JP3599599B2 - Gas concentration analyzer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention adsorbs and collects a dilute organic gas that causes air pollution to a porous glass polished into a plate that transmits ultraviolet and visible light, which is placed in a sample chamber of an ultraviolet and visible spectroscope, and thereafter, desorbed by heating at specific temperatures to the gas components, was measured to measure the ultraviolet-visible absorption spectrum in situ in the process, the gas enriched fraction to analyze the type and concentration of the organic gas from the change in intensity 析装 Related to the location.
[0002]
[Prior art]
In the analysis of an organic gas that causes air pollution, the concentration of the gas to be analyzed is generally low, so that a process of concentrating and recovering the low-concentration gas to be analyzed is required before the analysis operation. In conventional gas concentration analyzers, the gas to be analyzed is adsorbed on the adsorbent filled in the adsorption collection tube, and then the gas to be analyzed is recovered as a highly concentrated gas by a heat desorption device and introduced into the analyzer. The most common is a device that performs analysis.
[0003]
The procedure for using the conventional gas concentration analyzer and its problems will be briefly described below by taking a gas spectrometer (Japanese Patent Application No. 11-38606) as an example in which analysis means such as an ultraviolet spectrometer are combined. At the place where analysis is desired, the atmosphere containing the organic gas to be analyzed is introduced into the collection tube, and the organic gas is collected by the adsorbent. Thereafter, by heating the collection tube, the organic gas adsorbed by the adsorbent is desorbed as a concentrated gas, and the concentrated gas is introduced into an analyzer such as an ultraviolet spectrometer for analysis.
[0004]
In this procedure, the following problems occur. That is, there is a problem that the concentration of the gas recovered by the heat desorption tends to change due to leakage before analysis, adsorption to the wall surface, and the like. Further, it is difficult to keep the concentration of the concentrated gas uniform for a long time, and the signal intensity changes with time in the spectroscopic analysis. Therefore, it is difficult to increase the integration time to improve the S / N ratio.
[0005]
[Problems to be solved by the invention]
For the analysis of air polluting organic gas, it is necessary to concentrate and recover a low concentration of the gas to be analyzed in a stage prior to the analysis. However, as described above, in a conventional gas concentration analyzer that performs analysis following adsorption and collection of gas using a collection tube and recovery of concentrated gas by thermal desorption, a change in concentration occurs when the gas is introduced into the analyzer. It is difficult to improve the S / N ratio by integration, and there is a limit in improving sensitivity and accuracy in analysis.
[0006]
The present invention has been made in view of the above circumstances, and uses a porous glass that transmits ultraviolet and visible light as an adsorbent collector and a spectroscopic cell to concentrate the ultraviolet and visible spectra of a gas adsorbed in the porous glass. By analyzing without collecting as a gas, quantitative errors due to changes in concentration after collection are reduced, and by fixing the gas in the porous glass, the change in absorption intensity with time is reduced. aim to improve the S / N ratio Te, and an object thereof is to provide a gas enriched fraction 析装 location to achieve an improvement in sensitivity and accuracy in the analysis.
[0007]
[Means for Solving the Problems]
The gas concentration analyzer of the present invention in order to achieve the above object, and means Ru is concentrated to a desired concentration by adsorbing the organic gas in the porous glass that transmits ultraviolet-visible light, the organic gas in this way A means for measuring the ultraviolet / visible absorption spectrum of the adsorbed porous glass, a heating means for heating the porous glass adsorbing the organic gas at a predetermined temperature and desorbing the adsorbed organic gas, and the ultraviolet / visible absorption spectrum The intensity of the ultraviolet / visible absorption spectrum of the porous glass before and after desorption of the organic gas adsorbed by controlling the means for measuring and the heating means is repeatedly measured by changing the heating temperature, and the porous glass before and after desorption is measured. A method for analyzing the type and concentration of adsorbed gas components by obtaining an ultraviolet / visible absorption spectrum of only the desorbed component from the intensity change of the ultraviolet / visible absorption spectrum It is characterized in that it comprises and.
