Method for acquiring oxidation-reduction state of aqueous solution as hydrogen electrode potential, method for acquiring effective hydrogen gas partial pressure of aqueous solution, and device for acquiring oxidation-reduction state of aqueous solution as hydrogen electrode potential

Abstract

[Problem] To provide a method and a device for acquiring the oxidation-reduction state of an aqueous solution as a hydrogen electrode potential. [Solution] In the present invention, the hydrogen electrode potential of an aqueous solution is defined by the Nernst equation. The present invention includes: a step for measuring the hydrogen partial pressure and the temperature of a gas phase that is in equilibrium with an aqueous solution, and the pH of the aqueous solution; and a step for analyzing a hydrogen electrode potential from the pH, the temperature, and the inverse logarithmic pH2 of the hydrogen partial pressure, which have been measured. For example, when the room temperature is 25°C (T=298.15 K) and the pH is 7.0, the hydrogen electrode potential can be calculated from expression 32 and an approximate expression. When the pH is constant, a change in the hydrogen electrode potential of the aqueous solution can be calculated from expression 33 and an approximate expression.

Description

Method for obtaining the oxidation-reduction state of an aqueous solution as a hydrogen electrode potential, method for obtaining the effective hydrogen gas partial pressure of an aqueous solution, and device for obtaining the oxidation-reduction state of an aqueous solution as a hydrogen electrode potential

[0001] The present invention relates to a method for obtaining the redox state of an aqueous solution as a hydrogen electrode potential, a method for obtaining the effective hydrogen gas partial pressure of an aqueous solution, and an apparatus for obtaining the redox state of an aqueous solution as a hydrogen electrode potential.

[0002] Aqueous solutions have electrochemical properties, which are measured as electrode potential. Oxidation Reduction Potential (ORP) is an indicator of the oxidizing or reducing properties of an aqueous solution, and is measured using the electrometer body, a precious metal electrode (platinum or gold electrode), and a reference electrode. Potential is affected by temperature, so it must be measured at a constant temperature. Electrolysis of aqueous solutions produces oxygen (O2) and hydrogen (H2), so the potential window is narrow (1.24 V). Furthermore, when hydrogen ions are involved in the oxidation-reduction reaction, the equilibrium potential depends on the pH of the aqueous solution.

[0003] Generally, the oxidation-reduction potential (ORP) of an aqueous solution is the ratio of oxygen (O2) to hydrogen ions (H2). + The oxidation potential (ORP) increases (oxidizes) due to oxygen, while it decreases (reduces) due to hydrogen H2. Because gaseous oxygen and hydrogen behave as ideal gases even in aqueous solution, the partial pressure of the aqueous solution is equal to the partial pressure of the gas phase at equilibrium. According to the Nernst equation, the oxidation-reduction potential (ORP) changes in proportion to the partial pressure of oxygen and hydrogen. A standard hydrogen electrode is used as the reference electrode, and the hydrogen partial pressure is defined as 1 atmosphere. When used in experiments, it is constructed by inserting a platinum electrode into hydrochloric acid with an average activity of 1 that has been saturated by bubbling hydrogen gas at 1 atmosphere, and is defined as zero (0) mV at 25°C.

[0004] Dissolved oxygen (DO) and pH (hydrogen ion activity), which affect the oxidation of aqueous solutions, are measured using electrode potential. Dissolved oxygen is measured using a diaphragm with excellent oxygen permeability, and the concentration of permeated oxygen is detected with an electrode. When measuring pH with a glass electrode, an electromotive force is generated between the inside and outside of the thin glass membrane in proportion to the difference in pH, so the pH is measured from the electromotive force between the glass membrane and a reference electrode.

[0005] Another factor affecting the reduction of aqueous solutions is the relative hydrogen score (rH), proposed by de Clerck in 1923. rH is the logarithm of the inverse of hydrogen partial pressure (-log[hydrogen partial pressure]), and its nominal range is 0 to 42. It was cited by de Clerck in the 1950s as a measure for beer brewing. Studies of aquariums and various marine and oceanic redox systems have reported mathematical relationships between the redox potential (ORP), pH, and rH. For example, in 2008, Holmes-Farley reported a formula empirically approximated using the ORP and pH of aqueous solutions: rH = ORP / 29 + 2 × pH + 6.67. In other words, an index of the redox state of an aquatic environment can be established by calculating rH from the actual measured values ​​of ORP and pH.

[0006] The half-reaction with hydrogen is hydrogen ion H + and gaseous hydrogen gas H2

[0007] and the electrode potential is given by the Nernst equation as [H + (aq)] / [ H2(g)]. + [(aq)] is the hydrogen ion activity of the aqueous solution, and [H2(g)] is the activity of the partial pressure of hydrogen gas in the gas. Hydrogen, H2, exists in trace amounts due to atmospheric, biological, geological, or artificial sources, but measurements of the hydrogen electrode potential have not been performed other than as a standard hydrogen electrode or a reversible hydrogen electrode. This invention relates to a method and device for measuring the hydrogen electrode potential using effective hydrogen gas partial pressure.

[0008] In aqueous solutions, redox reactions occur through aerobic metabolism, anaerobic metabolism, and inorganic chemical reactions. Standard redox potentials for various redox substances have been reported based on the Nernst equation, and the direction of each redox reaction can be theoretically predicted. However, the standard redox potential does not determine the actual rate at which the redox reaction occurs. On the other hand, electrochemical kinetics assumes that metal corrosion reactions occur as both cathodic and anodic reactions at the same electrode, and the Butler-Volmer equation shows that the local current depends on the electrode potential. The direction and rate of the reaction are determined by the electrode potential (natural potential) when all currents in the redox system involved are zero. Therefore, the reaction rate of redox reactions involving electron transfer cannot be determined without measuring the electrode potential.

[0009] Although dissolved oxygen does not directly react with water molecules, it does shift the redox potential in a positive direction, i.e., more noble. Dissolved oxygen concentration is measured in water quality tests, and it is known that the presence of oxygen can cause the redox potential to rise to +200 to +400 mV. For example, in the water quality management of boiler water that oxygenates thermal power plants, detecting approximately 10 ppb of dissolved oxygen causes a sudden rise in the corrosion potential of pipes from approximately -400 mV to approximately 100 mV. When the electrode potential of an aqueous solution shifts to the positive side due to an increase in dissolved oxygen or hydrogen ion concentration, the Butler-Volmer equation of electrochemical kinetics indicates that the anodic (oxidation) reaction accelerates and the cathodic (reduction) reaction rate decreases, resulting in corrosion of the pipes. Measuring the corrosion potential of pipes is used as a water quality measurement method.

