Comprehensive Petroporphyrin Identification in Crude Oils Using Highly Selective Electron Transfer Reactions in MALDI-FTICR-MS

Abstract

Petroprophyrins are biomarkers used to extract information about petroleum genesis among other characteristics. Identification of particular types, such as Ni, Cu, Mn, vanadyl (VO), and oxygenated or sulfur-containing porphyrins, typically involves exhaustive isolation and purification processes followed by high-resolution mass spectrometry analysis using atmospheric pressure photoionization [APPI-(+)] or electrospray [ESI-(+)] sources. Simultaneous identification of all porphyrins present in a particular crude oil or organic-matter-rich sediment still remains an analytical challenge. Here, we report a straightforward petroporphyrin isolation and identification methodology based on a single-step liquid–liquid (L–L) extraction (crude oil: acetonitrile) and high-performance thin-layer chromatography fractionation (HPTLC, aminopropyl-bonded silica) followed by selective ionization via electron transfer in matrix-assisted laser desorption ionization (MALDI-FTICR). Mass spectrometric analysis of the extracts resulted in detection of 350 individual compounds in the acetonitrile extract and 518 in the HPTLC extract, corresponding to the porphyrin families N4VO, N4VO2, N4VO3, N4VOS, and N4Ni as verified by isotopic structure analysis. To the best of our knowledge, this observation constitutes the largest simultaneous identification of Ni, VO, and oxygenated and sulfur-containing porphyrins in a single crude oil sample. In addition, the use of MALDI significantly reduces the amount of sample required for analysis (pico to femtomole levels) in comparison with continuous infusion methods such as APPI and ESI.

Simplification of Heavy Matrices by Liquid–Solid Extraction: Part II—How to Separate the LMW, MMW, and HMW Compounds in Asphaltene Fractions for V, Ni, and S Compounds

“…Sulfur has a completely different behavior compared to that of V and Ni showing that sulfur is not mainly driving the aggregation/sequestration of V and Ni.Regarding Ni and V, similar behavior is obtained except for their LMW extracts, for which the Ni compounds consistently have a lower percentage than the V compounds. This can explain why, in most molecular MS studies,33 V petroporphyrins have primarily been identified because the Ni and V compounds in nanoaggregates associated with the HMW fraction are more difficult to ionize. 39 CONCLUSIONS The use of liquid-solid extraction as an adequate methodology for the separation of the V, Ni and S compounds present in asphaltenes based on their molecular weights is reported for the first time.…”

Advances and Challenges in the Molecular Characterization of Petroporphyrins

“…65 Notably, the authors documented the separation of three distinct fractions of vanadium and nickel compounds in maltenes based on molecular weight and aggregation tendency determined using GPC. 13 The same authors performed a similar study by directly applying the technique to asphaltene using successive extraction with dimethylformamide, acetone and finally acetonitrile. Again, two highly aggregated enriched porphyrin fractions were hypothesized in the DMF and acetone fractions based on GPC.…”

“…17 Molecular transformations yield a range of structurally diverse porphyrin families that correspond to N4VO, N4VO2, N4VO3, N4VOS, and N4Ni, depending on the peripheral functional groups, as shown in Figure 1 (bottom row). 13,16 Figure 1. Geochemical transformations of chlorophylls.…”

Comprehensive two-dimensional liquid chromatography with inductively coupled plasma mass spectrometry detection for the characterization of sulfur, vanadium and nickel compounds in petroleum products

“…Porphyrins, chelated with nickel and vanadyl, are widely described in the literature [5][6][7][8][9].…”