For many gas species (e.g., He, Ar, Kr, N₂, O₂, CO₂) the partial pressures measured with the miniRUEDI can usually be calibrated by simple peak-height comparison relative to ambient air or gas standard with well known partial pressures. However, depending on the composition of the analysed gases, the ion currents measured at certain m/z ratios may result from overlapping ion currents of multiple species.

We developed a method that extends the miniRUEDI peak-height comparison in order to resolve such overlap interferences. The method uses spectral deconvolution and was incorporated in the ruediPy software toolbox. The deconvolution method substantially improves the analytical accuracy in situations where mass-spectrometric interferences cannot be avoided.

Full details are availalble in the original publication: M.S. Brennwald, Y. Tomonaga, R. Kipfer: Deconvolution and compensation of mass spectrometric overlap interferences with the miniRUEDI portable mass spectrometer, MethodsX, 2020, doi: 10.1016/j.mex.2020.101038

Some typical examples for such overlap interferences:

• Methane (CH₄): The main CH₄ peaks occur at m/z = 15 and 16, which are affected by interference signals from ¹⁵N, ¹⁶O, and doubly ionised O₂ molecules.
• Neon (Ne): The peaks of the main Ne isotopes (at m/z = 20 and 22) overlap with those of isotopically heavy H₂O and the peaks of doubly ionised Ar and CO₂.
• Propane (C₃H₈), ethane(C₂H₆), or similar hydrocarbons in air-like samples: some peaks of the hydrocarbon mass spectra tend to overlap those of N₂ and CO₂.
• Hydrogen (H₂): the the mass-spectrometric peak of the H₂ in the sample gas may be masked by H₂ produced in the ion source of the mass spectrometer. Ionisation of molecules containing hydrogen may “knock off” one or multiple H atoms, which then interfere with the analysis of the H₂ in the sample gas. H₂ analysis therefore works best if the concentration in the sample gas is high (about 1‰ vol/vol or higher), and the concentrations of H-containing gas species is low.