JPWO2017150107A1 - Ion concentration measuring apparatus and ion concentration measuring method - Google Patents

Abstract

The ion concentration measuring apparatus 1 suppresses the influence of noise and directly measures the ion concentration contained in the measurement object. Specifically, the ion concentration measurement apparatus 1 obtains the concentration of potassium ions 102 present in the measurement object 100. The ion concentration measurement apparatus 1 includes a first electrode unit 2, a voltage generation unit 6, a sensor unit 3 that generates a current corresponding to a voltage provided to the measurement object 100, and a current output from the sensor unit 3. And a control unit 8 that obtains the concentration of potassium ions 102 based thereon. The control unit 8 includes a first current value (C1) generated by the sensor unit 3 when a positive voltage is provided, and a second current value generated by the sensor unit 3 when a negative voltage is provided. Based on the difference (ΔC), the current value acquisition unit 17 for obtaining (C2), the difference acquisition unit 18 for obtaining the difference (ΔC) between the first current value (C1) and the second current value (C2). A concentration acquisition unit 19 for obtaining an ion concentration (T).

Description

  The present invention relates to an ion concentration measuring apparatus and an ion concentration measuring method for obtaining an ion concentration present in a measurement object.

  In the agricultural field, so-called functional vegetables containing a large amount of specific components have attracted attention. Recent research results indicate that there is a relationship between ingredients in vegetables and specific ions in the soil. Known techniques for measuring the concentration of specific ions include, for example, a flame photometer and liquid chromatography.

  Furthermore, in the field using ion concentration measurement technology, simplification of measurement work has been desired. Such a technique includes a technique of collecting a sample from soil or a medium and measuring the ion concentration using the sample. For example, a portable potassium ion measuring instrument collects water in soil using a dropper and measures the ion concentration using the water. A measuring instrument using an oxidation-reduction reaction is also known.

R. Ishimatsu, A. Izadyar, B. Kabagambe, Y. Kim, J. Kim, and S. Amemiya, J. Am. Chem. Soc., Vol. 133, Issue 40, pp. 16300-16308, 2011. S. Mizutani, S. Takahashi, A. Kono, T. Hattori, T. Iwata, M. Ishida, K. Sawada, IEEE Sensors 2015 Conference, Busan, South Korea, Nov. 1-4, 2015.

  However, measurement by sampling requires labor for sampling and measurement work. Therefore, measurement by sampling is not suitable for applications in which the ion concentration in the soil is continuously monitored. Therefore, a technique for measuring the ion concentration by placing a measuring instrument on the soil itself has been studied. As a technique for measuring such an ion concentration, there is a technique of selecting an ion to be measured using an ion selective membrane and obtaining the concentration of the selected ion using a voltage or a current.

  The measurement range of a method using voltage (hereinafter referred to as “voltage detection type”) is about 10 μmol to 0.1 mol per unit volume (1 liter). On the other hand, the voltage detection type has a small change in voltage with respect to a change in ion concentration. Therefore, it is difficult to detect minute changes in ion concentration. Specifically, in the voltage detection type, the change in voltage when the ion concentration is changed by one digit is theoretically 59 mV. Therefore, the measurement using the voltage detection type is easily affected by noise.

  A method using current (hereinafter referred to as “current detection type”) uses a redox current. For example, as a technology relating to a current detection type, a PEDOT structure (Non-Patent Document 1) and a current detection type sensor (Non-Patent Document 2) using the PEDOT structure are known. In the current detection type, the current value is proportional to the ion concentration. Therefore, the current detection type has a higher resolution than the voltage detection type. However, in the measurement using the current detection type, the ion concentration is obtained by using the peak of the current. Therefore, the measurement using the current detection type is easily affected by spike noise.

  An object of the present invention is to provide an ion concentration measuring apparatus and an ion concentration measuring method capable of suppressing the influence of noise and directly measuring the ion concentration contained in a measurement object.

  An ion concentration measurement apparatus according to an aspect of the present invention provides a first electrode unit that alternately provides a positive voltage and a negative voltage to a measurement target, a voltage generation unit that generates a voltage, and a measurement target. A sensor unit that generates a current based on ions that are selectively captured in response to a provided voltage, and controls the voltage generation unit and is present in the measurement object based on the current output from the sensor unit. A control unit that obtains a concentration of ions, and the control unit provides a first current value generated by the sensor unit when a positive voltage is provided to the measurement target and a negative voltage provided to the measurement target. A second current value generated by the sensor unit when the current value is obtained, a difference value obtaining unit for obtaining a difference between the first current value and the second current value, and an ion based on the difference And a density acquisition unit for obtaining the density of

  In this measuring apparatus, a positive voltage and a negative voltage generated by the voltage generation unit are provided from the first electrode unit to the measurement object. The sensor unit generates an electric current based on ions that are selectively captured in response to a voltage provided to the measurement object. Therefore, this measuring apparatus can detect a current detection type ion concentration. According to this detection configuration, the influence of the charge of the measurement object is suppressed. Therefore, the measuring apparatus can reduce the influence of noise. Furthermore, the measuring device uses the difference between the first current value when a positive voltage is provided to the measurement object and the second current value when a negative voltage is provided to the measurement object. , Get the ion concentration. If this difference is used, it is possible to cancel the noise superimposed on the first current value and the second current value. Therefore, the measuring apparatus can further reduce the influence of noise. Therefore, the measurement apparatus has two configurations that reduce the influence of noise. Therefore, the measurement apparatus can directly measure the ion concentration contained in the measurement object even in an environment where a lot of noise occurs.

