Simple column chromatography separation procedure for polycyclic aromatic hydrocarbons: controlling factor(s)

The present study proposes a simple one-step column and less reagent-consuming experimental procedure for separating aromatic hydrocarbons, especially polycyclic aromatic hydrocarbon compounds (PAHs), in crude oils. Thus, the research aimed to determine the best and reliable column chromatography technique and identify the main controlling factor (s) a successful PAHs separation into sub-fractions. We found that the choice of the type of column is the requirement for a successful column chromatography separation. Using alumina and silica-alumina at a ratio of 1:1 for the separation of the aromatic fraction of crude oil from the Termit basin (Niger) into sub-fractions, our analysis revealed that, less time also less reagent-consuming, silica-alumina (1:1) column is chosen to be the best among the two columns (alumina and silica-alumina 1:1) for separating PAHs into various sub-fractions. Apart from the type of column, we found that the diameter of alumina pores is the main factor controlling a successful separation of the aromatic compounds into sub-fractions. This factor controls the time and the volume of reagent ratios necessary. Thus, using the following consecutive ratios of petroleum ether:dichloromethane at 93:7 (6 ml), 90:10 (30 ml), and 75:25 (20 ml), respectively mono-aromatic, di-aromatic, and tri-aromatic sub-fractions were successfully recovered, whereas further addition of 12 ml of pure dichloromethane effectively recovers compounds with more than 3 aromatic rings. Finally, stable carbon isotope data obtained in this current study confirmed that the procedure proposed here provides a reliable stable carbon isotope measurement of individual PAH with an average standard deviation of 0.5‰.