JP5935037B2 - Polarographic residual chlorine sensor - Google Patents

Description

  The present invention relates to a polarographic residual chlorine sensor that measures the concentration of residual chlorine such as chlorine, hypochlorous acid, and hypochlorite ions contained in water to be measured using a polarographic method.

  Conventionally, water used in a circulating bath, a pool, and the like is sterilized by introducing a chemical such as sodium hypochlorite. If the residual chlorine concentration in the water is high, the human body may be adversely affected, so the amount of residual chlorine is measured using a hypochlorous acid concentration measuring device using the DPD method or polarographic method, and the predetermined residual chlorine concentration We are monitoring to become.

  In general, the measurement of residual chlorine concentration by the polarographic method includes a working electrode, a counter electrode, and a reference electrode for keeping the voltage applied to the working electrode constant as shown in Patent Document 1, and these are used in the water to be measured. A predetermined voltage based on the potential of the reference electrode is applied between the working electrode and the counter electrode, and the current flowing between the working electrode and the counter electrode is measured. For example, it has calibration curve data of hypochlorous acid concentration with respect to the measured current value flowing between the working electrode and the counter electrode when a predetermined voltage is applied in advance, and the actually measured measured current value and this data are Compare to obtain hypochlorous acid concentration.

FIG. 14 shows an example of such calibration curve data. In this figure, the horizontal axis is the residual chlorine concentration X such as hypochlorous acid, and the vertical axis is the detection voltage Y obtained from the measured current value. Y = A ₁ X + A when a predetermined voltage is applied between the working electrode and the counter electrode. ₂ of the formula is obtained by previously measured that (operation parameters) is established. Since Y is known from the measured current value, the residual chlorine concentration X is calculated from this Y using the above equation (calculation parameter).

  In the measurement of residual chlorine concentration by this polarographic method, a predetermined voltage based on the reference electrode is applied between the working electrode and the counter electrode. In this case, the potential of the reference electrode is in a constant state due to its characteristics. Yes. Therefore, the potential of the working electrode can be set to a predetermined potential. At this time, by measuring the current flowing between the working electrode and the counter electrode, the hypochlorous acid concentration of the water to be measured can be estimated from the calibration curve data.

JP 2011-7508 A

Materials and Materials 115 (1999) No. 6 paper "Gold Dissolution and Gold Fine Powder Precipitation Using Disproportionation Reaction"

  Here, FIGS. 7 and 9 show examples of conventional working electrodes 100 and 101. The working electrodes 100 and 101 are made of, for example, gold as a conductive material. In this case, the working electrode 100 has a configuration in which an annular conductive material (gold) 103 is wound around a cylindrical base material 102 made of an insulating material such as a synthetic resin. It is composed of a cylindrical conductive material (gold) 103 itself.

  On the other hand, when a voltage is applied between the working electrode immersed in the water to be measured and the counter electrode, scales and the like are generated on the surface of each electrode, and this surface cleaning is performed by periodically switching the polarity. Due to the polarity switching, the conductive material of the working electrode is dissolved when used for a long time. As shown in FIGS. 11 and 12, this electrode dissolution tends to become more severe as the flowing current value is larger and the chloride ion concentration in the water to be measured is higher (the presence of chloride ions in an acidic environment). (For example, see Non-Patent Document 1 above).

  Therefore, in the case of the working electrode 100, the conductive material 103 disappears and becomes smaller as shown from left to right in FIG. In the case of the working electrode 101, the columnar working electrode 101 (conductive material) itself becomes thinner as shown from left to right in FIG. Thereby, the surface area of the conductive material 103 in contact with the water to be measured, that is, the electrode surface area (detection area) is reduced.

  FIG. 13 shows a situation where the detection area of the conductive material is reduced with the use time. Since the electrode reaction depends on the surface area, the area of the conductive material constituting the working electrode in contact with the water to be measured, that is, when the electrode surface area decreases, the measurement current is proportional to the electrode surface area. There is a problem that the value is greatly reduced and the sensitivity is lowered.

  The present invention has been made to solve the conventional technical problem, and an object thereof is to provide a polarographic residual chlorine sensor capable of reducing the change over time of the electrode surface area of the working electrode. It is.

