Ultra-Trace Determination of Co (ІІ) in Real Samples Using Ion Pair-Based Dispersive Liquid-Liquid Microextraction Followed by Electrothermal Atomic Absorption Spectrometry

Abstract

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