Negative-ion Electrospray Ionization Fourier Research Articles

Using landfill leachate to indicate the chemical and biochemical activities in elevated temperature landfills

Landfill leachate properties contain important information and can be a unique indicator for the chemical and biochemical activities in landfills. In the recent decade, more landfills are experiencing elevated temperature, causing an imbalance in the decomposition of solid waste and affecting the properties of the landfill leachate. This study analyzes the properties of leachate from two landfills that were experiencing elevated temperature (ETLFs), samples were collected from both elevated temperature impacted and non-impacted areas in each landfill. The accumulation of volatile fatty acids (VFA) in leachates from elevated temperature impacted areas of both landfill sites revealed that methanogenesis was inhibited by the elevated temperature, which was further confirmed by the more acidic pH, higher H/C elemental ratio, and lower degree of aromaticity of the elevated temperature impacted leachates. Also, carbohydrates depletion indicated possible enhancement of hydrolysis and acidogenesis by elevated temperature, which was supported by compositional comparison of isolated acidic species by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) at 21 T derived from both elevated temperature impacted and non-impacted areas in the same landfill site. Furthermore, leachate organics fractionation showed that leachates not impacted by elevated temperature contain less hydrophilic fraction and more humic fraction than elevated temperature-impacted leachates for both ETLFs.

Effect of salinity on molecular characterization of dissolved organic matter using ESI FT-ICR MS

Solid-phase extraction (SPE) coupled with negative-ion Electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been widely used for molecular characterization of dissolved organic matter (DOM). However, little attention has paid to test whether the salinity of the sample and the presence of chloride ions in water samples affect the molecular composition of DOM extracted by SPE (SPE-DOM). In this study, one natural organic matter standard and several natural waters were selected to investigate how salinity affects the molecular composition of SPE-DOM and the selectivity of chloride ion adducts formation with respect to the molecular structure of SPE-DOM in negative ion ESI FT-ICR MS analysis. The results show that the molecular composition of SPE-DOM varied in a sample made by different salinity; and the variation pattern of DOM composition was different among different water samples under the treatment of consistent salinity gradients. The chloride ions can't be completely removed from cartridges in conventional SPE, thus leading organic compounds in SPE-DOM to form [M+Cl]‾ adducts when performing ESI FT-ICR MS analysis. In addition, the molecules with high H/C and low O/C ratios were likely to form [M+Cl]‾ ions. The relative abundance of [M+Cl]‾ ions could increase with the increase of salinity. These results are instructive to guide the pretreatment and molecular characterization of DOM in water samples with different salinity. Overall, we proposed a modification to the SPE to minimum reduce the formation of chloride ion adducts during the isolation of DOM.

Molecular Characterization of Naphthenic Acids and Naphthenates in the Oil Sludge: A Case Study in Bohai Basin, China

Oil sludge deposition is a common phenomenon during oil transportation, storage, and processing. Detailed molecular characterization of sludges is a prerequisite for understanding the mechanisms of emulsification, naphthenate, and asphaltene deposition. In this study, naphthenic acids and their salts in the oil sludge from an offshore oil platform were characterized by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and high-temperature chromatography (HTGC). The results show that the oil sludge is a stable emulsion consisting mainly of water and crude oil. An insoluble fraction, which accounted for roughly 3 wt % of the sludge, was found containing a large amount Ca and Fe. The organic matter in solid was extracted by toluene/formate acid extraction and was identified as large-molecular binary, ternary, and quarternary naphthenic acids, including the C80 tetraacids (so-called “ARN”). HTGC results showed that the ARN accounted for more than half of the polybasic acids. It was considered that the Ca2+ in the formation water and large molecular polyacids in the crude oil is the key factor for the sludge formation; small molecular naphthenic acids and other polar components in the crude oil stabilize the emulsion of the sludge.

