Retention behaviour of higher fluorinated polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography

The retention behaviour of 18 di-, tri- and tetra-fluorinated phenanthrenes, chrysenes and benzo[g]chrysenes in column liquid chromatography was studied for a monomeric and a polymeric octaclecyl-bonded silica phase. The retention times were much longer than those of the parent compounds and strongly dependent on the F-substitution pattern. The influence of geometric factors like calculated length-to-breadth ratios (LB ratios) and planarity, and electronic factors such as dipole moment and London forces was investigated. A linear correlation was found between the dipole moment and/or the degree of fluorination and the retention factor for the monomeric phase, and additionally between the maximum LB ratio and the retention factor for the polymeric phase. These findings are interpreted using the models of partition and the slot-model, respectively. Polyfluorinated polycyclic aromatic hydrocarbons are not very similar to parent PAHs and are, therefore, less suitable as internal standards in PAH analysis than the monofluorinated analogues especially in cases when the similarity of physicochemical properties is critical.