JP2015034740A - Oxidation-reduction current measuring electrode unit and oxidation-reduction current measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform oxidation-reduction current measurement in a polarographic system or in a galvanic cell system without using a drive mechanism, accurately and stably.SOLUTION: An oxidation-reduction current measuring electrode unit comprises: a support chip 1 having a first surface 1a and a second surface 1b opposite to the first surface; a detection electrode 2 provided on the first surface 1a of the support chip 1 and immersed into a sample solution; a counter electrode 3 attached to the support chip 1 and immersed into the sample solution; and a shield 4 arranged so as to surround the detection electrode 2 and blocking the flow of the sample solution in contact with the detection electrode 2. The shield 4 is a cylindrical body having a peripheral surface across the first surface 1a to the second surface 1b of the support chip 1, and is opened on a lower end side and an upper end side.

Description

  The present invention relates to a redox current measuring electrode unit and a redox current measuring apparatus. More specifically, the present invention relates to a redox current measuring electrode unit and a redox current measuring device capable of measuring a redox current (electrolytic current) of a polarographic type or a galvanic cell type.

Conventionally, a polarographic method or a galvanic cell type oxidation-reduction current measuring device has been used for the purpose of measuring residual chlorine, dissolved ozone, chlorine demand, chlorine dioxide, and the like.
The oxidation-reduction current measured by these measurement methods is transported to the surface of the detection electrode only by natural diffusion due to a concentration gradient in a layer called a diffusion layer having a constant thickness, and is reduced on the surface. This is the diffusion current that flows when Conventionally, a stable diffusion layer has been formed in order to obtain an oxidation-reduction current (diffusion current) according to the concentration of the substance to be reduced. If a stable diffusion layer is always formed, the substance to be reduced in the sample solution is supplied to the detection electrode according to its concentration.

The stable diffusion layer can be formed by causing the sample liquid in contact with the detection electrode to flow relative to the detection electrode surface.
Examples of a method for causing the sample liquid in contact with the detection electrode to flow relative to the surface of the detection electrode include a method for allowing the sample liquid to flow while the detection electrode is stationary. However, when the relative flow is obtained only from the flow of the sample solution, the polarogram changes depending on the sample solution flow rate. Therefore, it is difficult to stably perform accurate measurement. Therefore, the sample liquid that contacts the detection electrode is caused to flow relative to the surface of the detection electrode by rotating or vibrating the detection electrode with respect to the sample solution.

The detection electrode used by rotating is called a rotating electrode, and the electrode used by vibrating is called a vibrating electrode. These electrodes rotate and vibrate at a linear velocity much higher than the normal flow rate of the sample liquid. For this reason, a stable diffusion layer can be formed regardless of the sample liquid flow rate, and the measurement value due to fluctuations in the sample liquid flow rate is not easily affected.
With rotating electrodes, a mercury contact is used to pull out the lead wire from the rotating sensing electrode without cutting it, a method that prevents the twisting of the lead wire by switching the rotation direction alternately, and the sensing electrode support is rotated. A method of moving the detection pole in a circular motion by moving it in a pestle shape (Patent Document 1) is known.
As a vibrating electrode, a method of vibrating a detection pole with an external vibrator (Patent Document 2), a method of vibrating using a built-in electromagnet (Patent Document 3), and the like are known.

No. 7-4566 Japanese Utility Model Publication No. 62-41240 No. 6-765

However, the methods of Patent Documents 1 to 3 require a drive mechanism that rotates or vibrates the detection pole. Therefore, there has been a problem that the apparatus becomes large.
In view of the above circumstances, the present invention provides an oxidation-reduction current measuring apparatus capable of accurately and stably performing oxidation-reduction current measurement of a polarographic system or a galvanic cell system without using a drive mechanism, and an oxidation used in the apparatus. It is an object of the present invention to provide an electrode unit for reducing current measurement.

