This paper proposes the use of easy ambient sonic-spray ionization mass spectrometry (EASI-MS) to detect markers of high-level oxidation in biodiesel via a simple and rapid single-shot analytical protocol. Soybean biodiesel was oxidized in Rancimat and then analyzed at different time periods by both EASI-MS and traditional physicochemical methods. Major changes in the EASI(+)-MS profile as well in the peroxide value, acidity, and kinematic viscosity were observed after the induction period (IP). Fatty acid methyl esters (FAME) and their respective hydroperoxides were primarily identified using EASI-MS in fresh biodiesel and at the initial stages of oxidation. After the IP, EASI-MS revealed the formation of dimers and low-mass non-volatile molecules, such as aldehydes, due to hydroperoxide breakdown. Both the dimers and aldehydes are attributed to secondary oxidation products. Therefore, EASI-MS was found to provide a fast, direct, and accurate technique to identify markers in biodiesel with high-level of oxidation.
Practical applications: EASI-MS is a useful technique to identify primary and secondary oxidation products formed in biodiesel in a single procedure that is rapid and does not require sample preparation. Therefore, EASI-MS has potential applications in biodiesel routine analysis to screen samples with high-levels of oxidation.
EASI-MS provides a fast, direct, and accurate technique to identify markers in biodiesel with high-level of oxidation.