Time-dependent molecular progression and acute toxicity of oil-soluble, interfacially-active, and water-soluble species reveals their rapid formation in the photodegradation of Macondo Well Oil

Photodegradation is a significant weathering process that transforms spilled oil, yet, the fate, degradation rate, and molecular transformations that occur through photoinduced pathways remain relatively unknown. The molecular complexity combined with the increased polarity of photoproducts challenges conventional analytical techniques. Here, we catalogue the molecular progression of photochemical transformation products of Macondo Well Oil by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We track the molecular compositions of oil-soluble, interfacially-active, and water-soluble oil species formed at varying time intervals in photomicrocosm experiments. Short photoirradiation periods (<24 h), not previously reported, are included to reveal rapid photooxidation of native oil components. Surface oil films exposed to solar irradiation were shown to increasingly contribute to the dissolved organic carbon pool as a function of increased irradiation time. FT-ICR MS analysis of acidic species of each fraction identifies tens of thousands of oil-soluble, interfacially-active, and water-soluble phototransformation products, including Ox, NOx, and SOx species. Oil-soluble species incorporate oxygen as a function of irradiation periods. After 96 h of irradiation, ~14 wt% of the photooxidized oil film was interfacially active and contained phototransformed species with up to 12 oxygen atoms per molecule. Water-soluble species correspond to highly oxygenated compounds. Importantly, photochemical oxidation is shown to occur within the first hour. Beyond 24 h, photoproducts remain compositionally similar, highlighting the rapid effect of photodegradation to transform oil species into water-soluble compounds. Molecular fingerprints provided by FT-ICR MS highlight the oxygen dependence on oil/water solubility. Microtox® analysis indicates that the toxicity of water-soluble photoproducts rapidly increases at early irradiation time points (first 24 h) compared to the dark control and reaches a maximum at 6 h of irradiation. Results highlight the temporal, molecular progression of photoproducts as they partition from oil-soluble to oil-soluble interfacially-active, and finally to water-soluble species.

Molecular Comparison of Solid-Phase Extraction and Liquid/Liquid Extraction of Water-Soluble Petroleum Compounds Produced through Photodegradation and Biodegradation by FT-ICR Mass Spectrometry.

We apply two widely used extraction techniques, liquid/liquid extraction and solid-phase extraction with styrene-divinylbenzene polymer with a proprietary nonpolar surface priority pollutant (PPL) to water-soluble compounds generated through photodegradation and biodegradation of petroleum. We compare the molecular composition of bio- and photodegraded water-soluble organic (WSO) acids by 21 T negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We highlight the compositional differences between the two extraction techniques for abiotic and biotic degradation processes and identify known toxic species (naphthenic acids) produced through hydrocarbon biodegradation identified by liquid/liquid extraction (LLE) that are not detected with solid-phase extraction (SPE) of the same sample. Photodegraded WSO compounds extracted by SPE-PPL correspond to species with higher O/C ratio and carbon number compared to LLE extracted compounds. Naphthenic acids, a recalcitrant class of nonaromatic carboxylic acids and known acute toxicants formed through biodegradation of oil, are detected in LLE extracts (up to C30 and double-bond equivalents, DBE < 3) but are not detected in SPE-PPL extracts. This suggests that LLE and SPE-PPL retain different water-soluble oil species based on the dominant type of oil weathering process.

Investigating biological nitrogen cycling in lacustrine systems by FT-ICR-MS analysis of nitrogen-containing compounds in petroleum

Biological nitrogen cycling plays an important role in bio, environmental and petroleum geochemistry. Until now most research has focused on marine environments using nitrogen isotopes, and in contrast, nitrogen cycling in lacustrine environments remains poorly understood. To fill this knowledge gap, we present a case study of crude oils from Permian brackish and saline alkaline lacustrine rocks in the Junggar Basin, northwestern China. To complement the large variation in nitrogen isotope values in lacustrine sediments, we analyzed the pyrrolic N-containing compounds of crude oil using negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). Our results show that pyrrolic compounds derived from biological sources are more abundant in oils from brackish lacustrine settings (i.e., the Jimusar Sag oils of the Junggar Basin) than in oils from alkaline lacustrine settings (i.e., the Mahu Sag oils of the Junggar Basin), which is mainly due to greater higher plant contributions to the latter. Higher plants provide abundant alkaloids and chlorophyll that are the biological precursors of pyrrolic N-containing compounds. In addition, anoxic, sulfate-type, brackish lacustrine settings provide abundant ferrous iron and sulfide that promote N fixation. This study provides the first insights into biological N cycling in brackish and alkaline lacustrine systems, which has significance for fossil fuel resources and their environmental impacts. Our data suggest that the N cycling in lacustrine systems might have an important role in entire Earth system N budget.