In order to achieve the above object, the present invention employs the following configuration.
[1] a detection electrode immersed in the sample solution;
A counter electrode disposed in the vicinity of the detection electrode and immersed in the sample solution;
An oxidation-reduction current measuring electrode unit comprising a shielding material arranged to surround the detection electrode within a range that does not prevent the sample solution from coming into contact with the detection electrode and suppressing flow of the sample solution in contact with the detection electrode.
[2] A support chip having a first surface and a second surface opposite to the first surface;
A detection electrode provided on the first surface of the support chip and immersed in the sample liquid;
A counter electrode attached to the support chip and immersed in the sample solution;
It is arranged so as to surround the detection electrode, and includes a shielding material that suppresses the flow of the sample liquid in contact with the detection electrode.
The shielding material is a cylindrical body having a peripheral surface extending from the first surface to the second surface of the support chip, and an opening is provided on the lower end side and the upper end side,
An electrode unit for measuring oxidation-reduction current, wherein the upper end side of the shielding material is located above the liquid surface of the sample liquid when immersed in the sample liquid.
[3] The oxidation-reduction current measuring electrode according to [1] or [2], wherein a cross-sectional area in a horizontal plane of a region surrounded by the shielding material is 1.5 to 6 mm when expressed as a radius of a circle having the same area. unit.
[4] The electrode unit for measuring redox current according to any one of [1] to [3], wherein the distance between the lower end of the region surrounded by the shielding material and the detection electrode is 1.5 to 6 mm.
[5] The oxidation-reduction current measurement electrode unit according to any one of [1] to [4];
An oxidation-reduction current measuring apparatus comprising: an ammeter that measures an oxidation-reduction current flowing between the detection electrode and the counter electrode.
[6] The oxidation-reduction current measuring apparatus according to [5], further comprising a voltage applying mechanism that applies an applied voltage between the detection electrode and the counter electrode.

  According to the oxidation-reduction current measurement electrode unit and the oxidation-reduction current measurement electrode unit of the present invention, it is possible to accurately measure the oxidation-reduction current of the polarographic method or the galvanic cell method without using a drive mechanism that rotates or vibrates the detection electrode. And can be carried out stably.

It is a schematic block diagram of the oxidation-reduction current measuring apparatus which concerns on one Embodiment of this invention. It is a front view of the electrode unit for oxidation-reduction current measuring devices concerning one embodiment of the present invention. It is II-II sectional drawing of FIG. It is a front view of the electrode unit for oxidation-reduction current measuring devices concerning other embodiments of the present invention. It is a front view of the electrode unit for oxidation-reduction current measuring devices concerning other embodiments of the present invention. It is a graph which shows the relationship between the free residual chlorine concentration in the applied voltage of 0V, and an electric current value. It is a graph which shows the relationship between the total residual chlorine concentration in applied voltage -0.2V, and an electric current value.

  FIG. 1 is an example of the oxidation-reduction current measuring apparatus of the present invention. As shown in FIG. 1, the apparatus 100 of this example includes an electrode unit 10 for measuring an oxidation-reduction current, a sample solution container 20, an applied voltage mechanism 30, an ammeter 40, an electrode unit 10, and an applied voltage mechanism 30. , And a wiring 50 that connects the ammeters 40 in series.

  As shown in FIGS. 2 and 3, the electrode unit 10 includes a support chip 1 having a first surface 1a and a second surface 1b opposite to the first surface 1a. A detection electrode 2 provided on one surface 1a and immersed in the sample solution S, a counter electrode 3 attached to the support chip 1 and immersed in the sample solution, and arranged so as to surround the detection electrode 2, and the detection electrode 2 It consists of the shielding material 4 which suppresses the flow of the sample liquid S in contact with the substrate and the holding material 5 which holds the support chip 1.

