JPH09292362A - Oxygen electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen electrode for oxygen partial pressure measurement in gas or liquid which is superior in stability with respect to the lapse of time of response speed. SOLUTION: This oxygen electrode is set in the housing of an oxygen electrode making silver of an opposite electrode and aqueous solution of halogen alkali metal salt respectively, and the housing is filled with electrolytic solution containing compounds, producing easy-to-dissolve-in-water compounds, by reacting difficult-to-dissolve-in-water silver halide with alkali metal salt, sodium thiosulfate, potassium carbonate, ammonium chloride or the like containing anion of silver ion and easy-to-dissolve-in-water ionic bond compound such as nitric acid ion, chloric acid ion, nitrous acid ion and sulfuric acid ion.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen electrode for measuring the partial pressure of oxygen in a gas or a liquid. More specifically, the present invention relates to an oxygen electrode having excellent stability over time.

[0002]

2. Description of the Related Art Oxygen electrodes, which measure the amount of oxygen that permeates oxygen permeable membranes using detection electrodes, are used in a wide variety of applications such as controlling fermentation processes, measuring the environment for water quality, and measuring in the medical field. And in recent years,
An enzyme sensor combined with an oxygen-consuming enzyme reaction on the surface of the oxygen permeable membrane has also been developed.

Oxygen electrodes are classified according to the principle of use.
There are polarographic type, galvanic battery type, density battery type, etc., which are used according to each application. Among them, the polarographic type has a sensing electrode, which has a sensing electrode serving as a cathode and a counter electrode serving as an anode, and an alkali halide as an electrolyte solution, in an electrode housing in which a part of the wall serving as a sensing portion is composed of an oxygen permeable film. Obtaining the partial pressure of oxygen in a gas or liquid by measuring the current flowing according to the amount of oxygen that permeates the oxygen permeable membrane when a specific potential is applied to the sensing electrode with an aqueous solution of a metal salt. It is of the form. Further, as the counter electrode material of the oxygen electrode,
Generally, a metal having a high overvoltage such as silver, lead, or mercury is used.

[0004]

However, in an oxygen electrode having silver as a counter electrode and an aqueous solution of an alkali metal halide as an electrolyte solution as described above, although an initial response speed is fast, a potential is applied to the detection electrode. It has a drawback that the response speed of the oxygen electrode decreases with the increase of the time.

Therefore, an object of the present invention is to provide an oxygen electrode which does not cause a decrease in response speed over time.

[0006]

Means for Solving the Problems As a result of repeated studies to solve the above-mentioned drawbacks, the inventors have found that the cause of the decrease in the response speed of the oxygen electrode is due to the substance deposited on the surface of the counter electrode. It was also found that the substance was a poorly water-soluble silver halide. Then, in the electrolyte solution enclosed in the electrode housing, a compound that reacts with the poorly water-soluble silver halide deposited on the surface of the counter electrode to form a readily water-soluble compound was applied, and thereby a potential was applied to the detection electrode. The inventors have found that the response speed does not decrease with time and can be used stably, and completed the present invention.

That is, the present invention is an oxygen electrode having a sensing electrode, a counter electrode and an electrolyte solution, wherein the counter electrode is silver and the electrolyte solution is an aqueous solution of a halogen alkali metal salt.
In addition, the oxygen electrode is characterized in that a compound that reacts with the poorly water-soluble silver halide to form an easily water-soluble compound is present in the electrolyte solution.

The reason why the oxygen electrode of the present invention constructed as described above suppresses the decrease in response speed over time is that the present inventors have found that the poorly water-soluble silver halide deposited on the surface of the counter electrode is easy. It is presumed that the substance is solubilized and removed from the surface of the counter electrode to accelerate mass transfer between the electrolyte solution and the detection electrode and the counter electrode.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings, but the present invention is not limited to these accompanying drawings.

FIG. 1 is a sectional view showing a typical structure of an oxygen electrode adopted in the present invention. In FIG. 1, reference numeral 1 is an electrode housing, 2 is a detection electrode, 3 is a counter electrode, 4 is an oxygen permeable membrane, and 5 is an electrolyte solution.

