Dissolution in Ethanol as a Sample Preparation Procedure for Determination of Metals in Biodiesel by FAAS

This work proposes an alternative method for determination of sodium, potassium, calcium, and magnesium in biodiesel by flame atomic absorption spectrometry (FAAS), using dissolution in ethanol for sample preparation. The ethanolic medium enabled the use of aqueous standards, and adjustment of the viscosity of the solutions was achieved using samples of washed biodiesel, free of the analytes. The analytical curves showed linear correlation coefficients (r) higher than 0.99, and the slopes obtained using different matrices indicated that the matrix had no influence on quantification of the analytes. The instrumental limits of detection (LOD) and quantification (LOQ) for all metals were in the ranges 0.05- 0.31 mg kg^-1 and 0.17-1.02 mg kg^-1,respectively. The recovery percentages were in the range 99-114%, with relative standard deviations (RSD) lower than 15%. The accuracy of the method was also evaluated by comparison with the Brazilian official method, and no significant differences were observed (p=0.05). These results suggest that ethanol dissolution can be used as an alternative method of sample preparation for determination of Na, K, Ca, and Mg in biodiesel samples by FAAS.