  The sensor unit includes a capture unit including an ionophore that selectively captures ions, and is electrically connected to the capture unit, and provides a mediator ion corresponding to the ions captured by the capture unit to the capture unit. A conductive part to be recovered from the capturing part, and electrically connected to the conductive part and the ground part, respectively, provide electrons corresponding to the mediating ions provided to the capturing part to the conductive part, and collect electrons from the conductive part. 2 electrode portions. According to this configuration, in the case of detecting cations as an example, when ions are captured by the capturing unit, the mediating ions corresponding to the supplemental ions are provided from the conductive unit to the capturing unit. Then, electrons corresponding to the mediating ions provided to the trapping part are provided from the ground part to the conductive part via the second electrode part. On the other hand, when ions are released from the capture unit, the mediating ions corresponding to the released ions are collected from the capture unit to the conductive unit. Then, the electrons corresponding to the mediating ions collected by the conductive part move from the second electrode part to the ground part. Therefore, the ions captured by the capturing unit can be obtained as the value of the current flowing between the ground unit and the second electrode unit. Further, the ions released from the capturing unit can be obtained as the value of the current flowing between the grounding unit and the second electrode unit. The anion detection method is the opposite. Therefore, the measuring apparatus can detect the current detection type ion concentration.

  The sensor unit further includes a substrate, the second electrode unit is provided on the substrate, the conductive unit is provided on the second electrode unit, and the substrate, the second electrode unit, and the conductive unit include a substrate. A through hole extending from the back surface of the conductive portion to the main surface of the conductive portion may be provided, and the capturing portion may be provided integrally with the main surface of the conductive portion, the through hole, and the back surface of the substrate. According to this capturing part, the capturing part provided on the main surface side of the conductive part and the capturing part provided on the back surface side of the substrate are connected by the capturing part provided in the through hole. Therefore, the second electrode portion and the conductive portion are wrapped by the integrated capturing portion. According to this structure, when insertion and extraction of the sensor unit with respect to the measurement object are repeated, the generation of a gap between the second electrode unit and the conductive unit is suppressed. Therefore, it is possible to maintain an electrical connection between the second electrode portion and the conductive portion. Therefore, the measuring device can maintain the function of the sensor unit for a long period of time.

  The conductive portion may include a conductive polymer that can reversibly exchange electrons and ions. According to this configuration, it is possible to suitably provide the mediating ions to the capturing unit. Furthermore, according to this configuration, the mediating ions can be recovered from the capturing unit.

  An ion concentration measurement method according to another aspect of the present invention provides ions to be selectively captured in response to a positive voltage by providing the measurement object with a positive voltage via the first electrode unit. A step of obtaining a first current value generated by the sensor unit that generates a current based on the second current generated by the sensor unit by providing a negative voltage to the measurement object via the first electrode unit; Obtaining a value, obtaining a difference between the first current value and the second current value, and obtaining an ion concentration based on the difference.

  In this measurement method, when a positive voltage is provided to the measurement object, a first current value corresponding to the ions captured by the capturing unit is obtained. Further, when a negative voltage is provided to the measurement object, a second current value corresponding to the ions released from the capturing unit is obtained. Therefore, this measurement method detects the ion concentration of the current detection type in which the ions captured by the capturing unit and the ions released from the capturing unit are obtained as values of the current flowing between the ground unit and the second electrode unit. It can be carried out. According to this measurement method, since the influence of the charge of the measurement object is suppressed, the influence of noise can be reduced. Further, in this measurement method, the ion concentration is obtained by using the difference between the first current value and the second current value. According to the step of obtaining the difference, the noise superimposed on the first current value and the second current value is canceled out. Therefore, the influence of noise can be further reduced. Therefore, according to this measuring apparatus, since it has two actions to reduce the influence of noise, it is possible to directly measure the ion concentration contained in the measurement object even in an environment where a lot of noise occurs.

  ADVANTAGE OF THE INVENTION According to this invention, the influence of noise is suppressed and the ion concentration measuring apparatus and ion concentration measuring method which can measure the ion concentration contained in the measurement object directly are provided.

FIG. 1 is a functional block diagram illustrating a configuration of an ion concentration measurement apparatus according to the embodiment. FIG. 2 is a perspective view showing a specific structure of the sensor unit. FIG. 3 is a diagram illustrating a cross section of the sensor unit. FIG. 4 is a diagram illustrating the relationship between the voltage provided to the measurement object and the current output from the sensor unit. FIG. 5 is a flowchart showing main steps of the ion concentration measurement method according to the embodiment. 6A is a diagram for explaining the operation of the sensor unit when a positive voltage is provided to the measurement object, and FIG. 6B provides a negative voltage to the measurement object. It is a figure for demonstrating operation | movement of the sensor part when it does. FIG. 7 is a graph showing the results according to Experimental Example 1. Part (a) of FIG. 7 shows the voltage provided to the measurement object, and part (b) of FIG. 7 shows the ion concentration in the solution. FIG. 7C is a diagram showing the current output from the sensor unit. FIG. 8 is a graph showing the relationship between the ion concentration in the solution and the current output from the sensor unit. FIG. 9 is a diagram for explaining a model according to Experimental Example 2. FIG. 10 is a graph showing the results of Experimental Example 3. FIG. 11 is a graph showing the results of Experimental Example 4.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals. In addition, redundant description is omitted.

  As shown in FIG. 1, the ion concentration measurement apparatus 1 obtains the concentration of ions contained in the measurement object 100. The measurement object 100 includes water 101. The water 101 contains ions. The measurement object 100 is, for example, soil in which agricultural products are planted. The soil contains a predetermined amount of water. This water contains various ions such as potassium ions 102. Hereinafter, the ion concentration measuring apparatus 1 according to the present embodiment will be described using the ion concentration measuring apparatus 1 that measures the concentration of potassium ions 102 in the soil as an example. The ions measured by the ion concentration measuring device 1 are not limited to potassium ions. As ions to be measured, desired ions can be selected according to the purpose of measurement. The ion concentration (T) is the amount (or number of moles) of ions contained per unit volume. In the following description, the unit volume is 1 liter. The amount (or mole) (mol) of potassium ions contained per liter is defined as the ion concentration (mol / L).

