JPH0319944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion-selective electrode, and more specifically, the present invention relates to an ion-selective electrode, and more specifically, the response potential characteristics of the individual electrodes obtained have almost no variation, and the response potential of the ion-sensitive membrane is stable even during long-term operation. This invention relates to an ion-selective electrode for detection and measurement.

In recent years, electrochemical measurement methods have been used to analyze biological samples, and in particular, the measurement of various ions using ion-selective electrodes has been attracting attention. An ion-selective electrode refers to an electrode that exhibits a potential that corresponds to a specific ion activity in a solution.Currently, solid membrane electrodes and liquid membrane electrodes that are sensitive to various ions, including glass membrane electrodes, are being developed. has been done.
FIG. 1 shows the main configuration of a conventionally used ion-selective electrode and measurement system. In other words, conventionally,
For measuring the potential difference between the inner and outer surfaces of the ion-sensitive membrane 4,
Internal standard solution 7 containing a certain amount of specific ions to be measured
and an internal reference electrode 6 are interposed between the potential detection lead wire 8 and the ion-sensitive membrane 4, and basically the interfacial potential Ei between the ion-sensitive membrane and the internal reference solution and the interfacial potential between the ion-sensitive membrane and the sample solution 2. Difference from E ₀ (Ei
−E ₀ ) is determined by measuring the potential difference between the external reference electrode 1 and the ion-selective electrode 5 with a high impedance voltmeter using each potential detection lead wire 8, 9,
Since Ei is constant, the specific ion activity in the sample solution was calculated by determining E ₀ .

However, such conventional ion-selective electrodes have an internal reference liquid as described above, making it difficult to miniaturize them, and also because they measure the potential difference indirectly via the internal reference electrode, they are not sensitive to ions. In some cases, problems occurred in stably detecting the response potential of the membrane.

For this reason, various types of electrodes called coated wire electrodes have recently been studied. As shown in Figure 2, this is a method in which an ion-sensitive membrane made of a polymeric substance is coated directly on the surface of a lead wire for detecting the potential of a metal such as platinum by brushing, etc., and the response potential can be directly detected. , it has the feature of being able to be made smaller. However, bubbles tend to enter such electrodes when coating the ion-sensitive membrane, and the interfacial state of the coating varies depending on the electrode, and the interfacial state fluctuates due to the difference in thermal expansion coefficient between the lead wire and the ion-sensitive membrane. However, it had drawbacks such as the inability to achieve electrical connection integration. The resulting electrodes had many problems in practical use, such as fluctuations in Ei and insufficient stable detection of response potential, large variations in response potential characteristics of individual electrodes, and the need for individual calibration. have.

The present invention has been made to solve these problems, and includes an ion-selective electrode configured to directly detect potential from an ion-sensitive membrane such as a coated wire electrode using a potential detection lead wire. By interposing at least a substance with good electronic and/or ionic conductivity made of mercury or its amalgam between the lead wire and the lead wire, stable detection of the response potential can be sufficiently obtained even for a long time. This was based on the discovery that there is almost no variation in the characteristics of individual electrodes.

Hereinafter, a specific example of an ion-selective electrode and a measurement system comprising the same according to the present invention will be described with reference to the accompanying drawings. FIG. 3 shows an ion-selective electrode with a stepped coated wire structure and its measurement system according to the present invention, in which an ion-sensitive membrane 4 is connected to a potential detection lead wire 8 via a material 11 having good electron and/or ion conductivity. covered with. FIG. 4 shows another specific example, in which an ion-sensitive membrane 4 is stretched over a conventional electrode container 10, and a lead wire 8 is connected via a material 11 with good electron and/or ion conductivity.
This is a so-called disk-shaped coated wire electrode that is electrically connected to the electrode.

In this invention, the material with good electronic and/or ionic conductivity includes mercury, its amalgam, or solid electrolyte.

The partner metal for the amalgam may be any metal that forms an amalgam with mercury. Examples include relatively low melting point metals such as gold, silver, platinum, zinc, cadmium, tin, palladium, lead and bismuth. These may be a mixture of one or more types. Among these, it is preferable to use paste-like amalgam because it is easy to manufacture electrodes.