The evolution of acids and neutral nitrogen-containing compounds during pyrolysis experiments on immature mudstone

Abstract Pyrolysis experiments were conducted on immature(Ro = 0.47%) organic-rich (TOC = 6.0%)mudstone, and the liquid products at 10 different temperature stages were detected by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI− FT-ICR MS). Seven classes of acids and neutral nitrogen-containing compounds, namely, N1, N2, O1, O2, O3, O4 and N1O1, were detected in all the products. The O2 class accounted for the largest proportion (50.56 %–91.65%) among all the products, followed by the O1 class (1.70 %–28.80%). The % O1 and % N1 classes showed a clear upward trend with the increase in experimental temperature due to their organic resources, and the % O2 class showed the exact opposite trend, which could be explained by the chemical reactions that occurred during the maturation process, such as decarboxylation and dehydration. In addition, the relative abundances of the classes with high double bond equivalents (DBE) (≥9) and low DBE (≤7) showed a significant upward trend and a clear downward trend, respectively. The main reasons were aromatization and condensation during thermal evolution. This series of thermal evolution characteristics indicated that a set of new thermal parameters, such as ∑%DBE ≥9/∑%DBE≤8 (O2 compounds) = 0.0007T2 - 0.372T + 48.594(R2 = 0.9088) may be used as a new maturity parameter after further verified with crude oils.

Insight into structural features of soluble portions from cellulose, cellobiose and monosaccharide methanolysis by GC/MS and ESI FTICRMS

Methanolysis of biomass has attracted increasing attention due to it has some advantages, such as low critical points and strong hydrogen donation ability. In this paper, methanolysis of cellulose, cellobiose (sucrose), and monosaccharide (glucose) were performed to obtain methanol-soluble portions (MSPs). The relatively volatile or less polar species in the MSPs were analyzed with a gas chromatograph/mass spectrometer (GC/MS), and the polar species were identified with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). According to analysis with GC/MS, the MSPs include ethers, esters, ketones, acids, sugars, phenols, and furans. The analysis with FTICRMS shows that the polar compounds in the MSPs are O1–O15 class species with 1–14 double bond equivalent (DBE) and 5–35 carbon atom number (CAN). The most abundant class species in MSPs from cellulose, sucrose, and glucose methanolysis are O5, O7, and O7, respectively. The species in MSPs from sucrose and glucose methanolysis center at higher DBE value and more CAN than those in MSP from cellulose methanolysis. Meanwhile, the oxygen atom number of O4–O10 class species in the MSPs were negatively correlated with the average DBE value. The results indicate that condensation intensively proceeded with the specific regularity during sucrose and glucose methanolysis.

Changes in groundwater dissolved organic matter character in a coastal sand aquifer due to rainfall recharge

Dissolved organic matter (DOM) in groundwater is fundamentally important with respect to biogeochemical reactions, global carbon cycling, heavy metal transport, water treatability and potability. One source of DOM to groundwater is from the transport of organic matter from the vadose zone by rainfall recharge. Changes in precipitation patterns associated with natural climate variability and climate change are expected to alter the load and character of organic matter released from these areas, which ultimately impacts on groundwater quality and DOM treatability. In order to investigate potential changes in groundwater DOM character after rainfall recharge, we sampled shallow groundwater from a coastal peat-rich sand aquifer in New South Wales, Australia, during an extended period of low precipitation (average daily precipitation rate < 1.6 mm day−1 over the 8 months prior to sampling), and after two heavy precipitation events (84 mm day−1 and 98 mm day−1 respectively). We assess changes in DOM composition after correcting for dilution by a novel combination of two advanced analytical techniques: liquid chromatography organic carbon detection (LC-OCD) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We also assess changes in water chemistry pre- and post-rainfall. Post-rainfall, we show that the dilution-corrected amount of highly aromatic DOM molecular formulae (i.e. those categorised into the groups polyphenolics and condensed aromatics) were 1.7 and 2.0 times higher respectively than in pre-rainfall samples. We attribute this to the flushing of peat-derived DOM from buried organic material into the groundwater. We also identify that periods of low precipitation can lead to low hydrophilic/HOC ratios in groundwater (median = 4.9, n = 14). Redundancy analysis (RDA) was used to compare the HOC fraction with FT-ICR MS compound groups. We show that HOC has a more aromatic character in pre-rainfall samples, and is less similar to the aromatic groups in post-rainfall samples. This suggests that the decline in water-borne hydrophobics observed post-rainfall could be associated with preferential adsorption of the hydrophobic aromatic DOM, making post-rainfall samples less treatable for potable water supply. Post-rainfall we also observe significant increases in arsenic (leading to concentrations greater than 3 times the World Health Organisation drinking water limit of 10 μg / L). Increases in coastal rainfall due to climate change may therefore alter the composition of groundwater DOM in coastal peatland areas in ways that may impact DOM bioavailability, and increase arsenic concentrations, reducing the ease of water treatment for human consumption. To the best of our knowledge, this is the first study to identify the chemical and molecular changes of shallow groundwater DOM pre-rainfall and post-rainfall in a sedimentary organic carbon rich environment through multiple analytical techniques.