In order to solve the above-mentioned problems, the polarographic residual chlorine sensor of the present invention immerses at least the working electrode and the counter electrode in water to be measured, and measures the current flowing between the working electrode and the counter electrode by an oxidation-reduction reaction. In a polarographic residual chlorine sensor that measures the residual chlorine concentration in the measurement water, the conductive material constituting the working electrode has a shape in which the cross-sectional area perpendicular to the axial direction is the same even at different positions in the axial direction. If one end surface in the axial direction, or both end surfaces are covered with an insulator, one end surface side is immersed in water to be measured , and the conductive material is covered with an insulator leaving one end surface, The other end surface in the axial direction of the conductive material is covered with an insulator, and when the conductive material is covered with an insulator leaving both end surfaces, the conductive material Both end faces, characterized that you have been exposed to the opening end surface of the insulator.

  The polarographic residual chlorine sensor of the invention of claim 2 is characterized in that, in the above invention, the insulator is an insulating case with one end or both ends open, and the conductive material is accommodated in this case. And

  A polarographic residual chlorine sensor according to a third aspect of the invention is characterized in that, in the first aspect of the invention, the insulator is applied to a conductive material.

  The polarographic residual chlorine sensor of the invention of claim 4 is characterized in that, in each of the above inventions, the conductive material constituting the working electrode is gold.

The polarographic residual chlorine sensor according to the invention of claim 5 is configured to immerse at least a working electrode and a counter electrode in water to be measured, and measure a current flowing between the working electrode and the counter electrode by an oxidation-reduction reaction, whereby residual chlorine in the water to be measured In a polarographic residual chlorine sensor that measures the concentration, the conductive material constituting the working electrode has a shape in which the cross-sectional area perpendicular to the axial direction is the same at different positions in the axial direction. One end face or both end faces are covered with an insulator, one end face side is immersed in the water to be measured, and the conductive material is a first conductive material disposed on the side immersed in the water to be measured And a second conductive material different from the first conductive material whose one end surface is in contact with the other end surface of the first conductive material, the first conductive material and the second conductive material And in the axial direction Area of the cross section perpendicular are identical, and measuring the current flowing between the second conductive material over the working electrode and counter electrode.

  The polarographic residual chlorine sensor of the invention of claim 6 applies a predetermined voltage to the working electrode based on the working electrode, the counter electrode, and the reference electrode immersed in the water to be measured in each of the above-described inventions, and the reference electrode potential, A measurement unit that measures the value of the current flowing between the counter electrode and the working electrode, and calibration curve data that indicates the relationship between the residual chlorine concentration and the current value at a predetermined voltage are retained, and measurement is performed using water to be measured based on the calibration curve data. And a calculation unit that obtains and outputs the residual chlorine concentration from the measured current value at the unit.

  A polarographic residual chlorine sensor according to a seventh aspect of the present invention is characterized in that in each of the above-mentioned inventions, the polarity of a voltage applied between the working electrode and the counter electrode is switched.

According to the present invention, at least the working electrode and the counter electrode are immersed in the water to be measured, and the current flowing between the working electrode and the counter electrode is measured by an oxidation-reduction reaction, thereby measuring the residual chlorine concentration in the water to be measured. In the chlorine sensor, the conductive material constituting the working electrode has a cross-sectional area orthogonal to the axial direction and has the same shape at different positions in the axial direction. The other end surface in the axial direction of the conductive material is covered with an insulator and the one end surface is immersed in the water to be measured , and the conductive material is covered with the insulator leaving one end surface. be covered by an insulator, when the conductive material is covered with an insulator while leaving both end faces, opposite end faces of the conductive material is in so that is exposed to the opening end surface of the insulator Therefore, the case of the insulator or the cross section of the conductive material exposed from the applied insulator becomes a detection surface immersed in the water to be measured, and the area of the cross section does not change in the axial direction. Become.

  As a result, even if a conductive material such as gold dissolves in the measured water, the polarity of the voltage applied between the working electrode and the counter electrode is changed over time, and the surface area of the electrode in contact with the measured water changes. Can be eliminated or minimized, and stable measurement of residual chlorine concentration can be realized over a long period of time.

