Combined modifier/in situ derivatization effects on supercritical fluid extraction of polycyclic aromatic hydrocarbons from soil

Abstract

Supercritical fluid extraction (SFE) of polycyclic aromatic hydrocarbons (PAHs) from a real environmental soil sample containing a high content of humic acids was enhanced by using modifier and in situ derivatization. The addition of 10 mol% methanol increased the ability of the supercritical CO 2 (recovery set to 100%) to displace PAHs from matrix active sites up to an average value of 145%. In situ derivatization was performed under dynamic SFE conditions using boron trifluoride (BF 3) in methanol as modifier. Comparing the results of the SFE extraction with methanol and with BF 3 in methanol showed that the addition of BF 3 increased the PAH recoveries further. Increasing BF 3 concentration gave higher extraction yields of PAHs. A second SFE of the same sample with CO 2–methanol improved the average extraction yield for only 2%, whereas a second SFE of a CO 2–methanol extracted sample with CO 2–methanol–BF 3 increased the average yield for 18%. Especially the recoveries of the penta- and hexacyclic PAHs were increased by the addition of BF 3. The results indicate that the strong Lewis acid BF 3 cleave humic substances of the matrix releasing aromatic acids in the extract which were detected by HPLC–diode array detection. As a result of this PAHs associated to the matrix were also released in the extract.