Development of a method based on accelerated solvent extraction and liquidchromatography/mass spectrometry for determination of arylphenoxypropionicherbicides in soil

A sensitive and specific analytical procedure for determining arylphenoxypr opionic herbicides in soil samples, using Ionspray ionization (ISI) liquid chromatography/mass spectrometry (LC/MS), is presented. Arylphenoxypropioni c acids are a new class of herbicides used for selective removal of most gr ass species from any non-grass crop, commercialized as herbicide esters. Pr evious studies have shown that the esters undergo fast hydrolysis in the pr esence of vegetable tissues and soil bacteria, yelding the corresponding fr ee acid. The feasibility of rapidly extracting arylphenoxypropionic herbici des from soil by accelerated solvent extraction (ASE) techniques was evalua ted. Four different soil samples were fortified with target compounds at le vels of 5 and 20 ng/g by following a procedure able to mimic weathered soil s. Herbicides were extracted by a methanol/water (80:20 v/v) solution (0.12 M) of NaCl at 90 degreesC. After clean-up using graphitized carbon black ( GCB) as absorbent, the extract was analyzed by HPLC/ISI-MS. The effect of c oncentration of acid in the mobile phase on the response of ISI-MS was inve stigated. The effects of varying the orifice plate voltage on the productio n of diagnostic fragment ions, and on the response of the MS detector, were also investigated. The ISI-MS response was linearly related to the amounts of analytes injected between 1 and 200 ng. The limit of detection (signal- to-noise ratio = 3) of the method for the pesticides in soil samples was es timated to be less than 1 ng/g. Copyright (C) 2001 John Wiley & Sons, Ltd.