Chromatography-isotope Ratio Mass Spectrometry Research Articles

A significant seawater sulfate reservoir at 2.0 Ga determined from multiple sulfur isotope analyses of the Paleoproterozoic Degrussa Cu-Au volcanogenic massive sulfide deposit, Western Australia

The Proterozoic rock record displays secular change from ferruginous to an oxic hydrosphere over the course of 2 billion years; however, debate continues on the periodicity, rate of change and steps in following atmospheric oxygenation that ultimately led to an oxygenated ocean. This is partly due to poor preservation of the Paleoproterozoic marine sedimentary record in the few hundred million years after the Great Oxidation Event. Whereas the 2.0 Ga rock record preserves only rare chemical sediments, it contains significant mafic igneous provinces, which are known to locally host volcanogenic massive sulfide (VMS) deposits. These hydrothermal environments fossilize the ancient interaction at the seafloor interface between volcanic rocks and seawater. In this context, the 2.01 Ga Degrussa VMS deposit of the Paleoproterozoic Capricorn Orogen, Western Australia offers an opportunity to probe the ancient ocean composition. The Degrussa VMS deposit preserves massive sulfide mineralisation (pyrite – chalcopyrite – pyrrhotite ± sphalerite ± galena) hosted in turbiditic sedimentary rocks interlayered with basaltic flows and cut by numerous gabbroic sills. Exhalite layers are composed of hematite and jasper associated with magnetite. This study documents the multiple sulfur isotope composition of the Degrussa VMS deposit through an integrated analytical approach, which comprises bulk fluorination gas chromatography isotope ratio mass spectrometry and in situ secondary ion mass spectrometry. By comparing the ultra-high precision bulk measurements (n = 21) with in situ measurements of variably-textured grains of pyrite, chalcopyrite and pyrrhotite (n = 252), we determine that VMS mineralisation yields δ34S between +2‰ and +5‰ with a peak at ∼+2.9‰, and negative Δ33S signal ranging from −0.08 to 0.00‰. A two component δ34S-Δ33S mixing model indicates 11% of H2S derived from thermochemically reduced seawater sulfate mixed with magmatic H2S. The most negative Δ33S values must be explained by interaction with sulfate in the near-surface, undergoing complex dissolution-reprecipitation reactions, necessitating a minimum seawater sulfate reservoir of ∼2 mmol/L, or 7% modern seawater at 2.01 Ga.

Isotope fractionation of micropollutants during large-volume extraction: heads-up from a critical method evaluation for atrazine, desethylatrazine and 2,6-dichlorobenzamide at low ng/L concentrations in groundwater

ABSTRACT Micropollutants are frequently detected in groundwater. Thus, the question arises whether they are eliminated by natural attenuation so that pesticide degradation would be observed with increasing residence time in groundwater. Conventional analytical approaches rely on parent compound/metabolite ratios. These are difficult to interpret if metabolites are sorbed or further transformed. Compound-specific stable isotope analysis (CSIA) presents an alternative for identifying degradation based on the analysis of natural isotope abundances in pesticides and their changes during degradation. However, CSIA by gas chromatography–isotope ratio mass spectrometry is challenged by the low concentrations (ng/L) of micropollutants in groundwater. Consequently, large amounts of water need to be sampled requiring enrichment and clean-up steps from interfering matrix effects that must not introduce artefacts in measured isotope values. The aim of this study was to evaluate the accuracy of isotope ratio measurements of the frequently detected micropollutants atrazine, desethylatrazine and 2,6-dichlorobenzamide after enrichment from large water volumes (up to 100 L) by solid-phase extraction with consecutive clean-up by HPLC. Associated artefacts of isotope discrimination were found to depend on numerous factors including organic matter content and extraction volume. This emphasizes the necessity to perform a careful method evaluation of sample preparation and sample pre-treatment prior reliable CSIA.

Leaf Wax Lipid Extraction for Archaeological Applications.

