LIQUID-CHROMATOGRAPHIC SEPARATION SCHEMES FOR PYRROLE AND PYRIDINE NITROGEN AROMATIC HETEROCYCLE FRACTIONS FROM CRUDE OILS SUITABLE FOR RAPID CHARACTERIZATION OF GEOCHEMICAL SAMPLES

The use of a polar aminocyano-bonded silica HPLC column (PAC) for the class separation of nitrogen compounds in crude oils is described. Elution of deasphalted oils with solvents of a composition gradient yielded well-defined pyrrole and pyridine nitrogen fractions which were characterized by gas chromatography in conjunction with flame ionization detection (FID), nitrogen phosphorus detection (NPD), and mass spectrometry (MS). Comparison is made with two open column chromatographic methods previously reported in the literature. The new separation schemes reported here have made it possible to identify more easily the isomeric nitrogen compounds, particularly the pyrrole nitrogen species. On the basis of comparison of crude oils with their potential source rocks, possible maturation and migration related fractionations of hindered and less hindered alkylcarbazole and benzocarbazole isomers are observed.