Electrochemical measurement device and electrochemical measurement method

Abstract

This electrochemical measurement device is for electrochemically measuring the concentration of a to-be-measured substance included in a sample liquid, the electrochemical measurement device comprising: a flow path through which the sample liquid flows; and a working electrode and a counter electrode having a liquid contact surface in contact with the sample liquid flowing through the flow path. The liquid contact surface of the working electrode and the liquid contact surface of the counter electrode are disposed so as to be offset from each other along the direction in which the flow path extends, and such that each portion of the surfaces directly face each other.

Description

[Technical Field]

[0001] The present invention relates to an electrochemical measurement device and an electrochemical measurement method. [Background technology]

[0002] For example, in the process of washing and sterilizing food, it is necessary to strictly control the chlorine concentration within a range that ensures proper sterilization, and therefore there is a demand for accurate measurement of the chlorine concentration in the washing solution used to wash food.

[0003] As an apparatus for accurately measuring the chlorine concentration in a cleaning solution, for example, a flow injection electrochemical apparatus is known that performs voltammetry measurement to analyze a sample by applying a voltage to a sample solution that is an electrolyte solution, as shown in Patent Document 1. In this apparatus, the cleaning solution that is the sample solution is sent to a measurement cell equipped with a working electrode, a reference electrode, and a counter electrode, and a predetermined voltage is applied to the working electrode, thereby measuring the chlorine concentration in the sample solution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-034408 Summary of the Invention [Problem to be solved by the invention]

[0005] When measuring the chlorine concentration or the like in a sample solution using the electrochemical measurement device described above, electromagnetic noise generated by other analytical devices or electric field treatment devices may enter the measurement cell through the sample solution, potentially reducing measurement accuracy. To reduce the influence of such noise, it is preferable to install the working electrode and the counter electrode as close as possible. However, if these electrodes are installed so that they completely face each other, bubbles generated on the liquid-contacting surface (sensor surface) of the working electrode may accumulate on steps or the like between the liquid-contacting surfaces of each electrode and the flow path, resulting in a problem of reduced measurement accuracy.

[0006] The present invention has been made to solve all of these problems at once, and its main objective is to reduce the retention of bubbles generated at the working electrode in an electrochemical measurement device while reducing the effects of electromagnetic noise. [Means for solving the problem]

[0007] That is, the electrochemical measuring device according to the present invention is for electrochemically measuring the concentration of a substance to be measured contained in a sample solution, and is characterized in that it comprises a flow path through which the sample solution flows, and a working electrode and a counter electrode having liquid-contacting surfaces that come into contact with the sample solution flowing through the flow path, and the liquid-contacting surfaces of the working electrode and the counter electrode are offset from each other along the direction in which the flow path extends, and are arranged so that parts of them face each other.

[0008] In an electrochemical measurement device configured in this manner, the working electrode and counter electrode are positioned close enough that portions of their wetted surfaces face each other, thereby reducing the effects of external electromagnetic noise transmitted to each electrode through the sample solution. Furthermore, the wetted surfaces of the working electrode and counter electrode are positioned offset from each other along the direction of the flow path while portions face each other, thereby creating turbulence in the flow of sample solution and allowing bubbles generated at the wetted surface of the working electrode to escape downstream without becoming trapped.

[0009] A specific embodiment of the electrochemical measurement device that prominently exhibits the effects of the present invention is one in which recesses are formed in the inner wall surface that forms the flow path at positions corresponding to the counter electrode and the working electrode, and the bottom surface of each recess is formed by the liquid-contacting surface of the working electrode and the counter electrode, respectively.

[0010] In the electrochemical measurement device, the flow path preferably includes a measurement flow path section facing the liquid contact surface of the working electrode and the liquid contact surface of the counter electrode, and the measurement flow path section is preferably formed so that the sample liquid is applied perpendicularly or obliquely from the upstream side to the downstream side to the liquid contact surface of the working electrode or the counter electrode, whichever is located downstream. If the measurement flow path section is formed in this manner, the sample liquid can be applied perpendicularly or obliquely to the liquid contact surface of the downstream electrode, thereby efficiently flushing away any air bubbles that have accumulated on the liquid contact surface of the downstream electrode.

