JP2011033589A - Diaphragm type electrochemical sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diaphragm type electrochemical sensor reducing the replacement frequency of an electrolytic solution of the diaphragm type electrochemical sensor. <P>SOLUTION: The diaphragm type electrochemical sensor 1 has: an electrolytic solution housing part 2B; an electrolytic solution 6 housed in the electrolytic solution housing part; a diaphragm 3 for preventing the outflow of the electrolytic solution in the electrolytic solution housing part and allowing the permeation of a component to be measured into the electrolytic solution in the electrolytic solution housing part; a working electrode 4 arranged adjacently with the diaphragm in the electrolytic solution housing part; and a counter electrode 5 arranged in a position relatively farther from the diaphragm than the working electrode and electrically connected to the working electrode via the electrolytic solution. The electrolytic solution contains an aqueous electrolytic solution 6A and a hydrophobic ionic liquid 6B as its components. The aqueous electrolytic solution and the ionic liquid are separated into a region for aqueous electrolytic solutions and a region for ionic liquids in contact with each other in the electrolytic solution housing part. The ionic liquid is on the side of the working electrode, and the aqueous electrolytic solution is on the side of the counter electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polarographic or galvanic cell diaphragm type electrochemical sensor used for measurement of residual chlorine, dissolved oxygen (DO), carbon dioxide gas, and the like.

  Conventionally, as a method for measuring the residual chlorine concentration of, for example, tap water, there are an absorptiometric method and an electrochemical measurement method using a DPD (diethyl-p-phenylenediamine) reagent. When it is desired to continuously measure the residual chlorine concentration, since the reagent is used in the absorptiometry, it is necessary to automate the supply and mixing of the reagent, which is inevitably expensive. On the other hand, the polarographic method or galvanic cell type oxidation-reduction current measurement method which is an electrochemical measurement method can measure the residual chlorine concentration without a reagent. That is, in the polarographic or galvanic cell type oxidation-reduction current measurement method, the working electrode where the redox reaction of the component to be measured is performed on the surface, and the redox reaction corresponding to the oxidation-reduction reaction on the working electrode is performed on the surface. An electrochemical sensor is used that has a counter electrode made in step 1. In a polarographic electrochemical sensor generally used as a residual chlorine sensor, the working electrode is in direct contact with the liquid to be tested and becomes dirty. Therefore, it is necessary to always clean the working electrode with an abrasive or the like. On the other hand, a diaphragm type electrochemical sensor having a gas permeable diaphragm that permeates the measurement target component is widely used so that the working electrode and the counter electrode do not come into contact with interfering ions in the test solution.

FIG. 6 shows a schematic configuration of a diaphragm type residual chlorine sensor as an example of a polarographic diaphragm type electrochemical sensor (hereinafter also simply referred to as “membrane type sensor”). The diaphragm type sensor 1 is, for example, a gas permeate that permeates a measurement target component (free residual chlorine such as Cl ₂ and HClO) that is fixed so as to close a front end opening of a hollow cylindrical sensor body (electrolyte cell) 2. It has a sex diaphragm 3. In a region partitioned from the outside by the diaphragm 3 of the sensor body 2, a working electrode 4 generally formed of gold (Au) or platinum (Pt), and generally silver (Ag) or silver-silver chloride (Ag / AgCl) The counter electrode 5 formed by In addition, an electrolytic solution 6 is accommodated in a region partitioned from the outside by the diaphragm 3 of the sensor body 2. As the electrolytic solution 6, a KCl aqueous solution (for example, 0.5 mol / L) is conventionally used. The working electrode 4 is disposed adjacent to the diaphragm 3 through a thin layer of the electrolytic solution 6, and the counter electrode 5 is immersed in the electrolytic solution 6. Note that the diaphragm type sensor 1 in FIG. 6 is a two-pole type having a working electrode and a counter electrode as measurement electrodes, but there is also a three-pole type having a reference electrode.

  Then, the sensor body 2 is immersed in the test solution, and a predetermined electrolytic voltage is applied between the working electrode 4 and the counter electrode 5 from the power source 7 via the lead wire 9 connected thereto, and the electrolytic current is applied. By measuring with an ammeter 8, the residual chlorine concentration in the test solution is measured.

