JPH0336187B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an ion-selective electrode, and more particularly to an ion-selective electrode that is easy to manufacture and easy to downsize.

[Technical background of the invention and its problems]

Ion-selective electrodes have traditionally had the characteristic of being able to selectively quantify the concentration of specific ions in a liquid, and have been used in a wide range of fields such as monitoring the concentration of specific ions and water quality analysis.

For example, in the case of a cation-selective electrode, the difference between the activity a ⁺ of the target cation and the potential E exhibited by the cation-selective electrode is E=E ⁰ +2.303 (RT/ZF) loga ⁺ ...(1), and in the case of an anion-selective electrode, the relationship between the activity a ^- of the anion of interest and the potential E shown by the anion-selective electrode is E=E. ⁰ −2.303(RT/ZF)loga ^- ...(2) A relationship is established in which the logarithm of the activity is proportional to the change in potential, and the activity of the target ion can be easily determined from the measured potential value. This is because it can be calculated.

In addition, in the above formulas (1) and (2), R is the gas constant,
T is the absolute temperature, Z is the ionic valence, F is Faraday's constant, and E ⁰ is the standard electrode potential of the system.

By using an ion-selective electrode in this way, it becomes possible to quantify ions in a wide concentration range simply by measuring the potential. In addition, using an ion-selective electrode,
By making the electrode part smaller, it becomes possible to measure a small amount of sample. Due to the convenience of such ion-selective electrodes, in recent years they have been used for medical purposes, especially for ions dissolved in blood, such as Na ⁺ , K ⁺ ,
Attempts to use it for quantifying ions such as Cl ^- are increasing. The structure of a conventional ion-selective electrode is shown in FIG. In the figure, 1 is an internal electrolyte, 2 is an ion selective membrane, 3 is a reference electrode, and 4
is the electrode cylinder.

Recently, in order to reduce the burden of blood collection from critically ill patients and children, there has been a demand for the development of even smaller ion-selective electrodes (capable of detecting minute amounts of blood). . However, since conventional electrodes have an internal electrolyte,
There was a limit to how much capacity could be reduced. For this reason, an ion-selective electrode without an internal electrolyte as shown in FIG. 2 was developed. This electrode has an ion selective membrane 22 coated directly on a needle-shaped reference electrode 23 made of a metal or a metal compound, and the upper part of the electrode is covered with an electrode cylinder 24.

The electrode shown in Fig. 2 can be attached to a container holding a blood sample (see Fig. 3) or a flow cell (Fig. 4) consisting of a blood circulation part and an electrode holding part, similar to the electrode shown in Fig. 1. It is installed and used. That is, in the container shown in FIG. 3, one end of each of the ion-selective electrode 31 and the reference electrode 32 is connected to an electrometer 33 for potential measurement, and the other end is connected to the test liquid 35 filled in the container 34. Ion concentration measurements are carried out in the immersed state. Further, in the flow cell shown in FIG. 4, the ion selective electrode 41 and the reference electrode 42 are fixed to a flow cell 44 filled with a test liquid 45, and the obtained signal is inputted to an electrometer 43 to detect ions. Concentration measurements are taken. Note that the test liquid in the flow cell 44 is transferred from A to B by the operation of a pump (not shown).
is ejected in the direction of

As for the electrodes mentioned above that do not have an internal electrolyte, it is possible to miniaturize the electrode itself, but in order to reduce the amount of sample liquid, it is necessary to further miniaturize the flow cell, etc. Must be. However, there are technical problems in that there is a limit to the miniaturization of flow cells and the like, and furthermore, miniaturization makes manufacturing difficult. Furthermore, when a flow cell-type ion-selective electrode reaches the end of its lifespan, either the electrode or the entire flow cell must be replaced; however, the former is a burden on the user, while the latter is a burden on the user. This method has the same disadvantage as the former, which is a burden on the user, as the expensive flow cell type electrode, which has been miniaturized by spending a great deal of time and effort, is discarded.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ion-selective electrode which can eliminate the above-mentioned drawbacks, can be manufactured by an extremely simple method, and can be used to reduce the amount of a test liquid.

[Summary of the invention]

As a result of intensive research to achieve the above object, the present inventors installed a reference electrode made of metal or a compound thereof on the outside of a cylindrical tube that serves as a flow path for the test liquid, and The present inventors have also discovered that simply covering the reference electrode with an ion-selective membrane exhibits a stable potential and functions as an ion-selective electrode, leading to the completion of the present invention.

That is, the ion-selective electrode of the present invention comprises: a test liquid flow tube containing an ion selective substance; a reference electrode attached to the outer wall of the tube; and a reference electrode covering the outer wall of the test liquid flow tube. an ion-selective membrane;

The present invention will be explained in more detail below.

