JPH036450A - Apparatus for measuring chlorine dioxide - Google Patents

Abstract

PURPOSE:To suppress the reduction of a liquid electrolyte and to prevent the contamination of a cathode by forming an anode from silver or silver/silver chloride while forming the cathode from gold or carbon and providing the third electrode composed of a noble metal or carbon to the periphery of the cathode. CONSTITUTION:A diaphragm 2 composed of polytetrafluoroethylene having a film thickness of 3 - 20mum is provided to one end of a cylindrical support 1 and a liquid electrolyte 3 composed of an acidic aqueous potassium chloride solution is received in the support 1 and a columnar insulator 6 is fixed to the support 1. An anode 4 is fixed to the outer periphery of the insulator 6 and a cathode 5 is fixed to the lower end thereof and one flat surface of the cathode 5 is arranged in contact with the diaphragm 2. The third annular electrode 7 provide din a concentric circular shape with respect to the cathode 5 is fixed to the periphery of the cathode 5 so that one flat surface thereof is arranged to the lower end of the insulator 6 in contact with the diaphragm 2. Voltages same or different are respectively applied to the cathode 5 and the electrode 7 from respective power supplies within a range generating a ClO2 reducing current and the ClO2 reducing current flowing between the anode 4 and the cathode 5 and transmitting through the diaphragm 2 is measured by an ammeter. The reducing current wherein the applied voltages are stable within a range of about 0 - 500mV can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for measuring the concentration of chlorine dioxide (CIO) in a liquid or gas by a diaphragm-type polarographic electrode method.

[Conventional technology]

Chlorine has traditionally been used to disinfect tap water and swimming pools, but it has become a problem as it has been found that chlorine produces carcinogenic trihalomethanes.

Therefore, recently, sterilization of tap water and swimming pools using chlorine dioxide, which does not produce trihalomethane, is being considered. In addition, since chlorine dioxide has strong oxidizing power, it is also used for bleaching textiles.

Therefore, in these fields, it is extremely important to appropriately control the concentration of chlorine dioxide in liquid or gas.

Methods for measuring chlorine dioxide include the iodine titration method (Chemical Disaster Prevention Guidelines (7)) and the diaphragm polarographic electrode method (Japanese Unexamined Patent Publication No. 1250-1983) for measuring dissolved chlorine dioxide in a liquid.
No. 95) is known.

However, the above-mentioned iodometric titration method is an intermittent measurement and is not suitable for continuous concentration control.

On the other hand, in the diaphragm polarographic electrode method, a diaphragm is provided at one end of the electrode cylinder, and an electrolytic solution such as a potassium chloride solution is filled inside the electrode cylinder, which is separated from the sample liquid side by the diaphragm. An anode is immersed in an electrolytic solution, and a cathode in contact with a diaphragm is placed facing each other, and a predetermined voltage is applied to the cathode with the anode as a reference, causing chlorine dioxide that has passed through the diaphragm to flow between the anode and cathode due to electrolysis. Although this method of measuring reduction current allows continuous measurement of chlorine dioxide in liquid or gas, it has the following problems.

That is, the diaphragm-type polarographic electrode method is generally used as an oxygen electrode, and the diaphragm normally used therein is polytetrafluoroethylene, but chlorine dioxide has a larger molecular diameter than oxygen and therefore does not pass through this diaphragm. Otherwise, the permeability was very poor and it was not suitable for measuring chlorine dioxide.

Therefore, recently, when measuring chlorine dioxide, the pore size is 0.
．． A diaphragm of 0.04 to 20 μm, for example a diaphragm made of polysilicon, polycarbonate, etc., is used. but,
Since the diaphragm having a large pore size that allows chlorine dioxide to pass through it well also allows water or water vapor to pass therethrough, the amount of electrolyte in the electrode decreases significantly, especially during measurements in a gas such as air. Therefore, it is necessary to provide a separate replenishment tank to constantly replenish the electrolyte, which has the drawback of making the device extremely complex.

Furthermore, when silver or silver/silver chloride is used as the anode, silver compounds from the anode dissolve into the electrolyte and deposit on the cathode surface, reducing the sensitivity and responsiveness of the electrode.
It was necessary to perform frequent cleaning and maintenance of the cathode.

