The application of cloud point extraction for the preconcentration and speciation of chromium by Flame Atomic Absorption Spectrometry

摘要

This paper outlines a method for the analysis of the oxidation states of Cr employing a suitable chelating agent and the cloud point phenomenon for Cr(III) and total Cr analysis. The method involves preconcentration of metal chelates followed by flame atomic absorption spectrometric analysis. We use Schiff base(N,N'-bis-(alpha-methyl salicylidene) propane-1, 3-diimine) as a chelating agent for cloud point extraction for the first time. Cr(III) reacts with chelating agent for the formation of a hydrophobic complex, which is subsequently entrapped in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of concentrated H,SO 4 and ethanol to the sample solution; Cr(III) subsequently reacts with chelating agent in a similar manner The condensed surfactant phase with the metal chelate is introduced into a flame atomic absorption spectrometer, whereby discrimination of Cr species is feasible by calculating the Cr(VI) Concentration from the difference between total Cr and Cr(III). After optimization of the complexation and extraction conditions, a good enrichment factor was obtained. The analytical curves were rectilinear up to 75 mug L-1 and the relative standard deviations were 2.3% for both species. The limits of detection are sufficiently low and lie around 0.1 mug L-1. The proposed method was applied successfully to the determination of Cr(III) and Cr(VI) in tap water and river water samples. The method was validated by the analysis of certified reference material BCR 544 for both species.