Evaluation of digestion procedures for simultaneous determination of Ca, P, Mg, K and Na in biodiesel by inductively coupled plasma optical emission spectrometry

Abstract

Neste trabalho foi avaliada a eficiência de dois procedimentos para digestão ácida de amostras de biodiesel visando à determinação de Ca, P, Mg, K e Na por espectrometria de emissão óptica com plasma acoplado indutivamente com configuração axial (ICP OES). Nas digestões em sistema aberto, foi utilizada a mistura contendo ácidos nítrico, sulfúrico e peróxido de hidrogênio e aquecimento condutivo; enquanto que no procedimento empregando forno de microondas com cavidade foi utilizada a mistura contendo ácido nítrico e peróxido de hidrogênio. Os procedimentos foram avaliados considerando-se limites de quantificação, precisão, acidez final dos digeridos e teor de carbono residual. Os teores de carbono residual nos digeridos foram 0,358 ± 0,012% para o sistema aberto com aquecimento convencional e 0,614 ± 0,023% para o sistema fechado com aquecimento assistido por radiação microondas, o que demonstra a alta eficiência dos procedimentos propostos. O sistema de digestão em forno de microondas com cavidade resultou em maior rapidez, segurança e resultados analíticos com percentuais de recuperação de 89,0-103,0% e desvios menores que 5%. Os limites de detecção obtidos, ≤ 0.40 µg g -1 , são adequados para a determinação dos analitos, conforme os limites estabelecidos na legislação brasileira. Três amostras de biodiesel produzidas de diferentes fontes foram analisadas. Em comparação com outros procedimentos propostos na literatura, o procedimento desenvolvido usando forno de microondas com cavidade apresenta vantagens, tais como não necessitar de soluções orgânicas para calibração e não usar solventes orgânicos tóxicos.In the present work, the efficiency of two procedures for the digestion of biodiesel was investigated for the simultaneous determination of Ca, P, Mg, K and Na by axial view ICP OES. In the open system with conventional heating, concentrated nitric and sulfuric acids were added to the samples, and the addition of hydrogen peroxide completed the digestion. In the microwave-assisted closed system, complete digestion was performed using concentrated nitric acid and hydrogen peroxide. The analytical performances were evaluated through limits of quantification, precision of the overall procedures, final acidity of the digests, and residual carbon contents. The contents of residual carbon for the biodiesel samples digested were 0.358 ± 0.012% using the open system with conventional heating and 0.614 ± 0.023% using the microwave-assisted closed vessel system, demonstrating the high efficiency of both proposed procedures. The optimized microwave-assisted decomposition procedure produced the fastest, safest and most accurate analytical results with recoveries of 89.0-103.0% and deviations lower than 5% in most cases. Low limits of detection were obtained (≤ 0.40 µg g -1 ), adequate for the established limits set out in Brazilian legislation for these analytes. Three biodiesel samples produced from different oil sources were analyzed. In comparison with other procedures proposed in the literature, the developed procedu...

Evaluation of Sample Preparation Procedures for Trace Element Determination in Brazilian Propolis by Inductively Coupled Plasma Optical Emission Spectrometry and Their Discrimination According to Geographic Region

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Determination of Ca, Mg, Na, and K in Biodiesel of Oilseed from Northern Brazil

“…Jesus et al (2010) and Edlundet al (2002) found Mg content in biodiesel samples. 15,19 The Na concentration obtained in samples were lower than the values found in biodiesel samples studied by Korn et al (2010). 20 The B2 and B4 samples presented high values of K. The value found in B2 could be due to bacuri oil used in the process of obtaining biodiesel.…”

Biodiesel Trace Element Analysis by Energy Dispersive X-ray Fluorescence Spectrometry Using Magnetic Solid-Phase Microextraction

“…The microwave oven was employed to promote the digestion using the following heating program: (I) 500 W (4 min); (II) 750 W (2 min); (III) 1000 W (15 min); (IV) 750 W (5 min); and (V) ventilation (15 min). After digestion, the samples were diluted to 25.0 mL with water …”