  The support chip 1 of this example is substantially flat and has four peripheral surfaces. One of the four peripheral surfaces is fixed to the holding material 5 so as to be suspended from the lower surface side of the holding material 5. Grooves 1c are formed in the remaining three of the four peripheral surfaces. At least the lower end side of the support chip 1 is immersed in the sample solution S in a state of being suspended from the holding material 5.

The detection pole 2 is provided in the vicinity of the corner on the lower end side away from the holding material 5 of the first surface 1 a of the support chip 1. The counter electrode 3 is disposed in the groove 1 c of the support chip 1. A conductive wire (not shown) from the detection electrode 2 to the holding material 5 side of the support chip 1 and a conductive wire (not shown) from the counter electrode 3 to the holding material 5 side of the support chip 1 are embedded in the support chip 1. It is.
The holding member 5 is provided with a through hole 5a corresponding to a position where the conductive wire from the detection electrode 2 of the support chip 1 is exposed, and is provided with a through hole 5b corresponding to a position where the conductive wire from the counter electrode 3 is exposed. ing. The wiring 50 enters the electrode unit 10 through the through holes 5 a and 5 b provided in the holding material 5, and is connected to a conductive wire embedded in the support chip 1.
As the detection electrode 2, a gold electrode, a platinum electrode, a glassy carbon electrode, or the like can be employed. As the counter electrode, a silver / silver chloride electrode in which silver chloride is plated on silver, a silver electrode, a gold electrode, a platinum electrode, a glassy carbon electrode, or the like can be used.

The shielding material 4 is a member that suppresses the flow of the sample liquid S in the shielding region by constituting a region surrounding the detection electrode 2 (hereinafter sometimes referred to as “shielding region”). The flow of the sample liquid S in the shielding region can be suppressed mainly for the following reason.
1) The outside of the shielding area where the sample liquid S is flowing is physically blocked from the shielding area.
2) By blocking the heat transfer from the outside of the shielding area, it is possible to prevent the occurrence of convection due to the temperature gradient in the shielding area even if the temperature fluctuates outside the shielding area.
3) By disposing the upper end of the shielding material 4 so as to be above the liquid level of the sample liquid S, the liquid level fluctuation of the sample liquid S outside the shielding area is prevented from reaching the shielding area.
4) By narrowing the shielding area, it is possible to prevent the flow factor of the sample liquid S, such as temperature change, vibration, and liquid level fluctuation, from occurring in the shielding area.

  The shielding member 4 of this example is a cylindrical body having a peripheral surface extending from the first surface 1a to the second surface 1b of the support chip 1, the entire lower end side being an opening 4a, and the entire upper end side being an opening 4b. Has been. When the lower end side of the support chip 1 is immersed in the sample liquid S, the sample liquid S enters the inside of the shielding material 4 from the opening 4a, and the detection electrode 2 surrounded by the shielding material 4 is immersed in the sample liquid S. It has become. When the lower end side of the support chip 1 is immersed in the sample liquid S, the opening 4b is arranged to be above the liquid surface of the sample liquid S, and the shaking of the liquid surface of the sample liquid S is applied to the shielding material 4. It is possible to prevent reaching the enclosed area.

The portion of the counter electrode 3 that is closest to the detection electrode 2 is located in a region surrounded by the shielding material 4. When the portion of the counter electrode 3 closest to the detection electrode 2 is located outside the region surrounded by the shielding material 4, the distance between the detection electrode 2 and the counter electrode 3 tends to increase. In that case, there is a possibility that the liquid resistance (resistance when the current passes through the sample liquid S) cannot be ignored. In particular, in the case of a reagentless type oxidation-reduction current measuring apparatus that does not use a reagent, the influence of the liquid resistance tends to increase, and therefore it is not preferable that the distance between the detection electrode 2 and the counter electrode 3 is increased.
Therefore, it is preferable that the portion of the counter electrode 3 that is closest to the detection electrode 2 is located within the region surrounded by the shielding material 4 and is disposed as close as possible to the extent that the detection electrode 2 is not short-circuited.

