Cyclodextrin-Modified Capillary Electrophoresis:  Determination of Polycyclic Aromatic Hydrocarbons in Contaminated Soils

A separation method using cyclodextrin-modified capillary electrophoresis has been developed for analysis of the 16 U.S. EPA priority pollutant PAHs in contaminated soils. In this procedure, a mixture of negatively charged sulfobutyl ether-β-cyclodextrin (SBβCD) and neutral methyl-β-cyclodextrin (MβCD) was added to the running buffer, and separation was effected on the basis of differential distribution (partitioning) of the PAH components between the two CD types. Satisfactory separation of all 16 PAHs was achieved in under 20 min with 35 mM SBβCD and 15 mM MβCD, with efficiencies for all components greater than 105 theoretical plates, as expected for CE methods. Injection and electrophoresis methods were identified such that samples provided in dichloromethane were diluted 10−50-fold in methanol and injected directly. Laser-induced fluorescence detection provided sensitive detection of 11 of the 16 components, with detection limits measured typically in the low microgram per liter (ppb) range. Contaminated soil was extracted using CO2 supercritical fluid, and the extract was provided in dichloromethane, methanol, and a 50/50 mixture. The diluted extract was analyzed using fluorescence detection, and 10 of the 11 compounds were detected above the detection limit. HPLC was used to verify the concentration of six of these components, giving fairly good agreement, though with a possible systematic underestimation of the concentration by the CE method.