Fluid Extraction of Fluometuron Herbicide from Soil

Soil was treated with "C-ring-labeled fluometuron [N,N-dimethyl-N'[3-(trifluoromethyl)phenyll urea] (0.516 and 5.16 pmol gl), air-dried, and stored for 6 months at 5 "C. The 14C was then extracted from soil with methanol by conventional extraction (twice with MeOH/H20 8020 v/v; 2:l extract/soil v/w) and with CO2 using a supercritical fluid extractor. Supercritical fluid extraction (SFE) method development included adding modifiers and varying C02 fluid density, extraction temperature, sample mass, and extraction time. Adding H2O to modify the sample was the single most effective variable which improved recovery. Extraction temperatures above 50 "C lowered recovery, presumably because of thermal instability of fluometuron. The optimum C02 density at 50 "C was 0.80 g mL-l. Static extraction times greater than 6 min and dynamic extraction times greater than 18 min did not significantly improve recovery. Recovery using optimum SFE conditions was comparable to that obtained using conventional methods. Extraction of aged field samples indicated that this technology can also be used to extract some common fluometuron metabolites.