Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has exposed the ultracomplexity of fossil fuels, thereby validating the compositional trends that rule petroleum distillation, known as the Boduszynski Continuum. Routine FT-ICR MS analysis of a single crude oil sample can reveal tens-of-thousands of unique molecular formulas; however, currently available ionization methods suffer from limitations for such complex mixtures that are not yet completely understood. Simply put, MS detects ions, and thus, it depends heavily on the ability of ion sources to indiscriminately volatilize and subsequently ionize samples of interest. Despite advances in soft ionization methods, the characterization of complex matrices remains a challenge due to the lack of an ion source, commercial or custom-built, that can vaporize and ionize all compounds without bias, save analyte concentration. However, atmospheric pressure photoionization (APPI) has been shown to provide the most uniform ion production for mixtures of petroleum model compounds and real samples, with little to no fragmentation. In this work, we investigated the molecular composition of PetroPhase 2017 asphaltenes and its extrography fractions, with a focus on the total vanadium content and molecular composition of vanadyl porphyrins as a function of aggregate size distribution, accessed through separate experiments: online gel permeation chromatography (GPC) inductively coupled plasma−MS (ICP−MS) and online GPC APPI FT-ICR MS (at 21 T). The results reveal that the extrography separation provides asphaltene fractions (i.e., acetone, Hep/Tol, and Tol/THF/MeOH) enriched in 51 V-containing compounds with distinctive aggregate size distributions. The acetone fraction features smaller aggregate sizes, as it elutes later in the GPC chromatogram than Hep/Tol and Tol/THF/MeOH fractions, and overall, presents up to ∼14-fold higher ionization efficiency in APPI. Such behavior suggests a correlation between aggregate size and production efficiency of monomeric ions in APPI. Bulk compositional trends accessed by GPC separation and highlighted by ICP−MS detection indicate that despite multiple separation steps (i.e. extrography followed by GPC), APPI FT-ICR MS can only access ∼37% of the total V-containing compounds. Although the more stable/larger aggregates dominate the size distributions of all asphaltene samples studied, it is the weakly aggregated/monomeric species that are preferentially observed by APPI-MS. Tendencies in the molecular composition of vanadyl porphyrins and S/O-containing compounds strongly suggest that London forces might be central in the self-assembly process of asphaltene nanoaggregates to produce more massive clusters. The results demonstrate that the observed compositional trends (albeit limited) can be accessed when coupling advanced chromatographic separations with online high-field FT-ICR MS detection.

This study probes the nanoaggregation behavior of asphaltenes by gel permeation chromatography (GPC). Compounds containing sulfur, vanadium, and nickel were monitored online with elemental detection by inductively coupled plasma mass spectrometry (ICP-MS), and four fractions that vary in nanoaggregation state were analyzed by positive atmospheric pressure photoionization 9.4 T Fourier transform ion cyclotron resonance mass spectrometry ((+)APPI FT-ICR MS). We also highlight some of the challenges associated with the analysis of asphaltene fractions by direct infusion. Nanoaggregate size and monomer ion yield were inversely correlated. The extremely low ionization efficiency for the largest aggregate GPC fractions collected from the asphaltenes limited their characterization to only a few of the most abundant heteroatom classes. However, for all of the characterizable heteroatom classes, aggregation closely correlated with increased relative abundance of larger, more aliphatic compounds. These observations agree with results from the parent whole crude oil, suggesting that the interactions among the more alkylated compounds in asphaltenes may be a major contributor to asphaltene nanoaggregation.

Multiscale characterization of asphaltenes and their extrography fractions titrated with n-heptane was performed. Chemical characterization via FT-ICR MS and GPC ICP HR-MS, stability monitoring via QCR, and AFM images of deposits indicate that "island"-enriched samples tend to form fewer, well-organized deposit aggregates, whereas samples with abundant "archipelago"-like molecules produce larger aggregates and less well-organized deposits. The combination of QCR and AFM leads to the conclusion that "island"-enriched samples lead to smaller deposits compared to "archipelago"-like molecules.

