Molecular weight distributions of asphaltenes and deasphaltened oils studied by laser desorption ionization and ion mobility mass spectrometry.

Laser desorption ionization (LDI) and ion mobility mass spectrometry (IM-MS) are applied to study molecular weight distribution and cross sections of petroleum asphaltene (ASPH) and deasphaltened oils (DAO). Ion mobility data confirmed the presence of gas-phase aggregation in LDI experiments. Most of the molecules with MW > 3000 g/mol in LDI result from gas-phase aggregation. Two-dimensional (2D) IM-MS trend lines are compared with model polymer systems to confirm the order of cross sections (polywax > polystyrene >> DAO > ASPH >> fullerenes), and these data illustrate that ASPH has a more condensed average structure than DAO.