JP2001242134A - pH sensor - Google Patents

Abstract

(57) [Summary] [Problem] Even if conditions such as the temperature of a glass electrode and the concentration of an internal solution fluctuate, the electromotive force is corrected in accordance with the fluctuation, and the pH value of the solution to be measured can be easily and quickly increased. It is another object of the present invention to provide a pH sensor that can be obtained accurately. SOLUTION: A glass electrode 12 having a pH-sensitive glass film 13, a reference electrode 19, a measurement cell 11 in which the glass electrode 12 and the reference electrode 19 are immersed, and a potential difference between an internal electrode 15 and the reference electrode 19 are detected. A pH sensor comprising: a voltage detecting section 20 for detecting a potential difference; a control section 21 to which a potential difference signal is input; and an operation calibration section 22 controlled by the control section 21 to calculate a pH value of the liquid to be measured from the potential difference. The glass electrode 12 is provided with a temperature sensor 17 for detecting the temperature of the standard solution 14, and a temperature signal detected by the temperature sensor 17 is input to the calculation and calibration unit 22 via the control unit 21, The pH value of the liquid to be measured is corrected based on

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pH sensor for detecting a hydrogen ion concentration in a liquid to be measured by measuring an electromotive force generated using a pH-sensitive glass film.

[0002]

2. Description of the Related Art Conventionally, the hydrogen ion concentration of
2. Description of the Related Art A pH sensor that detects using a sensitive glass film is known. FIG. 10 is a configuration diagram showing an outline of a pH sensor of a comparative example.

In FIG. 10, reference numeral 1 denotes a glass electrode having an outer shell formed of a pH-sensitive glass 2 and holding an internal liquid 3 and an internal electrode 4, and 5 denotes a glass formed of a liquid junction 6, an internal liquid 7, and an internal electrode 8. A reference electrode for setting a reference potential for the electrode 1.

The internal solution 3 of the glass electrode 1 is KCl
Is used, and the internal electrode 4 is made of silver-silver chloride or the like.
The potential of the internal liquid 3 in the inside can be detected. The internal solution 7 of the reference electrode 5 uses a KCl high concentration solution.

When measuring the pH (hydrogen ion concentration index) of the liquid to be measured, the glass electrode 1 and the reference electrode 5 are immersed in the liquid to be measured, and the internal electrode 4 in the glass electrode 1 and the internal electrode in the reference electrode 5 are immersed. The electromotive force between 8 is measured. Liquid junction 6 is internal liquid 7
And has the function of electrically connecting the liquid to be measured and the internal liquid 7 to each other.

The internal liquid 3 of the glass electrode 1 has a role of a conductor and a role of stabilizing the potential of the internal electrode 4. Similarly, the internal liquid 7 of the reference electrode 5 has a role as a conductor and a role to stabilize the potential of the internal electrode 8.

Further, a silver-silver chloride electrode which is insoluble in water, easily reaches equilibrium, and has a stable potential is used as a constituent material of the internal electrode.

Next, the principle of pH measurement using a pH-sensitive glass will be described.

When a glass containing about 10 to 30% of an alkali oxide is formed into a thin film, and an aqueous solution having a different hydrogen ion concentration is brought into contact with both surfaces of the glass, a potential difference is generated between both surfaces of the glass film. This potential difference E (V) is expressed by the following Nernst equation.

E = (α2.303RT / F) (pHa-pHb) + e Here, T is an absolute temperature (K), pHa is a pH value of an internal liquid (standard solution) of the glass thin film, and pHb is a glass thin film. Is the pH value of the external liquid (measurement liquid). R is a gas constant (8.3144 J / (K · mol)), F is a Faraday constant (96485 C / mol), α is sensitivity, and e is pHa
Is the potential difference E when pH and pHb are equal, that is, the asymmetric potential.

As described above, the potential difference (E) at the glass electrode 1, the pH value (pHa) of the standard solution, and the temperature (T) at the glass electrode 1 are set or obtained, respectively. The pH value (pHb) can be determined. However, the temperature (T) and the concentration of the standard solution (pH
If a) changes, the required pH value of the liquid to be measured also changes accordingly.

As a method of correcting such a fluctuation even if there is such a fluctuation and accurately obtaining a pH value, Japanese Patent Application Laid-Open No. 6-24 / 1994
In Japanese Patent Publication No. 2072 (hereinafter referred to as “A”), a calibration curve is created using two glass electrodes holding standard solutions having different concentrations, and the pH of the liquid to be measured is calculated based on the calibration curve.
A method for determining a value is disclosed.

Japanese Patent Application Laid-Open No. 8-304323 (hereinafter referred to as “B”) discloses a method of providing a working electrode having a negative temperature coefficient between a working electrode and a counter electrode and applying a constant voltage. A sensor using the principle of the polarography, in which a current flowing between the resistor and the counter electrode is compensated by a temperature change of the resistor, is disclosed.

[0014]

However, the conventional technique has the following problems. (1) A pH sensor as disclosed in JP-A or JP-B-B2 only corrects the value of the electromotive force measured using the temperature of the liquid to be measured or the outside air. When the temperature difference is large, there is a problem that an accurate pH value cannot be obtained. (2) In order to reduce the temperature difference, it is necessary to set the contact time between the liquid to be measured and the standard solution to be long. (3) The KCl concentration of the standard solution in the glass electrode and the concentration of the internal solution in the reference electrode fluctuate when the solution component crystallizes due to a change in temperature, or when the sealing of the internal solution or the like is incomplete. There is a problem that the value of the electromotive force must be calibrated by using a reference solution having a known concentration before measuring the liquid to be measured in order to correct the shift of the electromotive force due to the fluctuation. (4) In the case of the pH sensor disclosed in Japanese Patent Application Laid-Open No. H11-207, a plurality of glass electrodes must be provided in advance and a calibration curve needs to be set, so that the measurement procedure is complicated, costly and uneconomical. Was.

The present invention has been made to solve the above-mentioned problem, and even if conditions such as the temperature of the glass electrode and the concentration of the internal liquid fluctuate, the electromotive force is corrected in accordance with the fluctuation, and An object of the present invention is to provide a pH sensor that can easily, quickly and accurately determine the pH value of a measurement solution.