Furthermore, in the diaphragm polarographic method, chlorine dioxide passes through the diaphragm, dissolves in the electrolyte, reaches the quad, and causes an electrochemical reaction, but chlorine dioxide diffuses laterally in the diaphragm or in the electrolyte. Since there is variation in the time it takes to reach the cathode, there are also problems with responsiveness, such as a delay in response.

[Problem to be solved by the invention]

In view of such conventional circumstances, the present invention suppresses the decrease in electrolyte solution and eliminates the need to constantly replenish the electrolyte solution when measuring chlorine dioxide using a diaphragm type polarographic electrode method that allows continuous measurement. It is an object of the present invention to provide a chlorine dioxide measuring device that does not cause cathode contamination due to adhesion and has excellent sensitivity and responsiveness.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a diaphragm that permeates chlorine dioxide is provided at one end of the cylindrical support, and the anode and the diaphragm are in contact with the electrolytic solution inside the cylindrical support, which is isolated from the sample side by the diaphragm. A diaphragm-type polarographic electrode method is used to measure the reduction current of chlorine dioxide that has passed through the diaphragm flowing between the anode and the cathode by applying a voltage to the cathode that produces a reduction current of chlorine dioxide. In the measuring device, - (1) the anode is made of silver or silver/silver chloride and the cathode is made of gold or carbon, and a third electrode made of noble metal or carbon is provided around the cathode in contact with the diaphragm and concentrically with the cathode; and (2) the anode is silver or silver/chloride. The present invention provides the above measuring device, characterized in that the silver and cannide are made of gold or carbon, and the diaphragm is made of polytetrafluoroethylene with a thickness of 3 to 20 μm.

〔Example〕

A specific example of the chlorine dioxide measuring device according to the present invention will be explained with reference to the drawings.

FIG. 1 shows the diaphragm type polarographic N pole part which is the main part of the device of the present invention, and the film thickness is 3 to 20 μm at one end of the cylindrical support 1.
A diaphragm 2 made of polytetrafluoroethylene of 0.0 m is provided, and an acidic potassium chloride solution (composition 0.1M KC7
- Filled with electrolytic solution 3 consisting of 0° IMH (!lp H1). Inside the cylindrical support 1, there is a cylindrical insulator 6.
is fixed, an anode 4 is fixed to the outer periphery of the insulator 6, and a cathode 5 is fixed to the lower end of the insulator 6 so as to be immersed in the electrolytic solution 3, and one plane of the cathode 5 is placed in contact with the diaphragm 2. has been done. Further, a third annular electrode 7 is provided around the cathode 5 concentrically with the cathode 5, and is also fixed to the lower end of the insulator 6 with one plane in contact with the diaphragm 2. Anode 4 consists of silver or silver/silver chloride, cathode 5
is made of gold or carbon such as grapha carbon, and the third electrode 7 is made of a noble metal such as gold or platinum or carbon such as grapha carbon.

In the device of the present invention, the electrode portion shown in FIG.
The voltages flowing between the anode 4 and the cathode 5 are connected as shown in the equivalent circuit shown in FIG. The reduction current of chlorine dioxide that has passed through the diaphragm 2 is measured with an ammeter 8. Since the voltage applied to the third electrode 7 may be the same as the voltage applied to the cathode 5, the connection of the equivalent circuit shown in FIG. 2(b) is preferably simple.

When the electrode shown in Figure 1 of the device configured as shown in Figure 2 (b) is immersed from the diaphragm 2 side into a sample solution containing dissolved chlorine dioxide at a constant concentration (10-4M), and the applied voltage is varied. The applied voltage and current characteristics are shown in FIG. Applied voltage is O~500
It can be seen that the diffusion rate of chlorine dioxide becomes rate-limiting at mV, and a stable reduction current can be obtained. Incidentally, as the cathode, gold or graphy carbon is preferable, and platinum is not preferable because it increases the residual current.