[0011] In the electrochemical measurement device, the flow path is preferably formed so that the sample liquid is applied perpendicularly or obliquely to the liquid-contacting surface of the working electrode. In this way, the flow of the sample liquid is likely to become turbulent when it hits the liquid-contacting surface of the working electrode, and therefore even if bubbles are generated on the liquid-contacting surface, which is the sensor surface of the working electrode, the bubbles can be easily removed by the flow of the sample liquid.

[0012] In order to allow bubbles generated at the liquid-contacting surface of the working electrode to escape more easily without being retained, it is preferable that the measurement flow path section of the electrochemical measurement device is formed so that the sample liquid flows upward, and that the liquid-contacting surface of the working electrode and the liquid-contacting surface of the counter electrode are vertically offset along the measurement flow path section.

[0013] It is preferable that the electrochemical measurement device further includes a fluid blocking unit capable of blocking the flow of the sample liquid upstream of the working electrode and the counter electrode in the flow path, and is configured to electrochemically measure the concentration of the substance to be measured contained in the sample liquid while the flow of the sample liquid is blocked by the fluid blocking unit. In this way, by blocking the flow of sample liquid during measurement, it is possible to block external electromagnetic noise transmitted through the sample liquid, thereby improving measurement accuracy. Specific examples of such a fluid blocking portion include a roller pump, a diaphragm pump, and an on-off valve.

[0014] The electrochemical measurement device preferably has a second counter electrode provided upstream of the working electrode and the counter electrode in the flow channel. With this arrangement, the electromagnetic noise transmitted through the sample solution is absorbed by the second counter electrode, thereby reducing the influence of the electromagnetic noise transmitted to the downstream working electrode and counter electrode.

[0015] Furthermore, in the electrochemical measurement device, the working electrode and the counter electrode are preferably arranged in this order from upstream. In this way, electromagnetic noise transmitted from the downstream side of the working electrode through the sample solution can be absorbed by the counter electrode, thereby further improving measurement accuracy.

[0016] The electrochemical measurement method of the present invention is an electrochemical measurement method for electrochemically measuring the concentration of a substance to be measured contained in a sample solution using an electrochemical measurement device including a flow path through which a sample solution flows, and a working electrode and a counter electrode having liquid-contacting surfaces that come into contact with the sample solution flowing through the flow path, characterized in that the liquid-contacting surfaces of the working electrode and the counter electrode are shifted from each other along the direction in which the flow path extends, and are positioned so that parts of them face each other directly. According to such an electrochemical measurement method, it is possible to achieve the same effects as those of the electrochemical measurement apparatus of the present invention described above. [Effects of the Invention]

[0017] According to the present invention, in an electrochemical measurement apparatus, it is possible to reduce the influence of electromagnetic noise while reducing the retention of bubbles generated at the working electrode. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing the overall configuration of an electrochemical measurement apparatus according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically showing the structure of a measurement cell of the electrochemical measurement apparatus of the embodiment. [Figure 3] Enlarged view of part A in Figure 2. [Figure 4] FIG. 2 is a functional block diagram of the electrochemical measurement apparatus according to the embodiment. [Figure 5] FIG. 10 is a diagram schematically showing the structure of a measurement cell of an electrochemical measurement apparatus according to another embodiment. [Figure 6] FIG. 10 is a diagram schematically showing the structure of a measurement cell of an electrochemical measurement apparatus according to another embodiment. [Figure 7] FIG. 10 is a diagram schematically showing the structure of a measurement cell of an electrochemical measurement apparatus according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] An electrochemical measurement apparatus 100 according to one embodiment of the present invention will be described below with reference to the drawings.

