JPH01313754A - Method of measuring concentration of chlorine - Google Patents

Abstract

PURPOSE:To measure the low concn. of chlorine from the required quantity of electricity by taking the prescribed amt. of a sample into a cell for titration disposed with negative and positive electrodes made of silver, adding a required amt. of an acid reagent thereto, passing constant current and executing effective electrolysis to the disappearance of the chlorine ions. CONSTITUTION:The prescribed amt. of the sample 3 is exactly measured in the cell 1 for titration. A required amt. of the acid reagent 2 such as nitric acid is then added as a supply source of the hydrogen ions necessary for electrolysis. The constant current of DC is then passed between the positive electrode 6 consisting of a silver wire for electrolysis and the cathode 7 consisting of a silver electrode disposed in the cell 1 for titration while both are mixed uniformly by a stirring vane 5, so that the silver chloride is formed of the dissolved silver ions and the chlorine ions in the sample 3. The generation of the excess silver ions is detected by a pair of silver electrodes 8, 8 and the concn. of the chlorine in the reagent 3 is determined from the quantity of the electricity required to the disappearance of the chlorine ions in the reagent 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for measuring chlorine concentration in a liquid phase by coulometric titration, and is particularly applicable to the measurement of extremely low chlorine concentrations, which have been difficult to measure in the past. .

The present invention relates to a method for measuring chlorine concentration that can be performed using conventional coulometric titration equipment.

[Prior Art] A measurement method using coulometric titration is known as one of the methods for quantifying the chlorine concentration in a liquid phase.

As shown in Fig. 2, this measurement method involves placing a predetermined concentration of acid such as 15 to 20 nitric acid in which the chlorine component has been removed by electrolysis etc. in a glass titration cell 1 having a volume of about 30. It consists of a chain line for electrolysis, in which the reagent 2 is placed, and a sample 3 of about 0.2 mm is accurately weighed into it using a pipette 4, and the two are uniformly mixed by a stirring blade 5 while being placed inside the titration cell 1. Electrolysis is carried out by passing a constant current between the positive electrode 6 and the negative electrode 7 made of a silver electrode, and silver chloride is generated by the silver ions eluted from the positive electrode 6 into the electrolytic bath and the chlorine ions in the sample 3, The silver electrode pair 8.8 detects that all the chlorine ions in the sample 3 have reacted and excess silver ions have been generated, and the amount of electricity required for the chlorine ions in the reagent 3 to disappear is calculated based on the amount of electricity required for the chlorine ions in the reagent 3 to disappear. This is to find the chlorine concentration. This method is extremely convenient because it can measure the chlorine concentration in the liquid phase easily and within a short time without requiring any treatment such as evaporation or chemicals.

[Problems to be Solved by the Invention] However, the conventional method for measuring chlorine concentration using a coulometric titration device is to place a 15-20-acid reagent 2 into a titration cell 1 having a volume of about 30- 0.1 to 0.2
The measurement is carried out by adding sample 3 of - degree, and the acid reagent 2, which is a source of hydrogen ions, is present in excess. Therefore, it is possible to measure up to 10 times in a row, but since the amount of sample 3 added is extremely small, the measurable chlorine concentration is only about 50p, p, rti.
For example, 50p of tap water, purified water, or various foods.

It is not possible to measure chlorine concentrations below p, m. In addition, in order to make it possible to measure chlorine concentrations lower than this using the conventional method, it is possible to increase the amount of sample 3 added, but with conventional coulometric titration equipment, it is limited to the volume of titration layer cell 1. Because of this, the maximum increase in sample 3 is about 10-1, and even if it increases to the limit, it will only increase by 5.
p, l).

It is only possible to measure chlorine at a concentration of about 1.0 m with low accuracy. Furthermore, in order to significantly increase the capacity of the sample 3, it is necessary to increase the size of the titration cell 1 and the electrodes 6, 7, etc., which is not only economically disadvantageous, but also requires a relatively high cost if the device is made large. When measuring the concentration of chlorine, an unnecessarily large amount of sample 3 and acid reagent 2 are required.

The present invention has been made in view of the above circumstances, and provides a method for measuring chlorine concentration by coulometric titration, which allows extremely low chlorine concentration to be measured using a conventionally used coulometric titration device. be.

