JPH0772081A - Measuring apparatus for co2 concentration - Google Patents

Abstract

PURPOSE:To achieve the miniaturization and the detection with high sensitivity by holding a pH-sensitive pigment having an ion pair at a phase-transfer catalyst on the surface of a slab optical waveguide. CONSTITUTION:A polymer film including a pH-sensitive pigment (methacresol purple) having an ion pair formed at a phase-transfer catalyst is held on the surface of a slab optical waveguide manufactured by processing a soft glass slide by a thermal ion-exchange method, thereby, a CO2 sensor 1 is formed. Laser light from a light source 3 is guided into the sensor 1 via a polarizing plate 4 and a prism 5. On the other hand, a sample and air are sent to the sensor 1 from a CO2 injector 9 and an air injector 10. CO2 in the sample interacts with the responding methacresol purple, and then is projected out from a prism 6. At this time, a reducing amount of absorbance is changed by a concentration of CO2, which is detected by a photodiode 7. Accordingly, the concentration of CO2 is detected with high sensitivity through a linear response.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CO ₂ concentration measuring device, and more particularly to a device for measuring CO ₂ concentration using a slab optical waveguide.

[0002]

2. Description of the Related Art CO ₂ concentration measuring devices are used in places and devices for measuring and controlling carbon dioxide concentration, such as facility horticulture, disaster prevention, industrial use, and measurement of carbon dioxide concentration in carbonated beverages. Conventionally, as a CO ₂ concentration measuring device used for these purposes, a non-dispersive infrared absorption analyzer and a diaphragm type glass electrode analyzer have been known. The former utilizes the phenomenon that carbon dioxide molecules absorb infrared rays of a specific wavelength in the infrared region, and the latter utilizes the pH change that occurs when carbon dioxide permeates the diaphragm and dissolves in the internal liquid. Is.

[0003]

In recent years, there has been a growing need for CO ₂ sensors mainly in the air conditioning and environment fields.
In particular, there is a demand for a small-sized and low-cost CO ₂ sensor which has high selectivity and can perform high-sensitivity measurement in a short time. However, the conventional non-dispersive infrared absorption analyzer is expensive and easily affected by water vapor and dust, and requires a pretreatment device such as a filter or a dehumidifier, and the sample gas is sucked into the sample chamber in the device. Therefore, it is difficult to incorporate the device into other devices because the device is large-scaled. Further, there is a problem that the sensitivity is low to use as an atmosphere measuring instrument and it takes time to stabilize the apparatus.

Further, the diaphragm type glass electrode analyzer has problems that it takes a long time for measurement, its sensitivity is low and it is difficult to measure the atmosphere. An object of the present invention is to provide a small-sized and highly sensitive CO ₂ sensor that overcomes the above-mentioned drawbacks of the conventional device.

[0005]

The present inventors have succeeded in developing a CO ₂ sensor satisfying the above requirements by applying a slab optical waveguide. The CO ₂ sensor of the present invention has a slab optical waveguide carrying a pH-sensitive dye having a phase-transfer catalyst forming an ion pair on the surface thereof.
The pH-sensitive dye having an ion pair formed in the phase transfer catalyst can be supported by being contained in the polymer film.

As the pH-sensitive dye, for example, metacresol purple can be used, and as the phase transfer catalyst, a quaternary ammonium salt can be used. The slab optical waveguide can be, for example, a potassium ion slab optical waveguide produced by treating a slide glass by a thermal ion exchange method. The sensitivity of the sensor can be adjusted by the concentration of the pH-sensitive dye contained in the polymer film, and the responsiveness of the sensor can be improved by reducing the film thickness of the polymer film.

Since the CO ₂ sensor according to the present invention is small and has high sensitivity, it can be used for air conditioning equipment in indoor facilities, fermentation equipment, TOC, etc.
It can be used by incorporating it into various devices such as a meter. Further, it can be widely used in various facilities for controlling and measuring the carbon dioxide concentration in carbonated drinks such as for measuring the carbon dioxide concentration and for disaster prevention. Further, since the CO ₂ sensor according to the present invention utilizes the evanescent wave generated by the slab optical waveguide, superimposing an opaque film on the polymer film on the optical waveguide does not affect the measurement. Therefore, it is possible to superimpose the carbon dioxide gas permeable film on the polymer film. This protects the polymer film and enables selective detection of carbon dioxide gas.
It is possible to selectively measure carbon dioxide gas in the presence of NOx and to measure carbon dioxide concentration in water as well as in humid places. Also, the influence of dust can be avoided.

