Ion pair-based dispersive liquid-liquid microextraction technique was used for preconcentration and determination of ultra-trace levels of Co (ІІ) followed by electrothermal atomic absorption spectrometry (ETAAS). Thiocyanate (SCN−) forms an anionic complex with Co (ІІ) followed by addition of cetylpyridinium chloride (CPC) as a positive counterion to produce hydrophobic cobalt-thiocyanate-CPC complex. The resulting hydrophobic complex was extracted into the fine droplets of carbon tetrachloride by dispersive liquid-liquid microextraction (DLLME). In DLLME, a mixture of 1.5 mL of acetone (as disperser solvent) containing 40 μL of carbon tetrachloride (as extraction solvent) was rapidly injected into the sample solution to extract the hydrophobic cobalt-thiocyanate-CPC complex. Under the optimum conditions, the calibration curve was linear in the range of 0.08–1.5 μg L−1 of Co (ІІ) with a correlation coefficient of 0.9997. The relative standard deviation (RSD, %) based on six replicate analyses of 0.5 μg L−1 of Co (ІІ) was 3.7 %, and the limit of detection (LOD) was 0.02 μg L−1. The accuracy of the proposed method was evaluated by the analysis of a certified reference material and spike method. The proposed method was successfully applied for determination of ultra-trace levels of Co (ІІ) in different water samples and spinach leaves.

Keywords