The electrode housing 1 in the present invention is not particularly limited as long as it is a container in which the wall of the detection portion is composed of the oxygen permeable film 4, but as shown in FIG. The structure in which the part is composed of an oxygen permeable film is general.

The material of the portion other than the oxygen permeable membrane constituting the electrode housing 1 can be appropriately selected from known materials having resistance to the electrolyte solution contained therein. Examples of such a material include inorganic materials such as glass and ceramics, synthetic resins such as polypropylene, polyethylene, polyvinyl chloride, and epoxy resin.

The material of the oxygen permeable membrane 4 is not particularly limited as long as it is liquid impermeable and oxygen permeable, but the oxygen gas permeability coefficient is preferably 1 × 10 ^-12 ( cm ³ · cm · cm ⁻² · S ⁻¹ · cmHg ⁻¹ ) or more, and more preferably 1 × 10 ⁻¹⁰ or more. Specifically, polytetrafluoroethylene, polychlorotrifluoroethylene, fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polyolefin resin such as polypropylene, polystyrene, polyamide, polyvinyl chloride, polyethylene terephthalate, Polymethyl methacrylate and the like are generally mentioned. Among them, a fluororesin having high oxygen permeability is particularly preferable.

The thickness of the oxygen permeable film is not particularly limited, but from the viewpoint of detecting the permeated oxygen with a constant potential electrolytic current, 1
The thickness is preferably ˜100 μm, and particularly preferably 10 to 50 μm in consideration of the handleability of the film.

In the present invention, in order to measure the amount of oxygen that permeates the oxygen permeable membrane, as shown in FIG. 1, at least two electrodes, that is, the detection electrode 2 and the counter electrode 3 are required. That is,
The detection electrode 2 is an electrode for electrolyzing oxygen by an electrochemical reaction on its surface, and the counter electrode 3 is an electrode for forming a circuit for advancing the electrochemical reaction. The detection electrode can be selected from known electrodes and used appropriately, but an electrode made of an inert metal such as platinum or gold is particularly preferable. In addition, a silver electrode is used for the counter electrode 3 from the viewpoints of ease of measurement and harmfulness of the produced compound.

In the oxygen electrode of the present invention, in order to speed up the response speed, that is, the speed from the contact of oxygen with the surface of the oxygen permeable membrane of the electrode housing to the occurrence of the electrode reaction on the surface of the sensing electrode, the oxygen electrode is generally A structure in which the detection electrode is close to the oxygen permeable membrane is adopted. The term “proximity” means bringing the sensing electrode 2 and the oxygen permeable membrane 4 as close as possible to each other,
Specifically, a mode in which both are contacted via a spacer 8 as shown in FIG. 2 or without a spacer as shown in FIG. 1 is preferable.

As the other structure and use of the oxygen electrode of the present invention, known modes can be adopted without particular limitation. For example, as shown in FIG. 1, when it has a detection electrode and a counter electrode, the detection electrode 2 is electrically connected to the counter electrode 3 via the power supply 6 and the ammeter 7. An aqueous solution containing an alkali metal halide having high stability of the compound itself is enclosed as an electrolyte solution in the electrode housing 1 described above. Specifically, an aqueous solution containing potassium chloride, sodium chloride, sodium bromide and the like can be mentioned.

A feature of the present invention is that, as an electrolyte solution to be enclosed in such an electrode housing, an electrolyte solution containing a compound which reacts with a sparingly soluble silver halide deposited on the surface of a counter electrode to form an easily water-soluble compound. Is to use.

The easily water-soluble compound described above preferably has a solubility at 30 ° C. of 50 mg / dm ³ or more in order to effectively exhibit the effects of the present invention.

Further, in the present invention, the compound which reacts with the poorly soluble silver halide to form an easily water-soluble compound is not particularly limited as long as it is a compound having such an action, and it is well known. Things are used appropriately. For example, an alkali metal salt containing an anion such as nitrate ion, chlorate ion, nitrite ion, and sulfate ion, which forms an easily water-soluble ion-binding compound with silver ion, specifically exemplified by potassium nitrate, sodium nitrate, and chloric acid. Examples thereof include potassium, rubidium chlorate, lithium nitrite, potassium sulfate and the like, and sodium thiosulfate, and ammonium carbonate, ammonium chloride and the like. Of these, alkali metal salts of nitrate ions and chlorate ions, such as potassium nitrate, sodium nitrate, potassium chlorate, rubidium chlorate, and ammonium chloride, are preferably used because of their high water-solubilizing ability.

