Extraction induced by emulsion breaking as a tool for Ca and Mg determination in biodiesel by fast sequential flame atomic absorption spectrometry (FS-FAAS) using Co as internal standard

This paper reports, for the first time, the determination of Ca and Mg in biodiesel after their extraction from samples using the novel extraction induced by emulsion breaking. The quantification of the analytes in the extracts was performed by flame atomic absorption spectrometry operating at fast sequential mode (FS-FAAS) and using cobalt as internal standard. Several parameters that could affect the extraction efficiency of the method were studied such as the influence of surfactant (Triton X-114) and acid (HNO3) in the extractant solution. Also, operating parameters of the spectrometer (flame stoichiometry and observation height) were evaluated in order to allow sensitive measurements of Ca, Mg and Co in the same conditions. Quantitative extraction of the analytes can be obtained by using 20 mL of biodiesel and 4 mL of a solution containing 2.1 mol L−1 HNO3 and 7.5% m/v Triton X-114. In these conditions, the emulsions can be broken in 10 min of heating at 90 °C. The limits of quantification for Ca and Mg were 0.047 and 0.013 μg mL−1 , respectively. Five samples of soybean-based biodiesel were analyzed and recovery tests were performed, obtaining recovery percentages in the range of 88%-106%.