Evaluating the effect of ion source gas (N2, He, and synthetic air) on the ionization of hydrocarbon, condensed aromatic standards, and paraffin fractions by APCI(+)FT-ICR MS
Article
Souza, LM, Tose, LV, Cardoso, FMR et al. (2018). Evaluating the effect of ion source gas (N2, He, and synthetic air) on the ionization of hydrocarbon, condensed aromatic standards, and paraffin fractions by APCI(+)FT-ICR MS
. 225 632-645. 10.1016/j.fuel.2018.03.180
Souza, LM, Tose, LV, Cardoso, FMR et al. (2018). Evaluating the effect of ion source gas (N2, He, and synthetic air) on the ionization of hydrocarbon, condensed aromatic standards, and paraffin fractions by APCI(+)FT-ICR MS
. 225 632-645. 10.1016/j.fuel.2018.03.180
This study aimed to use different types of ion source gases [synthetic air, nitrogen (N2), and helium (He)] to compare the ionization efficiency of linear, branched, and cyclic hydrocarbon (HC) standards (i.e., hexatriacontane, squalene, and 5-α-cholestane, respectively), condensed aromatics (CA) standards (i.e., coronene, benz[a]anthracene, and n,n′-bis(3-pentyl)perylene-3,4,9,10-bis(dicarboximide)), one n-paraffin standard, containing carbon numbers ranging from C5 to C120, and two saturated HC fractions. In all cases, a positive-ion mode atmospheric pressure chemical ionization coupled to a Fourier transform ion cyclotron resonance mass spectrometer was used. Isooctane reagent was used to facilitate the ionization of n-paraffins. Three ionization mechanisms were observed: electron transfer ([M]rad+), proton transfer ([M+H]+), and hydride abstraction ([M−H]+). For the ionization of HC standards, synthetic air and He gases presented better ionization efficiency and produced mass spectra with greater mass accuracy and signal-to-noise rate. Moreover, linear HCs were preferentially ionized through hydride abstraction (production of [M−H]+ ions), whereas the ionization of unsaturated and cyclic HCs mostly occurred through the production of [M+H]+ and [Mrad+] species. The unique exception is related to 5-α-cholestane, which is ionized as [M−H]+ in the presence of synthetic air. For the CA standards, N2 and synthetic air promoted the detection of CA standards mainly by electron transfer mechanism, [M]rad+ species. Conversely, He favored the proton transfer ionization ([M+H]+) with minimal fragmentation or oxidation of the analyte. In all cases, synthetic air provided mass spectra with excellent signal-to-noise ratio. This performance was attributed to the high reactive-ionizing power of O2 gas over the HC and CA molecules. For the n-paraffin samples, synthetic air and He provided better ionization performance through hydride abstraction ([M−H]+). N2 favored the production and ionization of heteroatomic compound classes (Ox and NOx).
