The present study deals with the simultaneous determination of Co(II) and Fe(II) ions using derivative spectroscopy after preconcentration by surface-active ionic liquid-assisted cloud point extraction. Wider linear range, less detection limit and more reproducibility along with the improved extraction efficiency highlight the advantages of the proposed method compared to the conventional CPE method. On the other hand, in comparison to the hydrophilic ionic liquids, a more effective and efficient extraction medium is provided due to the formation of homogeneously dispersed micro-droplets of surface-active ionic liquid (SAIL) micelles. Some important variables affecting the extraction efficiency such as sample pH, the concentration of SAIL 1-hexadecyl-3-methylimidazolium chloride (C16MeImCl), the volume of Triton X-114, the concentration of the chelating agent, the concentration of NaCl, centrifugation conditions, equilibrium temperature and time were optimized. Under the selected optimized conditions, the resulting calibration graph obtained by derivative spectroscopy was linear in the range of 0.15 to 2.0 mg l-1 for cobalt and 0.05 to 0.75 mg l-1 for iron at zero-crossing wavelengths of 598 and 567 nm, respectively. The detection limits achieved were 0.07 mg l-1 for cobalt and 0.01 mg l-1 for iron ions. The relative standard deviation in all cases was less than 4%. The proposed method was successfully applied to the simultaneous determination of cobalt and iron ions in various real samples.
