Tandem-cartridge solid-phase extraction followed by GC/MS analysis for measuring partition coefficients of association of polycyclic aromatic hydrocarbons to humic acid

A tandem-cartridge solid-phase extraction system combining reversed-phase separation and dynamic ion exchange followed by GC/MS analysis was studied for measuring partition coefficients (K-doc) Of association Of polycyclic aromatic hydrocarbons (PAHs) to humic acid. Time course batch experiments revealed that the association of PAHs to humic acid included a slow stage with equilibrium time of 5-7 days. The disequilibrium and retention of the PAH-humic acid associate during reversed-phase separation lead to systematic negative error for the measured partition coefficients; more accurate results were achieved with a three-cartridge tandem system in which the negative error was assessed and corrected via the PAH analytes measured on the second reversed-phase cartridge. The potential and advantages of use of C-18 disk cartridges instead of conventional C-18 cartridges to set up the tandem sq-stern for measuring the partition coefficients were also studied. With the tandem-cartridge system, the measured partition coefficients did not change with most experimental conditions, but a trend of decreasing partition coefficients with humic acid concentration was observed, implying possible nonlinear association of the PAHs and humic acid.