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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.

In the present work, a minicolumn of XAD-4 loaded with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) is proposed as a preconcentration system for uranium determination in well, tap and mineral water samples by spectrophotometer using arsenazo III as the chromogenic reagent. Initially, a two-level (23) full factorial design was used for the preliminary evaluation of three factors, involving the following variables: sampling flow rate, elution flow rate, and pH. This design has revealed that, for the studied levels, buffer concentration and pH were significant factors. When the experimental conditions established in the optimization step were pH = 8.6, and an elution flow rate of 8.6 mL min−1using 0.5% m/v ascorbic acid, this system has allowed for the determination of uranium with a detection limit (LOD) (3σ/S) of 0.05 μg L−1and a quantification limit (LOQ) (10σ/S) of 0.16 μg L−1. The precision expressed as the relative standard deviation (R.S.D.) of 0.8% and 1.9% at 10.0 and 1.0 μg L−1, respectively- and a preconcentration factor of 184.5 for a sample volume of 50.0 mL. Accuracy was confirmed by uranium determination in the standard reference material, NIST SRM 1566b trace element units in Oyster Tissue samples, and spike tests with recuperations ranging from 93.2 to 105%; the procedure were applied for uranium determination in tap water, well water, and drinking water samples collected from Caetité and Cruz das Almas Cities, Bahia, Brazil. Five water samples were analyzed the uranium concentrations varied from 0.50 to 2.07 μg L−1