Ultrasonic-assisted cloud point extraction for determination of nickel in water samples by flame atomic absorption spectrometry

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.