[0010] Meanwhile, radiation decomposes water molecules in the cooling systems of nuclear power plants, generating chemical species such as oxygen. Therefore, hydrogen injection is used to prevent dissolved oxygen from shifting the redox potential toward a more noble direction in water quality management at nuclear power plants. Guidelines for hydrogen injection methods for recirculation systems were published in 1987. Injecting 1 ppm of hydrogen reduces the dissolved oxygen concentration in the recirculation system to 2 ppm, but the corrosion potential of steel remains above 0 mV. Even with the same dissolved oxygen concentration, injecting 1.3 ppm of hydrogen suppresses the corrosion potential of steel below -230 mV, protecting the recirculation system piping. As the hydrogen gas partial pressure increases, the electrode potential of the aqueous solution shifts negatively, becoming more noble. This accelerates the cathodic (reduction) reaction and reduces the anodic (oxidation) reaction, preventing corrosion of the piping. In other words, when the dissolved oxygen concentration in an aqueous solution is low, the hydrogen electrode potential of the aqueous solution, measured by hydrogen partial pressure measurement, can be used to evaluate the redox state.

[0011] Anaerobic respiration and fermentation occur under conditions of low oxygen levels. + The cathode (reduction) reaction reduces NADH to NADH in the electron transport chain, and + The anodic (oxidation) reaction, which oxidizes oxygen to oxygen, occurs in parallel. Therefore, the redox potential of an aqueous solution with little dissolved oxygen depends on the hydrogen electrode potential, so fluctuations in hydrogen partial pressure directly affect the cathode and anodic reaction rates. In anaerobic bacterial cultivation and fermentation such as brewing, the redox state is evaluated using the relative hydrogen score rH.

[0012] Under aerobic conditions where there is sufficient oxygen, the dissolved oxygen concentration is an important factor in the reaction rate. In aerobic respiration, oxygen is the final electron acceptor, and the oxygen partial pressure in tissues depends on the diffusion rate. However, since the oxygen diffusion rate is the rate-limiting step, the oxygen partial pressure in aqueous solution remains constant even in aerobic conditions. Even in aerobic respiration, organic matter is broken down to produce NAD. + The cathode (reduction) reaction reduces NADH to NADH in the electron transport chain, and +In parallel, an anodic (oxidation) reaction occurs, oxidizing the water to oxygen. Like anaerobic respiration, the decomposition of organic matter depends on the redox potential of the aqueous solution. Therefore, the relative hydrogen score (rH) has been used to manage water quality in aquariums and to evaluate the redox state of seawater and the ocean. However, some reports have suggested that the redox potential (ORP) should not be used to measure hydrogen.

[0013] The following Patent Document 1 discloses a method and an apparatus for measuring dissolved oxygen in a liquid using spectral information of light.

[0014] JP 2021-156616 A Figures 4 and 5, Claim 1

[0015] An aqueous solution is a solution in which solid, liquid, and gaseous substances are dissolved. The redox potential of an aqueous solution is affected by the concentration and ratio of the dissolved redox substances, dissolved oxygen, and pH. The measurement method and device described in Patent Document 1 can measure dissolved oxygen in an aqueous solution. In this invention, the concept of an aqueous solution includes not only the narrow definition of an aqueous solution but also all bodies of water in nature, such as oceans, lakes, and rivers. Dissolved oxygen and pH, which are factors that cause oxidation in an aqueous solution, can be directly measured. However, dissolved hydrogen, which is a factor that causes reduction in an aqueous solution, is approximated by the redox potential and pH as a relative hydrogen score. Therefore, it is necessary to measure the effective hydrogen gas partial pressure of the aqueous solution and directly calculate the hydrogen electrode potential of the aqueous solution.

[0016] The standard hydrogen electrode has a hydrogen ion activity of 1, which is the platinum electrode potential in equilibrium with 1 atmosphere of hydrogen gas, and is used as the reference for oxidation-reduction potential (0V). Hydrogen gas bubbles are generated so that the partial pressure of hydrogen gas in the aqueous solution becomes 1 atmosphere. The hydrogen electrode potential is calculated by the hydrogen half-reaction:

[0017] When measuring the hydrogen electrode potential of an aqueous solution, for example, in an aqueous solution used in a chemical reaction, a culture medium used for living organisms, or river water or seawater in the natural world, it is difficult to directly measure the hydrogen gas partial pressure due to solubility, so in the present invention, the hydrogen partial pressure of the gas phase in equilibrium with the aqueous solution is used.

[0018] That is, according to the present invention, there is provided a method for acquiring the redox state of an aqueous solution as a hydrogen electrode potential, comprising the steps of: acquiring the partial pressure of available hydrogen gas in a gas phase that is in equilibrium with an aqueous solution; acquiring the temperature of the gas phase; acquiring the hydrogen ion activity (pH) of the aqueous solution; calculating the inverse logarithm (pH2) of the partial pressure; and analyzing the hydrogen electrode potential of the aqueous solution using the temperature, the hydrogen ion activity (pH), and the inverse logarithm (pH2).

[0019] Furthermore, according to the present invention, there is provided a method for obtaining the effective hydrogen gas partial pressure of an aqueous solution, comprising the steps of: measuring the effective hydrogen gas partial pressure of a gas that has been brought into equilibrium by mixing a part of the aqueous solution with a gas having a known hydrogen gas partial pressure in a sealed container; and calculating the effective hydrogen gas partial pressure of the aqueous solution from the hydrogen partial pressure of the gas in the sealed container.

[0020] Furthermore, according to the present invention, there is provided a method for obtaining the effective hydrogen gas partial pressure of an aqueous solution, comprising the steps of: measuring the concentration of dissolved hydrogen gas in the aqueous solution; and calculating the effective hydrogen gas partial pressure of a gas phase in equilibrium with the aqueous solution using the concentration of dissolved hydrogen gas and the solubility of the dissolved hydrogen gas.

[0021] Furthermore, according to the present invention, there is provided an apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential, comprising: a hydrogen gas partial pressure acquisition unit that acquires the partial pressure of hydrogen gas in a gas phase that is in equilibrium with an aqueous solution; a temperature acquisition unit that acquires the temperature of the gas phase; a hydrogen ion activity (pH) acquisition unit that acquires the hydrogen ion activity (pH) of the aqueous solution; and a calculation unit that calculates the inverse logarithm (pH2) of the hydrogen gas partial pressure and analyzes the hydrogen electrode potential of the aqueous solution from the hydrogen gas index pH2 defined by the inverse logarithm (pH2), the temperature, and the hydrogen ion activity (pH).

[0022] When the hydrogen gas index pH2 is defined as the inverse logarithm of the effective hydrogen gas partial pressure (pH2=-log[hydrogen gas partial pressure (Pa) / 100 kPa]), the hydrogen gas index pH2 is calculated using a predetermined calculation formula stored in the storage means:

[0023] In a preferred embodiment of the method of the present invention for obtaining the redox state of an aqueous solution as a hydrogen electrode potential, the method further comprises the steps of reading out the value of the hydrogen electrode potential obtained by the predetermined arithmetic expression, calculating the hydrogen electrode potential using the predetermined arithmetic expression, and displaying the obtained hydrogen electrode potential and pH2.