[0016]

The pH sensor of the present invention comprises:
A standard solution is filled inside the pH-sensitive glass membrane,
A glass electrode in which the internal electrode is immersed in the standard solution,
A reference electrode that generates a reference potential, a measurement cell in which the liquid to be measured is filled and the glass electrode and the reference electrode are immersed,
A voltage detection unit that detects a potential difference between the internal electrode and the reference electrode; a control unit to which a signal of the potential difference is input; and a control unit that is controlled by the control unit and calculates a pH value of the liquid to be measured from the potential difference. A pH sensor provided with an operation calibration unit, wherein the glass electrode is provided with a temperature sensor for detecting the temperature of the standard solution, and a temperature signal detected by the temperature sensor is used for the operation calibration via the control unit. The pH value of the liquid to be measured is corrected based on the temperature of the standard liquid inputted to the unit.

Thus, even if the conditions such as the temperature of the glass electrode and the concentration of the internal liquid change, the electromotive force is corrected in accordance with the change, and the pH value of the liquid to be measured can be adjusted simply, quickly and accurately. A pH sensor that can be obtained can be provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pH sensor according to claim 1 is
A standard solution is filled inside the pH-sensitive glass membrane,
A glass electrode in which the internal electrode is immersed in the standard solution,
A reference electrode that generates a reference potential, a measurement cell in which the liquid to be measured is filled and the glass electrode and the reference electrode are immersed,
A voltage detection unit that detects a potential difference between the internal electrode and the reference electrode; a control unit to which a signal of the potential difference is input; and a control unit that is controlled by the control unit and calculates a pH value of the liquid to be measured from the potential difference. A pH sensor provided with an operation calibration unit, wherein the glass electrode is provided with a temperature sensor for detecting the temperature of the standard solution, and a temperature signal detected by the temperature sensor is used for the operation calibration via the control unit. The pH value of the liquid to be measured is corrected based on the temperature of the standard liquid.

As a result, the following effects can be obtained.

(A) Since the glass electrode has a temperature sensor for measuring the temperature of the standard solution, even if the temperature of the glass electrode fluctuates, this data and the temperature between the glass electrode and the reference electrode are measured. By substituting the value of the electromotive force into the Nernst equation, the pH value of the liquid to be measured can be easily and accurately obtained.

(B) Even when there is a temperature difference between the standard solution and the solution to be measured, the p of the solution to be measured is determined based on the temperature of the standard solution.
H can be determined appropriately.

(C) Since a sensor having a small detecting portion such as a thermocouple or a thermistor can be used as the temperature sensor, the response time can be shortened and the temperature of the standard solution can be quickly grasped. It can be performed.

(D) Since the temperature of the standard solution is directly obtained, the measurement can be performed in a shorter time as compared with a conventional pH sensor which has to wait until the solution to be measured and the standard solution reach thermal equilibrium.

(E) Since the glass electrode has a pH-sensitive glass film, the glass electrode is immersed in the liquid to be measured, so that the standard solution whose internal hydrogen ion concentration is known and the hydrogen ion concentration in contact with the outside are unknown. A potential difference due to a difference in hydrogen ion concentration is generated between the liquid to be measured and the electromotive force, and the hydrogen ion concentration in the liquid to be measured can be obtained.

(F) Since the reference electrode for setting the reference potential is provided, the relative potential of the glass electrode can be properly determined based on the equilibrium potential of the half-cell constituted by the reference electrode.

In the pH sensor, a glass electrode and a reference electrode are inserted into a liquid to be measured to form a battery, and an electromotive force generated between the two is measured by a voltmeter or potentiometer having a high internal resistance. Is a device for obtaining the hydrogen ion concentration of the liquid to be measured. The glass electrode used for this purpose has a potential difference in the pH-sensitive glass membrane that is a function of only the hydrogen ion concentration, that is, is independent of other coexisting substances, and has high hydrogen ion selectivity. It is necessary that the resistance be as low as possible and mechanically strong.

As the glass electrode, a solution in which a hydrochloric acid aqueous solution of a known concentration is placed in a glass tube having a pH-sensitive glass film at the tip and a silver-silver chloride electrode or a calomel electrode is inserted therein is used.

The reference electrode is also called a reference electrode, and is used in combination with the electrode in question to form a battery circuit for measuring the electrode potential in order to measure the electrode potential of the electrode constituting the battery or the electrode undergoing electrolysis. This electrode is used as a reference for measuring the relative value of the electrode potential. The reference electrode requires stability and reproducibility of the electrode potential, and a hydrogen electrode, a calomel electrode, a silver-silver chloride electrode, or the like can be used.

The temperature sensor is a temperature measuring device such as a thermocouple or a thermistor. These sensitive parts are immersed in a standard solution in a glass electrode, and are disposed. The temperature of the standard solution is set to a predetermined hydrogen ion concentration in advance. A sensor for obtaining data, which can be obtained by using this data to appropriately correct the hydrogen ion concentration or the hydrogen ion concentration index (pH) of the liquid to be measured based on the known Nernst equation. .

The pH sensor according to the second aspect is the first aspect.
In the above, a concentration sensor for detecting a change in the concentration of the electrolyte of the standard solution is immersed in the glass electrode.

As a result, the following operation can be obtained in addition to the operation of the first aspect.

(A) Because of the presence of the concentration sensor, even if the solution component of the standard solution is crystallized or deteriorated and its concentration fluctuates, the fluctuation between the reference electrode and the glass electrode due to the fluctuation is caused. By correcting the power deviation, the hydrogen ion concentration of the liquid to be measured can be properly obtained.

(B) Since the concentration of the standard solution can be directly measured, the change with time of the standard solution can be grasped in advance, the replacement time can be determined, and the management can be performed.
H can be measured.

As the concentration sensor, an electric conductivity meter for measuring the electric conductivity of the standard solution, a polarograph to which the electrochemical method is applied, an analyzer for extracting and analyzing the standard solution, and the like can be used.

The pH sensor according to the third aspect is the first aspect.
In 2 or 3, an inert gas is sealed in the glass electrode.

Thus, in addition to the function of claim 1 or 2, the following function is obtained.

(A) Since the inside of the pH-sensitive glass film is filled with an inert gas, the internal electrodes such as silver-silver chloride are oxidized by dissolved oxygen or the like, and the fluctuation of the potential due to the oxidation can be suppressed. The pH value of the liquid to be measured can be determined more accurately.

