Direct insertion probe high-resolution mass spectrometry for the rapid chemical description of petroleum heavy ends - Analysis of vacuum gas oils, bitumen, and asphaltenes

Despite the steady progress in analytical instrumentation and methodologies, the chemical description of petroleum heavy ends remains challenging, in particular, due to the structural and compositional diversity. In recent years, Fourier transform mass spectrometry, with its unbeaten resolving power and mass accuracy have shown to be a suitable tool for the molecular level characterization of petroleum, commonly referred to be as Petroleomics. Most often direct infusion approaches, such as electrospray ionization are utilized, and the elemental composition attribution to the individual resolved components allows in-depth analysis. The knowledge of the chemical composition for petroleum heavy ends can be regarded as a crucial aspect for their processing and utilization. Nonetheless, direct infusion techniques cannot adequately cope with the tremendous complexity, and coupling techniques or tandem mass spectrometry via fragmentation are approaches for further structural and isomeric differentiation. In this study, direct insertion probe (DIP) coupled to Fourier transform ion cyclotron resonance mass spectrometry (12 T, Bruker solariXR, FT-ICR MS) was used as a complementary technique. This setup allows vaporizing (desorption and intended pyrolysis) the sample material directly in the ionization chamber. Ionization was performed deploying atmospheric pressure chemical ionization (APCI) receiving a fingerprint for the polar constituents with high sensitivity towards oxygenated constituents as well as with atmospheric pressure photoionization (APPI) enabling the ionization of a wide range of components with high sensitivity for polycyclic aromatic hydrocarbons and, in particular, for Sulphur-containing species. Various petroleum heavy fractions were in the focus of this study, covering a broad range of sample materials, such as atmospheric residues, vacuum gas oils (VGO), vacuum residues, bitumen, and asphaltenes. Briefly, DIP FT-ICR MS has proven to be a rapid and flexible tool for the molecular description of petroleum heavy ends, allowing to easily investigate high viscose and solid materials with a minimum of sample preparation. The intended pyrolysis of macromolecular constituents allows investigating the core building blocks of these high molecular weight species. Additional fragmentation experiments via collision-induced dissociation of a selected m/z-range enabling another dimension of information on the alkylation pattern. Thus, atmospheric DIP featuring a typical analysis time of below 10 min and easy atmospheric pressure interface will be a complementary routine tool for petroleum heavy ends helping to unravel the ultra-complex composition.