Specific examples of the ion-sensitive membrane used in this invention include hydrogen ions, sodium ions, potassium ions, ammonium ions, chloride ions, calcium ions, fluorine ions, iodine ions, nitrate ions, cyanide ions, perchlorate ions, etc. and many other organic and inorganic ions, and solid membranes based on polymeric substances can be used. In addition, when using a solid membrane based on a certain type of amphoteric ion-exchange resin, selectivity for various ions increases, long-term stable potential response is obtained, and durability is excellent. It may be preferable. An example of an amphoteric ion exchange resin for a chloride sensitive membrane is a quaternary ammonium type styrene anion exchange resin with sulfonic acid groups introduced (the exchange capacity ratio of cation exchange groups to anion exchange groups is, for example, 75:25). can be mentioned. The thickness of the ion-sensitive membrane can be the same as that normally used in the field, and is usually 0.05~
Approximately 0.2mm is appropriate.

Examples of the metal of the potential detection lead wire used in this invention include platinum, silver, gold, etc., but any metal can be used as long as it is electrically and mechanically satisfactory.

Known electrode containers and the like can be used in this invention.

In this invention, the substance with good electron and/or ion conductivity has good adhesion to the ion-sensitive membrane, forms a solid solution at the interface with the ion-sensitive membrane, and forms a solid solution at the interface with the potential detection lead wire. Preferably one that can. In addition, in order to further improve the electrical bond between the ion-sensitive membrane and a substance with good electron and/or ion conductivity, a metal, preferably a metal, which has electron and/or ion conductivity, is applied to the surface of the ion-sensitive membrane in contact with the ion-sensitive membrane. A thin film of a metal that can form a solid solution with a good substance (for example, cadmium, silver, zinc, etc. when using mercury or its amalgam) is formed by physical vapor deposition (PVD) such as sputtering or chemical vapor deposition (CVD). , may be kept in close contact with each other. A specific example of such processing is shown in FIGS. 5 and 6. Note that the thickness of the metal thin film 12 should theoretically be at least a monomolecular layer or more, and normally about 0.01 to 0.5 mm is appropriate.

Further, the same process as described above may be performed on the potential detection lead wire, which may be preferable in some cases.

As for the method for producing the ion-selective electrode of the present invention, for example, for a disk-type electrode having a configuration as shown in FIGS. 4 and 6, after an ion-sensitive membrane is stretched over an electrode container, It can be manufactured by filling a material with good electronic and/or ion conductivity and providing lead wires using a known procedure. In addition, for a stick-type coated wire electrode, for example, the lead wire is first coated with a material having good electron and/or ion conductivity such as mercury or its amalgam, and then a desired ion-sensitive film is coated on top of the lead wire. It can be made. In particular, when the ion-sensitive substance is made of a polymeric substance, it is preferable because it can be easily produced by means such as coating.

As another specific example of the ion-selective electrode of the present invention, a flow cell system may be combined, as shown in FIG. In the figure, the sample solution flows from A to B. In addition, in the case of continuous measurement, etc., as shown in Figure 8, a coil-shaped coil is attached to the outer surface of a tubular object made of an ion-sensitive membrane via a material with good electron and/or ion conductivity such as mercury or its amalgam. It is also possible to carry out measurements by providing a lead wire 8' and passing the sample solution through the tube.

On the other hand, in the measurement system using the ion-selective electrode of the present invention, a known reference electrode such as a calomel electrode or a silver chloride electrode can be used as the external reference electrode.

In this invention, the metal potential detection lead wire is electrically connected to the ion-sensitive membrane through a material having good electron and/or ionic conductivity, such as mercury or its amalgam. The interfaces between the substance and the lead wire, and between the intervening substance and the ion-sensitive substance are electrically in close contact with each other.
That is, when mercury or its amalgam is used, a solid solution such as amalgam made of the metal of the lead wire is formed at the interface with the electroformed detection lead wire. Therefore, the lead wire and the intervening material are electrically connected and integrated. In addition, the interface between the intervening substance and the ion-sensitive membrane is easily bonded, particularly when a polymer membrane is used, and a solid solution is easily formed, so that they are in close electrical contact.

Therefore, the ion-selective electrode of this invention has less fluctuation in Ei, and compared to conventional coated wire electrodes, the response potential can be detected stably even during long-term operation, and there is almost no variation between individual electrodes due to manufacturing, resulting in high quality. It is also excellent in terms of management. Since it does not have an internal reference electrode, it can have a complicated shape as shown in FIGS. 7 and 8.

