V. Lopezavila et al., DEVELOPMENTS IN THE SUPERCRITICAL-FLUID EXTRACTION OF CHLOROPHENOXY ACID HERBICIDES FROM SOIL SAMPLES, Journal of agricultural and food chemistry, 41(11), 1993, pp. 2038-2044
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.