Vortex-assisted micro-solid-phase extraction followed by low-density solvent based dispersive liquid–liquid microextraction for the fast and efficient determination of phthalate esters in river water samples

A simple and efficient two-step method, vortex-assisted micro-solid-phase extraction (VA-μ-SPE) followed by low-density solvent based dispersive liquid–liquid microextraction (LDS-DLLME) combined with analysis by gas chromatography–mass spectrometry (GC–MS), was developed for the determination of trace level phthalate esters in environmental water samples. The analytes were firstly extracted and preconcentrated by vortex-assisted μ-SPE which was faster than conventional μ-SPE (6 min compared to 30 min), and then desorbed by ultrasonication into acetonitrile. The latter served as the dispersive solvent in the subsequent LDS-DLLME step which further pre-concentrated the analytes. Six phthalate esters were selected as model compounds for developing and evaluating the method. Some key parameters for VA-μ-SPE and LDS-DLLME, such as sorbent selection and amount, vortex time, ultrasonication solvent and time, extraction solvent type and volume for DLLME, the speed and time of centrifugation, were investigated. Under the most favorable conditions, good limits of detection (as low as 0.006 μg/L) and repeatability of extraction (RSDs below 9.2%, n = 5) were obtained. The developed method was applied to determine phthalate esters in environmental water samples.