[0020] The electrochemical measurement apparatus 100 of this embodiment is, for example, a flow injection type electrochemical measurement apparatus 100 that performs three-electrode voltammetry measurement to analyze a sample by applying a voltage to a sample liquid that is an electrolyte solution.

[0021] This electrochemical measurement device 100 can be used for various purposes, but in this example, it is connected to a flow path (also called a main flow path ML) through which a cleaning solution used to wash vegetables and other foods flows, and is configured to measure the concentration of residual chlorine (a substance to be measured) contained in the cleaning solution. Residual chlorine refers to all available chlorine contained in the aqueous solution. This available chlorine includes hypochlorous acid (HClO), hypochlorite ions (ClO - ), dissolved chlorine (Cl2), and combined chlorine such as monochloramine (NH2Cl), dichloramine (NHCl2), and trichloramine (NCl3).

[0022] Specifically, as shown in FIG. 1, this electrochemical measurement device 100 comprises a box-shaped casing 1 having an inlet port P1 and an outlet port P2 on its side wall, a sample flow path 2 inside the casing 1, both ends of which are connected to the inlet port P1 and the outlet port P2, respectively, through which the sample liquid introduced from the inlet port P1 flows and is guided to the outlet port P2, a sensor unit 3 provided on the sample flow path 2, a measurement circuit 4 for extracting signals from the sensor unit 3, and an information processing device 5 for calculating the concentration of components in the sample based on the voltage, current, etc. obtained by the measurement circuit 4.

[0023] The inlet port P1 is connected to a first branch pipe that forms a first branch flow path BL1 branching off from the main flow path ML, and the outlet port P2 is connected to a second branch pipe that forms a second branch flow path BL2 branching off from the main flow path ML. The sample liquid flowing through the main flow path ML passes through the first branch flow path BL1 and is taken into the sample flow path 2 via the inlet port P1, is sensed in the sensor unit 3, and then is returned to the main flow path ML via the second branch flow path BL2 via the outlet port P2.

[0024] The sample flow path 2 includes an inlet flow path 21 that guides the sample liquid introduced from the inlet port P1 to the sensor unit 3, a sensor flow path 22 provided in the sensor unit 3, and an outlet flow path 23 that guides the sample liquid that has left the sensor unit 3 to the outlet port P2. The upstream end of the sensor flow path 22 is connected to the downstream end of the inlet flow path 21, and the downstream end of the sensor flow path 22 is connected to the upstream end of the outlet flow path 23.

[0025] The sensor unit 3 includes a measurement cell 31 that defines the sensor flow path 22 therein, a working electrode 32 that is attached to the measurement cell 31 and has a liquid-contacting surface that comes into contact with the sample liquid flowing through the sensor flow path 22, a reference electrode 33, and a counter electrode 34. Here, the reference electrode 33, the working electrode 32, and the counter electrode 34 are provided in this order from upstream to downstream.

[0026] The measurement cell 31 is a flow cell type having a block shape, for example, as shown in FIGS. 2 and 3, with a sensor flow path 22 formed to penetrate the interior thereof. The sensor flow path 22 is formed by the inner wall of a tubular through-hole 311 that penetrates the measurement cell 31. The upstream end of the sensor flow path 22 is connected to an inlet 22a formed on one end face of the measurement cell 31, and the downstream end of the sensor flow path 22 is connected to an outlet 22b formed on the other end face of the measurement cell 31. The inlet 22a is connected to the downstream end of the inlet flow path 21, and the outlet 22b is connected to the upstream end of the outlet flow path 23. In this embodiment, the inlet 22a is formed on the bottom face of the measurement cell 31, and the outlet 22b is formed on the top face of the measurement cell 31. The sample liquid introduced from the inlet 22a flows from bottom to top (upward) through the sensor flow path 22 and is discharged from the outlet 22b.

[0027] More specifically, sensor flow path 22 includes inlet flow path section 221, the upstream end of which is connected to inlet 22a, and measurement flow path section 222, which is provided downstream of inlet flow path section 221 and faces liquid contact surface 321 of working electrode 32. The downstream end of measurement flow path section 222 is connected to outlet 22b.

