JPH07128282A - Hydrogen ion concentration detector - Google Patents

Abstract

PURPOSE:To provide a precise detector usable also at ordinary temperatures, as a hydrogen ion concentration detector for measuring pH value in an aqueous solution, in which a full solid type electrode is used to eliminate a liquid junction. CONSTITUTION:A hydrogen ion concentration detector is formed of a solid type detecting electrode 10 and a solid type standard electrode 20. The detecting electrode 10 is formed by bonding a counter electrode layer 13 of a metal fluoride compound of Sn and SnF2 to a solid electrolyte layer 12 of LaF3 monocrystal body, and the standard electrode 20 is formed by bonding a counter electrode layer 23 of Au or Pt to a solid electrolyte layer 22 of antimonic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen ion concentration detector for measuring hydrogen ion concentration in an aqueous solution.

[0002]

2. Description of the Related Art There have been various types of devices for measuring the concentration of hydrogen ions in an aqueous solution from a long time ago, and one using a glass electrode is known as a typical one. This glass electrode generally has an internal electrode and an internal electrolyte inside the container, and has a glass thin film at the lower end.

In the glass electrode, the glass thin film is hydrogen ion H.
^Since it has a selective permeability to ⁺ , a potential difference (membrane potential) based on the difference in ion concentration generated between the inner and outer surfaces of the glass membrane is generated, and this is measured to measure the hydrogen ion concentration and The pH value of the aqueous solution can be known.

The above-mentioned device for measuring hydrogen ion concentration using a general and general glass electrode has various problems, and various proposals have been made to solve these problems. There is one disclosed in Japanese Patent Laid-Open No. 52407.

The hydrogen ion concentration measuring device described in this publication has a hydrogen ion concentration measuring indicator electrode having a terminal connected to one electrode terminal of the measuring device and a terminal connected to the other electrode terminal. It is a device for measuring the hydrogen ion concentration in the aqueous solution by directly immersing the metal electrode body having it in an aqueous solution and measuring the potential difference generated between both terminals with the above measuring device. The electrode has a container having one end open and a closed end at the other end, and an internal electrode and an internal electrolyte inside thereof, and the closed end is formed of at least an oxygen ion conductive solid electrolyte, and the other metal electrode body. The surface contacting with the above aqueous solution is coated with any one selected from silver, silver alloys, or oxides of silver and silver alloys.

[0006]

In the pH measuring device using the above-mentioned glass electrode, as pointed out in the above-mentioned patent publication, (1) ions of the internal electrolyte are introduced into the measuring liquid through the liquid junction. To leak. As a result, the liquid to be measured may be contaminated or the true ion concentration may not be measured. (2) The original reference potential as the reference electrode may fluctuate due to a decrease in the internal electrolyte solution or a change in the concentration due to leakage from the liquid junction. (3) Also, the liquid junction may be clogged, and in this case, the above-mentioned electrical conduction cannot be obtained, which makes measurement difficult. (4) In order to obtain smooth electric conduction in the liquid junction, the internal liquid needs to be at a positive pressure condition at least as much as the liquid to be measured. There are various problems.

In order to solve the above problems, the structure of the liquid junction is made finer or the electrolyte is gelled to prevent deterioration and wear of the internal electrolyte, in order to reduce leakage as much as possible. Various methods of arranging a device for pressurizing the internal liquid are used. However, it is impossible to drastically solve the above-mentioned various problems as long as it has an electrolyte and a liquid junction in order to stabilize the potential as a reference electrode.

Therefore, in the hydrogen ion concentration measuring device disclosed in the above-mentioned patent publication, an electrode having an oxygen ion conductive solid electrolyte at the closed end of the container is used as an indicator electrode for measurement, and either silver, silver alloy or its oxide is used. Is a combination of a metal electrode body coated with as a reference electrode (or reference electrode),
It is said that the problems due to having a so-called liquid junction structure and having a liquid junction structure, or the problems due to having an internal electrolyte in the reference electrode can be all solved by using a reference electrode of a metal electrode body.

However, in the case of the above-mentioned measuring device, it is premised that the oxygen ion conductive solid electrolyte actually uses stabilized zirconia, whereby a high temperature measuring liquid or a high pressure measuring liquid is directly measured. I am going to do it.

When the stabilized zirconia is used as the solid electrolyte, the temperature range of use of the stabilized zirconia is about 200 ° C. or higher. Therefore, the primary cooling water for the reactor water of the target nuclear power plant, the boiler water, the chemical plant, etc. It can also be used under high temperature and high pressure conditions such as. Further, it is described that the temperature can be further lowered by devising measures such as increasing the purity of the stabilized zirconia.

