Ion Chromatography as a Sustainable Alternative for Monitoring Ethanol and Free Glycerol in Biodiesel

The amounts of glycerol and ethanol in purified biodiesel are standardized by regulatory agencies to ensure the performance of the biofuel in combustion. Therefore, the correct measurement of these components is essential to evaluate the final quality of biodiesel and to monitor its synthesis. In addition, evaluation of the composition in ethanol and glycerol is also relevant in modeling the kinetics of the transesterification reaction. Ion chromatography was evaluated as an alternative technique to identify and quantify ethanol and free glycerol in biodiesel samples from heterogeneous, homogeneous, and enzymatic catalysis. The analytical method exhibited detection limits of 0.1 and 0.94 mg·L^-1 and quantification limits of 0.3 and 2.83 mg·L^-1 for glycerol and ethanol, respectively. Additionally, the analytical method demonstrated suitable repeatability (RSD_glycerol = 0.14% and RSD_ethanol = 0.80%), reproducibility (RSD_glycerol = 1.27% and RSD_ethanol = 3.32%), and selectivity, proving to be reliable in relation to the matrix effects according to the validation guide of the Association of Official Analytical Chemists (AOAC). Ion chromatography has been demonstrated to be an alternative technique that is adequate for the quantification of ethanol and glycerol in different alkyl ester systems. Moreover, the technique dispenses the use of organic solvents, resulting in a considerable reduction of toxicity, analysis time, and analytical costs, and contributes to both environmental and operational securities.