The pH sensor according to the fourth aspect is the second aspect.
, The concentration sensor includes a pair of detection electrodes, and is configured to detect a change in the concentration of the standard solution by detecting the electrical conductivity of the standard solution between the pair of detection electrodes.

Thus, the following operation can be obtained in addition to the operation of the second aspect.

(A) Since only the electric conductivity between the electrode plates is measured, the state of the standard solution can be grasped easily and quickly.

(B) Since the electric conductivity can be converted to the concentration of the standard solution, the structure is simple, and the concentration sensor can be compactly stored in the glass electrode.

The pH sensor according to the fifth aspect is the first aspect.
5. In any one of Items 4 to 4, further comprising a temperature control unit that controls a temperature of the standard solution filled in the glass electrode within a predetermined temperature range.

Thus, in addition to the function of any one of claims 1 to 4, the following function is obtained.

(A) Since the temperature of the standard solution in the glass electrode can be constantly maintained within a predetermined range by using the temperature control unit, the temperature is set to a fixed value and p is calculated by the Nernst equation.
The calculation of the H value can be performed easily and quickly.

(B) Even if the temperature of the liquid to be measured fluctuates due to the outside air temperature or the like, the pH value can be accurately obtained.

(C) Since the temperature of the internal liquid can be kept constant, it takes time for the temperature to stabilize.
Measurement can be performed in a shorter time as compared with the H sensor.

The pH sensor according to the sixth aspect is the fifth aspect.
In the above, the temperature control unit is a Peltier element,
A temperature signal from the temperature sensor is input via the control unit, and the Peltier element generates or absorbs heat.

As a result, the following operation can be obtained in addition to the operation of the fifth aspect.

(A) Since the temperature control section is a Peltier element that can generate and absorb heat with one element, the temperature control section can be easily set even in a narrow space such as a glass electrode or a reference electrode. Can be.

(B) It is possible to switch between heat generation and heat absorption simply by reversing the direction of the current flowing through the Peltier element.
Temperature control can be performed quickly.

The Peltier element is an element formed by bonding different kinds of conductors (or semiconductors). When an electric current is applied to the element, the ratio of the electric current flowing to the free electrons to the electric current is not equal between the two conductors, so that the contact can generate or absorb heat other than Joule heat depending on the direction of the electric current.

The pH sensor according to the seventh aspect is the first aspect.
In any one of 1 to 6, the reference electrode is a container filled with an internal standard solution, a reference potential electrode immersed in the internal standard solution, the internal standard solution, and a liquid to be measured in the measurement cell. Is provided with a liquid junction for conducting the current.

Thus, the following operation is obtained in addition to the operation of any one of the first to sixth aspects.

(A) The reference electrode is composed of the internal standard solution, the reference potential electrode and the internal standard solution, and the liquid to be measured and the reference potential electrode are electrically connected via the liquid junction. The pH value can be measured more stably and more accurately than in the case of a reference electrode.

The pH sensor according to the eighth aspect is the seventh aspect.
In the reference electrode, a reference electrode temperature sensor for detecting the temperature of the internal standard solution is provided, and the arithmetic and control unit adjusts the pH value of the liquid to be measured based on a temperature signal detected by the reference electrode temperature sensor. Is corrected.

As a result, the following operation can be obtained in addition to the operation of the seventh aspect.

(A) Since the reference electrode has a reference electrode temperature sensor for measuring the temperature of the internal standard solution, even if the temperature of the reference electrode fluctuates, the data and the distance between the glass electrode and the reference electrode can be obtained. By substituting the value of the electromotive force measured in the above into the Nernst equation, the pH value of the liquid to be measured can be easily and accurately obtained.

(B) Even if there is a temperature difference between the internal standard solution and the solution to be measured, the pH of the solution to be measured can be properly determined based on the temperature of the internal standard solution.

(C) The reference electrode temperature sensor includes a thermocouple,
Since a thermistor or the like having a small detection portion can be used, the response time can be shortened, the temperature of the standard solution can be quickly grasped, and efficient measurement can be performed with little error.

(D) Since the temperature of the internal standard solution is directly obtained, the measurement can be performed in a shorter time as compared with a conventional pH sensor which has to wait until the solution to be measured and the internal standard solution reach thermal equilibrium.

The pH sensor according to the ninth aspect provides the pH sensor according to the seventh aspect.
(8) In the configuration (8), a reference electrode concentration sensor for detecting a change in the concentration of the internal standard solution is immersed in the reference electrode.

As a result, the following operation can be obtained in addition to the operation of the seventh or eighth aspect.

(A) Since the reference electrode is provided with the reference electrode concentration sensor, it is possible to monitor the state of the concentration change of the internal standard solution, which tends to flow out through a liquid junction, and perform measurement under appropriate conditions. It can be carried out.

(B) Since the pH sensor has the reference electrode having the internal standard solution, the magnitude of the membrane potential generated in the glass membrane can be appropriately evaluated based on the electromotive force generated by the half cell. .

According to a tenth aspect of the present invention, in the pH sensor according to the ninth aspect, the reference electrode concentration sensor includes a pair of detection electrodes, and detects the electric conductivity between the pair of detection electrodes to detect the concentration of the internal standard solution. It is configured to detect a change.

As a result, the following operation can be obtained in addition to the operation of the ninth aspect.

(A) Since only the electric conductivity between the detection electrodes is measured, the state of the internal standard solution can be grasped easily and quickly.

(B) Since the measured electric conductivity can be converted to the concentration of the internal standard solution, the apparatus configuration can be simplified, and the reference electrode concentration sensor can be compactly stored in the reference electrode.

An eleventh aspect of the present invention provides the pH sensor according to any one of the seventh to tenth aspects, wherein the container is filled with an inert gas.

Thus, in addition to the function of any of claims 7 to 10, the following function is obtained.

(A) Since the inside of the reference electrode is filled with an inert gas, deterioration of the internal standard solution due to dissolved oxygen or the like can be prevented, and fluctuations in potential due to this can be suppressed.
Further, the pH value of the liquid to be measured can be determined more accurately.

