Development of a liquid-nitrogen-induced homogeneous liquid-liquid microextraction of Co(II) and Ni(II) from water and fruit juice samples followed by atomic absorption spectrometry detection.

In this study, a simple and rapid sample preparation method named liquid-nitrogen-induced homogeneous liquid-liquid microextraction has been developed for the extraction and pre-concentration of Co(II) and Ni(II) ions before their analysis by flame atomic absorption spectrometry. For this purpose, first, acetonitrile containing 8-hydroxyquinoline is added into a sample solution and the mixture is vortexed. As a result, a homogeneous solution is formed. Subsequently, the solution is cooled using liquid nitrogen for a few seconds. By this process, due to difference in the freezing point of acetonitrile and water, the homogeneous state is broken and the analytes (as oxinate complexes) are extracted into liquid acetonitrile phase collected on top of the frozen aqueous phase. The linear dynamic ranges obtained for Ni(II) and Co(II) were 1.0-30 and 0.50-20 μg L, respectively. The obtained limits of detection were 0.36 and 0.20 μg L for Ni(II) and Co(II), respectively.