Two dispersive liquid-liquid microextraction methods coupled with gas chromatography-mass spectrometry for the determination of organophosphorus pesticides in field water

The methods 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) were developed for the analysis of 13 organophosphorus pesticides (OPPs) in water samples by gas chromatography-mass spectrometry (GC-MS). UDSA-DLLME required only 14 mL of 5-methyl-1-hexanol as the extraction solvent. The use of an up-and-down shaker allowed homogeneous and rapid emulsification of aqueous samples. OPP extraction was completed in 2 min. In WLSEME, a mixture containing 9 mu L of the extraction solvent (1-heptanol) and 250 mL of water as the dispersed solvent (containing 10 mg L-1, Triton X-100) was withdrawn and expelled four times within 10 s using a microsyringe to form a cloudy emulsion in the syringe. This emulsion was then injected into 5 mL of aqueous sample spiked with all of the above OPPs. The total extraction time was similar to 0.5 min. After optimisation, the linear range of the method was 0.1-100 mu g L-1 for UDSA-DLLME and 0.05-100 mg L-1 for WLSEME. The coefficient of determination was greater than 0.9958. The limits of detection ranged from 0.040 to 0.069 mu gL(-1) for UDSA-DLLME and 0.020 to 0.035 mu gL(-1) for WLSEME. Analyses of river water, lake water and underground water had absolute recoveries of 34 to 96% and relative recoveries of 84 to 115% for both methods. Other emulsification methods such as vortex-assisted, ultrasound-assisted and manual-shaking-enhanced ultrasound-assisted methods were also compared against the proposed UDSA-DLLME and WLSEME methods. The results reveal that UDSA-DLLME and WLSEME provided higher extraction efficiency and precision.