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A novel method for the determination of nickel was established by ultrasonic-assisted cloud point extraction (UA-CPE) prior to flame atomic absorption spectrometry (FAAS) analysis. The nickel reacted with N,N'-bis(salicylidene)-1,2-ethanediamine (BSE) to form hydrophobic chelates, which were extracted into the micelles of alpha-[3,5-dimethyl-1-(2-methylpropyl)hexyl]-omega- poly(oxy-2-ethanediyl) (Tergitol TMN-6). Tergitol TMN-6 was used as green nonionic surfactant. BSE was synthesized and checked by nuclear magnetic resonance (NMR) spectra. The phase diagrams of the binary system, water-surfactant (Tergitol TMN-6), and the ternary systems, water-surfactant-salt, were determined. The effects of experimental conditions including pH of sample solution, concentration of chelating agent and surfactant, ultrasonic power, equilibration temperature and incubation time were evaluated in order to enhance sensitivity of the method. Under the optimal conditions, the calibration graph was linear in the range of 10-500 μg L(-1). The values obtained for the limit of detection and enrichment factor were 1.0 μg L(-1) and 30, respectively. The method was successfully applied to the analysis of nickel in water samples.

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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 CCl(4) 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.