Study on the determination of heavy metals in water samples with ultrasound-assisted dispersive liquid–liquid microextraction prior to FAAS

A new, simple and rapid method based on dispersive liquid–liquid microextraction (DLLME) was developed for extracting and preconcentrating copper (Cu), nickel (Ni), lead (Pb) and cadmium (Cd) in water samples prior to flame atomic absorption spectrometry (FAAS) analysis. 1-(2-thiazolylazo)-naphthol (TAN) was used as chelating reagents, and non-ionic surfactant Triton X-114 and CCl₄ as disperser solvent and extraction solvent, respectively. Some influential factors relevant to DLLME, such as the concentration of TAN, type and volume of disperser and extraction solvent, pH and ultrasound time, were optimized. Under the optimal conditions, the calibration curve was linear in the range of 10–800 μg L⁻¹ for Cu and Ni, 10–500 μg L⁻¹ for Pb, and 10–1,000 μg L⁻¹ for Cd, respectively. The limits of detection for the four metal ions were below 0.5 μg L⁻¹, with the enhancement factors of 105, 66, 28 and 106 for Cu, Ni, Pb and Cd, respectively. The relative standard deviations (RSD, n = 6) were 2.6–4.1%. The proposed method was applied to determination of Cu, Ni, Pb and Cd in water samples and satisfactory relative recoveries (93.0–101.2%) were achieved.