Abstract
A new up-and-down shaker-assisted dispersive liquid– liquid microextraction (UDSA-DLLME) and water with low concentration of surfactant in dispersed solvent-assisted emulsion dispersive liquid–liquid microextraction (WLSEME) coupled with gas chromatography mass spectrometer (GC-MS) was developed for the analysis of the thirteen organophosphorus pesticides (OOPs) in aqueous samples. The method of UDSA-DLLME used only 14 μL of 5-methyl-1-hexanol as the extraction solvent. With the use of an up-and-down shaker, the emulsification of aqueous samples was formed homogeneously and quickly. The extraction of OOPs were completed in 2 min. After optimization, the linear range of the method was 0.1–100 μg L?1, and the coefficient of determination (r2) was greater than 0.9958. The limits of detection (LODs) ranged from 0.040 to 0.069 μg L?1, and the relative standard deviation was from 2.0 to 9.7 %. Real samples of river water, lake water, and underground water had absolute recoveries from 50 to 96 % and relative recoveries from 84 to 115 %. On the method of WLSEME, a microsyringe is used to withdrew and discharge 9 μL of the extraction solvent (1- heptanol) and 250 μL of water as the dispersed solvent (containing 10 mg L?1, Triton X - 100) 4 times within 10 s to form a cloudy emulsified solution in the syringe. This is then injected into an 5 mL aqueous sample spiked with all above OOPs. The total extraction time was about 0.5 min. After optimization, the linear range of the method was 0.05–100 μg L?1, and the coefficient of determination (r2) was greater than 0.9958. The limits of detection (LODs) ranged from 0.020 to 0.035 μg L?1, and the relative standard deviation was from 4.1 to 10.0 %. Real samples of river water, lake water, and underground water had absolute recoveries from 34 to 96 % and relative recoveries from 87 to 115%. Other emulsification methods such as vortex-assisted, and manual shaking-enhanced ultrasound-assisted methods were also compared with the proposed UDSA-DLLME and WLSEME. The results revealed that UDSA-DLLME and WLSEME performed with higher extraction efficiency and precision compared with the other methods and they provided an alternative to solve the common problems in DLLME and other assisted emulsification methods such as vortex, ultrasound, and manual shaking/ultrasound assisted, including degradation of analyte, increased solubility of the analytes and extraction solvents in aqueous solution, the use of toxic extraction solvents and large volumes of dispersed solvents.