JP5069646B2 - 3-electrode electrochemical measurement system - Google Patents

Description

  The present invention relates to a three-electrode electrochemical measurement apparatus that electrochemically measures the composition of the liquid to be measured, the electrode reaction mechanism, and the like using three electrodes, a working electrode, a counter electrode, and a reference electrode. The present invention relates to a potentiostat circuit that is connected to control the potentials thereof.

  As shown in FIG. 1, the conventional potentiostat circuit includes a positive voltage generation circuit 61 ′ that generates a positive voltage higher than the circuit ground potential by a certain voltage, a non-inverting input terminal In +, an inverting input terminal In−, And an operational amplifier circuit 62 having an output terminal Out.

  The non-inverting input terminal In + of the operational amplifier circuit 62 is connected to the positive voltage generating circuit 61 ', the inverting input terminal In- is connected to the reference electrode 4, the output terminal Out is connected to the counter electrode 3, and the working electrode 2 is connected to the operational amplifier 2. It is supposed to be grounded.

In any literature, the basic configuration of maintaining the working electrode 2 at the ground potential of the circuit remains the same even though there are many peripheral circuit devices (for example, Patent Document 1). Note that FIG. 2 of Patent Document 1 describes a configuration in which the working electrode 2 is not grounded, but this is a two-electrode type such as a galvanistat, which is completely different from the three-electrode type. They are not subject to comparison.
JP-T 09-502527

  By the way, when such an electrochemical measurement device is used in combination with another measurement circuit such as a conductivity meter in common with the ground potential, the internal liquid of the electrochemical measurement device has the same positive potential as the reference electrode. Therefore, if the internal liquid leaks, the current i ′ flows to the measurement target liquid via the internal liquid, which causes a measurement error in the conductivity meter and the like.

  Therefore, in the past, the effect of electrical measurement on other measuring devices has been achieved by using a robust electrode structure that does not cause leakage of internal liquids, or by floating the ground potential of the electrical circuit in each measuring device. Is trying to eliminate.

  However, for that purpose, a special sealing structure or a device for an electric circuit is required, which may cause a problem of increasing the cost.

  The present invention has been made in view of such problems, and its main purpose is to adversely affect the measurement of the other measurement device when measuring the same liquid to be measured simultaneously with the other measurement device. The object is to provide a three-electrode electrochemical measuring apparatus that can be reliably prevented with a simple configuration.

  That is, the three-electrode electrochemical measurement apparatus according to the present invention is configured so that the potential of the working electrode, the counter electrode immersed in the internal liquid and the reference electrode, and the potential of the working electrode with respect to the reference electrode is kept constant. A potentiostat circuit for controlling the potential of the counter electrode, and electrochemically measuring the property of the liquid to be measured by measuring the amount of current flowing between the working electrode and the counter electrode. The potentiostat circuit maintains the potential of the reference electrode at the ground potential of the circuit and holds the working electrode at a potential lower than the ground potential.

  According to such a configuration, since the reference electrode is kept at the ground potential of the potentiostat circuit, the internal liquid is also kept at the ground potential. Therefore, even if the internal liquid leaks into the liquid to be measured, the current influence on the other measurement circuit (for example, conductivity meter) that shares the ground potential with this potentiostat circuit can be reduced as much as possible. The measurement accuracy of the other measurement circuit can be maintained.

  A specific configuration of the potentiostat circuit includes a W terminal connected to the working electrode, a C terminal connected to the counter electrode, an R terminal connected to the reference electrode, and a constant voltage lower than the ground potential of the circuit. While generating a negative voltage, the negative voltage generation circuit having the negative voltage output terminal connected to the W terminal, and a non-inverting input terminal, an inverting input terminal and an output terminal, and grounding the non-inverting input terminal, And an operational amplifier circuit in which the inverting input terminal is connected to the R terminal and the output terminal is connected to the C terminal.

