JPH06249831A - Measurement of chlorous acid ion - Google Patents

Abstract

PURPOSE:To provide a method for invariably obtaining the correct concentration of the chlorous acid ions continuously in a simple manner, without being affected by the dissolved dioxidized chlorine, even if the temperature of the 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 for concentration is measured, carrying out compensation according to the temperature of the sample liquid for which the concentration of chlorous acid ion is measure separately.

Description

Detailed Description of the Invention

[0001]

The present invention relates, regardless of the temperature 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 Japanese Patent Laid-Open No. 2-296145 uses polarography, an error occurs in the measured value when the temperature of the sample solution changes. It has been found. In order to avoid the influence of temperature in the chemical analysis, it is general to carry out the measurement after keeping the temperature of the sample solution constant in advance by using a constant temperature bath or the like. However, since this method requires an operation for adjusting the temperature of the sample solution, the operation takes time, and this temperature adjustment has a drawback that continuous concentration control cannot be performed in the control of tap water or pool water. .

In view of such conventional circumstances, the present invention uses the method described in Japanese Patent Application Laid-Open No. 2-296145 to obtain a correct chlorite ion concentration, even when the temperature of the sample solution changes. The aim is to provide a method that can be sought.

[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 temperature.

One of the specific methods for performing temperature compensation according to the method of the present invention is: (1) For a plurality of reference solutions having known concentrations of chlorous acid at arbitrary different temperatures, each sub-method is based on the oxidation current according to the above method. Obtain the chlorate ion concentration measurement value, and (2) From each obtained concentration measurement value, a function having at least the temperature and the chlorite ion concentration corresponding to the temperature as variables, In advance, a calculation formula for calculating the correct chlorite ion concentration of (3) is measured, and then the concentration and temperature of chlorite ion based on the oxidation current according to the above method are measured for the sample solution, (4) Sample solution Is a method of calculating the temperature-compensated chlorite ion concentration of the sample liquid by substituting the measured concentration value of chlorite ion and the temperature in the above formula.

As another method for temperature compensation,
From each concentration measurement value corresponding to each temperature of the plurality of reference liquids obtained in (1), a table or figure having variables of temperature and chlorite ion concentration corresponding to the temperature is prepared in advance, and then the sample is prepared. It is also possible to obtain the temperature-compensated chlorite ion concentration of the sample liquid using either the table or the figure from the measured value of the chlorite ion concentration measured for the liquid and the temperature.

[0013]

The present inventors have studied the temperature dependence of the method described in JP-A-2-296145, and as a result, the measured concentration value is affected by the temperature of the sample solution, and the effect of temperature is quantified. Based on this finding, it was possible to compensate for the influence of temperature fluctuations and to obtain the correct chlorite ion concentration.

That is, in the method of the present invention, the relationship between the quantitatively changing temperature and the chlorite ion concentration is obtained in advance,
After expressing or recording this relationship as a calculation formula, table, or diagram, when measuring the actual sample solution, measure the temperature of the sample solution with a thermometer along with the measured concentration of chlorite ion in the sample solution. The correct chlorite ion concentration is calculated from the calculation formula using the value of, or read from a table or a figure.

However, even though the influence of temperature is quantitative, the degree thereof may vary depending on the measuring device used, particularly the structure of the working electrode, etc., so the method of the present invention is applied to each measuring device. Preferably. Moreover, it is preferable to measure the temperature at the same time as the measurement of the chlorite ion concentration in the same sample solution, but if the fluctuation range of the temperature is small, the temperature measurement interval is lengthened and one temperature measurement value is measured. It can also be used 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 equipped with a temperature sensor 10 for measuring temperature.
0 is connected to the thermometer 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 temperature of each of the two kinds of calibration solutions of 1 / l was adjusted to 25 ° C., and two-point calibration was performed using these two kinds of calibration solutions. Measurements were carried out on five kinds of sample liquids having different chlorite ion concentrations (all at a temperature of 25 ° C.) with the measuring device after calibration, and the known chlorite ion concentrations and the measured values are as shown in FIG. It showed good linearity.

Next, using the calibrated measuring device, the chlorite ion concentration was 1.0 mg / l (constant) and the temperature was 12.
With respect to 7 kinds of sample liquids between 5 ° C and 43.5, the measured concentration of chlorite ion and the temperature were measured at the same time, and the results are shown in Table 1 below. As can be seen from the measured values of temperature and concentration in Table 1 and FIG. 4 (○ in the figure) which is a graph thereof, the measured concentration values without temperature compensation are actually lower than the calibration temperature of 25 ° C. It is lower than the chlorite ion concentration and higher in the high temperature region, and it is clear that it is affected by the temperature of the sample solution.

