Characterization of nonvolatile polar compounds from Brazilian oils by electrospray ionization with FT-ICR MS and Orbitrap-MS

Abstract

Among the different types of available high-resolution mass spectrometers, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and Orbitrap-MS are important tools for the study of nonvolatile crude oil fraction composition. No in deep comparison between each analyzer was still performed, mostly with a wide broad of real crude oil samples. Therefore, in this study a representative set of 30 Brazilian crude oils with a wide range of American Petroleum Institute (API) gravity (13.1–53.7) were considered. The ICR and Orbitrap analyzers allowed the elemental composition to be obtained by accurate mass measurements, and the most abundant species were mainly N, N2, O3, O1, O2, NO2, NS, NOS, and OS classes. In general, FT-ICR MS favored the detection of higher molecular weight analytes in relation to Orbitrap-MS. The notable distribution of the heteroatom classes showed that crude oils with intermediate API gravity presented a higher relative abundance of nitrogenous compounds (Nx), while lighter oils presented a higher abundance of oxygenated compounds (O1). The heavier ones had a higher abundance of O2 class, which was not verified by Orbitrap-MS, where a prevalence of O2 class was detected in major crude oils. An increase in average molar weight values was observed when we changed technique (Orbitrap-MS → FT-ICR MS) and ionization mode (negative → positive), since FT-ICR MS detected substances with higher m/z. In this way, this work examines the application of two different high-resolution mass analyzers, and shows the versatility and analytical response of each one within petroleomics.