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Study of variables affecting extraction of organic solvents from solid sorbent sampling media using supercritical carbon dioxide.
Chromatographia 1996 Jun; 42(11/12):665-674
Conditions required for the extraction of four solvents characteristic of agents encountered in industrial hygiene sampling from three different sorbents were examined using an off line supercritical fluid extraction procedure. Toluene (108883) and isooctane (540841) were extracted from Anasorb-747, 1-butanol (71363) was extracted from silica gel, and 2-nitropropane (79469) was extracted from Anasorb-727; supercritical carbon-dioxide (124389) was used for all extractions. The effects of mode of extraction, temperature, density, and contact time of the supercritical fluid with the sorbent on the extraction process, were considered. Dynamic extractions were used as the extraction mode based on preliminary studies. The extraction of 2-nitropropane did not demonstrate measurable dependence on any of the factors studied. Dynamic extraction periods of 40 minutes were required to obtain quantitative recoveries of the other compounds. The logarithm of the fraction extraction could be generally modeled as a function of the reciprocal temperature and the logarithm of the density. The analyte and matrix used in the extraction were the primary factors affecting the fraction extracted, although a significant temperature and density dependence was also identified. The authors conclude that these results support previous findings of a reduction in the enthalpy required for supercritical fluid extraction of an analyte from a matrix relative to the enthalpy of vaporization of the analyte with the reduction increasing with the density of the supercritical fluid.
NIOSH-Author; Analytical-methods; Laboratory-techniques; Organic-solvents; Temperature-effects; Chemical-extraction; Solvent-extraction; Author Keywords: Supercritical fluid extraction; Supercritical CO2; Thimble volumes; Thermodynamic model; Desorption enthalpy
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