Na4EDTA-assisted sub-/supercritical fluid extraction procedure for quantitative recovery of polar analytes in soil
Guo, Fengmao, Qing X. Li, and Jocelyn P. Alcantara-Licudine
Supercritical carbon dioxide (SC-CO2) is effective in extracting nonpolar and slightly polar chemicals from soils. However, pure SC-CO2 is unsatisfactory for recovering polar chemicals in soils. A simple supercritical fluid extraction (SFE) procedure was developed to quantitatively recover polar and nonpolar chemicals from soils. The polar chemicals tested were aromatic acids and phenols. The nonpolar and slightly polar chemicals used as model compounds were common pesticides and environmental pollutants such as polycyclic aromatic hydrocarbons. The procedure required pretreatment of the samples with 15% water (g/g), 5% (ethylenedinitrilo)-tetraacetic acid tetrasodium salt (Na4EDTA)(g/g), and 50% methanol (ml/g) prior to extractions using SC-CO2 at 60oC and 34.5 MPa. Recoveries ranged from 90% to 106% for the aromatic acids using Na4EDTA-assisted SFE compared with only 7% to 63% recoveries of the corresponding chemicals when no Na4EDTA was used. The method quantitatively extracted 2,4-D and its close analogues aged in the soil for 2 to 30 days. The Na4EDTA-assisted SFE was also adequate for extracting phenolic analytes, including picric acid and pentacholorophenol, with recoveries from 85 % to 104%. Na4EDTA is a good enhancer for extraction of the 29 analytes representing a wide range of polarity from the soil using SC-CO2. The method is valuable for the analysts of parent pollutants and transformed products, particularly oxygen-borne metabolites in the environment.