Determination of sodium and potassium in biodiesel by flame atomic emission spectrometry, with dissolution in ethanol as a single sample preparation step

A method was developed for the determination of sodium and potassium by flame atomic emission spectrometry (FAES), using dissolution in ethanol as a single sample preparation step. Adjustment of the viscosity of standards was achieved using samples of washed biodiesel, free of the analytes. The analytical curves showed linear correlation coefficients (r) higher than 0.99. The limits of quantification (LOQ) in biodiesel/ethanol solution (1:20, w/v) were 4.00 and 3.60 mg kg−1 for Na and K, respectively. In 1:10 (w/v) biodiesel/ethanol solutions the LOQ were 2.16 and 2.00 mg kg−1 for Na and K, respectively. Recoveries in the range 91–108% were obtained in addition and recovery tests, with coefficients of variation (% CV) lower than 13%. The slopes of the analytical curves obtained using different matrices indicated that the matrix had no influence on quantification of the analytes. These results suggest that the proposed method offers a simple, rapid and low cost alternative for Na and K determination in biodiesel samples.