SUPERCRITICAL FLUID EXTRACTION OF THE FORTIFIED RESIDUES OF FLUAZIFOP-P-BUTYL (FUSILADE-II) AND ITS MAJOR METABOLITE, FLUAZIFOP-P, IN ONIONS

A supercritical fluid extraction (SFE) procedure is described to isolate fluazifop-P-butyl and its major metabolite, fluazifop-P acid, directly from onions without any further cleanup procedures. A sample of onions is homogenized and freeze-dried. The dry sample is added to a SFE extraction vessel between two layers of silanized glass wool to prevent the clogging of the frits by fine particles in the sample. A modifier solvent (1 mL of methanol) is added with a pipet directly onto the sample, which is then extracted with supercritical fluid (SF) carbon dioxide at 80-degrees-C and 400 atm for 10-min static followed by 60-min dynamic modes. The extract is trapped in three culture tubes connected in series, each containing methanol (3 mL). The methanol solutions are combined, evaporated, and analyzed by high-performance liquid chromatography (HPLC) with an ultraviolet (UV) detector. Alternately, the same extract may also be methylated and analyzed by a gas chromatograph (GC) with a mass selective detector (MSD). Using HPLC/UV, the average recoveries of fluazifop-P acid and the butyl ester at the fortification range 0.6-6.0 ppm are 94.4-78.3 % and 92.8-77.8%, respectively, with a limit of detection (LOD) of 0.2 ppm. When the extract is methylated and determined by GC/MSD, the average recoveries at fortification range 0.06-0.6 ppm are 89.1-101.2 % for the methyl ester and 96.9-100.6 % for the butyl ester with a LOD of 0.02 ppm for both analytes.