INFLUENCE OF AGING ON THE SUPERCRITICAL-FLUID EXTRACTION OF POLLUTANTS IN SOILS

Soil samples were contaminated with several solutes, two means of cont amination being evaluated to obtain homogeneous samples, in order to s imulate real samples. The soils were allowed to age and periodically s ampled. Letting the samples dry in a hood for less than 1 day resulted in a dramatic decrease in the recoveries, owing to evaporation of the spiking solvent. The extraction became generally more difficult as th e ageing time increased, but the nature of both the solute and the soi l had a strong influence on the results. Hence, a phosphonate and a ph osphate were always quantitatively extracted, whereas aromatics were s trongly retained in a very organic soil. Increasing the temperature, a t constant pressure, greatly enhanced the extraction of all the invest igated solutes. Similar results were obtained by adding methanol (10%, v/v) to the supercritical carbon dioxide; however, in that event, the dynamic time must be chosen with care, otherwise part of the extracte d solutes is eluted from the trap by the polar modifier.