The effect of the present invention is particularly remarkable when the inside of the housing is separated into two spaces by an electrically insulating wall, such as an oxygen dissolver, an ammonia electrode, a carbon dioxide electrode, and a hydrogen cyanide electrode, Fill the internal liquid and immerse the counter electrode and the reference electrode. The other space is filled with the liquid to be measured outside the housing through a gas permeable film (such as a Teflon (registered trademark) diaphragm) that is an electrically insulating film. The thing of the structure which has arrange | positioned the working electrode which faced can be mentioned.
In the case of a configuration in which both the working electrode and the counter electrode are electrically connected to the liquid to be measured without using an electrical insulating film, either the working electrode or the counter electrode is set to the ground potential. Becomes a positive potential or a negative potential, and the liquid to be measured is affected by the potential, so that the effect of the present invention is not likely to be remarkable.

Thus, according to the present invention configured as described above, the reference electrode and the counter electrode are maintained at the ground potential of the potentiostat circuit, and the internal liquid is also maintained at the ground potential. Even if it leaks, the influence of current on other measurement circuits (for example, conductivity meter) that share the ground potential with this potentiostat circuit can be reduced as much as possible, and the measurement accuracy of the other measurement circuits can be reduced. Can be maintained.
In addition, since there is little influence on other measurement circuits due to internal liquid leakage in this way, it is possible to simplify the liquid-tight structure for enclosing the internal liquid, or to omit devices such as floating between the measurement circuits. Therefore, cost reduction as a whole can be promoted.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  A dissolved oxygen meter X7, which is an electrochemical measurement device in this embodiment, is used as a constituent element of a water quality analyzer X capable of measuring various properties relating to water quality, as shown in FIG. .

  Therefore, before explaining the details of the dissolved oxygen meter X7, first, the outline of the water quality analyzer X will be briefly explained. FIG. 3 is a bottom view of the water quality analyzer X with the protective cover X13 removed.

  This water quality analyzer X continuously measures measurement items such as pH, conductivity, dissolved oxygen concentration, turbidity, and water temperature, and is shown in FIGS. As described above, an immersion type sensor main body X1 provided with a plurality of measurement sensors X3 to X8 for water quality measurement, an instrument main body X2 electrically connected to the sensor main body X1 via a waterproof electric cable CA, It has. For example, when water quality analysis of seawater is performed as a liquid sample, the electric cable CA is held, and the sensor body X1 is suspended in seawater and immersed in seawater.

  As shown in FIG. 2, the sensor body X1 has a substantially cylindrical shape, a plurality of types of measurement sensors X3 to X8, a mounting block body X11 to which these measurement sensors X3 to X8 are attached, a power source, and a memory function. A calculation unit including a calculation unit, a data logger that records time-series measurement data of the calculated water quality, etc., and a storage unit X12, and a lower end portion of the mounting block body X11 (end portion on the sensor mounting side) And a sensor protection cover X13 that protects the measurement sensor from the outside. Note that the mounting block body X11 and the arithmetic device housing X12 constitute a watertight case. The sensor protective cover X13 has a light shielding function for shielding light from the outside and an impact absorbing function for absorbing an impact received from the outside during installation and measurement, and an external liquid sample (for example, seawater) is taken into the sensor body. While guiding inside X1, the measurement sensors X3 to X8 are protected from the outside.

  Specifically, on the mounting surface X11A formed at the lower end of the mounting block body X11, as shown in FIG. 2, a pH glass electrode X31 for pH measurement and an internal solution of KCl having a high concentration (3.3 mol / L). PH sensor X3 composed of a comparison electrode X32 using a redox electrode, a redox electrode X4 for measuring a redox potential using the comparison electrode X32, for example, a conductivity sensor X5 using an AC quadrupole method, a transmission scattering method A turbidity sensor X6 using a polarimeter, a dissolved oxygen meter X7 using a polarographic method, a temperature sensor X8, and the like are provided so as to face the same direction. That is, each of the measurement sensors X3 to X8 is provided on the attachment surface X11A in a direction in which the central axis directions substantially coincide. The attachment surface X11A may be formed on the same plane or may have a stepped portion.

