JPH04291142A - Ion sensor - Google Patents

Abstract

PURPOSE:To enable a title item to be superb in storage stability regardless of the use of an internal liquid it is, to achieve a highly accurate measurement using the internal liquid on use, to enable it to be useful for applications where it is desirable to be thrown away, and to enable it to be miniaturized easily so that it can be effectively used for measuring ion activity of a small amount of measurement liquid. CONSTITUTION:An ion selection electrode is provided with a diaphragm for separating an ion sensitive film 2 and an inner electrode from an internal liquid 3. The diaphragm loses its function by an external operation. In a reference electrode, this ion sensitive film 2 may be used for the liquid channel part 2. An ion sensor can be constituted by using these ion selection electrode and the reference electrode. When it is not used (in storage), the internal liquid 3 is isolated from the ion sensitive film 2 and an internal pole by the isolation film 4. On the other hand, when it is used, it is allowed to contact an internal pole 6 by brecking or eliminating the isolation film by external operation.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to medical measurement (clinical examination),
This invention relates to an ion sensor that is used for water quality testing, process control in the food and chemical industries, and is especially suitable for disposable applications.

0002

2. Description of the Related Art An ion selective electrode and a reference electrode constituting an ion sensor have an internal liquid structure in which an electrolyte solution is sealed inside. Although this internal liquid structure has excellent accuracy, it requires maintenance and management and is difficult to downsize. In order to improve this point, the following reports have been made on attempts to solidify the internal liquid by gelation or the like, or to avoid using the internal liquid. Japanese Patent Publication No. 63-7
5551, 63-26566, 62-218850
, 62-47546, etc.

0003

[Problems with the prior art] However, a method in which the internal liquid is gelled using a gelling agent or a water-absorbing resin (Japanese Patent Laid-Open No. 63-2656
6, 62-218850, 62-47546) are
It is difficult to completely maintain the internal liquid properties, and measurement accuracy deteriorates during long-term storage. On the other hand, completely solid electrodes (Japanese Patent Application Laid-Open No. 63-75551) have better performance than conventional electrodes using internal liquids in terms of potential accuracy and output potential stability (reproducibility, individual differences, etc.). Inferior.

One of the applications of ion sensors is the analysis of electrolyte components in blood and urine. In this case, disposable use of the sensor is desirable for hygiene reasons, and high accuracy and storage stability are required. However, in the prior art, a satisfactory sensor has not been obtained.

[0005]

[Means for Solving the Problems] The ion-selective electrode of the present invention is provided with a diaphragm that isolates the internal liquid from the ion-sensitive membrane and the internal electrode, the isolation effect of which can be eliminated by external manipulation. It is characterized by As for the reference electrode, the ion-sensitive membrane may be replaced by a liquid junction. Furthermore, an ion sensor can be constructed by using such an ion selection electrode and a reference electrode.

[0006]

[Operation] When not in use, the ion-sensitive membrane (liquid junction in the case of a reference electrode) and internal electrode are separated from the internal liquid by a diaphragm, and by storing them in this state, changes in the sensitive membrane and internal electrode can be achieved. suppress. In other words, if the ion-sensitive membrane and the internal solution are in contact with each other even when not in use, as in the past, the components of the sensitive membrane may be eluted into the internal solution, or ions in the sensitive membrane and ions in the internal solution may exchange ions. This changes the composition of the sensitive membrane, causing fluctuations in ion sensitivity and thus in the output signal. In particular, in the case of an ion-selective electrode in which the ion-sensitive membrane is made of a solid electrolyte, the sensitive membrane (solid electrolyte) deteriorates significantly. Further, when the internal electrode and the internal liquid are in contact with each other, for example, in the case of an Ag/AgCl electrode, which is a normal internal electrode, Ag is eluted into the internal liquid, which also causes fluctuations in the output signal. However, in the present invention, such changes in the ion-sensitive membrane and internal electrode do not occur even during long-term storage.
The accuracy can be maintained at a high level.

When in use, this diaphragm is destroyed or removed by an external operation to eliminate its isolation effect, thereby creating a gap between the ion-sensitive membrane and the internal electrode (in the case of a reference electrode, between the liquid junction and the internal electrode). The internal liquid is allowed to flow into the Then, the measurement sample liquid is dropped onto the ion-sensitive membrane of the ion-selective electrode and the liquid junction of the reference electrode to perform the measurement.

[0008]

[Example] As shown in Figure 1, a flexible tube (1
) (silicone rubber, etc.), a glass ampoule (4) filled with Nasicon ceramic as the ion-sensitive membrane (2) and a saturated AgCl-1M-KCl solution as the internal liquid (3) and the liquid. After inserting a penetrating material (5) such as cotton-like pulp into the tube (1), a silver/silver chloride electrode (6) is inserted and sealed to form a sodium ion electrode. The silver/silver chloride electrode (6) was formed by applying an electric current to the surface of an Ag disk in contact with hydrochloric acid to precipitate AgCl. On the other hand, an electrode in which porous alumina ceramic was fitted as a liquid junction (2') instead of Nasicon ceramics was produced in the same manner and used as a reference electrode. These two electrodes are arranged to form a pair of ion sensors. The external terminal portion (7) of the silver/silver chloride electrode (6) was connected to an electrometer (not shown), and the potential difference between the two electrodes was measured as follows. First, bend the part of the tube (1) into which the glass ampoule (4) is inserted, break the glass ampoule (4) inside, and then
) by ion-sensitive membrane (2) and silver/silver chloride electrode (6)
Let the internal liquid seep between the