Thus, the diaphragm type sensor 1 has a structure having the working electrode 4, the counter electrode 5, and the electrolytic solution 6 inside the sensor body 2. Since the working electrode 4 is in the sensor body 2 and does not come into contact with the test solution, there is no possibility that the working electrode 4 is contaminated by components such as organic substances contained in the test solution. Further, since the working electrode 4 reacts with a component that has passed through the diaphragm 3, the working electrode 4 has a feature that it is not easily affected by the disturbing component. The reaction formulas of main oxidation-reduction reactions at the working electrode 4 and the counter electrode 5 of the diaphragm sensor 1 are as follows.
Working electrode ^{_{Cl 2 + 2e → 2Cl - (}} 1)
Counter electrode Ag → Ag ⁺ + e (2)

As shown in the above formula (1), in the working electrode 4, the reduction reaction of chlorine (Cl ₂ ) or hypochlorous acid (HClO) that has passed through the diaphragm 3 proceeds. Further, as shown in the above formula (2), the oxidation reaction proceeds at the counter electrode 5.

When the counter electrode 5 is silver, the oxidation of the counter electrode 5 proceeds when Ag is electrolyzed into Ag ⁺ to become Ag ^+, and this reaction occurs when the counter electrode 5 is in contact with an aqueous electrolyte such as an aqueous KCl solution. . That is, for the reaction at the counter electrode 5, it is indispensable that the counter electrode 5 is in contact with the aqueous electrolyte solution, such as by immersing the counter electrode 5 in the aqueous electrolyte solution.

  Then, utilizing the fact that the electrolytic current flowing between the working electrode 4 and the counter electrode 5 in association with this electrochemical reaction has a correlation with the residual chlorine concentration in the test liquid, the electrolytic current is measured. The residual chlorine concentration in the test solution can be determined from the value.

  As a technique related to the present invention, Patent Document 1 pays attention to the fact that the vapor pressure of the ionic liquid is extremely low, and uses an electrolytic solution composed of only the ionic liquid in order to prevent a decrease due to evaporation of the electrolytic solution. A chemical gas sensor is proposed.

JP 2004-333163 A

  Here, if the residual chlorine concentration is low such as the residual chlorine level of tap water, the diaphragm type sensor 1 may be usable for more than one year without replacing the electrolyte in continuous measurement, and is inexpensive. The structure can be measured for a long time.

  On the other hand, a chlorine solution with a high residual chlorine concentration (free residual chlorine concentration) (20 to 100 mg / L) is used as a sterilizing agent, and from the viewpoint of ensuring the effect and safety as a sterilizing agent. It is desired to control the residual chlorine concentration of the sterilizing agent to be constant. Even in the case of such a high concentration, as in the case of the low concentration, it is possible to measure the residual chlorine concentration in the test liquid with the diaphragm sensor 1.

  However, as the residual chlorine concentration in the test solution increases, a phenomenon that the response value decreases in a relatively short period of time appears, the electrolyte solution needs to be replaced, and the life as the diaphragm sensor 1 tends to be shortened. I understood that.

The reason why the life is shortened in this way is considered as follows. On the surface of the working electrode 4, a reduction reaction of free residual chlorine components (Cl ₂ , HClO, etc.) that have passed through the diaphragm 4 proceeds. On the other hand, in the portion of the diaphragm 3 around the working electrode 4 that is not in contact with the working electrode 4, free residual chlorine components that have passed through the diaphragm 3 are accumulated in the electrolyte 6 without being reacted.

When such unreacted free residual chlorine component is accumulated and its concentration is increased, the pH of the electrolytic solution 6 tends to be increased. As the pH increases, chlorine (Cl ₂ ) and hypochlorous acid (HClO) change their form to hypochlorite ions (ClO ⁻ ). However, in the sensor set for residual chlorine measurement, The response of chlorite ion is not obtained. In this electrochemical sensor, an electrolytic solution layer exists between the diaphragm 3 and the working electrode 4, and free residual chlorine components that have permeated through the diaphragm 3 come into contact with the electrolytic solution. Therefore, when used in a state where the pH of the electrolytic solution is high, a part of the free residual chlorine component that has permeated the diaphragm 3 changes to hypochlorite ions that do not respond due to the influence of the pH of the electrolytic solution. As a result, the indicated value decreases.

