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Title: Aplicação da espectrometria de absorção atômica com forno de grafite na determinação direta de manganês, chumbo e cromo em águas de produção
Keywords: Meio ambiente;  Petróleo;  Cromo (Cr);  Química inorgânica;  Manganês;  Chumbo (Pb);  Produção intelectual;  Química ambiental
Issue Date: 31-Jan-2010
Abstract: This work presents the development of analytical methodologies for the direct determination of manganese, lead and chromium in produced waters from petroleum exploration by graphite furnace atomic absorption spectrometry. In this context, several chemical modifiers such as Ir and Ir-W permanent modifiers, Pd and Pd-Mg were tested. Besides, the effect of the addition of hydrofluoric acid was evaluated. In the determination of Mn and Pb in no saline waters, Ir and ir-W permanent modifiers presented better performance than Pd and Pd-Mg, allowing pyrolysis temperatures up to 900ºC and 800ºC, respectively. On the other hand, in saline waters all modifiers presented similar efficiencies, being possible to employ pyrolysis temperatures of 1000ºC. It is only important to remark that permanent modifiers provided more efficient elimination of NaCl in the temperature range from 700ºC to 1000ºC. This way, because of the high salinity often found in produced waters, the Ir-W modifier was chosen for the determination of both analytes. Moreover, the addition of HF was suitable for the minimization of background signal in the measurement of Mn and Pb. However, in the case of Mn it was not possible to employ HF due to the decrease in the sensitivity. In the case of chromium, best results were attained when Pd was used as chemical modifier in combination with HF. In this condition an optimum pyrolysis temperature of 1100ºC was achieved, since in this level background signal was intensely reduced without loss of the analyte. All samples were analyzed by both standard calibration and standard addition methods in relation to all analytes studied. The ratio between slopes obtained was used to verify the presence of matrix interferences. In the optimum conditions established, the detection limits were 0.15 Ug/L, 2.0 Ug/L and 0.40 Ug/L and the relative standard deviations were 6.2 %, 3.3 % and 6.0 % for Mn, Pb and Cr, respectively.
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