Determination of Na and K in biodiesel by flame atomic emission spectrometry and microemulsion sample preparation

Abstract

Um método para determinação de Na e K em biodiesel proveniente de diferentes óleos vegetais é proposto. São combinadas as vantagens da FAES com a simplicidade da preparação da amostra por microemulsão e calibração usando padrões aquosos. As microemulsões foram preparadas pela mistura de biodiesel, n-propanol e solução aquosa ácida, permitindo o uso de padrões inorgânicos para a calibração. Foram comparadas a introdução discreta (DA) e aspiração contínua (CA) da amostra apresentando LODs semelhantes, na ordem de 0,1 g g -1 para ambos analitos, que são adequados para a determinação dos mesmos, conforme os limites estabelecidos na legislação brasileira. A exatidão do método foi avaliada por testes de recuperação, com resultados entre 83% e 120% e, por meio da comparação dos resultados obtidos por ICP OES.A method for the determination of Na and K in biodiesel, from different vegetable oils, is proposed. The advantages of the FAES were combined with the simplicity of microemulsion preparation and calibration using aqueous standards. Microemulsions were prepared by mixing biodiesel samples with n-propanol and aqueous acid solution, which allowed the use of inorganic aqueous standards for the calibration. Sample introduction through discrete aspiration (DA) or by continuous aspiration (CA) were compared, presenting similar LODs, in the order of 0.1 g g -1 for both analytes, adequate to the established limits in the Brazilian legislation. The accuracy of the method was checked through recovery tests, with results between 83% and 120%, and through the comparison of the results with those obtained by ICP OES.

Multi-element determination of Cu, Fe, Ni and Zn content in vegetable oils samples by high-resolution continuum source atomic absorption spectrometry and microemulsion sample preparation

“…Furthermore, some of these metals are subject to food legislation (Cypriano et al, 2008;Reyes & Campos, 2006), and have been used for detection of adulterations in oil samples (Gonzálvez, Armenta, & de la Guardia, 2010). It is important to emphasize either that in tropical countries with large territorial areas as Brazil, the cultivation of vegetable oil sources to produce biodiesel could also achieve an economic up-scale and the presence of metals in the raw material can affect the biodiesel quality (Chaves et al, 2008;de Jesus, Silva, & Vale, 2008;de Souza, Leocádio, & da Silveira, 2008;Vieira, de Oliveira, Gonçalves, de Souza, & Campos, 2009). However, the accurate determination of trace metals in this kind of samples is still an analytical challenge, owing to their low concentration level and the difficulties that arise due to the characteristics of the matrix.…”

Electrochemical Methods in Analysis of Biofuels

“…The use of microemulsions is a very interesting way to make biodiesel compatible with sample introduction systems used in FAAS because microemulsions are prepared in a very fast, simple and inexpensive way. This sample pretreatment strategy was adopted also by Chaves et al [75] for determination of K and Na in biofuel samples by FAAS. Another interesting sample pretreatment procedure is the dry decomposition in muffle furnaces.…”

Analytical Methodology for the Determination of Trace Metals in Biodiesel

“…Conversely, organic standards have several disadvantages, such as high cost, instability, they are very dangerous, carcinogenic, and often require the use of special apparatuses and equipment. However, numerous studies have used emulsified standards and not aqueous standards (Chaves et al, 2008a(Chaves et al, , 2008bJesus et al, 2008;Saint´Pierre et al, 2004;Giacomelli et al, 2004), justifying this choice based on the fact that in most cases emulsified standards are more stable, as well as the difference in sensitivity compared to aqueous standards. Figure 2 illustrates the results of the equations adjusted for the seven biodiesel samples evaluated by the analyte addition method, aiming at a comparison of the behavior of Cd in the different matrices (emulsified standards) and in aqueous standards.…”