Sorption of polycyclic aromatic compounds to humic acid as studied by high-performance liquid chromatography

Aldrich humic acid was chemically immobilized to the silanol surface of a column material to be used for highperformance liquid chromatography (HPLC). The retention factors to the humic acid column material of 45 polycyclic aromatics compounds (PAC) were determined by HPLC. The PAC include PAH, N-, S-, O-PAC and substituted PAC (9-substituted anthracenes, bromopyrenes, and quinoline derivatives). The sorption coefficient of quinoline to humic acid was directly determined at different pH. The good correlation achieved between the HPLC retention factors and literature K-oc values, including the presented one of quinoline, was applied to determine K-oc of 39 other PAC. The determined K-oc values were parametrized with regard to size, ring heteroatoms, and steric and substituent effects and were compared with literature values of water solubility and recently determined octanol-water partition coefficients. It is shown that the sorption of PAC to humic a cid is not only affected by hydrophobic interactions but also by hydrogen and especially ionic bonds. The investigation shows that the application of humic acid stationary HPLC phases is a valuable supplement to other techniques for determination of K-oc.