EXTRACTION OF POLYCYCLIC AROMATIC HYDROCARBONS FROM SOIL USING WATER UNDER SUBCRITICAL CONDITIONS

Abstract

Water under subcritical conditions (250°C, 4100 kPa) was used to extract polycyclic aromatic hydrocarbons (PAHs) from a Mexican hydrocarbon-contaminated soil. Extraction was carried out by continuously circulating the solvent through the sample contained in an extraction cell. After extraction, the non-extracted PAHs were eluted from the soil and then analyzed by high performance liquid chromatography. The elution and subsequent analysis were carried out by directly coupling the extraction cell, through a switching valve system, to a liquid chromatograph. The elution and analysis process takes place in a closed system that allows a fast, precise, and highly sensitive quantification of the studied compounds. Additional extraction experiments with spiked samples (silicon dioxide and nonpolluted soil) were carried out in order to asses the performance of the method. Extraction recoveries ranged from 95 to 100% with an average uncertainty of ±1.2%. In some cases it was possible to quantitatively extract PAHs at concentrations as high as 8522 mg· kg ^{− 1} .

Keywords:

• Anthracene
• 9,10-dihydroanthracene
• silicon dioxide
• soil
• subcritical water extraction

This work was supported by Instituto Mexicano del Petróleo under Research Projects D.00406 and I.00348. E. M. thanks the Consejo Nacional de Ciencia y Tecnología (CONACyT-México) for a research assistantship. The authors thank Mr. M. A. Ávila-Chávez for carrying out the Soxhlet extractions and for providing the soil samples.

Notes

^a 1:2 soil:water (w/v).

^a Mass of solvent used in the extraction experiment.

^b Concentration of the PAHs spiked in the solid matrix (mg of PAH per kg of silicon dioxide or per kg of soil).

^c Average of seven independent determinations.

^d Mixtures A, B, C and D are binary mixtures of anthracene +9,10-dihydroanthracene; the mass fraction of anthracene in each mixture was 4.36% (mixture A), 50.57% (mixture B), 91.75% (mixture C), and 5.27% (mixture D).

^e Average of three independent determinations. In all the experiments the average mass of solid matrix loaded into the column was 0.0950 g.

^a Hexane extractable material, as determined by EPA method 9071B (triplicate determination).

^b Determined from HPLC analysis (fluorescence detection) after Soxhlet extraction (16-h, 1:6 (v/v) toluene:methanol mixture; average of triplicate determinations).