(Embodiment 1) FIG. 1 is a configuration diagram showing an outline of a pH sensor according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 10 denotes the pH of the first embodiment.
A sensor, 11 is a measuring cell through which a liquid to be measured flows, and 12 is p
A glass electrode whose outer shell is formed by the H-sensitive glass film 13 and which is immersed in the liquid to be measured while holding the standard solution 14 and the internal electrode 15;
Reference numeral 16 denotes a concentration sensor for detecting the concentration of the standard solution 14 provided in the glass electrode 12, 17 denotes a temperature sensor for detecting the temperature of the standard solution 14, and 18 denotes the temperature of the standard solution 14 of the glass electrode 12. , A reference electrode for setting a reference potential, and 20 an internal electrode.
A voltage detection unit for measuring a potential difference between the reference signal 5 and the reference electrode 19; a control unit 21 to which a voltage signal from the voltage detection unit 20 is input; and a control signal 22 including the voltage signal from the control unit 21 Calculating unit for calculating the pH value of the liquid to be measured based on the potential difference and correcting the pH value using the temperature of the liquid to be measured, 23 is a data display unit such as a monitor, and 24 is a control unit. Power supply for supplying power to 21,
A control unit 21 amplifies the density signal of the density sensor 16 and
, A temperature detection unit for sending the temperature signal of the temperature sensor 17 to the control unit 21, and a temperature control unit 27 for controlling the heat generation and heat absorption unit 18.

The hydrogen ion sensitive glass film (pH sensitive glass film) 13 is a glass containing about 10 to 30% of an alkali oxide. As the thickness of the glass becomes thinner, the sensitivity becomes better, but if it is too thin, it becomes brittle in strength.
The range was set to 00 μm. The surface area of the hydrogen ion sensitive glass membrane 13 is too small decreases sensitivity, since too wide and the measurement becomes unstable, and the 0.5~2cm ^2. Although a calomel electrode using mercury can be used for the internal electrode 15, a silver-silver chloride electrode was used in consideration of the environment. Silver
The silver chloride electrode is a silver gland having a diameter of 1 mm and silver chloride of 30 to 160
mg carried in the range of 0.5 cm to 2 cm from the end of the silver wire. Measurement is possible if the tip of the internal electrode 15 is in contact with the standard solution 14. However, in this state, the measurement may become unstable, so that at least the portion not carrying silver chloride contacts the standard solution 14. The internal electrode 15 was set at a depth.

The standard solution 14 is prepared by dissolving a highly conductive chloride (for example, potassium chloride) in a buffer (for example, a neutral phosphate buffer) (for example, KCl having a molar concentration of 3.3 M).
Aqueous solution).

Before injecting the standard solution 14 into the glass electrode 12, degassing (for example, nitrogen purge or vacuum ultrasonic wave may be performed). As a result, dissolved oxygen in the liquid is removed, and the pH sensor 10 can be used stably for a long period of time.

The concentration sensor 16 comprises, for example, a pair of opposed electrode plates, and the concentration of the standard solution 14 can be calculated by measuring the electric conductivity of the solution between the electrode plates. The insertion position is preferably near the internal electrode 15.

The temperature sensor 17 may be, for example, a thermistor, a thermocouple, or an alcohol or mercury thermometer. The insertion position is preferably near the internal electrode 15.

The temperature control unit 27 provided with the heat absorbing and absorbing unit 18 is a heating and cooling device using a Peltier element. The heat generating / absorbing part 18 is a hydrogen ion sensitive glass film 13 of the glass electrode 12.
Is provided in a portion not in contact with

In the pH sensor 10, as a standard solution 14 for the glass electrode 12, a solution (for example, having a molar concentration of 3.3 M) in which a high conductivity chloride is dissolved in a buffer solution (for example, a neutral phosphate buffer solution). KCl solution).

As described above, since the membrane potential of the internal electrode 15 composed of a silver-silver chloride electrode changes depending on the temperature and the concentration of chloride ions, the temperature and the concentration of chloride ions are detected, and these are detected. Correction of the originally calculated pH value or maintenance of the temperature at a predetermined temperature enables appropriate calibration with the pH standard solution.

The procedure of the measurement operation of the pH sensor 10 configured as described above will be described below. The power supply 24 of the control unit 21 is turned on. The temperature (resistance value) is input from the temperature detecting unit 26. The density (conductivity) is input from the density detector 25. An upper limit value (T ₀ +1) and a lower limit value (T ₀ -1) are given to the temperature control unit 27, for example, a value that becomes ± 1 ° C. with respect to the initial temperature (T ₀ ) and the initial temperature (eg, 20 ° C.). Output in the temperature range. An initial voltage (V ₀ ) is input from the voltage detector 20. The temperature (T1) detected by the temperature detection unit 26 is T ₀ =
And temperature measurement every 30 seconds Once you become a _{T 1, T 0 -1 <T} n
When <T ₀ +1 (n = 1, 2, 3) is detected three times in a row, the value of the voltage (V ₁ ) detected by the voltage detection unit 20 is input to the calculation calibration unit 22. Temperature calculating calibration unit 22, using the density data, calculates and outputs the voltage (V ₁₎ of the correction voltage (V _2). The data of the initial voltage (V ₀ ) + the correction voltage (V ₂ ) is converted into a pH value and output to the data display unit 23.

FIG. 2 is a graph showing the measurement principle of the pH sensor showing the value of the potential in each conduction path between the internal electrode and the reference electrode in the pH sensor according to the first embodiment. In FIG. 2, the data indicated by ○, ●, and Δ indicate the pH values of the liquid to be measured at 4.01 and 6.86, respectively.
The state of the electromotive force of each part when set to 9.18 is shown. Here, the potential of each part can be calculated according to the Nernst equation, Ea is a large value depending on chlorine concentration, Ed is a fluctuation value depending on the Nernst equilibrium equation, and Ee and Ef are constant values specific to glass, respectively. , Eg
Is a value that depends on the pH of the standard solution 14, and Eh is a value that depends on the chlorine concentration of the standard solution 14.

That is, in the glass electrode 12, Ee, E
f, Eg, Eh represents the temperature dependence of the voltage at higher temperatures increases, Eh is also Cl ^- voltage and concentration of chloride ions is high or the like showing a concentration dependent decreases.

The value of Ea in the reference electrode 19 shows the same temperature dependency and concentration dependency as described above.

The pH sensor according to the first embodiment measures the sum of the electromotive force of each part, and the change in pH measures the change in Eα, and the other electromotive forces must be constant. . However, since the electromotive force of each part follows the Nernst equation, it depends on the temperature and the concentration, and fluctuates, and is corrected according to the temperature and the concentration.

