Ligandless green effervescence-assisted dispersive liquid-liquid microextraction method for trace analysis of Co(II) and Ni(II)

Heavy metal ions are present in relatively low concentrations in the environment. They are widely used in many industries. They are important pollutants in environment due to their toxic effect on human health. Cobalt and nickel are typical metal ions in environmental samples and have important roles in many physiological functions. However, high concentrations of these metal ions may be toxic and lead to side effects [1, 2]. Prior to assess low concentration, performing separation and preconcentration techniques are compulsory to eliminate or minimize matrix effects which leads to low detection limit and improved sensitivity of detection techniques towards metals.In conventional dispersive liquid-liquid microextraction, an extraction solvent is dispersed into an aqueous sample solution with the aid of a disperser solvent [3]. The presence of relatively high volume of the disperser solvent makes the aqueous phase relatively nonpolar and results in an increased solubility of the target lipophilic analytes into the aqueous sample solution leading to relatively low extraction efficiency.Ligandless gas-disperser liquid-liquid microextraction followed by graphite furnace atomic absorption spectrometry detection has been developed for the extraction and preconcentration of cobalt and nickel from aqueous samples. In the proposed method, initially a solid mixture of phthalic acid and sodium bicarbonate is placed in the bottom of a conical and dried glass test tube. Then µL-level of 1,1,2,2-tetrachloroethane as an extraction solvent is added to the tube. An aqueous solution of the analytes is transferred into the tube. The reaction between phthalic acid and sodium bicarbonate is immediately occurred, and the produced CO2 leads to dispersion of the extraction solvent as tiny droplets into the sample and subsequent extraction of the analytes. The cloudy solution is centrifuged and the sedimented phase is analyzed by the analytical method. Under the optimum conditions the calibration curves were linear in the range of 20-300 ng L-1. Repeatability of the proposed method, expressed as relative standard deviation, ranged from 3-5% and 4-7% for intra- and inter-day (n=6, C=50 ng L-1) precisions, respectively. Moreover, the detection limits and enrichment factors of the selected analytes were obtained in the ranges of 6-12 ng L-1 and 193-198, respectively. The accuracy of the developed procedure was checked by analyzing NRCC-SLRS4 Riverine water as a certified reference material. Finally, the proposed method has been successfully applied for the simultaneous analysis of the selected analytes in environmental water samples.