Determination of oxidation stability becomes a critical fundamental analysis to ensure biodiesel quality. The biodiesel’s degradation by oxidation may compromise fuel properties and engine durability due to forming products of fatty acid decomposition. In this present study, the oxidation stability of palm-oil biodiesel and its blends with diesel fuel (cetane number 48) was determined using EN 15751 (Rancimat Method) and ASTM D 7545 (Rapid Small Scale Oxidation Test, RSSOT Method). Here, the determination from either test was compared and analyzed using ANOVA and the mathematical function. Based on the result, diesel fuel has oxidation stability 11 times higher than palm-oil biodiesel, analyzed by the RSSOT method. Additionally, the correlation factor of oxidation stability of biodiesel samples in this work was 21.52 and for biodiesel blend (B20 to B90) it was 23.66 that was used as a conversion oxidation value between RSSOT and Rancimat method. The models presented a high correlation with the R2 values of 0.9535 for biodiesel samples and 0.9823 for biodiesel blend (B20-B90) indicated the accuracy of the models to predict the value of oxidation stability of both the Rancimat and the RSSOT accelerated oxidation methods.

Monoglycerides and glycerol are by-products contaminants, after transesterification, in biodiesel that can lead to severe operational and engine problems such as wax precipitation, filter plugging and engine deposits. Therefore, strict regulations have been made, and accurate quality control is required. In this work, levels of monoglycerides and glycerol were determined using gas chromatography (GC) equipment with flame ionization detector (FID) refers to standard methods ASTM D6584 and EN 14105. However, the monoglycerides determination still needs firmness and validation to develop standard calibration series to fit the constituent fatty acid components of the feedstock used. This paper shows three fatty acids, i.e., monoolein, monopalmitin, and monostearin, as major components in palm-based biodiesel, which would be prepared as standard calibration and determined from commercial biodiesel samples in the determination of monoglyceride levels accurately and thoroughly. The result shows that standard solutions produce a curve with high linearity; it was above 0.998 (for free glycerol, monopalmitin, monoolein, and monostearin) and its accuracy values were >95%. However, the result for eight commercial biodiesel samples in Indonesia had a range of 0.23-0.54% w/w for total monoglycerides, 0.07 to 0.14 (% w/w) for total glycerol, and < 0.01% w/w for free glycerol, which was fulfilling to the ASTM D6751 and EN 14214 specification requirements.