Mass Spectrometric Coverage of Complex Mixtures: Exploring the Carbon Space of Crude Oil

Physical removal of PAXHs from highly contaminated soil by density differentiation: studying the effectiveness on the molecular level

Contaminated soils from industrial sites, such as for coal mining or manufactured gas production, can contain polycyclic aromatic hydrocarbons (PAHs) with a concentration higher than 10 000 mg kg-1, which require an integrated approach for remediation. A physical treatment by separating organic contaminants from soil materials using the density difference could lower the cost for the upcoming chemical and/or biological treatment. In our study, a highly PAH contaminated soil was separated in a 39% (w/w) calcium chloride solution (ρ = 1.4 g cm-3) via stirring, aeration or ultrasonication. Both first and second methods could separate soil materials from organic particles efficiently. The light fraction comprised around 10% of the total soil weight but 80% of solvent extractable organics (SEO). Optical and transmission electron microscopic analysis showed the light fraction, which consisted of mainly black solid aggregates (BSA), differed strongly from soil materials. Additionally, the original contaminated soil, its light and heavy fractions and the corresponding water phase together with the manually separated BSA were analyzed on the molecular level using ultrahigh resolution mass spectrometry (HRMS) with different atmospheric pressure ionization (API) methods, such as electrospray (ESI) and atmospheric pressure photo ionization (APPI). Results showed that SEO, which were primarily associated with BSA and successfully separated through physical method, contained mainly condensed aromatic ring structures of pure hydrocarbons and nitrogen heterocycles with low oxygen content.

Analysis of natural organic matter via fourier transform ion cyclotron resonance mass spectrometry: an overview of recent non-petroleum applications

Among the different techniques for mass analysis, ultra-high-resolution Fourier transform ion cyclotron resonance (FTICR) is the method of choice for highly complex samples, as it offers unrivaled mass accuracy and resolving power, combined with a high degree of flexibility in hybrid instruments as well as for ion activation techniques. FTICR instruments are readily embraced by the biological and biomedical research communities and applied over a wide range of applications for the analysis of biomolecules such as carbohydrates, lipids, nucleic acids, and proteins. In the field of natural organic matter (NOM) analysis, petroleum-related studies currently dominate FTICR-MS applications. Recently, however, there is a growing interest in developing high-performance MS methods for the characterization of NOM samples from natural aquatic and terrestrial environments. Here, we present an overview of FTICR-MS techniques for complex, non-petroleum NOM samples, including data analysis and novel tandem mass spectrometry (MS/MS) methods for structural classifications. © 2020 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd.

Development of a Novel HPLC-MS Method to Separate Polar and Non-Polar Compounds in Biodiesel/Petrodiesel Mixtures

Due to a trend to higher sustainability, biodiesel is often mixed into petrodiesel. The analysis of these blends on a molecular level is not trivial, since huge differences in concentrations and polarity of the analytes require a large dynamic range of the analytical method, as well as the ability to investigate molecules of widely different polarities. A combination of high-performance liquid chromatography (HPLC) with high resolution mass spectrometry (HRMS) was identified as a promising method and a normal-phase (NP)-HPLC using amino-functionalized silica gel-based stationary phase delivered the best results with very fast (under 4 min) measurements, with distinct separation of the compounds and clean mass spectra of singular compounds. This method can also be easily modified to elute all FAMEs (fatty acid methyl esters) in one singular peak, thus making the separation even faster (under 3 min).

Investigating Molecular Transformation Processes of Biodiesel Components During Long-Term Storage Via High-Resolution Mass Spectrometry

Biodiesel is an important building block in renewable energy transformation. The main issue is that during storage biodiesel will undergo transformation processes that can lead to molecular changes, which then can cause applicational problems such as severe motor damage. To prevent this, a detailed understanding of the involved molecules and the emerging aging products is necessary. Biodiesel samples were stored for up to 12 months to monitor molecular changes, and all mixtures were investigated by using ultrahigh-resolution mass spectrometry (HRMS) with electrospray ionization (ESI). The data revealed that during storage large numbers of oxygen atoms were incorporated into the fatty acid methyl esters (FAMEs). This process was dominant for the first quarter of aging but then became overshadowed by dimerization of oxygenated FAMEs. This means that there are two main pathways for aging in biodiesel: polyoxygenation and oligomerization. These findings greatly pin down the possible causes for sedimentation giving a solid foundation for aging inhibition development.