Plant wax lipid molecules, chiefly normal (n-) alkanes and n-alkanoic acids, are frequently used as proxies for understanding paleoenvironmental and paleoclimatic change. These are regularly analyzed from marine and lake sediments and even more frequently in archaeological contexts, enabling the reconstruction of past environments in direct association with records of past human behavior. Carbon and hydrogen isotope measurements of these compounds are used to trace plant type and water-use efficiency, relative paleotemperature, precipitation, evapotranspiration of leaf and soil moisture, and other physiological and ecological parameters. Plant wax lipids have great potential for answering questions related to human-environment interactions, being for the most part chemically inert and easily recoverable in terrestrial sediments, including those dating back millions of years. The growing use of this technique, and comparison of such data with other paleoenvironmental proxies such as pollen and phytolith analysis and soil carbonate and tooth enamel isotope records, make it essential to establish consistent, best-practice protocols for extracting n-alkanes and n-alkanoic acids from archaeological sediments to provide comparable information for interpreting past climatic, ecosystem, and hydrological changes and their interaction with human societies. © 2020 The Authors. Basic Protocol 1: Total lipid extraction Support Protocol 1: Weighing the total lipid extract Support Protocol 2: Cleaning the PSE extraction cells Alternate Protocol 1: Soxhlet total lipid extraction Alternate Protocol 2: Ultrasonic total lipid extraction Basic Protocol 2: Separation of lipids by aminopropyl column chromatography Basic Protocol 3: Separation of lipids by silver-nitrate-infused silica gel column chromatography Support Protocol 3: Preparation of silica gel infused with 10% silver nitrate Basic Protocol 4: Methylation of n-alkanoic acids Basic Protocol 5: Gas chromatography mass spectrometry (GC-MS) Basic Protocol 6: Gas chromatography isotope ratio mass spectrometry (GC-IRMS).

Geographical Origin Classification of Chinese Wines Based on Carbon and Oxygen Stable Isotopes and Elemental Profiles

Wines from different regions have different qualities due to the impact of geographical location and climate. The sale of inferior wines seriously violates the fair-trade rights of consumers. This article provides an elemental analysis classification method for verifying the geographical origin of wines in the People's Republic of China. Inductively coupled plasma mass spectrometry, liquid chromatography isotope ratio mass spectrometry, and an isotope ratio mass spectrometer were used to analyze 142 wine samples collected from Helan Mountain, Xinjiang, Yunchuanzang, the Yanhuai Valley, and the Hexi Corridor regions. The data included elemental profiles, carbon isotope ratios (δ13C), and oxygen isotope ratios (δ18O). The results of multivariate analysis revealed that the geographical origin of wine is closely related to variations in elemental profiles and isotope ratios. Introducing δ18O and the elements Li, Mn, Ag, In, Th, Ta, and Re into the discriminant model yielded correct classification rates of the linear discriminant model of 90.8% for the training set and 87.3% for the test set.

Dual isotope ratio normalization of nitrous oxide by bacterial denitrification of USGS reference materials

We measured the δ values of N2O using gas chromatography isotope ratio mass spectrometry with a preconcentrator (precon-GC-IRMS). The instrumental precision of the mass spectrometer was restricted to below the shot noise limit, which agreed with the theoretical and experimental results of 0.02‰ (δ15N) and 0.04‰ (δ18O), respectively. The precision of the measured δ values was significantly improved by the temperature regulation protocol of the LN2 preconcentrator, which was monitored by various temperature sensors placed along the U-trap. The reproducibility of the He-diluted N2O gas measurements resulted in 0.063‰ (δ15N) and 0.075‰ (δ18O) due to additional sources of uncertainty in the vials used for autosampling and in the general preconcentration process. Multipoint normalization of the dual δ values of the measured N2O samples was conducted using United States Geological Survey reference materials denitrified by Pseudomonas aureofaciens. Kaiser's ion correction method, based on International Atomic Energy Agency parameters, exhibited low bias for the atomic isotope ratio reduction of the nitrate reference material, for which the oxygen anomaly was considerably high. Dedicated corrections for net isotope fractionation and water exchange were important in improving uncertainties in the procedure for normalizing the oxygen isotope ratio. Blank measurements for correcting biases in isotope ratios caused by pre-dissolved nitrate and nitrite ions in the water solvent led to further improvements, i.e. beyond unevenly controlled net isotope fractionation, throughout the bacterial denitrification process. The uncertainty evaluation revealed that three-point normalization can significantly improve the normalization accuracy compared with two-point normalization. In addition, an alternative strategy was suggested for assigning δ18O using a CO2 lab tank, allowing its use as a reference material for N2O gas tanks.

