Combining advanced NMR techniques with ultrahigh resolution mass spectrometry: A new strategy for molecular scale characterization of macromolecular components of soil and sedimentary organic matter

Molecular level characterization of complex biopolymers in nature is a key element to understanding the composition of natural organic matter (NOM) and fossil organic matter formation, such as kerogen and coal. Characterization of such geopolymers is difficult due to their heterogeneity and insolubility in common aqueous or organic solvents. Here, a strategy for extracting a representative sample is presented using the combined techniques of nuclear magnetic resonance (NMR) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for chemical analysis and characterization of NOM. A variety of NOM samples (wood, kerogen, bitumen, whole sediments) are shown as examples for implementing the strategy, which include solvent extractions using pyridine. For most samples, the extracts are confirmed to be chemically representative of the insoluble solid, by comparing the liquids NMR spectrum of the extract to that of the whole, unfractionated NOM utilizing high resolution magic angle spinning (HRMAS) NMR. To assist in unambiguous peak assignment, a technique for post acquisition spectral denoising, using wavelet transformation (WT), is also employed on the 1D and 2D NMR spectra. The findings from the NMR data lay a foundation for the subsequent electrospray ionization FTICR-MS analysis of the pyridine extracts, since this instrument has the limitation of only analyzing liquid samples. The FTICR-MS analyses can, therefore, be used to molecularly represent the structural components of the NOM. Various compositional insights have been obtained on these samples, indicating the efficacy of the analytical techniques used.     

Molecular characterization of dissolved black nitrogen via electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Combustion produces a complex mixture of polycondensed aromatic compounds known as black carbon (BC). Such products can become remobilized from char and soil in the form of dissolved BC (DBC). Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (ESI–FT-ICRMS) analysis of a variety of soil and char leachates showed that a significant proportion of DBC compounds contained one or more nitrogen atoms. While the presence of black nitrogen (DBN) in dissolved organic matter (DOM) has been reported, its molecular features were uncharacterized. Here we present results of FT-ICRMS characterization of DBN, where assigned formulae were validated on the basis on their ¹³C isotope signatures and fragmentation patterns obtained via collision induced dissociation. Possible chemical structures were assigned for several DBN formulae and suggest that nitrogen was incorporated into the core ring system as a pyrrole-type moiety. Most DBN compounds existed as part of homologous series where homologs differed by a mass corresponding to CO₂, suggesting that they were polysubstituted with carboxylic acid groups. The environmental contribution of such novel, aromatic, combustion-derived nitrogen compounds with respect to global nitrogen cycling remains elusive. The biogeochemical implications of the input of such fire-derived products to aquatic ecosystems as part of climate change therefore need to be assessed.     

利用飞行时间质谱初步分析苯酚水相光化学反应的产物分布特征

近年的实验室模拟和野外观测研究表明,酚类化合物的水相反应(aqueous-phase reaction)对环境二次有机气溶胶(secondary organic aerosol,SOA)的形成具有重要的贡献,因此探讨酚类化合物光化学过程中的演化特征有助于深化二次气溶胶形成的科学认识。本文以苯酚为研究对象,利用大气压喷雾电离(ESI)-飞行时间质谱(TOF-MS),对其在水相光化学反应下的产物分布特征进行了初步探讨。水相光照实验通过直接光解(无添加氧化剂)和光氧化反应(添加H_2O_2)两种情况进行。结果表明,两种方式进行的水相光化学反应均可能生成一系列的低聚物、羟基化化合物以及其他多官能团含氧产物。在m/z 150～400的区间内,添加H_2O_2的光氧化反应产物的分子式种类(150种)明显多于直接光解的形成产物(60种),但直接光解形成的高分子量产物(如低聚物等)离子丰度明显高于光氧化反应,直接光解的产物中可观察到四聚体化合物的生成;同时,水相光反应的产物在紫外-可见光波段内具有明显的光吸收增强特征。由此推断在大气中,以苯酚为代表的酚类化合物进入大气水相环境(云、雾水和气溶胶液态水)中发生的光化学过程对大气吸光性有机物或气溶胶的形成具有贡献作用。     

Structural characterization of gilsonite bitumen by advanced nuclear magnetic resonance spectroscopy and ultrahigh resolution mass spectrometry revealing pyrrolic and aromatic rings substituted with aliphatic chains