[0008]

[Operation] In the slab optical waveguide, by forming a thin film on the surface of a dielectric substrate such as glass that has a slightly higher refractive index than the substrate and the film thickness is on the order of the wavelength of light, It confines and guides light. The light is totally reflected on the surface of the waveguide, but at this time, it travels while bleeding out from the surface to about one tenth of the wavelength. This leaking light,
That is, the CO ₂ concentration can be measured by spectroscopically detecting the change of meta-cresol purple contained in the polymer film using the evanescent wave. According to this method, an AT using infrared rays based on a similar principle
Compared with the R method (total reflection absorption method), the effective optical path length can be increased by 2 to 3 digits, and highly sensitive measurement can be performed.

[0009]

EXAMPLES Examples of the present invention will be described below. [Example 1] A method for manufacturing a CO ₂ sensor according to the present invention will be described. First, a soft glass slide is doped with K ⁺ by a thermal ion exchange method to produce a slab optical waveguide. That is, it is about 2 x 7 cm in length and width, and about 2 m in thickness.
A glass slide made of soft glass of m is dipped in molten potassium nitrate (99.9%) and placed in an electric furnace heated to 400 ° C. as it is. After leaving it for 30 minutes, remove the slide glass soaked in the potassium nitrate solution from the electric furnace and set it to 10
After air-drying at room temperature for about a minute, it is washed with deionized water. In this way, the Na ⁺ ions in the slide glass are K ⁺
A layer having a high refractive index of K ^{+ and} having a thickness of about 1 to 5 μm, preferably about 1 is substituted in the vicinity of the surface of the slide glass by substituting with ions.
˜2 μm formed.

Next, on the surface of the slide glass slab optical waveguide thus prepared, a polymer film containing a pH-responsive dye having an ion pair formed on a phase transfer catalyst is carried as follows, Create a CO ₂ sensor. Here, an example in which meta-cresol purple is used as the pH-responsive dye will be described. That is, 1m of the following solution
l, 1 ml of the solution, 10 g of the solution and 1 ml of tributyl phosphate were mixed, a small amount (2 to 3 drops) of this mixed solution was placed on the optical waveguide, and it was sandwiched with another slide glass to obtain a uniform solution. After forming a film, it was left at room temperature for 2-3 hours to evaporate the solvent. By changing the sandwiching strength with the slide glass, films with various thicknesses of about 1 to 50 μm were prepared. The film thickness was measured with a micrometer.

Solution: 0.5 M trioctylmethylammonium hydroxide methanol solution. A filtrate obtained by adding wet silver oxide to 10 ml of a 0.5 M trioctylmethylammonium chloride (capricoat) methanol solution, anion-exchanged, and filtered.

Solution: Metacresol purple solution. A solution prepared by dissolving 0.012 g of meta-cresol purple (manufactured by Wako Pure Chemical Industries) in 1 ml of the solution and further adding 2.5 ml of methanol. Solution: Ethylcellulose solution 1 in a mixed solution of 20 ml of ethanol and 80 ml of toluene
A solution of 0 g of ethyl cellulose.

The phase transfer catalyst is used as a catalyst for transferring ions or the like to an organic layer such as a polymer or a plasticizer. In the case of the present embodiment, when CO ₂ is allowed to act on the deprotonated meta-cresol purple D ⁻ and the trioctylmethylammonium ion Q ⁺ which is the phase transfer catalyst forming an ion pair, as shown in the following formula. To
CO ₂ forms an ion pair with trioctylmethylammonium ion Q ⁺ as HCO ₃ ⁻ . At that time, the deprotonated meta-cresol purple D ⁻ is protonated and the color changes from blue to yellow. _{^{[Q + D - · xH 2}} O] + CO 2 ← → [Q + HCO 3 - · (x
-1) H ₂ O · HD] The quaternary ammonium salt is an excellent phase transfer catalyst for exchanging anions. Zephyramine, which is the same quaternary ammonium salt, can also be used as a phase transfer catalyst.

