Submitted to: International Association of Environmental and Analytical Chemistry
Publication Type: Abstract Only
Publication Acceptance Date: September 7, 1995
Publication Date: N/A
Technical Abstract: Methods commonly used to obtain sorption coefficients require that the soils be above field capacity moisture content so that the aqueous phase containing the herbicide to be quantified can be separated from the soil. We have developed a system using supercritical fluid CO2 that can remove herbicide from soil solution of unsaturated soil without first separating the solution from soil. Measured atrazine Kd values for a sandy soil profile at 4-5% moisture were: surface soil 1.21, lower root zone soil 1.14, and vadose zone soil 0.16. This method can measure rapid desorption kinetics; desorption equilibrium was reattained within 7 min and desorption Kds were constant, i.e. no desorption hysteresis, through removal of approximately 25% of the atrazine in the system. This system can easily determine the effect of temperature on herbicide sorption at low water contents. Atrazine soil solution concentrations at 4% moisture were linearly related to the inverse of the temperature (degree K) and the isosteric heat sorption (delta Hi) was determined to be -13.2 kcal mol**-1. These results indicate that selective use of supercritical fluids can be used to characterize sorption-desorption at low water contents in addition to increasing use for extracting herbicides from soil.