[0011]
The present invention provides an enrichment method comprising using a porous glass as an adsorption trapping agent and a spectroscopic cell for a gas to be analyzed, and analyzing the organic gas adsorbed and collected on the porous glass by an ultraviolet / visible spectrum. It is an analyzer. The porous glass used in the present invention is a plate-like glass whose surface is polished in order to suppress the intensity attenuation of transmitted light due to light scattering on the glass surface. Since highly pure glass from which is removed as much as possible is used, it can be used as a spectral cell. For this reason, compared with the conventional apparatus, it is possible to perform an analysis by an ultraviolet / visible spectrum without being recovered as a concentrated gas, and it is possible to reduce a quantitative error due to a change in concentration when the analyzer is introduced. In addition, by fixing the gas in the porous glass, the intensity change with time is reduced, and the integration time can be increased to improve the S / N ratio.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a configuration explanatory view showing an embodiment of the present invention.
[0014]
A gas flow tube 6 is installed in the sample chamber of the ultraviolet / visible spectroscope 1, and a small pump (not shown) is connected to the gas flow tube 6. The atmosphere containing the organic gas to be analyzed can be ventilated into the gas flow tube 6 at a desired place for a desired time. A porous glass 4 that transmits ultraviolet and visible light is installed in the gas flow tube 6, and a target organic gas is adsorbed and collected on the porous glass 4. Thereafter, the ultraviolet light generated from the ultraviolet light source 2 passes through the porous glass 4 adsorbing the organic gas through the entrance slit 3 and is irradiated on the diffraction grating 7. The light diffracted by the diffraction grating 7 is detected by a detector 8 and converted into an electric signal. The converted signal is input to a computer 11 via a counting circuit 10 and the ultraviolet / visible absorption spectrum of the porous glass 4 to which the organic gas is adsorbed. Perform the measurement. The ultraviolet / visible absorption spectrum of the adsorbed gas is obtained from the difference between this measurement result and the previously measured ultraviolet / visible absorption spectrum of the porous glass before gas adsorption. A heating device 5 is attached to the outer periphery of the gas flow tube 6 so as to heat the porous glass 4, and the heating device 5 is connected to a computer 11 via a temperature control electronic circuit 9 to control the temperature. Controlled. The heating device 5 is set at a predetermined temperature to desorb the organic gas molecules adsorbed on the porous glass 4 by heating, and the ultraviolet / visible absorption spectrum of only the desorbed component is determined from the intensity change of the ultraviolet / visible absorption spectrum before and after the desorption. Get. This is repeated by the number of gas components to be analyzed, and the analysis and measurement of the organic gas are performed.
[0015]
That is, after the organic gas is concentrated to a desired concentration by adsorbing the organic gas on the porous glass transmitting ultraviolet / visible light, the ultraviolet / visible absorption spectrum of the porous glass adsorbing the organic gas is measured, and the organic gas is absorbed. The type and concentration of the adsorbed gas are analyzed by calculating the difference between the ultraviolet and visible absorption spectra of the porous glass before adsorption.
[0016]
Further, the porous glass is heated and controlled at a temperature specific to the adsorbed gas in the sample chamber of the ultraviolet / visible spectrometer 1 so that the adsorbed gas is desorbed from the porous glass. The decrease in absorption of the desorbed gas is detected from the time change of the spectrum intensity, and the type and concentration of the gas are specified.
[0017]
Further, by heating the porous glass in the sample chamber of the ultraviolet / visible spectrometer 1 at a temperature at which the adsorbed gas is sufficiently desorbed, the porous glass is regenerated on the spot so that the measurement can be repeated. I do.
[0018]
Next, in order to confirm the effect of the gas concentration analysis method using porous glass, as an example, an ultraviolet absorption spectrum of an organic gas adsorbed on a porous glass polished into a plate shape that transmits ultraviolet and visible light, and an adsorbent The following shows a comparison with the case where a gas concentrated and recovered by heat desorption after adsorption of an organic gas is measured.
[0019]
Toluene gas diluted to a concentration of about 5 ppm with nitrogen gas is passed through the porous glass used in the present invention and the concentration collecting tube filled with an adsorbent used in a conventional apparatus for reference for only about 5 min each. Thereby, gas was sampled for both. FIG. 2A shows a spectrum obtained by subtracting the ultraviolet absorption spectrum of the porous glass before adsorption from the ultraviolet absorption spectrum of the porous glass to which the gas has been adsorbed. The reference adsorbent was heated at 200 ° C. for 15 minutes, and the ultraviolet absorption spectrum of the concentrated gas recovered by desorption is shown in FIG. 2 (b). Comparing the two spectra, the spectrum using porous glass shows little change in intensity with time, and the accumulation time can be obtained, whereas the concentration gas recovered from the conventional adsorbent has a large change in intensity with time and the integration time is large. It turns out that it is difficult to take long. From this, it is confirmed that when the porous glass is used, the S / N ratio can be improved.
