METHOD AND DEVICE FOR ANALYZING GAS

Abstract

Provided are a method and a device that do not require any pretreatment and measure and analyze impurities or hydrogen fluoride in corrosive gas with high sensitivity. The method and the device measure a fluorine-based gas in a sample containing a corrosive gas with a Fourier transform infrared spectrophotometer, wherein the Fourier transform infrared spectrophotometer includes a detector having an InGaAs detection element and a single-path gas cell having an optical path length of 0.01 m to 2 m, a cell window is made of a corrosion-resistant material, a measurement region ranges from 3800 to 14300 cm.sup.1 in wavenumber, and the concentration of the fluorine-based gas is quantified based on an amount of absorption of light having a predetermined wavenumber by the sample and a calibration curve.

Claims

1. A gas analyzing method for measuring a fluorine-based gas in a sample containing a corrosive gas with a Fourier transform infrared spectrophotometer, wherein the Fourier transform infrared spectrophotometer comprises a detector having an InGaAs detection element and a single-path gas cell having an optical path length of 0.01 m to 2 m, a cell window is made of a corrosion-resistant material, a measurement region ranges from 3800 to 14300 cm.sup.1 in wavenumber, and a concentration of the fluorine-based gas is quantified based on an amount of absorption of light having a predetermined wavenumber by the sample and a calibration curve.

2. The method according to claim 1, wherein the fluorine-based gas is hydrogen fluoride.

3. The method according to claim 1, wherein the cell window is made of one kind selected from the group consisting of CaF.sub.2, BaF.sub.2, MgF.sub.2, LiF and ZnSe.

4. The method according to claim 1, wherein the measurement region ranges from 3950 to 4200 cm.sup.1 in wavenumber.

5. A gas analyzing device comprising a Fourier transform infrared spectrophotometer for measuring a fluorine-based gas in a sample containing a corrosive gas, the Fourier transform infrared spectrophotometer including a light source, a beam splitter, a fixed mirror, a movable mirror, a measurement cell, a detector, and an information processing device, the detector includes a detector having an InGaAs detection element, the measurement cell is provided with a sample gas inlet and a sample gas outlet, and includes a single-path gas cell having an optical path length of 0.01 m to 2 m, a cell window in the measurement cell is made of a corrosion-resistant material, an interference mechanism is provided that includes the beam splitter, the fixed mirror, and the movable mirror so that light emitted from the light source is controlled to have a wavenumber range of 3800 to 14300 cm.sup.1 and impinges onto a sample, and the information processing device is configured to quantify a concentration of the fluorine-based gas from an amount of absorption of light having a predetermined wavenumber by the sample and a preset calibration curve.

6. The device according to claim 5, wherein the fluorine-based gas is hydrogen fluoride.

7. The device according to claim 5, wherein the cell window is made of one kind selected from the group consisting of CaF.sub.2, BaF.sub.2, MgF.sub.2, LiF and ZnSe.

8. The device according to claim 5, wherein light emitted from the light source is controlled to have a wavenumber range of 3950 to 4200 cm.sup.1 and impinges onto the sample.

9. The device according to claim 5, wherein when a spectrum based on an absorption amount detected by the detector is subjected to Fourier transform in the information processing device, Trapezium is used as an apodization function.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 is a diagram showing a schematic configuration of a Fourier transform infrared spectrophotometer in a gas analyzing device according to an embodiment of the present invention.

[0058] FIG. 2 shows absorption spectrum data of various compounds measured by a Fourier transform infrared spectrophotometer.

[0059] FIG. 3A is a diagram showing a schematic configuration of a multi-reflection long optical path gas cell in the Fourier transform infrared spectrophotometer.

[0060] FIG. 3B is a diagram showing a schematic configuration of a single-path gas cell in the Fourier transform infrared spectrophotometer.

[0061] FIG. 4 shows traces of baseline waveforms based on different apodization functions for the same baseline with respect to the absorption spectrum data obtained by the Fourier transform infrared spectrophotometer.

[0062] FIG. 5 is a spectrum of a standard gas (the concentration of hydrogen fluoride is 13.4 ppm) obtained by diluting hydrogen fluoride with nitrogen.

[0063] FIG. 6 is a calibration curve obtained by using a standard gas obtained by diluting hydrogen fluoride with nitrogen.

[0064] FIG. 7 is a diagram showing a spectrum of hydrogen fluoride in tungsten hexafluoride in Example 3.

EXAMPLES

[0065] Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

Example 1

[0066] A Fourier transform infrared spectrophotometer had the configuration shown in FIG. 1, and a detector having an InGaAs detection element was used as the detector. The measurement was performed by using, as the gas cell, a single-path short optical path gas cell having a length of 0.10 m (10 cm) and having no reflecting mirror.

[0067] A material made of calcium fluoride (CaF.sub.2) was used for the cell window of the single-path gas cell. The resolution was set at 2 cm.sup.1, the number of times of integration was set to 50 times, the measurement region was set at 3,950 cm.sup.1 to 4,200 cm.sup.1, and the apodization function was set to Trapezium. Other conditions were set based on the specification and description of the device used.

[0068] A hydrogen fluoride standard gas of 0.39 ppm to 23.29 ppm was adjusted by using a permeator as a calibration gas preparation device, a permeation tube for hydrogen fluoride, and nitrogen for dilution to measure a measurement target.

