JP2005345222A - Residual chlorine meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a residual chlorine meter capable of sharply reducing the electrodeposition of metal ions to the surface of a cathode caused by the oxidation reaction of an anode without requiring polishing or the like, capable of extending the life of the anode and capable of always keeping a stable reference potential in the case of a galvanic cell type. <P>SOLUTION: The anode 10 is constituted of a second-class electrode in a state that its electrode main body 18 is immersed in an electrolyte solution 16 of 0.001-0.0001 mol/L of KCl+1 mol/L of KNO<SB>3</SB>housed in a cylindrical body 15 with a liquid communication part 14. An inorganic cationic exchange agent 19 is housed in the cylindrical body 15 of the second-class electrode 10 and a ceramic member 20 is provided to the liquid communication part 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is for hygiene management such as, for example, tap water used for beverages, pool water, water for public bathing, water for food factories, etc., and does not become a medium for prevention of breeding of various bacteria and microorganisms or infectious diseases. In addition, the present invention relates to a residual chlorine meter used for monitoring the concentration of all available chlorine (free residual chlorine + combined residual chlorine) remaining in water into which a disinfectant such as sodium hypochlorite has been added. Specifically, by measuring a diffusion current flowing between a counter electrode (hereinafter referred to as an anode electrode) immersed in a test liquid (water) and a working electrode (hereinafter referred to as a cathode electrode), The present invention relates to a residual chlorine meter configured to measure a residual chlorine concentration in a test liquid.

For example, in a polarographic residual chlorine meter known as this type of residual chlorine meter, a voltage is applied between the cathode and anode electrodes soaked in a test solution, whereby a second type of electrode such as a silver / chloride salt is obtained. On the anode side made of silver,
Ag → Ag ⁺ + e ⁻
Ag ⁺ + ClO ⁻ → AgCl + 1 / 2O ₂
In the cathode electrode side made of a noble metal such as gold or platinum,
HClO + e ⁻ → 1 / 2H ₂ + ClO ⁻
Due to these redox reactions, a current (diffusion current) proportional to the residual chlorine concentration in the test solution flows from the anode electrode to the cathode electrode, and the diffusion current (cathode) The residual chlorine concentration of the test solution is measured by measuring the magnitude of the reduction current at the electrode).

  By the way, as a polarographic residual chlorine meter, an anode formed in a spiral shape with platinum so as to have a surface area more than 20 times that of the cathode electrode on the outer periphery of the cathode electrode formed in a disk shape with platinum. An electrode wound is known (for example, see Patent Document 1).

  In addition, as other residual chlorine meters, an electrode tip made of gold or platinum is fixed to the tip of an electrode body made of a synthetic resin cylinder, and a lead wire is connected to the electrode tip. A galvanic cell type residual chlorine meter is also known in which a thin silver wire is spirally wound around the outer periphery as an anode electrode, and silver chloride is plated on the spiral silver wire by electrolytic treatment or the like (for example, Patent Document 2).

JP 55-87942 A JP 62-43556 A

  In the conventional residual chlorine meter as described above, the metal ions dissolved by the oxidation reaction on the anode electrode side are electrodeposited on the electrode surface of the cathode electrode. Therefore, when performing continuous measurement, the applied voltage between both electrodes is It changes over time and the reduction current value at the cathode electrode becomes unstable. As a result, an error is likely to occur in the measurement value of the residual chlorine concentration by measurement of the reduction current value. In order to reduce measurement errors due to such metal ion electrodeposition, a motor is attached to the cathode electrode to rotate it, and for example, ceramic beads are accommodated in the test liquid, and the cathode electrode rotates. It is considered that the electrode surface is always polished by rubbing the surface and ceramic beads, but in this case, a complicated mechanism is required for polishing the cathode electrode, which increases the size and cost of the entire instrument. Unavoidable.

In addition, since the anode electrode made of a metal such as platinum or silver is bare or is plated with silver chloride, it is not only used for measuring the concentration of residual chlorine used in the immersion state in the test solution. It dissolves gradually at the time of measurement, and further, the dissolved metal ions such as silver ions react with the salt to generate dissolved chloroanions (AgCl2 ⁻ ) and the like, and as a result, the dissolution is further promoted. There was a problem that the electrode was consumed very much and lacked the durability life.

