Copper fractionation with dissolved organic matter in natural waters and wastewater—a mixed micelle mediated methodology (cloud point extraction) employing flame atomic absorption spectrometry

Abstract

A cloud point extraction–preconcentration methodology for the speciation analysis of free and organically complexed metal species in natural waters is presented. The method is based on the neutralization of the electrostatic charge of the humate–metal complexes with a positively charged surfactant in a high ionic strength solution environment. The resulting complexes are conveniently solubilized in the micelles of a non-ionic surfactant medium and are thus separated from the bulk aqueous phase. Free metal species are also determined by complexation with a conventional chelating agent under mild conditions. The overall procedure is easy, rapid and allows for a high sample throughput in terms of massive analysis of many samples in the same time period. The method offers substantially low detection limits of 8.5 and 0.9 µg l⁻¹ for bound and labile species respectively, with a calibration curve rectilinear in the wide range 40–150 µg l⁻¹ for the humate associated and 4–40 µg l⁻¹ for the free metal species. The method is free from interferences yielding recoveries in the range 97–102% for various samples of different matrixes.