Compound-specific carbon and nitrogen isotope analysis of amino sugars and their applications

Amino sugars (AS) are one of the important biochemical components in the natural organic matter pool. Clarifying the sources and transformations of AS would facilitate our understan-ding of the microbial regulation of organic matter. As an emerging technology, compound-specific isotope analysis of amino sugars (CSIA-AS) provides more detailed dynamic information of indivi-dual AS in natural environment. Here, we systematically summarized the determination methods of CSIA-AS and gave an overview on innovative applications in the cycling of AS. CSIA-AS can be performed by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and ion chromatography-isotope ratio mass spectrometry (IC-IRMS). Each method has its own advantages and disadvantages, but reliable results can be achieved after calibration. The mean residence time of AS is relatively low in soil organic matter, and the bacterial-derived muramic acid possesses a higher minera-lization rate than glucosamine, galactosamine, and mannosamine. The source and metabolic transformation of AS are affected by the substrate, which is related to the specific response of microbial community to different carbon and nitrogen sources. The promotion of CSIA-AS technology requires further optimization of method and integration with other approaches such as microbial screening to decipher the source, transformation, fate and regulatory mechanisms of organic matter.

Source apportionment of atmospheric volatile aromatic compounds (BTEX) by stable carbon isotope analysis: A case study during heating period in Taiyuan, northern China

Due to the high negative effects on health and environment, volatile aromatic compounds (benzene, toluene, ethylbenzene and xylene, BTEX) have drawn more and more attention recently. BTEX samples of four emission sources (coal combustion, vehicle exhaust, gasoline volatilization and solvent evaporation) and ambient air from three sampling sites (rural, urban and suburban) were collected during winter in Taiyuan, northern China. Gas chromatography–mass spectrometry and thermal desorption–gas chromatography–isotope ratio mass spectrometry were employed to investigate the composition characteristics and stable carbon isotopic (δ13C) analysis of BTEX, respectively. The results revealed that the δ13C value of BTEX for coal combustion, with the range of −23.8‰ to −25.2‰, was higher than that for vehicle exhaust, gasoline volatilization and solvent evaporation, ranging from −25.5‰ to −27.6‰, −28.0‰ to −30.9‰ and −27.7‰ to −32.1‰, respectively. Atmospheric BTEX concentrations were the highest at the suburban site (41.5 μg/m3) and the lowest at the rural site (27.0 μg/m3). The δ13C values of atmospheric BTEX at rural, urban and suburban sites ranged from −24.8‰ to −26.2‰ (average −25.3‰), −24.8‰ to −26.9‰ (average −26.0‰) and −23.9‰ to −25.4‰ (average −24.8‰), respectively, indicating that the suburban site was enriched in 13C relative to rural and urban sites. The B/T ratio results indicated that coal combustion was the primary source of atmospheric pollution in Taiyuan. The mean contribution of emission sources in all three sampling site were determined by adopting Isosource-based quantitative calculation. For rural, urban and suburban sites, coal combustion, as the major source, made mean contributions of 62.3%, 46.0% and 74.1%, while vehicle exhaust was responsible for 22.0%, 30.6% and 15.3%, respectively. Coal combustion and vehicle exhaust were the top two primary sources of BTEX in Taiyuan, especially coal combustion provided a half contribution to atmospheric BTEX. Therefore, implementing controls on coal combustion is crucial to reduce ambient volatile aromatic compound pollution, especially in areas with high coal consumption.