In this example, the inside of the cross section perpendicular to the axial direction of the shielding material 4 is a circle having a radius r. The radius r is preferably 1.5 to 6 mm, more preferably 2 to 4 mm, and even more preferably 2.5 to 3 mm. If the radius r is too large, the sample liquid S entering the shielding material 4 is likely to flow, and it is difficult to achieve the function of the shielding material 4 for suppressing the flow of the sample liquid S in contact with the detection electrode 2. If the radius r is too small, it is difficult for the sample liquid S to enter the shielding member 4, and it is difficult for the sample liquid S to contact the detection electrode 2.
Note that the preferred range of the radius r slightly varies depending on the wettability of the sample liquid S inside the shielding material 4 and the like.
The distance d between the opening 4a, which is the lower end of the region surrounded by the shielding material 4, and the detection electrode 2 (the distance between the opening 4a and the portion closest to the opening 4a of the detection electrode 2) is 1.5 to 6 mm. Is preferably 2 to 4 mm, and more preferably 2.5 to 3 mm. If the distance d is too small, the influence of the flow of the sample liquid S on the outside of the shielding material 4 is easily transmitted to the sample liquid S in contact with the detection electrode 2, and the shielding material that suppresses the flow of the sample liquid S in contact with the detection electrode 2. It becomes difficult to achieve function 4. If the distance d is too large, the electrode unit 10 becomes unnecessarily large, which is not preferable.

The applied voltage mechanism 30 has a function of applying one or more predetermined voltages between the detection electrode 2 and the counter electrode 3. The applied voltage mechanism 30 may be provided with a function of applying zero mV between the detection electrode 2 and the counter electrode 3, that is, a function of applying no voltage.
In addition, when it is set as the oxidation reduction current measuring apparatus of only a galvanic cell system which does not provide any voltage between the detection electrode 2 and the counter electrode 3, the applied voltage mechanism 30 is unnecessary.

In the apparatus 100 of this example, the diffusion layer is reduced as the substance to be reduced is consumed by measuring the oxidation-reduction current. Since the flow of the sample liquid S in contact with the detection electrode 2 is suppressed, the regeneration of the diffusion layer due to the movement of the substance to be reduced is negligible within a certain time from the start of the measurement of the redox current. Therefore, if the value of the redox current is read after a certain time has elapsed after the start of measurement of the redox current, the thickness of the diffusion layer at that time is reproducible and depends on the concentration of the substance to be reduced. A reproducible current value is obtained.
That is, the oxidation-reduction current measuring device of the present invention ensures the reproducibility of the diffusion layer thickness during the oxidation-reduction current measurement by suppressing the flow and vibration of the sample water around the detection electrode, and the concentration of the substance to be reduced. An oxidation-reduction current (diffusion current) can be obtained.

In the apparatus 100 of this example, it is preferable to read the value of the redox current within 2 minutes after the start of the measurement of the redox current, more preferably after 1 minute from 20 seconds, and after 1 minute from 30 seconds. It is more preferable to read.
“After the start of measurement of the oxidation-reduction current” means that the detection electrode 2 and the counter electrode 3 are immersed in the sample liquid in a state where a predetermined applied voltage is applied. When the applied voltage is changed after the detection electrode 2 and the counter electrode 3 are immersed in the sample solution, this means that the applied voltage is changed.
If the time until reading becomes longer, the reducible substance in the diffusion layer is greatly reduced, and therefore the regeneration of the diffusion layer due to the movement of the reducible substance cannot be ignored. If the transfer of the substance to be reduced is only by diffusion, after a lapse of 2 to 3 minutes, the regeneration rate of the diffusion layer should be constant and a balance with the consumption of the substance to be reduced by measurement should be obtained. However, even within the region surrounded by the shielding material 4, the flow of the sample liquid cannot be made completely zero, so that it is difficult to establish a balance between the regeneration rate of the diffusion layer and the consumption of the substance to be reduced by measurement. .
Therefore, if the time until reading is too long, the thickness of the diffusion layer becomes unstable and it becomes difficult to obtain reproducibility. In addition, the amount of current change with respect to the concentration becomes relatively small, and the detection sensitivity is lowered, which is not preferable.
On the other hand, a rapid current change (current drop) occurs immediately after the start of measurement. Therefore, if the time until reading is too short, the amount of current change with respect to the concentration becomes relatively large, but it becomes difficult to measure current with reproducibility.

