Abstract
The herbicide clopyralid offers a high selectivity in thistle control using low application rates. Contradictory results in soil leaching experiments using this herbicide indicate the need for a reliable procedure for trace analysis of clopyralid. The problem of poor extraction efficiency from soil that is rich in humic substances was solved by ultrasound-enhanced alkaline extraction. Analysis of the extract was performed by gas chromatography-mass spectrometry after derivatization with pentafluorobenzylbromide in an ultrasound-enhanced phase-transfer catalytic reaction. Tetrabutylammoniumbromide served as a phase-transfer catalyst. For improving analytical reliability, 2,5-dichlorobenzoic acid was used as an internal standard. The achieved detection (1 μg/kg = 1 ppb) and quantification (10 μg/kg) limits of clopyralid in soil were appropriate for determining the degradation behavior in herbicide-treated soils. The half-life of clopyralid in two differentially cultivated soils was determined in laboratory trials. Uncultivated soil that was rich in humic acids showed a higher half-life than cultivated soil.
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