However, as long as the stabilized zirconia is used, it is unlikely that it will operate normally at 90 ° C. or lower.
This is because stabilized zirconia does not show oxygen ion conductivity in the normal temperature range. Therefore, this measuring device seems to operate at high temperature and high pressure of 90 ° C or higher, and cannot be used when it is desired to measure the pH value of the aqueous solution at 90 ° C or lower, especially at room temperature which is a general measurement condition. .

On the other hand, a pH measuring device using a glass electrode can be used under normal temperature conditions, but its maximum use temperature is 110 to 130 ° C., and it cannot be used at a high temperature such as 500 ° C. The device has various problems as described above. Therefore, in consideration of the temperature condition to be used, it is the current situation that a reliable measuring device capable of accurately measuring the pH value under any temperature condition has not yet been obtained.

In the present invention, in consideration of various problems associated with the above-mentioned conventional pH measuring apparatus, all the electrodes are solid type electrodes, so that the liquid junction is eliminated and the temperature is wide from room temperature to high temperature. An object of the present invention is to provide a hydrogen ion concentration detector capable of accurately measuring the hydrogen ion concentration by reacting sensitively to the hydrogen ion concentration.

[0014]

As a means for solving the above-mentioned problems, the present invention detects each terminal of a detection electrode for measuring hydrogen ion concentration and a reference electrode which is a reference of electromotive force measured by this detection electrode. In the hydrogen ion concentration detector for detecting the hydrogen ion concentration in the aqueous solution by measuring the potential difference generated between both terminals by directly immersing both electrodes in the aqueous solution, the detection electrode is a LaF _{3 unit.} The crystalline solid electrolyte layer was bonded to a conductive metal to which a detection terminal was connected, and the reference electrode was composed of a solid electrode.

In this case, it is preferable that the solid electrode as the reference electrode is formed by bonding antimonic acid as a solid electrolyte layer and a metal layer as a counter electrode.

Further, it is preferable that the conductive metal of the sensing electrode is a mixture of a metal and a metal fluoride, a combination of these mixtures and a mixture, or an inert metal that does not form a fluoride.

[0017]

The hydrogen ion concentration of the detector of the present invention having the above structure can be accurately measured by using LaF _{3 of the} solid electrolyte as a detection electrode having a half-cell structure and using the solid electrode as the reference electrode. In this way, by using a solid electrode structure for both the detection electrode and the reference electrode, the liquid junction used in conventional detectors can be eliminated, and therefore the ionic aqueous solution slightly moves through the liquid junction. However, the problem that the hydrogen ion concentration of the aqueous solution to be measured changes is fundamentally solved.

Further, as described above, the hydrogen ion concentration measuring device according to the above-mentioned patent publication operates in a high temperature range from about 100 ° C. to about 600 ° C., whereas the detector according to the present invention changes from a normal temperature range to a high temperature range. Can be measured up to. This is because the detection electrode uses LaF ₃ solid electrolyte having ion conductivity even in the normal temperature range. Further, the reference electrode may be a solid electrolyte layer made of antimonic acid and a conductive metal bonded thereto, and in this case, it is possible to measure from a normal temperature range to about 300 ° C. When another solid electrolyte is used instead of antimonic acid, it can be measured even in a high temperature range of 600 ° C. or higher. It has been confirmed that such a hydrogen ion concentration detector can measure the hydrogen ion concentration based on the following considerations.

First, as shown in FIG. 5, a prototype electrode was prepared by joining a sensing electrode to one side of a solid electrolyte layer of LaF ₃ used as a sensing electrode and a counter electrode of a mixed metal of Sn and SnF _{2 to} the other side. Created. When various experiments were tried using this prototype device, the following was found.

(1) Response Characteristics of Prototype Element FIG. 6A shows the pH dependence of the electromotive force at 25 ° C. of the prototype element using the LaF ₃ single crystal.
Any element (detection electrode: Pt or Au) is p in water
A linear decrease in electromotive force is seen with an increase in H. That is, it can be seen that the electromotive force of these elements responds to H ⁺ ions or OH ⁻ ions in water in accordance with the Nernst equation. In addition, since the slope of the straight line is about −30 mV / decade in any element, H ⁺ ions or O
It seems that an electrode reaction containing two electrons is occurring with respect to the H ⁻ ion.

