Single-sample cloud point determination of iron, cobalt and nickel by flow injection analysis flame atomic absorption spectrometry - application to real samples and certified reference materials

A preconcentration methodology utilizing the cloud point phenomenon is described for the determination of iron, cobalt and nickel by flame atomic absorption spectrometry (FAAS). The method employs the formation of complexes of the metallic species with ammonium pyrrolidinedithiocarbamate (APDC), which are subsequently entrapped in the micelles of the surfactant TX-114, upon increase of the solution temperature to 70 degreesC. The surfactant micelles, after their dilution to an acidified methanolic solution, are delivered to the nebulizer of the FAAS by a flow injection analysis (FIA) manifold, allowing for the reproducible injection of a small volume of the sample. The ability to handle the final texture of the injected solution allows for the single-step determination of these metal ions, in a single sample, without interferences. Analytical curves were rectilinear up to concentrations of 350 mug l(-1) for Fe, 200 mug l(-1) for Co and 250 mug l(-1) for Ni with detection limits of 19, 5 and 11 mug l(-1), respectively. The method was applied to the analysis of several real and spiked samples yielding satisfactory results. The recoveries obtained were in the range of 97-103% for spiked samples and 98-99.5% for a Certified Reference Material (CRM).