Molecular characterization of polar heteroatom species in oilsands bitumen-derived vacuum residue fractions by Fourier transform ion cyclotron resonance mass spectrometry

A Canadian in situ oilsands bitumen-derived vacuum residue (VR) was subjected to supercritical fluid extraction and fractionation (SFEF) into 13 extractable fractions and an unextractable end-cut and characterized by positive- and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results of negative-ion ESI FT-ICR MS showed that the N1 class species was the most abundant and the multifunctional group compounds, such as N1O1, N1O2, N1S1, N1S2, and N2 class species became abundant as the SFEF fraction became heavier. In positive-ion ESI mode, the relative abundance of N1 class species decreased gradually in the heavy SFEF fractions while that of multifunctional group compounds increased. The relative abundance of N4V1O1 increased dramatically in heavy fractions and the end-cut. The distributions of polar heteroatom species of VR derived from oilsands bitumen were similar with those of VR derived from the Venezuela Orinoco extra heavy oil.

Identification of organooxygen compounds in the methanol-soluble portion from the methanolysis of pretreated rice straw with Trichoderma sp. AH

The effect of pretreatment (PT) with Trichoderma sp. AH on the organooxygen compounds (OOCs) in methanol-soluble portions (MSPs) obtained from the methanolysis of raw and pretreated rice straw (RS) was investigated. According to the analyses with a gas chromatograph/mass spectrometer (GC/MS) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer, molecular masses (MMs) of the OOCs range from 100 to 500 u and are dominant from 300 to 450 u. The relative abundances of detected compounds with MMs from 300 to 350 u in MSP of pretreated RS are higher than those in MSP of raw RS. The predominant compounds in MSPs of raw and pretreated RSs are On (n = 1–10) with double bond equivalent (DBE) values of 1–28 and carbon atom numbers (CANs) of 4–35. The most abundant classes in MSPs of raw and pretreated RSs are O5 and O4, respectively. Besides, N1On (n = 0–9) classes with DBE values of 1–23 and CANs of 4–35 were also identified. These results facilitate understanding the effect of pretreatment with Trichoderma sp. AH on RS conversion and OOC selectivity from the methanolysis of RS and the application of MSP in producing transportation fuel.

Characterization of soluble portions from cellulose, hemicellulose, and lignin methanolysis

Methanolysis of the three biomass components was conducted to afford soluble portions (SPs) and residues. Cellulose has the highest SP yield, followed by hemicellulose and lignin. The relatively volatile or less polar species in the SPs were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and the polar species were identified with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). According to analysis with GC/MS, sugars, esters, and phenols are the predominant compounds in cellulose- and hemicellulose-, and lignin-derived SPs, respectively. The analysis with FTICRMS shows that the molecular masses in the SPs range from 100 to 500 u and those in cellulose-/hemicellulose-derived SPs dominate from 250 to 300 u but in lignin-derived SP concentrates from 300 to 350 u. The identified compounds were assigned to On class species with double bond equivalent (DBE) values of 1–14 and carbon atom numbers of 5–35. The most abundant class species in cellulose-, hemicellulose-, and lignin-derived SPs are O5, O5, and O2, respectively. The van Krevelen diagrams of On class species suggest that primary species in lignin-derived SP are mainly located in a relatively narrow region with atomic ratio of O/C 0.0–0.3 and atomic ratio of H/C 1.0–1.3, while those in cellulose- and hemicellulose-derived SPs are principally located in a wider region with atomic ratio of O/C 0.2–0.8 and atomic ratio of H/C 0.8–1.5. The oxygen atom numbers of O4−O10 class species was negatively correlated with the average DBE value, which indicates a cyclic structure or double bond will be generated (opened or saturated) with the removal (addition) of oxygen atoms.

