Direct sulfur-containing compounds analysis in petroleum via (+) ESI FT-ICR MS using HBF4 as ionization promoter

Abstract

Molecular-level characterization of sulfur-containing compounds has attracted particular attention due to its relative high abundance and negative impact on the refining process. In this paper, a novel analytical method for selective ionization of sulfidic and/or isolated thiophenic compounds (thiophene rings that are not condensed with aromatic systems) and condensed thiophenic compounds (thiophene rings that are condensed with aromatic systems, DBE ≥ 6, DBE = number of rings plus double bonds to carbon) in petroleum samples was developed by using fluoroboric acid (HBF4) as ionization promoter. Positive-ion electrospray ionization [(+) ESI] Fourier transform ion cyclotron resonance mass spectrometry was followed to characterize the molecular composition. Sulfidic and/or isolated thiophenic compounds were mainly ionized as protonated molecular ions ([M+H]+), while condensed thiophenic compounds (DBE ≥ 6) were mainly ionized as molecular radical cations (M+). The method was validated by various sulfur-containing model compounds and then applied to vacuum gas oil, crude oil and heavy oil samples. (+) ESI coupled with HBF4 additive is a simple method for selective ionization of sulfides and thiophenes in high-sulfur-content petroleum samples and has the potential for the characterization of sulfides and thiophenes in other complex mixtures.