DEVELOPMENTS IN THE SUPERCRITICAL-FLUID EXTRACTION OF CHLOROPHENOXY ACID HERBICIDES FROM SOIL SAMPLES

Extraction of chlorophenoxy acid herbicides from soil samples with supercritical carbon dioxide as extractant and tetrabutylammonium hydroxide and methyl iodide as derivatization agents was investigated. The extraction was carried out at 400 atm and 80-degrees-C for 15 min static, followed by 15 min dynamic, at a carbon dioxide flow rate of approximately 1.5 mL/min (as liquid). The use of other derivatization agents (trimethylphenylammonium hydroxide, benzyltrimethylammonium chloride, and benzyltriethylammonium chloride) proved to be less effective than the tetrabutylammonium hydroxide/methyl iodide combination. Attempts to extract other compounds currently listed in the EPA SW-846 Method 8151 using supercritical carbon dioxide and tetrabutylammonium hydroxide/methyl iodide were unsuccessful, either because these compounds did not derivatize (dalapon, dinoseb, and 4-nitrophenol) or because decomposition occurred (DCPA diacid, pentachlorophenol, and picloram), apparently in the injection port of the gas chromatograph. An in-situ derivatization and supercritical fluid extraction of the chlorophenoxy acids with pentafluorobenzyl bromide/triethylamine reagent also proved to be feasible for qualitative determination of these compounds.