Extraterrestrial amino acids and L‐enantiomeric excesses in the CM2 carbonaceous chondrites Aguas Zarcas and Murchison

AbstractThe abundances, distributions, enantiomeric ratios, and carbon isotopic compositions of amino acids in two fragments of the Aguas Zarcas CM2 type carbonaceous chondrite fall and a fragment of the CM2 Murchison meteorite were determined via liquid chromatography time‐of‐flight mass spectrometry and gas chromatography isotope ratio mass spectrometry. A suite of two‐ to six‐carbon aliphatic primary amino acids was identified in the Aguas Zarcas and Murchison meteorites with abundances ranging from ~0.1 to 158 nmol/g. The high relative abundances of α‐amino acids found in these meteorites are consistent with a Strecker‐cyanohydrin synthesis on these meteorite parent bodies. Amino acid enantiomeric and carbon isotopic measurements in both fragments of the Aguas Zarcas meteorites indicate that both samples experienced some terrestrial protein amino acid contamination after their fall to Earth. In contrast, similar measurements of alanine in Murchison revealed that this common protein amino acid was both racemic (D ≈ L) and heavily enriched in 13C, indicating no measurable terrestrial alanine contamination of this meteorite. Carbon isotope measurements of two rare non‐proteinogenic amino acids in the Aguas Zarcas and Murchison meteorites, α‐aminoisobutyric acid and D‐ and L‐isovaline, also fall well outside the typical terrestrial range, confirming they are extraterrestrial in origin. The detections of non‐terrestrial L‐isovaline excesses of ~10–15% in both the Aguas Zarcas and Murchison meteorites, and non‐terrestrial L‐glutamic acid excesses in Murchison of ~16–40% are consistent with preferential enrichment of circularly polarized light generated L‐amino acid excesses of conglomerate enantiopure crystals during parent body aqueous alteration and provide evidence of an early solar system formation bias toward L‐amino acids prior to the origin of life.

Compound-Specific Isotope Analysis of Human Hair: Predicting Behaviors and Biometrics beyond Dietary Factors.

This study describes the use of amino acid quantitation and amino-acid-specific isotope ratio analysis of scalp hair of American individuals to predict soft biometric traits about the donors. The scalp hair of each donor was washed, dried, homogenized and acid hydrolyzed before analysis using liquid chromatography-isotope ratio mass spectrometry (LC-IRMS). A variety of statistical tests examined the relationships between the amino acid variables and biometric questionnaire responses, the latter of which could be assessed as continuous variables-in the case of age or body mass index (BMI)-or as categorical variables in the case of sex and alcohol consumption. Correlations between biometric factors and amino acid δ13C values were more significant after controlling for the extent of 13C in the subjects' diets. Multivariate analysis revealed that the sex of a donor could be correctly predicted with cross-validated accuracies of 80% using the isotope ratios and 89% using amino acid quantities. Using amino acid δ13C values or quantities, the age of a subject could only be predicted with an accuracy of ±27 years (95% CI). Hair treatments, such as chemical straitening and dying, did not have any measurable effect on the isotope ratios or quantities of amino acids in the hair. Unexpectedly, the δ13C values of sulfur-containing amino acids were significantly different between teetotalers and subjects who consumed alcohol daily. Further refinement of this study, including larger cohorts with controlled behavioral states or genetic factors, could provide helpful investigative leads in forensic casework.

The influence of sample matrix on the accuracy of nitrite N and O isotope ratio analyses with the azide method.

