Cloud point formation based on mixed micelles in the presence of electrolytes for cobalt extraction and preconcentration

A new micelle-mediated phase separation of metal ions, applied for preconcentrating trace levels of cobalt as a prior step to its determination by flame atomic spectroscopy, has been developed. Two methods were proposed employing both Triton X-100 and sodium dodecyl sulfate (SDS) as a mixed micellar system while the phase separation was induced by HCl or NaCl addition. Cobalt was complexed with pyridylazo compounds (PAN, PAR, 5-Br-PADAP) in an aqueous surfactant medium and it was concentrated in the surfactant rich phase after phase separation. The chemical variables affecting the cloud point extraction were evaluated, optimized and successfully applied to cobalt determination in pharmaceutical samples. Under the optimized conditions, the preconcentration system permitted limits of detection as 1.1 and 1.6 μg l−1 cobalt, respectively, when HCl and NaCl were used. Both proposed methods showed linear calibration within a 25–200 μg l−1 cobalt range. The extraction efficiency was investigated at different cobalt concentrations (40–185 μg l−1) and good recoveries (98–102%) were obtained by using NaCl as electrolyte. The results obtained were compared with those observed with ET AAS.