Continuous Ultrasound-Assisted Leaching of Phenoxyacid Herbicides in Soil and Sediment with in-situ Sample Treatment

Summary Ultrasound, water and Na₂EDTA·2H₂O have been used for continuous leaching with in-situ sample treatment of acid herbicides (namely, bentazone, 2,4-D, trichlopyr, 2,4,5-T and 2,4,5-Tp) from different types of soil (namely, clayey, slimy, sandy, organic and limy) and one sediment. The subsequent steps for quantitation of the leached analytes (namely, preconcentration, individual chromatographic separation and UV detection) were performed using a flow injection manifold that permits automation of the overall process. The main factors contributing to the leaching efficiency—namely, ultrasound radiation amplitude, probe position, percentage of duty cycle of ultrasound exposure, extractant flow-rate and temperature of the water bath in which the extraction cell is immersed—were optimized by means of a central composite design. Also, the kinetics of the leaching step with Na₂EDTA·2H₂O was studied. In all cases, the recoveries of the target analytes were higher than 92%. The detection and quantification limits were 10 and 30 ng g^–1, respectively, for all analytes, but trichlopyr (detection and quantification limits 5 and 12 ng g^–1, respectively). The relative standard deviations for repeatability range between 2.8–5.3%.