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.

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Electron-transfer ionization in matrix-assisted laser desorption/ionization (ET-MALDI) is widely used for the analysis of functional materials that are labile, unstable, and reactive in nature. However, conventional ET matrices (e.g., trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malononitrile (DCTB)) still lack in performance due to cluster formation, reactivity with analytes, and vacuum instability. In this contribution, we report the use of α-cyanophenylenevinylene derivatives as UV MALDI matrices for the analysis, by ET ionization, of nanoparticles, polymers, porphyrins, and fullerenes. The synthetic versatility of the phenylenevinylene (PV) core allowed us to modulate physicochemical properties, fundamental for efficient formation of primary ions in the gas phase under MALDI conditions, such as planarity, ionization potentials, molar absorptivity, and laser thresholds. For instance, introduction of −CN groups in vinyl positions of the PV core induced structural disruption in planarity in the new α-CNPV derivatives, shifting their maximum molar absorptivity to UV wavelengths and increasing their ionization energy values above 8.0 eV. UV MALDI-relevant photophysical properties in solution and solid state are reported (λmax and ε355nm). LDI spectra of α-CNPVs exhibit predominant signals due to M+• and [M + H]+ species, whereas the standard matrix DCTB shows peaks associated with clusters and nondesirable products. The mass spectrometry (MS) performance of six α-CNPV derivatives was assessed for the ionization of a standard compound, with α-CNPV-CH3 and α-CNPV-OCH3 exhibiting better analytical figures of merit than those of a standard matrix (DCTB). These new matrices display high vacuum stability (79%) for up to 240 min of residence in the ionization source, in contrast with DCTB with 13%. Vacuum stability is vital, particularly for applications such as high-throughput analysis and imaging MS. In addition, when a mixture of 20 analytes (PAHs, porphyrins, and triphenylamine dyes) ranging from m/z 300 to 1700 was analyzed via ET-MALDI, we observed analyte coverage of 90% with the α-CNPV-CH3 derivative, whereas DCTB afforded only 70%. Finally, α-CNPV-CH3 was tested and compared with DCTB, as ET-MALDI matrix for petroporphyrins, conjugated polymers, gold nanoparticles, and fullerene derivatives analysis, outperforming in most cases the standard matrix.

Heavy crude oils constitute the largest reserves; however, their extraction faces several challenges as a result of their high asphaltene content. Reducing the viscosity by physicochemical treatments or chemical transformation on heavy asphaltenes is still a challenge because of matrix complexity. On the other hand, the 1,3-dipolar cycloaddition (1,3-DC) reaction has been used to increase the solubility and rheological properties of graphene and fullerenes, suggesting that 1,3-DC on heavy crude oils can modify directly the chemical structure of titled compounds affecting their aggregation. Starting from Colombian heavy oils and purified asphaltenes, we used a set of chemical modifiers based on long-chain aliphatic and aromatic aldehydes and N-hexylglycine, followed by in situ reactions at several concentrations. Rheological measurements showed a significant reduction on crude oil viscosities up to 98% depending upon the alkyl chain and concentration; furthermore, 1,3-DC reactions between purified asphaltenes and chemical modifiers were followed by nuclear magnetic resonance experiments, which give credence to the viscosity reduction of heavy crude oils based on chemical reactivity.

We compare the performance of atmospheric pressure photoionization (APPI), laser desorption ionization (LDI), and electron-transfer matrix-assisted laser desorption ionization (ET-MALDI) for the analysis of petroporphyrin (PP)-enriched extracts. APPI, one of the most used ionization sources for crude oil analysis because of its low matrix and ion suppression effects, provides a broad picture of the crude oil extract, including PPs. APPI analysis resulted in a complex spectrum with more than 12000 radical cations where signals from high ionization energy (IE) species with abundant heteroatoms (N x O y S z ) predominate, masking the PP target group. LDI shows species with aromatic cores or conjugated functionalities particularly susceptible to UV laser excitation and ionization. A reduction in N-containing compounds (N x O y , N x S z ) and an increase in PPs signals indicate some selectivity in LDI. ET-MALDI resulted in a less complex spectrum with 3500 radical cations mainly from aromatic species, including NiPP and VOPPs. PPs’ selective ionization in ET-MALDI occurs via thermodynamically favored charge exchange reactions between the matrix radical cations and the analytes. ET-MALDI results in fewer ions per nominal mass than APPI and LDI, a situation benefiting signal resolution and mass accuracy in FT-ICR-MS. Identifying more than 350 PPs in crude oils (N4VO, N4VO2, N4VO3, N4VOS, and N4Ni) was possible by combining isotopic structure analysis and data refinement using the Kendrick mass defect (KMD) plots. The PP compositional space in ET-MALDI includes 269 species corresponding to N4VO and N4Ni classes, in contrast with 65 in APPI and 53 LDI. The compound classes N4VOS, N4VO2, and N4VO3 were not observed in APPI or LDI.