  For example, as shown in FIG. 7, when continuous measurement was performed at a residual chlorine concentration (free residual chlorine concentration) of about 100 mg / L, the indicated value decreased after 4 days. FIG. 7 shows the ratio of the measured value obtained by the diaphragm sensor 1 to the elapsed time in the continuous measurement when the value obtained by measuring the same test solution by the spectrophotometric method using the DPD reagent is 100%. Yes. When the electrolyte solution 6 of the diaphragm type sensor 1 after 7 days was extracted and the residual chlorine concentration was measured by an absorptiometric method using a DPD reagent, it was 80 mg / L. At this time, when the electrolyte solution 6 of the diaphragm sensor 1 is replaced, the indicated value is restored to the original value (measured value ratio of about 100%), and the electrolyte solution 6 of the diaphragm sensor 1 is deteriorated (unreacted free residual chlorine). It was observed that component accumulation, pH fluctuation, etc.) affected the measured values.

  Thus, although it is possible to measure the high concentration residual chlorine concentration with the diaphragm type sensor 1, the lifetime as a sensor is short and it is difficult to put it into practical use at present.

  That is, if frequent replacement of the electrolytic solution is necessary, inconvenience may occur due to the fact that the measured value during the electrolytic solution replacement operation cannot be obtained in continuous measurement.

  In the above description, the diaphragm type residual chlorine sensor has been described as an example of a diaphragm type residual chlorine sensor. However, the component that affects the measured value, such as unreacted components, accumulates in the electrolyte solution. Accordingly, the problem that the indicated value of the sensor becomes unstable and the life of the sensor is shortened also applies to the diaphragm type sensor used for measuring dissolved oxygen (DO), carbon dioxide gas, and the like.

  In addition to the polarographic sensor, a galvanic cell sensor is also known as a diaphragm sensor. As shown in FIG. 8, the galvanic cell diaphragm sensor generally has no power source, and is different from the polarographic diaphragm sensor in that no voltage is applied from the outside during use. Even in such a galvanic cell type diaphragm type sensor, the same problem as the polarographic type diaphragm type sensor may occur.

  Accordingly, an object of the present invention is to provide a diaphragm type electrochemical sensor capable of reducing the frequency of replacement of the electrolyte of the diaphragm type electrochemical sensor.

  Another object of the present invention is to extend the life of the diaphragm-type electrochemical sensor, thereby increasing the maintenance work interval and reducing the missing measurement values in continuous measurement. An electrochemical sensor is provided.

  The above object is achieved by the diaphragm electrochemical sensor according to the present invention. In summary, the present invention provides an electrolytic solution storage unit, an electrolytic solution stored in the electrolytic solution storage unit, and prevents the electrolytic solution from flowing out of the electrolytic solution storage unit, and the electrolytic solution in the electrolytic solution storage unit. A diaphragm that allows permeation of a component to be measured into the electrolyte, a working electrode that is disposed adjacent to the diaphragm in the electrolyte container, and the electrolyte solution that is disposed farther from the diaphragm than the working electrode In the diaphragm type electrochemical sensor having a counter electrode electrically connected to the working electrode via the electrolyte, the electrolyte includes an aqueous electrolyte and a hydrophobic ionic liquid as components, and the aqueous electrolyte And the ionic liquid are divided into a region of the aqueous electrolyte solution and a region of the ionic liquid that are in contact with each other in the electrolyte container, the ionic liquid is on the working electrode side, and the aqueous electrolyte solution is the counter electrode This is on the side A diaphragm type electrochemical sensor according to claim.

  According to one embodiment of the present invention, the hydrophobic ionic liquid has a quaternary ammonium salt structure composed of a quaternary ammonium cation and a fluorine-containing anion.

  The diaphragm type electrochemical sensor of the present invention may be of a polarographic type or a galvanic cell type.