  The instrument main body X2 includes a display unit for displaying measurement data from the sensor main body X1, a power key, a function key, a measurement start / end key, a calibration key, a select key, an up / down key, and the like. When the sensor main body X1 is submerged by operating the electric cable CA, measurement data based on the output from each of the measurement sensors X3 to X8 is recorded in the memory function unit, and the measurement value is displayed on the display unit. Is done.

  Therefore, as shown in FIG. 4, the dissolved oxygen meter X7, which is an electrochemical measurement device according to this embodiment, includes the electrode mechanism 1 including three electrodes, that is, the working electrode 2, the counter electrode 3, and the reference electrode 4, and the above-described action. A potentiostat circuit 6 for controlling the potential of the counter electrode 3 so that the potential of the electrode 2 with respect to the reference electrode 4 is kept constant, and the amount of current flowing between the working electrode 2 and the counter electrode 3 is By measuring, the amount of dissolved oxygen in the liquid to be measured is measured. Each part is described in detail below.

  The electrode mechanism 1 is immersed in the liquid to be measured. As shown in FIG. 5, as shown in FIG. 5, the hollow casing 5 in which the internal space Q is filled, and the three electrodes held in the casing 5. 2, 3, 4.

  The casing 5 has a cylindrical casing main body 51 in which the oxygen permeable membrane 7 is stretched at the front end opening, and is screwed into the base end opening of the casing main body 51 to close the opening in a liquid-tight manner. And a base member 52.

  The base member 52 is made of an insulating resin for partitioning the internal space of the housing 5 into two parts: a first space in which the working electrode 2 is inserted and a second space in which the counter electrode 3 and the reference electrode 4 are inserted. And includes a columnar member 521 extending inside the housing body 51 and a disk-shaped member 522 provided on the outer periphery of the base end portion of the columnar member 521. A screw groove provided on the outer peripheral surface of the disk-like member 522 is configured to be screwed into the base end opening of the housing body 51 and press the seal member O. A columnar working electrode 2 is passed through the center of the columnar member 521 so that the center axis coincides, and a cylindrical counter electrode 3 is fitted outside the columnar member 521. . Further, the reference electrode 4 is passed through the peripheral edge of the disk-shaped member 522.

  By the way, the three electrodes 3, 4, 5 are liquid-tightly penetrated through the base member 52 without interposing a seal member or the like. Therefore, in this embodiment, the base member 52 and the three electrodes are integrally formed by an injection molding method in which the three electrodes are arranged in advance in the mold, the resin is injected into the gap, and the base member 52 is formed. ing.

  In addition, the cylindrical member 521 and the distal end surface 8 of the working electrode 2 are formed in a partial spherical shape, and when the casing body 51 is screwed to the base member 52, the oxygen permeable membrane 7 is in contact with the distal end surface 8. It is configured to stick with a certain amount of tension. With this configuration, the internal liquid Q penetrates between the oxygen permeable membrane 7 and the tip surface 8 by capillary action or the like, and a gap between the inner surface of the oxygen permeable membrane 7 and the tip surface 8 is about 10 μm or less. Operates to maintain a constant value. The peripheral edge of the tip surface 8 is subjected to R processing so that no edge is formed, and the capillary phenomenon is smoothly performed between the oxygen permeable membrane 7 and the edge.

  According to such a configuration, the dissolved oxygen that has passed through the oxygen permeable membrane 7 is reduced by the working electrode 2 and a reduction current i proportional to the dissolved oxygen concentration (DO concentration) flows. By measuring with an ammeter, the dissolved oxygen concentration of the liquid to be measured can be measured.

  In this embodiment, however, the potentiostat circuit 6 is devised to keep the potential of the reference electrode 4 at the ground potential of the potentiostat circuit 6 and the working electrode 2 at a potential lower than the ground potential. To keep in.