[0024] Furthermore, a preferred embodiment of the method of the present invention for obtaining the redox state of an aqueous solution as a hydrogen electrode potential comprises a step of displaying the change in the hydrogen electrode potential as a fluctuation in the hydrogen gas index pH2.

[0025] Furthermore, a preferred embodiment of the device of the present invention for acquiring the redox state of an aqueous solution as a hydrogen electrode potential is one in which the hydrogen gas partial pressure acquisition unit, the temperature acquisition unit, and the hydrogen ion activity (pH) acquisition unit are attached, forming a non-flow area that prevents the flow of liquid and gas, and having a flow area or membrane that allows the flow of at least hydrogen gas.

[0026] In addition, when the hydrogen gas index pH2 is defined as the inverse logarithm of the effective hydrogen gas partial pressure (pH2=-log[hydrogen gas partial pressure (Pa) / 100 kPa]), the hydrogen gas index pH2 is calculated using a predetermined calculation formula stored in a storage means:

[0027] and calculating the hydrogen electrode potential by the predetermined arithmetic expression; and means for displaying the obtained hydrogen electrode potential and pH2.

[0028] In the method and apparatus of the present invention for obtaining the oxidation-reduction state of an aqueous solution as a hydrogen electrode potential, the effective partial pressure of hydrogen gas in the gas phase in equilibrium with the aqueous solution, the temperature, and the hydrogen ion activity (pH) of the aqueous solution are obtained. The effective partial pressure fugacity of hydrogen gas [H2] is expressed as a ratio to the reference pressure P0. Using the reference pressure P0 and the hydrogen gas partial pressure PH2,

[0029] Then, the hydrogen electrode potential can be calculated using the following equation, which includes the gas constant R (8.31 J / K / ml), absolute temperature K (K), and Faraday's constant F (96485 C / mol).

[0030] Next, the hydrogen electrode potential is analyzed using the measured temperature, pH, and the inverse logarithm of the effective hydrogen gas partial pressure (pH2). For example, when the temperature T is 25°C (298.15K), the hydrogen electrode potential is Eh = 0.0296 × pH2 - 0.0592 × pH (V). When the pH is 7.0, Eh = 29.6 × pH2 - 414.4 (mV). In other words, the hydrogen electrode potential can be calculated by measuring the partial pressure of gaseous hydrogen gas in equilibrium with the aqueous solution, the temperature, and the pH of the aqueous solution.

[0031] The change in hydrogen electrode potential of an aqueous solution, ΔEh, can be calculated from the change in pH2, ΔpH2, when the pH is constant.

[0032] Next, if necessary, the oxidation-reduction state is expressed by the hydrogen electrode potential and the inverse logarithm of the hydrogen gas partial pressure (pH2). For example, when the temperature is 25°C (298K),

[0033] It should be noted that the display of the hydrogen electrode potential and the inverse logarithm of the hydrogen gas partial pressure (pH2) is not essential at this stage, and an electrical signal indicating these values ​​may be output. That is, such an electrical signal may be used to notify the user of the hydrogen electrode potential and the inverse logarithm of the hydrogen gas partial pressure (pH2) by voice, or such an electrical signal may be transmitted to a remote location where it may be displayed or printed, or various operations may be performed using such an electrical signal.

[0034] Hydrogen gas is stable at room temperature and pressure, and does not undergo chemical reactions with anything other than fluorine. The enzyme that catalyzes the reversible oxidation-reduction reaction of molecular hydrogen H2 is hydrogenase, which is important in anaerobic metabolism. Until now, the concentration of dissolved hydrogen in aqueous solutions under anaerobic conditions has been measured as an indicator of pollution. However, hydrogen gas exists in trace amounts in the environment from atmospheric, microbial, geological, and anthropogenic sources. Hydrogen gas is a strong reducing agent, and even trace amounts affect the electrode potential of an aqueous solution. Therefore, hydrogen gas is one of the determining factors of the electrode potential of an aqueous solution.

[0035] In the present invention, the effective hydrogen partial pressure of the gas phase in equilibrium with an aqueous solution is measured using a housing formed from a non-flow region that prevents the flow of liquid and gas and a housing having a flow region or membrane that allows the flow of at least hydrogen gas. For a liquid in a closed space, the hydrogen partial pressure of the gas phase in equilibrium is measured. For an aqueous solution in an open space, a closed space in equilibrium with the aqueous solution is formed using a measuring device, and the hydrogen partial pressure of the gas phase in equilibrium is measured. Alternatively, a closed space in equilibrium with the aqueous solution to be measured is formed using a semipermeable membrane through which hydrogen gas passes, and the hydrogen partial pressure of the gas phase in equilibrium is measured.

[0036] Another method involves mixing a portion of the solution with a gas of known hydrogen partial pressure in a sealed container and measuring the effective hydrogen partial pressure of the resulting gas. Measurements can be performed by inserting the measurement device housing into the sealed container, or by injecting the equilibrated gas into a measurement device, such as a high-sensitivity sensor gas chromatograph (SGHA-P3-A, Nissha FIS Inc.), measuring hydrogen concentrations of 10 to 10,000 ppb (parts per billion), and then determining the hydrogen partial pressure. The effective hydrogen partial pressure of the solution is then calculated from the hydrogen partial pressure of the gas in the sealed container. For example, a potential-detecting gas sensor can measure hydrogen partial pressures with a sensitivity of 0.1 ppm to 2%. Since atmospheric pressure is 1 atmosphere, the hydrogen partial pressure = 1 atmosphere × hydrogen gas concentration. The temperature of the gas phase and the pH of the solution are also measured.

[0037] When the dissolved hydrogen concentration is measured directly, the hydrogen gas partial pressure is calculated from the dissolved hydrogen concentration using Henry's law.

[0038] where k H is Henry's constant, C aq is the molar concentration of dissolved hydrogen, and P is the partial pressure of hydrogen gas in contact with the liquid. Using the molecular weight of hydrogen, 2.0, hydrogen gas partial pressure = dissolved hydrogen gas concentration ÷ (Henry's constant × 2.0). To solve the problem, measure the dissolved hydrogen gas concentration in the aqueous solution, and use the aforementioned hydrogen gas concentration and hydrogen gas solubility to calculate the effective hydrogen gas partial pressure in the gas phase that is in equilibrium with the aqueous solution. For example, at 25°C,

[0039] At an atmospheric pressure of 1 bar (atm), the hydrogen concentration is

[0040] Therefore, the partial pressure of hydrogen gas

[0041] The effective partial pressure of hydrogen [H2] is the standard atmospheric pressure P 0 =1bar=1×10 5 It is expressed as the ratio of Pa to PH2. is.

