JPH0446202Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention relates to a moisture measuring cell. More specifically, it is possible to measure moisture contained in various gases, liquids, and solid samples with high precision and accuracy. moisture concentration,
In particular, it relates to a moisture measuring cell suitable for detecting minute amounts of moisture concentration.

(b) Conventional technology Traditionally, methods for quantifying the concentration of water in various media, especially gases and liquids, include the Karl Fischer method, gas chromatography, and methods for measuring physical changes in resistance, electric capacity, weight, etc. due to water adsorption. A method using a moisture (humidity) sensor to detect moisture based on
Methods such as detecting weight changes due to infrared heating are selected and put into practical use depending on the application.

(c) Problems that the invention aims to solve The most widely used of these is the Karl-Fitscher method, but this method requires a long measurement time (usually 10 to 20 minutes) and is difficult to measure in trace amounts of moisture. It requires a large amount of sample (usually 50 g or more) (absorbing liquid in the case of gas), and it also causes chemical reactions with the Karl Fischer reagent and coexisting components in the sample, and is hygroscopic, so it is difficult to use when measuring trace amounts of moisture. Errors tend to occur and the measurement range is ¹⁰⁰ μg to ¹⁰⁵ μg (H ₂ O concentration 10 ppm to
There was a problem that it was regulated to 100% wt/vol).

On the other hand, the method using a humidity sensor is a simpler method than the above-mentioned Karl Fischer method, but the measurement target system is limited and there are problems in terms of sensitivity to trace amounts of moisture and durability.

Regarding this point, the present inventors discovered a piezoelectric type (oscillation frequency detection type) humidity sensor that can detect up to 0.1 μg of moisture (approximately 1 ppm in H ₂ O concentration) (Japanese Patent Laid-Open No. 59-24234). ).

However, although such humidity sensors are stable and have excellent sensitivity to moisture, they are also sensitive to organic solvents, resulting in reduced measurement accuracy and accuracy when using sample gases that contain organic solvents as coexisting substances. This was particularly problematic during trace analysis.

This invention was developed in view of the above situation, and is intended to provide a moisture measurement cell that can measure trace amounts of moisture in gaseous samples or vaporized samples that coexist with organic solvents with high precision and accuracy. .

(d) Means and action for solving the problem Thus, according to this invention, two humidity systems are provided that are equipped with a gas inlet and a gas outlet, and have different sensitivities to moisture but substantially the same sensitivity to organic solvents. A moisture measuring cell is provided which includes a built-in sensor and includes a differential calculation section that can determine the moisture concentration in the introduced gas based on the difference in output between these two humidity sensors.

The most distinctive feature of this invention is that two humidity sensors having different characteristics as described above are built into one cell. When a gas containing an organic solvent is introduced into this cell, each humidity sensor produces an output corresponding to the contained moisture and the contained organic solvent, but since the output for the organic solvent is the same, there is a difference in the output between them. corresponds to the true water concentration. Therefore, by this subtraction, it is possible to remove the influence of the contained organic solvent on the measured value, and use an appropriate concentration conversion factor or a calibration curve to calculate the moisture concentration in the introduced gas and the concentration of water in various samples before gasification. It becomes possible to detect moisture content with high precision and accuracy.

The two types of humidity sensors in this invention preferably have a humidity sensitive film based on a plasma polymerized film formed on a piezoelectric element. A method for imparting the above two types of characteristics to such a humidity sensor is as follows:
A method of controlling the amount of hydrophilic groups introduced into the plasma polymerized membrane is suitable. A moisture-sensitive film can be obtained by chemically treating the surface of a plasma-polymerized film to introduce hydrophilic groups such as ammonium groups and sulfonate groups, but by adjusting the chemical treatment time, the above two effects can be achieved. It is possible to obtain two humidity sensors with characteristics. In particular, a pair of electrodes is formed on a piezoelectric element plate by vapor deposition, and this is subjected to plasma polymerization under the vapor of a hydrophobic organic compound.
After forming a polymer film between these electrodes or on at least one electrode, and then subjecting it to plasma polymerization under the vapor of an organic amino compound to form an amino group-containing polymer film on the polymer film, A humidity sensor is manufactured by a method in which the amino groups in the amino group-containing polymer membrane are converted into ammonium salt-type hydrophilic groups by holding the film in alkyl halide vapor, and the treatment time with the alkyl halide is controlled at this time. It was also discovered that by doing so, it is possible to easily obtain two types of humidity sensors that have the same sensitivity to organic solvents and different sensitivities to moisture. Such a moisture-sensitive film basically consists of an inner layer made of a plasma-polymerized polymer layer of a hydrophobic organic compound, and a surface layer formed thereon of an amino group-containing polymer layer formed by plasma polymerization of an organic ammonium compound. In addition, the amino group-containing polymer layer of the surface layer has an ammonium salt type hydrophilic group introduced by converting an amino group, and is preferable from the viewpoint of responsiveness and durability as a sensor.