By the way, when the pH in water is changed (HCl, NaOH), NaCl in water is neutralized by a neutralization reaction.
The concentration is increasing each time. Nevertheless, it was found that the reproducibility of the electromotive force of this element with respect to pH change was very good. That is, the potential of the detection electrode of this element is Na ⁺
It seems that there is almost no effect on changes in the concentration of ions or Cl ⁻ ions. However, the electromotive force of this element responds to changes in the concentration of dissolved oxygen in water.

FIG. 6B shows the dependency of electromotive force at 25 ° C. on the dissolved oxygen concentration in water. A linear increase in electromotive force is observed with increasing dissolved oxygen concentration in any of the elements (detection electrodes: Pt, Au). Therefore, it can be seen that the electromotive force of this element responds to dissolved oxygen in water in accordance with the Nernst equation. Further, since the inclinations are all about 30 mV / decade, it is considered that an electrode reaction containing two electrons with respect to dissolved oxygen is occurring at the detection electrode of this element.

As described above, the electromotive force of this element is the pH of water.
It has been found that it responds well to changes, but when applied as an actual pH sensor, it is inconvenient that the electromotive force also depends on changes in the concentration of dissolved oxygen. Therefore, when various devices were examined as devices that did not depend on the change in the concentration of dissolved oxygen, they arrived at a device having a half-cell structure having no detection electrode.

The detector element having the above-mentioned structure of the present invention obtained in the above-mentioned examination process will be described below.

(2) Response characteristics of all-solid-state pH electrode FIG. 7A shows characteristics relating to pH dependency in water of each detection electrode when the material of the detection electrode is changed using the Ag / AgCl electrode as a reference electrode. FIG. First, the electromotive force (A in the figure) of a detector in which an element (half-cell) using a LaF ₃ single crystal and an Ag / AgCl electrode is combined linearly decreases (slope: about − 30 mV / decad
e) is seen, and it can be seen that the electromotive force of this detector also has the same response ((a) in FIG. 6) as the element with the detection pole. On the other hand, in the detector using antimonic acid as the detection electrode (B in the figure) and the detector using the metal electrode made of silver as the detection electrode (C in the figure), the electromotive force is almost equal to the pH change. It shows a constant value without depending.

The symbols in the figure are, for example, B. Gold (Au) and antimonic acid (Sb ₂ O ₅ .n).
H ₂ O) detection electrode in the test solution, Ag / AgCl electrode reference electrode is saturated with silver chloride 3.5MKCl
This means immersing in a solution, connecting both solutions using a salt bridge, and measuring the electromotive force of the detector based on the hydrogen ion concentration in the test solution.

FIG. 7B is a graph showing characteristics relating to the dissolved oxygen concentration dependency in water of each detection electrode when the material of the detection electrode is changed similarly using the Ag / AgCl electrode as the reference electrode. As shown in the drawing, a detector (A in the figure) in which an element using antimonic acid (half cell) and an Ag / AgCl electrode are combined, an element (half cell) using LaF ₃ single crystal, and Ag / AgCl
In any of the detectors combined with AgCl electrodes (B in the figure) and the detectors combined with silver metal electrodes and Ag / AgCl electrodes (C in the figure), the electromotive force changes the dissolved oxygen concentration. Shows a constant value with little dependence on. This is different from the electromotive force response of a similar element having a detection pole ((b) of FIG. 6).

FIG. 7C shows the underwater p of the detector of the present invention.
It is a figure which shows the characteristic regarding H dependence. As shown in the figure, a detector (A in the figure) that combines an element using LaF ₃ single crystal as a detection electrode and an element using antimonic acid as a reference electrode, and an element using LaF ₃ single crystal as a detection electrode The electromotive force of the detector (B in the figure) in which a metal electrode made of silver was combined as the reference electrode showed a linear decrease (slope: about 30 mV / decade) with an increase in pH in water. It can be seen that the electric power also has the same response ((a) in FIG. 6) as the element with the detection pole. This detector structure is noted here in that it is entirely solidified. Further, since the elements and metal electrodes used in these detectors do not depend on the dissolved oxygen concentration in water as shown in FIG. 7B, these detectors change the electromotive force due to the change in the dissolved oxygen concentration. It is clear that it does not happen.

From these three results ((a), (b) and (c) in FIG. 7), when the detector of the present invention is applied as a pH electrode, selectivity with respect to pH (independent of dissolved oxygen) It turns out that it is excellent.

