Characterization of Dissolved Metals and Metallic Nanoparticles in Asphaltene Solutions by Single-Particle Inductively Coupled Plasma Mass Spectrometry

Even though evaluating the metal content in asphaltenes is now a routine analysis, determining the nature of the metals present in asphaltenes has continued to be an elusive subject. In this work, we presented, for the first time, the application of single-particle inductively coupled plasma mass spectrometry (spICP MS) in hydrocarbon media to determine the presence of metal-containing nanoparticles in asphaltene solutions. This method also offers the unique ability to differentiate between metal-containing nanoparticles and dissolved metals. The study of three asphaltene samples from different origins indicates that vanadium and nickel are entirely dissolved probably as part of soluble coordination complexes, such as porphyrins. In clear contrast, we found that molybdenum and iron are forming part of nanoparticles and report nanoparticle distributions. We found that nanoparticle distributions for molybdenum are very similar for the different asphaltenes, while for iron oxide, the size increases as the content of this metal in the sample increases. Relative concentrations of these metals in nanoparticles indicate that most molybdenum is present as soluble compounds in the organic medium, while iron is predominantly forming nanoparticles. This study demonsttates the applicability of spICP MS in hydrocarbon media as a potential and routine technique to characterize metals in asphaltenes, crude oils, and petroleum-derived materials.