JP2506761B2 - Gas detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Present Invention] An object of the present invention is to provide a highly sensitive and compact optical gas concentration sensor.

[Prior art]

As a gas concentration sensor using a chemical reaction, there are an electric method using a semiconductor and an optical method using an optical fiber, and the present invention belongs to a technique using the optical method.

One of the recent technologies in this field is the technology disclosed in Japanese Patent Laid-Open No. 61-1786622, which is a method of conducting light generated by absorption of evanescent waves leaching at the interface between a gas and a photoconductive medium into the gas. This is to utilize the change in the amount of light. However, the specific absorption wavelength of a general colorless gas is in the infrared region or the ultraviolet region, and since the absorption coefficient at that wavelength is small, high sensitivity cannot be expected. Further, the detector itself has a difficulty in reducing the price and the size.

Further, the technique of Japanese Patent Publication No. 58-48850 is a method of measuring the change in the amount of transmitted light by applying a substance around the photoconductive medium, which is in contact with gas and whose light transmission capacity changes.
According to this method, if a substance whose light absorption coefficient changes in the visible light wavelength region when contacted with a gas is selected and applied, it can be used even at a wavelength shorter than infrared, and at the time of light reflection, light absorption Since this occurs, the more light is reflected in the waveguide, the higher the detection sensitivity.

Further, the gas detection device and the liquid detection device that the applicant previously applied are formed by a plate-shaped body having a flat surface or a curved surface as a photoconductive medium instead of the optical fiber of Japanese Patent Publication No. 58-48850. , A use of a photoconductive medium in which at least one of the side surfaces of the plate is covered with a light reflecting layer.

However, the so-called sensing layers formed by coating on these photoconductive media are all dry solid layers,
The chemical reaction between the gas and the sensing layer became worse than the reaction in the solution, and there was another sense of sensitivity to changes in the gas concentration.

[Characteristics and effects of the present invention]

The present invention, by containing a non-volatile water-soluble liquid organic compound in the sensing layer, because it is present in the liquid form, sensitivity compared to the case of the conventional solid dry sensing layer,
It has succeeded in improving the response speed.

[Nonvolatile water-soluble liquid organic compound]

As the organic compound that imparts so-called sensation to the detection layer, any compound can be used as long as it can stably impart sensation to the detection layer for a long time and does not interfere with the detection reaction. A non-volatile degree is that the boiling point is 100 ° C or higher.

Polyhydric alcohols are inexpensive and easily available substances, and are preferable as the compound. Typical examples are propanetriol (glycerin), butanetriol, ethylene glycol, propylene glycol,
Butylene glycol and the like.

In addition to polyhydric alcohols, water-soluble, non-volatile esters and ethers (for example, low adducts of ethylene oxide) can be mentioned.

[Photoconductive medium]

The photoconductive medium in the present invention may be a conventional optical fiber, but a particularly preferred photoconductive medium is a plate having a flat surface or a curved surface, and at least one side surface of the plate is a light reflecting layer. It has a covered structure. Particularly preferably, as shown in the drawing, all side surfaces are covered with a light reflecting layer except that an incident light portion and a light receiving portion are provided in one portion on one side surface. By adopting such a structure, the light incident from the incident light section is repeatedly reflected by the reflection layer as shown in the drawing, and then goes out from the light receiving section. Since it can be made very long, it has the same effect as the case where an extremely long optical fiber is used as a photoconductive medium in spite of a small plate-shaped body.

As the photoconductive medium, conventionally known optical materials such as inorganic substances such as glass and quartz and organic polymers such as polymethylmethacrylate (PMMA) and polymethylpenlane can be used.

Further, the shape of the plate-like body does not necessarily have to be a rectangular parallelepiped, and various modifications can be made without departing from the gist of the present invention.

The incident light section and the light receiving section can be attached to the side surface of the plate-shaped body as shown in FIG. 1, but for example, as shown in FIGS. For example, the incident light portion and the light receiving portion can be formed via a prism, or the end portion of the plate-shaped body itself can be cut into a prism shape to form the incident light portion and the light receiving portion as shown in FIG. You can also

Also, the refractive index of the sensing layer material is 1.4 or more, and it is easy to select a photoconductive medium having a refractive index higher than this (for example, borosilicate glass, fluoride glass).

[Detection layer]

The sensing layer contains a substance that selectively reacts with a specific substance in a gas to selectively change the light transmission ability of the photoconductive medium, that is, a sensing substance and a non-volatile water-soluble liquid organic compound. The composition may be formed as a layer on at least one surface, and particularly preferably both surfaces, of the upper and lower surfaces of the plate-shaped body.

It is appropriate to use a resin binder for forming the detection layer, and as the resin binder, a water-soluble binder is preferable in order to make the presence of the non-volatile water-soluble liquid compound uniform, and starch, cellulose, collagen, etc. Natural polymers or synthetic polymers such as PVA, polyacrylamide, polyethylene glycol, polyethylene oxide are suitable.

[Light reflection layer]

The light reflecting layer can be formed by vacuum vapor deposition or silver mirror reaction of an inorganic substance such as Al, Au, and Ag. More specifically, it is preferable to mask the portions such as the incident light portion and the light receiving portion where the light reflection layer is not formed and deposit metal.

