ANALYTICAL METHOD FOR THE SORPTION OF HYDROPHOBIC ORGANIC POLLUTANTS IN CLAY-RICH MATERIALS

A method using dialysis tubing for phase separation was developed for measuring nonionic, hydrophobic organic compound sorption in clay-rich geologic media such as aquitards. The complications caused by nonsettling particles when centrifugation is used for phase separation are eliminated. Slurried sample was sealed in the tubing and placed into a sample bottle, which was filled with synthetic groundwater amended with the sorbate of interest. Particles are retained within the tubing during equilibration, whereas the sorbate may diffuse through the tubing yielding equal aqueous-phase concentrations inside and out. Following equilibration, the aqueous phase outside the tubing was analyzed, and sorbed mass was determined by difference. Equilibration occurred within 48-72 h. Analyte loss through the Teflon-lined septa was shown to be proportional to concentration and ac counted for less than or equal to 6% of the total analyte mass when the sorbed mass fraction accounted for 26-82%. Pentane extraction of selected samples showed comparable mass recoveries in samples and soil-free controls.