Abstract Recent research has revealed the successful use of thermogravimetric analysis (TGA) in dynamic mode as an alternative method for determining degrees of oil conversion into biodiesel. This paper reports the results obtained with the use of TGA in quasi-isothermal mode (TGA-qISO) and with quantitative proton nuclear magnetic resonance (1H qNMR) to investigate the compositions of blends of soybean oil and biodiesels (10:0, 8:2, 6:4, 4:6, 2:8, and 0:10, m:m). Also, reported are data acquired by applying a programmed sequence of TGA-qISO and gas chromatography with flame ionization detection (GC-FID) steps to a biodiesel witness sample and samples prepared by a partner laboratory. All the biodiesels were obtained by transesterification via the methyl route using homogeneous basic catalysis. Thermogravimetric curves (TG) clearly distinguished between mass losses caused by ester volatilization and those resulting from oil thermal decomposition. Ester contents calculated by TGA-qISO proved concordant with 1H qNMR and GC-FID data, with maximum differences of around 0.5% and 1.4%, respectively.
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