Examples of the above-mentioned hydrophobic organic compounds include various organic compounds that do not have a hydrophilic group, such as vinyl aromatic compounds such as styrene and divinylbenzene, aromatic compounds such as benzene and toluene, and aromatic compounds such as ethylene and propylene. Examples include unsaturated hydrocarbons. Two or more types of these may be used. It can also have a multilayer structure. Among these, it is preferable to use styrene, which is easily plasma polymerized.

The organic amino compounds mentioned above include diallylamine, diamylamine, diethylallylamine,
Examples include amines having at least one linear substituent such as N,N,N',N'-tetramethylhexanediamine, and cyclic or aromatic amines such as aniline, pyridine, and phenethylamine; in addition to these, triethylamine, Examples include ethylenediamine, diethylenetriamine, triethylenetetramine, and the like. Two or more types of these may be combined. Among these, it is preferable to use tertiary amines having linear substituents such as tetramethylhexanediamine and diethylallylamine.

It is preferable that the chemical treatment of the amine groups in the above-mentioned amine group-containing polymer film is carried out by keeping the amine groups in the vapor of alkyl halide. As the alkyl halide in this case, it is appropriate to use lower alkyl monohalides, specific examples of which include methyl chloride, ethyl chloride, methyl iodide, methyl bromide, and the like. By contact with such alkyl halide vapor, the amino groups present in the amino group-containing polymer membrane are alkylated to form hydrophilic ammonium salts such as quaternary ammonium salts, tertiary amine salts, and secondary amine salts. converted into a sexual group. This contact is
Although the reaction can be accelerated by carrying out the reaction under heating, the reaction may be carried out at room temperature. It is preferable to adjust the halogenated alkyl vapor so that it contacts the sensor formed with the amino group-containing polymer film at a flow rate of about 1/min under normal pressure.

FIG. 2 shows changes in the responsiveness of water and organic solvents depending on the time of the chemical treatment. It should be noted that each humidity sensor used was manufactured in the same manner as in the examples described later. It can be seen that by adjusting the chemical treatment time in this way, the sensitivity to moisture changes. This is based on the fact that the amount of hydrophilic groups introduced into the surface layer of the plasma polymerized membrane increases. The fact that the sensitivity does not change even after chemical treatment is performed for two days or more means that the amount of introduced hydrophilic groups is saturated. On the other hand, no change in sensitivity to organic solvents was observed even after chemical treatment for 6 hours or more. In other words, the sensitivity is constant regardless of the amount of water functional groups (hydrophilic groups), and it is thought that the adsorption mechanisms of water and organic solvent to the moisture-sensitive film are completely different. Therefore, by changing the chemical treatment time, two types of humidity sensors having the same sensitivity to organic solvents and one with low sensitivity and one with high sensitivity to water can be easily produced.

Generally, the physical characteristics of a crystal diaphragm are expressed as follows.

Here, ΔfH ₂ O, ΔfO are frequency changes due to moisture and organic solvent, ΔMH ₂ O, ΔMO are mass changes on the quartz plate due to moisture and organic solvent, f is resonance frequency, Ar is surface area of quartz plate, P is piezoelectric crystal density,
When N is a frequency constant, the following relationship holds true.

ΔfH ₂ O/f=-f・ΔMH ₂ O/Ar・P・N ΔfO/f=-f・ΔMO/Ar・P・N Here, K=−f ² /Ar・P・N and Δf Letting be the frequency change of the total water and organic solvent, the following equation is obtained.

Δf=ΔfH ₂ O+ΔfO =K·ΔMH ₂ O+K·ΔMO A similar relational expression holds for the two sensors a and b of the present invention, but a and b are added to distinguish between the two.

Δf _a = Δf _a H ₂ O+Δf _a O Δf _b = Δf _b H ₂ O+Δf _b O Here, the output difference ΔΔf between both sensors, which is the difference in frequency change between sensors a and b, is expressed by the following equation.

ΔΔf=Δf _a −Δf _b =Δf _a H ₂ O+Δf _a O−(Δf _b H ₂ O+Δf _b O) The sensor of this invention has a low sensitivity (sensor a) and a high sensitivity (sensor b) for moisture. However, since the same sensitivity is applied to organic solvents, the second term (organic solvent term) can be eliminated.

Δf _a O−Δf _b O≒0 In the end, the output difference ΔΔf between both sensors can be easily expressed as follows.

ΔΔf=Δf _a H ₂ O−Δf _b H ₂ O As a result, by detecting the output difference between both sensors, the influence of the coexisting organic solvent can be removed, and based on this output difference, the calibration curve and By setting the concentration conversion factor, moisture can be measured with high precision and accuracy.
In addition, from the viewpoint of accuracy, it is preferable to select a sensor in which the difference in moisture responsiveness between the two sensors is as large as possible.