  The ion concentration measurement apparatus 1 includes a first electrode unit 2, a sensor unit 3, and a measurement unit 4 as physical components. The measurement unit 4 includes a voltage generation unit 6, an ammeter 7, and a control unit 8.

  The first electrode unit 2 is disposed inside the measurement object 100. The first electrode unit 2 provides a predetermined voltage to the measurement object 100. The first electrode unit 2 is made of, for example, platinum. In addition, the 1st electrode part 2 may be comprised with a glass reference electrode or gold | metal | money. The first electrode unit 2 provides a voltage to the water 101 in the soil that is the measurement object 100. A voltage generation unit 6 is connected to the first electrode unit 2. The voltage generator 6 generates a positive pulse voltage or a negative pulse voltage. The voltage generator 6 provides a positive pulse voltage or a negative pulse voltage to the first electrode unit 2. The voltage provided from the first electrode unit 2 to the measurement object 100 is provided from the voltage generation unit 6. The first electrode unit 2 repeatedly supplies a positive voltage (E1) and a negative voltage (E2) to the measurement object 100 alternately. For example, the first electrode unit 2 provides +0.5 mV as the positive voltage (E1). Moreover, the 1st electrode part 2 provides -0.5mV as a negative voltage (E2) (refer the (a) part of FIG. 7). A positive voltage (E1) and a negative voltage (E2) are repeatedly and alternately provided. The period is 100 seconds as an example.

  The sensor unit 3 is separated from the first electrode unit 2 inside the measurement object 100. Therefore, a part of the measurement object 100 is disposed between the sensor unit 3 and the first electrode unit 2. Specifically, water 101 in soil is disposed between the sensor unit 3 and the first electrode unit 2. The sensor unit 3 generates a current. This current corresponds to the voltage provided from the first electrode unit 2 to the measurement object 100. Further, the value of this current is acquired by an ammeter 7 connected to the sensor unit 3. The sensor unit 3 includes a capturing unit 9, a conductive unit 11, and a second electrode unit 12.

The trap 9 selectively captures ions present in the water. That is, the trap 9 is an ion selective functional membrane. The capturing unit 9 is configured by a base material including an ionophore. A substrate containing an ionophore has a function of selectively capturing ions. As an example, the capturing unit 9 selectively captures potassium ions 102. Therefore, the trap 9 is a potassium ion sensitive membrane. An example of an ionophore that selectively captures potassium ions is valinomycin. The trap 9 includes a dopant. The dopant includes tetra n-butylammonium perchlorate (TBAClO ₄ ).

The conductive part 11 provides a mediating ion to the capturing part 9. In addition, the conductive part 11 recovers the mediating ions from the capturing part 9. The conductive part 11 is made of a conductive polymer material. The conductive polymer material reversibly exchanges electrons and ions. Examples of the conductive polymer material include polyethylene dioxythiophene (PEDOT). The conductive part 11 includes a dopant. Examples of the dopant include tetra n-butylammonium perchlorate (TBAClO ₄ ).

  The second electrode unit 12 is connected to the ground unit 13 via the ammeter 7. The ammeter 7 is disposed outside the measurement object 100. The second electrode unit 12 provides electrons to the conductive unit 11. The second electrode unit 12 collects electrons from the conductive unit 11. The 2nd electrode part 12 is comprised with the metal material which has electroconductivity. Examples of the metal material include gold, copper, and aluminum.

  When a positive voltage (E1) is provided to the first electrode unit 2, potassium ions 102 having a positive charge are captured by the capturing unit 9. When the potassium ion 102 is captured by the capturing unit 9, the capturing unit 9 is charged to a positive potential. In order to cancel the positive charge in the capturing unit, the conductive unit 11 provides a mediating ion having a negative potential to the capturing unit 9. When the conductive part 11 provides the mediating ions to the trapping part 9, the conductive part 11 is charged to a positive potential. The second electrode portion 12 provides electrons having a negative charge to the conductive portion 11 so as to cancel the positive charge in the conductive portion 11. The electrons are provided from the ground unit 13. An ammeter 7 is provided between the ground unit 13 and the second electrode unit 12. Therefore, a current is generated when electrons are provided from the ground unit 13 to the second electrode unit 12. The magnitude of this current corresponds to the amount of potassium ions 102 captured by the capturing unit 9. Therefore, the concentration of potassium ions 102 can be obtained by using the magnitude of the current acquired by the ammeter 7.

  Here, a specific structure of the sensor unit 3 is illustrated. As shown in FIG. 2, the sensor unit 3 further includes a circuit board 14 in addition to the capturing unit 9, the conductive unit 11, and the second electrode unit 12 described above. The circuit board 14 includes a conductive pattern. The conductive pattern ensures electrical connection between the second electrode portion 12 and the ammeter 7. Further, the circuit board 14 is inserted into the measurement object 100. Therefore, the tip of the circuit board 14 has a sharp shape. According to this shape, the circuit board 14 can be easily inserted into the soil. The circuit board 14 has a thin plate shape. On the main surface 14 a of the circuit board 14, the circular second electrode portion 12 is provided. The shape of the second electrode portion 12 is not limited to a circle. The second electrode unit 12 may have a desired shape such as a rectangular shape. For example, the second electrode portion 12 may be a land provided on the main surface 14a. A circular conductive part 11 is provided on the second electrode part 12. The conductive part 11 is formed by electroless plating as an example.

  As shown in FIG. 3, the capturing unit 9 includes a capturing surface 9a and a first connecting surface 9b. The capture surface 9 a contacts the measurement object 100. The first connection surface 9b is a surface opposite to the capturing surface 9a. The conductive portion 11 has a second connection surface 11a and a third connection surface 11b. The 3rd connection surface 11b is a surface on the opposite side to the 2nd connection surface 11a. The second connection surface 11 a faces the first connection surface 9 b of the capturing unit 9. The second connection surface 11a is electrically connected to the first connection surface 9b. The second electrode portion 12 has a fifth connection surface 12a. The fifth connection surface 12 a faces the third connection surface 11 b of the conductive portion 11. The fifth connection surface 12a is electrically connected to the third connection surface 11b.

