Normal electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR) mass spectrometry in negative-ion mode has been used to compare the composition of Russian and North Sea crude oils and their eight different distillation fractions (160-210, 210-260, 260-310, 310-360, 360-410, 410-460, 460-510, and 510-560 °C). This is the first time that the polar compound distribution, especially species containing O, O 2 and N atoms, has been studied as a function of temperature. The results obtained are consistent with measured total acid number and nitrogen values; the North Sea crude oil had higher acid but lower nitrogen content compared to the Russian crude oil. The influence of high acid content on the ionization efficiency of other polar species (O and N) in oil samples is also presented for the first time.

This paper discusses an FT-ICR mass spectrometry study of Russian and North Sea crude oils and their six distillation fractions (260–310, 310–360, 360–410, 410–460, 460–510, and 510–560 °C) by positive electrospray ionization (ESI) mode. Only one major heteroatom class, N class (pyridine benzologues), was found for both crude oils and for every distillation fraction. The relative abundance of N class was found to be somewhat higher for North Sea oil than the Russian oil, containing higher series (DBE values) and carbon distributions. On the other hand, the second most abundant class found for crude oils, the NS class, was found to be more abundant for Russian than North Sea oil samples, in accordance with experimentally measured sulfur values for crude oils. Correspondingly, Russian oil contained a higher series and also carbon distributions NS compounds, in comparison to North Sea oil. The oxygen containing sulfur compounds (OS class) were present only at a low distillation temperature (<410 °C) fractions. The results show that compounds present at trace amounts are more easily observed from distillation fractions than in crude oils.