FACTORS CONTROLLING QUANTITATIVE SUPERCRITICAL-FLUID EXTRACTION OF ENVIRONMENTAL-SAMPLES

The development of quantitative supercritical fluid extraction (SFE) m ethods for the recovery of organic pollutants from environmental sampl es requires three steps: quantitative partitioning of the analytes fro m the sample into the extraction fluid, quantitative removal from the extraction vessel, and quantitative collection of the extracted analyt es. While spike recovery studies are an excellent method to develop th e final two steps, they are often not valid for determining extraction efficiencies from complex real-world samples such as soils and sedime nts, exchaust particulates, and sludges. SFE conditions that yield qua ntitative recoveries of spiked analytes may recover <10% of the same a nalytes from real-world samples, because spiked pollutants are not exp osed to the same active sites as the native pollutants. Because of the heterogeneous nature of environmental samples, the partitioning step may be controlled by analyte solubility in the extraction fluid, kinet ic limitations, and/or the ability ot the extraction fluid to interrup t matrix-analyte interactions. While the interactions that control SFE rates from heterogenous environmental samples are not well understood , a generalized scheme for developing quantitative SFE methods is prop osed based on interactive considerations of the collection efficiencie s after SFE, fluid flow parameters in the extraction cell, analyte sol ubility, extraction kinetics, and analyte-matrix-extraction fluid inte ractions. The proposed development scheme includes increasing SFE extr action rates by the use of more polar fluids than CO2 such as CHClF2, the addition of organic modifiers to CO2, and the use of high temperat ure extractions with pure CO2. Validation of quantitative extractions based on multiple extraction methods (SFE followed by liquid solvent e xtractions) is also described.