In addition, these two types of sensors have the following characteristics in terms of responsiveness:
It is preferable to incorporate the device so that its moisture-sensitive surface is parallel to the direction of gas introduction.

(e) Example Reference numeral 1 shown in FIG. 1 shows a humidity measuring device using the moisture measuring cell of this invention. In the figure, the humidity measuring device 1 includes a carrier gas (nitrogen gas) supply path 3,
A liquid sample vaporization chamber (4; approximately 250°C, internal volume: 2 ml) and a moisture measuring cell 2 are connected in this order through a pipe.
The carrier gas supply path 3 is equipped with a dryer 31 filled with a molecular sieve, in which water in the carrier gas is removed. Further, the vaporization chamber 4 is provided with an injection port 41 through which a liquid sample from the syringe 4 is injected into the vaporization chamber 4, where it is gasified and transferred to the moisture measuring cell 2 using a carrier gas.

The moisture measurement cell 2 consists of a cylindrical container (diameter 18 mm x height 12 mm) equipped with a gas inlet 21 and a gas outlet 22 facing each other on the circumference, and inside the container there are two disc-shaped humidity chambers. Sensors a and b are arranged parallel to the gas introduction direction (arrow) with an interval of about 8 mm. Humidity sensor a consists of gold electrodes formed on both sides of a 9.022 MHz disc-shaped crystal oscillator 6, and then plasma polymerized under styrene monomer (under 1 torr).
1KHz) followed by plasma polymerization (0.7 torr) under N,N,N',N'-tetramethylhexanediamine.
An oscillation frequency detection type humidity sensor that has a moisture sensitive film 5 in which a plasma polymerized film of approximately 0.7 μm is formed by performing a plasma-polymerized film of about 0.7 μm (see below, 1 KHz), and the surface thereof is further brought into contact with methyl chloride gas for 6 hours to introduce ammonium groups. It is. The sensitivity of this sensor to water and organic solvents is shown in Figure 2a (in the figure, black circles indicate sensitivity to 0.5 μm of water; white circles indicate sensitivity to anhydrous propanol).
(indicates sensitivity to 10μ). On the other hand, humidity sensor b was manufactured under the same conditions as sensor a, except that the chemical treatment time with methyl chloride gas was changed to 48 hours, and its sensitivity is as shown in FIG. 2b.

Based on the output difference between the two sensors a and b, the differential calculation section 23 calculates the moisture concentration in the introduced gas. That is, the frequency changes of both sensors a and b are measured by the frequency measuring devices 231, 231' and the differential amplifier 2.
32, only the difference is output to the frequency/voltage converter 233 and recorded on the recorder 24, and the water concentration is determined based on this intensity. On this occasion,
As mentioned above, the difference in frequency change is substantially caused only by water, which is not affected by the organic solvent.

FIG. 3 shows the peaks obtained when water in 10 μm of an organic solvent (propanol) was actually measured using this device, and FIG. 4 shows an example of a calibration curve obtained using this device.

It can be seen that by using the moisture measuring cell described above, the concentration of moisture can be measured with high precision and accuracy without being affected by propanol coexisting in the introduced gas. The same was true for other organic solvents (acetone, ethanol, trichlene).

(F) Effects According to the moisture measuring cell of this invention, it is possible to selectively detect the concentration and amount of moisture in various samples in which organic solvents coexist, and in some cases, in organic solvents. In particular, it improves the quantification limit of conventional humidity sensors, which was limited by the presence of coexisting organic solvents, and is useful for measuring and managing trace amounts of moisture (ppm order).

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram illustrating a humidity measuring device using the moisture measuring cell of this invention, FIG. 2 is a graph for explaining the sensitivity of the humidity sensor used in this invention, and FIGS. Each figure is a graph for explaining the moisture responsiveness of the moisture measuring cell of this invention. a, b...humidity sensor, 2...moisture measurement cell,
5...Moisture sensitive film, 6...Crystal oscillator, 21...Gas inlet, 22...Gas outlet, 23...Differential calculation section, 24...Recorder.

Claims (1)

[Claims for Utility Model Registration] 1. Two types of plasma polymerization moisture sensitive devices equipped with a gas inlet and an outlet and having the same sensitivity to organic solvents and different sensitivities to moisture by controlling the treatment time with an alkyl halide. A moisture measuring cell comprising a built-in humidity sensor formed by forming a membrane and a differential calculation section capable of determining the moisture concentration in introduced gas based on the difference in output between these two humidity sensors. 2. The moisture measuring cell according to claim 1, which is a registered utility model, and includes two humidity sensors built in so that their humidity sensing surfaces are parallel to the gas introduction direction.