  ADVANTAGE OF THE INVENTION According to this invention, reduction of the replacement frequency of the electrolyte solution of a diaphragm type electrochemical sensor can be aimed at. Further, according to the present invention, by extending the life of the diaphragm type electrochemical sensor, it is possible to lengthen the maintenance work interval and to reduce the missing measurement in the continuous measurement.

It is a schematic diagram which shows schematic structure of one Example of the diaphragm type electrochemical sensor which concerns on this invention. It is a graph which shows stability of the indicator value of the diaphragm type electrochemical sensor according to this invention. It is a graph which shows the linearity of the indicator value of the diaphragm type | mold electrochemical sensor according to this invention. (A) The graph which shows the responsiveness of the diaphragm type electrochemical sensor according to the present invention, and (b) the responsiveness of the conventional diaphragm type sensor. It is a schematic diagram which shows schematic structure of the other Example of the diaphragm type electrochemical sensor which concerns on this invention. It is a schematic diagram which shows schematic structure of an example of the conventional diaphragm type electrochemical sensor. It is a graph which shows a mode that an indication value falls in the conventional diaphragm type electrochemical sensor. It is a schematic diagram which shows schematic structure of the other example of the conventional diaphragm type electrochemical sensor.

  Hereinafter, the diaphragm type electrochemical sensor according to the present invention will be described in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic configuration of one embodiment of a diaphragm type electrochemical sensor according to the present invention. In this embodiment, the diaphragm type electric sensor is a polarographic diaphragm type residual chlorine sensor. As shown in FIG. 1, the overall configuration of the diaphragm type sensor 1 of the present embodiment is the same as the conventional one described with reference to FIG. Accordingly, in FIG. 1, elements having the same or equivalent functions and configurations as those in FIG. 6 are denoted by the same reference numerals. In this embodiment, the electrolytic solution 6 is different from the conventional one.

  In the present embodiment, the diaphragm type sensor 1 has a gas permeable diaphragm 3 fixed so as to close the distal end opening 2A of the hollow cylindrical sensor body 2. A working electrode 4 and a counter electrode 5 are disposed in an electrolyte solution storage portion 2B that is a region partitioned from the outside by a diaphragm 3 of the sensor body 2. In addition, the electrolyte solution 6 is stored in the electrolyte solution storage portion 2B so as to be in contact with the working electrode 4 and the counter electrode 5. The working electrode 4 is disposed adjacent to the diaphragm 3 via a thin layer of an electrolytic solution 6 (especially, an ionic liquid 6B described later), and the counter electrode 5 is immersed in the electrolytic solution 6 (especially an aqueous electrolytic solution 6A described later). The The counter electrode 5 is disposed relatively farther from the diaphragm 3 than the working electrode 4 and is electrically connected to the working electrode 4 via the electrolytic solution 6.

The diaphragm 3 prevents the electrolyte solution 6 from flowing out of the electrolyte solution storage part 2B, prevents the test solution from entering the electrolyte solution storage part 2B, and enters the electrolyte solution storage part 2B from the test solution. Any gas permeable membrane that allows permeation of the component to be measured (free residual chlorine such as Cl ₂ and HClO) can be used. As the diaphragm 3, FEP (tetrafluoroethylene-hexafluoropropylene copolymer), ODPE (low density polyethylene), PTFE (tetrafluoroethylene), PFA (perfluoroalkoxy), ETFE (ethylene-tetrafluoride). Ethylene copolymer) and the like can be used. The diaphragm 3 is preferably a fluororesin thin film. In this example, PTFE was used.

  As the working electrode 4, platinum (Pt), gold (Au), or the like is generally used, but platinum (Pt) is used in this embodiment. In general, silver-silver chloride (Ag / AgCl), silver (Ag), or the like is used as the counter electrode 5. In this embodiment, silver-silver chloride (Ag / AgCl) was used. The working electrode 4 is provided so as to be enclosed in an electrode support member having a cylindrical shape or the like formed of an electrically insulating material such as glass or resin (epoxy resin or the like) and to be exposed at least partially from the tip. In addition, the counter electrode 5 may be provided on the outer periphery of the electrode support member farther from the diaphragm 3 than the working electrode 4. In the present embodiment, the diaphragm type sensor 1 is a two-pole sensor, but may be a three-pole sensor provided with a reference electrode.

