Liquid chromatography of petroleum carbazoles

A method for isolating petroleum carbazole concentrates based on liquid chromatography on silica gel is described. The method includes developing with the eluent containing Et3N ( 30%) as an active component. A total carbazole concentrate was separated into C1, C2, C3 and C4 subfractions by means of reverse phase HPLC (Sepharon/C18 phase; elution with CH3CN/H2O, 7:3). Reverse phase HPLC separation of petroleum carbazoles was found to be governed only by the number of carbon atoms in the molecule, and is without structural selectivity. Each of C1, C2, C3 and C4 carbazole subfractions was fractionated into positional isomers by HPLC on silica gel. When hexane/Et3N/isopropanol (64:35:1) was used as the mobile phase the N---H exposed (with H-atoms at both C-1 and C-8) carbazoles eluted first followed by the shielded isomers (with substituents in at least the C-1 and C-8 positions).