In the electrode of the present invention, the constituent material of the test liquid flow tube is
The composition of the ion-selective membrane agent varies depending on whether or not it has an affinity for the ion-selective substance. Note that the term "affinity" as used in the present invention means that the ion selective substance has a property of being easily diffused.

FIG. 5 shows an example of the structure of an ion-selective electrode in which the material of the sample liquid flow tube has an affinity for the ion-selective membrane agent. In the figure, 51 is a test liquid distribution tube, 52 is a reference electrode wound around the tube 51, and 53 is an ion selective membrane that covers the outer wall of the tube 51 and the reference electrode 52. As the constituent material of the tube 51, any material can be used as long as it has an affinity for the ion-selective membrane agent, but preferably an organic polymer material is used. Examples of such organic polymer materials include polyvinyl chloride, polyvinylidene chloride, polystyrene, and polymethyl methacrylate. Conventionally known materials are used for the reference electrode 52, and specific examples include metals such as Pt, Au, Ag, Cu, and Cr, and metal compounds thereof (eg, halides). On the other hand, an ion selective membrane is usually composed of an ion selective substance and an organic polymer material, but may contain additives such as a plasticizer or a membrane electrical resistance reducing agent. Conventionally known materials are used as these materials. The ion selective substance may be either a cation or anion selective substance; the Na ⁺ selective substance is monensin, the K ⁺ selective substance is valinomycin, and the Cl ^- selective substance is quaternary ammonium salt (methyl It is preferable to use tridodecyl ammonium chloride, etc.). In addition, as organic polymer materials,
It is preferable to use polyvinyl chloride, polyvinideline chloride, polystyrene, polymethyl methacrylate, silicone rubber, and the like. Further, as the plasticizer, it is preferable to use dioctyl adipate, dioctyl phthalate, orthonitrophenyl octyl ether, or the like. In addition, as membrane electrical resistance reducing agents, for example, in the case of K ⁺ ion selective membrane agents,
It is preferable to use potassium tetraphenylborate or the like. The ion selective substance is usually added in an amount of 0.5 to 30% by weight based on the organic polymer material.

In the above electrode, the cross-sectional shape of the test liquid flow tube is preferably circular, but the shape is not particularly limited as long as it does not hinder the flow of the test liquid. Further, the reference electrode may be attached in any manner as long as it is attached to the test liquid flow tube so that it does not move easily. Furthermore, the ion selective membrane usually covers the area around the sample liquid flow tube around the wound part of the reference electrode, but if the reference electrode can be fixed without separating from the sample liquid flow tube, it is possible to The tube and reference voltage may be covered in any manner.

The ion selective electrode described above is manufactured as follows. First, a reference electrode is wound around the outer wall of the test liquid flow tube. Next, an ion-selective membrane agent is prepared by dissolving an ion-selective substance, an organic polymer substance, and if necessary a plasticizer, etc. in a solvent, and the membrane agent is applied to cover the outer wall of the tube and the reference electrode, and then dried. and evaporate the solvent. In addition, examples of solvents include acetone, benzene,
Carbon tetrachloride, tetrahydrofuran, etc. are used.

The electrodes obtained in this way vary depending on the material and wall thickness of the test liquid flow tube, but for example, if the electrode is made of polyvinyl chloride and has a wall thickness of about 0.5 mm, after manufacturing,
Usually, it does not show sensitivity to ions in the test liquid until 30 to 50 hours have passed. This is because the ion-selective substance in the ion-selective membrane will not diffuse to the inner wall of the test liquid flow tube until a certain period of time has elapsed. It is not clear how much ion-selective substance needs to be diffused into the sample liquid flow tube for the electrode to show sensitivity to ions, but for example, an outer diameter of 2.4 mm and a wall thickness of 0.8 mm is not clear. In the case of a test liquid flow tube made of a polyvinyl chloride tube, good sensitivity can be obtained as long as 5 to 50 mg of ion-selective membrane agent is applied to the outer wall of the tube.

Next, FIG. 6 shows an example of the structure of an ion-selective electrode in which the material of the test liquid flow tube has no affinity for the ion-selective membrane agent. In the figure, 61 is a test liquid distribution tube, 62 is a reference electrode wound around, 63 is an ion selection membrane, and 64 is a hole bored in tube 61. Examples of the constituent material of the tube 61 include polyethylene, polyfluoroethylene, cellulose acetate, and the like. Also, the diameter of the hole 64 is 10μ
It is also possible to use a porous material such as ceramic as the constituent material of the tube 61.
The pores 64 are filled with an ion-selective membrane agent, and the number of pores may be any number as long as it is one or more. Further, the shape of the hole is not limited to a circular shape, and any shape may be used as long as the hole communicates with the outer wall and the inner wall of the test liquid flow tube. Note that the reference electrode and ion selection membrane are made of the same material as the electrode shown in FIG. 5. The above electrode is manufactured in the same manner as the electrode described above, except that the ion-selective membrane agent is applied to the outer wall of the tube so as to fill the pores as well. In addition, in the case of this electrode, sufficient ion sensitivity can be obtained at the same time as drying the ion selective membrane.