[0020]

[Table 1] Sample liquid              Sample temperature (° C) 12.5 16.9 21.4 25.0 27.7 35.9 43.5 Concentration measured value (mg / l) 0.63 0.71 0.90 1.00 1.07 1.52 2.16

Therefore, from the measured values of the chlorite ion concentration and the sample solution temperature shown in Table 1 and FIG. 4 obtained by the measurement of the reference liquid, a function having the chlorite ion concentration and the temperature as variables is obtained. When the formula for calculating the correct chlorite ion concentration at an arbitrary specified temperature was calculated, the formula 1 below was obtained:

[Formula 1] log (chlorite ion concentration value) = log (concentration measurement value) -0.0172 (sample solution temperature -25)

Therefore, in the data processing section 8 of the measuring apparatus, the equation 1
The calculation formula is stored, and the temperature-compensated concentration value compensated by the difference in temperature is calculated by the data processing unit 8 according to Formula 1 from the measured value of the concentration of chlorite ion and the temperature, and the calculated value is displayed / printed. 9 is displayed or printed. Then, the concentration values of the temperature-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) 0.63 0.71 0.90 1.00 1.07 1.52 2.16 Temperature compensation concentration value (mg / l) 1.03 0.98 1.04 1.00 0.96 0.99 1.04

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 temperature compensation by the method of the present invention is dependent on the temperature variation of the sample solution. No, always the actual chlorite ion concentration of 1.0 m
It can be seen that it shows a value approximately equal to g / l. Therefore, by using this measuring device, it is possible to always know the correct chlorite ion concentration at a temperature of 25 ° C., no matter what temperature the sample liquid is measured thereafter. When a temperature other than 25 ° C. is selected as a meaningful arbitrary temperature when obtaining the above calculation formula, it is possible to obtain a calculation formula for calculating a correct temperature compensation concentration value at the arbitrary temperature.

Next, the relationship between the temperature and the chlorite ion concentration was summarized in a table or a diagram, and a method for temperature-compensating the chlorite ion concentration measured value was carried out using this table or the diagram. First,
Using the measuring device of FIG. 1 before storing the above calculation formula, a large number of samples were prepared by changing the temperature in the range of 5 ° C. to 45 ° C. with each standard liquid having a chlorite ion concentration of 0.1 to 3.0 mg / l. Concentration and temperature of chlorite ion are simultaneously measured for the reference solution of, and the result is the correct chlorite ion concentration and each temperature in vertical and horizontal columns, and each chlorite ion concentration measurement corresponding to each temperature is measured. The values were entered in the intersections 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 temperature and the left and right vertical axes represent the measured concentration of chlorite ion and the correct concentration value.

After that, the concentration and temperature of chlorite ion in the sample solution were measured using the same measuring device. The temperature-compensated chlorite ion concentration could be determined by applying the obtained chlorite ion concentration measured value and temperature to a table or a figure. That is, by extracting the corresponding concentration measurement value in the column of the temperature from the table, the correct concentration value (temperature compensation concentration value) at an arbitrary temperature corresponding to the concentration measurement value can be obtained. On the other hand, in the case of the figure, if the intersection of the temperature and the concentration measurement value is obtained, and a curve or a straight line passing near the intersection is translated to the intersection, the temperature corresponding to the arbitrary temperature on the translated curve or straight line is obtained. The correct density value (temperature-compensated density 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 temperature of the sample solution changes, the accurate chlorite ion concentration can be always obtained by performing temperature compensation 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 is a graph showing the relationship between the chlorite ion concentration of a sample liquid at a constant temperature and the measured value obtained by a measuring device according to the method of the present invention.

FIG. 4 is a graph showing the relationship between the temperature of the sample solution and the chlorite ion concentration expressed on a logarithmic scale in the case of temperature compensation and the case of no temperature compensation by 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 Processor 9 Display / Printer 10 Temperature Sensor 11 Thermometer

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 ions is applied to the working electrode as a reference, and the chlorite in the sample solution is based on the flowing oxidation current. A method for measuring chlorite ion, which comprises measuring the ion concentration and compensating the measured value of the chlorite ion concentration according to the temperature 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 at arbitrary different temperatures are used, based on the oxidation currents obtained by the method. Obtain the measured value of acid ion concentration, and (2)
From each obtained concentration measurement value, a function having at least the temperature and the chlorite ion concentration corresponding to the temperature as a variable, a calculation formula for calculating the correct chlorite ion concentration at any specified temperature, In advance, (3) After that,
For the sample solution, the chlorite ion concentration and temperature based on the oxidation current according to the above method were measured, and (4) the measured chlorite ion concentration value and temperature of the sample solution were substituted into the above formula,
A method for measuring chlorite ion, comprising calculating a temperature-compensated chlorite ion concentration of a sample solution. 3. Instead of the calculation formula of (2) in claim 2, from the respective concentration measurement values corresponding to the respective temperatures of the plurality of reference liquids obtained in the above (1), the temperature and the corresponding temperature are corresponded. Prepare a table or figure with the chlorite ion concentration as a variable in advance, and then use either the table or the figure from the measured chlorite ion concentration value and the temperature measured for the sample solution to determine the temperature of the sample solution. The method for measuring chlorite ion according to claim 2, wherein the compensated chlorite ion concentration is obtained. 4. The measurement of the chlorite ion according to claim 1, wherein the measurement of the temperature of the sample liquid is performed simultaneously with the measurement of the concentration of chlorite ion of the sample liquid. Method.