SEDL / STP / STP1019-EB / STP18674S

Tandem Mass Spectrometry for the Determination of Trace Steranes in Crude and Shale Oils

Johnson, JV
Assistant research scientist and associate professor, University of Florida, Gainesville, FL

Yost, RA
Assistant research scientist and associate professor, University of Florida, Gainesville, FL

Wong, CM
Chemist, Lawrence Livermore National LaboratoryNASA, Ames Research Center, LivermoreMoffett Field, CACA

Pages: 12    Published: Jan 1989

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Abstract

Triple quadrupole tandem mass spectrometry (MS/MS) has been used to characterize the MS/MS behavior of five sterane standards and then to determine the sterane distribution in two shale oils and a crude oil without prior sample cleanup. Comparisons were made between electron ionization (EI) MS/MS and methane positive-chemical ionization (PCI) MS/MS of the sterane standards and the three oils. The EI-MS/MS of the molecular ions (M⁺) of the steranes was determined to be more sensitive and selective than PCI-MS/MS of the corresponding (M - H)⁺ ions. With solids probe/EI-MS/MS parent scan of m/z 217 (the most characteristic daughter ion for steranes), it was possible to obtain the sterane distribution in the three oils. However, due to chemical interferences, only the most abundant steranes could be confirmed by the complete EI-MS/MS daughter spectra of the detected molecular ions. In addition, severe contamination of the instrument resulted due to introduction of the oils into the vacuum system on the solids probe. Some sample cleanup would be beneficial in order to enhance the ability to detect low-level steranes and to prevent instrument contamination.