Micelle-mediated methodology for speciation of chromium by flame atomic absorption spectrometry

Abstract

The concept of cloud point phenomenon is used to perform metal speciation after the studied metallic forms have reacted with suitable ligands for the formation of hydrophobic complexes, which are subsequently entrapped in the surfactant micelles. As an analytical demonstration, trace concentrations of Cr(III) and Cr(VI) were conveniently detected in samples with a complex matrix, such as sea water, without any laborious and expensive treatment using flame atomic absorption spectrometry. The speciation of Cr is performed using Triton X-114 as surfactant and, as chelating agents, ammonium pyrrolidinedithiocarbamate for Cr(VI) and 8-hydroxyquinoline for Cr(III). Analytical curves were rectilinear up to concentrations of 130 µg l⁻¹ for Cr(III) and 85 µg l⁻¹ for Cr(VI) with detection limits of 1.4 µg l⁻¹ and 0.65 µg l⁻¹, respectively. The method affords recoveries in the range 96–104% and a relative standard deviation lower than 2.2%. It is proved that the method can be successfully employed as an alternative to the commonly used preconcentration and speciation analytical techniques. By selecting the appropriate complexing agent(s) other metal speciations are feasible provided that some detailed study precedes the application.