  The working electrode 4 and the counter electrode 5 are connected to a power source 7 via a lead wire 9. In addition, an ammeter 8 is connected so that an electrolytic current can be measured when a predetermined electrolytic voltage is applied from the power source 7 between the working electrode 4 and the counter electrode 5.

  At the time of measurement, the sensor body 2 is immersed in the test solution, a predetermined electrolytic voltage is applied between the working electrode 4 and the counter electrode 5 from the power source 7, and the electrolysis current is measured by the ammeter 8, Measure the residual chlorine concentration in the test solution. At this time, the redox reaction like the above-mentioned formulas (1) and (2) mainly occurs at the working electrode 4 and the counter electrode 5 of the diaphragm type sensor 1.

As described above, when a conventional diaphragm sensor measures a sterilizing agent having a high residual chlorine concentration (free residual chlorine concentration) (20 to 100 mg / L), the life of the diaphragm sensor tends to be shortened. There is. As described above, this is because the unreacted free residual chlorine components (Cl ₂ , HClO, etc.) are accumulated in the conventional aqueous electrolyte such as KCl aqueous solution. It is thought that this is because of the decrease.

  Therefore, in this embodiment, according to the present invention, the diaphragm type sensor 1 includes an electrolytic solution 6 containing an aqueous electrolytic solution 6A and a hydrophobic ionic liquid 6B as components, and the aqueous electrolytic solution 6A and the ionic liquid 6B. In the electrolytic solution container 2B, the region is divided into a region (aqueous electrolytic solution phase) of the aqueous electrolytic solution 6A in contact with each other at the interface S and a region (ionic liquid phase) of the ionic liquid 6B, and the ionic liquid 6A is on the working electrode 4 side. The aqueous electrolyte 6A is on the counter electrode 5 side.

  That is, due to the structure of the diaphragm type sensor 1, it is difficult to prevent the unreacted free residual chlorine component from diffusing into the electrolyte container 2B. Therefore, if the free residual chlorine component that has entered does not accumulate in the aqueous electrolyte but is extracted into the ionic liquid, a one-way reaction occurs, and the concentration of the unreacted free residual chlorine component in the aqueous electrolyte does not increase. Thus, a decrease in the indicated value can be prevented.

  That is, for reasons such as reaction efficiency, it is preferable that the entire counter electrode 5 is in contact with the aqueous electrolyte solution 6A under normal use conditions. Since the aqueous electrolyte solution 6A is on the counter electrode 5 side, the counter electrode 5 is immersed in the aqueous electrolyte solution 6A. As a result, in the counter electrode 5, an oxidation reaction (Ag electrolysis of Ag described above) is mainly performed. ) Will proceed stably. On the other hand, it is preferable that the entire diaphragm 3 including the contact portion between the working electrode 4 and the diaphragm 3 is in contact with the ionic liquid 6B for the reason that the unreacted free residual chlorine component does not enter the aqueous electrolyte 6A. .

  As the aqueous electrolyte solution 6A, any electrolyte aqueous solution that can be used as the electrolyte solution of the diaphragm type sensor 1, such as those conventionally used in general, can be used. As the electrolyte of the aqueous electrolyte 6A, KCl, NaCl, phosphate, phthalate, citrate and the like are suitable. Further, the concentration of the electrolyte in the aqueous electrolyte solution 6A is preferably 0.01 to 1 mol / L.

  The ionic liquid is generally a salt composed of an organic cation and an anion at room temperature and having ionic conductivity, and is also referred to as a room temperature molten salt. In general, ionic liquids are characterized in that they are stable in air, incombustible, non-volatile, highly heat resistant, and have a wide potential window. Typical ionic liquids include salts composed of combinations of nitrogen-containing aromatic cations such as alkylimidazolium ions and alkylpyridinium ions and various anions. In addition, there are salts composed of aliphatic onium cations such as aliphatic quaternary ammonium ions and aliphatic sulfonium ions and trifluorosulfonylimide anions.

