CHARACTERIZATION OF NAPHTHENIC ACIDS IN PETROLEUM BY FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

The naphthenic acids in petroleum are considered a class of biological markers. Their potential use in source correlation and as an indicator of biodegradation has been reported in the past. Their presence in waste water at refineries also causes corrosion problems and fish toxicity. Due to their highly complicated nature, detailed characterization of the acids has been difficult. Two newer mass spectrometric methods were recently developed at Shell to analyze the acid components, namely fluoride ion chemical ionization and negative ion fast atom bombardment mass spectrometry (FABMS). This report demonstrates that FABMS is a simple and efficient approach for analyzing the naphthenic acids, including the heavy, higher molecular weight components. The components are characterized on the basis of group type and carbon number distributions. A comparison of FAB and CI results show that the group type distributions obtained from both methods agree surprisingly well. The geochemical implication of the naphthenic acids is investigated by using a set of well-characterized crude oil samples. It is found that the naphthenic acid distribution can be used as a fingerprint for correlating the sources of oils and source rocks.