An optimised single-reagent method for the speciation of chromium by flameatomic absorption spectrometry based on surfactant micelle-mediated methodology

The toxicity of chromium in the environment is dependent on the species in which it exists. This paper outlines a method for the analysis of the oxida tion states of Cr employing a suitable chelating agent and the cloud point phenomenon for Cr(VI) and total Cr analysis. The method involves preconcent ration of metal chelates followed by air-acetylene flame atomic absorption spectrometric analysis. The chelating agent chosen for this task is the amm onium pyrrolidinedithiocarbamate, which reacts with either Cr(VI) or total Cr under specific experimental conditions. The condensed surfactant phase w ith the metal chelate(s) is introduced into a flame atomic absorption spect rometer, whereby discrimination of Cr species is feasible by calculating th e Cr(III) concentration from the difference between total Cr and Cr(VI). A multivariate design was employed to study the variables affecting the overa ll analytical performance for total Cr assay. The analytical curves are rec tilinear up to 100 mug l(-1) for both oxidation states of the metal. The li mits of detection are 0.6 mug l(-1) and the relative standard deviation (n = 5) at a concentration of 30 mug l(-1) for both species is around 2.0%. Th e method was validated by analysing BCR 544 reference material certified fo r both Cr species. High recoveries in the range 96-107% were attained for t he environmental and biological samples tested.