[0042] Hydrogen partial pressure P in the sealed container X The partial pressure of hydrogen gas in the aqueous solution P H2 When measuring the temperature of the closed container and the aqueous solution, the partial pressure of hydrogen gas in the container before adding the aqueous solution is P A The volume of the gas phase in the closed vessel is V A The volume of the liquid phase is V S Since the number of moles of gas before and after equilibrium is the same, the gas constant is Using

[0043] For example, when the temperature is 25°C (298.15K), If

[0044] The solubility of gases is based on Sander R.'s Compilation of Henry's Law Constants for Inorganic and Organic Species of Potential Importance in Environmental Chemistry.

[0045] According to the present invention, under conditions where the dissolved oxygen can be considered constant, the redox potential of the aqueous solution is measured as the hydrogen electrode potential, and changes in the redox potential of the aqueous solution can be evaluated using pH2, allowing the redox state to be managed.

[0046]

[0023] Fig. 1 is a schematic diagram showing a preferred embodiment of a temperature, hydrogen gas partial pressure, and pH measuring unit constituting a part of the apparatus of the present invention for executing a method for obtaining the redox state of an aqueous solution as a hydrogen electrode potential, the schematic diagram showing a unit used in a closed space where the aqueous solution to be measured and a gas in contact with the aqueous solution are in equilibrium. Fig. 2 is a schematic diagram showing a preferred embodiment of a temperature, hydrogen gas partial pressure, and pH measuring unit constituting a part of the apparatus of the present invention for executing a method for obtaining the redox state of an aqueous solution as a hydrogen electrode potential, the schematic diagram showing a unit used in an open space where the aqueous solution to be measured and a gas in contact with the aqueous solution are not in equilibrium. Fig. 3 is a schematic diagram showing a preferred embodiment of a temperature, hydrogen gas partial pressure, and pH measuring unit constituting a part of the apparatus of the present invention for executing a method for obtaining the redox state of an aqueous solution as a hydrogen electrode potential, the schematic diagram showing a unit used in a closed container where the aqueous solution to be measured and a gas in contact with the aqueous solution, a gas with a known hydrogen partial pressure, are mixed together in an airtight container and reach equilibrium. 1 is a schematic diagram showing a preferred embodiment of an apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential of the present invention, which executes a method for acquiring the redox state of an aqueous solution as a hydrogen electrode potential of the present invention; 2 is a block diagram showing an example of an apparatus used for verifying the hydrogen electrode potential of an aqueous solution obtained by the method for acquiring the redox state of an aqueous solution as a hydrogen electrode potential of the present invention and / or the apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential of the present invention; 3 is a graph illustrating verification by an apparatus used for verifying the hydrogen electrode potential obtained by the method and apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential of the present invention.

[0047] A preferred embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic diagram showing a preferred embodiment of a temperature / hydrogen gas partial pressure / pH measuring unit 20A constituting part of an apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential, which executes a method for acquiring the redox state of an aqueous solution as a hydrogen electrode potential of the present invention. This schematic diagram shows an apparatus used in a closed space where gases in contact with an aqueous solution 9 to be measured are in equilibrium. The apparatus shown in FIG. 1 has a housing 1 that is placed in close proximity to, but not in contact with, the water surface 8A of the aqueous solution 9 to be measured. In a laboratory, the aqueous solution 9 is contained in an appropriate container (not shown). However, in natural environments such as oceans, lakes, and rivers, the housing 1 is placed near the water surface 8A.

[0048] The housing 1 has a non-flow area (shown by a solid line in FIG. 1 ) that prevents the permeation and flow of liquid and gas throughout the entire housing 1 except for a portion adjacent to the water surface 8A of the aqueous solution 9. The housing 1 also has a gas flow area 2 (shown by a dashed line in FIG. 1 ) that allows the permeation and flow of at least hydrogen gas but prevents the permeation and flow of liquid within the portion adjacent to the water surface 8A. The housing 1 is equipped with the following three measurement units (acquisition units): a hydrogen gas partial pressure measurement unit 4 that acquires the hydrogen gas partial pressure of the gas 3A within the internal space 3 of the housing 1; a temperature measurement unit 5 that acquires the temperature of the gas 3A within the internal space 3 of the housing 1; and a pH measurement unit (also called a pH meter) 6 that measures the pH of the aqueous solution 9. The hydrogen gas partial pressure measurement unit 4 is disposed in the gas phase that is in equilibrium with the aqueous solution to measure the hydrogen gas exponent pH2 and hydrogen electrode potential of the aqueous solution. The hydrogen gas partial pressure measuring unit 4 may be, for example, a semiconductor hydrogen concentration meter that detects the change in electrical resistance that occurs when the heated metal oxide semiconductor comes into contact with hydrogen gas as the hydrogen gas concentration, such as the SG8541 manufactured by Riken Keiki Co., Ltd. The hydrogen gas partial pressure is calculated by multiplying the measured hydrogen concentration by 1 atmosphere (10 5 Pa) can be calculated.

[0049] The sensor part at the lower tip of the pH measurement unit 6 in the figure is inserted into the aqueous solution 9. That is, in the case of FIG. 1 , only the sensor part at the tip of the pH measurement unit 6 is immersed in the aqueous solution 9, while the part of the housing 1 close to the water surface 8A is above the water surface 8A and is not immersed in the aqueous solution 9. With this configuration, gas 3A in equilibrium with the aqueous solution 9 flows into the internal space 3 of the housing 1 through the gas flow region 2. The gas flow region 2 can be configured by an opening provided at the bottom of the housing 1 or a membrane that allows the permeation and flow of gas 3A containing at least hydrogen gas. Therefore, the hydrogen gas partial pressure and temperature of gas 3A in equilibrium with the aqueous solution 9 are acquired and measured by the hydrogen gas partial pressure measurement unit 4 and the temperature measurement unit 5, respectively.

[0050] The output signals of the hydrogen gas partial pressure measuring unit 4, temperature measuring unit 5, and pH measuring unit 6 are supplied to a calculation / control unit 24 of the hydrogen electrode potential measuring device, which will be described later, via corresponding interfaces 4A, 5A, and 6A, respectively. The device comprises a housing 1 formed from a non-flow region that prevents the flow of liquid, a gas flow region 2 that allows the flow of at least hydrogen gas, a hydrogen partial pressure measuring unit 4 that measures the hydrogen partial pressure of gas 3A in space 3 within housing 1, a temperature measuring unit 5 that measures the temperature of gas 3A to be measured, a pH measuring unit 6 that measures the pH of aqueous solution 9, and interfaces 4A, 5A, and 6A that serve as means for outputting information on the hydrogen gas partial pressure, temperature, and pH, respectively. The positions of the water surface 8 of aqueous solution 9 and the measuring device are shown.

