JPH1164275A - Oxidation-reduction potential measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten measuring time by modeling an electric circuit of an electrode reaction and providing additional circuits for speeding up reaction rates in an aqueous solution of an electrode potential. SOLUTION: The combined potential output between a working electrode 3 and a reference electrode 2 is directly connected to a liquid crystal display circuit 23 and a liquid crystal 24 via a differential amplifier 22. A compensating circuit 26 with a manual switch to impress a reduction potential among a bias potential adjusting circuit 25 to offset a bias potential equivalent to the standard single-electrode potential of the reference electrode 2, the working electrode 3, and the reference electrode 2 is provided. In the case of using a microcomputer, this device is constituted of a CPU 30 to sample input signals from an A/D converting circuit 29, a liquid crystal 24, an automatic start switch 32, a start/stop switch 33, etc. The automatic start switch 32 is a switch for sampling signals induced in the initial stage of the immersion of the reference electrode 2 and the working electrode 3 into a sample liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simplifying the oxidation-reduction potential of all water and aqueous solutions in drinking water, industrial water, chemicals, body fluids of humans and animals, fruits, vegetables, etc. in natural and artificial environments. Related to a device for measuring. In addition to the information on the hydrogen ion concentration obtained by the PH meter, it serves as a criterion for judging the safety of drinking water and industrial water, and also serves as an index for qualitative analysis of chemicals and for measuring the oxidation-reduction power inherent to food, soil, living organisms and the like.

[0002]

2. Description of the Related Art The oxidation-reduction potential of water is measured in the process of oxidizing river water for the purpose of obtaining water suitable for drinking or industrial use. The measurement method is based on a standard hydrogen electrode containing a reference solution and a platinum electrode. An oxidation-reduction potential measuring device using an electrode as a counter electrode is used. This type of measuring device is also used in tests of chemical solutions and the like. That is, the conventional oxidation-reduction potential measuring instruments are mainly for industrial facilities and laboratories, and as handling precision instruments that require specialized knowledge, simplicity of handling and low cost are not required. It can be said that there was not much. On the other hand, with the recent global pollution of the atmosphere and rivers, interest in securing safe drinking water in general households has increased, and the significance of maintaining the residual concentration of contaminants and PH at appropriate levels as standards for water quality evaluation. Are fully recognized. With respect to the oxidation-reduction potential of drinking water, those exhibiting a positive high potential are unsuitable for the human body, and so-called reduced water has become popular as drinking water. In addition, knowledge on the evaluation based on the oxidation-reduction potential of food (for example, Patent Application No. 298842 in 1994) and the effectiveness of detecting the oxidation-reduction potential of body fluids as an index for human health management (for example, Japanese Patent Application No. 320662). The proposal is already in the stage of commercialization. An oxidation-reduction potential measuring instrument used in these fields is an oxidation-reduction potential measuring instrument mainly using a standard hydrogen electrode and a platinum electrode as counter electrodes as described above. In order to avoid the inconvenience of using a liquid, a device using a metal electrode instead of a standard hydrogen electrode has been used in part, but it has not yet come into widespread use due to the instability of the accuracy of oxidation-reduction potential measurement.

[0003]

