JPH01253636A - Measurement of concentration of alcohols - Google Patents

Abstract

PURPOSE:To make it possible to measure the concentration of alcohol in fluid accurately in high sensitivity, by bringing metal oxide which indicates coloring phenomenon when light is projected into contact with a fluid incorporated in alcohol, and measuring the change in coloring degree. CONSTITUTION:As an alcohol sensor 2, a transparent conductive film 22 is formed on a glass substrate 21, and a metal oxide film 23 such as WO3 and MO3 in the amorphous state is formed on the film 22. A fluid to be measured 8 is filled in a transparent container 1. Light is projected to the sensor 2 from a light source 6. The film 23 is colored in correspondence with the concentration of alcohol in the fluid 8. The colored quantity is measured with a photodetector 7. Thus, the concentration of the alcohol in the fluid 8 can be obtained accurately. When the measurement is finished, a power source 4 is connected to a lead wire 25 of the sensor 2, and a specified potential is applied. Then, the transparent state is restored.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for measuring alcohol concentration, and in particular,
Metal oxides that show a coloring phenomenon when irradiated with light,
This method utilizes a novel phenomenon discovered by the present inventors, in which the degree of coloring changes depending on the concentration of alconyls in the fluid when brought into contact with a fluid containing alcohols.

[Prior Art] Conventionally, there have been the following methods for measuring alcohol concentration in a gas or liquid fluid.

One of the long-known chemical analytical methods is a method that takes advantage of the fact that when iodine is added to a solution containing alcohol and boiled, iodoform is produced. This method is not suitable for detecting trace amounts of alcohol, cannot be applied to detecting alcohol contained in the air, and has the disadvantages that the procedure is complicated and quantitative performance is not necessarily sufficient.

Therefore, in recent years, various chemical sensors, such as gas sensors or biosensors, have been developed to compensate for the above drawbacks.

A well-known example of the gas sensor is a semiconductor force sensor, in which when alcohol is adsorbed onto the surface of a metal oxide semiconductor, the structure of the space charge layer on the surface of the semiconductor changes and the resistance of the semiconductor increases. This method takes advantage of the phenomenon that .

Furthermore, as the biosensor, one is known in which an enzyme (alcohol oxitase) membrane that reacts with ethanol and consumes oxygen is attached to the tip of a diaphragm oxygen electrode (for example, a C1ark type electrode). There is. Zunawachi,
Ethanol is indirectly detected by detecting the amount of oxygen consumed by the enzyme membrane with the diaphragm oxygen electrode.

[Problems to be Solved by the Invention] However, it is difficult to say that all of these conventional methods achieve a detection sensitivity that is sufficiently low to meet the currently required detection sensitivity. It lacks selectivity because it is responsive to organic substances other than the above (for example, the biosensor does not react with the alcohol oxitase or with acetic acid, formic acid, etc. in addition to alcohols). (consumption of oxygen), it does not fully meet the demand for accurately determining the concentration of alcohol alone, has a complicated structure, and has problems in durability.

An object of the present invention is to provide a novel method for measuring alcohol concentration that can eliminate such drawbacks.

1. Means for Solving the Problems] The present invention addresses a novel phenomenon discovered by the inventor, namely:
Metal oxides that show a coloring phenomenon when irradiated with light,
This is based on the phenomenon that when the liquid is brought into contact with a fluid containing alcohol, the degree of coloring changes depending on the concentration of alcohol in the fluid.Using this new phenomenon, the coloring This device makes it possible to accurately and sensitively determine the alcohol concentration in the fluid by determining the degree of change, and has the following configurations.

(1) When metal oxide, which shows a coloring phenomenon when irradiated with light, is brought into contact with a fluid containing alcohol,
A method for measuring alcohol concentration, characterized in that the alcohol concentration in the fluid is determined by determining a change in the degree of coloring by utilizing a phenomenon in which the degree of coloring changes depending on the concentration of alcohol in the fluid. .

(2) In the alcohol concentration measuring method according to claim (1), the coloring is erased by applying a voltage to the metal oxide after determining the alcohol concentration. Alcohol concentration measurement method.

[Operation] In the configuration (1), since the degree of coloring changes depending on the alcohol concentration in the fluid, the alcohol concentration in the fluid is determined by determining the change in the degree of coloring. be able to.

In this case, the degree of coloring varies greatly even if the fluid contains a trace amount of alcohol,
Moreover, it has been confirmed that the amount of change in the degree of coloring and the alcohol concentration can be almost exactly matched.

Therefore, this method makes it possible to accurately determine the alcohol concentration in a fluid containing vl of alcohols. In this case, it has also been confirmed that detection sensitivity can be further improved by setting the metal oxide to a more negative potential.