[0051] When the gas 3A and the aqueous solution 9 are in equilibrium in a closed space, the pH measuring unit 6 is immersed in the aqueous solution 9 above the water surface 8 of the aqueous solution 9. The gas 3 in equilibrium with the aqueous solution 9 is measured by the hydrogen gas partial pressure measuring unit 4 through the opening of the gas flow region 2 or a membrane that is permeable to the gas 3.

[0052] FIG. 2 is a schematic diagram showing a preferred embodiment of a temperature / hydrogen gas partial pressure / pH measuring unit 20B constituting part of an apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential according to the present invention, which executes a method for acquiring the redox state of an aqueous solution as a hydrogen electrode potential according to the present invention. This schematic diagram shows a device used in an open space when the aqueous solution 9 to be measured and the gas 3B in contact with the aqueous solution 9 are not in equilibrium. In FIG. 2, elements that are the same as or correspond to those in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The following describes the configuration of FIG. 2 that differs from FIG. 1. In FIG. 2, a portion of the lower part of the housing 1 in the drawing is immersed in the aqueous solution 9. At this time, at least the gas flow region 2 is immersed in the aqueous solution 9, and the housing 1 is placed in the aqueous solution 9 so that the aqueous solution 9 and the closed space within the housing 1 are separated by the gas flow region 2. The gas 3B in the closed space 3 within the housing 1, surrounded by the non-flow region, reaches equilibrium with the aqueous solution 9 through the gas flow region 2. This equilibrium gas 3B is measured by the hydrogen gas partial pressure measuring unit 4. In realizing the temperature / hydrogen gas partial pressure / pH measuring unit 20B, a waiting time is set in advance for the space 3 inside the housing 1 in Figure 1 to reach equilibrium with the hydrogen in the aqueous solution 9. The time for hydrogen diffusion is determined by the size of the space inside the housing 1 and the size of the gas flow region 2. In Figure 2, the gas flow region 2 is the time for diffusion through an opening or a membrane that is permeable to gas 3B.

[0053] In an open space where the gas 3B and the aqueous solution are not in equilibrium, the gas flow region 2, including the non-flow portion of the substrate 1 through which neither the gas 3B nor the liquid passes, is immersed in the aqueous solution 9, above the water surface 8 of the aqueous solution 9. The pH meter 6 is immersed in the aqueous solution 9. At this time, at least the gas flow region 2 is immersed in the aqueous solution 9, and the pH meter 6 is placed in the aqueous solution 9 so that the aqueous solution 9 and the closed space within the substrate 1 are sandwiched between the gas flow region 2. The gas 3B in the closed space within the substrate 1 surrounded by the non-flow portion reaches equilibrium with the aqueous solution 9 through the gas flow region 2, the opening, or the membrane through which the gas 3B passes. The gas 3B in this equilibrium state is measured by the hydrogen gas partial pressure measurement unit 4.

[0054] 3 is a schematic diagram showing a preferred embodiment of a temperature / hydrogen gas partial pressure / pH measuring unit 20C constituting part of an apparatus for obtaining the redox state of an aqueous solution 9 as a hydrogen electrode potential, which executes a method for obtaining the redox state of an aqueous solution as a hydrogen electrode potential of the present invention. The diagram shows the aqueous solution 9 to be measured and the gas 3B in contact with the aqueous solution 9, which is used when the gas 3B has a known hydrogen partial pressure and is mixed in a sealed container to reach an equilibrium state. In FIG. 3, elements that are the same as or correspond to those in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The following describes the parts of the configuration of FIG. 3 that are different from those in FIG. 1.

[0055] A portion of the aqueous solution 9 and a gas 3 with a known hydrogen gas partial pressure are mixed in a sealed container 10, and the effective hydrogen gas partial pressure of the gas 3B that has reached equilibrium is measured. At this time, at least the gas flow region 2 is immersed in the aqueous solution 9, and the container 1 is placed in the aqueous solution 9 so that the aqueous solution 9 and the closed space 3 in the container 1 are sandwiched between the gas flow region 2. The gas 3B in the closed space 3 of the housing 1 surrounded by the non-flow portion reaches equilibrium with the aqueous solution 9 through the gas flow region 2, the opening, or the membrane 8 through which the gas 3B passes. The gas 3B in this equilibrium state is measured by the hydrogen gas partial pressure measuring unit 4.

[0056] In realizing the temperature / hydrogen gas partial pressure / pH measuring units 20A, 20B, 20C, a waiting time is set in advance for the space 3 within the housing 1 in Figures 1 to 3 to reach equilibrium with the hydrogen in the aqueous solution 9. The hydrogen diffusion time is determined by the size of the space 3 within the housing 1 and the size of the gas flow region 2. In Figure 1, the gas flow region 2 is the time for diffusion through an opening or a membrane that is permeable to gas 3A. In Figure 2, it is the time for diffusion through a membrane that is permeable to gas 3B in the gas flow region 2.

[0057] Figure 4 is a block diagram showing a preferred embodiment of the hydrogen electrode potential measuring device for an aqueous solution of the present invention. A preferred embodiment of the hydrogen electrode potential measuring method for an aqueous solution of the present invention will also be described with reference to Figure 4. The temperature, hydrogen gas partial pressure, and pH measuring units 20A, 20B, and 20C shown in Figures 1 to 3 are designated by the reference numeral 20 in Figure 4. In other words, one of the arrangements shown in Figures 1 to 3 is selected depending on the measurement situation.

[0058] In the present invention, the hydrogen electrode potential of the aqueous solution 9 is measured. However, because it is difficult to directly measure the hydrogen gas partial pressure in, for example, aqueous solutions used in chemical reactions, culture media used in living organisms, or river water or seawater in nature due to solubility, the present invention uses the hydrogen partial pressure of the gas phase in equilibrium with the aqueous solution. The hydrogen gas partial pressure measurement unit 4 is placed in the gas phase in equilibrium with the aqueous solution 9 to measure the hydrogen gas index pH2 and hydrogen electrode potential of the aqueous solution 9. In addition to the above-mentioned devices, the hydrogen gas partial pressure measurement unit 4 can also be a Clark electrode-type hydrogen gas concentration meter that uses a platinum catalyst with a membrane to detect changes in current due to voltage as the dissolved hydrogen gas concentration, such as the hydrogen microsensor, micromanipulator, and microsensor multimeter from Unisense (Denmark). The hydrogen gas partial pressure at equilibrium can be calculated by dividing the measured dissolved hydrogen gas concentration by the saturated dissolved hydrogen gas concentration determined by temperature. The output signals of the temperature, hydrogen gas partial pressure, and pH measuring unit 20 indicate the measured hydrogen gas partial pressure, temperature, and pH, and are sent to the calculation / control unit 24. A predetermined calculation formula is stored in advance in the memory unit 26, and the calculation results of the calculation / control unit 24 are stored as needed. The input unit 22 is used to give a command to the calculation / control unit 24 to start calculation, and to set the value of the hydrogen ion exponent pH, which will be described later, in the calculation / control unit 24.