In order to easily measure the oxidation-reduction potential of domestic water such as drinking water, bath water, washing water, etc., a conventional redox method using a fragile glass tube or a liquid that is difficult to enclose is used. It is not suitable for a potential measuring instrument. To avoid this difficulty, an oxidation-reduction potential measuring instrument using a different kind of metal electrode pair is used in part. However, the problems of the oxidation-reduction potential measuring device using the metal electrode pair include the instability of the electrode potential of the metal electrode and the low reaction rate. The instability of the electrode potential is due to the instability of the reaction between the metal used as the electrode and the aqueous solution to be measured. That is, FIG.
The principle of an oxidation-reduction potential measuring device using a metal electrode pair according to 1-a and 1-b is as follows. An electromotive force Et4 generated between a reference electrode metal 2 and a working electrode metal 3 immersed in an aqueous solution 1 to be measured. Is the standard electrode potential Emo5 generated on the reference electrode side and the oxidation-reduction potential Er of the aqueous solution to be measured generated on the working electrode side.
The electromotive force is led to the voltmeter 9 by the lead wires 7 and 8 connected to both electrodes. Ered
Is the case where the direction is negative with respect to the potential of the aqueous solution. Reference numerals 10 and 11 denote contact surfaces of both electrodes with the aqueous solution 1. 12 is the electric resistance of the aqueous solution. Here, if the standard electrode potential Emo of the reference electrode is known, the difference between the detected electromotive force Et and Emo becomes the oxidation-reduction potential Ered of the aqueous solution to be measured. That is, Ered = Et−Emo (1)

However, in practice, the reference electrode potential Emo, which should be a constant, changes depending on the PH value of the aqueous solution and the metal ion concentration. In addition to the standard electrode potential, a component of the oxidation-reduction potential Ered of the aqueous solution is also applied to the reference electrode side, causing an error. In the metal material 2 of the reference electrode which requires ion dissociation as a necessary condition, an oxidized compound or a hydroxide compound is generated on the metal surface depending on the properties of the aqueous solution, and the electrode potential changes. FIG. 2 shows these error factors in an electrical equivalent circuit model. The oxidation-reduction potential induced at the working electrode 3 is affected by an oxide compound or a hydroxide compound film formed on the platinum surface similarly to the reference electrode side.
Thirteen charge potentials. That is, in the measurement, it takes a time corresponding to the formation and disappearance of the surface film capacitance from immersing the electrode in the aqueous solution to showing a stable equilibrium potential. Here, Rp14 and Rred15 are C
It is a series resistance attached to p and Ered. Cm16, R
m17 is a capacitance on the reference electrode side and a series resistance attached thereto. The standard monopolar potential of the working electrode is represented by Epo18, the standard monopolar potential of the reference electrode is represented by Emo5, and their resistance components are represented by Rpo19 and Rmo20. Potential Eim21
Is the Nernst potential determined by the dissolved concentration of metal ions in the reference electrode. According to the observations of the present inventors, as an example, in an aqueous solution showing a reduction potential of −100 mV in a stationary state, it takes about 10 to 80 seconds from the time of immersion of the electrode to the time of the potential equilibrium. This time is affected by the surface area of the electrode, the conductivity of the aqueous solution, and the like, but is considered to be the time required for the disappearance of the hydroxide compound film formed on the platinum surface before immersion. On the other hand, the time until potential equilibrium when immersed in an aqueous solution having a high oxidation-reduction potential after immersion in an aqueous solution having a low oxidation-reduction potential is within several seconds to 10 seconds. That is, the time required to obtain a stable measurement value varies depending on the value of the oxidation-reduction potential of the aqueous solution before and after the measurement. Such a case where it takes time in minutes to obtain an accurate oxidation-reduction potential cannot be said to be satisfactory as a characteristic of a simple oxidation-reduction potential measuring instrument. The present invention intends to overcome the drawbacks of the oxidation-reduction potential measurement device composed of only metal electrodes, to improve the measurement accuracy, and to shorten the measurement time.

[0005]

The principle of the present invention will be described with reference to FIG. FIG. 3A is an equivalent circuit which simplifies the circuit model of FIG. 2 and shows the potential between the metal electrodes immersed in the solution and the charged state of the metal surface. The time response characteristic of the output voltage from the initial value to the steady value can be obtained by directly using the circuit model of FIG. However, in the circuit of FIG. 2, the standard electrode potential Epo of the platinum electrode is set to zero or the series resistance Rp
These are ignored assuming that o is large. Although the correspondence with the physical model of the electrode reaction is not always clear, the series resistance components Rp and Rm of the electrode capacitances Cp and Cm are Rred.
It is convenient to assume that it is negligibly small for avoiding computational complexity and understanding the actual phenomenon.
Here, the oxidation-reduction potential Ered of the aqueous solution is a positive potential unlike FIG. The reference electrode potential is also set to a plus potential. FIG. 3B shows the state of electric charge in the circuit when the oxidation-reduction potential Ered of the aqueous solution suddenly changes from the positive potential to the negative potential, that is, the oxidation state of the working electrode surface. It means that it takes a long time to obtain a stable value of the potential because the surface charge is diffused in the circuit.