Pyrogenic dissolved organic matter produced at higher temperature is more photoactive: Insight into molecular changes and reactive oxygen species generation

Pyrogenic dissolved organic matter (pyDOM) is the photolabile fraction in the dissolved organic matter pool. However, the molecular changes and reactive oxygen species generation of pyDOMs under continuous irradiation, and how these vary with feedstock type and pyrolysis temperature, are not well understood. In this study, the soluble fractions of 300 and 450 ºC biochars (pyDOM300 and pyDOM450) were subjected to photo-irradiation. PyDOM450 was of higher aromaticity, molecular variety, but lower unsaturation than pyDOM300. The molecular weight, aromaticity, and double bond equivalents of pyDOMs generally decreased after photo-irradiation. The degradation pattern of pyDOMs can be divided into two stages. In the initial 24 h, pyDOM300 degraded faster than pyDOM450, with the more profound transformation of condensed aromatics and carbohydrate into aliphatic/proteins, lignins, and tannins in pyDOM300. After 720 h irradiation, however, the degradation ratio of pyDOM450 (36.2-43.9%) exceeded that of pyDOM300 (23.7-30.3%), with the initially preserved condensed aromatics in pyDOM450 further transforming into aliphatic/proteins and tannins. This was potentially attributed to the generation of more reactive oxygen species (·OH and ¹O₂) in pyDOM450. This study uncovered the photodegradation mechanisms of pyDOMs at molecular scale and helped to understand their cycling and effects on environment.

Getting a better overview of a highly PAH contaminated soil: A non-targeted approach assessing the real environmental contamination

Over the last 40 years, soils contaminated with polycyclic aromatic hydrocarbons (PAH) were monitored according to a list of 16 PAH, established by the U.S. Environmental Protection Agency (EPA). This, however, is underestimating the danger to the environment and humanity because other high molecular weight PAHs, heterocycles (PAXH, X = N, O, S) and alkylated derivatives can also occur at the contaminated site. Here, a new non-targeted approach of highly contaminated soil (64.5 ± 9.5 g kg^-1 solvent extractable organics from the German Ruhrgebiet) is introduced, where ultrahigh resolution mass spectrometry is combined with multiple ionization methods to get a better overview of anthropogenic contamination at a former industrial site. In total, 21,958 elemental compositions were assigned for positive and negative mode measurements. The approach is strongly increasing the amount of data that can be obtained from a single contaminated soil, making an assessment of the real environmental risk possible. In addition to highly aromatized and (alkylated) high molecular weight PAH, other PAXH especially basic and neutral PANH with very high aromaticity were also detected. This shows that while regulations and routine analysis are still stuck in the 1960 s, modern analytical methods are present in the 21st century.

ESI-MS Analysis of Thiol-yne Click Reaction in Petroleum Medium

Petroleum contains a large number of heteroatomic compounds, but today, most of them are not efficiently utilized. The constant development of the sustainability concept recalls for rethinking the usage of fossil resources with improved chemical utility. In order to initiate research aimed at involving active petroleum compounds in chemical transformations, a new analytical method for product detection is needed. Here, we study the click reaction of thiols with alkynes, leading to the formation of α-vinyl sulfides directly in the petroleum environment. The reaction was carried out using an (IMes)Pd(acac)Cl catalyst, which demonstrated tolerance to petroleum components. In this study, the concentration of thiols ranged from 1 M to 0.01 M (from 8% to 0.1%). To detect products at low concentrations, a special alkyne labeled with an imidazole moiety was used. This approach made it possible to observe the formation of vinyl sulfides by electrospray ionization mass spectrometry (ESI-MS), which provides an opportunity for further optimization of the reaction conditions and future developments for the direct involvement of oil components in chemical reactions.

Studying the Complexity of Biomass Derived Biofuels

Biofuel produced from biomass pyrolysis is a good example of a highly complex mixture. Detailed understanding of its composition is a prerequisite for optimizing transformation processes and further upgrading conditions. The major challenge in understanding the composition of biofuel derived from biomass is the wide range of compounds with high diversity in polarity and abundance that can be present. In this work, a comprehensive analysis using mass spectrometry is reported. Different operation conditions are studied by utilizing multiple ionization methods (positive mode atmospheric pressure photo ionization (APPI), atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) and negative mode ESI) and applying different resolving power set-ups (120 k, 240 k, 480 k and 960 k) and scan techniques (full scan and spectral stitching method) to study the complexity of a pyrolysis biofuel. Using a mass resolution of 960 k and the spectral stitching scan technique gives a total of 21,703 assigned compositions for one ionization technique alone. The number of total compositions is significantly expanded by the combination of different ionization methods.

Flexibilization of Biorefineries: Tuning Lignin Hydrogenation by Hydrogen Partial Pressure

The present study describes an interesting and practical catalytic system that allows flexible conversion of lignin into aromatic or aliphatic hydrocarbons, depending on the hydrogen partial pressure. A combination of experiment and theory shows that the product distribution between aromatics and aliphatics can be simply tuned by controlling the availability of hydrogen on the catalyst surface. Noticeably, these pathways lead to almost complete oxygen removal from lignin biomass, yielding high-quality hydrocarbons. Thus, hydrogen-lignin co-refining by using this catalytic system provides high flexibility in hydrogen storage/consumption towards meeting different regional and temporal demands.