[0020]
In order to confirm the effect of the gas concentration analysis method using another porous glass, the UV absorption spectrum of the porous glass immediately after sampling the sample gas and the porous glass after heating and desorption at the specific temperature for desorption of toluene gas were used. The ultraviolet absorption spectrum of the toluene gas obtained by measuring the ultraviolet absorption spectrum and calculating the difference spectrum before and after this is shown in FIGS. 3A and 3B and will be described below.
[0021]
Gases were collected by flowing a binary mixed gas of toluene and o-xylene, each diluted to a concentration of about 5 ppm with nitrogen gas, through the porous glass used in the present invention for about 5 minutes. FIG. 3A shows an ultraviolet absorption spectrum of the porous glass to which the mixed gas has been adsorbed and an ultraviolet absorption spectrum of the porous glass after toluene gas has been heated and desorbed at a desorption specific temperature. FIG. 3 (b) shows an ultraviolet absorption spectrum obtained by subtracting the ultraviolet absorption spectrum of the porous glass after the heating and desorption of toluene gas from the ultraviolet absorption spectrum of the porous glass to which the mixed gas has been adsorbed. This corresponds to the ultraviolet absorption spectrum of a single component of toluene gas. By repeating this for the number of gas components to be detected, the type and concentration of each gas can be detected. The porous glass is regenerated by performing a heat treatment at the end of the analysis, and can be used repeatedly without removing it from the apparatus.
[0022]
【The invention's effect】
As described above, the present invention uses a porous glass that transmits ultraviolet and visible light as an adsorbent and a spectroscopic cell, and analyzes the ultraviolet and visible spectrum of the adsorbed gas without collecting it as a concentrated gas. Quantitative error due to a change in the concentration of the compound can be reduced and the S / N ratio can be improved. These make it possible to improve sensitivity and accuracy in the analysis of air pollutant organic gas.
[0023]
In addition, since the present invention eliminates the need for a gas concentration and recovery device as in the conventional device, it can be used in combination with a small ultraviolet / visible spectrometer using a non-scanning spectrometer to provide a portable small air pollution organic gas analyzer. The device can be configured.
[Brief description of the drawings]
FIG. 1 is a configuration explanatory view showing an embodiment of the present invention.
FIGS. 2A and 2B are characteristic diagrams for explaining an embodiment of the present invention. FIG. 2A is an ultraviolet absorption spectrum of toluene adsorbed on a porous glass of the present invention, and FIG. 5 is an ultraviolet absorption spectrum of toluene gas concentrated and recovered by the method.
FIG. 3 is a characteristic diagram illustrating separation and detection of toluene gas from a multi-component gas by a thermal desorption method according to an embodiment of the present invention. It is an ultraviolet absorption spectrum obtained, and (b) is an ultraviolet absorption spectrum of toluene gas obtained by difference spectrum calculation before and after thermal desorption.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 UV-visible spectroscope 2 Ultraviolet light source 3 Incident slit 4 Porous glass 5 Heating device 6 Gas flow tube 7 Diffraction grating 8 Detector 9 Temperature control electronic circuit 10 Counting circuit 11 Computer

Claims (1)

Means for concentrating to a desired concentration by adsorbing an organic gas on porous glass that transmits ultraviolet and visible light, and means for measuring the ultraviolet and visible absorption spectrum of the porous glass that has absorbed the organic gas with this means, Heating means for heating the porous glass having the organic gas adsorbed thereto at a predetermined temperature to desorb the adsorbed organic gas, means for measuring the ultraviolet / visible absorption spectrum, and controlling the heating means for the adsorbed organic gas. The intensity change of the ultraviolet / visible absorption spectrum of the porous glass before and after desorption is repeatedly measured by changing the heating temperature, and based on the intensity change of the ultraviolet / visible absorption spectrum of the porous glass before and after desorption, the ultraviolet / visible absorption of only the desorbed component Means for analyzing the type and concentration of the component of the adsorbed gas by obtaining a spectrum.

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