Mixed-mode separation of polycyclic aromatic hydrocarbons (PAHs) in electrokinetic chromatography

A mixed-mode separation technique has been developed and optimized for the separation of the 16 Environmental Protection Agency (EPA) priority polycyclic aromatic hydrocarbons (PAHs). The procedure utilized two different buffer additives as pseudo-stationary phases with different selectivities towards the analytes. Sodium dioctyl sulfosuccinate (DOSS) displayed selectivities for PAHs which were somewhat similar to the C₁₈ phase in reversed-phase high performance liquid chromatography (HPLC). High acetonitrile content required for an effective separation prevented the formation of micelles as confirmed by fluorescence spectroscopy. Consequently, the separation could be attributed to the solvophobic association of the PAH molecules with hydrophobic chains of the DOSS surfactant. In another mode of separation, sulfobutylether-β-cyclodextrin (SB-β-CD) separated the 16 PAHs on the formation of inclusion complexes with the PAHs, and exhibited different selectivities for the PAHs compared to DOSS. SB-β-CD and DOSS were then combined in the running buffer to form a mixed pseudo-stationary phase for the separation of the 16 PAHs. Due to the different selectivities of SB-β-CD and DOSS for the PAHs, the separation of the 16 PAHs was appreciably improved compared to that using DOSS or SB-β-CD alone. All the 16 PAHs were baseline-resolved using an optimized running buffer containing 22.5 mM DOSS, 15 mM SB-β-CD, 15% acetonitrile and 5 mM hydroxypropyl-β-cyclodextrin in 6 mM berate at pH 9.