(Embodiment 2) FIG. 3 is a configuration diagram showing an outline of a pH sensor according to Embodiment 2 of the present invention.

In FIG. 3, 30 is the pH sensor of the embodiment, 31 is a container filled with an internal standard solution 32, 33 is a reference potential electrode immersed in the internal standard solution 32, and 34 is connected to the temperature detecting section 26 A reference electrode temperature sensor 35 communicated with the concentration detector 25; and a temperature controller 27 for controlling the temperature of the internal standard solution 32.
A heat absorbing / absorbing section 37 connected to the internal standard liquid 32 and a liquid junction for conducting the liquid to be measured in the measuring cell 11;
Is a reference electrode provided with an internal standard solution 32, a container 31, a reference potential electrode 33, a reference electrode temperature sensor 34, a reference electrode concentration sensor 35, a heat-absorbing part 36, and a liquid junction 38. In addition,
The pH sensor 30 according to the second embodiment differs from the pH sensor 10 according to the first embodiment only in the structure of the reference electrode and the connection method thereof. The same reference numerals are used and their detailed description is omitted.

As the internal standard solution 32 of the reference electrode 38, a high-concentration solution of a highly conductive chloride (for example, a saturated KCl solution) was used.

The liquid junction 37 is made of a porous polymer such as porous polyethylene, porous polyester, and porous acrylic having water absorbency, or a porous ceramic such as alumina, silica, and zirconia having water absorbency. It has a function of providing conduction between the liquid to be measured and the internal standard liquid 22 and holding the internal standard liquid 32 so as not to flow into the liquid to be measured.

An inert gas such as helium gas or argon gas or a substantially inert nitrogen gas is sealed in the upper portions of the reference electrode 38 and the glass electrode 12, and among these gases, the cost is low. It is preferable to use nitrogen gas.

Here, a silver-silver chloride electrode was used as the reference potential electrode 33. The silver-silver chloride electrode is a silver gland having a diameter of 1 mm and 30 to 160 mg of silver chloride 0.5 cm from the end of the silver wire.
It was carried in the range of ~ 2 cm. The reference potential electrode 33 was set to such a depth that its tip portion was in contact with the internal standard solution 32 and at least the portion where silver chloride was not carried was in contact with the internal standard solution 32.

The internal standard solution 32 is prepared by dissolving a highly conductive chloride (for example, potassium chloride) in a buffer solution (for example, a neutral phosphate buffer solution) (for example, KC having a molar concentration of 3.3 M).
aqueous solution).

Before injecting the internal standard solution 32 into the container 31, deaeration (for example, nitrogen purge or vacuum ultrasonic wave may be used)
Perform Thereby, the dissolved oxygen in the liquid is removed, and the pH sensor 30 can be used stably for a long time.

The reference electrode concentration sensor 35 is composed of, for example, a pair of opposed electrode plates. The concentration of the internal standard solution 32 can be calculated by measuring the electric conductivity of the solution between the electrode plates. The insertion position is preferably near the position facing the reference potential electrode 33.

The reference electrode temperature sensor 34 may be, for example, a thermistor, a thermocouple, or an alcohol or mercury thermometer.
The insertion position is preferably near the reference potential electrode 33.

The heating and absorbing section 36 is a heating and cooling device using a Peltier element, and is controlled by the temperature control section 27.

The procedure of the measurement operation of the pH sensor 30 configured as described above will be described below. The power supply 24 of the control unit 21 is turned on. The temperature (resistance value) is input from the temperature detecting unit 26. The density (conductivity) is input from the density detector 25. An upper limit value (T ₀ +1) and a lower limit value (T ₀ -1) are given to the temperature control unit 27, for example, a value that becomes ± 1 ° C. with respect to the initial temperature (T ₀ ) and the initial temperature (eg, 20 ° C.). Output in the temperature range. An initial voltage (V ₀ ) is input from the voltage detector 20. The temperature (T1) detected by the temperature detection unit 26 is T ₀ =
And temperature measurement every 30 seconds Once you become a _{T 1, T 0 -1 <T} n
When <T ₀ +1 (n = 1, 2, 3) is detected three times in a row, the value of the voltage (V ₁ ) detected by the voltage detection unit 20 is input to the calculation calibration unit 22. Temperature calculating calibration unit 22, using the density data, calculates and outputs the voltage (V ₁₎ of the correction voltage (V _2). The data of the initial voltage (V ₀ ) + the correction voltage (V ₂ ) is converted into a pH value and output to the data display unit 23.

Even if the temperature of the heat-generating / absorbing portion 18 of the glass electrode 12 and the heat-generating / absorbing portion 36 of the reference electrode 38 are simultaneously controlled by the temperature control section 27, such a control may cause a difference in the transient response due to a shift in the transient response. Since the voltage fluctuates within a certain range, the voltage does not become constant, and it is necessary to perform correction based on this voltage fluctuation.

FIG. 4 is a graph showing potential values in respective conduction paths between the internal electrode and the reference potential electrode in the pH sensor according to the second embodiment. In FIG.
The data of marks, ●, and Δ indicate the state of the electromotive force at each part when the pH value of the liquid to be measured was set to 4.01, 6.86, and 9.18, respectively. Here, all potentials of each part can be calculated according to the Nernst equation. Ea is a value having a large chlorine concentration dependency, and Ed is
Is a fluctuation value depending on the Nernst equilibrium equation, Ee and Ef are constant values specific to glass, and Eg is p of the standard solution 14.
Eh is a value that depends on H, and Eh is a value that depends on the chlorine concentration of the standard solution 14.

That is, in the glass electrode 12, Ee, E
f, Eg, Eh represents the temperature dependence of the voltage at higher temperatures increases, Eh is also Cl ^- concentration shows concentration dependence of high and voltage drops in.

In the reference potential electrode 33 of the reference electrode 34, Ea shows the same temperature dependency and concentration dependency as described above.

The pH sensor according to the second embodiment is similar to the pH sensor according to the first embodiment.
There is a difference in that a liquid junction and an internal standard solution are used for the reference electrode, thereby stabilizing the electromotive force of the reference electrode. However, as in the first embodiment, the reference electrode also fluctuates in temperature and concentration. The variation width is smaller than that in the first embodiment using a single electrode as the reference electrode, but the variation is because the reference electrode has an internal liquid, and therefore, by performing temperature and concentration corrections, The pH value can be determined precisely.