Studying Natural Buckyballs and Buckybowls in Fossil Materials

Buckyballs (fullerenes) were first reported over 30 years ago, but still little is known regarding their natural occurrence, since they have so far only been found at sites of high-energy incidents, such as lightning strikes or meteor impacts, but have not been reported in low-energy materials like fossil fuels. Using ultrahigh-resolution mass spectrometry, a wide range of fullerenes from C30 to C114 was detected in the asphaltene fraction of a heavy crude oil, together with their building blocks of C10n H10 stoichiometry. High-level DLPNO-CCSD(T) calculations corroborate their stability as spherical and hemispherical species. Interestingly, the maximum intensity of the fullerenes was found at C40 instead of the major fullerene C60 . Hence, experimental evidence supported by calculations show the existence of not only buckyballs but also buckybowls as 3-dimensional polyaromatic compounds in fossil materials.

Petroleomics: Tools, Challenges, and Developments

The detailed molecular characterization of petroleum-related samples by mass spectrometry, often referred to as petroleomics, continues to present significant analytical challenges. As a result, petroleomics continues to be a driving force for the development of new ultrahigh resolution instrumentation, experimental methods, and data analysis procedures. Recent advances in ionization, resolving power, mass accuracy, and the use of separation methods, have allowed for record levels of compositional detail to be obtained for petroleum-related samples. To address the growing size and complexity of the data generated, vital software tools for data processing, analysis, and visualization continue to be developed. The insights gained impact upon the fields of energy and environmental science and the petrochemical industry, among others. In addition to advancing the understanding of one of nature's most complex mixtures, advances in petroleomics methodologies are being adapted for the study of other sample types, resulting in direct benefits to other fields.

Evaluation of the combination of different atmospheric pressure ionization sources for the analysis of extremely complex mixtures

RATIONALE

Characterization of complex samples remains a challenging task due to the high number of compounds present. Matrix effects, ion discrimination and suppression are limiting factors which force the use of different methods for the same sample to gain a broad understanding of complex mixtures.

METHODS

Various ionization techniques such as electrospray ionization (ESI), atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization (APCI) have been used in various problems for complex mixture analysis. Especially demanding is the analysis of energy-related hydrocarbon mixtures, such as crude oil. Here, the different ionization sources alone and in combination with each other have been used on an ultrahigh resolution Orbitrap mass spectrometer to study a light crude oil.

RESULTS

Despite the great variety of the available ionization sources, there is no single technique which can fully characterize the crude oil. Each ionization technique shows a selectivity towards specific types of compounds. While ESI is the method of choice for the detection of polar compounds, APPI and APCI favor the detection of nonpolar and low-to-medium polar compounds, respectively. The combination of ESI/APPI favors hydrocarbons and oxygen-containing species.

CONCLUSIONS

Combining different ionization methods can be used as an alternative in order to gain more information about compounds present in a complex mixture although a combination of different ion sources could enhance suppression effects.

A Detailed Look at the Saturate Fractions of Different Crude Oils Using Direct Analysis by Ultrahigh Resolution Mass Spectrometry (UHRMS)

SARA (Saturates, Aromatics, Resins, Asphaltenes) fractionation is a common simplification technique used for decades in petrochemical analysis. A large number of studies are dealing with the different fractions, but overall, the saturate fraction is strongly neglected. Of the very few available studies on the saturates fraction, almost all have been performed using gas chromatographic (GC) techniques. This discriminates the results of the saturate fraction especially since non-volatile, high molecular weight and polar constituents are mostly excluded. Here, for the first time, saturate fractions of different crude oils from different origins are analyzed using direct infusion ultrahigh resolution mass spectrometry (UHRMS), to study the compositions on a molecular level. Electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) are used in positive mode. The observed results show the presence of different heteroatom containing classes, with different chemical identities (i.e., presence of thiophenes, mercaptans and cyclic-sulfides in case of S-containing compounds). These results show the high affinity of some specific compounds towards different ionization techniques. Finally, the saturate fraction is shown to include much more than only volatile, saturated and aliphatic compounds. The detected compounds in this fraction present a very wide variety, not only in terms of their carbon atoms per molecule and their aromaticity, but also with regard to their functional groups and structural arrangements.