Gilsonite, a naturally occurring asphaltite bitumen, consists of a complex mixture of organic compounds. In the present study, advanced one and two dimensional solid state and solution ¹H, ¹³C and ¹⁵N nuclear magnetic resonance (NMR) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) were employed to investigate its composition and structure. ¹³C NMR yielded a carbon aromaticity of 27%. Aromatic moieties in gilsonite were primarily single rings or small clusters of fused rings. Half of the aromatic carbons of gilsonite can be accounted for by pyrroles. ¹⁵N and ¹³C cross polarization-magic angle spinning (CP-MAS) NMR showed that most nitrogen in gilsonite was pyrrolic. The aromatic rings were heavily substituted with alkyl chains, as evidenced by ¹H¹³C correlation spectra. Advanced solid state NMR spectral editing techniques clearly identified specific functional groups such as CCH₃, CCH₂, and CCH₂ (exomethylene). ¹H¹³C wideline separation (WISE) NMR helped identify mobile and non-protonated alkyl carbons. FT-ICR-MS indicated that ∼64% of calculated formulae generated by ESI were aliphatic, while only about 0.8–2.5% of formulae contained possible aromatic rings. All of the assigned formulae contained at least one heteroatom (N, O or S), indicating that ionization by ESI was selective for the polar fraction of gilsonite and potentially less reflective of the overall chemical character of gilsonite than NMR spectroscopy. By combining the information obtained from advanced NMR and ultrahigh resolution MS we propose a structural model for gilsonite as a mixture of many pyrrolic and a few fused aromatic rings highly substituted with and connected by mobile aliphatic chains.     

Role of water in hydrocarbon generation from Type-I kerogen in Mahogany oil shale of the Green River Formation

Hydrous and anhydrous closed-system pyrolysis experiments were conducted on a sample of Mahogany oil shale (Eocene Green River Formation) containing Type-I kerogen to determine whether the role of water had the same effect on petroleum generation as reported for Type-II kerogen in the Woodford Shale. The experiments were conducted at 330 and 350 °C for 72 h to determine the effects of water during kerogen decomposition to polar-rich bitumen and subsequent bitumen decomposition to hydrocarbon-rich oil. The results showed that the role of water was more significant in bitumen decomposition to oil at 350 °C than in kerogen decomposition to bitumen at 330 °C. At 350 °C, the hydrous experiment generated 29% more total hydrocarbon product and 33% more C₁₅₊ hydrocarbons than the anhydrous experiment. This is attributed to water dissolved in the bitumen serving as a source of hydrogen to enhance thermal cracking and facilitate the expulsion of immiscible oil. In the absence of water, cross linking is enhanced in the confines of the rock, resulting in formation of pyrobitumen and molecular hydrogen. These differences are also reflected in the color and texture of the recovered rock. Despite confining liquid-water pressure being 7-9 times greater in the hydrous experiments than the confining vapor pressure in the anhydrous experiments, recovered rock from the former had a lighter color and expansion fractures parallel to the bedding fabric of the rock. The absence of these open tensile fractures in the recovered rock from the anhydrous experiments indicates that water promotes net-volume increase reactions like thermal cracking over net-volume decrease reactions like cross linking, which results in pyrobitumen. The results indicate the role of water in hydrocarbon and petroleum formation from Type-I kerogen is significant, as reported for Type-II kerogen.     

Determination of element/Ca ratios in foraminifera and corals using cold- and hot-plasma techniques in inductively coupled plasma sector field mass spectrometry