The electrode of the present invention is not particularly limited to the electrode having the above-mentioned configuration. For example, in the electrode shown in FIG. Furthermore, in the electrode shown in FIG. 5, the test liquid flow tube itself may be made of the same material as the ion selective membrane. Furthermore, it is possible to cover the ion-selective membrane with an outer box such as a housing, or to provide multiple electrode parts that can separately detect ions such as Na ⁺ , K ⁺ , and Cl ^- in one electrode, thereby increasing the number of items. is also possible. Note that a reference electrode is used in the measurement, and a conventionally known electrode is used as the reference electrode.

[Effects of the Invention] The ion-selective electrode of the present invention can use a tube that has been conventionally used as a flow path for a test liquid, and has a reference electrode and an ion-selective membrane on the outer wall of the tube. Since it can be obtained by simply forming, manufacturing is extremely simple and easy. In addition, since it is possible to design a tube with a small capacity in advance according to the amount of test liquid, it is extremely easy to reduce the amount of test liquid. It costs about 1/50th of that. Furthermore, by using the electrode of the present invention, it is possible to design the electrode according to the inner diameter of the pipe for inflowing and discharging the sample liquid due to its structure. It is easy to integrate, reduces the labor and time required for measurement, and as a result, the cost of measurement becomes low. Therefore, its industrial value is extremely large.

[Embodiments of the invention]

First, an Ag wire with a diameter of 1 mm was wrapped once around the outer wall of a soft vinyl chloride tube with an outer diameter of 2.4 mm, an inner diameter of 0.8 mm, and a length of 20 mm.

On the other hand, an ion-selective membrane agent was prepared according to the following procedure. First, 20 mg of valinomycin, 1.7 g of dioctyl adipate, 1 potassium tetraphenylborate.
mg, polyvinyl chloride 1.3g in tetrahydrofuran
A potassium ion selective membrane agent was prepared by dissolving in 10 ml.

Next, this membrane agent was applied in several portions to cover the outer wall of the flexible vinyl chloride tube and the Ag wire, and the solvent in the membrane agent, tetrahydrofuran, was evaporated and dried to form potassium as shown in Figure 5. An ion selective electrode was obtained.

The sensitivity of the obtained electrode to ions is
When measured using a KCl10 ^-5 to ^{10 -1} M solution,
The results shown in FIG. 7 were obtained. As is clear from the figure, there is almost no sensitivity to ions 10 hours after production, but as time passes, the sensitivity gradually increases until it reaches 58 mV/decade after 100 hours, almost matching the theoretical value (20°C). It became.

Next, the above electrode and a known reference electrode, which had been manufactured for 100 hours, were mounted on the sample line of a commercially available analyzer to measure the potassium ion concentration in the serum. Continuous measurements were performed on 5000 samples, but
It displayed a stable potassium ion concentration with no inferiority to conventional ion-selective electrodes.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of a conventional ion-selective electrode that requires an internal electrolyte, Figure 2 is a vertical cross-sectional view of a conventional coated wire type ion-selective electrode that does not require an internal electrolyte, Figures 3 and 4. The figures show how to attach and use ion-selective electrodes, the former being a batch type and the latter a flow cell type. Figures 5 and 6 are from this book. FIG. 7 is a vertical cross-sectional view of the ion-selective electrode according to the invention. When a material having an affinity for the ion-selective membrane agent is used in the test liquid flow tube shown in FIG. 5, the inner wall of the tube exhibits ion selectivity. FIG. 3 is a diagram showing the change in sensitivity over time until it becomes as shown in FIG. 1... Internal electrolyte, 2, 22, 53, 63...
Ion selective membrane, 3, 23, 52, 62...Reference electrode, 4, 24... Electrode barrel, 31, 41... Ion selective electrode, 32, 42... External reference electrode, 3
3,43...Electrometer, 34...Test liquid receptor, 44...Flow cell, 35,45...
Test liquid, 51, 61... Test liquid distribution pipe, 64...
Hole.

Claims (1)

[Claims] 1. A test liquid flow tube containing an ion-selective substance;
An ion-selective electrode comprising: a reference electrode attached to the outer wall of the tube; and an ion-selective membrane covering the outer wall of the sample liquid flow tube and the reference electrode. 2. The ion-selective electrode according to claim 1, wherein the test liquid flow tube is made of the same material as the ion-selective membrane. 3. The ion-selective electrode according to claim 1, wherein the test liquid flow tube has one or more holes, and the holes are filled with the same material as the ion-selective membrane.