[Effect]

In the present invention, polytetrafluoroethylene is used as the diaphragm for the oxygen electrode, but the film thickness is 3 to 20 μm.
By making the thickness thinner, the permeability of chlorine dioxide can be improved, and as shown in FIG. 3, a reduction current large enough to enable sensitive measurement can be obtained. Moreover, since polytetrafluoroethylene is hardly permeable to water or water vapor, the amount of electrolyte from the diaphragm due to evaporation or the like is less likely to decrease, and there is no need to constantly replenish the electrolyte. Note that if the polytetrafluoroethylene film thickness is less than 3 μm, pinholes are likely to occur, and if it exceeds 20 μm, the permeability of chlorine dioxide decreases rapidly and the generated reduction current becomes small, making sensitive measurements impossible. .

Furthermore, in the present invention, by providing the third electrode, the chlorine dioxide contained in the diaphragm or electrolyte can be prevented from diffusing laterally and can reach the cathode straight, improving responsiveness. be done. FIG. 4 shows a concentration of 10-4 using the device of the present invention and a conventional device that does not include a third electrode.
It is a graph showing the responsiveness when a sample solution containing M chlorine dioxide was measured at an applied voltage of 300 mV.

Furthermore, by providing the third electrode, the silver compound dissolved in the electrolyte from the anode is deposited on the third electrode, but not on the quad surrounded by the third electrode. Therefore, even if silver or silver/silver chloride is used for the anode, the cathode is not contaminated, good sensitivity and responsiveness can be obtained, and stable measurements can be made over a long period of time without cleaning and maintenance.

〔Effect of the invention〕

According to the present invention, in a chlorine dioxide measuring device using a diaphragm-type polarographic electrode method capable of continuous measurement, the reduction in electrolyte can be suppressed by selecting a diaphragm, eliminating the need for constant replenishment of the electrolyte, thereby simplifying the size. Furthermore, by providing the third electrode, it is possible to prevent silver compounds from adhering to the cathode, simplify cleaning and maintenance, and improve sensitivity and responsiveness.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an electrode portion which is a main part of the device of the present invention, FIG. 2(a) and (1)) are equivalent circuit diagrams of the device of the present invention, and FIG. 4 is a graph showing the applied voltage and current characteristics of the device, and FIG. 4 is a graph showing the responsiveness of the device of the present invention. 1. Cylindrical support 2. Diaphragm 3. Electrolyte 4. Anode 5. Cathode 6. Insulator 7. Third electrode 8. Ammeter

Claims (1)

[Claims] (1) A diaphragm that allows chlorine dioxide to pass through is provided at one end of the cylindrical support, and an anode and a cathode in contact with the diaphragm are placed in an electrolytic solution inside the cylindrical support, which is isolated from the sample side by the diaphragm. In a chlorine dioxide measuring device using a diaphragm polarographic electrode method, which applies a voltage that produces a chlorine dioxide reduction current to the cathode and measures the reduction current of chlorine dioxide that has passed through a diaphragm flowing between the anode and the cathode, the anode is A third electrode made of silver or silver/silver chloride and a cathode made of gold or carbon, and made of a noble metal or carbon provided around the cathode in contact with a diaphragm in a concentric circle with the cathode;
The chlorine dioxide measuring device described above, characterized in that the third electrode is equipped with a cathode in a range that produces a reduction current of chlorine dioxide, and a power source that applies the same or different voltage. (2) A diaphragm that allows chlorine dioxide to pass through is provided at one end of the cylindrical support, and an anode and a cathode in contact with the diaphragm are placed in an electrolytic solution inside the cylindrical support, which is isolated from the sample side by the diaphragm. , by applying a voltage to the cathode that produces a reduction current of chlorine dioxide,
In a chlorine dioxide measurement device using a diaphragm-type polarographic electrode method that measures the reduction current of chlorine dioxide that has passed through a diaphragm flowing between an anode and a cathode, the anode is made of silver or silver/silver chloride and the cathode is made of gold or carbon, and the diaphragm The above-mentioned chlorine dioxide measuring device, wherein the chlorine dioxide measuring device is made of polytetrafluoroethylene with a film thickness of 3 to 20 μm.