  Furthermore, in the case of a galvanic cell type residual chlorine meter in which both the cathode and anode electrodes are a combination of a noble metal such as gold or platinum and a base metal such as silver, it is eluted by an oxidation reaction of the anode electrode made of a base metal such as silver. Metal ions such as silver ions are electrodeposited on the cathode electrode, causing a reduction in the reduction current value, or chloride ions enter the test solution as interfering substances. For example, the concentration of chloride ions in tap water is necessary for concentration measurement. As a result, the plateau current may not be obtained depending on the type and properties of the test solution, and the predetermined residual chlorine concentration may not be measured by measuring the reduction current value. There was also a problem.

  The present invention has been made in view of the above circumstances, and its purpose is to electrodeposit metal ions on the cathode electrode surface accompanying the oxidation reaction on the anode electrode side without requiring a complicated mechanism such as electrode polishing. The continuous measurement of residual chlorine concentration can be performed with high accuracy at all times, and the durability of the anode electrode can be extended. In the case of the galvanic cell type, the chloride concentration of the test solution can be reduced. Regardless, the object is to provide a residual chlorine meter that can always maintain a stable reference potential.

  In order to achieve the above object, the residual chlorine meter according to the present invention measures the concentration of residual chlorine in the test liquid by measuring the diffusion current flowing between the counter electrode immersed in the test liquid and the working electrode. In the residual chlorine meter configured to measure, the counter electrode is configured so as to be immersed in an electrolyte solution in which the electrode body is housed in a tubular body with a liquid junction portion and is unlikely to generate a liquid-liquid potential difference. It is characterized by being.

  According to the residual chlorine meter of the present invention having the above-described characteristic configuration, the metal ions dissolved by the oxidation reaction of the electrode body on the counter electrode (anode electrode) side are eluted into the electrolyte solution contained in the cylinder, and the Electrodeposition of dissolved metal ions on the electrode surface of the working electrode (cathode electrode) can be minimized. Therefore, it is possible to stabilize the reduction current value at the cathode electrode and continuously measure the residual chlorine concentration by measuring the reduction current value without providing a complicated mechanism for constantly polishing the electrode surface on the cathode electrode side. It can always be performed accurately. In addition, since the anode electrode is not affected by the coexistence of the redox substance, and its consumption can be reduced as much as possible, it is possible to extend the durability life of the anode electrode and thus the residual chlorine meter. Play.

  In addition, as described in claim 2, the electrode body of the counter electrode (anode electrode) is composed of a second type electrode such as silver / silver chloride, and the working electrode (cathode electrode) is a noble metal such as gold or platinum. In the residual chlorine meter, the electrolyte solution to be accommodated in the cylinder with the liquid junction is a galvanic solution by reducing the chloride ion concentration of the solution by using potassium chloride and potassium nitrate dissociated in a solvent. In the battery type, for example, it is possible to maintain a constant reference potential without being affected by the chloride ion concentration of the test solution such as tap water, and the plateau regardless of the type and properties of the test solution. A predetermined residual chlorine concentration measurement can be reliably performed by ensuring a stable current in the region and measuring a reduction current value. Further, the use of potassium nitrate, particularly a high-concentration potassium nitrate solution, can significantly reduce the generation of liquid junction potential at the liquid junction. The second type electrode refers to a metal electrode covered with a hardly soluble base.

In the residual chlorine meter according to the present invention, as described in claim 3, an ion trap that traps metal ions eluted by an oxidation reaction of the electrode body in the cylinder of the second type electrode constituting the anode electrode By adopting a configuration in which a ceramic member that prevents the diffusion of the metal ions is provided in the liquid junction portion, the metal ions such as silver ions and the dissolved chloro ion (AgCl2 ^-) or the like is captured (adsorbed) to the ion trapping agent, thereby preventing the formation of chlorides, such as silver chloride, a ceramic member, can be suppressed that they ions diffuse in the electrolyte solution, which Therefore, it is possible to prevent the fluctuation of the liquid potential caused by closing the liquid junction part of the second type electrode, and to always apply a constant voltage applied to the plateau region.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is an external perspective view showing the overall configuration of a residual chlorine meter 1 according to the present invention. This residual chlorine meter 1 has a display unit 2 for displaying a measured value of residual chlorine concentration and an instrument body 4 having an operation unit 3. And a residual chlorine sensor section 5 and a signal transmission cord 8 for detachably connecting the residual chlorine sensor section 5 and the instrument body 4 via male and female connectors 6 and 7.