  The plurality of through holes 21 are provided in the circuit board 14, the second electrode part 12, and the conductive part 11, respectively. Specifically, the plurality of through holes 21 include a hole portion 14c, a hole portion 12c, and a hole portion 11c. The hole 14 c is provided in the circuit board 14. The hole portion 12 c is provided in the second electrode portion 12. The hole portion 11 c is provided in the conductive portion 11. The through hole 21 extends from the second connection surface 11 a of the conductive portion 11 to the back surface 14 b of the circuit board 14.

  The capturing unit 9 is provided so as to cover the circuit board 14, the second electrode unit 12, and the conductive unit 11. Specifically, the capturing unit 9 is formed on the main surface 14 a of the circuit board 14, the second connection surface 11 a of the conductive unit 11, the inside of the through hole 21, and the back surface 14 b of the circuit board 14. Provided. Therefore, the capturing unit 9 provided on the second connection surface 11 a of the conductive unit 11 has a function of capturing the potassium ions 102 in the sensor unit 3. The capturing part 9 provided in the above-described place is integrated.

  Here, the second electrode portion 12 is formed of a metal material. On the other hand, the conductive portion 11 is formed of a polymer material. Therefore, it is difficult to increase the bonding strength between the second electrode portion 12 and the conductive portion 11. According to the capturing part 9 described above, the capturing part 9 provided on the second connection surface 11 a side of the conductive part 11 and the capturing part 9 provided on the back surface 14 b side of the circuit board 14 are provided in the through hole 21. It can also be said that they are connected by the captured part 9. Then, the second electrode portion 12 and the conductive portion 11 are integrated and wrapped by the capturing portion 9 that is difficult to peel off from the circuit board 14. Therefore, when the insertion and extraction of the sensor unit 3 with respect to the soil that is the measurement target 100 is repeated, the generation of a gap between the second electrode unit 12 and the conductive unit 11 is suppressed. Therefore, the ion concentration measuring apparatus 1 can maintain the function of the sensor unit 3 for a long period of time.

  As shown in FIG. 1, the controller 8 controls the operation of the voltage generator 6. Further, the control unit 8 obtains the concentration of potassium ions 102 based on the current value provided from the ammeter 7. The control unit 8 is a computer system as an example. The control unit 8 is physically a main storage device such as a CPU (Central Processing Unit), a RAM (Random Access Memory) and a ROM (Read Only Memory), an input device such as a keyboard, an output device such as a display, a hard disk, etc. It is configured as a normal computer system including an auxiliary storage device. Each function of the control unit 8 to be described later is to operate a input device and an output device under the control of the CPU by reading predetermined computer software on hardware such as a CPU, RAM, ROM, etc. Or by reading and writing data in an auxiliary storage device.

  The control unit 8 includes a recording unit 16, a current value acquisition unit 17, a difference acquisition unit 18, and a concentration acquisition unit 19 as functional components. The recording unit 16 is, for example, a ROM. The recording unit 16 records the current value provided from the ammeter 7 and the drive signal provided to the voltage generation unit 6 in association with each other. The recording unit 16 records the conversion coefficient (D). The conversion coefficient (D) is used to obtain the ion concentration (T) using the current value. The recording unit 16 is connected to the ammeter 7. The recording unit 16 receives the current value. The recording unit 16 is connected to the voltage generation unit 6. The recording unit 16 receives the drive signal. The recording unit 16 is connected to the current value acquisition unit 17. Then, the recording unit 16 provides the drive signal and the current value associated with each other to the current value acquisition unit 17. The recording unit 16 is connected to the density acquisition unit 19. Then, the recording unit 16 provides the conversion coefficient (D) to the density acquisition unit 19.

  The current value acquisition unit 17 obtains a current value. This current value is for obtaining a difference (ΔC) in the current value necessary for obtaining the ion concentration (T). The current value acquisition unit 17 is connected to the recording unit 16. The current value acquisition unit 17 obtains information in which the time and the current value are associated with each other. Note that the current value acquisition unit 17 may obtain information in which the drive signal and the current value are associated with each other. The current value acquisition unit 17 obtains a first current value (C1) and a second current value (C2). The current value acquisition unit 17 outputs the first current value (C1) and the second current value (C2) to the difference acquisition unit 18.

  The first current value (C1) is a value of a current generated in the sensor unit 3 when a positive voltage (E1) is provided to the first electrode unit 2. Specifically, the first current value (C1) is a current value at a timing immediately before switching from the positive voltage (E1) to the negative voltage (E2). The second current value (C2) is a value of a current generated in the sensor unit 3 when a negative voltage (E2) is provided to the first electrode unit 2. Specifically, the second current value (C2) is a current value at a timing immediately before switching from the negative voltage (E2) to the positive voltage (E1).

  The difference acquisition unit 18 obtains a difference (ΔC) in current values necessary for acquiring the ion concentration (T). The difference acquisition unit 18 is connected to the current value acquisition unit 17. Then, the difference acquisition unit 18 receives the first current value (C1) and the second current value (C2). The difference acquisition unit 18 calculates a difference (ΔC = C1−C2) between the first current value (C1) and the second current value (C2). The difference acquisition unit 18 outputs the difference (ΔC) to the concentration acquisition unit 19.

