Desenvolvimento de métodos de geração de vapor acoplados à espectrometria de absorção atômica para determinação da concentração de Hg em amostras de biodiesel e coproduto glicerina

Abstract

This work presents studies involving vapor generation methods for the quantification of Hg in biodiesel and byproduct glycerin. In Chapter 1, the concentration of Hg in biodiesel samples was evaluated using the photochemical vapor generation coupled to cold vapor atomic absorption spectrometry technique (PVG CV-AAS). For the development of the method, the main parameters were optimized to assess the best conditions for generation of volatile species of Hg. For this, the biodiesel samples were prepared in formic acid 20% (v/v) and ethanol 76% (v/v). The calibration curve was linear in the range from 2.5 to 10.0 μg L -1 . The limits of detection and quantification were 0.05 and 0.17μgL -1 , respectively and the relative standard deviations were less than 1.2%. Due to lack of a certified reference material of biodiesel with values for Hg, the accuracy of the method was assessed by recoveries tests and the values obtained ranged between 81 to 112%. There were no concentrations of Hg in biodiesel samples, considering the limit of detection. In Chapter 2, were applied three steam generation methods (photochemical generation of steam, chemical vapor generation with NaBH4 and SnCl2) in order to evaluate the mercury removal efficiency in pharmaceutical grade glycerin samples and crude glycerin derived from the process biodiesel production. For each method, the ideal conditions for the Hg vapor generation were optimized. For the proposed method photochemical reduction was required only a simple dilution of pharmaceutical grade glycerin samples with formic acid and water, and the samples crude glycerine, solubilization with formic acid, ethanol and water. By a comparison of the slopes of the calibration curves obtained, the generation efficiency of the system was determined to be 108% of that obtained by chemical reduction system with NaBH4 and 67% for the SnCl2.The limits of detection for the methods PVG-CV AAS, CV AAS with NaBH4, and CV AAS with SnCl2, were 0.12, 0.11, and 0.04 μg L−1, respectively. Due no adequate biodiesel certified reference material was not available with value for Hg, the accuracy was evaluated by recoveries tests and the values ranged between 84.4 to 106.6%. There was no Hg content in glycerin samples, considering the limit of detection. When methods were compared, the PVG-CV AAS presented adequate sensitivity for the quantification of Hg in biodiesel and glycerin samples, with limits of detection comparable to conventional methods for the determination of Hg by vapor generation. Also, provided a direct approach to the generation of volatile species of Hg without needing to use unstable reagents as NaBH4 and SnCl2 for the reduction and contributing with the green chemistry.