Water with low concentration of surfactant in dispersed solvent-assisted emulsion dispersive liquid–liquid microextraction for the determination of organochlorine pesticides in aqueous samples

A novel sample preparation method, “water with low concentration of surfactant in dispersed solvent-assisted emulsion dispersive liquid–liquid microextraction (WLSEME)”, coupled with gas chromatography using an electron capture detector (GC-ECD) was developed for the analysis of the organochlorine pesticides (OCPs), heptachlor, α-endosulfan, 4,4-DDE, 2,4-DDD and endrin, in aqueous samples. A microsyringe is used to withdrew and discharge 10–12 μL of the extraction solvent and 60–120 μL of water as the dispersed solvent (containing 1 mg L−1, Tween 80) 4 times within 10 s to form a cloudy emulsified solution in the syringe. This is then injected into an 8 mL aqueous sample spiked with all above OCPs. Dodecyl acetate and 2-dodecanol were both selected as extraction solvents to optimize their conditions separately. The total extraction time was about 0.5 min. Under optimum conditions, using dodecyl acetate (12 μL) as extraction solvent, the linear range of the method was 10–1000 ng L−1 for all OCPs, and the the limits of detection (LODs) ranged from 1 to 5 ng L−1. The absolute recoveries and relative recoveries were from 20.8 to 43.5% and 83.2 to 109.8% for lake water, and 19.9–49.2% and 85.4–115.9% for seawater respectively. In the second method, 2-dodecanol as extraction solvent, the linear range was from 5 to 5000 ng L−1 for the target compounds, and the LODs were between 0.5 and 2 ng L−1. The absolute recoveries and relative recoveries ranged from 25.7 to 42.2% and 96.3–111.2% for sea water, and 22.4–41.9% and 90.7–107.9% for stream water. This could solve several problems, which commonly occur in ultrasound-assisted emulsification micro-extraction (USAEME), dispersive liquid–liquid micro-extraction (DLLME) and other assisted emulsification methods. These problems include analyte degradation, increased solubility of the extraction solvent and analyte, and high toxicity and large volume of the organic solvent used.