Indirect hydrogen monitoring by chemi-ionisation following an associative ionisation pathway after metastable helium atoms production by electron impact ionisation: Protonation and deuteration of carrier gas

•During hydrogen analysis unusual carrier gas protonation and deuteration are reported.•Hydrogen and deuterium are detected thanks to this phenomenon.•We investigate the possible mechanisms of ionisation to explain these signals.•Expected Penning ionisation is not the main channel of ionisation.

Gas chromatography (GC) is an analytical tool very useful to investigate the composition of gaseous mixtures. However, hydrogen (H2) detection after a GC separation is only possible with a Thermal Conductivity Detector (TCD), a Helium Ionisation Detector (HID) or expensive Atomic Emission Detector (AED). Recently, indirect H2 detection by GC coupled to mass spectrometry (MS) was demonstrated but the mechanism of carrier gas protonation remained unclear. With electron impact as ionisation source of MS and helium (He) as GC carrier gas, H2 is not ionised according the expected Penning ionisation neither according to the Associative ionisation. Rearrangement ionisation (RI) was found to be the main channel for H2 and D2 ionisation under GC–MS conditions used in most of laboratories using GC–MS, leading to the formation of [He−H]+ and [He−D]+ ions.

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