Selective speciation of trace chromium through micelle-mediated preconcentration, coupled with micellar flow injection analysis-spectrofluorimetry

A new method based on the cloud point extraction (CPE) technique was applied for the differentiation and the selective determination of Cr species. Cr(III) reacts with 8-hydroxyquinoline (8-HQ) in a surfactant solution yielding a hydrophobic complex, which then is entrapped 'in situ' in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by sulfite which subsequently reacts with 8-HQ in a similar manner. In order to increase the sample throughput a flow injection analysis (FIA) system allied to fluorimetric detection was employed. Using a simple FIA configuration the greatest sensitivity was obtained which under the optimum working conditions, allows the reliable determination of Cr(III) and/or Cr(VI) at levels as low as 0.2 mug l(-1),in various samples even in those with complex matrix (sea water, pharmaceuticals). The whole procedure is straightforward, without any laborious, expensive and hazardous treatment and was proved to tolerate interferences among the cations and anions tested. Moreover, the analytical approach offers distinct advantages over the commonly used analytical methods especially for large number of samples with complex matrixes, which would unavoidably require arduous and delicate pretreatment. (C) 2001 Elsevier Science B.V. All rights reserved.