We have developed a rapid and precise procedure for measuring multiple elements in foraminifera and corals by inductively coupled plasma sector field mass spectrometry (ICP-SF-MS) with both cold- [800 W radio frequency (RF) power] and hot- (1200 W RF power) plasma techniques. Our quality control program includes careful subsampling protocols, contamination-free workbench spaces, and refined plastic-ware cleaning process. Element/Ca ratios are calculated directly from ion beam intensities of ²⁴Mg, ²⁷Al, ⁴³Ca, ⁵⁵Mn, ⁵⁷Fe, ⁸⁶Sr, and ¹³⁸Ba, using a standard bracketing method. A routine measurement time is 3–5 min per dissolved sample. The matrix effects of nitric acid, and Ca and Sr levels, are carefully quantified and overcome. There is no significant difference between data determined by cold- and hot-plasma methods, but the techniques have different advantages. The cold-plasma technique offers a more stable plasma condition and better reproducibility for ppm-level elements. Long-term 2-sigma relative standard deviations (2-RSD) for repeat measurements of an in-house coral standard are 0.32% for Mg/Ca and 0.43% for Sr/Ca by cold-plasma ICP-SF-MS, and 0.69% for Mg/Ca and 0.51% for Sr/Ca by hot-plasma ICP-SF-MS. The higher sensitivity and enhanced measurement precision of the hot-plasma procedure yields 2-RSD precision for μmol/mol trace elements of 0.60% (Mg/Ca), 9.9% (Al/Ca), 0.68% (Mn/Ca), 2.7% (Fe/Ca), 0.50% (Sr/Ca), and 0.84% (Ba/Ca) for an in-house foraminiferal standard. Our refined ICP-SF-MS technique, which has the advantages of small sample size (2–4 μg carbonate consumed) and fast sample throughput (5–8 samples/hour), should open the way to the production of high precision and high resolution geochemical records for natural carbonate materials.     

Palaeoenvironments associated with caddisfly-dominated microbial-carbonate mounds from the Tipton Shale Member of the Green River Formation: Eocene Lake Gosiute

Caddisfly‐dominated microbial‐carbonate mounds and avian eggshell fragments are common in a nearshore, oolite facies of the Tipton Shale Member of the Eocene Green River Formation. The fossils occur in a 9 m thick carbonate sequence exposed on the south‐west flank of Essex Mountain, Sweetwater County, Wyoming. The eggshell was determined to be of avian origin by examination of the radial eggshell microstructure by scanning electron microscopy and polarized light microscopy. Common allochems in the limestone include: ooids, pisoids, oncoids, ostracods, gastropods, intraclasts, caddisfly larval/pupal cases, fish bones, avian bones and avian eggshell fragments. Carbonate mineralogy varies between 95% calcite and 95% dolomite. Oxygen stable isotopes vary between −10·1 and −1·3‰ (V‐PDB). Carbon and oxygen stable isotopes co‐vary. Co‐variance of oxygen and carbon stable isotopes indicates that Lake Gosiute was hydrologically closed during the formation of this oolite sequence. Positive excursions of oxygen stable isotope values are correlated with dolomite, caddisfly cases and avian eggshell fragments. These factors are probably associated with lake regression and more saline conditions. Negative excursions of oxygen stable isotope values are correlated with calcite, gastropods and intraclasts. These factors are probably associated with lake transgression and lake freshening. In the 9 m oolite sequence studied there are at least two inferred transgressions, three regressions and two storm events. The caddisfly cases and avian eggshell fragments occur in sediments formed only during low‐stands of the lake as determined by other lake level proxies (dolomites and more positive oxygen stable isotope values). As avian eggshell fragments were formed under subaerial conditions, the avian eggshell fragments independently confirm lake regression. In addition, the occurrence of avian eggshell fragments during saline phases of the lake may indicate that the birds which produced the eggshell preferred saline conditions (or that their food preferred saline lake water).     

Evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis: A case study using a Brazilian source rock with Type I kerogen

Hydrous pyrolysis (HP) experiments were used to investigate the petroleum composition and quality of petroleum generated from a Brazilian lacustrine source rock containing Type I kerogen with increasing thermal maturity. The tested sample was of Aptian age from the Araripe Basin (NE-Brazil). The temperatures (280–360 °C) and times (12–132 h) employed in the experiments simulated petroleum generation and expulsion (i.e., oil window) prior to secondary gas generation from the cracking of oil. Results show that similar to other oil prone source rocks, kerogen initially decomposes in part to a polar rich bitumen, which decomposes in part to hydrocarbon rich oil. These two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation. During bitumen decomposition to oil, some of the bitumen is converted to pyrobitumen, which results in an increase in the apparent kerogen (i.e., insoluble carbon) content with increasing maturation.The petroleum composition and its quality (i.e., API gravity, gas/oil ratio, C₁₅₊ fractions, alkane distribution, and sulfur content) are affected by thermal maturation within the oil window. API gravity, C₁₅₊ fractions and gas/oil ratios generated by HP are similar to those of natural petroleum considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. API gravity of the HP expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes. C₁₅₊ fractions (i.e., saturates, aromatics, resins and asphaltenes) show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition. Gas/oil ratios (GOR) initially decrease from 508–131 m³/m³ during bitumen generation and remain essentially constant (81–84 m³/m³) to the end of oil generation. This constancy in GOR is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments. Alkane distributions of the HP expelled oils are similar to those of natural crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. Isoprenoid and n-alkane ratios (i.e., pristane/n-C₁₇ and phytane/n-C₁₈) decrease with increasing thermal maturity as observed in natural crude oils. Pristane/phytane ratios remain constant with increasing thermal maturity through the oil window, with ratios being slightly higher in the expelled oils relative to those in the bitumen. Generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous, with the exception of elevated ethane contents. The general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of HP to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality.     

