A Screening Method to Evaluate Soybean Oil-Based Biodiesel Oxidative Quality During Its Shelf Life

Biodiesel quality is negatively affected by oxidation, which occurs primarily during the storage and distribution steps. Therefore, the use of suitable analytical methods to assess the oxidation of this biofuel is a fundamental requirement. A direct ambient ionization mass spectrometric technique (EASI-MS) was tested as a screening method to evaluate the oxidative quality of biodiesel during its shelf life. Using EASI-MS, the relative abundance of the hydroperoxide ion of m/z 349 was monitored during the induction period (IP) in soybean and a blend of soybean/beef-tallow (70/30) biodiesel samples. The peroxide value obtained by AOCS Cd 8b-90 was used as a standard method to evaluate the EASI-MS data by comparison. The results showed that the peroxide value and EASI-MS data were highly correlated during the IP for both samples (r > 0.98). Relative abundances of the ion of m/z 349 below 72 % was also found to characterize biodiesel in an initial oxidation stage, whereas abundances exceeding 72 % indicated biodiesel samples nearing the end of their stability. EASI-MS was therefore found to provide a simple and effective analytical protocol to evaluate the oxidative quality of biodiesel during the IP.