Further, according to the configuration (2), by performing the voltage application operation after measuring -degrees and before the next measurement, the coloring in the previous measurement is erased, and the influence of the previous measurement is reflected in the next measurement. This makes it possible to perform repeated measurements.

[Example] Hereinafter, a method for measuring alcohol concentration according to an example of the present invention will be described.

(First Example) Figure 1 is a cross-sectional view showing the configuration of an apparatus for carrying out the alcohol concentration measuring method according to the first example of the present invention, and Figure 2 is a partially enlarged view of Figure 1. FIG.

In the figure, reference numeral 1 indicates a transparent container, and this transparent container 1
An alcohol sensor 2 and an electrode 3 are housed inside.
The structure is such that a voltage can be applied between the sensor 2 and the electrode 3 by a DC power source 4. Note that an ammeter 5 is connected between the power source 4 and the electrode 3 so that the current flowing due to the voltage application can be monitored.

The alcohol sensor 2 has a transparent conductive film 22 on a glass substrate 21, as shown in an enlarged cross-sectional view in FIG.
is formed, and on this transparent conductive film 22, a metal oxide wA23 in which a metal oxide such as tungsten oxide (WO3) or molybdenum oxide (MO3) is in an amorphous state is formed. Conductive film 22
One end of a copper lead wire 25 is connected to the power source 4 by a silver paste 24 or the like, and the other end of this copper lead wire 25 is connected to the power source 4.

Further, a light source 6 for causing a coloring phenomenon in the metal oxide 23 is provided at a portion outside the transparent container 1 and facing the surface of the metal oxide film 23 of the alcohol sensor 2.
A light detector 7 for measuring the amount of coloring of the metal oxide 23 is arranged at a position opposite to the light source 6 across the transparent container 1.

The transparent container 1 is filled with a fluid 8 such as a solution or gas containing alcohol to be measured (FIG. 1 shows the case filled with a solution).

In this case, the transparent conductive film 22 has electrical conductivity,
Any material may be used as long as it is transparent to visible light, such as S n O2, In20i, or ZnO.
It can be composed of Note that in some cases, this conductive film 2
2 may be omitted and the copper lead wire 25 may be directly connected to the metal oxide 23.

Further, the electrode 3 may be made of any material that is not attacked by ordinary solvents such as platinum or carphone, and its shape and size do not matter.

Further, the power source 4 is preferably a direct current power source with variable polarity of positive and negative, and for example, a dry battery or the like may be used.

Further, as the light source 6, a mercury lamp, a xenon lamp,
A tungsten lamp, a laser device, or the like is used, and as the optical detector 7, for example, a phototube, a Si solar cell, or the like can be used.

In order to carry out the method of this example in the above-mentioned apparatus,
First, the transparent container 1 is filled with a fluid 8 to be measured (for example, water containing alcohol, benzene, or air), and then the alcohol sensor 2 is irradiated with light from the light source 6.

As a result, the metal oxide film 23 becomes colored in accordance with the concentration of alcohol contained in the fluid 8. By measuring the amount of coloring with the optical detector 7, Concentration can be determined.

At this time, the power source 4 is turned off, or a voltage is applied such that only a current that cannot be detected by the ammeter 5 flows.

Next, when the measurement is completed, the alcohol sensor 2 is turned on so that the alcohol sensor 2 has a positive potential by turning on the power source 4 or by opening the applied voltage. A predetermined voltage is applied between the electrode 3 and the electrode 3.

As a result, the coloring of the metal oxide film 23 is erased and the original transparent state is restored, so that the metal oxide film 23 can be used for the next measurement.

Note that when the alcohol concentration of the fluid 8 to be measured is low and the degree of coloring of the metal oxide film 23 is low, the light irradiation time from the light source 6 is lengthened, the amount of irradiation light is increased, or The amount of coloring can be increased by changing the voltage applied from the power source 4 and setting the potential of the alcohol sensor 2 to be slightly more negative than its equilibrium potential (for example, about -0.2 V). Of course, these processing operations may be performed alone or in combination. By increasing the amount of coloring through these operations, it is possible to increase the change in the degree of coloring that changes depending on the concentration of alcohol. That is, by performing these processing operations, the detection sensitivity of alcohol can be improved. Furthermore, even after performing these processing operations, the alcohol sensor 2 can be returned to its original transparent state by setting it to a positive potential as described above, and the next measurement can be carried out. I can do it.

Note that the method of this embodiment does not necessarily require the use of a device having the above-mentioned configuration, and includes, for example, the operation of bringing the alcohol sensor 2 into contact with the fluid to be measured;
The alcohol sensor 2 is
This can also be carried out by coloring the alcohol sensor 2 and then measuring the absorbance of the alcohol sensor 2 using a visible/ultraviolet spectrophotometer or the like to determine the degree of coloring.