Furthermore, the ion-selective electrode of the present invention can be easily miniaturized, ultra-miniaturized, or semi-solid, and is also effective for in-vivo measurements. Specifically, we use an ultra-fine potential detection lead wire made of platinum or gold with a diameter of approximately 10 μm, and attach it to an intervening substance layer and an ion-sensitive membrane (for example, the above-mentioned zwitterion ion Ultra-small (extremely thin) electrodes can be obtained by coating the electrodes with an exchangeable resin membrane, which can be inserted directly into the living body, making in-vivo measurements easy and safe, and very effective.

Examples of this invention are shown below.

Example 1 An ion selective electrode as shown in FIG. 4 was prepared. The ion-sensitive membrane was prepared by dissolving valinomycin in dioctyl sebacate, mixing it with a tetrahydrofuran solution of polyvinyl chloride to dissolve it uniformly, and then evaporating the tetrahydrofuran solution to obtain 1.3% by weight of valinomycin and 68.2% by weight of dioctyl sebacate. %, polyvinyl chloride was obtained, and this was used as a potassium ion sensitive membrane, silver was used as a potential detection lead wire, and cadmium was used as a material with good electronic and/or ion conductivity. Amalgam was used. In this way, three potassium ion-selective electrodes were prepared, and the response potentials corresponding to various potassium concentrations (activities) were measured using the same external reference electrode (calomel electrode) for each electrode, and the response potential characteristics were determined. Examined. As a result, as shown in FIG. 9, there was almost no variation in the response potential characteristics of the respective potassium ion electrodes.

As a comparative example, a conventional coated wire electrode having the same configuration was similarly measured. The results are also shown in FIG. As described above, conventional electrodes have a problem in practical use because of large variations in the characteristics of each electrode. As a reference example, the potential characteristics of a conventional potassium electrode having an internal reference electrode are also shown.

Furthermore, similar experiments were conducted except that a solid electrolyte made of silver sulfide/silver chloride was used instead of amalgam, and exactly the same results were obtained.

Example 2 The electrode of the present invention obtained in Example 1 was immersed in a solution containing potassium ions at a constant concentration, and changes in response potential characteristics over a long period of time were measured. Compared with the characteristics. The results are shown in FIG.

As described above, it has been found that the ion-selective electrode of the present invention can stably detect response potentials even during long-term operation.

A similar experiment was conducted except that a solid electrolyte made of silver sulfide/silver chloride was used instead of amalgam, and similar results were obtained.

Similar results were also obtained when an organic thin film such as polyphenylenediamine was used instead of amalgam or solid electrolyte.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the main structure of a conventional ion-selective electrode and its measurement system, and FIG. 2 is a sectional view showing the structure of a conventional coated wire electrode. 3 to 6 are cross-sectional views showing specific examples of the ion-selective electrode and its measurement system according to the present invention, respectively. FIGS. 7 and 8 are sectional views of essential parts showing another specific example of the ion-selective electrode according to the present invention. FIG. 9 is a graph showing various response potential characteristics in Example 1, and FIG. 10 is a graph showing temporal changes in response potential in Example 2. DESCRIPTION OF SYMBOLS 1... External reference electrode, 2... Sample solution, 3... Sample container, 4... Ion sensitive membrane, 5... Ion selective electrode,
6... Internal reference electrode, 7... Internal standard liquid, 8, 8',
9... Potential detection lead wire, 10... Electrode container, 11
...substance with good electronic and/or ionic conductivity, 12.. metal thin film, 13.. salt bridge, C.. variation in response potential characteristics of conventional coated wire electrodes,
D... Variation in response potential characteristics of the ion selective electrode of this invention, E... Response potential characteristics of a conventional electrode having an internal reference electrode, F... Response potential of the ion selective electrode of this invention, G... Conventional coated wire electrode response potential.

Claims (1)

[Claims] 1. A coated wire type characterized in that mercury or its amalgam is interposed between the inner surface of an ion-sensitive membrane made of a solid membrane based on a polymeric substance and a potential detection lead wire. Ion selective electrode. 2. The electrode according to claim 1, wherein the potential detection lead wire is made of platinum or gold and has a diameter of 10 μm or less. 3 A thin metal film is closely attached to the inner surface of an ion-sensitive membrane made of a solid film based on a polymeric substance, and mercury or its amalgam is interposed between the thin metal film and the potential detection lead wire. Features a coated wire type ion selective electrode. 4. The electrode according to claim 3, wherein the electroforming detection lead wire is made of platinum or gold and has a diameter of 10 μm or less.