A Green Enrichment Method of Copper, Manganese and Nickel in Water Samples via Cloud Point Extraction

A new, cost-effective, and environmental-friendly cloud point extraction methodology was described for enrichment of copper, manganese and nickel in several water samples. The method involves the complexation of copper, manganese or nickel with 2-amino-6-(1,3-thiazol-2-diazeyl)-phenol at pH 7.0, then extraction into Triton X-114. After dilution of the surfactant-rich phase with acidified methanol, the enriched analytes concentration was estimated by flame atomic absorption spectrometry. Parameters that influenced cloud point extraction, such as pH, reagent, surfactant and nitric acid concentrations, centrifuge rate and time, temperature, incubation time, as well as interferences were evaluated and optimized. The preconcentration factor was 100, enrichment factors were 14, 11.10 and 11.30 and the detection limits were 0.37, 1.20, and 1.30 µg L-1 for copper, manganese, and nickel, respectively. The method presented relative standard deviation as precision were 2.20%, 2.50 and 3.20% for copper, manganese, and nickel, respectively. The accuracy of the new preconcentration procedure was checked by the analysis of the standard reference materials (SRM 1570a Spinach Leaves and SRM 1515 Apple Leaves), and successfully applied to determine Cu2+, Mn2+ and Ni2+ in real water samples with relative recovery values in the range of 95.0%–99.0% for the spiked samples.