Coupling supercritical CO2 and subcritical (hot) water for the determination of Dacthal and its acid metabolites in soil

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 mas recovered from soil in 15 min by supercritical carbon dioxide at 150 degrees C and 400 bar. The mono-and diacid metabolites were extracted from soil in 10 min under the subcritical water conditions of 50 degrees C and 200 bar. The metabolites were trapped in situ on a strong anion-exchange disk placed over the exit frit of be 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 eaters by adding 100 mu L of ethyl iodide and heating the vial at 100 degrees 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.