[When the specific substance in the gas is ammonia]

Japanese Patent Publication Sho 58-48850 as a substance to detect ammonia
Although any of the substances disclosed in the publication can be used,
The following (i) to (iii) are particularly preferable.

(I) Utilization of pH indicator In this case, it is preferable to use the indicator and a suitable buffer in combination. For example, a buffer solution capable of maintaining a specific pH and an indicator showing a color reaction at that pH are spin-coated in the form of an aqueous polymer solution on a plate-like body which is a photoconductive medium.

 Table 1 shows an example of a combination of a buffer solution and an indicator.

The light used is arbitrary, but when an indicator whose absorbance changes in the range of 500 to 700 nm is used, the complex refractive index of the detection layer is 50
It varies for wavelengths from 0 to 700 nm. And, with light of such a wavelength, it is possible to use an inexpensive and small light source such as an LED as the light source.

(Ii) Utilization of a group of substances that generate indophenol or indothymol as a detection substance Preferable combination example Phenol + chloramine T α-naphthol + sodium hypochlorite thymol + chloramine T thymol + sodium hypochlorite can be used. Turns blue in the presence of ammonia.

[When the specific substance in the gas is carbon gas]

A wide range of pH indicators are available. Its specific embodiment is almost the same as that of ammonia except that it is the same in terms of acid and alkali, and is omitted.

Example 1 As a photoconductive medium, a BK-7 plate (10 mm × 10 mm × 0.3 m)
m), an LED (wavelength 660 nm) was used as an incident light source, a silicon photodiode was used as a light receiving portion, and an incident light portion and a light receiving portion were set on one side surface of the medium [same configuration as in FIG. 1 (A)].

Light-receiving part, and light-receiving part by vacuum deposition on the side of the photoconductive medium,
Both wide surfaces were masked to form an Al reflective layer having a thickness of 2000Å.

Next, a coating solution containing 1 wt% of BTB, 4 wt% of polyacrylamide, 44 wt% of water, 50 wt% of ethanol, and 1 wt% of glycerin was prepared, and this was spin-coated (3000 rpm.2 seconds) to form a detection layer on the flat surface of BK-7.

This sensing layer can retain a certain amount of water by using glycerin.

Example 2 The same as Example 1 except that the coating liquid having the following composition was used.

Composition of coating liquid BTB 1 wt% Polyacrylamide 4 wt% Water 39 wt% Ethanol 50 wt% Glycerin 6 wt% Control example The same as Example 1 except that the following composition containing no glycerin was used as the coating liquid.

Composition of coating liquid BTB 1wt% Polyacrylamide 4wt% Water 45wt% Ethanol 50wt% Glycerin 0wt%

[Brief description of drawings]

FIG. 1 (A) is a top view showing an example of a photoconductive medium element used in the device of the present invention. FIG. 1 (B) is a sectional view thereof. FIG. 2 is an example showing how the incident light section and the light receiving section are attached to the photoconductive medium element used in the device of the present invention. 3 to 5 show the modified examples. FIG. 6 is a graph clarified that Examples 1 and 2 show a sensitive reaction as compared with the control example. DESCRIPTION OF SYMBOLS 1 ... Plate-shaped photoconductive medium, 2 ... Reflection layer 3 ... Detection layer, 4 ... Incident light part 5 ... Light receiving part, 6 ... Light 7 ... Evanescent wave, 8 ... Prism 9 ... … Light source, 10… Measuring device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-51-70694 (JP, A) JP-A-52-98545 (JP, A) Special table JP-A-6500631 (JP, A) International publication No. 86 / 05589 (WO, A)

Claims (5)

(57) [Claims] 1. A sensing layer containing a sensing substance that, when contacted with a specific substance in a gas, selectively reacts with it to measurably change the light transmission capacity of the photoconductive medium. Identification in gas, comprising a photoconductive medium on the outer surface, a light source arranged to transmit light into the photoconductive medium, and means for measuring the light emitted from the photoconductive medium. An optical detection device for detecting a substance, wherein the detection layer contains a non-volatile water-soluble liquid organic compound. 2. The non-volatile water-soluble liquid organic compound is at least one compound selected from the group consisting of polyhydric alcohols, non-volatile water-soluble esters and non-volatile water-soluble ethers. A gas detection device according to claim 1. 3. The photoconductive medium is formed by a plate-like body having a flat surface or a curved surface, and at least one of the side surfaces of the plate-like body is covered with a light reflecting layer. A gas detection device according to claim 1. 4. The plate-like body having a detection layer containing a detection substance which, when brought into contact with a specific substance in a gas, selectively reacts with the substance to change the light transmission ability of the photoconductive medium to a measurable amount. The gas detection device according to claim 1, wherein the gas detection device is formed on at least one of the front and back sides of the above. 5. A photoconductive medium is formed by a plate-shaped body having a flat surface or a curved surface, and an incident light section and a light-receiving section are provided on one and the same side surface of the plate-shaped body, and light is emitted on all side surfaces except this portion. 2. A reflection layer is provided, or a light reflection layer is provided on all side surfaces, and an optical coupling member is provided on a flat surface or a curved surface of the plate-like member to serve as an incident light portion and a light receiving portion. Gas detector.