JPH09210947A - How to store chemical sensors - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To store a chemical sensor having an electrolytic solution, for stable storage for a long period of time regardless of changes in the external atmosphere. An aqueous solution in which a water-soluble substance is dissolved, or a gel-like substance or hydrophilic fiber containing the aqueous solution is enclosed in a storage container together with a chemical sensor.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for storing a chemical sensor. In recent years, a small chemical sensor applying a semiconductor fine processing technology has been developed and used in various fields such as environmental measurement, fermentation industry, and clinical medicine. For example, the oxygen sensor measures the dissolved oxygen concentration in water for the purpose of water quality conservation,
Alternatively, it is used for measuring the oxygen concentration in the fermentation tank for the purpose of improving alcohol fermentation efficiency. If the chemical sensor is large and expensive, it is common to install it in a certain environment, such as a fully air-conditioned laboratory, and measure the sample brought in. If it is small and inexpensive, it can be carried to the place where the measurement is needed and used on the spot, and after use, it can be stored as it is on the spot, and taken out and used repeatedly when necessary. In such cases, it is required that the chemical sensor can be stored during repeated use without degrading the sensor performance.

[0002]

2. Description of the Related Art FIGS. 2 (a) and 2 (b) show the structure of an oxygen sensor manufactured by utilizing a semiconductor fine processing technique (Japanese Patent Laid-Open No. 63-238548). In the oxygen sensor shown in FIG. 2 (a), a cathode electrode 12 and an anode electrode 13 made of Ag are formed via a silicon oxide film 11 on a silicon substrate 10 cut into a strip shape having a width of 2 mm and a length of 15 mm. ing. And
An electrolyte solution 14 is injected so as to connect the cathode electrode 12 and the anode electrode 13, and these are covered with an oxygen permeable film 15, and further, for connecting the cathode electrode 12 and the anode electrode 13 to an external measuring device. The pad 17 is formed via the lead wire 16. An aqueous solution of sodium chloride, an aqueous solution of potassium hydroxide, or the like is used as the electrolyte solution 14, and the amount is 1
It is very small, about μl.

The oxygen sensor shown in FIG. 2 (b) is manufactured by laminating a glass substrate 18 and a silicon substrate 19 provided with a recess by anisotropic etching by anodic bonding. 20 is enclosed, and the oxygen permeable film 21 is covered thereover. Further, similarly to the one shown in FIG. 2A, a pad 22 for connecting a cathode electrode and an anode electrode (not shown) to an external measuring device is formed.

In the oxygen sensor described above, the moisture in the electrolytic solution evaporates through the oxygen permeable membrane when exposed to an atmosphere of extremely low humidity, and conversely when exposed to an atmosphere of high humidity. Since the water content invades through the oxygen permeable membrane, the electrolytic solution swells, which causes fluctuations in the sensor characteristics. In particular, when the swelling of the electrolytic solution progresses, the oxygen permeable membrane covering the electrolytic solution may rupture. Therefore, the oxygen sensor is sealed in the storage container and shielded from the external atmosphere at the time of shipment, but after being taken out of the storage container for use, the oxygen sensor is directly exposed to the external atmosphere and is affected thereby. Generally, as long as the humidity around the oxygen sensor does not change drastically, the characteristic variation of the oxygen sensor due to the external atmosphere is small and can be neglected. I had saved it.

[0005]

However, in the above-mentioned method, since the storage container is unsealed, the outside air easily enters the inside of the container and the oxygen sensor is affected by the outside atmosphere. When the chemical sensor having the electrolytic solution is disposable only once, or when it is used within a short period of about several days, no remarkable characteristic change occurs. However, the amount of electrolyte used in recent miniaturized chemical sensors, such as the oxygen sensor described above, is extremely small, about 1 μl. Furthermore, generally, the smaller the volume, the larger the surface area to volume ratio. When it is used repeatedly over a period of several months or more in an environment where the humidity fluctuates greatly, the sensor characteristics may fluctuate or become unusable during that period because it is more easily affected by the atmosphere. However, there is a problem in that the reliability is lowered due to the occurrence of the problem.

Therefore, an object of the present invention is to stably store a chemical sensor having an electrolytic solution for a long period of time regardless of changes in the external atmosphere.

[0007]

The solution to the above-mentioned problems is characterized in that an aqueous solution in which a water-soluble substance is dissolved, or a gel-like substance or hydrophilic fiber containing the aqueous solution is enclosed in a storage container together with a chemical sensor. Or the water-soluble substance is sodium chloride or calcium chloride, or the gel-like substance is agar or gelatin. This is achieved by the above method for storing the chemical sensor, or the method for storing the chemical sensor, wherein the hydrophilic fiber is made of cloth or paper.

In general, the humidity in the external atmosphere is low, so that the electrolytic solution evaporates when the vapor pressure inside the container into which the external atmosphere has entered becomes low, and conversely, when the vapor pressure inside the container becomes high to the saturated vapor pressure, the water vapor in the container becomes Penetrates the electrolyte and swells. Therefore, in order to suppress the fluctuation of the water content in the electrolytic solution, the vapor pressure in the container may be kept at a constant level that does not reach the saturated vapor pressure. When water is enclosed in the storage container together with the chemical sensor, the vapor pressure increases due to the evaporation of water and the decrease of water in the electrolyte can be suppressed, but the inside of the container reaches the saturated vapor pressure. And the electrolyte swells. It is difficult to accurately control the amount of water so that the saturated vapor pressure is not reached, because the external atmosphere may be affected each time the lid of the storage container is opened.