In this case, as in the invention of claim 5, at least the working electrode and the counter electrode are immersed in the water to be measured, and the residual chlorine concentration in the water to be measured is determined by measuring the current flowing between the working electrode and the counter electrode by an oxidation-reduction reaction. In the polarographic residual chlorine sensor to be measured, the conductive material constituting the working electrode has a shape in which the cross-sectional area perpendicular to the axial direction is the same at different positions in the axial direction. Or, both ends are covered with an insulator, one end surface side is immersed in the water to be measured, and the conductive material is a first conductive material disposed on the side immersed in the water to be measured; A second conductive material different from the first conductive material whose one end surface is in contact with the other end surface of the first conductive material, and the first conductive material and the second conductive material include: Of the cross section perpendicular to the axial direction Product is the same, if to measure the current flowing between the second conductive material over the working electrode and the counter electrode, a second conductive material by dissolving the conductive material is in contact with the sample water The life of the working electrode can be detected by the change in the measured current value due to the operation.

  Further, if a so-called three-electrode system is used as in claim 6, it is possible to realize a more accurate measurement of the residual chlorine concentration.

It is a block diagram of the polarographic residual chlorine sensor of one Example of this invention. It is a perspective view of one Example of the working electrode of the polarographic residual chlorine sensor of FIG. It is a figure which shows the time-dependent change of the working electrode of FIG. It is a perspective view of the other Example of the working electrode of the polarographic type residual chlorine sensor of FIG. It is a figure which shows the time-dependent change of the working electrode of FIG. It is a figure which shows a time-dependent change of the electrode surface area (detection area) of the working electrode of FIG. It is a perspective view of the conventional working electrode. It is a figure which shows the time-dependent change of the working electrode of FIG. It is a perspective view of another conventional working electrode. It is a figure which shows the time-dependent change of the working electrode of FIG. It is a figure explaining the relationship between the electric current value which flows into a working electrode, and melt | dissolution of an electroconductive material. It is a figure explaining the relationship between the chloride ion concentration in to-be-measured water, and melt | dissolution of an electroconductive material. It is a figure which shows the time-dependent change of the electrode area (detection area) of the conventional working electrode. It is a figure which shows an example of the calibration curve data (calculation parameter) of a polarographic type residual chlorine sensor.

  Hereinafter, a polarographic residual chlorine sensor 1 according to an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, a polarographic residual chlorine sensor 1 according to an embodiment includes, for example, a working electrode 2, a counter electrode 4, and a reference electrode as electrodes immersed in measured water 8 (for example, pool water) stored in a container 10. 6 is a so-called three-electrode polarographic residual chlorine sensor, and further includes a measurement unit 12 and a calculation unit 14.

  The working electrode 2 will be described in detail later. As the conductive material constituting the working electrode 2, gold is used in the embodiment. The counter electrode 4 is made of platinum in the embodiment, and the reference electrode 6 is made of silver / silver chloride in the embodiment. In addition, platinum may be used as the conductive material of the working electrode 2, and the counter electrode 4 may be made of carbon fiber or the like.

Due to the characteristics of the reference electrode 6, the electrode potential in the measured water is constant. When the potential of the reference electrode 6 is set with respect to the standard hydrogen electrode SHF, it is +0.199 Vvs. SHE. The electrode reaction of the reference electrode 6 is represented by the following chemical formula A.
Chemical reaction formula A AgCl + e ⁻ ← → Ag + Cl ⁻

Further, in the residual chlorine sensor 1, a current obtained by a reduction reaction (shown in chemical reaction formulas B and C) mainly at the working electrode 2 of hypochlorous acid and hypochlorite ions contained in the water 8 to be measured by a polarographic method ( The concentration of hypochlorous acid or the like is measured from the relationship between the reduction current) and the voltage.
Chemical reaction formula B ClO ⁻ + H ₂ O + 2e ⁻ → Cl ⁻ + 2OH ⁻
Chemical reaction formula C HOCl ⁻ + 2e ⁻ → Cl ⁻ + OH ⁻

  The measurement unit 12 applies a predetermined voltage of −0.2 V to +0.6 V, for example, −0.1 V, to the working electrode 2 with the potential of the reference electrode 6 as a reference, and the value of the current flowing between the counter electrode 4 and the working electrode 2 ( Measure the measured current value. The calculation unit 14 is composed of a microcomputer, and the relationship between the concentration of residual chlorine such as hypochlorous acid measured by applying a voltage used for measurement to the working electrode 2 and the current value (converted to a detection voltage) is calculated. The calibration curve data shown (for example, the calculation parameters in FIG. 14) is held, and the detected current value at the measurement unit 12 by the water to be measured 8 is converted into the detection voltage based on the calibration curve data, and then the detected voltage value From FIG. 14, the residual chlorine concentration at that time is obtained and output.

