| 摘要 |
The invention comprises a mass spectrometer 1 and a method of mass spectrometry that is especially useful for the measurement of the isotopic composition of hydrogen in the presence of a helium carrier gas. Interference to the accurate measurement of the small HD+ peak at mass-to-charge ratio 3 by the much larger He+ peak at mass-to-charge ratio 4 is reduced by provision of an energy filter 35 in the ion detector assembly used to collect HD+ ions. This prevents ions of He+ which have lost energy through scattering, etc giving rise to a signal from the HD+ detector and distorting the deuterium hydrogen isotopic ratio measurement. Such a mass spectrometer 1 is typically used in conjunction with a continuous flow inlet system 4 based on an elemental analyzer that converts hydrogen present in a sample to gaseous hydrogen in a flow of helium carrier gas. Another embodiment of the invention provides a similar mass spectrometer useful for carbon or oxygen isotopic determinations in carbon dioxide gas.
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