Partial resolution of sources of n-alkanes in the saline portion of the Parachute Creek Member, Green River Formation (Piceance Creek Basin, Colorado)

Systematic variations in the 13C contents of individual extractable n-alkanes (C16-C29) can be modelled quantitatively and interpreted as indicating contributions from at least five distinct sources. These appear to be cyanobacterial (C16-C18, delta 13C = -37% vs PDB), phytoplanktonic (C16-C23, delta = -32%), chemoautotrophic bacterial (C20-C29, delta = -38%), phytoplanktonic or heterotrophic bacterial (C20-C29, delta = -30%), and vascular plants (C23-C29, delta = -29%). Hydrous pyrolysis of related kerogens yields large quantities of additional n-alkanes with different and much more uniform delta values. The latter materials are apparently derived from the thermolysis of aliphatic biopolymers whose presence in the Green River Oil Shale has been recognized visually.     

不同成熟度家用蜂窝煤燃烧排放烟炱颗粒的Py-GC/MS研究

主要利用热解-气相色谱/质谱联用技术(Py-GC/MS)对不同成熟度的家用蜂窝煤燃烧排放烟炱(soot)颗粒的化学特征进行研究,并探讨了成熟度对燃煤排放soot颗粒热解产物的影响。结果显示:不同成熟度的燃煤排放soot颗粒热解产生类似的产物。这些化合物均以芳香化合物(58.1%～92.0%)为主,另外还含有酚类化合物(0.66%～32.3%)、脂肪烃(0.21%～9.57%)、呋喃类化合物(1.42%～2.57%)、含硫化合物(NA～4.12%)和含氮化合物(NA～3.91%)等,表明不同成熟度蜂窝煤燃烧排放的soot颗粒都是以高度芳香性的结构为核心,连接有含氧、氮等杂原子基团组成。研究结果还显示,原煤成熟度对soot颗粒的热解特征具有一定的影响。总体上,soot颗粒热解产物中芳香化合物的百分含量随着煤样成熟度的增加呈现递增趋势,而酚类化合物的百分含量则随着煤样成熟度的增加逐渐降低,另外含氮化合物主要存在于低成熟度煤样燃烧排放的soot颗粒样品中。本文研究结果表明了随着煤成熟度的升高,燃烧排放的soot颗粒的芳香性逐渐增强,含O、N等不稳定结构逐渐减少。含硫化合物是燃煤排放soot颗粒的特征化合物,主要存在于高成熟度燃煤排放的soot颗粒中。这些结果对于了解不同成熟度的燃煤排放soot颗粒样品中分子结构和组成具有重要的意义。     

Use of comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry for the characterization of biodegradation and unresolved complex mixtures in petroleum

A comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOFMS) method has been developed for separation of a series of petroleum samples using a polar/non-polar column set configuration. Groups of oils were selected to provide samples from the same oil family to assist in comparison of compositional changes during biodegradation. The groups also represented different sources and ages to allow an assessment of the application of GC × GC for the differentiation of oil source, as well as fluid history. The increased resolution and separation afforded by the GC × GC technique provides more complete compositional information on complex biodegraded oil samples than one-dimensional GC, and improves the ability to study biodegradation trends. Among the components identified, it is proposed that alkyl-decahydronaphthalenes constitute a significant contribution to the UCM.     

