Comparabilidade da informação contábil em empresas brasileiras após a adoção das normas internacionais de contabilidade

Abstract

Gold is a valuable metal occurring usually at very low concentrations in complex natural samples. Gold analysis thus needs preconcentration methods. Classical liquid-liquid extraction involves hazardous organic solvents. Alternatively, cloud point extraction involves non-toxic and nonvolatile surfactants. Here, we analyzed ore samples. The complex of Au(III) with sulphapyridylazo resorcin was extracted by the cloud point method. Concentrations were measured by flame atomic absorption spectrometry. We tested the effects of pH, reagent concentration, Triton X-100 surfactant concentration, equilibration temperature and time. Results show that the best detection limit of the method was 0.48 μg L -1 for Au with a preconcentration factor of 31 times. Calibration is linear in range of 6.4-2,000 μg L -1 , and relative standard deviations are lower than 5 %. Quantum chemical computations reveal the plausible structure of the gold-ligand complex. This report represents the first determination of gold using sulphapyridylazo resorcin as a ligand. © 2014 Springer International Publishing Switzerland.