Hereinafter, p in Embodiments 1 and 2 will be described.
Examples 1 to 11 performed using the H sensors 10 and 30 will be described. Here, FIGS. 5 to 9 show the case where the pH value is set to 6.86 using the buffer solution whose pH value is set to 6.86 as the liquid to be measured.
The figure shows the results of measuring the electromotive force between the glass electrode 12 and the reference electrode 19, that is, the change over time of the asymmetric potential e when pHa = pHb, using the standard solution 14 set to 86.

[0105]

Embodiments (Embodiments 1 to 3) Embodiment 1 shown in FIG.
Mark) indicates the concentration sensor 16 disposed on the glass electrode 12 side.
The electrical conductivity of the standard solution 14 is obtained using an electrical conductivity meter composed of a pair of electrodes, and the concentration of the standard solution 14 is converted and corrected based on the obtained electrical conductivity.
9 or a change with time of a voltage which is an asymmetric potential between the reference electrodes 34.

Example 2 (square mark) shown in FIG.
The electric conductivity of the internal standard solution 32 is obtained by an electric conductivity meter as the reference electrode concentration sensor 35 provided in 4, and the change over time of the asymmetric potential corrected by converting the concentration into a concentration is measured.

In the embodiment 3 (x mark) shown in FIG. 5, the density sensor 1 is provided on both electrodes of the glass electrode 12 and the reference electrode 34, respectively.
6. The electric conductivity is measured using the electric conductivity meter of the reference electrode concentration sensor 35, whereby the concentrations of the standard solutions of both the standard solution 14 and the internal standard solution 32 are obtained, converted, corrected and corrected. It shows the change with time of the potential.

The comparative example (比較) shown in FIG. 5 shows data when a concentration sensor such as an electric conductivity meter is not provided.

Here, a method of correcting an asymmetric potential using the electric conductivity of the internal liquid will be described. The asymmetric potential obtained by the Nernst equation fluctuates depending on the concentration and the temperature of the internal liquid, and an error accompanying such fluctuation is corrected.

That is, the measurement was made between the glass electrode and the reference electrode.
Voltage E₀Is E as described above.₀= Ea + Eb + Ec +
It is represented by Ed + Ee + Ef + Eg + Eh. Ea, E
b, Ec, Ed, Eg, Eh are each Nernst formula
And Ee and Ef are specific to each glass.
It has a constant value. Ea is a characteristic value of the silver chloride electrode.
A and Eb include the characteristic value B of the liquid junction, and Ec includes the characteristic value D of the liquid junction potential.
For example, Ea indicates the concentration of the standard solution as C₀age
And Ea = 2.303 × (RT₀/ F) × log
(C ₀) + A.

As described above, when each temperature and concentration fluctuate due to environmental changes, the voltage fluctuates for each part,
At this time, the voltage E ₁ measured between the electrodes is obtained by using the correction voltage e ₁ having the temperature T and the concentration C as variables, and E ₁ = E ₀ + e
1 (T, C), which allows the voltage to be corrected.

The theoretical approximation formula is as follows. That is, the temperature of the target solution, the concentration, as is but a minute hydrogen ion concentration changes, the voltage E is approximate equation: E = E ₀ + 2.303 ×
(R / F) × ｛(logH ₀ + logC ₀ ) × ΔT + B
(LogC ₀ ') × ΔT'}. Where ΔT
= T ₁ −T ₀ , ΔT ′ = T ₁ ′ −T ₀ ′, where H ₀ is the hydrogen ion concentration in the liquid inside the glass, C ₀ is the Cl concentration in the glass electrode,
C ₀ ′ is the reference electrode Cl concentration.

The above calculation method is an example showing that the temperature, concentration, and the like can be corrected in the form of a function, and the present invention is not limited to the method using these equations. For example, it is also possible to obtain control data of the temperature or the density and the voltage to be corrected in advance by an experiment, and thereby to perform appropriate correction.

As is clear from FIG. 5, the comparative example (△)
Although the asymmetric potential changes with time near 50 mV at 1000 h, an electric conductivity meter was used on the glass electrode 12 side in Example 1 and an electric conductivity meter was used on the reference electrode 19 side in Example 2. The sample used had an asymmetric potential change over time of 1000.
h is stable within ± 10 mV. Further, in Example 3 in which the electric conductivity meter was used for both electrodes, the change with time of the asymmetric potential was stable within 1000 m within ± 3 mV.

(Embodiments 4 to 6) Embodiments 4 to 6 shown in FIG.
Is obtained by measuring the temperature of each internal liquid using a thermistor as a temperature sensor section inside the glass electrode 12 and / or the reference electrode 19, and using this to correct the asymmetric potential.

Example 4 (marked with a triangle) uses a thermistor for the glass electrode 12.

The fifth embodiment (square mark) uses a thermistor inside the reference electrode 19.

Example 6 (marked by x) uses a thermistor inside both electrodes.

In the comparative example (△), the temperature of the liquid to be measured was measured using the same thermistor as in Examples 4 to 6, and the pH value was corrected at this temperature.

Here, the room temperature is changed from 10 ° C. every 12 hours to 2 hours.
The results when the temperature is alternately changed to 5 ° C. are shown.

As is clear from FIG. 6, in the comparative example, the asymmetric potential changes with time by as much as 50 mV at 1000 h despite the temperature correction of the liquid to be measured, whereas the glass electrode 12 of Example 4 In the case of using a thermistor inside, or the case of using the thermistor inside the reference electrode 19 of Example 5, the change over time of the asymmetric potential was ± 10 m at 1000 h.
It is stable within V. In Example 6, in which a thermistor is used inside both electrodes, the asymmetric potential changes over time at 1000 h are stable within ± 3 mV.

(Embodiments 7-9) Embodiments 7-8 shown in FIG.
Shows the change over time of the asymmetric potential when the temperature of the internal liquid is obtained by a thermistor and the Peltier element is controlled so that the temperature becomes a predetermined temperature. Here, the temperature setting is 20
° C, and the room temperature was alternately changed from 5 ° C to 35 ° C every 12 hours.

Example 7 (◇) shows the results of an experiment in which a Peltier element was provided on the glass electrode 12.

Example 8 (square mark) is one in which a Peltier element is provided on the reference electrode 19.

Example 9 (marked by x) The glass electrode 12 and the reference electrode 19 are provided with Peltier elements on both sides.

