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

One parameter to examine biodiesel quality has to do with the existence of metals, given that their presence can negatively affect fuel stability, by virtue of the alteration to their physicochemical properties. Given the significance of monitoring the concentration of metals in biodiesel, this work is aimed at developing a different mode for multielement determination through the use of energy dispersive X-ray fluorescence (EDXRF) spectrometry. For this purpose, an extraction procedure using sample preparation by emulsification associated with magnetic solid-phase microextraction was proposed for separation of Cd, Pb, Cr, V, and Mo from biodiesel samples for posterior analysis using EDXRF spectrometry. The emulsion was prepared by mixing the sample with n-propyl alcohol and 0.01 mol L–1nitric acid alongside subsequent contact with the solid phase (CoFe2O4nanoparticles impregnated with alizarin fluorine blue). Constrained mixing design was used to optimize the emulsion composition, and the recommended conditions were 36% (v v–1) n-propyl alcohol, 42% (v v–1) biodiesel, and 22% (v v–1) nitric acid solution for a total volume of 10 mL, using 100 mg of nanoparticles. The proposed extraction allowed enrichment factors of 9.3, 23, 27, 9.7, and 10 for Cd, Cr, V, Pb, and Mo, respectively. The limits of detection were found to be 13, 32, 17, 14, and 25 μg kg–1for Cd, Pb, Cr, V, and Mo, respectively. Recovery tests were performed by adding 200 μg kg–1of all analytes in question to six varying biodiesel samples with outcomes that registered between 85 and 114%. The recommended procedure was applied in the analysis of biodiesel, and the highest concentrations observed were 166 μg kg–1for Cd, 106 μg kg–1for Cr, 137 μg kg–1for Pb, 82 μg kg–1for V, and 92 μg kg–1for Mo.