  An ionic liquid can be composed of various ions. For example, some liquids are in the range of −30 ° C. to 300 ° C., but in the present invention, they may be liquids at least at the normal use temperature of the diaphragm type sensor 1, for example, −10 ° C. to 50 ° C. In the present invention, the ionic liquid must be hydrophobic (insoluble in water) and cause phase separation without mixing even when mixed with an aqueous electrolyte. In the present invention, the ionic liquid needs to exhibit sufficient electrical conductivity as an electrolyte for a diaphragm type sensor when used with an aqueous electrolyte.

  The ionic liquid that can be suitably used in the present invention is as follows.

  The hydrophobic ionic liquid 6B used in the present invention is used so that the aqueous electrolytic solution 6A and the ionic liquid 6B are separated into an aqueous electrolytic solution phase and an ionic liquid phase that are in contact with each other at the interface S in the electrolytic solution storage part 2B. As an ionic liquid, a quaternary ammonium salt structure comprising a quaternary ammonium cation and a fluorine-containing anion is preferred. The salt structure composed of a quaternary ammonium cation and a fluorine atom-containing anion is a salt structure of a monomer containing a quaternary ammonium salt structure and a polymerizable functional group, and is aliphatic, alicyclic, aromatic, or It is a salt structure consisting of a heterocyclic quaternary ammonium cation and a fluorine atom-containing anion. As used herein, “quaternary ammonium cation” means an onium cation of nitrogen, and includes a heterocyclic onium ion such as imidazolium.

  As a specific example of the cation, in the case of an ammonium cation, N, N, N-trimethyl-N-propylammonium ion and the like can be mentioned as the aliphatic quaternary ammonium ion. As specific examples of the cation, in the case of an imidazolium cation, 1,3-diallylimidazolium, 1-allyl-3-alkylimidazolium ion, 1-alkyl-3-allylimidazolium ion, 1-alkyl-3 -Methylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-ethyl-3-methylimidazolium ion and the like. Specific examples of the cation include N-methyl-N-propylpyrrolidinium ion and N-methyl-N-butylpyrrolidinium ion in the case of pyrrolidinium cation. Further, specific examples of the cation include N-methyl-N-propylpiperidinium ion in the case of piperidinium cation.

  On the other hand, specific examples of anions include trifluoromethanesulfonylimide ion.

  The ratio between the aqueous electrolyte solution 6A and the ionic liquid 6B is 1: 0. For the reason that the two-phase structure composed of the aqueous electrolyte solution 6A and the ionic liquid 6B is maintained while the counter electrode 3 is in contact with the aqueous electrolyte solution 6A. The ratio is preferably 2 to 1: 2. Further, typically, in the electrolytic solution storage part 2B, the electrolytic solution 6 is separated into each phase of the aqueous electrolytic solution 6A and the ionic liquid 6B, and the ionic liquid 6B is on the working electrode 4 side which is the lower side in the vertical direction. Thus, the interface S between the aqueous electrolyte 6A and the ionic liquid 6B is in contact with the interface so that the aqueous electrolyte 6A comes to the counter electrode 5 which is the upper side in the vertical direction, that is, in the normal use state of the diaphragm type sensor 1. The mixing ratio of the aqueous electrolyte solution 6A and the ionic liquid 6B may be set so as to be positioned between the position of the working electrode 4 and the position of the counter electrode 5 in the intersecting direction (typically substantially vertical direction). preferable.

  In this embodiment, as the electrolytic solution 6, an aqueous electrolytic solution 6A that is a 0.1 mol / L KCl aqueous solution generally used in a conventional diaphragm type sensor and a hydrophobic ionic liquid 6B are 1: 1. A mixture was used. 1,3-diallylimidazolium bis (trifluoromethanesulfonyl) imide was used as the hydrophobic ionic liquid 6B.

The ionic liquid 6B used in this example has ionic conductivity, but has a property of extracting many various components such as CO, CO ₂ , NOx, SOx, and HCl without being almost dissolved in water. Further, since the ionic liquid 6B has a specific gravity greater than that of water, the electrolytic solution 6 is, in a normal use state, the aqueous electrolytic solution 6A and the ionic liquid 6B in the cylindrical electrolytic solution containing portion 2B oriented in a substantially vertical direction. The phase of the ionic liquid 6B is arranged on the diaphragm 3 side, that is, the working electrode 4 side, and the aqueous phase is arranged on the counter electrode 5 side.