FIG. 3C is a circuit diagram showing the basic configuration of the present invention, in which a potential Em having the working electrode side as a cathode is applied in series to the circuit of FIG. 3B. Here, by setting Et + Em ≧ 0 (2), a current using the working electrode as a cathode flows in the circuit, and the reduction of the electrode surface is accelerated. In addition, Et, E
The sign of m is all based on the reference electrode.
Et in equation (2) is the redox potential Ered of the aqueous solution to be measured.
And the standard single-electrode potential Emo of the reference electrode, which changes to positive or negative depending on the measurement object. When Et indicates zero or a negative value, a positive voltage may be applied. However, if the measurement range on the negative side of the oxidation-reduction potential of the target aqueous solution is limited, applying the constant potential Em given by the following expression (3) satisfies the expression (2) for all the measured aqueous solutions. . Em = (Ered −) − Emo (3) where (Ered−) is the lower measurement limit potential on the negative side of the oxidation-reduction potential. The redox potential / time characteristic of FIG. 4 shows the effect of shortening the measurement time by the circuit of FIG. 3-c. Er in the figure
ed (A) is a time response characteristic of the oxidation-reduction potential measured by ordinary measurement, and Ered (B) is a potential Em based on the equation (3).
Is a characteristic when. According to the potential application method of the present invention, it takes about 80 seconds to reach the oxidation-reduction potential Ered2 of the aqueous solution to be measured -200 mV from the initial value of +400 mV in the ordinary measurement to the minus 200 mV. The time is reduced to 10 seconds or less. The value of the applied potential Em and the application time are 800 millivolts and 3 seconds, respectively. Here, the timing of the application is the same as the immersion of the metal electrode in the aqueous solution to be measured, but the same effect can be obtained even if the application is performed intermittently after the immersion.

The negative voltage applied to the working electrode does not always need to be obtained from an external circuit, and other metal electrodes immersed in the aqueous solution to be measured, particularly a metal electrode having a negative standard unipolar potential, are connected to the working electrode. Thus, the working electrode can be reduced. For example, when Emo is negative and larger than Ered in FIG. 3A, the reference electrode can be used as the anode and the working electrode can be used as the cathode by short-circuiting the circuit. However, metals that are generally considered to be resistant to corrosion have a positive or small negative standard unipolar potential, and metals that are vulnerable to corrosion have a large negative standard unipolar potential. It is not recommended to use a metal electrode having a negative standard monopolar potential for the reference electrode from the viewpoint of corrosion resistance, so it is recommended to use another replaceable metal electrode having a negative standard monopolar potential as the anode electrode. .

As a basic operation of the measurement of the oxidation-reduction potential as an object of the present invention, it is necessary to provide a switching function for applying a required voltage to the circuit during or immediately after the metal electrode is immersed in the aqueous solution to be measured. However, it is desirable not only to do this manually but also to automate it. The trigger input of the switching operation includes an on / off signal of a circuit power supply and a reset signal. However, the redox potential of the aqueous solution to be measured may vary depending on the location and time, so that the operation of applying the voltage as needed in response to the fluctuation of the observed potential over time is automated. As a trigger input for automation, it is possible to use an external input signal or a sudden fluctuation value of the observed potential at intervals of a predetermined time. Since a sudden change in the observed potential is also generated by oscillating the electrode before or after immersion or during immersion, a differential value of the potential change is set to a certain value or more, this is detected, and a trigger input is made.

