Extraction and fractionation of basic nitrogen compounds in vacuum residue by solid-phase extraction and characterization by ultra-high resolution mass spectrometry

- Solid-phase extraction was used to fractionate basic nitrogen-containing molecules from vacuum residue.
- The method was able to extract and fractionate N-containing compounds according to their molecular weight.
- The extraction permitted to extend vacuum residue molecular characterization by reducing the ESI ionic suppression effect.

A method to fractionate and separate nitrogen compounds according to their carbon number is presented here. Typical Brazilian vacuum residue was submitted to solid-phase extraction using a strong cation exchanger to fractionate the basic nitrogen compounds according to their molecular weight. The method described in this paper extended vacuum residue characterization by gradually removing the most basic species that suppress the ionization of compounds with higher mass (and thus less efficiently ionized). Approximately 1393 peaks were assigned when untreated vacuum residue was directly infused into a positive-ion electrospray ionization (ESI(+)) mass spectrometer coupled to Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). In contrast, more than 3500 different nitrogenous elemental compositions were attributed after fractionation. Nitrogen compounds with carbon numbers up to C100 were detected. Also, new classes (NO, N2O, and NOS) of nitrogen compounds were detected after the fractionation.