Molecular characterization of organic matter in sediments from the Keg River formation (Elk Point group), western Canada sedimentary basin

Distributions of free and sulfur-bound biomarkers in organic-rich sediments from the lower and upper Keg River formation (Elk Point group, western Canada) reveal deposition of these sediments under reducing conditions, in agreement with the geological data. The predominance of aryl isoprenoids of Chlorobiaceae origin indicates that photic zone anoxia occurred during time of deposition. A series of novel aryl isoprenoids with a carboxylic acid function was identified by GC–MS and the structure of the predominant 3-methyl-5-(2′,3′,6′-trimethylphenyl)pentanoate was proven by synthesis of an authentic standard. The occurrence of these acids gives evidence that oxidative breakdown at least partially accounts for the diagenetic fate of aromatic carotenoids. Li/EtNH₂ desulfurization of two kerogen concentrates yielded only low amounts of sulfur-bound hydrocarbons, and suggests that either sulfur sequestration was not a predominant process or, more probably, that a major part of the hydrocarbons, initially sulfurized, were released upon maturation, giving further evidence that (poly)sulfide bonds are cleaved at relatively low levels of thermal stress.     

Sr fluxes and Sr/Sr characterization of river waters from a karstic versus granitic watershed in the Yangtze River

The watershed in the southern Jiangxi Province (Jiangxi Province is called simply Gan) (SGW) and the watershed in the central Guizhou Province (Guizhou Province is called simply Qian) (CQW) are two subtropical watersheds of the Yangtze River in China. Both watersheds have similar latitudes and climate, but distinct differences in basin lithology. These similarities and differences provide a good natural laboratory in which to investigate weathering processes and Sr end-members in river waters. This work aims to identify and contrast the sources, fluxes and controls on Sr isotopic composition in the river waters of these two areas. Results showed that the ⁸⁷Sr/⁸⁶Sr in the SGW waters ranged from 0.716501 to 0.724931, with dissolved Sr averaging 27 μg l^− 1. Rhyolites and granites are two major sources for the dissolved Sr. The SGW waters receive 42% of their Sr from silicates weathering, 32% from carbonates and 3.2% from evaporites. ⁸⁷Sr/⁸⁶Sr in the CQW waters has a lesser variation from 0.707694 to 0.710039, but higher Sr contents (average of 208 μg l^− 1). Dolomite, limestone and dolomitic limestone are major sources of Sr in the waters. The CQW waters receive 69% of their Sr from carbonates, 1.7% from silicates and 0.9% from evaporites. The chemical erosion rate and Sr flux in the CQW are 122 t km^− 2 a^− 1 and 0.079 t km^− 2 a^− 1, respectively, which are higher than those of the SGW (56 t km^− 2 a^− 1 and 0.021 t km^− 2 a^− 1, respectively). These data suggest that the intensive carbonates weathering occurred in the karstic area in the upper-reach of the Yangtze River exert great influence on the high Sr concentration and low Sr isotopic ratios in the River.     

The nature and fate of natural resins in the geosphere--VIII. NMR and Py-GC-MS characterization of soluble labdanoid polymers, isolated from Holocene class I resins

Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state ¹³C- and ¹H NMR and ¹³C-¹H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py-GC-MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride-methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py-GC-MS, solid-state ¹³C CP/MAS and ¹³C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators.     

Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.     

具彩色斑纹颅形贝在广西桂林下石炭统黄金组中的发现:兼论颅形贝属的地质地理分布

文中描述了产自广西桂林地区下石炭统黄金组下部的颅形贝属一新种,桂林颅形贝(Cranaena guilinensis)。新种以平直的前结合缘和背壳上发育中槽为特征。在4枚标本上发现保存有放射状的彩色条带,表明该种当时生活在温暖海域的浅水环境。对该属70个种的地质地理分布和生物多样性变化的初步分析表明,该属可能起源于早泥盆世欧美大陆西北缘的老世界区,之后的地理分布和生物多样性发展以北美地区为中心,经历了中泥盆世—晚泥盆世早期和早石炭世2次比较明显的辐射演化、迁移扩散高峰和晚泥盆世晚期的1次严重衰退。第1次高峰是中泥盆世—晚泥盆世早期,该属的生物多样性达到巅峰,生物地理分布范围扩大到欧美大陆之外的西伯利亚板块、哈萨克斯坦板块和华南板块等;第2次高峰是早石炭世,该属的生物多样性虽不及前一次,但获得了最广泛的地理分布,不仅在北方大陆有分布,而且已进入到冈瓦纳大陆边缘。晚泥盆世晚期该属的1次严重衰退显然与F/F灭绝事件有关。早石炭世之后,该属进入衰退阶段,最终在二叠纪初灭绝。