  The concentration acquisition unit 19 obtains the ion concentration (T). The density acquisition unit 19 is connected to the recording unit 16. The density acquisition unit 19 receives the conversion coefficient (D). Further, the density acquisition unit 19 is connected to the difference acquisition unit 18. The density acquisition unit 19 receives the difference (ΔC). The concentration acquisition unit 19 obtains the ion concentration (T = D × ΔC) using the conversion coefficient (D) and the difference (ΔC). The concentration acquisition unit 19 outputs the ion concentration (T) to the recording unit 16. Here, the conversion coefficient (D) is a coefficient for converting the difference (ΔC) in the current value into the density (T). The conversion coefficient (D) is acquired in advance by performing a preliminary test. Then, the conversion coefficient (D) is recorded in the recording unit 16.

  Next, an ion concentration (T) measurement method using the ion concentration measurement apparatus 1 will be described with reference to FIGS. 4, 5, and 6.

  First, the 1st electrode part 2 and the sensor part 3 are arrange | positioned inside the measurement object 100 (FIG. 5: step S1). For example, when the 1st electrode part 2 and the sensor part 3 are rod-shaped, they are each inserted in the soil which is the measuring object 100. FIG. At this time, the first electrode unit 2 and the sensor unit 3 are separated from each other by about 1 cm.

  Next, a positive voltage (E1) is provided to the measurement object 100 (FIG. 5: Step S2). This step S <b> 2 is performed by the control unit 8, the voltage generation unit 6, and the first electrode unit 2. The control unit 8 provides a drive signal. This drive signal includes information that causes the voltage generator 6 to output a positive voltage (E1). The voltage generator 6 generates a positive voltage (E1) based on the drive signal. The voltage generator 6 is provided to the first electrode unit 2. Then, the first electrode unit 2 provides a positive voltage (E1) to the measurement object 100.

  Here, the operation of the sensor unit 3 when a positive voltage (E1) is provided to the measurement object 100 will be described in detail.

  As shown in part (a) of FIG. 6, the measurement object 100 has potassium ions 102. The potassium ion 102 has a positive charge. This potassium ion 102 is a measurement target of the measurement method according to the present embodiment. When a positive voltage (E1) is provided to the first electrode unit 2, the potassium ions 102 having a positive charge move away from the first electrode unit 2. The potassium ions 102 are captured by the capturing unit 9 of the sensor unit 3. Here, the capturing unit 9 includes an ionophore 22 that selectively captures potassium ions 102. Therefore, another ion different from the potassium ion 102 is not captured by the capturing unit 9.

When the potassium ion 102 is captured by the capture unit 9, the capture unit 9 has a positive charge. At this time, mediating ions are provided from the conductive portion 11 to the capturing portion 9 so as to eliminate the charging of the capturing portion 9. The mediator ion has a negative charge. The mediating ion in this embodiment is a chlorine ion 104. The chlorine ions 104 are based on TBACLO ₄ doped in the trap 9 and the conductive portion 11. When chlorine ions 104 having a negative charge are provided from the conductive part 11 to the capturing part 9, the conductive part 11 has a positive charge. At this time, the electrons 103 are provided from the second electrode portion 12 to the conductive portion 11 so as to eliminate the charging of the conductive portion 11. The electrons 103 are provided from the ground unit 13. When the electrons 103 move from the ground unit 13 to the second electrode unit 12, a current is generated. The magnitude of the current is obtained by the ammeter 7. The ammeter 7 is disposed between the ground unit 13 and the second electrode unit 12. The current value obtained by the ammeter 7 is output to the control unit 8.

  Next, a first current value (C1) is obtained (FIG. 5: Step S3). This step S3 is performed by the sensor unit 3, the ammeter 7, and the current value acquisition unit 17 of the control unit 8. The control unit 8 acquires the current value output from the sensor unit 3 using the ammeter 7 over a period in which the positive voltage (E1) is provided. Then, the control unit 8 stores the acquired current value in the recording unit 16. As shown in part (b) of FIG. 4, the absolute value of the current value recorded in the recording unit 16 increases in a spike shape immediately after providing the positive voltage (E1). Thereafter, the absolute value of the current value decreases exponentially. Then, the absolute value of the current value converges to a predetermined value. In step S3, the current value acquisition unit 17 converges the value (point P1) as the first current value (C1). Various methods can be used to obtain the converged value (point P1) as the first current value (C1). For example, you may obtain the average of the electric current value in a convergence period. Further, the current value immediately before switching from the positive voltage (E1) to the negative voltage (E2) may be obtained.

  Next, a negative voltage (E2) is provided to the measurement object 100 (FIG. 5: Step S4). This step S4 is performed by the control unit 8, the voltage generation unit 6, and the first electrode unit 2. The control unit 8 provides a drive signal. This drive signal includes information that causes the voltage generator 6 to output a negative voltage (E2). The voltage generator 6 generates a negative voltage (E2) based on the drive signal. The voltage generator 6 is provided to the first electrode unit 2. The first electrode unit 2 provides the measurement object 100 with a negative voltage (E2).

  Here, the operation of the sensor unit 3 when a negative voltage (E2) is provided to the measurement object 100 will be described in detail. When a negative voltage (E2) is provided, an operation opposite to that when a positive voltage (E1) is provided is performed.

  As shown in part (b) of FIG. 6, the potassium ions 102 are captured by the capturing unit 9 immediately before the negative voltage (E2) is provided. And when the negative voltage (E2) is provided to the 1st electrode part 2, the potassium ion 102 which has a positive charge is attracted to the 1st electrode part 2 to which the negative voltage (E2) was provided. . That is, the potassium ions 102 are released from the capturing unit 9. When the potassium ions 102 are released from the capturing unit 9, the chlorine ions 104 are collected by the conductive unit 11. Chlorine ions 104 are present in the capture unit 9 in order to keep the potential balance of the capture unit 9 balanced. When the chlorine ions 104 are recovered by the conductive portion 11, the electrons 103 are recovered by the second electrode portion 12. The electrons 103 exist in the conductive part 11 in order to keep the balance of the potential of the conductive part 11. The electrons 103 collected by the second electrode unit 12 move to the ground unit 13. The movement of electrons from the second electrode portion 12 to the ground portion 13 generates a current. This direction of current is opposite to the direction of current that occurs when a positive voltage (E1) is provided. The magnitude of the current is obtained by the ammeter 7. The ammeter 7 is disposed between the second electrode portion 12 and the ground portion 13. The current value obtained by the ammeter 7 is output to the control unit 8.