Therefore, if an aqueous solution in which a water-soluble substance such as sodium chloride is dissolved is put in a storage container, the water-soluble substance absorbs the water in the container when the vapor pressure in the container is high. Will be maintained at a constant level close to this without reaching the saturated vapor pressure.
That is, when the vapor pressure in the storage container becomes low, the water content in the aqueous solution evaporates and the vapor pressure in the storage container rises. Conversely, when the vapor pressure in the storage container becomes high, the water vapor in the storage container becomes water-soluble. Since the vapor pressure is absorbed by the substance and the vapor pressure is lowered, the humidity inside the container is kept substantially constant, and the fluctuation thereof can be suppressed, and the fluctuation of the water content in the electrolytic solution can be prevented. Therefore, both evaporation and swelling of the electrolytic solution can be suppressed, and the chemical sensor containing the electrolytic solution can be stored for a long period of time.

When an aqueous solution in which a water-soluble substance such as sodium chloride is dissolved is soaked in a gel-like substance or a hydrophilic substance, the oxygen sensor is not soaked in these substances in the storage container and these It is mechanically supported by the substance, which is convenient for stable long-term storage.

[0011]

1 (a) to 1 (f) are sectional views showing an embodiment of the present invention. In this embodiment, as shown in the figure, a substantially cylindrical storage container 1 having a diameter of about 10 mm and a height of 50 mm is used, and inside thereof, a width of 2 mm shown in FIGS. 2 (a) and 2 (b),
A case where the strip-shaped oxygen sensor 3 having a height of 15 mm is stored will be described.

FIG. 1 (a) shows a state in which about 20 μl of 0.8 M sodium chloride aqueous solution 4 is dropped inside the storage container 1 with a micropipette and the oxygen sensor 3 is placed so as not to come into contact with the sodium chloride aqueous solution 4. Is. When the electrolytic solution is completely covered with the oxygen permeable film, the amount of the sodium chloride aqueous solution 4 added may be increased and the oxygen sensor 3 may be submerged and stored in the sodium chloride aqueous solution 4. When the electrolyte inlet is open due to the structure of the oxygen sensor 3, it is supported on the bottom of the storage container 1 as shown in Fig. 1 (b) to prevent the sodium chloride aqueous solution 4 from mixing into the electrolyte. It is also possible to provide the table 5 and place the oxygen sensor 3 on it.

Further, 2% by weight of agar is dissolved in an aqueous solution of sodium chloride and heated, and 1/2 to 1/3 of the internal volume of the container is obtained.
When a certain amount is poured and left to stand, the agar hardens inside the storage container and becomes a gel. Then, the oxygen sensor 3 may be placed on the gel substance 6. The amount of agar dissolved
By setting the content to about 1% by weight, the agar can be cured in a flexible state, and the oxygen sensor 3 can be pierced into the agar for storage (FIG. 1 (c)). According to this method, the oxygen sensor 3 is stably supported without moving in the container. Further, as seen in FIG. 1 (c), by storing the oxygen sensor 3 by piercing it, the surface of the oxygen sensor 3 comes into close contact with the gel substance 6 and is shielded from the surrounding atmosphere. Therefore, when the lid 2 of the storage container is opened, the oxygen sensor 3 is not exposed to the sulfide or the like that enters the container together with the external atmosphere. It has the effect of preventing corrosion of the metal film used.

Further, if the depression is formed as shown in FIG. 1 (d) by fitting the gel material in a convex mold and curing it, the surface area of the gel material 6 in the storage container increases. The amount of water vaporized or absorbed by the aqueous sodium chloride solution also increases accordingly, and it is possible to suppress fluctuations in the vapor pressure inside the storage container in a short time when the lid of the storage container is opened and closed. Also in this case, the hardness of the gel substance can be lowered by changing the amount of agar dissolved in the sodium chloride aqueous solution, and the oxygen sensor can be pierced into the gel substance for storage. Also, as shown in Fig. 1 (e),
As shown in (f), the gel substance 6 may be placed on the side wall or lid of the storage container.

Although sodium chloride was used as the water-soluble substance in the above examples, the same effect can be obtained by using calcium chloride or the like. Although agar was used as the gel-like substance, the same effect can be obtained by using gelatin instead of agar. Further, the same effect can be obtained when a hydrophilic fiber such as cloth, paper or cotton is placed on the bottom of the container and the one impregnated with the aqueous sodium chloride solution or calcium chloride solution is used.

[0016]

As described above, according to the present invention, the characteristics of the chemical sensor can be stably maintained for a long period of time, which is useful for expanding the usable range of the chemical sensor and improving its reliability. .

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing the structure of an oxygen sensor.

[Explanation of symbols]

1 Storage Container 11 Silicon Oxide Film 2 Lid 12 Cathode Electrode 3 Oxygen Sensor 13 Anode Electrode 4 Sodium Chloride Aqueous Solution 14, 20 Electrolyte 5 Support Stand 15, 21 Oxygen Permeation Membrane 6 Gel Material 16 Lead Wires 10, 19 Silicon Substrate 17, 22 Pad 18 Glass substrate

Claims (4)

[Claims] 1. A method for storing a chemical sensor having an electrolytic solution, comprising enclosing an aqueous solution in which a water-soluble substance is dissolved, or a gel-like substance or hydrophilic fiber containing the aqueous solution together with the chemical sensor in a storage container. A method for storing a chemical sensor characterized by the above. 2. The method for storing a chemical sensor according to claim 1, wherein the water-soluble substance is sodium chloride or calcium chloride. 3. The method for storing a chemical sensor according to claim 1, wherein the gel-like substance is composed of agar or gelatin. 4. The method for storing a chemical sensor according to claim 1, wherein the hydrophilic fiber is made of cloth or paper.