[0059] The hydrogen electrode potential of the aqueous solution calculated by the calculation / control unit 24 is sent to the display unit 28 and displayed as a numerical value. The input unit 22, calculation / control unit 24, memory unit 26, and display unit 28 can also be configured with a personal computer's keyboard and mouse, central processing unit (CPU), memory (RAM, ROM), and display. In this case, the aforementioned interfaces 4A, 5A, and 6A are used as necessary to supply the output signals of the temperature, hydrogen gas partial pressure, and pH measurement unit 20 to the personal computer's USB input unit in an appropriate format. In addition to displaying the hydrogen electrode potential of the aqueous solution, the display unit 28 can also display the calculated hydrogen gas index pH2, the measured temperature, and the measured pH. In addition to the above calculations, the calculation / control unit 24 can also control the memory unit 26 and the display unit 28 in accordance with instructions from the device operator input via the input unit 22.

[0060] The storage unit 26 stores in advance an arithmetic expression for calculating the hydrogen electrode potential Eh of an aqueous solution. The basis of the arithmetic expression is as follows:

[0061] For example, when the temperature T is 25°C (298.15K), the hydrogen electrode potential is Eh = 0.0296 × pH2 - 0.0592 × pH (V). Here, since the pH of the aqueous solution is measured simultaneously as described above, an appropriate value can be input to the calculation unit via the input unit 22. On the other hand, since the range of change in pH is small in a pH buffer solution, it can also be fixed at, for example, 7.0. Therefore, it is possible to input 7.0 as the pH via the input unit 22 and store this 7.0 in advance in the memory unit 26 for use, but it is also possible to input 7.0 as the pH and use the stored value, and then use the basic calculation formula described above. Therefore, when the pH is fixed at 7.0, the simplified calculation formula is stored in the memory unit 26 instead of the basic calculation formula. The basic and simplified arithmetic expressions can be stored in the memory unit 26. Both the basic and simplified arithmetic expressions can be stored in the memory unit 26, and either of the arithmetic expressions can be read out and provided to the calculation / control unit 24 in response to an instruction from the input unit 22 as needed. The output signals from the temperature, hydrogen gas partial pressure, and pH measurement unit 20 indicate the measured hydrogen gas partial pressure, temperature, and pH, and are sent to the calculation / control unit 24. These three pieces of information are sent sequentially, for example, in a time-sharing manner. The memory unit 26 stores predetermined arithmetic expressions and stores the results of calculations performed by the calculation / control unit 24 as needed. The input unit 22 is used to give the calculation / control unit 24 an instruction to start calculations and to set the value of the hydrogen ion exponent pH, which will be described later, in the calculation / control unit 24.

[0062] The hydrogen electrode potential of the aqueous solution calculated by the calculation / control unit 24 is sent to the display unit 28 and displayed as a numerical value. In addition to displaying the hydrogen electrode potential of the aqueous solution, the display unit 28 can also display the calculated hydrogen gas index pH2, the measured temperature, and the pH. In addition to the above calculations, the calculation / control unit 24 can also control the memory unit 26 and the display unit 28 in accordance with instructions from the operator of the device inputted via the input unit 22.

[0063] As an alternative method, the memory unit 26 stores in advance an arithmetic formula for calculating the hydrogen electrode potential E of an aqueous solution. When the dissolved hydrogen concentration is measured directly, the hydrogen gas partial pressure is calculated from the dissolved hydrogen concentration using Henry's law. For example, when the temperature is 25°C and the atmospheric pressure is 1 bar (atm), the saturated hydrogen concentration is 1.6 ppm, so the basis of the arithmetic formula is the hydrogen gas partial pressure

[0064] In addition, a part of the solution is mixed with a gas of known hydrogen gas partial pressure in a sealed container, and the effective hydrogen gas partial pressure Px of the gas in equilibrium is measured. At this time, the hydrogen partial pressure P X The partial pressure of hydrogen gas in the aqueous solution P H2 When measuring the temperature of the closed container and the aqueous solution, the partial pressure of hydrogen gas in the container before adding the aqueous solution is P A The volume of the gas phase in the closed vessel is V A The volume of the liquid phase is V SSince the number of moles of gas before and after equilibrium is the same, the basic formula using the gas constant R is

[0065] Next, the above simplification can be used to calculate the variation in hydrogen electrode potential. For example, when pH is constant, the variation in hydrogen electrode potential ΔEh is calculated from the change in hydrogen gas index pH2 ΔpH2 as

[0066] When the temperature is 25°C (298.15K), the fluctuation of the hydrogen electrode potential is can be approximated as follows.

[0067] In a preferred embodiment of the measurement device, when the aqueous solution to be measured is in a closed space, hydrogen gas is in equilibrium between the gas and liquid phases, so the hydrogen partial pressure in the gas phase, temperature, and pH of the aqueous solution are measured. The gas 3A in the closed space is in equilibrium with the liquid, and the hydrogen gas partial pressure in the gas phase is measured. Next, in the case of an aqueous solution in an open space, hydrogen gas is not in equilibrium between the gas and liquid phases, so the measurement device is partially or completely immersed in the liquid to bring the device and the liquid into equilibrium. The hydrogen partial pressure of the gas 3B in the device is measured. The temperature of the gas phase and the pH of the aqueous solution are also measured. If the measurement device cannot be immersed in the aqueous solution, the aqueous solution is collected in a separate container, and the hydrogen partial pressure of the gas phase in equilibrium with the enclosed gas 3B is measured at the same temperature as the aqueous solution. The temperature and pH of the aqueous solution are measured simultaneously.

[0068] Next, a preferred embodiment of a system used in the hydrogen electrode potential acquisition method and the hydrogen electrode potential verification method obtained by the apparatus of the present invention will be described. FIG. 4 is a block diagram showing a preferred embodiment of the method used in the hydrogen electrode potential acquisition method for an aqueous solution and the hydrogen electrode potential verification method obtained by the apparatus of the present invention. This system includes a medical oxygen source 30, an oxygen-hydrogen gas supply source 32, a flowmeter 34, a switching valve 38, a bubbling device 40, a thermometer, a pH and potential measuring device 46 provided in a container 41 constituting the bubbling device 40, an interface 50, a display 52, and a memory unit 54. The bubbling device 40 can be a device commonly used as an air humidifier. Externally supplied gas is introduced into the container 41 via a conduit 42, the introduced gas is bubbled in the liquid in the container 41, and the gas is then discharged from the upper space of the container 41 to the outside via an exhaust pipe 44.