  Further, when concentration measurement is performed by applying such a predetermined voltage, a scale in the water 8 to be measured adheres to the surfaces of the working electrode 2 and the counter electrode 4. In order to eliminate this, the measuring unit 12 periodically switches the polarity of the voltage applied between the working electrode 2 and the counter electrode 4.

  As shown in FIG. 1, the sensor is not only the electrode immersed in the water to be measured 8 but also arranged / wired on the substrate and attached to the flow path through which the water to be measured flows. 4 and 6 may be in contact with the water to be measured.

  Next, the structure of the working electrode 2 used in the present invention will be described with reference to FIGS. The working electrode 2 of the embodiment is composed of a conductive material 16 made of gold and a case 17 made of an insulator such as a hard synthetic resin in which the conductive material 16 is housed. In this case, the conductive material 16 has a columnar shape, and the area of the cross section (horizontal cross section in FIG. 2) orthogonal to the axial direction (vertical direction in FIG. 2) of this cylinder is any position where the axial direction is different. The same shape is obtained even when cut by.

  The case 17 has a cylindrical shape with both ends opened. One end surface 16A of the conductive material 16 is exposed from the opening at one end of the case 17, and the other conductive material 16 is opened from the opening at the other end of the case 17. The peripheral surface of the remaining other conductive material 16 is covered with a case 17 so that the end face is exposed. Then, a substrate or a lead wire is connected to the other end surface of the conductive material 16, one end surface side of the conductive material 16 is immersed in the measured water 8, and only this one end surface 16 A is in contact with the measured water 8. It is configured.

  With the above configuration, when the measurement unit 12 applies a predetermined voltage between the reference electrode 2 and the counter electrode 4 to measure the residual chlorine concentration, the conductive material (gold) 16 of the reference electrode 2 is measured as described above. Dissolve in water 8. However, since only one end surface 16A of the conductive material 16 of the reference electrode 2 is in contact with the water 8 to be measured, dissolution occurs only on this one end surface 16A, and from one end of the case 17 as shown in FIG. The one end face 16A moves backward in the other end direction (axial direction).

  At this time, since the area of the cross section perpendicular to the axial direction of the conductive material 16 is formed to be the same even in a different one in the axial direction as described above, the dissolution at the one end face 16A is substantially uniform over the entire surface. If it occurs, even if dissolution proceeds from the left side to the right side in FIG. 3, the area of the one end face 16A (including the cross section) in contact with the water 8 to be measured, that is, the detection area (electrode surface area). ) Does not change.

  FIG. 6 shows the change over time of the detection area (the area of the one end face 16A) of the working electrode 2 of the example. Initially, the surface of the one end face 16A becomes rough, and its surface area increases slightly, but after that it shows a constant value. Therefore, when the working electrode 2 of the embodiment is used, the measured current value hardly changes even when used over time.

  As described above, the conductive material 16 constituting the working electrode 2 has the same cross-sectional area perpendicular to the axial direction even at different positions in the axial direction, leaving both end surfaces in the axial direction. Since it is covered with the case 17 (insulator) and the one end face 16A side is immersed in the measured water 8, the cross section of the conductive material 16 exposed from the case 17 becomes a detection surface immersed in the measured water 8. And the area of this cross section does not change in the axial direction.

  As a result, even when the conductive material 16 is dissolved in the measured water 8 after switching the polarity of the voltage applied between the working electrode 2 and the counter electrode 4 and used over time, the electrode in contact with the measured water 8 It becomes possible to eliminate or minimize the change in the surface area, and to realize stable measurement of residual chlorine concentration over a long period of time.

  Next, FIG. 4 shows another embodiment of the working electrode 2 in the present invention. The same reference numerals as those in FIG. 2 are the same. Also in this case, only one end surface 16A of the conductive material (gold) 16 is in contact with the water 8 to be measured. However, the conductive material 16 is on the opening side of one end of the case 17, and its one end surface 16 </ b> A comes into contact with the water 8 to be measured. However, a second conductive material 18 such as silver different from the conductive material 16 is provided on the other end surface side of the conductive material 16, and one end surface thereof is in contact with the other end surface of the conductive material 16. In addition, the case 17 continuously covers the peripheral surface of the second conductive material 18, the other end surface of the second conductive material 18 is exposed, and a lead wire 19 is connected to the second conductive material 18. taking measurement.