As shown in all the graphs, all the above tests were conducted at room temperature of 25 ° C., and it can be seen that the measurement temperature range includes room temperature. Further, when the electrode of the solid electrolyte is bonded and fixed to the case with the fixing material, the above-mentioned use limit temperature is determined by the heat resistant temperature of the fixing material.

In the second invention, a solid electrode in which a metal layer is bonded to antimonic acid is used as a reference electrode. In this case, the metal layer may be any conductive layer. The characteristics are as described above.

In the third invention, the conductive metal of the detection electrode is a mixture of metal and metal fluoride or a combination of these mixtures and mixture. In this case, the metal may be any metal as long as it can form a metal fluoride.

On the contrary, it may be composed only of an inert metal which does not form a fluoride. This inert metal is
A metal that does not react with fluoride ions, such as Pt,
Au and Pd are known. This is because lanthanum fluoride, which is the electrolyte of the detection electrode, is a fluoride ion conductor, so that a stable potential cannot be obtained with a material other than the above conductive metal.

As can be seen from the above, the detectors according to any of the above-mentioned inventions use solid-state electrodes as electrodes, and unlike the conventional glass electrodes, liquid junctions are not provided, so they are operated. In this case, there is no restriction on the directionality, such as the fact that it must always face downward, and it is not a specific shape such as a glass electrode, but various shapes such as a circuit board shape or an injection needle. The shape has a large degree of freedom.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a hydrogen ion concentration detector of the embodiment. As shown in the figure, this concentration detector comprises a detection electrode 10 for measuring the hydrogen ion concentration and a reference electrode 20 for generating a reference electromotive force.

The detection electrode 10 comprises a solid electrolyte layer 12 of LaF ₃ single crystal at the end of a container 11 of a Pyrex glass tube.
Is provided with a counter electrode layer 13 made of a metal mixture of Sn and SnF ₂ , which is bonded to the fixing portion 14 of epoxy resin.
It consists of one fixed in place. Lead wire 15 is provided on the counter electrode layer 13.
Are connected, and the tip thereof is guided to the detector 30. 1
6 is an insulating coating.

On the other hand, the reference electrode 20 has the same structure, but as the solid electrolyte layer 22, antimonic acid (Sb ₂ O _{5) is used.}
4H ₂ O) and the counter electrode layer 23 is a solid electrode using Au or Pt, and is fixed by an epoxy resin fixing portion 24. In each of the detection electrode 10 and the reference electrode 20, the solid electrolyte layers 12 and 22 are closely fixed to the counter electrode layers 13 and 23 by sputtering or the like. Further, the solid electrolyte layers 12 and 22 and the glass containers 11 and 21 are fixed by the fixing portion 14 made of epoxy resin.
This is to prevent the liquids 3 and 23 from coming into direct contact with the test liquid.

The lead wire 25 is also connected to the counter electrode layer 23, and the tip of the lead wire having the insulating coating 26 is connected to the detector 30. Although the upper end of the container 11 is shown in a closed state, it is not always necessary to close the upper end and it may be open to the atmosphere. However, in that case, all the lead wires 15 are covered with an insulating material.

FIG. 2 shows a schematic structure of the concentration detector of the second embodiment. This embodiment is functionally the same as that of the first embodiment, except that the detection electrode 10 and the reference electrode 20 are integrally formed. Both electrodes are partition walls 121
And the solid electrolyte layers 12 and 22 are insulated and fixed by the fixing portion 124 made of epoxy resin.

FIG. 3 shows a schematic structure of the concentration detector of the third embodiment. The concentration detector of this embodiment also has the same basic configuration as that of the first embodiment, but the detection electrode 10 and the reference electrode 20 are the same.
The shape is slightly different.

In the concentration detector of this embodiment, for example, the diameter of the container 11 is in mm so that the hydrogen ion concentration in human blood can be measured, and the tip of the solid electrolyte side is a syringe. It is sharply cut like this and the whole is micronized into an extremely small size.

Although not shown, a glass thin film may be provided on the surface of the solid electrolyte layers 12 and 22 in order to prevent a very small amount of reaction when they come into direct contact with blood and to ensure safety. Good.

The functions of all the three embodiments having the above-mentioned configurations are exactly the same. As shown in FIG. 1, when the detection electrode 10 and the reference electrode 20 are immersed in the aqueous solution B in the container A, the reference electrode 20 of antimonic acid does not react to the change in the dissolved oxygen concentration at all as described above, and Aqueous solution B
Shows a constant reference voltage that does not change depending on the hydrogen ion concentration of.