[0069] As can be seen from FIG. 5, calibration curves of a linear equation and a quadratic equation based on the least squares method were prepared by using the peak of hydrogen fluoride appearing at 4075 cm.sup.1 from the spectrum of the hydrogen fluoride standard gas of each concentration. As a result of preparing the calibration curves, a strong correlation was obtained with the determination coefficient R.sup.2=0.99 or more in all cases in the range of the hydrogen fluoride concentration of 0.47 ppm or more. FIG. 6 shows a part of the prepared calibration curve which was prepared in the range of 0.47 ppm to 4.71 ppm in hydrogen fluoride concentration.

Comparative Example 1

[0070] The detector was changed from a detector having an InGaAs detection element of Example 1 to a detector having an MCT detection element and a TGS detection element, and the hydrogen fluoride standard gas was measured as in the case of Example 1.

Example 2

[0071] The ratio of the peak of hydrogen fluoride appearing at 4075 cm.sup.1 to the average of right and left noises most adjacent to the peak of hydrogen fluoride appearing at 4075 cm.sup.1 (hereinafter referred to as S/N ratio) was determined from the hydrogen fluoride spectra of the hydrogen fluoride standard gases obtained in Example 1 and Comparative Example 1, and it is shown in Table 1.

TABLE-US-00001 TABLE 1 S/N ratio by S/N ratio by MCT S/N ratio by TGS Concentration InGaAs detection detection detection of hydrogen element element element fluoride (integration of (integration of (integration of standard gas 50 times) 128 times) 128 times) 26.79 ppm 7.54 8.86 23.29 ppm 5.92 13.40 ppm 6.05 5.13 8.01 6.70 ppm 6.34 4.45 3.14 4.71 ppm 6.02 3.76 1.59 2.35 ppm 5.59 0.76 1.13 ppm 5.19 0.78 ppm 5.81 0.59 ppm 4.35 0.47 ppm 4.98 0.39 ppm 2.82

[0072] In Table 1, the S/N ratio can be improved in accuracy by increasing the number of times of integration in a Fourier transform step, but the measurement time is longer as the number of times increases. The following Table 2 shows the relationship between the number of times of integration and the measurement time when the Fourier transform infrared spectrophotometer was used.

TABLE-US-00002 TABLE 2 InGaAs MCT TGS detection detection detection element element element Integration 2 minutes 1 minute 3 minutes of 128 and 8 seconds and 58 seconds and 48 seconds times Integration 1 minute 59 seconds 1 minute of 64 times and 8 seconds and 52 seconds Integration 49 seconds 46 seconds 1 minute of 50 times and 28 seconds

[0073] As can be seen from Tables 1 and 2, by increasing the number of times of integration, the S/N ratio is improved, but more measurement time is required. For this reason, when efficient or quick measurement is required in process analysis or the like, it is necessary to avoid the number of times of integration from increasing more than necessary. Therefore, it can be understood that the use of the detector having the InGaAs detection element improves the measurement sensitivity and also enables quick measurement. In other words, it was confirmed that the detector having the InGaAs detection element had less noise and was able to analyze a trace concentration more than the detector having the MCT detection element and the TGS detection element.

[0074] In the above Table 1, a measurement result obtained by using the detector having the InGaAs detection element is shown as a calibration curve in FIG. 6. As described above, a highly accurate calibration curve having a determination coefficient R.sup.2=0.99 or more could be obtained.

[0075] From Table 1, a hydrogen fluoride standard gas was measured in combination of a Fourier transform infrared spectrophotometer having an InGaAs detector installed therein and a 0.10 m (10 cm) gas cell having no reflecting mirror therein, and as a result, quantitativity was observed up to 0.5 ppm for the hydrogen fluoride concentration. From this, it is estimated that it is possible to quantify up to 0.05 ppm when a 1.0 m gas cell is used for measurement.

[0076] From Table 1, as a comparative example, the gas cell used in Example 1 was used, the detector having the InGaAs detection element was changed to the detector having the MCT and TGS detection elements, the number of times of integration was changed to 128 which was 2.56 times of that in Example 1, and the hydrogen fluoride standard gas was measured. As a result, the lower limit of quantification of hydrogen fluoride was 6 to 7 ppm.

Example 3

[0077] By using the calibration curve obtained in Example 2, a corrosive gas (tungsten hexafluoride) containing hydrogen fluoride was measured.

[0078] FIG. 7 is a diagram showing the spectrum of hydrogen fluoride in tungsten hexafluoride. The horizontal axis (X axis) represents the wavenumber (unit: cm.sup.1), and the vertical axis (Y axis) represents the absorbance. Among these, the concentration of hydrogen fluoride was determined based on the wavenumber of 4047 cm.sup.1 which provided a highest peak of hydrogen fluoride, and it was 5.1 ppm.

[0079] As described above, it was possible to quantify a trace of impurities such as hydrogen fluoride of 1 ppm or less in a gas sample containing a corrosive component without a multi-reflection long optical path gas cell having a reflecting mirror therein. Since no reflecting mirror is used inside the gas cell, the durability of the analyzing device and the stability of the measurement (the influence of noise is small and reproducibility is excellent) are also enhanced. Further, no pretreatment is required.

INDUSTRIAL APPLICABILITY

[0080] According to the present invention, a method and a device can be provided which measure and analyze the impurities, hydrogen fluoride or the like in a corrosive gas containing halogen atoms.

EXPLANATION OF REFERENCE SIGNS

[0081] 1 Fourier transform infrared spectrometer [0082] 2 light source [0083] 3 beam splitter [0084] 4 movable mirror [0085] 5 fixed mirror [0086] 6 measurement cell [0087] 7 detector [0088] 8 information processing device [0089] 10 multi-reflection long optical path gas cell [0090] 11 reflecting mirror [0091] 12 gas cell [0092] 20 single-path gas cell [0093] 21 gas cell [0094] 22, 23 gas inlet or outlet