FIG. 3 is a graph showing the results of an experiment examining the detection sensitivity of the alcohol sensor 2 in this example. In the figure, the vertical axis is the change in absorbance, and the horizontal axis is the volume percent of ethanol in the benzene solution. The experimental conditions in this case are as follows.

W was applied to the surface of the alcohol sensor glass substrate or the surface of the glass substrate coated with SnO2 by vacuum evaporation.
A thin film (thickness: 0.1 to 1 μm) of O3 was formed (Note that when the WO5 thus formed was analyzed by X-ray diffraction, no crystalline peak was observed, and it was confirmed that it was in an amorphous state. ).

The liquid benzene to be measured contains ethanol or various volume percentages (it has been confirmed that almost the same results can be obtained when propylene carbonate is used instead of benzene).

Light source 500W ultra-high pressure mercury lamp measurement procedure The alcohol sensor is immersed in the fluid having various ethanol concentrations to be measured. 2 minutes). At this time, the absorbance of the alcohol sensor at a wavelength of 750 nm to 800 nm is measured before the light irradiation. Next, the absorbance of the alcohol sensor at a wavelength of 750 nm to 800 nm after light irradiation is measured, and then the absorbance before and after the light irradiation is compared. The above graph is a plot of the comparison results for each ethanol concentration.

In addition, neither the inventor nor the above-mentioned alcohol sensor has investigated what compounds other than ethanol cause the color change to occur, and it was found that methanol,
Inpropatool, n-propatool and n-butanol show a color change, or benzene, acetone,
No color change was observed for pure solutions of water and chloroform. In addition, the degree of color change is based on methanol>
Ethanol〉Improper Tool〉n-Propanol〉n
- butanol.

Furthermore, Figure 4 shows the results of similar measurements of the alcohol sensor described above, using dry nitrogen containing methanol as the fluid to be measured, under almost the same experimental conditions as described above. It is. In Figure 4,
The vertical axis is the absorbance change and the horizontal axis is the volume percent of methanol in dry nitrogen.

Note that even if air containing a small amount of ethanol is selected as the measurement target, the alcohol sensor 2 described above will cause a color change (750
It has been confirmed that the absorbance changes with respect to light with a wavelength of μm.

(Second Embodiment) FIG. 5 is a sectional view showing the configuration of an apparatus for carrying out the alcohol concentration measuring method according to the second embodiment of the present invention, and FIG. 6 is a partially enlarged view of FIG. 5. FIG.

This embodiment can increase the detection sensitivity of alcohol compared to the first embodiment.

In the figure, reference numeral 100 is a transparent container, the bottom of which has been removed, and which is placed on the alcohol sensor 20.0. Further, an electrode 103 is housed within the alcohol sensor 200, and a voltage can be applied between the sensor 200 and the electrode 103 by a power source 104.

Further, a light source 106 is arranged below this alcohol sensor 200, and furthermore, a light detector 107 is arranged on the right side of the alcohol sensor 200 in the figure.

As shown in a partially enlarged cross-sectional view in FIG. 6, the alcohol sensor 200 has a transparent conductive film 202 formed on a glass substrate 201, and tungsten oxide (WOs) Alternatively, a metal oxide film 203 is formed in which a metal oxide such as molybdenum oxide (M 03 ) is in an amorphous state. In this case, the transparent conductive film 202 has electrical conductivity. However, the conductive film 202 may be made of any material as long as it is transparent to visible light, such as SnO□, In20i, ZnO, etc. In some cases, the conductive film 202 may be omitted.

Further, the electrode 103 may be made of platinum, carbon, or other material that is not attacked by ordinary solvents, and its shape and size do not matter.

Furthermore, the power source 104 is preferably a direct current power source with variable polarity between positive and negative, and for example, a dry battery or the like may be used.

Further, as the light source 106, a mercury lamp, a xenon lamp, a tungsten lamp, a laser device, or the like can be used. In this case, the light source 106 may be placed above the transparent container 100.

The transparent container 100 is filled with a fluid 108 such as a solution or gas containing alcohol to be measured (FIG. 5 shows the case filled with a solution).

By the way, the glass substrate 201 and the fluid -16=108 generally have a lower refractive index than the metal oxide M2O3 and the transparent conductive film 202. The portions can function as so-called optical waveguides in which the interfaces between them and the glass substrate 201 and the fluid 108 serve as total reflection surfaces.

In this embodiment, the light R for measuring the absorbance of the part functioning as an optical waveguide is incident on the part functioning as an optical waveguide, and the emitted light r is detected by the optical detector 107, thereby forming the metal oxide film. This is to measure the change in the degree of coloring of 203. In this case, it goes without saying that the metal oxide film 203 is colored in advance by the light source 106.