[0069] The medical oxygen source 30 delivers reduced-pressure medical oxygen from a medical oxygen cylinder. The oxygen-hydrogen gas supply source 32 delivers a mixed gas containing 0.5 L of oxygen and 1.0 L of hydrogen per minute. The reduced-pressure medical oxygen delivered from the medical oxygen source 30 and the mixed gas containing oxygen and hydrogen delivered from the oxygen-hydrogen gas supply source 32 are supplied to the bubbling device 40 via a flow meter 34, with either the reduced-pressure medical oxygen delivered from the medical oxygen source 30 or the mixed gas containing oxygen and hydrogen delivered from the oxygen-hydrogen gas supply source 32 selected by a selector valve 38. The bubbling device 40 is generally used as an air humidifier, and its container 41 can contain a phosphate buffer solution (10 mM, pH 7.1) 56. For example, PBS(-) 166-23555 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. can be used as such a phosphate buffer solution. A preferred embodiment of the method for verifying the hydrogen electrode potential of an aqueous solution of the present invention will be described with reference to FIG. 2.

[0070] A phosphate buffer solution (10 mM, pH 7.1) 56 is placed in a container 41 constituting the bubbling device 40. The temperature, pH, and oxidation-reduction potential (ORP) of the phosphate buffer solution in the container 41 are measured using a pH and oxidation-reduction potential measuring device 46. Examples of the temperature, pH, and oxidation-reduction potential measuring device 46 include the pH6600 and ORP-6600S manufactured by Custom Co., Ltd. The output signals from the temperature, pH, and oxidation-reduction potential measuring device 46 are transmitted to a display unit 52 and a memory unit 54 via a signal transmission line 48 and an interface 50. After the pH and reduction potential are measured and stored in the memory unit 44, the switching valve 38 is operated to supply medical oxygen to the bubbling device 40 at a first predetermined flow rate for a first predetermined time. Here, the first predetermined flow rate is 0.5 L / min, and the first predetermined time is 1 hour. For example, medical oxygen manufactured by Air Water Corporation can be used as the medical oxygen.

[0071] After the first predetermined time of supply is completed, the temperature, pH, and oxidation-reduction potential ORP of the phosphate buffer solution in the container 41 are measured again by the pH and reduction potential measuring device 46, and the measured potentials are stored in the memory unit 54. Next, the oxidation-reduction potential ORP measured after supplying medical oxygen is corrected using the oxidation-reduction potential ORP measured before supplying medical oxygen. For example, if the oxidation-reduction potential ORP measured before supplying medical air is 310 mV, this potential is set to the reference potential of 0 mV. In other words, if the oxidation-reduction potential ORP measured after supplying medical air is 305 mV, 310 mV is subtracted from this value to determine a change in hydrogen electrode potential of −5 mV.

[0072] The phosphate buffer solution in the container 41 is discharged, and new phosphate buffer solution is placed in the container 41. The temperature, pH, and oxidation-reduction potential ORP of the new phosphate buffer solution in the container 41 are measured in the same manner as described above. After the measurements and storage of the measured values ​​are completed, an oxygen-hydrogen mixed gas containing a predetermined concentration of hydrogen is supplied to the bubbling device 40 at a second predetermined flow rate for a second predetermined time. Here, the second predetermined flow rate is 1.5 L / min, and the second predetermined time is 1 hour. The predetermined concentration is, for example, 66%, and a hydrogen supply device such as the Helix Hydrogen Supply System, Hycelvator EH90, can be used.

[0073] After the second predetermined time of gas supply has ended, the temperature, pH, and oxidation-reduction potential ORP of the new phosphate buffer solution in the container 41 are measured again by the pH and potential measuring device 46 and stored. The oxidation-reduction potential ORP measured after the oxygen-hydrogen mixed gas has been supplied is corrected by the oxidation-reduction potential ORP measured before the oxygen-hydrogen mixed gas was supplied. If the measured potential is −161 mV, 41 mV is subtracted as described above to determine the change in hydrogen electrode potential as −202 mV.

[0074] Using the two ORP values ​​obtained in this way, we investigated the change in ORP with respect to pH2, assuming a pH of 6.2 before bubbling with medical oxygen and oxygen-hydrogen mixed gas, and a pH of 0.18 after bubbling with oxygen-hydrogen gas containing a predetermined concentration of hydrogen. That is, there was no statistically significant change in the ORP or pH before and after bubbling with hydrogen-free medical oxygen. On the other hand, as shown in the graph of Figure 3, the ORP was +41 mV when the pH of the hydrogen-containing oxygen-hydrogen mixed gas was 6.2 before bubbling, and -161 mV when the pH of the hydrogen-containing oxygen-hydrogen mixed gas was 6.2 after bubbling. The graph of Figure 4 was created by connecting these points. While the ORP did not change with bubbling with medical oxygen, it decreased with the oxygen-hydrogen mixed gas (medical oxygen: -5.2 ± 3.4 mV, hydrogen-oxygen mixed gas: -203 ± 21 mV, p = 0002). There was no significant difference in pH change before and after oxygen bubbling. When using an oxygen-hydrogen mixed gas (10 Pa), the pH changed from 7.06 to 7.16 before and after bubbling. The definition of pH in the United States: Measurement of pH. Definition, Standards, and Procedures. Pure Appl. Chem. 74, 2169-2200 (2002) states that one of the factors affecting pH measurement is log [hydrogen gas partial pressure (Pa) / 100 kPa].

[0075] To minimize measurement errors, the graph in Figure 4 was created by measuring the potential multiple times (e.g., three or more times) and averaging the results. In Figure 6, the graph of ORP before and after hydrogen gas bubbling shows the standard deviation of the redox potential (ORP) at pH 6.2 before and after bubbling. The redox potential (ORP) at pH 0.18 after bubbling is shown in Figure 6. The redox potential (ORP) changes with the bubbling of the oxygen-hydrogen mixed gas, and this change approximates the change in hydrogen electrode potential using the Nernst equation. The hydrogen gas concentration in the hydrogen-oxygen mixed gas increased from 0.6 ppm in the atmosphere before bubbling to 1.0 / (0.5 + 1.0) = 0.66, resulting in a hydrogen gas partial pressure of 0.6 x 10 -6 The reverse logarithm of the hydrogen gas partial pressure was pH = -log(0.6 × 10 -6 ) = 6.22, so pH2 = -log(66 × 10 -2 ) = 0.18, so the approximate formula is:

[0076] The change in redox potential due to

[0077] This is the change in the actual measured value.

[0078] It can be seen that the change in hydrogen electrode potential obtained by the calculation formula (2) is close to the change in oxidation-reduction potential.

