JP2582846B2 - Moisture measurement method using purple membrane - Google Patents

Description

The present invention relates to a method for measuring moisture. In particular, the present invention relates to a method for accurately measuring a trace amount of water in a gas.

<Prior Art> Several methods for measuring moisture in a fluid such as a gas or a liquid are known and used in practice. One of them is a method utilizing the fact that water molecules have absorption in the infrared region. However, this method is of course not applicable to the measurement of moisture in a sample having absorption at the same position as water molecules.
Further, this method is not suitable for measuring a trace amount of water. Another commonly used method is to titrate using a Karl Fischer reagent.
Although it is possible to measure even a trace amount of water of about pm, the measurement must be of a batch type, and one measurement requires a time of at least several minutes.

<Problems to be Solved by the Invention> The present invention aims to provide a method for optically measuring a trace amount of water.

The present inventor has found that the absorbance at 400-700 nm of the purple membrane and its pattern vary greatly depending on the moisture content of the environment in which it is placed. This change is reversible and very fast, so by measuring the absorbance of the purple membrane or its pattern, the moisture content of the environment in which it is placed can be determined.

According to a more detailed description of the present invention, purple membrane is present in the plasma membrane of extreme halophiles (Halobacteria),
It contains 25% lipid and 75% protein, and it is known that the protein is only one kind of bacteriorhodopsin. To collect this, bacterial cells are put into distilled water to rupture the cells, centrifuged to obtain a membrane fraction, and then a purple membrane fraction is taken from this by a sucrose density gradient centrifugation method. Removal of sucrose by dialysis gives a purple membrane. Bacteriorhodopsin in purple membrane has a molecular weight of about 26000
In the purple film, it exists as a trimer, heat, acid,
It is known that it has a property that it is resistant to alkali and hardly deteriorates.

In the present invention, the purple film is supported on a support such as a transparent glass in a thin film form and is subjected to moisture measurement. The thickness of the purple membrane on the support may be extremely thin, and if it is too thick, it takes time for moisture to penetrate into the inside and equilibrate with the surrounding moisture, and the response may be slow. is there.

The easiest way to deposit a purple membrane on a glass plate is to
The aqueous suspension of the purple membrane may be uniformly applied on a glass plate and then dried. However, the thin film thus formed is
If the drying is extremely advanced, it may occasionally peel off from the glass. Since the purple film has a negative charge, a film having a positive charge such as polylysine is applied on the glass surface in advance, and if a thin film of the purple film is formed thereon, peeling can be performed. It is effective to reduce.

Also, since the purple membrane responds to moisture even when partially modified with a chemical modifier, the purple membrane is crosslinked with a crosslinking agent such as glutaraldehyde, and this is applied to a glass plate and crosslinked to form a purple membrane. May be formed on a glass plate.

As still another method, a transparent moisture-permeable diaphragm can be superimposed on the violet thin film formed as described above for measurement. As the diaphragm, a porous synthetic resin film having many fine physical pores, a synthetic resin film having a molecular structure irrespective of the physical pores, and the like can be used. Many such films are known, including polyamino acid urethane, and are commercially available.

When a thin purple film formed on a glass plate is left in the air, the absorbance at each wavelength and the pattern of the absorbance change according to the amount of moisture in the air. For example, FIG. 1 shows a purple solution formed by applying an aqueous solution containing several milligrams of a purple film in 1 ml onto a transparent glass plate so that the absorbance becomes 0.9, and leaving it in a room at room temperature to dry. It is one of the experimental examples showing how the absorbance and the absorption spectrum of a thin film change with the moisture in the atmosphere. In the experiment, a sealable container was installed in the sample chamber of the absorbance measuring device, and a glass plate carrying a purple film was interposed on the optical path connecting the light source and the light receiving unit, so as to be orthogonal to this.
The absorption spectrum of the purple membrane was measured while reducing the pressure in the container at room temperature. As is clear from FIG. 1, the wavelength (λmax) showing the maximum absorbance under the atmospheric pressure was about 565 nm, but the wavelength showing the maximum absorbance gradually shifted to the shorter wavelength side as the degree of decompression increased, It is about 533 nm under a vacuum of about 10 ^-2 torr. (The atmosphere was depressurized in this experiment to reduce the moisture concentration in the atmosphere. It can be confirmed that the absorbance does not change even when the pressure is returned to the atmospheric pressure by introducing the gas into the container).

As is clear from FIG. 1, the wavelength showing the maximum absorbance differs depending on the moisture content of the atmosphere. If a calibration curve showing the relationship between the two is created, the absorbance curve of the unknown sample is measured. Its moisture content can be determined. Alternatively, as another method, a violet film is supported on a glass plate, and a calibration curve showing the relationship between the absorbance and the water content at a specific wavelength, for example, 565 nm, is prepared using the film,
The water content of the unknown sample can then be determined by measuring the absorbance at that wavelength.

FIG. 2 shows that, as in the experiment of FIG. 1, the glass plate-supported purple membrane was placed in a vessel that can be hermetically sealed, placed on the optical path of an absorbance measuring device, and the vessel was pumped at room temperature by a vacuum pump. It is a measurement of how the absorbance changes when the inside is gradually reduced in pressure and then instantaneously returned to normal pressure. As a light source, a light emitting diode (Toshiba TLY124, λmax = 585nm,
Δλ = 32 nm), and a photoelectric conversion element (S1113, Hamamatsu Photonics, λmax = 560 nm (almost constant at 540 to 580 nm)) was used as a light receiving section. , The transmittance gradually increases.However, when the pump is stopped and the valve is opened to allow outside air to enter, the transmittance instantaneously drops significantly and returns to the state before the vacuum pump was activated in a short time. In other words, it can be seen that the absorbance change due to moisture in the purple membrane is reversible and the response is very prompt.

<Effect> According to the present invention, a trace amount of water in the atmosphere can be measured quickly and accurately without using any reagent. Further, according to the present invention, a trace amount of water in the atmosphere can be continuously measured.

[Brief description of the drawings]

FIG. 1 is an experiment 1 showing how the absorption spectrum of the visible part of the purple film changes depending on the moisture content of the atmosphere.
It is an example. In the figure, the moisture content of the atmosphere is Native
It decreases from PM to Dried PM. FIG. 2 is an example of an experiment showing how the transmittance of the purple film changes when the moisture content of the atmosphere changes rapidly.

Claims (2)

(57) [Claims] 1. A method for measuring water content, comprising bringing a fluid whose water content is to be measured into contact with a purple membrane directly or via a moisture-permeable partition, and measuring the absorbance of the purple membrane which changes depending on moisture. Law 2. The method according to claim 1, wherein the purple membrane is partially modified with a chemical modifier.