DIRECT COMPARISON OF SOXHLET AND LOW-TEMPERATURE AND HIGH-TEMPERATURE SUPERCRITICAL CO2 EXTRACTION EFFICIENCIES OF ORGANICS FROM ENVIRONMENTAL SOLIDS

Supercritical fluid extraction (SFE) with pure CO2 was used at 50, 200, and 350 degrees C to extract PAHs, N- and S-heterocyclics, chlorinated phenols, and pesticides from a variety of soil and soot samples. The extraction efficiencies were directly compared to those obtained using 18 h of Soxhlet extraction with identical analysis methods. While SFE efficiencies at 50 degrees C (30 min) typically were lower than Soxhlet (18 h) recoveries, SFE at 200 degrees C generally gave good quantitative agreement with Soxhlet extraction. Further increases in SFE temperature to 350 degrees C did not yield increased recoveries (except for PAHs from the soot sample), but did show evidence of causing thermal degradation of some species (particularly aromatic amines), and the possible production of some PAHs. The increases in SFE extraction efficiencies observed at 200 and 350 degrees C were not explained by volatility considerations alone, since thermal desorption at these temperatures did not yield recoveries as high as SFE.