[0079] The present invention can be used in the alcohol brewing industry, nutrition research, food processing, agriculture, pharmaceutical development and manufacturing, and the medical industry. Both the conventional relative hydrogen score rH and the present invention are effective in managing the brewing process of wine, beer, sake, and other products. Furthermore, both the conventional relative hydrogen score rH and the present invention are effective as a means of evaluating the redox state (e.g., antioxidant status and spoilage potential) of fruit juices and other products in nutritional antioxidant research and the food processing industry. Furthermore, both the conventional relative hydrogen score rH and the present invention are useful in inorganic chemistry (oxidation and reduction) of metals, biochemistry of metal oxidation or reduction, organic agriculture, measurement and formulation of soil nutrients in gardening, environmental drainage and remediation research, groundwater research including analysis of surface water, underground aquifers, and water from deep wells, and seawater management for aquariums. Furthermore, because the present invention directly measures hydrogen partial pressure, the hydrogen electrode potential is expected to be used more effectively than the relative hydrogen score.

[0080] For example, in organic electrochemistry, controlled-potential electrolysis is suitable for its high selectivity in organic electrosynthesis. Generally, electrode reactions of organic compounds are complex, and multiple products are often obtained. When an aromatic carbonyl compound is electrolytically reduced under acidic conditions, both the alcohol and pinacol products are simultaneously obtained. There are two limiting currents, and to selectively obtain the pinacol product, controlled-potential electrolysis can be performed within the potential range corresponding to these limiting currents. In other words, appropriate reaction conditions can be determined by measuring the hydrogen electrode potential of the aqueous solution, as well as the dissolved oxygen concentration (DO) and hydrogen ion concentration (pH).

[0081] Furthermore, in biochemistry and medical science, all energy generation in living organisms requires oxidation-reduction reactions via the electron transport chain. Energy is obtained from the decomposition of glucose using nicotinamide adenine dinucleotide (NADH) as an electron donor. In anaerobic respiration and fermentation, the potential difference with alcohol, the final electron acceptor, is small, and NAD + The balance of the redox reaction of / NADH is strongly affected by fluctuations in the hydrogen electrode potential. The relative hydrogen score rH of the prior art is also useful in the present invention.

[0082] Aerobic respiration uses oxygen as the final electron acceptor, so NAD+ The difference between the redox potential of H2O / NADH and that of H2O / O2 is large, and the reaction rate is oxygen-dependent. However, even in aerobic respiration, if the oxygen diffusion capacity is exceeded, a state of relative hypoxia will occur. In a state of relative hypoxia, NAD + The potential difference between / NADH and H2O / O2 decreases, so NAD + The change in the oxidation-reduction potential of NAD / NADH greatly affects the rate of aerobic respiration. + The relative hydrogen score rH of the prior art is also useful in the present invention. Therefore, biological redox reactions can be utilized in various industries by determining optimal conditions based on the hydrogen electrode potential in addition to dissolved oxygen and pH.

Claims

1. A method for obtaining the redox state of an aqueous solution as a hydrogen electrode potential, comprising the steps of: obtaining the effective hydrogen gas partial pressure of a gas phase in equilibrium with an aqueous solution; obtaining the temperature of the gas phase; obtaining the hydrogen ion activity (pH) of the aqueous solution; calculating the inverse logarithm (pH2) of the partial pressure; and analyzing the hydrogen electrode potential of the aqueous solution using the temperature, the hydrogen ion activity (pH), and the inverse logarithm (pH2).

2. When the hydrogen gas index pH2 is defined as the inverse logarithm of the effective hydrogen gas partial pressure (pH2=-log[hydrogen gas partial pressure (Pa) / 100 kPa]), the hydrogen gas index pH2 is calculated using a predetermined calculation formula stored in a storage means:

2. The method for acquiring the redox state of an aqueous solution as a hydrogen electrode potential according to claim 1, further comprising the steps of: reading out the hydrogen electrode potential obtained by the predetermined arithmetic expression; calculating the hydrogen electrode potential using the predetermined arithmetic expression; and displaying the obtained hydrogen electrode potential and pH2.

3. The method for acquiring the redox state of an aqueous solution as described in claim 2, further comprising a step of displaying the change in the hydrogen electrode potential as a fluctuation in the hydrogen gas index pH2.

4. When the hydrogen ion activity (pH) is buffered or there is no change in the hydrogen ion activity (pH), the change in the hydrogen electrode potential ΔEh as a change in the redox state of the aqueous solution is calculated using the change in the antilogarithm (pH2) ΔpH2 according to the following formula: and a step of calculating the change in the hydrogen electrode potential obtained by the calculation. The method for acquiring an oxidation-reduction state of an aqueous solution as a hydrogen electrode potential according to claim 1 , further comprising the steps of:

5. A method for obtaining the effective hydrogen gas partial pressure of an aqueous solution, comprising the steps of: measuring the effective hydrogen gas partial pressure of the gas that has been mixed in an equilibrium state with a portion of the aqueous solution and a gas of known hydrogen gas partial pressure in a sealed container; and calculating the effective hydrogen gas partial pressure of the aqueous solution from the hydrogen partial pressure of the gas in the sealed container.

6. A method for obtaining an effective hydrogen gas partial pressure of an aqueous solution, comprising the steps of: measuring a concentration of dissolved hydrogen gas in the aqueous solution; and calculating an effective hydrogen gas partial pressure in a gas phase in equilibrium with the aqueous solution, using the dissolved hydrogen gas concentration and the solubility of the dissolved hydrogen gas calculated from the Henry's constant.

7. An apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential, comprising: a hydrogen gas partial pressure acquisition unit for acquiring the partial pressure of hydrogen gas in a gas phase in equilibrium with an aqueous solution; a temperature acquisition unit for acquiring the temperature of the gas phase; a hydrogen ion activity (pH) acquisition unit for acquiring the hydrogen ion activity (pH) of the aqueous solution; and a calculation unit for calculating the inverse logarithm (pH2) of the hydrogen gas partial pressure and analyzing the hydrogen electrode potential of the aqueous solution from the hydrogen gas exponent pH2 defined by the inverse logarithm (pH2), the temperature, and the hydrogen ion activity (pH).

8. An apparatus for acquiring the redox state of an aqueous solution as a hydrogen electrode potential as described in claim 7, comprising a housing to which the hydrogen gas partial pressure acquisition unit, the temperature acquisition unit, and the hydrogen ion activity (pH) acquisition unit are attached, forming a non-flow area that prevents the flow of liquids and gases, and having a flow area or membrane that allows the flow of at least hydrogen gas.

9. When the hydrogen gas index pH2 is defined as the inverse logarithm of the effective hydrogen gas partial pressure (pH2=-log[hydrogen gas partial pressure (Pa) / 100 kPa]), the hydrogen gas index pH2 is calculated using a predetermined calculation formula stored in the storage means: and calculating the hydrogen electrode potential by the predetermined arithmetic expression; and displaying the obtained hydrogen electrode potential and pH2.

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