E. P. da S. Santos, E. F. de Souza, T. C. P. M. Ramos, M. S. da Silva, and A. R. Fiorucci, “Evaluation of Potentiometric Methods for Acid Number Determination in Commercial Biodiesel Samples and Proposal of Alternative Method”, Orbital: Electron. J. Chem., vol. 10, no. 1, pp. 47-53, Jan. 2018.