| 摘要 |
PROBLEM TO BE SOLVED: To measure the concentration of a trace impurity such an oxygen in a high purity gas with high sensitivity and high precision by quickly regulating the ionizing part of a mass spectrometer to an optimum pressure. SOLUTION: A gas inlet passage 4 and a gas discharge passage 5 connected to an ionizing part 1 have mass flow controllers 21, 22, respectively, so that the internal pressure of the ionizing part 1 can be set to a desired pressure higher than the atmospheric pressure while confirming the pressure displayed on a pressure gauge 23. Calibrating gases of 10ppb of oxygen, carbon dioxide and moisture in nitrogen are generated, respectively, and the ion intensities in a pressure, for example, from the atmospheric pressure (10<5> Pa) to 3.3×10<5> Pa are measured. At a result, the sensitivities are increased as the pressure becomes high, the sensitivity of oxygen is about 15 times, compared with the atmospheric pressure, and those of carbon dioxide and moisture are 13 times and 10 times, respectively. Further, the fluctuating coefficient (standard deviation/average value×100)% is minimized as the pressure of the ionizing part 1 is increased, which shows that a highly precise analysis can be performed.
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