On the surface of the working electrode 4, a reduction reaction of free residual chlorine components (Cl ₂ , HClO, etc.) that have permeated and diffused through the diaphragm 3 proceeds as in the above-described formula (1). On the other hand, at the counter electrode 5, the oxidation reaction proceeds as in the above-described formula (2).

  The unreacted free residual chlorine component that has permeated through the diaphragm 3 does not reach the phase of the aqueous electrolyte 6A on the counter electrode 5 side, but is extracted to the phase of the ionic liquid 6B on the working electrode 4 side. In order to examine the extraction ability of the ionic liquid 6B, 5 ml of the ionic liquid 6B solution and 2 mL of an aqueous solution having a residual chlorine concentration of 200 mg / L are prepared, and the residual chlorine concentration of the aqueous solution is determined by spectrophotometry using a DPD reagent after mixed extraction. It was measured. As a result, in the case of the ionic liquid 6B used in this example, it was possible to extract all free residual chlorine components from 2 mL of an aqueous solution having a residual chlorine concentration of 200 mg / L with a volume of 5 mL of the ionic liquid 6B. It was. This indicates that even if an ionic liquid exists between the working electrode 4 and the diaphragm 3, the measurement is not hindered. Therefore, unlike the conventional diaphragm type electrochemical sensor, there is no contamination of the unreacted free residual chlorine component in the aqueous electrolyte 6A and its properties can be maintained for a long time, or the working electrode 4 and the periphery of the diaphragm 3 are ionic liquid. By being immersed in 6B, it becomes possible to maintain stable reaction conditions on the working electrode 4, and it is possible to perform measurement for a much longer time as compared with the conventional diaphragm type electrochemical sensor.

  Next, the results of examining the stability of the indicated value of the diaphragm type sensor of this example will be described. FIG. 2 shows the ratio of the measurement value obtained by the diaphragm type sensor 1 of this example to the number of days in the continuous measurement when the value obtained by measuring the same test solution by the absorptiometry using the DPD reagent is 100%. Against. As shown in FIG. 2, even when the residual chlorine concentration (free residual chlorine concentration) was continuously measured at about 100 mg / L, measurement for two months or more was possible. As described above with reference to FIG. 7, in the conventional diaphragm type sensor using only the aqueous electrolyte as the electrolyte, a decrease in the indicated value was observed after 4 days in the experiment under the same conditions. Therefore, in the diaphragm type sensor 1 of a present Example, it turns out that the replacement frequency of the electrolyte solution 6 can be reduced remarkably and the lifetime of a sensor can be extended significantly.

  Moreover, as shown in FIG. 3, the linearity of the measured value of the electrolysis current with respect to the residual chlorine concentration of the diaphragm type sensor 1 of this example was good.

  Furthermore, as shown in FIG. 4, the response characteristic (FIG. 4A) of the diaphragm type sensor 1 of the present embodiment is the responsiveness (FIG. 4) of a conventional diaphragm type sensor using only an aqueous electrolyte as the electrolyte. It was better than (b)). In aqueous electrolytes, unreacted free residual chlorine component remains between the diaphragm and the working electrode, and this is measured by diffusing in the electrolyte and eventually reaching equilibrium and reaching a certain concentration. It is presumed that Since unreacted free residual chlorine components are consumed at the working electrode before the equilibrium state is reached, the current value of this amount is also detected, so it takes time to reach a constant current value and the responsiveness deteriorates it is conceivable that. On the other hand, in the ionic liquid, since there is no unreacted free residual chlorine component from the beginning, it is not affected at all, and chlorine permeated from the test solution through the diaphragm can be directly detected as a current value. Therefore, it is considered that the responsiveness is good and a constant current value is reached immediately.

  The results shown in FIGS. 4A and 4B are obtained by performing the following experiment. That is, several aqueous solutions having different chlorine concentrations were prepared by diluting in stages, and measurements were sequentially performed from the lower chlorine concentration. As shown in FIG. 4, in FIG. 4 (a), the number increases from (1) to (10), and in FIG. 4 (b), the number increases from (1) to (7). The chlorine concentration was increased.