[0009]

FIG. 5 shows an embodiment of a system configuration comprising the circuit of the present invention. FIG. 5A shows an oxidation-reduction potential measuring device in which the combined potential output between the operation and reference electrodes is directly connected to the liquid crystal display circuit 23 and the liquid crystal 24 through the differential amplifier 22. A bias potential adjusting circuit 25 for offsetting a bias potential corresponding to a standard monopolar potential of a reference electrode,
A compensation circuit 26 having a manual switch for applying a reduction potential between the reference electrodes is provided. 27 is a DC power supply built in the chassis, and 28 is a main body chassis. FIG. 5B shows a central processing unit 30 for sampling and calculating an input signal from an analog / digital conversion circuit 29 and a DC power supply 2 for a liquid crystal display 24 using a microcomputer.
7, a power on / off switch 31, an automatic start switch 32, and a start / stop switch 33. The automatic start switch 32 is connected to the sample liquid 1 of the electrodes 2 and 3.
This is a switch for automatically sampling a signal induced in the early stage of immersion in the device. The purpose of measuring the oxidation-reduction potential is to collect comparative values of multiple samples or to observe the change over time of a single sample over a long period of time.The former requires a shorter data collection time. In contrast, the latter is considered low. Switch 3 corresponding to these two measurement modes
2, 33 are appropriately selected.

[0010]

FIG. 6 shows an embodiment according to the present invention. The reference electrode 2 is a plate whose main material is zinc, titanium, copper, tin, silver or an alloy thereof, and is attached concentrically to a cylindrical plastic housing 34. The working electrode 3 is made of a platinum-plated titanium rod and is attached to the center of the end of the housing 34 so as to maintain a constant gap from the electrode 2 and have sufficient electrical insulation except when immersed in a sample solution. It has become. Both electrodes are connected to the main body chassis 28 in the housing via lead wires 4 and 5 and a lead cable 35 and a cable connector 36. The liquid crystal display 24 displays three digits in the range of positive and negative 999 millivolts. The automatic start switch 32 automatically samples a signal induced in the initial stage of immersion of the electrodes 2 and 3 in the sample solution 1, detects start, applies a reduction voltage, and waits for the detected oxidation-reduction potential to stabilize. Hold. The start / stop switch 33 is a switch for manually performing an operation of starting observation and holding sampling data. Electrode housing spacer 34
-2 and the electrode housing hook 34-3 are the housing 34 and the container 3
This is for facilitating attachment and detachment of 7.

FIG. 8 shows an example of an arrangement structure of a compensating electrode for adding a metal electrode 2-2 other than the working reference electrode according to the present invention and applying a reduction voltage to the working electrode as needed. is there. For example, when the compensating electrode metal 2-2 is tin, a reduction current can be supplied to the working electrode by short-circuiting the platinum electrode 3 serving as the working electrode with the electrode 2-2 as long as the above-mentioned expression (2) is satisfied. Further, if the compensating electrode metal 2-2 is made of platinum, a reducing action can be generated by applying a small voltage from the outside between the platinum electrode 3 and the electrode 2-2 regardless of the condition of the equation (2). .

As described above and with reference to the accompanying drawings, an object of the present invention is to provide a small and lightweight solid metal which is easy to handle, and which has been used to improve measurement accuracy and reduce measurement time. It is to provide a potential measuring device. In other words, by modeling the electric circuit of the electrode reaction,
An additional circuit has been devised to increase the reaction rate of the electrode potential in an aqueous solution, and the measurement time has been reduced by half to one-tenth compared to the conventional apparatus. Also, by clarifying the fluctuation of the oxidation-reduction potential of the liquid to be measured and the error factors, it was possible to select a metal material having a small error and a parameter unique to the metal material. According to the present invention, it is possible to obtain an inexpensive and highly reliable oxidation-reduction potential measuring device that is not only used for large-scale facilities and test and research facilities but is always available in ordinary households, and is lightweight and easy to handle for personal use. By measuring the oxidation-reduction power of familiar substances such as drinking water, living water, soil, food, and body fluids of living organisms at any time, it is possible to contribute to a healthy life.