[0028] The working electrode 32 has a sensor surface (liquid-contacting surface) 321 for detecting the object to be measured by applying a voltage in contact with the sample liquid. Specifically, the working electrode 32 is, for example, a diamond electrode in which the sensor surface 321 is made of boron-doped diamond that has conductivity due to the addition of a high concentration of boron.

[0029] The reference electrode 33 is an electrode that serves as a reference for the potential of the working electrode 32, and in this embodiment, a silver / silver chloride electrode is used.

[0030] The counter electrode 34 allows current to flow smoothly through the working electrode 32 when a certain potential is set at the working electrode 32. In this embodiment, like the working electrode 32, a boron-doped diamond electrode is used.

[0031] The working electrode 32, reference electrode 33, and counter electrode 34 are all attached to the measurement cell 31 so that their liquid-contacting surfaces 321, 331, and 341 come into contact with the sample liquid in the sensor flow path 22. Specifically, the measurement cell 31 has a plurality of thin-walled portions 312 that are relatively thinner than the other portions, and each thin-walled portion 312 has an opening 313 that penetrates through the thickness and communicates with the sensor flow path 22. The electrodes 32, 33, and 34 are attached to the thin-walled portions 312 so that their liquid-contacting surfaces 321, 331, and 341 cover the openings 313 from the outside. A sealing member S, such as an O-ring or a gasket, is interposed between the liquid-contacting surfaces 321, 331, and 341 of the electrodes 32, 33, and 34 and the outer wall surface of the thin-walled portions 312, providing a watertight seal between them.

[0032] Furthermore, upstream of the sensor unit 3 in the sample flow channel 2 (specifically, inlet flow channel 21), a fluid cutoff unit 6 capable of cutting off the flow of sample liquid is provided. Specifically, the fluid cutoff unit 6 in this embodiment is a roller pump (tubing pump). When this roller pump is driven, the sample liquid flows through the inlet flow channel 21 to the sensor unit 3, and when the roller pump is stopped, the flow of sample liquid in the inlet flow channel 21 is cut off, and the delivery of sample liquid to the sensor unit 3 is stopped.

[0033] The measuring circuit 4 applies a voltage to the working electrode 32, the reference electrode 33, and the counter electrode 34, and detects a current value at the applied voltage, and includes, for example, a potentiostat.

[0034] The information processing device 5 is a dedicated or general-purpose computer equipped with a CPU, internal memory, input / output interface, A / D converter, etc. Based on a predetermined program stored in the internal memory, the CPU and peripheral devices of the information processing device 5 cooperate to perform the functions of a voltage control unit 51 that controls the voltage applied to the measurement circuit 4, a calculation unit 52 that determines a current-residual chlorine concentration curve from the relationship between the current signal output from the measurement circuit 4 and the residual chlorine concentration and calculates the residual chlorine concentration in the sample based on this current-residual chlorine concentration curve, and a fluid control unit 53 that controls the fluid shutoff unit 6, as shown in Fig. 4 .

[0035] In the electrochemical measurement device 100 of this embodiment, the flow of sample liquid is blocked by the fluid blocking unit 6 to stop the liquid from being sent to the sensor unit 3, and the voltage control unit 51 applies a voltage to the measurement circuit 4, and the calculation unit 52 calculates the concentration of residual chlorine.

[0036] In the electrochemical measurement device 100 of this embodiment, the liquid contact surface 321 of the working electrode 32 and the liquid contact surface 341 of the counter electrode 34 are offset from each other along the direction in which the sensor flow path 22 extends, and are arranged so that parts of them face each other.

