The influence of operating conditions on the evaluation of biological marker compound distributions in petroleum geochemistry by gas chromatorgaphy and gas chromatography/mass spectrometry

The effects of the operating conditions for gas chromatoraphy and gas chromatography/mass spectrometry (g.c./m.s.) on the observed distributions of biological marker compounds in petroleum are considered. Resolution and the accuracy and precision of quantification were investigated for components of geochemical significance. Methylsilicone stationary phases were generally suitable for aliphatic biomarker analysis, although some components co-eluted on these phases. The inclusion of ca. 5% phenyl groups into methylsilicone phases provided improved resolution of certain alkane biomarkers, and also allowed satisfactory analysis of classes of aromatic biomarker compounds. Vaporising and non-vaporising injection techniques in g.c./m.s. were compared for accuracy and reproducibility of relative component quantification. Cooled on-column injection wa found to be the most suitable technique in biomarker analysis. The effect of long-term variation in the operating conditions for the spectrometer on the reproducibility of quantification data was found to be at least as significant as the effect of the sample injection technique.