Desenvolvimento de método analítico para determinação de metais por técnicas de Espectrometria Atômica em amostras de glicerina

Abstract

Among the by-products originating from the production of biodiesel, the glycerin deserves special attention due to their high volume that is produced during the process. However, this by-product may have organic impurities (alcohol and fatty acids) and inorganic (metals which are derived from the catalysts used in the production of biodiesel). These impurities can difficult the use of crude glycerin in cosmetic, pharmaceutical and also in food industry. In order to improve the quality monitoring from crude glycerin from biodiesel production, in this work were developed simple, rapid and low cost methods for determination of metals such as Ca, Mg and K in samples of crude glycerin using Atomic Spectrometry techniques. The proposed method for determination of Ca, Mg and K consisted of solubilization 1 g of sample in water for a volume final of 50 mL. Two methods for comparison have also been developed: solubilization of 0.5 g sample in a solution containing 34% formic acid for a volume final of 10 mL for determination of Ca and Mg and solubilization of 0.5 g of sample in ethanol for a volume final of 10 mL for the determination of K. The results obtained with the solubilization in water were in agreement with those obtained solubilization with formic acid for Ca and Mg and solubilization with ethanol for K. Therefore, it is concluded that the solubilization in water is a simple and viable method for glycerin sample preparation. The values of limits of detection for Ca, K, Mg using the solubilization in water were 0.315; 0.059 and 0.157 mg kg, respectively. Calibration curves were prepared according to each proposed method and showed good linearity. To evaluate the accuracy, recovery assays were performed with both the methods and the recoveries ranged from 90-115%, with values of relative standard deviation less than 8%, indicating good accuracy of the measure. Four crude glycerin samples obtained from biodiesel plants of RS were analyzed after treatment with the different methods of sample preparation and the obtained results of concentration of Ca, Mg and K were in agreement with the found values. Thus, it is possible to conclude that the solubility in water is a new, simple and efficient method for sample preparation and determination of metals in glycerin.