This work is the second installment of a study that probes the aggregation behavior of asphaltenes by gel permeation chromatography (GPC). In part 1, analysis of GPC aggregate fractions collected from the 2017 PetroPhase asphaltene sample by direct infusion revealed an inverse correlation between aggregate size and aromaticity. However, characterization of the largest aggregate fractions by direct infusion was hampered by solvent contaminant peaks and dynamic range limitations due to the extremely low ionization efficiencies of the larger, more aliphatic species that comprise those fractions. Here, we couple the GPC separation with online detection by positive atmospheric pressure photoionization ((+)­APPI) 21 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to overcome those problems and reveal that the most abundant species that comprise the largest aggregate segment are indeed the most aliphatic. The ability to characterize difficult-to-analyze samples, like asphaltenes, is the first major advantage of online coupling. Another benefit is the increased chromatographic resolution afforded by online coupling, which enables a finer examination in the most aggregated region and reveals a local trend opposed to the global trend. The very first species to elute in the largest aggregates were more condensed polyaromatic compounds, and the larger, more aliphatic species elute shortly thereafter in much greater relative abundance.

The effect of silver triflate (AgOTf) on the interaction between vanadium and asphaltene nanoaggregates was investigated by gel permeation chromatography inductively coupled plasma high-resolution mass spectrometry (GPC ICP-HR-MS). The results showed that disaggregation of some vanadium compounds linked to asphaltene nanoaggregates occurred when silver triflate was added. Ag + can partially move some porphyrins from the high-molecular-weight (HMW) region to the low-molecularweight (LMW) region. It was inferred that the interaction between Ag + and the porphyrins surroundings led to a decrease in the size of the nanoaggregates (HMW region) and an increase in the "free" V porphyrin compounds (MMW and LMW regions). Asphaltenes from a similar origin, presenting the same vanadium GPC ICP-MS profile, gave different GPC ICP-MS profiles after AgOTf addition, which could be linked to the difference in geochemistry of the samples.

Asphaltenes are among the most challenging components in petroleum processing because they contain high amounts of heteroatoms (i.e., S, N, O, V, and Ni) thought to be responsible for strong aggregation tendencies, precipitation, and fouling problems. The role of vanadium and nickelcontaining petroleum compounds (i.e., "petroporphyrins") in aggregation and fouling is not completely understood because asphaltene composition and structure is still a subject of debate in the petroleum chemistry community. Characterization of asphaltenes, namely, molecular analysis that employs no chromatographic separation, often fails to reveal their comprehensive composition. The work herein presents asphaltene fractionation by 1) solid/liquid extraction, which allows for separation of single-core ("island") and multicore ("archipelago) structural motifs, and 2) high-performance thin layer chromatography (HPTLC) with cellulose as the stationary phase and DCM/MeOH as the eluent, which facilitates access to petroporphyrins.Characterization is performed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and matrix-assisted laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI FT-ICR MS). The results demonstrate that even with multiple separation steps, a large quantity of vanadyl porphyrins remains inaccessible for molecular analysis by MALDI FT-ICR MS, which raises the question of what portion of a complex sample of asphaltene can be revealed by ultrahigh resolution mass spectrometry. Furthermore, the results show that easily accessible porphyrins migrate with the solvent front in HPTLC. Thus, HPTLC can be used to isolate and identify "free" porphyrins, not locked into asphaltene aggregates; however, further development of separation methods is required to access the most difficult and problematic asphaltene fractions, which do not migrate and impose analytical challenges due to their stronger aggregation tendency.

Asphaltenes are considered the most problematic components of heavy oils because they can self-aggregate which leads to precipitation and causes various problems during oil recovery, transportation and refining. The contribution of the porphyrins present in asphaltenes to the aggregation cannot be studied by direct elementary analysis techniques since in this form, the porphyrins are complexed with metals. Thus, gel permeation chromatography inductively coupled plasma-mass spectrometry (GPC-ICP MS) has been used in previous studies. The results

In the field of petroleomics and metallopetroleomics, the gel permeation chromatography (GPC) technique coupled with high-resolution detection technologies has made significant contributions as an analytical and preparative tool for over five decades. This bibliographic minireview highlights the study of the supramolecular and structural behavior of heavy crude oil and its fractions, as well as their reactivity to various processes by use of GPC. The preferred mobile phase is tetrahydrofuran (THF), whereas the stationary phase is polystyrene−divinylbenzene copolymer to avoid compound retention in the column. Other techniques such as HPTLC, RPLC, and NPHPLC have been used to provide multidimensional separations complementary to GPC. The high molecular weight (HMW) fraction, due to its greater polarity, reactivity to polymerization, and resistance to hydrodemetallization processes, has been the focus of interest for years. GPC coupled with high-resolution techniques has proven to be reliable for the detection of organic and inorganic species in bio-oils, making it a valuable tool for researchers and industry professionals in the context of feedstocks changes and new energy production.