Metal speciation analysis of petroleum: Myth or reality?

Metals occurring in crude oil in a great variety of complexed forms are minor but important constituents as they affect the refining and production operations, as well as participate in geochemical processes. These roles of metals are thought to be related to their chemical state the knowledge of which requires performing speciation analysis. While exact metal speciation in crude oil still remains obscure, earnest efforts to decipher it based on using up-to-date hyphenated techniques have been attempted in the past decade. With various levels of fractionation of vanadium and nickel species, liquid chromatography with ICP-MS detection allows for an insight into metal distribution in crude oil or its fractions, according to species molecular weight or polarity. Further speciation information on the metal coordination in a variety of porphyrin compounds can be gained by the use of Fourier transform ion cyclotron resonance mass spectrometry. Individual species of mercury are often available for quantification with gas chromatography-ICP-MS as the method of choice. This mini-review is aimed at revealing and giving rise to the development of those speciation strategies and approaches that can achieve the objectives of identification, characterization and determination of metal species in crude oil and its fractions.