Coupling Supercritical CO2 and Subcritical (Hot) Water for the Determination of Dacthal and Its Acid Metabolites in Soil

Abstract

Dacthal and its mono- and diacid metabolites were sequentially extracted from soils by first performing a supercritical carbon dioxide extraction to recover Dacthal, followed by a subcritical (hot) water extraction step to recover metabolites. Dacthal was recovered from soil in 15 min by supercritical carbon dioxide at 150 °C and 400 bar. The mono- and diacid metabolites were extracted from soil in 10 min under the subcritical water conditions of 50 °C and 200 bar. The metabolites were trapped in situ on a strong anion-exchange disk placed over the exit frit of the extraction cell. Metabolites are combined with Dacthal by placing the disk into the GC autosampler vial containing the SFE extract. The metabolites then are simultaneously eluted from the disk and derivatized to their ethyl esters by adding 100 μL of ethyl iodide and heating the vial at 100 °C for 1 h. Using this approach, only a single sample is analyzed, and because the disk-catalyzed alkylation reaction does not transesterify Dacthal, the speciation of Dacthal is maintained. In addition, no sample cleanup steps are required, the use of diazomethane for derivatization is avoided, and the method consumes a total of 5 mL of nonchlorinated organic solvent.