Application of multi-response experimental design for optimization of simultaneous microextraction of Cu(II) and Ni(II) from aqueous samples followed by graphite furnace atomic absorption spectrometry determination

A simple, rapid and efficient method has been developed for extraction,¬ and preconcentration of copper and nickel ions in water samples by air–assisted liquid–liquid microextraction (AALLME) and solidified floating organic drop (SFOD) coupled with graphite furnace atomic absorption spectrometry (GFAAS). The metal ions in the aqueous were complexed with sodium diethyldithiocarbamate, and then a low–density solvent with a melting point near room temperature such as 1-dodecanol was used as the extraction solvent and the emulsion was rapidly formed by pulling in and pushing out the mixture of aqueous sample solution and extraction solvent repeatedly using a 5 mL glass syringe. After centrifugation, the extractant droplet could be easily collected from the top of the aqueous samples by solidifying it at a temperature lower than the melting point. The solidified extractant was melted at room temperature. Finally 10µl of the enriched analytes in the melted phase were injected to GFAAS [1]. Response surface method, Central Composite design (CCD), was used to design experiments and study the effect of parameters those affect the extraction yields. Studied parameters and their ranges were; pH (2-12), solvent volume (50-150μL), ligand volume (40-140μL) and % NaCl (0-6 w/v). The obtained experimental data, extraction yields, were fitted to a full quadratic model using multiple regression analysis. The results showed that, the extraction conditions have significant effects on extraction yield of both copper and nickel ions. A multi-response optimization method [2], Derringer and suich method, was used to find the optimal conditions for simultaneous extraction of both analytes (pH 8.5, solvent volume 120μL, ligand volume 140μL and % NaCl 4.5 w/v). In this condition, maximum extraction yield, 99.9% for copper and 77.11% for nickel, were obtained. The proposed method was used to determine of analytes in different water samples.