Chapter 3 Separation methods in the analysis of polycyclic aromatic sulfur heterocycles

Abstract

Compounds containing a sulfur atom in an aromatic ring are derivatives of thiophene and are called polycyclic aromatic sulfur heterocycles (PASH). The simplest member of this class of compounds is benzothiophene which corresponds to naphthalene. In organic geochemistry, PASHs and their alkyl derivatives yield information on important parameters such as the maturity of a crude oil. Polar bonded phases, especially aminopropylsilane phases, are extensively used in normal-phase liquid chromatography of polycyclic aromatic compounds (PACs). Sulfur heterocycles with a terminal thiophene ring elute somewhat later than the corresponding polycyclic aromatic hydrocarbons (PAHs). Thus benzothiophene elutes after naphthalene, and the three naphthothiophenes, possessing a terminal heterocyclic ring, appear after the corresponding PAH, phenanthrene. Alkylation has only a small effect on the retention on aminopropylsilane phases, smaller than on silica and alumina. Two main routes are employed for the group separation of PAHs and PASHs—(1) the oxidation of the sulfur aromatics to their sulfones followed by a chromatographic separation in the normal-phase mode; and (2) the complexation with palladium chloride deposited on silica gel.