Hollow-Fiber Liquid-Phase Microextraction (HF-LPME) Coupled On-Line to Liquid Chromatography for the Determination of the Herbicides 2,4-Dichlorophenoxyacetic Acid and 2-Methyl-4-chlorophenoxyacetic Acid and Their Main Metabolites in Soil Samples

Abstract

The use of hollow-fiber liquid-phase microextraction (HF-LPME) is very promising for the clean-up, enrichment, and analysis of chlorophenoxyacetic acid herbicides and their metabolites from environmental and biological samples. An on-line methodology coupling HF-LPME (using a hydrophobic polypropylene hollow fiber of 57 cm length, 0.3 mm i.d., 0.2 μm pore size, and 75% porosity) and HPLC-UV has been developed for the analysis of these compounds in soil samples taken from environments treated with these herbicides. Di-hexyl ether was found to be the best solvent for the enrichment of the target herbicides. The use of supported liquid membranes has shown a high and efficient clean-up of the dissolved organic matter present in soil extracts. The enrichment factors achieved with the on-line methodology have allowed us to reach the detection limits of 0.1–0.3 µg·kg−1 soil, by analyzing 20 mL of alkaline extract as a donor solution and using 1 mL of stripping solution, which has permitted us to detect and follow the presence of these compounds in soil samples until nine days after the application of the herbicide. The on-line method has been applied in a preliminary study to assess the mobility of the chlorophenoxyacetic acid herbicides through soils. It has also been found that degradation of these compounds in soil is relatively fast and some metabolites were detected in soils just one day after the application of the herbicide. The high enrichment factors obtained with the HF-LPME procedure allow for the obtainment of low detection limits, which permits the use of a simple HPLC detector, such as UV, which simplifies and reduces the cost of analyses.