Example 2 C produced as described above
An embodiment of a CO ₂ measuring device according to the present invention incorporating an O ₂ sensor is shown in FIG. In this embodiment, the CO using the slab optical waveguide formed on the slide glass is used.
_{2 On the} sensor 1, FEP (fluoroethylene propylene)
A PTFE (polytetrafluoroethylene) cover was pressure-bonded with a pinch cock or a set screw through a spacer made of, to prepare a PTFE flow cell 2 having an optical path length of 18 mm. The light source 3 has an oscillation wavelength of 632.
An 8 nm He-Ne laser was used. The laser light is polarized by the polarizing plate 4, introduced into the CO ₂ sensor 1 using the slab optical waveguide by the prism 5, interacts with meta-cresol purple in the sample in response to CO ₂ , and then exits from the prism 6. Then photodiode 7
Detected by. 8 is a galvanometer.

In this embodiment, the thickness of the polymer film is 5 μm. After assembling the device as shown in FIG. 1, photometry is performed without flowing the sample, and in order to ensure the uniformity of the optical waveguide and the polymer film, a sensor having a base current value of 100 nA or more for the photodiode 7 is selected. use. Meta-cresol purple in the polymer film exists as an anion and exhibits a blue color, but becomes yellow when CO ₂ is present as described above. Therefore, the light of 632.8 nm is easily transmitted through the waveguide, and the absorbance is reduced.

CO ₂ was measured by the above-mentioned apparatus.
The sample used was a CO ₂ standard gas (manufactured by GL Sciences) diluted with nitrogen gas to various concentrations.
_{2 When the} sample and the air were alternately sent from the injector 9 and the air injector 10, a change in absorbance as shown in FIG. 2 was observed. Further, the amount of decrease in absorbance at this time varies depending on the CO ₂ concentration as shown in FIG. 3, and it can be seen that the response is linear and the sensitivity is good in the CO ₂ concentration range of 0 to 2%.

Next, the concentration of meta-cresol purple was set to 10
When a sensor was prepared using the doubled polymer film and the same measurement was performed, the results shown in FIG. 4 were obtained. In the figure, the white circles show the response of the sensor in which the polymer film was prepared using the solution, and the black circles show the response of the sensor when the metacresol purple added to the solution was 0.12 g. FIG. 4 shows that the absorbance response is proportional to the concentration of meta-cresol purple, and it is possible to adjust the sensitivity of the sensor by changing the concentration of meta-cresol purple.

Further, according to the above method, two kinds of polymer films having a film thickness of 2 μm and a film thickness of 45 μm were prepared, and the change of the reaction time until the change of the absorbance reached 63.2% of the peak was examined. The result is shown in FIG. The response time of the sensor with a film thickness of 2 μm is 1
It was 1/0 or less. In the present invention, since the evanescent wave is used, the film thickness of the polymer film is theoretically 100 n.
About m is sufficient, and the actual thickness of the film did not affect the sensitivity. Therefore, if the polymer film formed on the slab optical waveguide is thinned, a sensor with good responsiveness can be manufactured.

Further, when a CO ₂ sensor was prepared in the same manner by using bromothymol blue and bromothymosol green in addition to the meta-cresol purple adopted in the present invention as the pH responsive dye, when CO ₂ was injected, the absorbance was reversed. It could not be measured because it rose or there was no response. In this embodiment, the slab optical waveguide is formed on the slide glass, and the slab optical waveguide and the light beam are coupled by the prism. However, the glass substrate forming the slab optical waveguide does not necessarily have to be the slide glass. In addition to the prism, various means can be considered for the optical coupling portion of the slab optical waveguide and the light beam, that is, the input / output portion. An example thereof is shown in FIG.