Influence of Resins on Crystallization and Gelation of Waxy Oils

In the present work, we employed model oil systems to examine the effects of resins upon the gelation and crystallization of waxy oils. Two types of waxes were explored, namely, n-tetracosane (wax A) and a commercial wax with a melting temperature of 52–54 °C (wax B). The resins were extracted from a deoiled asphalt from Venezuelan residue by the saturates, aromatics, resins, and asphaltenes fractionation method. The results from negative-ion electrospray ionization Fourier transform ion cyclotron resonance-mass spectrometry suggest that resins consist of one to four fused benzenes rings or one to two fused naphthalene rings constructed by N1, N1O1, N1S1, N1O1S1, N1O2, O1, O1S1, and O2 class species containing stacking aromatic rings. For both types of waxes examined, adding resins to the waxy oils suppresses wax precipitation and modifies the morphology of wax crystals, which collectively leads to lower gelation temperature and lower yield stress. Up to 7 °C of reduction in gelation temperature, 60% of r...

Molecular transformation of dissolved organic matter in high-temperature hydrogen peroxide oxidation of a refinery wastewater

Advanced oxidation processes have been extensively used in industrial wastewater treatment. However, the molecular transformation of dissolved organic matter (DOM) during oxidation process is poorly known. In this study, a refinery wastewater was oxidized at high temperature using H2O2. Negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was applied to analyze the molecular changes of DOM. 68 heteroatom class species including Ox, OxS1, OxS2, N1Ox, N2Ox, N3Ox, and N1OxS1 were assigned from a single spectrum of the raw water, in which Ox and OxS1 class species were dominant. The molecular composition changed during oxidation. Sulfur- and nitrogen-containing compounds were almost completely removed. The removal of oxygen compounds by oxidation and the new production of oxygen compounds were simultaneous. Chain scission and oxidation of Ox compounds were the major reactions. Abundant chlorinated compounds were detected in the oxidation product. These compounds are considered as reaction products of DOM molecules with chloride ions in the water.

Geochemical characteristics and significance of heteroatom compounds in lacustrine oils of the Dongpu Depression (Bohai Bay Basin, China) by negative-ion Fourier transform ion cyclotron resonance mass spectrometry

Abstract Saline and freshwater lacustrine oils from the Dongpu Depression (Bohai Bay Basin) were characterized by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). ESI-FT-ICR MS detected a large range of nitrogen and oxygen compounds in the oils, mostly comprising N1, O1, O2 and N1O1 species. The low mature oils are dominated by O1 species with double bond equivalent of 4 (DBE = 4; mainly alkylphenols), O2 species with DBE = 5–6 (i.e., hopanoid, secohopanoic and steroid acids) and DBE = 1 (i.e., fatty acids), indicating a genetic relationship between oxygen compounds and their precursors. The nitrogen and oxygen compounds were significantly influenced by maturity, with the lower maturity oils analyzed enriched in O2 species, particularly fatty acids and 4–5 ring naphthenes with biologically sourced hydrocarbon skeletons: ratios of O2/N1 > 0.7; C20–30/C15–45-DBE1-O2 > 0.4; and DBE5–6/DBE12–22-O2 > 6.0 may be useful indicators of low maturity. With increasing maturity, the condensation degree of the compounds increased and the carbon number decreased. The relative abundances of N1 and O1 species with the following specific DBE carbon number ranges were particularly sensitive to maturity: DBE9–12/DBE15–18-N1, C20–28/C29–40-DBE12-N1, C20–30/C31–50-DBE15-N1, DBE9–12/DBE4–20-O1 and C20–30/C31–50-DBE8-O1. In some instances the FT-ICR MS proxies provided a more reliable indication of high maturity levels than traditional sterane based maturity parameters. However, several of these species were also responsive to other influences, namely C20–28/C29–40-DBE12-N1 and C20–30/C31–50-DBE15-N1 ratios reflected an organofacies control and DBE9–12/DBE4–20-O1 and C20–30/C31–50-DBE8-O1 ratios changed with thermochemical sulfate reduction (TSR)– confirmed by δ34S variances of OSCs. In light of the multiple controls on the nitrogen and oxygen compounds, DBE9–12/DBE15–18-N1 ratio seems unaffected by organofacies or TSR and was considered the most reliable maturity proxy displaying a similar or better maturity relationship than Ts/(Ts + Tm). Aside from secondary alteration effects, the freshwater samples showed several compositional differences to the saline samples, albeit from a limited data set, including generally higher O2 and N1 (particularly low MW) product abundances, lower abundances and quite different distribution of O1 products. These distinctions suggest ESI FT-ICR MS analysis has potential for distinguishing these sample types.

