Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 12/20/1995
Publication Date: N/A
Technical Abstract: Use of supercritical fluids (SF) to extract trace organics, such as pesticides, from soil is gaining increasing use in environmental analyses. For a given SF, solvent strength can be adjusted by varying the temperature and pressure, and by the addition of organic modifiers. By manipulating SF polarity and solvent strength, it is also possible to characterize the binding of pesticides to soil. For instance, using low density SF-CO2 to extract atrazine from the aqueous phase of field-moist soil, sorption coefficients could be measured; sorption Kd - 1.2, isosteric heat of sorption = -13.2 kcal mol**-1. This method can measure rapid desorption kinetics; desorption equilibrium was reattained within 7 min and there was no desorption hysteresis through removal of 25% of the atrazine in the system. Using SF-CO2 and SF-CO2/5% methanol with varying densities, it could be shown that the binding mechanism changed and became stronger the longer atrazine "aged" in soil.