Field ionization mass spectrometric study of high molecular weight hydrocarbons in a crude oil and a solid bitumen

The occurrence of high molecular weight hydrocarbons in a selected solid bitumen (ozocerite) and a waxy yellow crude oil from the Uinta Basin (Utah) have been studied by field ionization-mass spectrometry (FIMS). The FIMS spectra consisted predominantly of molecular ions ranging up to near mass 2000, and correspond to several series of hydrocarbons ranging up to C110. The use of FIMS permits the range of hydrocarbons identified in geological materials to be extended far beyond that identified by the usual chromatographic techniques. Moreover, from the FIMS spectra it was possible to extract the molecular ions corresponding to series of hydrocarbons with different degree of unsaturation or ring closures (different Z-numbers). The ozocerite solid bitumen consisted mainly of series of branched alkanes (CnH2n+2) and cyclic alkanes (CnH2n and CnH2n−2) up to C110 with a predominance of monocyclic alkanes in the high molecular weight region (above C40). The waxy yellow crude oil, on the other hand, contained only acyclic compounds, mainly n-alkanes, ranging up to C100.