Determination of hydrocarbon types in petroleum and coal-derived products by thin-layer chromatography/densitometry

Different methodologies based on thin-layer chromatography (TLC)/densitometry were used to separate and quantitate hydrocarbon types in middle distillates (gas oil), heavy distillates (lubricant) from petroleum, and coal-derived products. Thus, petroleum products were separated into saturates and aromatics by development, using n-hexane (9 min) followed by dichloromethane (4.5 min), of silica gel plates impregnated with berberine sulfate. Detection of saturates and aromatics was performed by fluorescence scanning using 365 nm as the excitation wavelength. Alternative detection of aromatics can be performed on either silica gel or berberine-impregnated plates by using ultraviolet (UV) densitometry at 250 nm. On the other hand, polar coal-derived products were separated into aromatics, polar compounds, and uneluted components by using silica gel plates and development with toluene (12 min), followed by dichloromethane-methanol (95 + 5, v/v), with detection by UV densitometry at 250 nm. In all cases, external standard calibration was used for quantitation. Results were validated by using standard methods or well-established techniques of the petrochemical industry. The potential usefulness of TLC/densitometry is discussed.