Study of variables affecting extraction of organic solvents from solid sorbent sampling media using supercritical carbon dioxide

The extraction of four solvents from three sorbents, using supercritical carbon dioxide was studied. Toluene and isooctane were extracted from Anasorb 747®, a synthetic carbon; 1-butanol from silica gel; and 2-nitropropane from Anasorb 727®, a porous organic polymer. Preliminary experiments indicated that dynamic extraction was required; these experiments also fixed the duration of extraction of the analytes. All extractions were performed at 1.0 mL min−1. The temperature and density of the supercritical extraction fluid were then varied, according to a fractional factorial statistical design. The amounts remaining on the sorbent were determined via solvent desorption of the analytes and gas chromatography of the eluents. The fraction extracted data were modeled as a function of temperature and density according to a thermodynamic approach that permitted computation of constant-density enthalpies of desorption. This study indicates a significant temperature- and density-dependence for quantitative extraction of isooctane and toluene from Anasorb 747®and 1-butanol from silica gel, with no measurable temperature-or density-dependence for extraction of 2-nitropropane from Anasorb 727®. The extracted analytes were also collected via cryotrapping; only higher level masses of 1-butanol were quantitatively recovered. The dependence of the extraction efficiency on the thimble volumes passed over the matrix is discussed.