The electrode unit 10 in the apparatus 100 may be changed to the electrode unit 11 in FIG. 4 or the electrode unit 12 in FIG. 4 and 5, the same reference numerals are given to the same components as those in FIG. 1, and detailed description thereof will be omitted.
The electrode unit 11 of FIG. 4 has the same configuration as the electrode unit 10 except that the counter electrode 3 is provided on the first surface 1 a of the support chip 1 along with the detection electrode 2. The electrode unit 12 in FIG. 5 is provided with grooves 1d and 1d on both sides of the center in the height direction of the support chip 1 (height direction when immersed in the sample solution S), and the counter electrode 3 is a portion of the grooves 1d and 1d. The configuration is the same as that of the electrode unit 10 except that the electrode unit 10 is wound around the support chip 1.

Moreover, the cross section of the shielding member 4 in the electrode unit 10 is not limited to a circle, and may be an ellipse or a polygon. However, the cross-sectional area of the region surrounded by the shielding material 4 is preferably 1.5 to 6 mm, more preferably 2 to 4 mm when expressed as a radius r ′ of a circle having the same area. More preferably, it is 5 to 3 mm. If the radius r ′ is too large, the sample liquid S that has entered the shielding material 4 easily flows, and it is difficult to achieve the function of the shielding material 4 that suppresses the flow of the sample liquid S that contacts the detection electrode 2. If the radius r ′ is too small, it is difficult for the sample liquid S to enter the shielding member 4, and it is difficult for the sample liquid S to contact the detection electrode 2.
Note that the preferred range of the radius r ′ slightly varies depending on the wettability of the sample liquid S inside the shielding material 4 and the like.

Further, the shielding material 4 surrounding the detection electrode 2 is not limited to a cylindrical body whose upper and lower ends are fully open, and does not prevent the sample liquid S from entering the shielding material 4, and the detection electrode 2. Any material can be used as long as the flow of the sample solution S in contact with the substrate can be suppressed.
For example, the upper end side of the cylindrical body may be covered with the upper base, and a hole through which air can flow is opened on the peripheral surface near the upper base or the upper base. Further, the openings on the upper end side and the lower end side of the cylindrical body may be each closed with a mesh that can pass liquid.
Even if the counter electrode 3 is not attached to the support chip 1, the counter electrode 3 may be disposed in the vicinity of the detection electrode 2 to the extent that the oxidation-reduction current between the counter electrode 3 and the detection electrode 2 can be detected. Further, as long as the liquid resistance does not cause a problem, the portion of the counter electrode 3 that is closest to the detection electrode 2 may be disposed outside the region surrounded by the shielding material 4.