  As described above, according to the present embodiment, it is possible to reduce the replacement frequency of the electrolyte solution 6 of the diaphragm type sensor 1. Further, according to the present embodiment, by extending the life of the diaphragm type sensor 1, it is possible to lengthen the interval of maintenance work and to reduce missing measurement in continuous measurement.

  In this embodiment, the diaphragm type sensor 1 is described as a diaphragm type residual chlorine sensor. However, the present invention can also be applied to a diaphragm type sensor used for measuring dissolved oxygen (DO), carbon dioxide gas, and the like. . By applying the present invention, it is possible to solve the above-described problems caused by accumulation of components that affect measurement values such as unreacted components in the electrolyte solution of these sensors.

  In this embodiment, the diaphragm type sensor has been described as a polarographic sensor. However, the present invention can also be applied to a galvanic cell type diaphragm sensor. As shown in FIG. 5, a galvanic cell type diaphragm sensor generally has no power source, and is different from a polarographic diaphragm sensor in that no voltage is applied from the outside during use. More specifically, the galvanic cell type diaphragm type sensor 1 has a consumable electrode inside, and itself operates as a battery, and does not require a power source. Gold or platinum is used as the working electrode (cathode) 4 and lead is used as the consumable counter electrode (anode) 5. Also in such a galvanic cell type diaphragm type sensor, the present invention is applied, and the electrolytic solution 6 includes an aqueous electrolytic solution 6A and a hydrophobic ionic liquid 6B as its components, and the aqueous electrolytic solution 6A and the ionic liquid. 6B is divided into a region of the aqueous electrolyte 6A and the region of the ionic liquid 6B that are in contact with each other in the electrolyte container 2B. The ionic liquid 6B is on the working electrode 4 side, and the aqueous electrolyte 6A is on the counter electrode 5 side. To be. As a result, the same problems as the polarographic diaphragm sensor can be solved.

Furthermore, the present invention detects a test gas such as nitrogen oxide (NOx), sulfur dioxide (SO ₂ ), carbon monoxide (CO) in addition to a polarographic type or galvanic cell type as a diaphragm type sensor, The present invention can also be applied to a potentiostatic gas sensor used to measure the amount. In the case of this gas sensor, the working electrode is often formed directly on the diaphragm, and the test gas can pass through the diaphragm and partially remain on the surface of the working electrode to become a disturbing component gas. Interfering gas components can be extracted to extend the lifetime of the sensor.

1 Diaphragm electrochemical sensor (diaphragm sensor)
2 Sensor body 2A Opening 2B Electrolyte container 3 Separator 4 Working electrode 5 Counter electrode 6 Electrolyte 6A Aqueous electrolyte 6B Ionic liquid S Interface

Claims (3)

An electrolytic solution storage unit, an electrolytic solution stored in the electrolytic solution storage unit, and preventing the electrolytic solution from flowing out of the electrolytic solution storage unit and permeating the measurement target component to the electrolytic solution in the electrolytic solution storage unit A permissible diaphragm, a working electrode disposed adjacent to the diaphragm in the electrolytic solution housing portion, and disposed farther from the diaphragm than the working electrode and electrically connected to the working electrode via the electrolytic solution. A diaphragm-type electrochemical sensor having an electrically connected counter electrode,
The electrolytic solution includes, as its components, an aqueous electrolytic solution and a hydrophobic ionic liquid, and the aqueous electrolytic solution and the ionic liquid are in contact with each other in the electrolytic solution storage portion and the ionic liquid. A diaphragm type electrochemical sensor, wherein the ionic liquid is on the working electrode side and the aqueous electrolyte is on the counter electrode side.   2. The diaphragm type electrochemical sensor according to claim 1, wherein the hydrophobic ionic liquid has a quaternary ammonium salt structure composed of a quaternary ammonium cation and a fluorine-containing anion.   The diaphragm type electrochemical sensor according to claim 1 or 2, which is of a polarographic type or a galvanic cell type.

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