FIG. 6A shows an example in which the optical fiber 12 is directly connected to the end face of the slab optical waveguide 11. This connection is made with an adhesive. When an optical fiber is used, there is an advantage that the positional relationship between the light source and the photodetector and the CO ₂ sensor can be freely set. FIG. 6B shows an example in which the slab optical waveguide and the prism are integrated. That is, this is an example in which the slab optical waveguide 11 is formed on one surface of a relatively thick glass substrate 14 and both ends of the glass are obliquely cut to form a light incident / emission portion. FIG. 6 (c) shows that the surface of the slab optical waveguide 11 is subjected to holographic interferometry (Hiroshi Nishihara, “Optical Integrated Circuits”, Ohmsha, Ltd., pages 215 to 220, issued June 20, 1987). Grating 1
6 is formed and used as a light incident / emission part. By forming the grating 16 on the surface of the glass substrate by the above method and further laminating an optical waveguide layer, the structure shown in FIG.
It is also possible to form it at the interface between the glass substrate and the slab optical waveguide as in (d). In this case, light rays are made incident on the glass substrate from the surface opposite to the surface on which the slab optical waveguide 11 is formed.

Further, the sensor of the present invention can basically measure CO ₂ without using a flow cell. For example, as shown in FIG. 6 (a), the CO ₂ sensor according to the present invention connected by an optical fiber is simply placed in a carbon dioxide gas atmosphere to cause a pH response in the polymer film, and Carbon dioxide can be monitored. Furthermore, by using the CO ₂ sensor according to the present invention, it is possible to construct an integrated sensor that realizes from the acquisition of chemical information to the information processing such as spectroscopy on one chip.

[0022]

The CO of the present invention utilizing a slab optical waveguide
_{The 2} sensor is very compact and can be manufactured at low cost, so it is suitable to be used by incorporating it into other devices. Further, the response is fast and the sensitivity is high, and it is possible to measure the CO ₂ concentration in the atmosphere without the need to suck or inject the sample gas. Furthermore, by providing a CO ₂ permeable film on the sensor surface, it becomes possible to directly measure the CO ₂ concentration in the liquid.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a CO ₂ concentration measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a response of a slab optical waveguide sensor according to the present invention to CO ₂ .

FIG. 3 is a graph showing the relationship between CO ₂ concentration and absorbance decrease amount.

FIG. 4 is a diagram showing a relationship between a dye concentration in a polymer film and an absorbance response.

FIG. 5 is a diagram showing a relationship between a film thickness of a polymer film and a response time.

FIG. 6 is a diagram showing an example of an optical coupling portion of a slab optical waveguide.

[Explanation of symbols]

1 Slide glass on which a slab optical waveguide is formed 2 Flow cell 3 Laser light source 4 Polarizing plate 5,6 Prism 7 Photodiode 8 Galvanometer 9 CO ₂ injector 10 Air injector 11 Slab optical waveguide 12 Optical fiber 14 Glass substrate 16 Grating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hirofumi Akano 2-46-28 Ariwaki-cho, Handa-shi, Aichi (72) Inventor Yoshiya Kawamura 132 Furuwata, Kochino-cho, Konan-shi, Aichi

Claims (8)

[Claims] 1. A CO ₂ sensor for measuring CO ₂ using a slab optical waveguide. _2. A CO ₂ sensor, wherein a pH-sensitive dye having an ion pair formed on a phase transfer catalyst is carried on the surface of a slab optical waveguide. 3. A CO ₂ sensor characterized in that metacresol purple having an ion pair formed on a phase transfer catalyst is carried on the surface of a slab optical waveguide. 4. The CO ₂ sensor according to claim 3, wherein the phase transfer catalyst is a quaternary ammonium salt. 5. The CO ₂ sensor according to claim 1, wherein the slab optical waveguide is a potassium ion slab optical waveguide. 6. A light source, a CO ₂ sensor according to claim 1, and a photodetector, wherein the light beam from the light source is incident on the CO ₂ sensor, and the CO ₂ sensor is provided. A CO ₂ concentration measuring device, wherein the light intensity of the light beam emitted from the device is detected by the photodetector. 7. The light source, the CO ₂ sensor, and the C
The CO ₂ concentration measuring device according to claim 6, wherein an O ₂ sensor and the photodetector are connected by an optical fiber. 8. The CO ₂ sensor has a light incident portion grating and a light emitting portion grating, and a light beam from the light source is passed through the light incident portion grating to the CO ₂ sensor.
7. The CO ₂ concentration measuring device according to claim 6, wherein the light beam from the CO ₂ sensor which is made incident on _two sensors and emitted from the light emitting section grating is detected by the photodetector.