Coupling continuous subcritical water extraction, filtration, preconcentration, chromatographic separation and UV detection for the determination of chlorophenoxy acid herbicides in soils

Subcritical water extraction has been coupled with filtration, preconcentration and chromatographic analysis for the determination of acid herbicides in different types of soil. Two experimental designs were used for the optimization of the leaching step. The use of water as extractant in the continuous mode at a flow-rate of 1 ml/min and 85 °C was sufficient for quantitative extraction of the analytes. A static extraction time was unnecessary for reducing the extraction time to 1 h. A minicolumn containing C18-Hydra as sorbent proved an excellent material for the quantitative preconcentration of the herbicides prior to individual chromatographic separation. A flow-injection manifold was used as interface for coupling the four steps, thus allowing automation of the whole analytical process. Recoveries of the target analytes ranged between 94.2 and 113.1%, and repeatabilities, expressed as relative standard deviations, were between 0.61 and 6.83%.