Dispersive liquid–liquid microextraction coupled with single-drop microextraction for the fast determination of sulfonamides in environmental water samples by high performance liquid chromatography-ultraviolet detection

Abstract

A new model of fast and convenient liquid–liquid–liquid microextraction (LLLME), combining low-density solvent-based solvent-demulsification dispersive liquid–liquid microextraction (LDS-SD-DLLME) and single drop microextraction (SDME), was introduced to separate sulfonamides from environmental water samples for the first time. The extraction procedure includes a 2 min LDS-SD-DLLME fore extraction and a 15 min SDME back-extraction. A mixture of an extraction solvent (1-octanol) and disperser solvent (methanol) was rapidly injected into the aqueous sample to form an emulsion for pre-extraction. Then a demulsifier solvent (acetonitrile) was injected into the extraction system. The emulsion turned clear in a few seconds and a layer of the organic phase formed at the top of the aqueous phase. Finally, a drop of acceptor solution was introduced into the upper layer and SDME was carried out for the back-extraction. The whole procedure does not need any electric equipment (centrifuge, stirrer or ultrasonic cleaner) because the centrifugation in DLLME and the stirring step typically involved in SDME and LLLME are avoided by the successful coupling of LDS-SD-DLLME and SDME. Four sulfonamides were first transferred from the donor phase to the organic phase by the LDS-SD-DLLME pre-extraction and then back-extracted into the acceptor droplet directly suspended in the upper layer of the organic phase. Factors affecting extraction efficiency were studied, including the organic solvent, the disperser solvent, the demulsifier solvent, the composition of the donor phase and acceptor phase, and the extraction time. Under optimal conditions, the method showed a low detection limit (0.22–1.92 μg L⁻¹) for the four sulfonamides, and good linearity (from 1.0–500 to 10–500 μg L⁻¹, depending on the analytes) and repeatability (RSD below 4.6%, n = 3). The simple, fast, and efficient feature of the proposed method was demonstrated by the analysis of sulfonamides in lake water, fishery water and wastewater samples.