Multiple objective optimization of air assisted liquid-liquid microextraction combined with solidified floating organic drop microextraction for simultaneous determination of trace copper and nickel

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Abstract
The impact of rising levels of various heavy metals in the environment from multiple industrial, agriculture, domestic, and technological activities is of great concerns, as heavy metals cause serious health effects for both humans and wildlife. An effective and green chemistry procedure was used for simultaneous extraction of ultra-trace copper and nickel ions in natural waters (e.g. river and well waters) by air assisted liquid-liquid microextraction combined with solidified floating organic drop microextraction (AALLME-SFOD). The extraction of metal ions was conducted in a timescale of several minutes by conversion to metal chelates using sodium diethyldithiocarbamate (DDTC) as a chelating agent prior to AALLME-SFOD procedure, and 1-dodecanol as an extraction solvent to initiate the phase separation of the complex. The response surface methodology (RSM) and central composite design (CCD) were used to optimize the large number of experimental variables (i.e. pH, solvent volume, ligand volume, % NaCl). The analysis of variance (ANOVA) has been applied to evaluate all parameters and their mutual interactions on the extraction yields. The desirability function of Derringer and Suich was applied as a metric for optimization of multiple response variables. The optimized AALLME-SFOD technique proved to be highly effective for the pre-concentration of Cu(II) and Ni(II) from a range of aqueous media (i.e. river and well waters) and provides a quick and easy method, while utilizing compact and low cost equipment with micro-volume organic solvent consumption (e.g. ~120 μL for 5 mL water samples). Quantitation of copper and nickel with Graphite furnace atomic absorption spectroscopy (GFAAS) under the optimum conditions, were linear over the range of (20–100) and (20–200) ng L−1 respectively. Limit of detection for Ni(II) was at 4.5 ng L−1 and 10.4 ng L−1 for Cu(II).

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