  With this configuration, when the conductive material 16 is dissolved as shown from the left side to the right side in FIG. 5 and the second conductive material 18 comes into contact with the water 8 to be measured, the measured current value is Therefore, the life of the working electrode 2 can be detected by detecting the change in the measured current value by the measuring unit 12.

  In each of the above-described embodiments, both end surfaces of the case 17 are opened to expose both end surfaces of the conductive material 16. However, for example, only the one end surface 16A may be exposed and the other end may be covered (closed). . In that case, the lead wire is inserted into the case 17 through the other end surface of the case 17 and connected to the conductive material 16 or the second conductive material 18.

  In the embodiment, the case 17 is used as an insulator, and the conductive materials 16 and 18 are stored in the case 17. However, the present invention is not limited to this, and one end surface or both end surfaces are left on the peripheral surface. An insulator may be applied.

  Furthermore, in the embodiments, the present invention has been described with a so-called three-electrode polarographic residual chlorine sensor. However, the present invention is not limited to this, and the present invention is also effective for a polarographic residual chlorine sensor using only a working electrode and a counter electrode without using a reference electrode. is there.

DESCRIPTION OF SYMBOLS 1 Polarograph type residual chlorine sensor 2 Working electrode 4 Counter electrode 6 Reference electrode 8 Water to be measured 12 Measuring unit 14 Calculation unit 16 Conductive material 17 Case 18 Second conductive material 19 Lead wire

Claims (7)

In a polarographic residual chlorine sensor that measures the residual chlorine concentration in the measured water by immersing at least the working electrode and the counter electrode in measured water and measuring the current flowing between the working electrode and the counter electrode by oxidation-reduction reaction,
The conductive material constituting the working electrode has a shape in which the cross-sectional area orthogonal to the axial direction is the same at different positions in the axial direction, and one end surface in the axial direction, or both end surfaces are The axial direction of the conductive material when the one end face side is immersed in the water to be measured and the conductive material is covered with the insulator leaving the one end face. The other end surface of the conductive material is covered with the insulator, and when the conductive material is covered with the insulator leaving the both end surfaces, the both end surfaces of the conductive material are covered with the insulator. polarographic residual chlorine sensor characterized that you have been exposed to the open end face.   2. The polarographic residual chlorine sensor according to claim 1, wherein the insulator is an insulating case having one end or both ends open, and the conductive material is accommodated in the case.   The polarographic residual chlorine sensor according to claim 1, wherein the insulator is applied to the conductive material.   The polarographic residual chlorine sensor according to claim 1, wherein the conductive material constituting the working electrode is gold. In a polarographic residual chlorine sensor that measures the residual chlorine concentration in the measured water by immersing at least the working electrode and the counter electrode in measured water and measuring the current flowing between the working electrode and the counter electrode by oxidation-reduction reaction,
The conductive material constituting the working electrode has a shape in which the cross-sectional area orthogonal to the axial direction is the same at different positions in the axial direction, and one end surface in the axial direction, or both end surfaces are The first end surface side is immersed in the water to be measured, and the conductive material is disposed on the side immersed in the water to be measured; A second conductive material different from the first conductive material whose one end surface is in contact with the other end surface of the first conductive material, the first conductive material, the second conductive material, Then, the polarographic residual chlorine sensor is characterized in that the cross-sectional area orthogonal to the axial direction is the same, and the current flowing between the working electrode and the counter electrode through the second conductive material is measured. The working electrode immersed in the water to be measured, the counter electrode, and a reference electrode;
Applying a predetermined voltage to the working electrode based on the potential of the reference electrode, and measuring a current value flowing between the counter electrode and the working electrode;
Calibration curve data indicating the relationship between the residual chlorine concentration and the current value at the predetermined voltage is held, and based on the calibration curve data, the residual chlorine concentration is obtained from the measured current value at the measurement unit by the water to be measured. The polarographic residual chlorine sensor according to claim 5, further comprising an arithmetic unit for outputting. Polarographic residual chlorine sensor according to any one of claims 5 or請 Motomeko 6, characterized in that switching the polarity of the voltage applied between the said working electrode the counter electrode.

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