Determination of sodium in biodiesel by flame atomic emission spectrometry using dry decomposition for the sample preparation

This work reports a method for sodium determination in biodiesel fuel by flame atomic emission spectrometry (FAES) using the dry decomposition for the sample preparation. Two calibration methods for the sodium quantification were evaluated: the standard addition and the external standard. In either cases significant matrix effects or loss of sensibility were not observed. For all determination, the external standard was chosen as a calibration method and the limit of detection (LOD) and limit of quantification (LOQ) were 1.3 and 4.3 mg Na kg−1 of biodiesel, respectively. The accuracy method was checked by means of addition and recovery tests and recovered results varied from 93% to 110%. The relative standard deviations of the results were less than 4.0% in all cases. Afterwards, the performance method was checked in different biodiesel samples from vegetable and animal matrices collected in Mato Grosso State, Brazil. The sodium concentration in these samples varied from below LOQ to 28.7 mg Na kg−1 of biodiesel. The simplicity, accuracy and precision of the proposed method suggest that it can be a good alternative for sodium determination in biodiesel samples.