  FIG. 2 is an enlarged vertical cross-sectional view of the main part showing the configuration of the residual chlorine sensor unit 5. This residual chlorine sensor unit 5 is built in the instrument body 4 via the signal transmission cord 8 and the connectors 6 and 7. An anode electrode (counter electrode) 10 connected to the measurement detection circuit 9 and a cathode electrode (working electrode) 11, and both the electrodes 10, 11 are made of tap water or the like introduced into the liquid tank 12. A voltage is applied between the electrodes 10 and 11 from the measurement detection circuit 9 while being immersed in the test solution 13, and at this time, a diffusion current flowing between the electrodes 10 and 11 is detected by the measurement detection circuit 9. By displaying on the display unit 2, the residual chlorine concentration in the test liquid 13 is measured.

The anode electrode 10 in the residual chlorine sensor unit 5 has a liquid junction 14 at the lower end thereof. For example, a liquid potential difference is hardly generated between the test solution 13 and the tube 15 made of a glass tubular body. An electrolyte solution 16 is accommodated, and an electrode body 18 made of silver / silver chloride formed by melting and adhering silver chloride to the tip of a silver bar 17 is provided in the electrolyte solution 16 as a second type electrode in an immersed state. Has been. The electrolyte solution 16 is obtained by, for example, dissociating 0.001 to 0.0001 mol / L potassium chloride (KCl) and 1 mol / L potassium nitrate (KNO ₃ ) into a solvent (water).

Further, an ion trapping agent that desorbs and captures silver ions (Ag ⁺ ) and dissolved chloroanions (AgCl 2 ^{− and the} like) eluted by the oxidation reaction of the electrode body 18 of the anode electrode 10 at the bottom of the cylindrical body 15. As described above, the inorganic cation exchanger 19 is accommodated, and the liquid junction portion 14 is provided with a ceramic member 20. The inorganic cation exchanger 19 is, for example, a ZrO ₂ type, and specifically, trade name IXE manufactured by Toa Gosei Chemical Co., Ltd. is used. In addition, as the porous ceramic member 20, for example, an Al ₂ O ₃ based porous ceramic is used.

  On the other hand, an electrode chip made of gold (Au) or platinum (Pt) at the lower end of an inner cylinder 21 made of synthetic resin that is penetrated and fixed to the cylinder 15 so that the lower end protrudes from the bottom of the cylinder 15. 22 is fixedly held in a watertight state, and a lead wire 23 electrically connected to the electrode chip 22 is inserted into the inner cylinder 21 and connected to the signal transmission cord 8, whereby the cathode electrode 11. Is configured.

  In the residual chlorine meter 1 configured as described above, the anode electrode (counter electrode) 10 and the cathode electrode (working electrode) 11 are immersed in a test solution 13 such as tap water introduced into the liquid tank 12. When a voltage is applied between the electrodes 10 and 11 from the measurement detection circuit 9 of the meter body 4, an oxidation reaction occurs on the anode electrode 10 side and a reduction reaction occurs on the cathode electrode 11 side. Due to the reaction, a current (diffusion current) proportional to the residual chlorine concentration in the test solution 13 flows from the anode electrode 10 toward the cathode electrode 11, and the magnitude of the diffusion current is detected by the measurement detection circuit 9. By displaying on the display unit 2, the residual chlorine concentration of the test solution 13 is measured.