The isotope ratios of nitrogen (15 N/14 N) and oxygen (18 O/16 O) in nitrite (NO2 - ) can be measured by conversion of the nitrite into nitrous oxide (N2 O) with azide, followed by mass spectrometric analysis of N2 O by gas chromatography isotope ratio mass spectrometry (GC/IRMS). While applying this method to brackish samples, we noticed that the N and O isotope ratio measurements of NO2 - are highly sensitive to sample salinity and to the pH at which samples are preserved. We investigated the influence of sample salinity and sample preservation pH on the N and O isotope ratios of the N2 O produced from the reaction of NO2 - with azide. The N2 O isotope ratios were measured by GC/IRMS. Under the experimental reaction conditions, the conversion of NO2 - into N2 O was less complete in lower salinity solutions, resulting in respective N and O isotopic offsets of +2.5‰ and -14.0‰ compared with seawater solutions. Differences in salinity were also associated with differences in the fraction of O atoms exchanged between NO2 - and water during the reaction. Similarly, aqueous NO2 - samples preserved at elevated pH values resulted in the incomplete conversion of NO2 - into N2 O by azide, and consequent pH-dependent isotopic offsets, as well as differences in the fraction of O atoms exchanged with water. The addition of sodium chloride to the reaction matrix of samples and standards largely mitigated salinity-dependent isotopic offsets in the N2 O product, and nearly homogenized the fraction of O atom exchange among samples of different salinity. A test of the hypobromite-azide method to measure N isotope ratios of ammonium by conversion into NO2 - then N2 O revealed no influence of sample salinity on the N isotope ratios of the N2 O product. We outline recommendations to mitigate potential matrix effects among samples and standards, to improve the accuracy of N and O isotope ratios in NO2 - measured with the azide method.

Origin and depositional environments of source rocks and crude oils from Niger Delta Basin: Carbon isotopic evidence

ABSTRACT Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin, Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry. The bulk carbon isotopic values of the whole rock extracts, saturate and aromatic fractions range from –28.7‰ to –26.8‰, –29.2‰ to –27.2 ‰ and –28.5 ‰ to –26.7 ‰, respectively while the bulk carbon isotopic values of the whole oils, saturate and aromatic fractions range from –25.4 ‰ to –27.8 ‰, –25.9 ‰ to –28.4 ‰ and –23.5 ‰ to –26.9 ‰, respectively. The average carbon isotopic compositions of individual alkanes (nC12-nC33) in the rock samples range from –34.9‰ to –28.2‰ whereas the average isotopic values of individual n-alkanes in the oils range from –31.1‰ to –23.8‰. The δ13C isotope ratios of pristane and phytane in the rock samples range from –29.2 ‰ to –28.2 ‰ and –30.2 ‰ to –27.4 ‰ respectively while the pristane and phytane isotopic values range from –32.1‰ to –21.9‰ and –30.5‰ to –26.9‰, respectively. The isotopic values recorded for the samples indicated that the crude oils were formed from the mixed input of terrigenous and marine organic matter and deposited under oxic to sub-oxic condition in lacustrine-fluvial/deltaic environments. The stable carbon isotopic compositions were found to be effective in assessing the origin and depositional environments of crude oils in the Niger Delta Basin.

An untargeted 13C isotopic evaluation approach for the discrimination of fermented food matrices at natural abundance: Application to vinegar

A non-destructive and comprehensive 13C isotopic evaluation approach based on 1H NMR spectroscopy was developed. The carbon isotope distribution (CID) of most of the components (S/N ≥ 1000) in food matrices were evaluated using frequency distribution of peak area ratios (PAR) of decoupling to non-13C-decoupling spectra at natural abundance. The approach was applied successfully to vinegar and it was found that the PAR of fermented vinegars is obviously narrower than that of the blended one and the one produced via chemically defined culture medium. Besides, the extra additives can also be evaluated by their characteristic PAR values. It was found that the sugars are the most commonly added components into the blended vinegars. The results obtained from the developed approach show good validity (baseline effect, RSD < 0.1%) and internal reproducibility (RSD < 0.1%). Practicability of the method is confirmed by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) detection method. The results imply that the proposed approach could be used not only for the discrimination but also for the primary authentication of the blended components in the fermented food matrices.

