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

Abstract

Environmental context Conventional sample pretreatment for the determination of pesticides in environmental samples is time consuming and labour intensive. We report two dispersive liquid–liquid micro-extraction methods that provide rapid homogeneous emulsification in aqueous samples within 2min. These simple and environmentally friendly extraction methods are particularly suitable for the measurement of organophosphorus pesticides in field water. Abstract 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 14μL 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 2min. In WLSEME, a mixture containing 9μL of the extraction solvent (1-heptanol) and 250μL of water as the dispersed solvent (containing 10mgL–1, Triton X-100) was withdrawn and expelled four times within 10s using a microsyringe to form a cloudy emulsion in the syringe. This emulsion was then injected into 5mL of aqueous sample spiked with all of the above OPPs. The total extraction time was ~0.5min. After optimisation, the linear range of the method was 0.1–100μgL–1 for UDSA-DLLME and 0.05–100μgL–1 for WLSEME. The coefficient of determination was greater than 0.9958. The limits of detection ranged from 0.040 to 0.069μgL–1 for UDSA-DLLME and 0.020 to 0.035μgL–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.