The concentration of the compound in the above electrolyte solution which reacts with the sparingly soluble silver halide to form a water-soluble compound is such that the electrolyte solution is easily water-soluble with respect to the sparingly soluble silver halide deposited on the counter electrode. The concentration is not particularly limited as long as it is a concentration capable of chemical conversion. Although such a suitable concentration depends on the type of compound used, generally, if the concentration is 20 mM or more, a decrease in response speed can be prevented. A particularly preferred concentration is 50 to
It is 500 mM. At a concentration within this range, a high current that causes deterioration of the oxygen electrode is unlikely to flow, and good performance as an oxygen electrode is exhibited.

Measurement of the oxygen concentration using the oxygen electrode of the present invention can be carried out for the oxygen partial pressure in a gas or liquid sample as in the case of a normal oxygen electrode.

The electrode of the present invention can also be applied as an enzyme sensor by immobilizing an enzyme such as glucose oxidase or uricase on the outer surface of the oxygen permeable membrane.

[0024]

As described in detail above, the oxygen electrode of the present invention is
The response speed of the electrode does not decrease with time. Therefore, it can be used as a stable enzyme electrode in the control of fermentation process, environmental measurement of water quality, measurement in the medical field, enzyme sensor and the like.

[0025]

EXAMPLES Examples will be given below to more specifically describe the present invention, but the present invention is not limited to these examples.

Example 1 An oxygen electrode having the structure shown in FIG. 1 was constructed. That is, inner diameter 10
A 1 mm diameter gold wire is embedded as a detection electrode 2 in a 1 mm housing 1, a 1 mm diameter silver wire is provided as a counter electrode 3 on the outside of a detection electrode support having an outer diameter of 7 mm, and an oxygen permeable film is 25 μm thick. The polytetrafluoroethylene film of was used. In the above housing, as an electrolyte solution, a 3.5% aqueous solution of potassium chloride was further added with a compound which reacts with the poorly water-soluble silver halide shown in Table 1 to form an easily water-soluble compound at a concentration shown in Table 1. The thing was enclosed.

Each of the above-mentioned 10 oxygen electrodes was manufactured, -0.8 V was applied to the detection electrode against the counter electrode, and the current value flowing between both electrodes was measured for each oxygen electrode to obtain the average value. .

Further, at a temperature of 20 ° C., with reference to the steady-state current value of the oxygen electrode in the nitrogen stream, the change amount up to the steady-state current value after the oxygen electrode was moved from the nitrogen stream to the atmosphere over time. The time required for the change amount to reach 90% of the steady-state current value was measured for each oxygen electrode, and the average value thereof was determined and used as the response time. In addition, 20
After applying −0.8 V to the counter electrode of the oxygen electrode at −20 ° C. for 13 weeks, the response time was measured as described above.

The results are shown in Table 1.

A concentration of 0 indicates that there is no compound which reacts with the sparingly soluble silver halide to form a readily water-soluble compound.

From the results shown in Table 1, when the electrolyte solution contains a compound which reacts with the sparingly soluble silver halide to form a readily water-soluble compound, the response speed decreases with time (increases the response time). You can see that there is no.

[0032]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic diagram of an oxygen electrode of the present invention.

FIG. 2 is a schematic diagram of an oxygen electrode of the present invention.

[Explanation of symbols]

 1 Electrode Housing 2 Detection Electrode 3 Counter Electrode 4 Oxygen Permeation Membrane 5 Electrolyte Solution 6 Power Supply 7 Ammeter 8 Spacer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromasa Yamamoto 1-1 Mikagecho, Tokuyama City, Yamaguchi Prefecture Tokuyama Corporation

Claims (1)

[Claims] 1. An oxygen electrode having a detection electrode, a counter electrode and an electrolyte solution, wherein the counter electrode is silver and the electrolyte solution is an aqueous solution of an alkali metal halide, and the sparingly water-soluble silver halide is contained in the electrolyte solution. An oxygen electrode, wherein a compound that reacts with a compound to form a water-soluble compound is present.