Supercritical Carbon Dioxide for Determining Atrazine Sorption by Field-Moist Soils
1996
Rochette, Elizabeth A. | Koskinen, William C.
Supercritical fluid extraction (SFE) with carbon dioxide (SF-CO₂) has been used effectively as a method for the extraction of pesticides from soils. This study was intended to test its potential as a means of removing atrazine from soil water for quantification, to allow calculation of sorption coefficients (Kds) of atrazine in soils having water contents below field capacity. Low-density SF-CO₂ removed atrazine from soil solutions without first requiring separation of the solution from the soil. The Kds obtained by the SF-CO₂ method for the topsoil and the lower root zone samples were 1.21 ± 0.04 and 1.14 ± 0.03, respectively, while that of the vadose zone soil was 0.16 ± 0.00. Desorption was rapid; equilibrium was reattained within 7 min. Desorption Kds for the topsoil and lower root zone soil were constant for successive desorption equilibrations, through removal of approximately 25% of the applied atrazine from the system. The SF-CO₂ method can be used to determine the effect of changes in water content and temperature on sorption. It was found that little atrazine can be extracted by the SF-CO₂ method from desiccated soil though large amounts of water (16%) caused a dramatic increase in the Kd values determined with SF-CO₂. The soil solution concentration at 4% soil water content related linearly to the inverse of the temperature (T, K) and the isosteric heat (ΔHᵢ) was determined to be −55.2 ± 1.7 kJ mol⁻¹. The SF-CO₂ method is promising as a technique to characterize herbicide sorption-desorption from field-moist soils.
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