[0037] Specifically, both the working electrode 32 and the counter electrode 34 are disposed so that their liquid contact surfaces 321, 341 face the measurement flow path section 222, and the liquid contact surface 321 of the working electrode 32 and the liquid contact surface 341 of the counter electrode 34 face each other with a partial overlap across the measurement flow path section 222. The measurement flow path section 222 is formed to allow the sample liquid to flow upward, and the working electrode 32 and the counter electrode 34 are disposed so that their liquid contact surfaces 321, 341 are offset vertically along the measurement flow path section 222. Here, the working electrode 32 is disposed below (upstream), and the counter electrode 34 is disposed above (downstream).

[0038] Furthermore, recesses 22r are formed on the inner wall surface forming the measurement flow path section 222 at positions corresponding to the counter electrode 34 and the working electrode 32. The bottom of each recess 22r is formed by the liquid contact surface 321, 341 of the corresponding electrode 32, 34. The bottoms of the recesses 22r are offset along the extension direction of the measurement flow path section 222, and are arranged so that parts of the recesses 22r face each other (parts of the recesses 22r overlap and face each other). Note that "parts of the liquid contact surface 321 and the liquid contact surface 341 facing each other" means that parts of the liquid contact surfaces 321 and 341 face each other across the measurement flow path section 222, and these surfaces 321 and 341 may be parallel to each other or may be inclined relative to each other.

[0039] By arranging the working electrode 32 and the counter electrode 34 in this manner, the sample liquid flows upward in a meandering manner rather than flowing straight upward in the measurement flow path section 222. Furthermore, in the measurement flow path section 222, the sample liquid can be applied obliquely from the upstream side to the downstream side to the liquid-contacting surface 341 of the counter electrode 34. This generates turbulent flow of the sample liquid near the liquid-contacting surfaces 321, 341 of the working electrode 32 and the counter electrode 34, and allows air bubbles generated on the sensor surface 321 to be efficiently pushed toward the outlet 22b without accumulating.

[0040] Furthermore, the introduction channel section 221 of this embodiment is formed so that the sample liquid taken in through the introduction port 22a is directed perpendicularly (including at an angle close to perpendicular) or obliquely toward the liquid-contacting surface 321 of the working electrode 32. Here, the introduction channel section 221 is formed so that the sample liquid taken in through the introduction port 22a first flows upward, then changes direction to flow sideways, and the sample liquid hits the liquid-contacting surface 321 of the working electrode 32. By forming the introduction channel section 221 in this shape, the flow of the sample liquid that hits the liquid-contacting surface 321 of the working electrode 32 becomes turbulent, and air bubbles generated on the liquid-contacting surface 321 can be efficiently washed away. As a result, the measurement accuracy can be further improved.

[0041] According to the electrochemical measurement apparatus 100 of this embodiment configured as described above, the working electrode 32 and the counter electrode 34 are brought close enough that portions of their liquid-contacting surfaces 321, 341 face each other, thereby reducing the influence of external electromagnetic noise transmitted to the electrodes 32, 34 through the sample solution. Furthermore, the liquid-contacting surface 321 of the working electrode 32 and the liquid-contacting surface 341 of the counter electrode 34 are arranged so that they face each other in part but are offset from each other along the direction in which the flow path extends. This causes turbulence in the flow of the sample solution, allowing air bubbles generated on the liquid-contacting surface 321 of the working electrode 32 to escape downstream without being retained.

[0042] The present invention is not limited to the above-described embodiment.

[0043] For example, although the fluid cutoff unit 6 in the above embodiment is a roller pump, this is not limiting. The fluid cutoff unit 6 in other embodiments may be any device capable of completely cutting off the flow of sample liquid through the inlet flow path, such as a diaphragm pump or an on-off valve. Furthermore, the electrochemical measurement apparatus 100 in other embodiments may not be provided with a fluid cutoff unit 6 on the sample flow path 2.

[0044] 5, the electrochemical measurement apparatus 100 of another embodiment may include a second counter electrode 3435 upstream of the working electrode 32 and the counter electrode 34 in the sensor flow channel 22. A boron-doped diamond electrode may be used as this second counter electrode 3435, as with the downstream counter electrode 34. The second counter electrode 35 may be attached to the measurement cell 31, for example, so that its liquid-contacting surface comes into contact with the sample liquid flowing through the inlet flow channel section 221.

