High Resolution Mass Spectrometric View of Asphaltene–SiO2 Interactions

Asphaltene adsorption properties on mineral surfaces are fundamental to understanding wettability changes in rocks and fluid behavior in reservoirs. In this contribution we report an analytical approach to investigate the molecular features responsible for asphaltene–silica interactions. We used high performance thin layer chromatography silica plates and an elutropic series of solvents to fractionate asphaltenes according to their particular affinity with the mobile and stationary phases. We observed three characteristic asphaltene fractions (with R f ́s of 0, 0.69, and 0.90), which were in turn desorbed and analyzed by atmospheric pressure photoionization FT-ICR mass spectrometry (APPI-FT-ICR-MS). In general, polar noneluted compounds highly retained by the silica surface with R f = 0 exhibit molecular compositions with N 1, N n O o and O o ( o = 1, 2, 3 and n = 1, 2) classes and the lowest H/C ratios compared to the other subfractions. Polar CH 2 Cl 2:MeOH-eluted compounds, with R f = 0.69, have predominantly HC, N 1, N 3, N 1 O 1, N 3 O 1, N 3 O 2, O 1 S 1, O 1 S 2, and S 1 compound classes. Finally, toluene-eluted compounds with R f = 0.90 exhibit mostly N n O o S 1 and O o S 1 compound classes. We established trends between compound retention characteristics and molecular features such as aromaticity, heteroatom/C ratios, and degree of alkylation. Additionally, we show that fractionation of asphaltene samples on silica surfaces expose many species not observed when analyzing the whole asphaltene mixture by APPI-FT-ICR-MS.