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 microextraction methods that provide rapid homogeneous emulsification in aqueous samples within 2 min. 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 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 mL of the extraction solvent (1-heptanol) and 250 mL of water as the dispersed solvent (containing 10 mg L À1 , Triton X-100) was withdrawn and expelled four times within 10 s using a microsyringe to form a cloudy emulsion in the syringe.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 ,0.5 min. After optimisation, the linear range of the method was 0.1-100 mg L À1 for UDSA-DLLME and 0.05-100 mg L À1 for WLSEME. The coefficient of determination was greater than 0.9958. The limits of detection ranged from 0.040 to 0.069 mg L À1 for UDSA-DLLME and 0.020 to 0.035 mg L À1 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.Additional keywords: field water, OPPs, organophosphorus pesticides, UDSA-DLLME, up-and-down shaker-assisted dispersive liquid-liquid microextraction, water with low concentration of surfactant dispersive liquid-liquid microextraction, WLSEME

Analytical Methods for Pesticide Residues in the Water Environment

“…The proposed method was successfully applied for extraction and determination of the OCPs in water and fruit samples. The method's UDSA-DLLME and WLSEME were developed for the analysis of 13 OPPs in water samples by GC-MS (Chu et al, 2014). After optimization, the linear range of the method was 0.1-100 µg L -1 for UDSA-DLLME and 0.05-100 mg L -1 for WLSEME.…”