  Next, a second current value (C2) is obtained (FIG. 5: Step S5). This step S5 is performed by the sensor unit 3, the ammeter 7, and the current value acquisition unit 17 of the control unit 8. The control unit 8 acquires the current value output from the sensor unit 3 using the ammeter 7 over a period during which the negative voltage (E2) is provided. Then, the control unit 8 stores the acquired current value in the recording unit 16. As shown in part (b) of FIG. 4, the absolute value of the current value recorded in the recording unit 16 increases in a spike shape immediately after providing the negative voltage (E2). Thereafter, the absolute value of the current value decreases exponentially. Then, the absolute value of the current value converges to a predetermined value. In step S5, the current value acquisition unit 17 converges the value (point P2) as the second current value (C2).

  Next, a difference (ΔC) in current value is obtained (FIG. 5: Step S6). This step S6 is performed by the difference acquisition unit 18 of the control unit 8. The difference acquisition unit 18 obtains a difference (ΔC = C1−C2) between the first current value (C1) and the second current value (C2).

  Next, an ion concentration (T) is obtained (FIG. 5: Step S7). This step S7 is performed by the density acquisition unit 19 of the control unit 8. The concentration acquisition unit 19 uses the difference (ΔC) and the conversion coefficient (D) to obtain the concentration of potassium ions 102 (T = D × ΔC).

  By performing the above steps S1 to S7, the concentration of the potassium ion 102 is obtained.

  In the ion concentration measuring apparatus 1 and the ion concentration measuring method according to the present embodiment, when the potassium ions 102 are captured by the capturing unit 9, chlorine ions 104 are provided from the conductive unit 11 to the capturing unit 9. Chlorine ions 104 correspond to the number of potassium ions 102. The number of chlorine ions 104 provided to the capture unit 9 corresponds to the electrons 103. The electrons 103 are provided from the ground unit 13 to the conductive unit 11 via the second electrode unit 12. On the other hand, when the potassium ions 102 are released from the capturing unit 9, the chlorine ions 104 are collected from the capturing unit 9 to the conductive unit 11. The number of chlorine ions 104 collected in the conductive part 11 corresponds to the electrons 103. The electrons 103 move from the second electrode unit 12 to the ground unit 13. Therefore, by obtaining the number of potassium ions 102 captured by the capturing unit 9 and the number of potassium ions 102 released from the capturing unit 9, the value of the current flowing between the ground unit 13 and the second electrode unit 12 is obtained. Is obtained. Therefore, the ion concentration measuring apparatus 1 can detect the current detection type ion concentration (T). According to this structure, the influence of the electric charge which the measurement object 100 has is suppressed. Therefore, the ion concentration measuring apparatus 1 can reduce the influence of noise. Further, the ion concentration measuring apparatus 1 provides the first current value (C1) when a positive voltage (E1) is provided to the measurement object 100 and the negative voltage (E2) to the measurement object 100. The ion concentration (T) is obtained by utilizing the difference (ΔC) between the second current value (C2) at the time. According to this difference (ΔC), it is possible to cancel noise superimposed on the first current value (C1) and the second current value (C2). Therefore, the ion concentration measuring apparatus 1 can further reduce the influence of noise. The ion concentration measuring apparatus 1 has two configurations that reduce the influence of noise. Therefore, the ion concentration measuring apparatus 1 can directly measure the ion concentration (T) contained in the measurement object 100 even in an environment where a lot of noise occurs. That is, the ion concentration measuring apparatus 1 can perform on-site real-time measurement of the ion concentration.

  Here, the water 101 contained in the soil that is the measurement object 100 may have a predetermined charge. For example, when the ion concentration (T) is obtained by using a voltage detection type measurement device, the influence of the charge of water is also included in the measurement value. Therefore, first, water is collected as a measurement sample. Subsequently, the collected water is left for a predetermined time. As a result, the water charge is discharged. Then, after standing, the ion concentration (T) is measured. Therefore, the voltage detection type measuring device is not suitable for continuously measuring the ion concentration (T) in the soil. Moreover, the state of water in the soil changes due to irrigation. For example, the state of charge of water changes due to irrigation or the like. Therefore, the measurement value of the measurement device may fluctuate every time it is measured.

  On the other hand, the ion concentration measurement apparatus 1 and the ion concentration measurement method according to the present embodiment are current detection type apparatuses and methods that obtain an ion concentration (T) as a current value. Therefore, the ion concentration measuring apparatus 1 and the ion concentration measuring method can reduce the influence of the electric charge that the measurement object 100 has. Therefore, the ion concentration measuring apparatus 1 and the ion concentration measuring method can stably obtain the ion concentration (T) even in an environment where water in the measurement object 100 moves with time.

  The present invention is not limited to the embodiment described above. The present invention can be variously modified without departing from the gist of the present invention.

  The ion absorption rate of plants and the like is also related to the ratio between a plurality of ions. Although the mineral sensor which concerns on this embodiment can acquire the absolute value of specific ion concentration, the method of arrange | positioning multiple types of sensors in a sensor part and performing data processing by the ratio can also be performed.

  The apparatus and method according to the present embodiment have a feature that measurement is possible when the amount of water is smaller than 100%, such as in a culture medium. When measuring the inside of a medium with a water content smaller than 100%, the data can be converted to data with a water content of 100%, that is, only the solution by interpolating the measurement data using a water content sensor. Thereby, measurement data can be used for the preparation of the fertilizer for additional fertilization. For example, when the moisture content is 50% and the measurement data is obtained as 1 mmol / L, 1 / 0.5 = 2 mmol / L can be calculated as the concentration when the solution is 100%.