Improved Method for Differentiation of Synthetic and Natural Endogenous Anabolic Steroids using Gas Chromatography Isotope Ratio Mass Spectrometry (GC/C/IRMS) followed by Two-Fold High Performance Liquid Chromatography (HPLC) Cleanup Method: A Perspective

Abstract: Background: Androgenic Anabolic Steroids (AAS) are also synthetic derivatives of testosterone, modified to improve its anabolic actions. The misuse of AAS is of particular concern in sports and society. Gas chromatography-mass spectrometry had some limitations and allows identification and characterization of steroids and their metabolites in the urine but may not be able to distinguish between pharmaceutical (Exogenous) and endogenous origin. Thus, it is of great importance to discriminate endogenous steroids such as testosterone or testosterone prohormones from their chemically identical synthetic copies. The abuse of Androgenic Anabolic Steroids (AAS) by sports person is banned by World Anti-doping Agency (WADA) as per the WADA Prohibited list 2019. Methodology: The gas chromatography-combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique differentiates between natural and synthetic endogenous steroids by comparing compounds specific 13C/12C ratio. However, the analytes have to be efficiently isolated and purified prior to GC/C/IRMS analysis. Results and Discussion: HPLC Cleanup method prior to analysis by GC−C/IRMS needs to be developed and validated for discriminating the origin of anabolic androgenic steroids. These methods involves the solid-phase extraction, enzymatic hydrolysis with β-glucuronidase, HPLC-fractionation for the cleanup and analysis by GC−C/IRMS. The difference (Δ13C) of urinary δ13C values between synthetic analogues and Endogenous Reference Compounds (ERC) by GC-C/IRMS would be used to elucidate the origin of steroids. The present perspective gives an overview of the use of anabolic-androgenic steroids in sport and methods used in anti-doping laboratories for their detection in urine, with special emphasis on GC−C/ IRMS technique after two-fold HPLC cleanup. Key words: Endogenous Steroids, Exogenous Steroids, HPLC Cleanup, Doping, GC/C/ IRMS.

Toward Improved Accuracy in Chlorine Isotope Analysis: Synthesis Routes for In-House Standards and Characterization via Complementary Mass Spectrometry Methods.

Increasing applications of compound-specific chlorine isotope analysis (CSIA) emphasize the need for chlorine isotope standards that bracket a wider range of isotope values in order to ensure accurate results. With one exception (USGS38), however, all international chlorine isotope reference materials (chloride and perchlorate salts) fall within the narrow range of one per mille. Furthermore, compound-specific working standards are required for chlorine CSIA but are not available for most organic substances. We took advantage of isotope effects in chemical dehalogenation reactions to generate (i) silver chloride (CT16) depleted in 37Cl/35Cl and (ii) compound-specific standards of the herbicides acetochlor and S-metolachlor (Aceto2, Metola2) enriched in 37Cl/35Cl. Calibration against the international reference standards USGS38 (-87.90 ‰) and ISL-354 (+0.05 ‰) by complementary methods (gas chromatography-isotope ratio mass spectrometry, GC-IRMS, versus gas chromatography-multicollector inductively coupled plasma mass spectrometry, GC-MC-ICPMS) gave a consensus value of δ37ClCT16 = -26.82 ± 0.18 ‰. Preliminary GC-MC-ICPMS characterization of commercial Aceto1 and Metola1 versus Aceto2 and Metola2 resulted in tentative values of δ37ClAceto1 = 0.29 ± 0.29 ‰, δ37ClAceto2 = 18.54 ± 0.20 ‰, δ37ClMetola1 = -4.28 ± 0.17 ‰ and δ37ClMetola2 = 5.12 ± 0.27 ‰. The possibility to generate chlorine isotope in-house standards with pronounced shifts in isotope values offers a much-needed basis for accurate chlorine CSIA.

Molecular and isotopic analyses on prehistoric pottery from the Virués-Martínez cave (Granada, Spain)