Examples 7 to 9 are comparative examples (比較).
The temperature is corrected using a measuring device for detecting the temperature of the liquid to be measured in the same manner as in the above. As is clear from FIG. 7, in the comparative example, the asymmetric potential changes as much as 70 mV at 1000 h despite the temperature correction of the liquid to be measured. Change over time is 1000
h is stable within ± 10 mV. In Example 9, it can be seen that the change with time of the asymmetric potential is stable within ± 3 mV at 1000 h.

(Embodiment 10) Embodiment 10 shown in FIG.
As is clear from the graph, in the comparative example (△), the change over time in the asymmetric potential changes by 50 mV at 1000 h, whereas in the case of Example 10, the change over time in the asymmetric potential is 1000 h.
It can be seen that is stable within ± 10 mV.

(Embodiment 11) Embodiment 11 (◇) shown in FIG.
(Marked) means that an electric conductivity meter and a thermistor are used for both electrodes, a Peltier element is installed on both electrodes, and an inner liquid that has been degassed by a nitrogen purge is used for the glass electrodes, and is filled with nitrogen gas. .

As is clear from FIG. 9, the comparative example (△)
It can be seen that the change with time of the asymmetric potential changes by as much as 50 mV at 1000 h, while the change with time of the asymmetric potential is stable within ± 10 mV at 1000 h in Example 11 (marked with ◇).

[0130]

According to the pH sensor according to the first aspect,
Thereby, the following effects can be obtained.

(A) Since the glass electrode has a temperature sensor for measuring the temperature of the standard solution, even if the temperature of the glass electrode fluctuates, this data and the temperature between the glass electrode and the reference electrode are measured. By substituting the value of the electromotive force into the Nernst equation, the pH value of the liquid to be measured can be easily and accurately obtained.

(B) Even when there is a temperature difference between the standard solution and the solution to be measured, the p-value of the solution to be measured is based on the temperature of the standard solution.
H can be determined appropriately.

(C) Since a temperature sensor such as a thermocouple or a thermistor having a small detection portion can be used as the temperature sensor, the response time can be shortened and the temperature of the standard solution can be quickly grasped. It can be performed.

(D) Since the temperature of the standard solution is directly obtained, the measurement can be performed in a shorter time as compared with the conventional pH sensor which has to wait until the solution to be measured and the standard solution reach thermal equilibrium.

(E) Since the glass electrode has a pH-sensitive glass membrane through which hydrogen ions pass, the glass electrode is immersed in the liquid to be measured so that the hydrogen ions in contact with the standard solution whose internal hydrogen ion concentration is known are in contact with the outside. By generating a potential difference due to a difference in hydrogen ion concentration between the liquid to be measured and an unknown concentration, the electromotive force can be measured to determine the hydrogen ion concentration in the liquid to be measured.

(F) Since the reference electrode for setting the reference potential is provided, the relative potential of the glass electrode can be properly determined based on the equilibrium potential of the half-cell constituted by the reference electrode.

According to the pH sensor of the second aspect, the following effects can be obtained in addition to the effects of the first aspect.

(A) Because of the presence of the concentration sensor section, even if the solution component of the standard solution is crystallized or deteriorated and its concentration fluctuates, the fluctuation between the reference electrode and the glass electrode due to the fluctuation is caused. By correcting the power deviation, the hydrogen ion concentration of the liquid to be measured can be properly obtained.

(B) Since the concentration of the standard solution can be directly measured, the change with time of the standard solution can be grasped in advance, the replacement time can be determined, and the management can be performed.
H can be measured.

According to the pH sensor of the third aspect, the following effects can be obtained in addition to the effects of the first or second aspect.

(A) Since the inside of the pH-sensitive glass film is filled with an inert gas, the internal electrodes such as silver-silver chloride are oxidized by dissolved oxygen or the like, and the fluctuation of the potential due to this can be suppressed. The pH value of the liquid to be measured can be determined more accurately.

According to the pH sensor of the fourth aspect, the following effects can be obtained in addition to the effects of the second aspect.

(A) Since only the electric conductivity between the electrode plates is measured, the state of the standard solution can be grasped easily and quickly.

(B) Since the electric conductivity can be converted into the concentration of the standard solution, the structure is simple, and the concentration sensor can be compactly stored in the glass electrode.

According to the pH sensor according to the fifth aspect, the following effects can be obtained in addition to the effects of any one of the first to fourth aspects.

(A) Since the temperature of the standard solution in the glass electrode can be constantly maintained within a predetermined range by using the temperature control unit, the temperature is set to a fixed value, and p is calculated by the Nernst equation.
The calculation of the H value can be performed easily and quickly.

(B) Even if the temperature of the liquid to be measured fluctuates due to the outside air temperature or the like, the pH value can be accurately obtained.

(C) Since the temperature of the internal liquid can be kept constant, it takes time for the temperature to stabilize.
Measurement can be performed in a shorter time as compared with the H sensor.

According to the pH sensor of the sixth aspect, the following effects can be obtained in addition to the effects of the fifth aspect.

(A) Since the temperature control section is a Peltier element that can generate and absorb heat with one element, the temperature control section can be easily set even in a narrow space such as a glass electrode or a reference electrode. Can be.

(B) It is possible to switch between heat generation and heat absorption simply by reversing the direction of the current flowing through the Peltier element.
Temperature control can be performed quickly.

According to the pH sensor of the present invention, the following effects can be obtained in addition to the effects of any one of the first to sixth aspects.

(A) The reference electrode is composed of an internal standard solution, a reference potential electrode and an internal standard solution, and the liquid to be measured and the reference potential electrode are electrically connected via a liquid junction. The pH value can be measured more stably and more accurately than in the case of a reference electrode.

According to the pH sensor of the eighth aspect, the following effects can be obtained in addition to the effects of the seventh aspect.

(A) Since the reference electrode has a reference electrode temperature sensor for measuring the temperature of the internal standard solution, even if the temperature of the reference electrode fluctuates, the data and the distance between the glass electrode and the reference electrode are obtained. By substituting the value of the electromotive force measured in the above into the Nernst equation, the pH value of the liquid to be measured can be easily and accurately obtained.

(B) Even if there is a temperature difference between the internal standard solution and the solution to be measured, the pH of the solution to be measured can be properly determined based on the temperature of the internal standard solution.

