Simultaneous Cloud Point Extraction and Determination of Zn, Co, Ni and Pb by Flame Atomic Absorption Spectrometry, Using 2-Guanidinobenzimidazole as the Complexing Agent

A simple Cloud Point Extraction (CPE) method has been proposed for the simultaneous preconcentration and determination of Zn(II), Co(II), Ni(II) and Pb(II). The pH of the sample solution was adjusted to 9 with buffer solution and the cations were complexed with 2-guanidinobenzimidazole. Triton X-114 was added as a non-ionic surfactant. After the phase separation at 4\pm1\degree C, the surfactant-rich phase was diluted to 1.5 ml using an ethanolic solution of HNO_3 and the analytes were determined by flame atomic absorption spectrometry. The influence of variables, such as pH, ligand concentration, surfactant concentration, etc. upon the complexation and extraction, was studied. Preconcentration of a 50 ml sample solution in the presence of Triton X-114 (0.05% V/V) provided detection limits of 8.8, 4.9, 7.8 and 11 ng ml^{-1} for Zn, Ni, Co and Pb, respectively. The dynamic linear range of concentration, relative standard deviation and enhancement factors are as follows: 8.8-80, 4.9-3000, 7.8-2000, 11-6000 ngmL^{-1}; 5.2%, 4.%, 7.8%, 3.2% and 13, 15.5, 15, 29.6 for Zn, Ni, Co and Pb, respectively.