Extração induzida por quebra de emulsão: uma nova estratégia para determinação de metais traços em amostras de óleo

• Autor(a) principal: Brum, Daniel Mares
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/221
• topic: Óleo; Extração induzida; Quebra de emulsão; Metais; Oil; Extraction induced; Emulsion breaking; Metals; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

The present work reports the development of a novel methodology for the determination of trace metals in organic liquids. The method is based on the extraction induced by emulsion breaking, which is carried out with the formation of a stable emulsion between the oil (10 mL) and an aqueous phase (2 mL) containing a surfactant and acid. After that, the emulsion is broken by heating or centrifugation and the water phase containing the extracted metals is collected and analyzed using different analytical techniques. The work related here was divided in four steps. In the first step, Cu, Fe, Ni and Pb were determined in diesel oil. Several parameters that could affect the extraction, such as the concentration and nature of the surfactant (Triton X-100 and Triton X-114), the HNO3 concentration and the temperature employed for emulsion breaking were evaluated. Quantitative extractions were obtained by mixing 10 mL of diesel oil with 2 mL of an aqueous solution containing 7% m/v Triton X-114 and 10% v/v HNO3. The second step described the extraction/ preconcentration of Zn in diesel oil samples followed by its determination by FAAS using a flow injection system. The proposed methodology was optimized using a multivariate approach based on the Doehlert design. The studied variables were the surfactant concentration (1-9% m/v), HNO3 concentration (1-19% v/v) and the temperature used for emulsion breaking. Good theoretical description of the behaviour of data was verified. The optimum conditions were 5% m/v Triton X- 114, 15% v/v HNO3 and a temperature of 80oC. In the third step, a careful study was performed about the application of the proposed procedure in the metals determination in diesel oil by ICP-MS, which present serious limits for the analysis of samples with high content of carbon (as diesel oil). In this context, a method was developed for the determination of Al, Cu, Mn, Ni, Sn and V in diesel oil. In this case, the emulsions were broken by centrifugation for 60 min at 3500 rpm and ambient temperature. The optimum conditions for the extraction were similar to those observed previously (5% m/v Triton X-114 and 10% v/v HNO3). Finally, a systematic study was performed to verify the influence of the type of surfactant used in the emulsification (Triton X-114, Triton X-100, Twee 20 and sodium dodecylsulfate) and the nature of the acid (HNO3 and HCl) employed for the extraction. The extraction of several elements was evaluated (As, Cr, Cu, Mn, Pb and V) and mineral oil spiked with the analytes of interest (Conostan standards) was used. This study revealed that only As can not be efficiently extracted when HCl (< 40%) or HNO3 (< 60%) are used. In general, the extraction efficiencies were lower when sodium dodecilsulfate was employed as emulsifier agent. All results showed that the proposed procedure is advantageous because the metals can be measured in the aqueous medium and the calibration can be done in the same condition. Also, the extraction make possible the preconcentration of the analytes, improving the limits of detection and quantification.