The analysis of the organic residues in archaeological pottery usually involves the use chromatography and mass spectrometry techniques. The identification of organic compounds processed in archaeological vessels, which generally degrade over archaeological timescales, provides insights about their origin and uses of the vessels. This paper provides an advance of archaeometric characterization of the organic residues in seventeen pottery vessels from the end of the 4th millennium BCE found in the Virués-Martínez cave (Granada, Spain), using gas chromatography–mass spectrometry (GC–MS), gas chromatography-isotope ratio mass spectrometry (GC-C-IRMS), and ultra-performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS). To our knowledge this is the first study on the use of UPLC-HRMS on archaeological residues. Despite the fact that the identification of plant remains continues to be elusive, this study demonstrates the potential usefulness of UPLC-HRMS technique to study the polar fraction of plant residues, thus allowing us to formulate more specific hypotheses about the vegetal compounds that have survived in association with the pottery vessels (erucamide, matricarin, piptamine, piceatannol). Our results indicate that the occupants of the cave used the vessels to process plant materials and also degraded animal fats (ruminant fat) and it is very likely that the vessels were used for a variety of purposes, with accumulation of by-products over time, and were not made exclusively for funerary practices. The δ13C values C16:0 and C18:0 fatty acids obtained open a debate on the consumption of dairy compounds in the Iberian Peninsula during the end of the Neolithic and beginning of the Copper Age.

Stable Carbon Isotope Compositions and Source Apportionments of Volatile Aromatic Compounds in the Urban Atmosphere of Taiyuan, China

This study used Tenax TA absorption tubes to sample volatile aromatic compounds from different emission sources and functional zones in Taiyuan City, Shanxi Province, China. Thermal desorption-gas chromatography-isotope ratio mass spectrometry (TD-GC-IRMS) was subsequently employed to analyze the stable carbon isotope characteristics of the volatile aromatic compounds. The results revealed that the stable carbon isotope ratio (δ13C) of the volatile aromatic compounds emitted through diesel, gasoline, and solvent volatilization, vehicle exhaust, and domestic coal combustion ranged from (-30.79±0.98)‰ to (-29.10±0.14)‰, (-30.96±0.88)‰ to (-28.02±1.77)‰, (-32.13±0.59)‰ to (-27.67±0.49)‰, (-27.58±0.16)‰ to (-25.50±0.75)‰, and (-25.14±0.93)‰ to (-23.44±1.32)‰, respectively. The δ13C value of styrene was (-23.44±1.32)‰, which was only detected in the fumes emitted through domestic coal combustion. Additionally, the sample analysis based on data collected from four different functional zones of Taiyuan City revealed the following:① the δ13C values of the atmospheric volatile aromatic compounds in the mixed residential and traffic zone ranged from (-25.61±2.20)‰ to (-23.91±0.78)‰. Compared with other functional zones, the emissions in this zone were enriched with13C; and ② the δ13C values measured in the industrial zone ranged from (-29.15±1.06)‰ to (-24.53±1.07)‰; the emissions in this functional zone were relatively low in 13C compared with other zones. A comparison of the δ13C values of the atmospheric volatile aromatic compounds and emission sources indicated that the main sources of volatile aromatic compounds at the four sampling points in Taiyuan were vehicle exhausts and domestic coal combustion, while the air sampled in the industrial functional zone was heavily affected by the volatilization of solvents.

Biodegradation and photooxidation of phenolic compounds in soil—A compound-specific stable isotope approach

Phenolic compounds occur in a variety of plants and can be used as model compounds for investigating the fate of organic wastewater, lignin, or soil organic matter in the environment. The aim of this study was to better understand and differentiate mechanisms associated with photo- and biodegradation of tyrosol, vanillin, vanillic acid, and coumaric acid in soil. In a 29 d incubation experiment, soil spiked with these phenolic compounds was either subjected to UV irradiation under sterile conditions or to the native soil microbial community in the dark. Changes in the isotopic composition (δ13C) of phenolic compounds were determined by gas chromatography–isotope ratio mass spectrometry and complemented by concentration measurements. Phospholipid-derived fatty acid and ergosterol biomarkers together with soil water repellency measurements provided information on soil microbial and physical properties. Biodegradation followed pseudo-first-order dissipation kinetics, enriched remaining phenolic compounds in 13C, and was associated with increased fungal rather than bacterial biomarkers. Growing mycelia rendered the soil slightly water repellent. High sample variation limited the reliable estimation of apparent kinetic isotope effects (AKIEs) to tyrosol. The AKIE of tyrosol biodegradation was 1.007 ± 0.002. Photooxidation kinetics were of pseudo-zero- or first-order with an AKIE of 1.02 ± 0.01 for tyrosol, suggesting a hydroxyl-radical mediated degradation process. Further research needs to address δ13C variation among sample replicates potentially originating from heterogeneous reaction spaces in soil. Here, nuclear magnetic resonance or nanoscopic imaging could help to better understand the distribution of organic compounds and their transformation in the soil matrix.