Examples for clarifying the effects of the present invention will be described below. The reagents used in the following examples were prepared as follows.
Demineralized water: Tap water was treated with activated carbon to obtain demineralized water.
Sodium hypochlorite solution: After diluting a sodium hypochlorite solution having an effective chlorine concentration of about 12% with ion-exchanged water to an effective chlorine concentration of about 50 mg / L, the water test method 2011 edition “30.3 Diethyl-p- The effective chlorine concentration is determined by “iodine titration method” described in (14) Standard chlorine water of “Absorption photometry with phenylenediamine”. This was used as a stock solution and diluted with demineralized water at the time of use to obtain sodium hypochlorite solutions of various concentrations.
Dichlorosulfamic acid solution: A sodium hypochlorite solution having an effective chlorine concentration of about 12% was dissolved in ion-exchanged water so that the effective chlorine concentration with respect to 1 mol of sodium sulfamate and sodium sulfamate was 2 mol. The effective chlorine concentration was confirmed by the “iodine titration method” described in (14) standard chlorine water of the water supply test method 2011 edition “30.3 Absorption photometric method with diethyl-p-phenylenediamine”. This was used as a stock solution and diluted with demineralized water at the time of use to prepare dichlorosulfamic acid solutions of various concentrations.
Monochlororosulfamate solution: A sodium hypochlorite solution having an effective chlorine concentration of about 12% was dissolved in ion-exchanged water so that the effective chlorine concentration with respect to 1 mol of sodium sulfamate and 1 mol of sodium sulfamate was 1 mol. The effective chlorine concentration was confirmed by the “iodine titration method” described in (14) standard chlorine water of the water supply test method 2011 edition “30.3 Absorption photometric method with diethyl-p-phenylenediamine”. This was used as a stock solution, and diluted with demineralized water at the time of use to obtain a monochlororosulmic acid solution of each concentration.

The DPD analysis values in the following examples were determined by the following method according to the DPD method defined in the water test method 30.3.
(A) Preparation of DPD reagent 1.0 g of N, N-diethyl-phenylenediamine sulfate and 24 g of anhydrous sodium sulfate were mixed to prepare a DPD (N, N-diethyl-p-phenylenediamine) reagent.
(B) Preparation of phosphate buffer solution (pH = 6.5) 35.4 mL of 0.2 mol / L sodium hydroxide solution was added to 100 mL of 0.2 mol / L potassium dihydrogen phosphate, and trans-1,2 was added thereto. -0.13 g of cyclohexanediaminetetraacetic acid hydrate was dissolved to prepare a phosphate buffer solution (pH = 6.5).
(C) Measurement of free residual chlorine concentration Take 2.5 mL of phosphate buffer in 50 mL of stoppered container, add 0.5 g of DPD reagent to this, then add sample solution and ion-exchanged water to make the total volume 50 mL. Mixed. Next, about 3 mL of the mixed solution is taken into an absorption cell, and the absorbance at a wavelength of 528 nm is measured 10 seconds after mixing using a photoelectric spectrophotometer. From the calibration curve prepared in advance, the free residual chlorine concentration is determined. Asked.
(D) Total residual chlorine concentration About 50 g of potassium iodide was added to and dissolved in 50 mL of the mixed solution obtained in the above (c). Next, about 3 mL of the solution after addition of potassium iodide was taken in an absorption cell, and the absorbance at a wavelength of 528 nm after 2 minutes after addition of potassium iodide was measured using a photoelectric spectrophotometer. From a calibration curve prepared in advance, The total residual chlorine concentration was determined.

Using the oxidation-reduction current measuring apparatus shown in FIGS. 1 to 3, oxidation reduction at various applied concentrations of sodium hypochlorite solution, dichlorosulfamic acid solution, and monochlororosulphamic acid solution at an applied voltage of 0 mV or an applied voltage of −200 mV. The current value was examined.
The detection electrode 2 was a gold electrode having a diameter of 1 mm, and the counter electrode 3 was a silver / silver chloride wire obtained by plating a silver wire having a diameter of 0.6 mm with silver chloride. The distance between the detection electrode 2 and the portion of the counter electrode 3 closest to the detection electrode 2 was 2 mm. The shielding material 4 was a circular cylindrical body having an inner cross-sectional radius r of 5 mm. The distance d between the opening 4a, which is the lower end of the region surrounded by the shielding material 4, and the detection electrode 2 was 4 mm. The timing for reading the value of the redox current was 30 seconds after the start of the redox current measurement.