On the other hand, the detection electrode 10 does not change with the change in the dissolved oxygen concentration, but it is sensitive to the change in the hydrogen ion concentration. Therefore, with reference to the measured potential of the reference electrode 20, the potential difference is detected by the detector 30.
The hydrogen ion concentration can be measured by measuring with.

In this case, since the reference voltage has a predetermined value for a specific material forming the reference electrode, it is measured in advance, and the hydrogen ion is calculated from the electromotive force of the potential difference obtained with respect to the measurement reference. The concentration is measured.

FIG. 4 shows a schematic structure of the fourth embodiment. In this embodiment, the sensing electrode 10 is exactly the same as in the first embodiment, but the reference electrode 20 'is different in construction as shown. The reference electrode 20 'includes a metal electrode body 22' and an insulating coating portion 23 'that covers the base portion of the metal electrode body 22'.
It is connected to the lead wire 25 'through 4'. 26 '
Is an insulating coating.

As the metal electrode, silver, silver alloy or silver,
A silver alloy coated with its oxide, or a metal ground layer of aluminum, nickel, copper, iron, etc. coated with silver or a silver alloy by plating or laminating, and the outer side of which is oxidized with silver or a silver alloy. It may be the one with the object attached.

In the case of this embodiment, the basic operation is similar to that of the previous embodiment, and the metal electrode body 20 'acts as a reference electrode, and the potential difference due to the hydrogen ion concentration detected by the detection electrode 10 is changed. It is detected by the detector 30. The potential level determined by the metal type of the metal electrode body is previously measured as in the previous embodiment, and the hydrogen ion concentration is detected based on the reference potential.

[0049]

[Effect] As described in detail above, L is used as the detection electrode.
A combination of a single crystal solid electrolyte layer of aF ₃ with a conductive metal and a solid electrode as a reference electrode is used, and both electrodes are solid so that a liquid junction is not required and operation at room temperature is possible. Since it is possible, various problems with conventional glass electrodes can be solved all at once and the hydrogen ion concentration in the aqueous solution can be accurately measured in a wide temperature range from normal temperature to high temperature, and the detector can be miniaturized. The electrode is solid and has no liquid junction, so it is not restricted in directionality such that it has to be directed in a specific direction when it is operated. Since it can be configured as a shape, it has a large degree of freedom in shape, and it has various advantages such as no need for maintenance after use, and it can be widely applied to various fields that require measurement of hydrogen ion concentration. Innovative benefits can be obtained.

[Brief description of drawings]

FIG. 1 is an overall schematic view of a hydrogen ion concentration detector according to a first embodiment.

FIG. 2 is an overall schematic view of a hydrogen ion concentration detector according to a second embodiment.

FIG. 3 is an overall schematic view of a hydrogen ion concentration detector according to a third embodiment.

FIG. 4 is an overall schematic view of a hydrogen ion concentration detector according to a fourth embodiment.

[Fig. 5] Overall schematic diagram of prototype detector

FIG. 6 is a diagram showing the measurement result of the pH value and the dissolved oxygen concentration of the prototype device.

FIG. 7 is a diagram showing the measurement results of pH value and dissolved oxygen concentration of various electrodes.

[Explanation of symbols]

 10 Detection Electrode 11, 21 Glass Container 12, 22 Solid Electrolyte Layer 13, 23 Counter Electrode Layer 14, 24 Fixing Part 15, 25 Lead Wire 16, 26 Insulation Coating

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeki Kuwata 7-234, Matsubara-cho, Niihama-shi, Ehime

Claims (3)

[Claims] 1. A sensing electrode for measuring hydrogen ion concentration,
Each terminal of the reference electrode, which is the reference of the electromotive force measured by this detection electrode, is connected to the detector, and both electrodes are directly immersed in the aqueous solution and the potential difference generated between both terminals is measured to measure the potential difference in the aqueous solution. In the hydrogen ion concentration detector for detecting the hydrogen ion concentration, the detection electrode is a solid electrolyte layer of LaF ₃ single crystal to which a conductive metal having a detection terminal is connected, and the reference electrode is a solid electrode. A hydrogen ion concentration detector characterized in that 2. A hydrogen ion concentration detector characterized in that the solid electrode as the reference electrode comprises a solid electrolyte layer of antimonic acid and a metal layer joined as a counter electrode. 3. The conductive metal of the detection electrode is a mixture of a metal and a metal fluoride, a combination of these mixtures and a mixture, or an inert metal that does not form a fluoride. The hydrogen ion concentration detector described.