Analysis of the herbicide clopyralid in cultivated soils

Abstract

Clopyralid is a broad-spectrum herbicide for thistle control in vegetable cultivation. Its application rate amounts to 0.2 kg/ha. However, contradictory results in soil leaching experiments require a reliable routine procedure for trace analysis of clopyralid in soil. Previously reported methods for clopyralid analysis in several matrices either proved to be insufficient for analysis in soil and leaching water or require the use of critical chemicals and are too complicated for routine analysis. The problem of poor extraction recovery of clopyralid from soil rich in humic acids was solved by phase transfer extraction of soil samples. Analysis of the extract was performed by GC-MS directly after the extractive phase transfer catalytic reaction. Tetrabutylammoniumhydroxide served as a phase transfer catalyst. For improving analytical reliability, 2.5-dichlorobenzoic acid was used as an internal standard. Detection limit (1 μg/kg=1 ppb) and quantification limit (10 μg/kg) of clopyralid in soil were found to be appropriate for determining the behaviour in herbicide treated soils. The leaching and disappearance of clopyralid in two differently tilled soils were determined in field trials.