Next, the ion sensing part (2) and the liquid junction part (2'
), and the potential was measured by dropping the measurement liquid so as to simultaneously cover both. The responses obtained for NaCl solutions of various concentrations were
It followed Nernst's equation (Figure 3). The response time (time until the potential stabilizes) was also short, about 30 to 60 seconds after dropping. Furthermore, the output potential was investigated using the 10 sensors of the above-mentioned example in a 100 mM NaCl solution. As a comparative example electrode, a combination of an all-solid-state sodium ion selective electrode (ion-sensitive membrane is Nasicon ceramic, internal electrode is carbon resin) and a commercially available reference electrode was used, and both electrodes were immersed in the sample solution. By doing so, the output potentials of the 10 comparative example sensors were also investigated. As a result, for the sensor of this example, the variation in output potential between individual sensors (coefficient of variation CV) was within 0.3%, which is much better than the variation between the comparative example sensors (approximately 6%). (Table 1).

[Table 1] Another structure is to use a hard tube (1) instead of a flexible tube, and use a pin (8) as shown in Figure 3.
Similar results were obtained when the glass ampoule (4) was broken by inserting the ampoule.

[0010] The diaphragm can be made of various materials such as glass, plastic, and ceramic, as long as it does not dissolve or react with the internal liquid and does not impede measurement accuracy even when broken. The diaphragm may be not only an ampoule-shaped membrane that surrounds the internal liquid, but also a flat membrane that simply partitions the internal liquid, the ion-sensitive membrane, and the internal liquid so that they do not come into contact with each other. In the case of this flat plate-shaped diaphragm, when using the electrode, the diaphragm is pulled out by an external operation or removed by changing its direction, thereby causing the internal liquid to flow toward the sensitive membrane and the internal electrode. can be brought into contact with. However, ampoule-shaped envelope membranes are preferable from the viewpoint of storage stability and are suitable for mass production because electrode manufacturing is easier and the internal liquid is better sealed.

[0011] The liquid penetrating material does not necessarily need to be added. However, the presence of the liquid penetrating material allows the internal liquid to permeate evenly and homogeneously into the container, and to bring it into contact with the ion-sensitive membrane and the internal electrode. The ion-sensitive membrane may be made of beta alumina, ion-conductive glass, or the like. The liquid junction is not limited to porous ceramics, and may be any material that functions to connect the internal liquid and the measurement liquid and is particularly insoluble in the liquid, such as a plastic film having pinholes. Further, when the internal liquid is used as an ion sensor, the ion selection electrode and the reference electrode may be embedded and integrated into one insulating support. When measuring the ionic activity of a small amount of measurement liquid such as blood, when the measurement is carried out by dropping the liquid rather than by osmosis, the usage method (2) of the above embodiment is used.
(using two electrodes side by side) is equally effective. The ion selective electrode, reference electrode, and ion sensor of the present invention are widely applicable to measuring the activity of various ions in addition to Na ions.

0012

[Effects of the Invention] Although the internal liquid is used as is, the condition of each electrode component can be maintained as it was at the beginning, so long-term storage is possible without maintenance. In other words, with conventional electrodes or sensors that use internal liquids (including gelled ones), the internal liquid usually changes over time after six months to a year, reducing measurement accuracy. According to the electrode or sensor of the present invention, storage stability is maintained semi-permanently, and the degree of composition can be measured in the same manner as in the initial state during subsequent use. However,
Once used, problems similar to those of the prior art arise. Therefore, it is extremely effective for applications that require high accuracy and storage stability but are preferably disposable, such as medical measurements for analyzing blood, urine, etc.

[0013] Furthermore, it is easy to integrate the ion selection electrode and the reference electrode into a compact ion sensor. In particular, due to its high storage stability over a long period of time, there is no need for storage or maintenance at all, and it can be extremely miniaturized while maintaining a high level of measurement accuracy. Therefore, it is effective when measuring the ion activity of a trace amount of the measurement liquid.

[Brief explanation of the drawing]

[Figure 1] Cross-sectional view showing the ion selection electrode or reference electrode of Example 1

[Figure 2] Cross-sectional view showing the ion selection electrode or reference electrode of Example 2

FIG. 3 is a graph showing potential changes based on Na ion concentration in a measurement test using the ion sensor consisting of the ion selection electrode and reference electrode of Example 1.

[Explanation of symbols]

2 Nasicon ceramic (ion sensitive membrane) 2' Porous alumina ceramic (liquid junction) 3 AgCl-KCl
Solution (internal solution) 4 Glass ampoule (diaphragm) 6 Silver/silver chloride electrode (internal electrode)

Claims (5)

[Claims] 1. An ion-selective electrode comprising a diaphragm that isolates an internal liquid from an ion-sensitive membrane and an internal electrode, the isolation effect of which can be eliminated by external manipulation. 2. The ion selective electrode according to claim 1, wherein the ion sensitive membrane is a solid electrolyte. 3. A reference electrode comprising a diaphragm that isolates an internal liquid from a liquid junction and an internal electrode, the isolation effect of which can be eliminated by external manipulation. 4. An ion sensor comprising at least one of the ion selection electrode according to claim 1 and the reference electrode according to claim 3. 5. The ion sensor according to claim 4, which is used for disposable purposes.