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

Abstract 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.