Determination of polycyclic aromatic sulfur heterocycles in fossil fuel-related samples

An analytical method is described for the separation, identification, and q uantification of a number of polycyclic aromatic sulfur heterocycles (PASHs ) in three fossil fuel-related samples including two Standard Reference Mat erials (SRMs), SRM 1597 (coal tw) and SRM 1582 (petroleum crude oil), and a decant oil. The compounds measured include the 3 possible naphtho[b]thioph enes; dibenzothiophene and selected methyl-, ethyl-, dimethyl-, and trimeth yl-substituted isomers; the 3 possible benzo[b]naphthothiophenes; and the 3 0 methylbenzo[b]naphthothiophenes isomers. Because of the occurrence of pol ycyclic aromatic hydrocarbons and PASHs together with their large number of possible alkyl-substituted isomers, the analytical method described requir es a number of prerequisites: effective sample cleanup, selective stationar y phases, and selective methods of detection. The sample cleanup involves s olid-phase extraction using aminopropylsilane cartridges with different sol vent mixtures followed by normal-phase liquid chromatographic isolation of the PASHs based on the number of aromatic carbons. These aromatic ring frac tions are then separated by capillary gas chromatography using two stationa ry phases with different selectivities, 5% phenyl-substituted methylpolysil oxane stationary phase and 50% phenyl-substituted methylpolysiloxane statio nary phase, and analyzed with mass-selective detection and atomic emission detection. A liquid crystalline stationary phase was also used to separate the methylbenzo[b]naphthothiophene isomers in the crude oil sample. Advanta ges and limitations of each chromatographic and detection technique are dis cussed.