Qualitative and quantitative analysis of dibenzothiophene, its methylated homologues, and benzonaphthothiophenes in crude oils, coal, and sediment extracts.

Polycyclic aromatic sulfur heterocyclics (PASHs) consist mainly of thiophene class compounds, and are the most important organosulfur compounds in crude oils and sediment extracts. Dibenzothiophene (DBT) and its methylated homologues were identified on mass chromatograms by comparison with retention indices published in the literature. Some isomers of dimethyldibenzothiophene and trimethyldibenzothiophene that were tentatively identified in previous reports have been determined here by comparison with calculated retention indices and taking the substitution pattern of the methyl groups into account. The response factors relating that of dibenzothiophene to internal standards were obtained by GC-MS analyses of mixture solutions with different concentration ratios. We concluded that DBT-d8 (octadeutero-dibenzothiophene) is the optimal internal standard for quantitative analyses of the thiophene compound class in oils, coal, and sediment extracts. Calibration experiments for each class of compounds are absolutely necessary when quantifying polycyclic aromatic hydrocarbons and other heterocyclics with a stable isotope labeled internal standard.