Cloud point preconcentration and flame atomic absorption spectrometric determination of cobalt and nickel in water samples

Cloud point methodology was successfully used to preconcentrate trace amounts of Co and Ni as a prior step to their determination by flame atomic absorption spectrometry. 1-Nitroso-2-naphthol and polyethylene glycol-p-nonylphenylether (PONPE 7.5) are used as hydrophobic ligand and nonionic surfactant, respectively. Optimization was performed of the variables effecting complexation and phase separation. Additionally, the influence of viscosity on the analytical signal was investigated. Under the experimental conditions used, preconcentration of only 10 mL of sample in the presence of 0.075% (v/v) PONPE 7.5 permitted the detection of 1.09 mug L-1 of Ni and 1.22 mug L-1 of Co with enhancement factors of 29 and 27 for Ni and Co, respectively. The relative standard deviations (n = 5) at concentrations of 80 and 50 mug L-1 for Co and Ni were 2.53 and 2.89%, respectively. Good recoveries in the range of 96-105% were obtained for spiked samples. The effect of different interferent species was studied. The proposed method was, applied to the determination of Ni and Co in different water samples.