Na4EDTA-assisted in situ derivatization pressurized Tfluid extraction of polar herbicides in soil

Pressurized fluid extraction (PFE) is becoming popular for solid extraction due to its advantages of considerable time and solvent saving. The use of PFE was evaluated for the recovery of six agrochemicals from a Hawaiian soil. Six acid herbicides spiked at a 0.5mg/kg level in soils were extracted with pressurized and heated acetone (1500psi, 100°C) and analyzed by gas chromatography-mass spectrometry (GC-MS) in negative chemical ionization (NCI) mode after ex situ derivatization of the analytes. In situ derivatization of the analytes with pentafluorobenzyl bromide (PFBBr) in presence of ethylenediaminetetraacetic acid tetrasodium salt (Na4EDTA) was accomplished as one step in the PFE extraction cell, followed by GC-MS quantification. The effect of the amount of derivatizing reagents, static extraction time and roles of PFBBr and Na4EDTA on the extraction were investigated. Use of Na4EDTA significantly improved the recoveries of the analytes, with results from 69 to 117% (an overall average of 92±16%). The analysis time reduced from several hours (up to 24h) for the conventional extraction to less than 1h, and the good and consistent recoveries make this method very attractive for the analysis of acidic herbicides traditionally presenting difficulties for their test at low levels.