The usefulness of a gas chromatograph and a mass spectrometer in tandem to analyze odor constituents is limited by the sensitivity of the mass spectrometer and by the large amount of helium carrier gas compared with the amount of sample. A time-of-flight mass spectrometer was fitted with a tightly enclosed source and operated in a continuous ionization mode to increase instrument sensitivity. A gate pulse was applied to the front end of the magnetic electron multiplier to eliminate the electrons due to the helium pulse before they reached the multiplier dynode strips. This procedure prevented saturation of the multiplier by the helium carrier gas.
W. K. Rohwedder, E. Selke, and E. D. Bitner, "Source and Multiplier Modifications of a Time-of-Flight Mass Spectrometer to Increase Sensitivity," Appl. Spectrosc. 18, 134-136 (1964)
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