electric conductivity to a table or a figure, the electric conductivity-compensated chlorite ion concentration could be obtained. That is, if the corresponding concentration measurement value in the column of the conductivity is extracted from the table, the correct concentration value (conductivity compensation concentration value) at an arbitrary conductivity corresponding to the concentration measurement value can be obtained. On the other hand, in the case of the figure, if the intersection between the conductivity and the concentration measurement value is obtained, and a curve or a straight line passing near the intersection is moved in parallel to the intersection, an arbitrary conductivity is obtained on the parallel-moved curve or straight line. The corresponding correct concentration value (conductivity compensation concentration value) can be obtained.

[0027]

According to the present invention, the concentration of chlorite ion can be easily and continuously measured without being affected by dissolved chlorine dioxide. JP-A-2-296145
In the method using polarography described in the publication, even if the electric conductivity of the sample solution changes, the accurate chlorite ion concentration can be always obtained by compensating the electric conductivity of the measured value.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a specific example of a measuring apparatus for carrying out the method of the present invention.

FIG. 2: Chlorite ion (ClO ₂ ) of chlorous acid (HClO ₂ ).
₂ is a graph showing the relationship between the degree of dissociation α into ₂ ⁻ ) and pH.

FIG. 3 shows the chlorite ion concentration of a sample liquid having a constant conductivity,
It is a graph which shows the relationship with the measured value calculated by the measuring device concerning the method of the present invention.

FIG. 4 is a graph showing the relationship between the conductivity of a sample liquid and the concentration of chlorite ion expressed on a logarithmic scale, with and without the conductivity compensation according to the method of the present invention.

[Explanation of symbols]

 1 Electrolytic Cell 2 Sample Liquid Inlet 3 Sample Liquid Outlet 4 Working Electrode 5 Counter Electrode 6 Reference Electrode 7 Potentiostat 8 Data Processing Section 9 Display / Print Section 10 Conductivity Cell 11 Conductivity Meter

Claims (4)

[Claims] 1. Immersing a working electrode and a counter electrode or a working electrode and a reference electrode and a counter electrode into a sample solution, and moving the working electrode made of a noble metal or carbon and the sample solution relatively to each other. In the case of a pole, the counter electrode is used as a reference and in the case of a three pole, a voltage that causes an oxidation current of chlorite ion is applied to the working electrode as a reference, and chlorite in the sample solution is based on the flowing oxidation current. A method for measuring chlorite ion, comprising measuring the ion concentration and compensating the measured value of the chlorite ion concentration according to the conductivity of the sample solution. 2. The method for measuring chlorite ion according to claim 1, wherein (1) a plurality of reference liquids with known concentrations of chlorous acid having arbitrary different conductivities are prepared based on the oxidation current by the method. Obtain the measured concentration of chlorate ion, and (2)
From each obtained concentration measurement value, it is a function having at least the conductivity and the chlorite ion concentration corresponding to the conductivity as a variable, and calculates the correct chlorite ion concentration at the arbitrarily specified conductivity. Obtain the formula in advance, (3)
Then, the concentration and conductivity of chlorite ion based on the oxidation current by the above method were measured for the sample solution, and (4) the measured concentration and conductivity of chlorite ion of the sample solution were substituted into the above formula. , A method for measuring chlorite ion, which comprises calculating a conductivity-compensated chlorite ion concentration of a sample solution. 3. Instead of the calculation formula of (2) in claim 2, from the respective measured concentration values corresponding to the respective conductivity of the plurality of reference liquids obtained in (1), the conductivity and the conductivity can be obtained. In advance, a table or a figure with a variable chlorite ion concentration corresponding to was prepared, and then from the measured concentration and conductivity of the chlorite ion measured for the sample liquid, using either the table or the figure.
3. The method for measuring chlorite ion according to claim 2, wherein the conductivity-compensated chlorite ion concentration of the sample solution is determined. 4. The chlorite ion according to claim 1, wherein the conductivity of the sample solution is measured simultaneously with the measurement of the concentration of chlorite ion in the sample solution. Measuring method.