Here, silver ions (Ag ⁺ ) and dissolved chloroanions (AgCl 2 ^{− and the} like) dissolved by the oxidation reaction of the electrode body 18 made of silver / silver chloride on the anode electrode 10 side are contained in the electrolyte solution 16 in the cylinder 15. Is captured by the inorganic cation exchange agent 19 provided in the substrate, and the formation of silver chloride is prevented. The trapped silver ions (Ag ⁺ ) and dissolved chloroanions (AgCl 2 ⁻ etc.) are contained in the test liquid 13 by the ceramic member 20 provided in the liquid junction 14 below the inorganic cation exchanger 19. Is prevented from diffusing. As a result, it is possible to reduce the electrodeposition of silver ions (Ag ⁺ ) and dissolved chloroanions (AgCl 2 ⁻ etc.) onto the surface of the electrode tip 22 of the cathode electrode 11, Even if a complicated mechanism for polishing the surface of the electrode tip 22 is not provided, the reduction current value at the cathode electrode 11 can be stabilized and the continuous measurement of the residual chlorine concentration can always be accurately performed.

  Further, since the anode electrode 10 is not affected by the coexistence of the redox substance and its consumption is reduced as much as possible, the durability life of the anode electrode 10 and consequently the residual chlorine sensor portion 5 of the residual chlorine meter 1 is extended. can do.

Further, by using 0.001 to 0.0001 mol / L KCl + 1 mol / L KNO ₃ solution as the electrolyte solution 16 accommodated in the tubular body 15 with the liquid junction part 14, chloride ions of the electrolyte solution 16 are used. It is possible to maintain a constant reference potential without being affected by the chloride ion concentration of the test liquid 13 such as tap water, and the plateau regardless of the type and properties of the test liquid 13. The applied voltage for obtaining the current in the region can be secured stably, and the predetermined residual chlorine concentration can be reliably measured by measuring the reduction current value. In addition, by using a potassium nitrate solution having a high concentration of 1 mol / L KNO ₃ , it is possible to remarkably reduce the generation of liquid junction potential at the liquid junction 14, as well as the electricity between the electrode surface of the anode electrode 10 and the potassium nitrate solution interface. The double layer can reduce impedance and achieve improved measurement sensitivity.

  In the above embodiment, the electrode body 18 of the anode electrode 10 made of silver / silver chloride and the electrode tip 22 of the cathode electrode 11 applied to the galvanic cell type residual chlorine meter 1 made of gold or platinum has been described. However, it goes without saying that the electrode main body 18 may be made of a second type electrode such as silver / silver chloride, and the electrode tip 22 may be applied to a polaro residual chlorine meter made of a noble metal such as gold or platinum. Even in this case, the effect of preventing the electrodeposition of metal ions on the cathode electrode 11 and the effect of extending the durability life can be achieved in the same manner.

It is an external appearance perspective view which shows the structure of the whole residual chlorine meter which concerns on this invention. It is an expanded vertical sectional view of the principal part which shows the structure of the residual chlorine sensor part in a residual chlorine meter same as the above.

Explanation of symbols

1 Residual chlorine meter 10 Anode electrode (counter electrode)
11 Cathode electrode (working electrode)
13 Test solution 14 Liquid junction 15 Tube 16 Electrolyte solution (0.001 to 0.0001 mol / L KCl + 1 mol / L KNO ₃ solution)
19 Inorganic cation exchanger (ion trapping agent)
20 Ceramic parts

Claims (4)

In the residual chlorine meter configured to measure the residual chlorine concentration in the test liquid by measuring the diffusion current flowing between the counter electrode immersed in the test liquid and the working electrode,
The residual chlorine meter, wherein the counter electrode is configured so as to be immersed in an electrolyte solution in which an electrode main body is contained in a cylinder with a liquid junction portion and is less likely to generate an inter-liquid potential difference.   The electrode body of the counter electrode is made of a second type electrode such as silver / silver chloride, the working electrode is made of a noble metal such as gold or platinum, and the electrolyte solution dissociates potassium chloride and potassium nitrate into a solvent. The residual chlorine meter according to claim 1, wherein   In the cylinder of the second type electrode constituting the counter electrode, an ion trap agent for trapping metal ions eluted by the oxidation reaction of the electrode body is housed, and the liquid ion portion contains the metal ions. The residual chlorine meter according to claim 1 or 2, wherein a ceramic member for preventing diffusion is provided.   The residual chlorine meter according to claim 3, wherein the ion trapping agent is an inorganic cation exchanger.

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