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

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, N-2, O-3, O-1, O-2, NO2, NS, NOS, and OS classes. In general, FT-ICR MS favored the detection of higher molecular weight analyzes 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 (N-x), while lighter oils presented a higher abundance of oxygenated compounds (O-1). The heavier ones had a higher abundance of O-2 class, which was not verified by Orbitrap-MS, where a prevalence of O-2 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.