Pushing the analytical limits: new insights into complex mixtures using mass spectra segments of constant ultrahigh resolving power

A new strategy has been developed for characterization of the most challenging complex mixtures to date, using a combination of custom-designed experiments and a new data pre-processing algorithm. In contrast to traditional methods, the approach enables operation of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with constant ultrahigh resolution at hitherto inaccessible levels (approximately 3 million FWHM, independent of m/z). The approach, referred to as OCULAR, makes it possible to analyze samples that were previously too complex, even for high field FT-ICR MS instrumentation. Previous FT-ICR MS studies have typically spanned a broad mass range with decreasing resolving power (inversely proportional to m/z) or have used a single, very narrow m/z range to produce data of enhanced resolving power; both methods are of limited effectiveness for complex mixtures spanning a broad mass range, however. To illustrate the enhanced performance due to OCULAR, we show how a record number of unique molecular formulae (244 779 elemental compositions) can be assigned in a single, non-distillable petroleum fraction without the aid of chromatography or dissociation (MS/MS) experiments. The method is equally applicable to other areas of research, can be used with both high field and low field FT-ICR MS instruments to enhance their performance, and represents a step-change in the ability to analyze highly complex samples.

Comparing Crude Oils with Different API Gravities on a Molecular Level Using Mass Spectrometric Analysis. Part 1: Whole Crude Oil

Different ionization techniques based on different principles have been applied for the direct mass spectrometric (MS) analysis of crude oils providing composition profiles. Such profiles have been used to infer a number of crude oil properties. We have tested the ability of two major atmospheric pressure ionization techniques, electrospray ionization (ESI(±)) and atmospheric pressure photoionization (APPI(+)), in conjunction with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The ultrahigh resolution and accuracy measurements of FT-ICR MS allow for the correlation of mass spectrometric (MS) data with crude oil American Petroleum Institute (API) gravities, which is a major quality parameter used to guide crude oil refining, and represents a value of the density of a crude oil. The double bond equivalent (DBE) distribution as a function of the classes of constituents, as well as the carbon numbers as measured by the carbon number distributions, were examined to correlate the API gravities of heavy, medium, and light crude oils with molecular FT-ICR MS data. An aromaticity tendency was found to directly correlate the FT-ICR MS data with API gravities, regardless of the ionization technique used. This means that an analysis on the molecular level can explain the differences between a heavy and a light crude oil on the basis of the aromaticity of the compounds in different classes. This tendency of FT-ICR MS with all three techniques, namely, ESI(+), ESI(−), and APPI(+), indicates that the molecular composition of the constituents of crude oils is directly associated with API gravity.

Monitoring Membrane Lipidome Turnover by Metabolic 15N Labeling and Shotgun Ultra-High-Resolution Orbitrap Fourier Transform Mass Spectrometry

Lipidomes undergo permanent extensive remodeling, but how the turnover rate differs between lipid classes and molecular species is poorly understood. We employed metabolic ¹⁵N labeling and shotgun ultra-high-resolution mass spectrometry (sUHR) to quantify the absolute (molar) abundance and determine the turnover rate of glycerophospholipids and sphingolipids by direct analysis of total lipid extracts. sUHR performed on a commercial Orbitrap Elite instrument at the mass resolution of 1.35 × 10⁶ (m/z 200) baseline resolved peaks of ¹³C isotopes of unlabeled and monoisotopic peaks of ¹⁵N labeled lipids (Δm = 0.0063 Da). Therefore, the rate of metabolic ¹⁵N labeling of individual lipid species could be determined without compromising the scope, accuracy, and dynamic range of full-lipidome quantitative shotgun profiling. As a proof of concept, we employed sUHR to determine the lipidome composition and fluxes of 62 nitrogen-containing membrane lipids in human hepatoma HepG2 cells.

Analysis of Photoirradiated Water Accommodated Fractions of Crude Oils Using Tandem TIMS and FT-ICR MS

For the first time, trapped ion mobility spectrometry (TIMS) in tandem with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is applied to the analysis of the low energy water accommodated fraction (WAF) of a crude oil as a function of the exposure to light. The TIMS-FT-ICR MS analysis provided, in addition to the heteroatom series identification, new insights into the WAF isomeric complexity (e.g., [m/z; chemical formula; collision cross section] data sets) for a better evaluation of the degree of chemical and structural photoinduced transformations. Inspection of the [m/z; chemical formula; collision cross section] data sets shows that the WAF composition changes as a function of the exposure to light in the first 115 h by initial photosolubilization of HC components and their photo-oxidation up to O_4-5 of mainly high double bond equivalence species (DBE > 9). The addition of high resolution TIMS (resolving power of 90-220) to ultrahigh resolution FT-ICR MS (resolving power over 400k) permitted the identification of a larger number of molecular components in a single analysis (e.g., over 47k using TIMS-MS compared to 12k by MS alone), with instances of over 6-fold increase in the number of molecular features per nominal mass due to the WAF isomeric complexity. This work represents a stepping stone toward a better understanding of the WAF components and highlights the need for better experimental and theoretical approaches to characterize the WAF structural diversity.