[0045] In the electrochemical measurement apparatus 100 of the above embodiment, the inlet flow path section 221 is formed so that the sample liquid taken in from the inlet 22a is applied perpendicularly or obliquely to the liquid contact surface 321 of the working electrode 32, but this is not limiting. In other embodiments, the inlet flow path section 221 may be formed so as to extend straight from bottom to top, as shown in Fig. 6 .

[0046] In the electrochemical measurement apparatus 100 of the above embodiment, the sample liquid is applied obliquely from the upstream side to the downstream side to the liquid contact surface 341 of the counter electrode 34 in the measurement flow path section 222, but this is not limited to this. In other embodiments, as shown in Fig. 7, the measurement flow path section 222 may be formed so that the sample liquid is applied perpendicularly (including at an angle close to perpendicularly) from the upstream side to the downstream side to the liquid contact surface 341 of the counter electrode 34.

[0047] In the above embodiment, the working electrode 32 is provided so as to be located upstream of the counter electrode 34, but this is not limited thereto. In other embodiments, the counter electrode 34 may be provided so as to be located upstream of the working electrode 32.

[0048] Furthermore, although the electrochemical measurement apparatus 100 in the above embodiment is of a three-electrode type, the present invention is not limited to this. The electrochemical measurement apparatus 100 in other embodiments may be of a two-electrode type, a four-electrode type, a six-electrode type, or the like.

[0049] In other embodiments of the electrochemical measurement device 100, the working electrode 32 is not limited to a boron-doped diamond electrode, but may also be a conductive diamond electrode doped with a Group 13 or Group 15 element such as nitrogen or phosphorus. The working electrode 32 is not limited to a diamond electrode, but may also be a carbon electrode containing carbon, such as a carbon electrode, glassy carbon electrode, or diamond-like carbon electrode, or an electrode made of a precious metal such as gold or platinum, or an alloy containing these precious metals. The reference electrode 33 in other embodiments is not limited to a silver / silver chloride electrode, but may also be, for example, a standard hydrogen electrode, a mercury / mercury chloride electrode, or a hydrogen palladium electrode. The counter electrode in other embodiments is not limited to a diamond electrode, but may also be, for example, a carbon, stainless steel, gold, silver, silver chloride, platinum, SnO2, or other electrode.

[0050] Furthermore, the substance to be measured in other embodiments is not limited to the aforementioned residual chlorine, but may be other inorganic substances such as ozone, bromine, hydrogen peroxide, etc. Furthermore, the electrochemical measurement apparatus 100 in other embodiments may be used not only in the food industry but also for various sample solutions such as tap water, drinking water, water from rivers and lakes, industrial wastewater, industrial waste liquids, laboratory reagents, human waste, water supply and sewage, medical reagents, cooling water for air conditioning, and leachate treatment.

[0051] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Industrial Applicability]

[0052] According to the present invention described above, in an electrochemical measurement apparatus, it is possible to reduce the retention of bubbles generated at the working electrode while reducing the influence of electromagnetic noise. [Explanation of symbols]

[0053] 100 Electrochemical measurement device 22 Sensor flow path 32...Working electrode 321... Wetted surface (sensor surface) 34 Counter electrode 341... Wetted surface

Claims

1. An electrochemical measurement device that electrochemically measures the concentration of a measurement target substance contained in a sample solution, a flow path through which the sample liquid flows; a working electrode and a counter electrode having liquid-contacting surfaces that come into contact with the sample liquid flowing through the flow path; a liquid-contacting surface of the working electrode and a liquid-contacting surface of the counter electrode are arranged so as to be offset from each other along the direction in which the flow path extends and so as to have parts of them directly face each other; a recess is formed in an inner wall surface forming the flow channel at a position corresponding to each of the counter electrode and the working electrode, The bottom surface of each recess is formed by the liquid-contacting surfaces of the working electrode and the counter electrode.