The results are shown in FIGS. 6 and 7, “hypochlorous acid” indicates a sodium hypochlorite solution, “dichloro” indicates a dichlorosulfamic acid solution, and “monochloro” indicates a monochlororosulmic acid solution.
Further, the horizontal axis of FIG. 6 is the DPD analysis value of the free residual chlorine concentration, and the horizontal axis of FIG. 7 is the DPD analysis value of the total residual chlorine concentration.
As shown in FIG. 6, it was found that the oxidation-reduction current at an applied voltage of 0 mV has a good correlation with the free residual chlorine concentration (DPD analysis value). Further, as shown in FIG. 7, since the redox current value at an applied voltage of −200 mV correlates with the concentrations of both “monochloro” and “dichloro”, the redox current corresponding to the combined residual chlorine and the free residual chlorine It was found that a current obtained by adding the redox current corresponding to the concentration can be obtained.

  As shown in FIG. 6 and FIG. 7, according to the oxidation-reduction current measuring apparatus of the present invention, it can be confirmed that the oxidation-reduction current (diffusion current) according to the concentration of the substance to be reduced can be obtained accurately and stably. It was. Since the oxidation-reduction current measuring device and the oxidation-reduction current measurement electrode unit of the present invention do not need to cause the sample liquid in contact with the detection electrode to flow relative to the detection electrode surface due to vibration, rotation, or the like, Miniaturization is possible and maintenance is easy.

  The oxidation-reduction current measuring device and the oxidation-reduction current measurement electrode unit of the present invention can easily obtain residual chlorine, dissolved ozone, chlorine demand, chlorine dioxide, etc. by measuring the oxidation-reduction current of a polarographic system or a galvanic cell system. it can.

DESCRIPTION OF SYMBOLS 1 ... Support chip, 2 ... Detection pole, 3 ... Counter electrode, 4 ... Shielding material, 5 ... Holding material,
10-12 ... Electrode unit, 20 ... Sample container, 30 ... Applied voltage mechanism, 40 ... Ammeter,
50 ... wiring,
71 ... Measurement cell, 72 ... Detection electrode, 74 ... Counter electrode, 78 ... Applied voltage mechanism, 79 ... Ammeter

Claims (6)

A sensing electrode immersed in the sample solution;
A counter electrode disposed in the vicinity of the detection electrode and immersed in the sample solution;
An oxidation-reduction current measuring electrode unit comprising a shielding material arranged to surround the detection electrode within a range that does not prevent the sample solution from coming into contact with the detection electrode and suppressing flow of the sample solution in contact with the detection electrode. A support tip having a first surface and a second surface opposite the first surface;
A detection electrode provided on the first surface of the support chip and immersed in the sample liquid;
A counter electrode attached to the support chip and immersed in the sample solution;
It is arranged so as to surround the detection electrode, and includes a shielding material that suppresses the flow of the sample liquid in contact with the detection electrode.
The shielding material is a cylindrical body having a peripheral surface extending from the first surface to the second surface of the support chip, and an opening is provided on the lower end side and the upper end side,
An electrode unit for measuring oxidation-reduction current, wherein the upper end side of the shielding material is located above the liquid surface of the sample liquid when immersed in the sample liquid.   The electrode unit for measuring redox current according to claim 1 or 2, wherein a cross-sectional area in a horizontal plane of a region surrounded by the shielding material is 1.5 to 6 mm when expressed as a radius of a circle having the same area.   The electrode unit for redox current measurement according to any one of claims 1 to 3, wherein the distance between the lower end of the region surrounded by the shielding material and the detection electrode is 1.5 to 6 mm. The electrode unit for redox current measurement according to any one of claims 1 to 4,
An oxidation-reduction current measuring apparatus comprising: an ammeter that measures an oxidation-reduction current flowing between the detection electrode and the counter electrode.   The oxidation-reduction current measuring apparatus according to claim 5, further comprising an applied voltage mechanism that applies an applied voltage between the detection electrode and the counter electrode.