  The apparatus according to the present embodiment may further include an EC sensor that can measure the total ion concentration in the present sensor that measures the specific ion concentration. According to this EC sensor, the ratio to the total ion concentration can be calculated. Thereby, specific ion concentration adjustment can be added to appropriate fertilizer concentration (overall ion concentration) management.

  The apparatus according to the present embodiment may appropriately select the above-described configuration according to the purpose. Furthermore, the apparatus according to the present embodiment may have all the above-described configurations.

<Experimental example 1>
In Experimental Example 1, the ion concentration measuring device 1 was used to confirm the relationship between the ion concentration (T) and the difference (ΔC). In Experimental Example 1, as shown in part (a) of FIG. 7, a positive voltage (E1: +0.5 V) and a negative voltage (E2: −0.5 V) are repeatedly provided to the measurement object 100. did. The period is 100 seconds. The ion concentration (T) of the measurement object 100 provided with such a voltage is set to a first concentration (T: 0.1 mM), a second concentration (T: 1.0 mM), and a third concentration (T: 5 mM) and the fourth concentration (T: 10 mM) was changed stepwise (see part (b) of FIG. 7). As a result, a time history of the current value shown in part (c) of FIG. 7 was obtained.

  A first current value (C1: (+0.143 μA)) and a second current value (C2: −0.17 μA) at the first concentration (T: 0.1 mM) were obtained. A difference of 1 (ΔC1: 0.31 μA) was obtained, and the first current value (C1: +0.15 μA) at the second concentration (T: 1.0 mM) and the second current value (C2: -0.18 μA) and a second difference (ΔC2: 0.33 μA), a first current value (C1: at a third concentration (T: 5.0 mM)). +0.20 μA) and a second current value (C2: −0.56 μA), and a third difference (ΔC3: 0.76 μA) was obtained at a fourth concentration (T: 10 mM). A first current value (C1: +0.45 μA) and a second current value (C2: −1.40 μA) were obtained, and a third difference (ΔC3: .85Myuei) was obtained. As a result, according to the ion concentration (T) increases, the difference ([Delta] C) was also found to increase.

<Experimental example 2>
In Experimental Example 2, the relationship between the ion concentration (T) and the difference (ΔC) was confirmed using the ion concentration measurement apparatus 1. FIG. 8 is a graph showing the ion concentration (T) and the difference between current values (ΔC). As shown in FIG. 8, it was confirmed that there is a proportional relationship between the ion concentration (T) and the difference (ΔC) between the current values. This slope is the conversion coefficient (D). Specifically, the approximate straight line shown in FIG. 8 is shown as ΔC = 2.92 × 10 ⁻⁴ × T + 2 × 10 ⁻⁶ . Therefore, the calibration curve was T = 3.4 × 10 ³ × ΔC−6.8 × 10 ⁻³ .

<Experimental example 3>
In Experimental Example 3, the results obtained with the ion concentration measuring apparatus 1 according to the present embodiment and the results obtained with the existing current detection type ion concentration measuring apparatus were compared in a common measurement environment. As an existing current detection type ion concentration measuring apparatus, a compact potassium ion meter: B-731 manufactured by HORIBA was used. A model 106 was prepared as shown in FIG. Model 106 simulates soil with water containing ions. Model 106 is rock wool. The first electrode part 2 and the sensor part 3 of the ion concentration measuring apparatus 1 according to the present embodiment were inserted into the rock wool. Moreover, the water discharged | emitted from rock wool was collect | recovered using the container 107 arrange | positioned under the rock wool. The ion concentration of the recovered water was obtained using an existing voltage detection type ion concentration measuring device 108.

  FIG. 10 is a graph showing the relationship between the dripping amount of water and the ion concentration measuring apparatus 1. FIG. 10 is a graph showing the relationship between the dripping amount of water and the ion concentration measuring device 108. Plot B1 shows the cumulative dripping amount of water. Plot B2 shows the sensor output of the ion concentration measuring apparatus 1. Plot B3 shows the sensor output of the ion concentration measuring apparatus 108. Region K1 represents a period during which water having an ion concentration of 17 mM was dropped. Region K2 represents a period during which water having an ion concentration of 8.5 mM was dropped. Referring to FIG. 10, a change in which the sensor output (plot B2) of the ion concentration measuring apparatus 1 increases appears for a while after the dropping of the solution having an ion concentration (T) of 17 mM is started. Subsequently, a change in which the sensor output (plot B2) of the ion concentration measuring apparatus 1 decreased after a predetermined time had elapsed after the dropping of the solution having an ion concentration (T) of 8.5 mM was started. Therefore, even when the solution having a high ion concentration (T) is changed to a solution having a low ion concentration (T), the ion concentration measuring apparatus 1 can obtain a sensor output corresponding to the change in the ion concentration (T). I understood it.

  And when the sensor output (plot B2) of the ion concentration measuring apparatus 1 was compared with the sensor output (plot B3) of the existing ion concentration measuring apparatus, it was confirmed that the same tendency was shown. Therefore, it was found that the ion concentration measuring apparatus 1 according to the present embodiment can continuously measure the ion concentration (T) in an environment simulating soil.

<Experimental example 4>
In Experimental Example 4, the stability of the sensor output of the ion concentration measurement apparatus 1 according to this embodiment was confirmed. In Experimental Example 4, first, the first electrode unit 2 and the sensor unit 3 of the ion concentration measuring apparatus 1 were inserted into the soil of the cultivation site. Thereafter, sensor output was obtained over time. During this period, no irrigation work is performed. That is, the ion concentration (T) in the soil that is the measurement object 100 is in a stable state. FIG. 11 shows the change over time of the sensor output of the ion concentration measuring apparatus 1. As shown in FIG. 11, the sensor output did not have a significant fluctuation that could be attributed to disturbance noise. Therefore, it was found that the ion concentration measuring device 1 arranged in a stable state of the ion concentration (T) can output a stable value.