(C) The reference electrode temperature sensor includes a thermocouple,
Since a thermistor or the like having a small detection portion can be used, the response time can be shortened, the temperature of the standard solution can be quickly grasped, and efficient measurement can be performed with little error.

(D) Since the temperature of the internal standard solution is directly obtained, the measurement can be performed in a shorter time as compared with a conventional pH sensor which has to wait until the solution to be measured and the internal standard solution reach thermal equilibrium.

According to the pH sensor of the ninth aspect, the following effects can be obtained in addition to the effects of the seventh or eighth aspect.

(A) Since the reference electrode is provided with the reference electrode concentration sensor, it is possible to monitor the state of the change in the concentration of the internal standard solution, which tends to flow out through a liquid junction, and perform measurement under appropriate conditions. It can be carried out.

(B) Since the pH sensor has a reference electrode having an internal standard solution, the magnitude of the membrane potential generated in the glass film can be appropriately evaluated based on the electromotive force generated by the half cell. .

According to the pH sensor of the tenth aspect,
As a result, the following effect can be obtained in addition to the effect of the ninth aspect.

(A) Since only the electric conductivity between the detection electrodes is measured, the state of the internal standard solution can be grasped simply and quickly.

(B) Since the measured electric conductivity can be converted into the concentration of the internal standard solution, the device configuration can be simplified, and the reference electrode concentration sensor can be compactly stored in the reference electrode.

According to the pH sensor according to the eleventh aspect,
Thereby, the following effects can be obtained in addition to the effects of any one of claims 7 to 10.

(A) Since the inside of the reference electrode is filled with an inert gas, deterioration of the internal standard solution due to dissolved oxygen or the like can be prevented, and fluctuations in potential due to this can be suppressed.
Further, the pH value of the liquid to be measured can be determined more accurately.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an outline of a pH sensor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a pH value indicating a potential value in each conduction path between an internal electrode and a reference electrode in the pH sensor according to the first embodiment.
Graph showing the measurement principle of the sensor

FIG. 3 is a configuration diagram showing an outline of a pH sensor according to a second embodiment of the present invention.

FIG. 4 is a graph showing potential values in respective conduction paths between an internal electrode and a reference potential electrode in the pH sensor according to the second embodiment.

FIG. 5 is a diagram showing a change over time of an asymmetric potential when a standard solution is managed using a concentration sensor.

FIG. 6 is a diagram showing a change with time of an asymmetric potential when temperature control is performed using a temperature sensor.

FIG. 7 is a diagram showing a change with time of an asymmetric potential when a temperature control unit is used.

FIG. 8 is a diagram showing a change over time of an asymmetric potential when a nitrogen gas purge is applied.

FIG. 9 is a diagram showing a change over time of an asymmetric potential when an electric conductivity meter, a thermistor, and a Peltier element are applied.

FIG. 10 is a configuration diagram showing an outline of a pH sensor of a comparative example.

[Explanation of symbols]

 Reference Signs List 10 pH sensor 11 Measurement cell 12 Glass electrode 13 pH sensitive glass film 14 Standard solution 15 Internal electrode 16 Concentration sensor 17 Temperature sensor 18 Heat absorption / absorption section 19 Reference electrode 20 Voltage detection section 21 Control section 22 Operation calibration section 23 Data display section 24 Power supply 25 Concentration detection unit 26 Temperature detection unit 27 Temperature control unit 30 pH sensor 31 Container 32 Internal standard solution 33 Reference potential electrode 34 Reference electrode temperature sensor 35 Reference electrode concentration sensor 36 Heat absorption unit 37 Liquid junction 38 Reference electrode

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G01N 27/36 G01N 27/30 371C 371Z (72) Inventor Hirofumi Nakamura 1006 Odakadoma, Kadoma, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Toshihiko Matsuda 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (11)

[Claims] 1. A glass electrode having a pH-sensitive glass film filled with a standard solution, an internal electrode immersed in the standard solution, a reference electrode for generating a reference potential, and a liquid to be measured. The measurement electrode in which the glass electrode and the reference electrode are immersed, a voltage detection unit that detects a potential difference between the internal electrode and the reference electrode, a control unit to which a signal of the potential difference is input, and the control unit A pH sensor that is controlled and calculates a pH value of the liquid to be measured from the potential difference, wherein the glass electrode is provided with a temperature sensor that detects the temperature of the standard solution, A pH sensor, wherein a temperature signal detected by a sensor is input to the calculation calibration unit via the control unit, and a pH value of the liquid to be measured is corrected based on a temperature of the standard solution. 2. The pH sensor according to claim 1, wherein a concentration sensor for detecting a change in the concentration of the electrolyte in the standard solution is immersed in the glass electrode. 3. The pH sensor according to claim 1, wherein an inert gas is sealed in the glass electrode. 4. The density sensor has a pair of detection electrodes,
The pH sensor according to claim 2, wherein a change in the concentration of the standard solution is detected by detecting an electric conductivity of the standard solution between the pair of detection electrodes. 5. The pH according to claim 1, further comprising a temperature controller for controlling the temperature of the standard solution filled in the glass electrode within a predetermined temperature range. Sensor. 6. The Peltier element according to claim 5, wherein the temperature control section is a Peltier element, and a temperature signal from the temperature sensor is input via the control section, and the Peltier element generates or absorbs heat. The pH sensor as described. 7. A liquid in which said reference electrode is filled with a container filled with an internal standard solution, a reference potential electrode immersed in said internal standard solution, and a liquid which connects said internal standard solution and a liquid to be measured in said measuring cell. The pH sensor according to any one of claims 1 to 6, further comprising: 8. The reference electrode is provided with a reference electrode temperature sensor for detecting a temperature of the internal standard solution, and the operation control section is configured to detect a temperature of the liquid to be measured based on a temperature signal detected by the reference electrode temperature sensor. The pH sensor according to claim 7, wherein the pH value is corrected. 9. The pH sensor according to claim 7, wherein a reference electrode concentration sensor for detecting a change in the concentration of the internal standard solution is immersed in the reference electrode. 10. The reference electrode concentration sensor according to claim 9, wherein the reference electrode concentration sensor includes a pair of detection electrodes, and detects a change in the concentration of the internal standard solution by detecting electric conductivity between the pair of detection electrodes. The pH sensor as described. 11. The pH sensor according to claim 7, wherein an inert gas is sealed in a container of the reference electrode.