  Specifically, as shown in FIG. 2, the potentiostat circuit 6 includes a W terminal connected to the working electrode 2, a C terminal connected to the counter electrode 3, and an R terminal connected to the reference electrode 4. A negative voltage generating circuit 61 that generates a negative voltage lower than the ground potential by a certain voltage and has the negative voltage output terminal connected to the W terminal, a non-inverting input terminal In +, an inverting input terminal In−, and an output terminal Out are provided. And an operational amplifier circuit 62 in which the non-inverting input terminal In + is grounded, the inverting input terminal In− is connected to the R terminal, and the output terminal Out is connected to the C terminal.

  According to such a configuration, the reference electrode 4 and the counter electrode 3 are maintained at the ground potential of the potentiostat circuit 6 although there are some transient fluctuations depending on the response speed of the circuit 6 and the like. The internal liquid Q is also kept at the ground potential. Therefore, even if the internal liquid Q leaks into the liquid to be measured, another measurement circuit (in this example, the pH sensor X3, the oxidation-reduction electrode X4, the conductivity) that shares the ground potential with the potentiostat circuit 6. The current influence on the sensor X5) can be reduced as much as possible, and the measurement accuracy of the other measurement circuit can be maintained.

  In addition, since there is little influence on other measurement circuits due to leakage of the internal liquid Q in this way, the device such as simplifying the liquid-tight structure for enclosing the internal liquid Q or floating the measurement circuits is omitted. As a result, cost reduction as a whole can be promoted.

  The present invention is not limited to the above embodiment. For example, if the property of the liquid to be measured is electrochemically measured using three electrodes, such as polarography, the present invention is applied and the same effects as those of the above-described embodiment can be obtained. Further, the negative potential generating circuit may be one in which the negative potential can be variably adjusted automatically or by an external operation. Of course, in the above-described embodiment, only a basic example of a potentiostat circuit is given, and changes and additions may be made in the peripheral portion.

  In addition, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

The electric circuit diagram which shows an example of the conventional potentiostat circuit. 1 is an overall perspective view showing an overall view of a water quality analyzer according to an embodiment of the present invention. The bottom view which shows the internal structure of the water quality analyzer in the same embodiment. The fragmentary longitudinal cross-section which shows the electrode mechanism of the dissolved oxygen meter which concerns on one Embodiment of this invention. The electric circuit diagram which shows an example of the potentiostat circuit in the same embodiment.

Explanation of symbols

X7 ... Three-electrode electrochemical measuring device (dissolved oxygen meter)
2 ... Working electrode 3 ... Counter electrode 4 ... Reference electrode 6 ... Potentiostat circuit

Claims (2)

A working electrode, a counter electrode immersed in an internal liquid, and a reference electrode; and a potentiostat circuit for controlling the potential of the counter electrode so that the potential of the working electrode with respect to the reference electrode is kept constant. A three-electrode electrochemical measurement device that electrochemically measures the property of the liquid to be measured by measuring the amount of current flowing between the working electrode and the counter electrode ;
Another measuring sensor for measuring the measurement target liquid being measured by the three-electrode electrochemical measuring device, and an analyzer comprising:
The potentiostat circuit of the three-electrode electrochemical measurement device and the measurement circuit of the measurement sensor share a ground potential,
Analyzer the potentiostat circuit, the potential of the reference electrode with keeping the ground potential of the potentiostat circuit is characterized in that for holding the working electrode at a lower potential than the ground potential. The potentiostat circuit is
A negative voltage generating circuit that generates a negative voltage lower than the ground potential by a constant voltage, and has a negative voltage output terminal connected to the working electrode;
An operational amplifier circuit having a non-inverting input terminal, an inverting input terminal, and an output terminal, wherein the non-inverting input terminal is grounded, and the inverting input terminal is connected to a reference electrode and the output terminal is connected to a counter electrode. The analyzer according to claim 1, wherein