Characterization of nitrogen and sulfur-containing species in Zhaotong lignite and its extracts from ultrasonic extraction

Zhaotong lignite (ZL) was sequentially extracted with cyclohexane, carbon disulfide, methanol, acetone, and isometric carbon disulfide/acetone mixed solvent to afford extracts 1–5 (E1–E5) under ultrasonic radiation at room temperature. In addition, ZL was characterized with solid-state 13C nuclear magnetic resonance (SS 13C NMR), Raman spectrometer and X-ray photoelectron spectrometer (XRPES), while the extracts were analyzed with a gas chromatograph/mass spectrometer along with a positive-ion (PI) and negative-ion (NI) electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESIFTICRMS). According to the characterization with SS 13C NMR, aliphatic carbons count for 59.5% of all the organic carbons in ZL, and each aromatic cluster contains 2 or 3 aromatic rings on average. The pyrrolic nitrogen and sulfones are the most abundant nitrogen and sulfur forms, respectively, in ZL based on the analysis with XRPES. ESIFTICRMS resolved thousands of basic and non-basic species, and the molecular masses are mainly concentrated in the range of 350–600 and 300–500 u, respectively. Acidic S1O3 class species with double bond equivalent values of 3–8 and carbon numbers of 6–39 are dominant species and could be attributed to acidic group-substituted thiophenes. Main nitrogen-containing species detected in the PI mode are basic N1O0–3, N2S2, and N2O1–8S1–2. Most of the species were speculated to contain some core structures, such as pyridines, pyrimidines, or pyrazines.

Analytical advanced techniques in the molecular-level characterization of Brazilian crude oils

The study focused on the analytical characterization at the molecular level of twenty-five Brazilian oils by applying two analytical advanced techniques: comprehensive bidimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI(−)-FT-ICR MS), using crude oil samples directly with minimal sample preparation and without any fractionation steps. First, individual compounds present in the classes were detected, identified and semi-quantified using a polar/non-polar column set, which has proved to be more effective in separating compounds. Later, the ESI(−)-FT-ICR MS was optimized for crude oil analysis and characterization of the less volatile polar compounds (oxygen-, nitrogen- and sulfur-containing compounds). Many classes were identified via GC×GC-TOFMS, such as n-alkanes, branched alkanes, alkyl-monocyclic alkanes, alkyl-bicyclic alkanes, saturated polycyclic, alkyl-benzenes, alkyl-naphthalenes, alkyl-phenanthrenes, alkyl-chrysene, alkyl-indanes, alkyl-tetrahydro-naphthalenes, pyrenes, fluorenes and sulfur compounds. The high chromatographic resolution power of GC×GC-TOFMS (for volatile compounds) with the high dynamic m/z range of FT-ICR MS allowed the chemical characterization of the crude oils with the identification of polar, volatile and nonvolatile compound classes. ESI(−)-FT-ICR MS data suggest that many heteroatomic compounds were detected, with m/z values ranging from 200 to 800, resulting in percentages of assignable peaks higher than 75% (composed of O3, N2, O2, NO2, O and N heteroatom classes). All assignable signals showed ultrahigh resolution and accuracy mass. Detailed information on the composition of these oils is very important for predicting the physical and chemical characteristics of the crude oil (e.g., total acid number) and its products using small sample amounts, and offers new possibilities for crude oil fingerprinting.