[Means for Solving the Problems] In the present invention, a titration cell in which four negative and negative silver electrodes are arranged is used, a predetermined amount of a sample containing chlorine is accurately measured into the titration cell, and the titration cell is By adding the necessary amount of acid reagent to the sample, electrolyzing the gastric sample by passing a constant current between the electrodes until the chlorine ions disappear, and determining the chlorine concentration in the sample from the amount of electricity required. This is a means to solve the above problem.

In the present invention, a conventional titration apparatus can be used as is. That is, referring to FIG. 1, first, 30M1
For example, a titration cell 1 having a volume of about 50p, p
, m, hereinafter generally 20 to O, ip, p.

About 15 to 20 tn of sample 3 with a chlorine concentration of about
Accurately measure a predetermined amount within the range A with an accuracy of 1% or less. Next, as a source of hydrogen ions necessary for electrolysis, add an acid reagent such as nitric acid in the required amount, for example, when the concentration of nitric acid is 1
Weigh and add 0.100mg for 4.5N, 0.200d for 5-6N, and 0.500- for 2-3N using micropipette 4 with an accuracy of 1% or less. do. Next, as in the conventional method, while uniformly mixing the two with a stirring blade 5, a 0.000.degree. A constant DC current of approximately 0.004 to 0.005 A/h is applied to generate silver chloride from the dissolved silver ions and the chlorine ions in the sample 3. After electrolyzing until the chlorine ions disappear, surplus silver ions are generated, but this generation is detected by the silver electrode pair 8.8, and from the amount of electricity required for the chlorine ions in the reagent 3 to disappear, the reagent 3 is detected. This is to find the chlorine concentration in the water.

Note that the present invention measures extremely low chlorine concentrations, and before titration, the titration cell 1, the electrodes 6, 7, and
The chlorine attached to 8.8 and the chlorine contained in acid reagent 2 affect the measured value. Therefore, for the titration cell 1 and the electrodes 6, 7, 8, and 8 used, adhering chlorine must be removed in advance by, for example, placing an acid reagent of about 15 to 20% in the titration cell 1 and electrolyzing it. do.

For acid reagent 2, for example, a predetermined amount of acid reagent 2 is added to 20 N pure water, the chlorine concentration is determined by the means of the present invention, and the basic chlorine amount is subtracted from the actual measured value. Find the amount of chlorine contained in.

[Example 7] The following table shows the measured values for Examples and Comparative Examples of the present invention, in which the amount of chlorine contained in purified water and tap water was determined. In the example, 0.2 mN of 3.5N nitric acid was added to 201 g of the sample, and in the comparative example, 0.2 mN of the sample was added to 20% ρ of 3.5N nitric acid.
were added, and titration was performed at a current of 0.005 A/h. In addition, in the table, × indicates that the measurement could not be performed.

According to the above results, in both Examples 1 and 2 of the present invention, the concentration of chlorine contained could be accurately measured, whereas in Comparative Example 1, there was a tendency that measurement could be performed or not at each titration. Even if measurements are possible, the measured values are inconsistent and unreliable.

Furthermore, in Comparative Example 2, the concentration of chlorine contained was too low to be measured. Therefore, it is clear that the present invention is capable of measuring extremely low concentrations of chlorine compared to conventional methods.

[Effects of the Invention] According to the present invention having the above-described configuration, extremely low chlorine concentrations, which could not be measured in the past, can be measured very easily and reliably using a conventionally used coulometric titration device. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the case where the present invention is implemented, and FIG. 2 is a schematic diagram showing a conventional titration method. 1... Titration cell, 2... Acid reagent, 3... Sample, 6... Positive electrode, 7... Negative electrode, 8.8... Silver electrode.

Claims (1)

[Claims] Using a titration cell equipped with a silver cathode and yang electrode, a predetermined amount of a sample containing chlorine is accurately measured into the titration cell, a required amount of acid reagent is added thereto, and a constant current is applied between the electrodes. A method for measuring chlorine concentration, characterized in that the chlorine concentration in the sample is determined from the amount of electricity required by electrolyzing the sample until chlorine ions disappear.