The light R is preferably a laser beam or a xenon lamp made monochromatic using an interference filter or the like.
This monochromatic light is made to enter the optical waveguide portion through a lens 109 (or a prism or a diffraction grating may be used instead of the lens), as shown in FIG. .

Thereby, the change in the degree of coloring of the metal oxide film 203 can be measured with extremely high sensitivity, and therefore the concentration of alcohol in the fluid 108 can be measured with extremely high sensitivity.

Note that the sensitivity can be improved by performing measurements while keeping the metal oxide 203 at a negative potential, and the point that the metal oxide 203 can be set at a positive potential to enable the next measurement after the -th measurement is completed is as described above. This is the same as in the first embodiment.

Further, the fluid 108 to be measured is not limited to a liquid, but may be a gas. In this case, the operation of setting the metal oxide 203 at a positive potential to perform the next measurement after completing the - measurement is to add sodium sulfate or the like to the transparent container 100 after the measurement to make it ionic conductive. This can be done by applying a voltage from the power source 104 while filling the aqueous solution.

(Third Embodiment) FIG. 7 is a sectional view showing the configuration of an apparatus for carrying out the alcohol concentration measuring method according to the third embodiment of the present invention, and FIG. 8 is a partially enlarged view of FIG. 7. FIG.

In this embodiment, so to speak, the optical waveguide in the second embodiment is constructed of an optical fiber 300, the incident light R is introduced from one end of the optical fiber 300, which is the optical waveguide, and the output light r is emitted from the other end. is detected by an optical detector 307.

That is, as shown in FIG. 8, the cladding 303 portion of the optical fiber 300 is
The core 302 is made of SiO.
□It is made of glass or polymer resin.

Then, the optical fiber 300 is immersed in the fluid to be measured, and the optical fiber 300 is irradiated with light (1) that colors the metal oxide of the cladding 303 of the optical fiber 300.
By measuring the emitted light r, the cladding 30
The change in the degree of coloring of the metal oxide in No. 3 is measured to determine the concentration of alcohols in the fluid.

Note that the thickness of the metal oxide of the cladding 303 is 0.
The thickness is approximately 1 to 1 μm.

According to this embodiment, the effective area as a sensor can be large, and the number of total reflections of the light R within the fiber is large, so by appropriately selecting the length of the optical fiber 300, it is possible to This makes it possible to measure alcohols with extremely high sensitivity.

In each of the above examples, tungsten oxide (WO) and molybdenum oxide (MOs) were used as metal oxides.
), but the present invention is not limited thereto, and can also be applied to other metal oxides that exhibit a coloring phenomenon when irradiated with light,
For example, transition metal oxides such as vanadium oxide and iridium oxide, and other metal oxides may be used, and it has been confirmed that these metal oxides also have certain effects.

[Effects of the Invention] As detailed above, the present invention utilizes a novel phenomenon discovered by the present inventor, namely, the application of a metal oxide that exhibits a coloring phenomenon when irradiated with light to a fluid containing alcohol. By utilizing the phenomenon that the degree of coloring changes depending on the alcohol concentration in the fluid when the fluid comes into contact with the fluid, and determining the change in the degree of coloring, the alcohol concentration in the fluid can be determined accurately and sensitively. It made it possible to ask for it.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of an apparatus for implementing the alcohol concentration measuring method according to the first embodiment of the present invention, FIG. 2 is an enlarged sectional view of a part of FIG. 1, and FIG. and the fourth
The figure is a graph showing the results of an experiment investigating the detection sensitivity of the alcohol sensor 2 in this embodiment, and FIG. 5 shows the configuration of an apparatus for implementing the alcohol concentration measuring method according to the second embodiment of the present invention 6 is an enlarged cross-sectional view of a part of FIG. 5, FIG. 7 is a diagram showing the configuration of an apparatus for implementing the alcohol concentration measuring method according to the second embodiment, and FIG. 7 is an enlarged cross-sectional view of a part of FIG. 7. 1.100...Transparent container, 2.200,300...Alcohol sensor, 21
．． 201... Glass substrate, 22.202... Transparent conductive film, 23.203... Metal oxide film, 3.103... Electrode, 4.104... Power supply, 6.106... Light source, 7.107,307... Optical detector, 8,108
...Fluid to be measured, 300...Optical fiber 302...Core, 303...Clad being metal oxide.

Claims (2)

[Claims] (1) When a metal oxide that exhibits a coloring phenomenon when irradiated with light is brought into contact with a fluid containing alcohol, the degree of coloring changes depending on the alcohol concentration in the fluid. A method for measuring alcohol concentration, characterized in that the alcohol concentration in the fluid is determined by determining the change in the degree of coloring. (2) In the alcohol concentration measuring method according to claim (1), the coloring is erased by applying a voltage to the metal oxide after determining the alcohol concentration. Alcohol concentration measurement method.