Abstract
Pyridine/water extracts of selected crude petroleums were separated by polarity on a high performance liquid chromatography (HPLC) octadecylsilane column (ODS) into three fractions; low, moderate, and high polar. The moderate and low polar fractions were examined by electron impact mass spectroscopy (EIMS) to elucidate structural and behavioral characteristics of vanadyl petroporphyrin and metallo-nonporphyrin compounds. The EIMS results indicated vanadyl petroporphyrins in Cerro Negro and Wilmington moderate polar fractions and possibly in the Wilmington low polar fraction. These EIMS results showed the presence of petroporphyrins in the above-mentioned fractions, but no discrete information about the metallo-nonporphyrins. A highly polar nickel fraction from a Wilmington crude petroleum pyridine/water extract, separated on the ODS column, was further purified on a cyano normal phase column. This fraction had a nickel concentration of approximately 15,000 wppm, and was examined by EIMS mass spectroscopy. The spectral results indicated several homologous series structures possible for the binding sites of nickel. Further examination of the same fraction by positive ion fast atom bombardment (FAB+) mass spectroscopy, using a metal ion exchange technique, showed a substantially simplified spectrum and indicated the possibility of the nickel binding sites being small molecular weight naphthenic (carboxylic) acid salts. Gilsonite, a bitumen, was analyzed by reversed-phase HPLC with graphite furnace atomic absorption (RP-HPLC-GFAA) element specific detection, which indicated that the nickel is predominantly bound as metallopetroporphyrin, while a small portion eluted as a highly polar metallo-nonporphyrin fraction. These results are important in the identification of nonporphyrin metal-containing compounds in heavy crude petroleums and residua and could be beneficial for future petroleum exploration as metallo-biomarkers.
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