This work describes the characterization of esters derived from waste frying oil, sewage scum, and domestic fat trap residue. The innovative aspects of this work include the use of domestic fatty residues, study of the influence of the gas chromatography injection conditions on correct determination of the esters content, and the use of deactivated silica to purify esters from alternative sources in order to be able to classify them as biodiesel. Thermogravimetric analyses of the samples showed mass losses characteristic of evaporation and ester decomposition, which could be correlated with the esters content. Infrared spectra showed no significant OH, indicative of low acid values. The esters contents were determined by gas chromatography, with C-17:0 and C-18:1 esters as external standards, in accordance with the EN 14103:2003/2011 and NBR 15764:2015 methodologies. Better responses for the quantification of esters content were achieved using a PTV injector, rather than an isothermal injector, and heptane as the solvent in the analysis. The initial esters contents of the materials were between 86 and 98%. Deactivated silica was used as an adsorbent to remove undesirable contaminants, so that the esters contents of the samples complied with the minimum value required by legislation (>96.5%). (C) 2018 Elsevier Ltd. All rights reserved.