| 摘要 |
PURPOSE:To prevent a detector from deteriorating in sensitivity by inhibiting ions of an unnecessary gas component from reaching the detector. CONSTITUTION:A mass scan is made repeatedly and continuously and a mass spectrum is measured to perform mass spectrometry, but the object of this mass spectrometry is an extremely small amount of impurity gas and main component gas is unnecessary for the mass spectrometry. For the purpose, data on unnecessary main component gas other than the object gas is inputted previously to a control circuit 16 and when unnecessary gas is admitted to an ion source 4, a control signal is supplied from the circuit 16 to an aperture power source 14 for a mass scan time corresponding to the mass range of the unnecessary gas. Then a voltage for stopping ion passage is applied to at least either of an ion projection part 8 and an ion incidence part 10 to prevent ions of unnecessary gas components from reaching the detector 6, which is therefore prevented from deteriorating in sensitivity.
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