  The ion concentration measurement apparatus according to the present invention is, in short, an ion concentration measurement apparatus that obtains the concentration of ions existing in a measurement object, and is arranged on the measurement object so that a positive voltage and a negative voltage are applied to the measurement object. A first electrode unit that alternately provides a voltage of the voltage, a voltage generation unit that generates the positive voltage and the negative voltage, and a measurement object that is spaced apart from the first electrode, A sensor unit that generates a current corresponding to a voltage provided to the measurement object, and controls the voltage generation unit, and the ions present in the measurement object based on a current output from the sensor unit A control unit that obtains the concentration of the ion, and the sensor unit includes a capture unit including an ionophore that selectively captures the ions, and the ions that are electrically connected to the capture unit and captured by the capture unit Corresponding to The intermediate ions are provided to the trapping unit, and are electrically connected to the conductive unit that collects the intermediate ions from the trapping unit, the conductive unit, and the ground unit, respectively. A second electrode unit that provides corresponding electrons to the conductive unit and collects the electrons from the conductive unit, and the control unit is provided with the positive voltage to the measurement object. A current value acquisition unit that obtains a first current value that is sometimes generated by the sensor unit and a second current value that is generated by the sensor unit when the negative voltage is provided to the measurement object; A difference acquisition unit that obtains a difference between the first current value and the second current value; and a concentration acquisition unit that obtains the concentration of the ions based on the difference.

  The ion concentration measurement method according to the present invention is an ion concentration measurement method for obtaining a concentration of ions existing in a measurement object, and provides a positive voltage to the measurement object via a first electrode unit. A step of obtaining a first current value generated by a sensor unit that is arranged apart from the first electrode in the measurement object and generates a current corresponding to a voltage provided to the measurement object; Obtaining a second current value generated by the sensor unit by providing a negative voltage to the measurement object via the first electrode unit; and the first current value and the second And obtaining the concentration of the ions based on the difference. In the step of obtaining the first current value, the positive voltage is applied to the measurement object. By being offered before A capturing unit including an ionophore that selectively captures ions captures the ions, and the ions are captured by the capturing unit, whereby a mediating ion corresponding to the ions captured by the capturing unit is captured by the capturing unit. The conductive part provided to the trap provides the mediator ion to the capture unit, and the mediator ion is provided to the capture unit, whereby electrons corresponding to the median ion provided to the capture unit are supplied to the conductive unit. In the step of providing the electron to the conductive portion by the second electrode portion to be provided and obtaining the second current value, the negative voltage is provided to the measurement object, thereby capturing the capture portion. The released ions are released from the trapping part, and the ions are released from the trapping part, whereby the conductive part collects the mediating ions from the trapping part, and from the trapping part to the medium By ions is recovered, the second electrode portion to recover the electrons from the conductive portion.

DESCRIPTION OF SYMBOLS 1 ... Ion concentration measuring device, 2 ... 1st electrode part, 3 ... Sensor part, 4 ... Measurement unit, 6 ... Voltage generation part, 8 ... Control part, 9 ... Capture part, 11 ... Conductive part, 12 ... 2nd Electrode part, 13 ... grounding part, 14 ... circuit board, 21 ... through hole, 16 ... recording part, 17 ... current value acquisition part, 18 ... difference acquisition part, 19 ... concentration acquisition part, 22 ... ionophore, 100 ... measurement Object, 101 ... water, 102 ... potassium ion, 103 ... electron, 104 ... chlorine ion (mediating ion).

Claims (5)

A first electrode portion that alternately provides a positive voltage and a negative voltage to the measurement object;
A voltage generator for generating the voltage;
A sensor unit for generating a current based on ions selectively captured in response to a voltage provided to the measurement object;
A control unit that controls the voltage generation unit and obtains the concentration of the ions present in the measurement object based on the current output from the sensor unit;
The controller is
A first current value generated by the sensor unit when the positive voltage is provided to the measurement object, and a first current value generated by the sensor unit when the negative voltage is provided to the measurement object. A current value acquisition unit for obtaining a current value of 2;
A difference acquisition unit for obtaining a difference between the first current value and the second current value;
An ion concentration measurement apparatus comprising: a concentration acquisition unit that obtains the concentration of the ions based on the difference. The sensor unit is
A capturing part including an ionophore that selectively captures the ions;
A conductive portion electrically connected to the capture portion, providing a mediation ion corresponding to the ions captured by the capture portion to the capture portion, and recovering the mediation ions from the capture portion;
A second electrode that is electrically connected to the conductive portion and the ground portion, respectively, provides electrons corresponding to the mediating ions provided to the trapping portion to the conductive portion, and collects the electrons from the conductive portion. And an ion concentration measuring device according to claim 1. The sensor unit further includes a substrate,
The second electrode portion is provided on the substrate,
The conductive portion is provided on the second electrode portion,
The substrate, the second electrode portion, and the conductive portion are provided with through holes from the back surface of the substrate to the main surface of the conductive portion,
The ion concentration measuring apparatus according to claim 2, wherein the capturing unit is provided integrally with a main surface of the conductive unit, the through hole, and a back surface of the substrate.   The ion concentration measuring device according to claim 2, wherein the conductive portion includes a conductive polymer capable of reversibly transferring electrons and ions. By providing a positive voltage to the measurement object via the first electrode unit, a first sensor unit that generates a current based on ions selectively captured in response to the positive voltage is generated. Obtaining a current value;
Obtaining a second current value generated by the sensor unit by providing a negative voltage to the measurement object via the first electrode unit;
Obtaining a difference between the first current value and the second current value;
Obtaining a concentration of the ions based on the difference;
A method for measuring ion concentration.

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