Relationships of structures of nitro-polycyclic aromatic hydrocarbons with high-performance liquid chromatography retention order

Forty six structurally related nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) and their corresponding parent PAHs were employed to study the relationships between structure and HPLC retention time. Using reversed-phase HPLC, larger molecules had longer retention times, while saturation of the aromatic rings shortened the retention time. Isomers with a perpendicular nitro group had shorter retention times than if the nitro substituent was parallel to the ring system. The addition of a nitro group caused a substantial decrease in retention time when compared to its parent PAH. When using normal-phase HPLC, an additional benzo ring increased the retention time. The presence of one or two nitro groups on the molecule also increased the retention time, while saturation of a benzo ring decreased the retention time. These results suggest that the polarity of the PAH or nitro-PAH is the principal factor for determining its HPLC retention time.