SUPERCRITICAL-FLUID EXTRACTION WITH CARBON-DIOXIDE FOR THE DETERMINATION OF TOTAL PETROLEUM-HYDROCARBONS IN SOIL

Supercritical fluid extraction (SFE) With CO2 Was used for the determination of total petroleum hydrocarbons (TPH) in real-world fuel-spill soil samples containing heavy fuel oil, diesel fuel, light crude oil, gasoline or kerosene (TPH content, mg g-1, approximately 150, approximately 15, approximately 15, approximately 9 and approximately 1 respectively). Quantitative extraction by SFE was accomplished at 40 MPa CO2 and 150-degrees-C extractor temperature, and TPH results were comparable (within standard deviations) with those obtained by Freon-113 Soxhlet extraction (4 h) for all samples except the soils containing gasoline and kerosene. SFE of the gasoline-contaminated sample extracted at 40 MPa CO2 and 65-degrees-C resulted in higher TPH quantities than those obtained from Soxhlet extraction (134% SFE vs. Soxhlet), owing to more efficient collection of BTEX (benzene, toluene, ethylbenzene and xylenes) and other volatile components with SFE. Comparable TPH results for the soil extracts were obtained from analyses using gas chromatography with flame ionization detection and infrared spectrometry. Quantitative reproducibility for replicate SFE extracts was good (r.s.d. 2-10%), and the quantity of Freon-113 solvent was reduced from 150 ml for Soxhlet to < 10 ml.