[Brief description of the drawings]

FIG. 1A is a configuration diagram of an oxidation-reduction potential measuring device using a different kind of metal. FIG. 1B is a basic electrical equivalent circuit thereof.

FIG. 2 shows an electrical equivalent circuit model representing the electrode reaction and oxidation-reduction potential of all different metals in an aqueous solution according to the principle of the present invention.

FIG. 3A is an equivalent circuit diagram that gives a time response at an initial stage of an electrode reaction of the circuit model of FIG. 2; Fig. 3-b
FIG. 3 is an equivalent circuit diagram showing a reduction current. FIG. 3C is a basic configuration diagram of the compensation circuit according to the present invention.

FIG. 4 shows a time response characteristic of a measured potential of the oxidation-reduction potential measuring apparatus according to the present invention, as compared with that of a conventional apparatus.

FIG. 5A is an electric circuit block diagram of one embodiment of the present invention. FIG. 5B is a basic configuration diagram of a circuit having a built-in automation and automatic calculation function according to the present invention.

FIG. 6 is an external view of a measurement state of an electrode unit housing, a circuit, a liquid crystal display unit, a control switch unit, and a main body housing unit of the present invention.

FIG. 7 is a basic circuit configuration diagram of a compensation electrode according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aqueous solution to be measured 2 Reference electrode 2-2 Compensation electrode 3 Working electrode 4 Interelectrode potential 5 Reference electrode potential 6 Working electrode potential 7 Reference electrode side lead wire 8 Working electrode side lead wire 9 Voltmeter 10 Reference electrode contact surface 11 Working electrode Contact surface 12 Resistance of aqueous solution 13 Working electrode virtual capacitance 14 Series resistance of working electrode virtual capacitance 15 Series resistance of working electrode potential 16 Reference electrode virtual capacitance 17 Series resistance of reference electrode virtual capacitance 18 Standard single electrode potential of working electrode 19 Working electrode 20 Standard monopolar potential of reference electrode 20 Standard monopolar potential of reference electrode 21 Nernst potential of metal ion of reference electrode 22 Differential amplifier 23 Liquid crystal drive circuit 24 Liquid crystal 25 Single electrode potential offset adjustment circuit of reference electrode. 26 Reduction Potential Compensation Circuit 27 DC Power Supply 28 Case 29 Analog / Digital Conversion Circuit 30 CPU Device 31 Power On / Off Switch 32 Automatic Start Switch 33 Start / Stop Switch 34 Electrode Case 34-2 Electrode Case Spacer 34-3 Electrode Case Body hook 35 Connection cable 36 Cable connector 37 Switch box

Claims (3)

[Claims] 1. A working electrode comprising platinum or a metal plated with platinum as a working electrode, a metal having a higher ionization tendency than platinum or a metal comprising an alloy thereof as a reference electrode, and a working electrode immersed in an aqueous solution to be measured and the reference electrode. Et induced potential
An oxidation-reduction potential measuring apparatus characterized in that a potential Em that satisfies the following equation is applied at any time or intermittently to Et in a cascade with the working electrode as a cathode. Et + Em ≧ 0 2. Platinum or a metal plated with platinum is used as a working electrode, and a metal having a higher ionization tendency than platinum or a metal made of an alloy thereof is used as a reference electrode. At any time,
Alternatively, an oxidation-reduction potential measuring device comprising another metal electrode for supplying a negative current intermittently. 3. The method according to claim 1, wherein the time-dependent switching operation is started when power is turned on, when electrodes are immersed, when observed values are reset, or when the oxidation-reduction potential of the aqueous solution to be measured fluctuates. An oxidation-reduction potential measuring apparatus characterized by being automatically automated.