The influence of terminal group and repeat unit structure on mass-mobility correlations observed for homologous series

Mass-mobility correlations were investigated by ion mobility-mass spectrometry (IM-MS) for 11 structurally-unique homologous series composed of commercially-available compounds. Structural variation involved the inclusion of different repeat units (i.e., glucose, propylene glycol, or ethylene glycol) in oligomeric series and different terminal groups in CH₂-homologous series. Terminal group structures included both aliphatic and aromatic acids, as well as aliphatic and aromatic amines. Mass-mobility correlations were also investigated for select CH₂-homologous series identified in a pyrolysis bio-oil and compared with results observed for commercial series. A linear mass-mobility correlation (R ² ≥ 0.996) was established for all series except those in which a substantial change in the gas-phase conformation of ions was probable. Slopes observed for CH₂-homologous series with a single terminal group were significantly steeper than slopes observed for series containing two terminal groups. Additionally, a correlation between slope and double bond equivalents (DBE) suggested that the CH₂-homologous series identified in bio-oil were structurally similar to commercial series containing two terminal groups.