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

Extraction of chlorophenoxy acid herbicides from soil samples with sup ercritical carbon dioxide as extractant and tetrabutylammonium hydroxi de and methyl iodide as derivatization agents was investigated. The ex traction 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 approxi mately 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 t o extract other compounds currently listed in the EPA SW-846 Method 81 51 using supercritical carbon dioxide and tetrabutylammonium hydroxide /methyl iodide were unsuccessful, either because these compounds did n ot derivatize (dalapon, dinoseb, and 4-nitrophenol) or because decompo sition occurred (DCPA diacid, pentachlorophenol, and picloram), appare ntly in the injection port of the gas chromatograph. An in-situ deriva tization and supercritical fluid extraction of the chlorophenoxy acids with pentafluorobenzyl bromide/triethylamine reagent also proved to b e feasible for qualitative determination of these compounds.