Ionic liquid-based dispersive liquid–liquid microextraction followed high-performance liquid chromatography for the determination of organophosphorus pesticides in water sample

Using 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) ionic liquid as extraction solvent, organophosphorus pesticides (OPPs) (parathion, phoxim, phorate and chlorpyifos) in water were determined by dispersive liquid–liquid microextraction (DLLME) combined with high-performance liquid chromatography (HPLC). The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C8MIM][PF6] dispersed entirely into sample solution with the help of disperser solvent (methanol). Parameters including extraction solvent and its volume, disperser solvent and its volume, extraction time, centrifugal time, salt addition, extraction temperature and sample pH were investigated and optimized. Under the optimized conditions, up to 200-fold enrichment factor of analytes and acceptable extraction recovery (>70%) were obtained. The calibration curves were linear in the concentration range of 10.5–1045.0 μg L−1 for parathion, 10.2–1020.0 μg L−1 for phoxim, 54.5–1089.0 μg L−1 for phorate and 27.2–1089.0 μg L−1 for chlorpyifos, respectively. The limits of detection calculated at a signal-to-noise ratio of 3 were in the range of 0.1–5.0 μg L−1. The relative standard deviations for seven replicate experiments at 200 μg L−1 concentration level were less than 4.7%. The proposed method was applied to the analysis of four different sources water samples (tap, well, rain and Yellow River water) and the relative recoveries of spiked water samples are 99.9–115.4%, 101.8–113.7% and 87.3–117.6% at three different concentration levels of 75, 200 and 1000 μg L−1, respectively.