Analysis of Geologically Relevant Metal Porphyrins Using Trapped Ion Mobility Spectrometry–Mass Spectrometry and Theoretical Calculations

• Published in: Energy & fuels 2016-12, Vol.30 (12), p.10341-10347
• Main Authors: Benigni, Paolo, Bravo, Carlos, Quirke, J. Martin E, DeBord, John D, Mebel, Alexander M, Fernandez-Lima, Francisco
• Format: Article
• Language: English
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.6b02388

The structural characterization of metal porphyrins has been traditionally challenging as a result of their large structural and compositional diversity. In the present paper, we show the advantages of gas-phase, postionization separations for the fast identification and structural characterization of metal octaethylporphyrins (Me–OEP) from complex mixtures using trapped ion mobility spectrometry (TIMS) coupled to ultrahigh-resolution mass spectrometry (FT-ICR MS). TIMS–FT-ICR MS allows for the separation of Me–OEP (Me = Mn, Ni, Zn, VO, and TiO) within a crude oil sample based on accurate mass and mobility signatures (with a mobility resolving power of R IMS ∼ 150–250). Accurate collision cross sections are reported for Me–OEP in nitrogen as bath gas (CCSN2 ). Inspection of the Me–OEP mobility spectra showed a single mobility component distribution for Me–OEP (Me = Mn, Ni, and Zn) and a multi-component distribution for the two metal carbonyls, vanadyl (VO) and titanyl (TiO) Me–OEP. Candidate structures were proposed at the DFT/B3LYP/6-31g­(d) level for all Me–OEP mobility bands observed. Inspection of the optimized Me–OEP candidate structures shows that manganese, zinc, and free OEP adopt a planar conformation, the nickel-complexed OEP structure adopts a “ruffled” conformation; and the metal oxide OEP adopts a dome conformation, with carbonyl pointing upward, perpendicular to the plane of the structure.