Characteristics and geochemical significance of heteroatom compounds in terrestrial oils by negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

Terrestrial oils and rock extracts from the Nanpu Sag (Huanghua Depression, Bohai Bay Basin, China) were characterized by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography mass spectrometry (GC-MS). Molecular composition of neutral nitrogen and acidic oxygen compounds, mainly by N1, O1, and O2 species were investigated in the samples. Increases in relative abundance and molecular condensation degree of oxygen-containing compounds and a decrease in the carbon number range of N1 species were observed with the changes of kerogen from Type I to III for both the source rock extracts and the relevant oils, which indicates the influence of source input and discrimination potential. We also observed an apparent increase in the condensation degree and a decrease in the carbon number of the N1, O1 and N1O1 species with increasing maturity. The carbon numbers and double bond equivalent (DBE) values of the N1 and N1O1 species in the extracts showed a positive relationship (an approximately linear distribution) during thermal evolution. These results indicate that thermal maturity has a crucial influence on the composition. The relative abundance ratios of N1 and O1 species with specific DBE values and carbon number ranges, C16–20/C21–50-DBE12-N1, C20–24/C25–50-DBE15-N1, C11–15/C16–27-DBE4-O1, DBE12/DBE9-N1, and DBE8–9/DBE4-O1 are proposed as thermal maturity indicators for the evaluation of mature and post-mature source materials. A strong primary migration fractionation effect on the heteroatom compounds was also observed, implying that these compounds can be used as migration auxiliary proxies.

Fractionation of Interfacial Material Reveals a Continuum of Acidic Species That Contribute to Stable Emulsion Formation

The acidic components of Athabasca bitumen interfacial material (IM) were isolated and subsequently fractionated based on hydrophobicity by a modified aminopropyl silica (MAPS) method to determine whether low-molecular-weight IM acids are preferentially ionized in negative-ion electrospray ionization (ESI (−)) and, thus, bias the compositional information obtained by direct infusion (dilute and shoot) mass spectral analysis. Characterization by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that MAPS fractionation of IM acids extends the detection of high-m/z (>600-Da) IM compounds by 2-fold, yields an approximate 10-fold increase in the number of assigned formulas, and exposes a continuum of acidic species that includes the first definitive identification of doubly charged acids in interfacial material. Comparison of the heteroatom contents of singly and doubly charged Ox species, combined with the acid-targeted extraction procedure, strongly suggests that the chemical functionalities are similar for the two ion types and are largely composed of mono- and dicarboxylic acids. Excitation emission matrix spectroscopy (EEMS) revealed that the most hydrophobic IM fractions approach the size and aromaticity of bitumen asphaltenes, but despite the increase in hydrophobicity, these asphaltene-like acids form the tightest emulsions, as revealed in simple bottle tests. Thus, the most surface-active material from Athabasca bitumen comprises low-molecular-weight, acidic, resin-like species, as well as larger (higher-molecular-weight) acidic asphaltene-like compounds.

Stepwise structural characterization of hydrocarbon compounds and polar components during atmospheric residue hydrotreatment

A continuous fixed-bed micro-reactor was adopted to conduct a hydrotreatment experiment on the atmospheric residue obtained from Saudi Arabia. The feedstock and hydrotreated liquid products were subjected to high-temperature gas chromatography to undertake simulated distillation analysis, and to gel permeation chromatography to carry out molecular size investigations. 1H NMR and element analysis were carried out to derive structural parameters. Positive- and negative-ion electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry was combined with other analytical means to explore the stepwise structural characterization of polar components (especially the nitrogen (N)-containing compounds) when passing through beds filled with different catalysts during the hydrotreatment process. According to the different numbers of nitrogen, oxygen, and sulfur atoms, N-containing compounds could be divided into Nx, NxOy, and NxSy class species. The results indicated that hydrotreatment process led to more concentrated distribution of hydrocarbon molecules in the products. The heteroatoms, which accounted for the largest proportion in the feedstock and liquid products, were N1 class species. During the hydrotreatment process, the relative abundance of N1, N2, N1O1, N1O2, and N1S1 class species changed significantly with the progress of hydrotreatment process, however the conversion regularity varied among heteroatomic compounds.