2. the flow path includes a measurement flow path portion facing a liquid-contacting surface of the working electrode and a liquid-contacting surface of the counter electrode, 2. The electrochemical measurement device according to claim 1, wherein the measurement flow path section is formed so that the sample liquid is applied perpendicularly or obliquely from the upstream side to the downstream side to the liquid contact surface of the working electrode or the counter electrode, which is arranged downstream.

3. 3. The electrochemical measurement apparatus according to claim 1, wherein the flow path is formed so that the sample liquid is applied perpendicularly or obliquely to the liquid-contacting surface of the working electrode.

4. the measurement flow path section is formed so as to allow the sample liquid to flow upward; 4. The electrochemical measurement device according to claim 2, wherein the liquid-contacting surface of the working electrode and the liquid-contacting surface of the counter electrode are vertically offset along the measurement flow path.

5. a fluid blocking unit capable of blocking the flow of the sample liquid, the fluid blocking unit being located upstream of the working electrode and the counter electrode in the flow path; 5. The electrochemical measurement device according to claim 1, wherein the device is configured to electrochemically measure the concentration of a substance to be measured contained in the sample liquid while the flow of the sample liquid is blocked by the fluid blocking unit.

6. 6. The electrochemical measurement apparatus according to claim 5, wherein the fluid blocking unit is a roller pump, a diaphragm pump, or an on-off valve.

7. 7. The electrochemical measurement device according to claim 1, wherein a second counter electrode is provided upstream of the working electrode and the counter electrode in the flow path.

8. 8. The electrochemical measurement apparatus according to claim 5, wherein the working electrode and the counter electrode are arranged in this order from upstream to downstream.

9. 1. An electrochemical measurement method for electrochemically measuring a concentration of a measurement target substance contained in a sample liquid using an electrochemical measurement device including a flow path through which a sample liquid flows, and a working electrode and a counter electrode having liquid-contacting surfaces that come into contact with the sample liquid flowing through the flow path, a liquid-contacting surface of the working electrode and a liquid-contacting surface of the counter electrode are displaced from each other along the direction in which the flow path extends, and are arranged so that parts of the working electrode and the counter electrode face each other; a recess formed in an inner wall surface forming the flow path at a position corresponding to each of the counter electrode and the working electrode, and a bottom surface of each recess formed by the liquid-contacting surface of each of the working electrode and the counter electrode.

10. An electrochemical measurement device for electrochemically measuring the concentration of a substance to be measured contained in a sample solution, comprising: a flow path through which the sample liquid flows; a working electrode and a counter electrode having liquid-contacting surfaces that come into contact with the sample liquid flowing through the flow path; a liquid-contacting surface of the working electrode and a liquid-contacting surface of the counter electrode are arranged so as to be offset from each other along the direction in which the flow path extends and so as to have parts of them directly face each other; the flow path includes a measurement flow path portion facing a liquid-contacting surface of the working electrode and a liquid-contacting surface of the counter electrode, An electrochemical measurement device in which the measurement flow path section is formed so that the sample liquid is applied vertically or obliquely from the upstream side to the downstream side to the liquid contact surface of the working electrode or the counter electrode, which is located downstream.

11. An electrochemical measurement method for electrochemically measuring the concentration of a substance to be measured contained in a sample liquid using an electrochemical measurement device comprising a flow path through which a sample liquid flows, and a working electrode and a counter electrode having liquid-contacting surfaces that come into contact with the sample liquid flowing through the flow path, a liquid-contacting surface of the working electrode and a liquid-contacting surface of the counter electrode are displaced from each other along the direction in which the flow path extends, and are arranged so that parts of the working electrode and the counter electrode face each other; a measurement flow path section facing the liquid contact surface of the working electrode and the liquid contact surface of the counter electrode in the flow path is formed so that the sample liquid is applied perpendicularly or obliquely from the upstream side to the downstream side to the liquid contact surface of the working electrode or the counter electrode, which is arranged downstream.

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