Qualitative characterization of oxygen-containing compounds in fuel extracts by using (-) electrospray ionization coupled to a linear quadrupole ion trap/orbitrap mass spectrometer

Abstract

Qualitative characterization of oxygen-containing compounds (OCCs) in fuels is imperative, as these compounds detrimentally influence fuel stability. Hence, development of analytical methods that enable thorough qualitative information will likely enhance correlations between composition and fuel failures. In this work, (-) electrospray ionization (ESI)coupled to a linear quadrupole ion trap/orbitrap mass spectrometer provided detailed qualitative analysis of OCCs in jet fuels, marine gas oil (MGO)and diesel. The high resolving power and mass accuracy of the orbitrap and soft ionization of ESI advanced the current OCC qualitative knowledge of fuels as the number of OCCs classes identified exceeded previous works. Up to nine, twenty and nine different homologue ion series (i.e.,ions with the same empirical formula (e.g.,CnH2n-7O) but differ by 14 Da (m/z 149, 163, 177, etc.)) were detected in the jet fuels, diesel and MGO, respectively. Additional detailed qualitative information included the average ring and double equivalent values, carbon numbers and molecular weights for the detected OCCs in each fuel. With limited fragmentation of ions, Kendrick Mass Defectplots were made that enabled straightforward comparison of the OCC compositions offuels. Clear qualitative differences were noted among the different types of fuels (i.e.,jet fuels compared to diesel) and when the threejet fuels were compared to each other. As the method demonstrated proficiency at providing detailed compositional information, it may be employed for future storage and thermal stress testing of fuels to monitor and evaluate compositional changes. Overall, the method demonstrated qualitative proficiency and may be used to establish important links between composition and fuel stability; this is a critical prerequisite for improving fuel quality.