ABSTRACT
The use of biomarkers as an aid to petroleum exploration is well documented in the literature. Normally biomarker distributions are determined by gas chromatography-mass spectrometry (GC-MS) using single ion monitoring and multiple ion detection. The GC step generally requires fractionation of the sample prior to analysis. This paper describes an alternative and rapid method to determine the distribution of biomarkers in unfractionated crude oils. The method uses tandem mass spectrometry (MS/MS) and involves the monitoring of parent/daughter ion relationships for various groups of biomarkers. The resulting parent ion distributions permit a rapid screening of oils to determine those derived from similar or different sources. Major advantages of the method are speed of analysis, no requirement for fractionation, and ability to determine distributions of different classes of biomarkers which are not readily separable by GC-MS. A major disadvantage is the inability to resolve stereoisomers. However the rapidity of the analysis means that after the initial screening only a relatively small number of samples need to be analysed by GC-MS or GC-MS/MS. This paper describes examples of the various biomarker distributions in crude oils as determined by MS/MS and GC-MS/MS. It also demonstrates that many classes of biomarkers extend far above the carbon number range previously determined by GC-MS alone.