Characterization of a novel marine origin aerobic nitrifying–denitrifying bacterium isolated from shrimp culture ponds

A novel marine origin Bacillus subtilis strain H1 isolated from a shrimp culture pond effectively removed NH₄⁺‐N, NO2-‐N and NO3-‐N, with a maximum ammonium, nitrite and nitrate removal rate of 2.35 mg NH₄⁺‐N L⁻¹ hr⁻¹ per OD, 9.64 mg NO2-‐N L⁻¹ hr⁻¹ per OD and 0.75 mg NO3-‐N L⁻¹ hr⁻¹ respectively. The gas chromatography–isotope ratio mass spectrometry results indicated that N₂O was emitted when ¹⁵NH₄Cl, Na¹⁵NO₂ or Na¹⁵NO₃ was used. Additionally, N₂ was also produced when Na¹⁵NO₂ was used. Single‐factor experiments suggested that the optimal conditions for NH₄⁺‐N and NO2-‐N removal were glucose as a carbon source, C/N 15, initial pH 7.5, 30 g/L NaCl, 28°C and a shaking speed of 160 rpm. Orthogonal tests showed that the optimal conditions for NH₄⁺‐N removal were C/N 15, pH 9, 10 g/L NaCl and shaking speed 160 rpm when ammonium chloride was used as the substrate. The optimal conditions for NO2-‐N removal were C/N 10, pH 6, 10 g/L NaCl and a shaking speed of 160 rpm when sodium nitrite was used as the substrate. In summary, B. subtilis strain H1 had highly efficient aerobic nitrifying–denitrifying ability and high adaptability, suggesting that it is potentially valuable to marine aquaculture.

Multipoint normalization of δ18O of water against the VSMOW2-SLAP2 scale with an uncertainty assessment

In this study, we measured the oxygen stable isotope ratio of drinking water using gas chromatography isotope ratio mass spectrometry. The δ18O value of drinking water was normalized based on the Vienna Standard Mean Ocean Water 2 (VSMOW2), Standard Light Antarctic Precipitation 2 (SLAP2), and Greenland Ice Sheet Precipitation (GISP) scale by CO2 equilibrium for 24 h. The isotope ratio responses of a dummy sample drifted as much as 0.145‰ due to a significant decrease in the amount of injected sample. The autodilution technique improved measurement precision of the δ18O of dummy sample two-fold compared to that without autodilution to 0.025‰. The autodilution of an injected concentration of equilibrated CO2 also helped improve the measurement precision of the isotope ratio response. The drift of the ratio responses was tested using linear model regression to validate linearity within the sample concentration and isotope ratio ranges. Measurement reliability was assessed using various statistical approaches. One-way analysis of variance verified non-reproducible results of individual measurements. Normalization uncertainties were then assessed by various normalization schemes including two-point and three-point values consisting of the VSMOW2, SLAP2, and GISP standards, showing equivalent results associated with similar extent of normalization uncertainties among various normalization methods. In particular, the uncertainty of the GISP (0.09‰) contributed to one-third of the total normalization uncertainty, implying that the three-point normalization can be improved by a potential standard of which uncertainty is equivalent to the bracketing standards, VSMOW2 (0.02‰) and SLAP2 (0.02‰).

New Concepts for the Determination of Oxidation Efficiencies in Liquid Chromatography-Isotope Ratio Mass Spectrometry.

In liquid chromatography coupled to isotope ratio mass spectrometry (LC-IRMS), analytes are separated on an LC system and consecutively oxidized to CO2, which is required for the determination of compound-specific carbon isotope ratios. Oxidation is performed in an online reactor by sulfate radicals. Reaction conditions in the interface depend on the flow conditions determined by the LC method and the flow rates and concentrations of oxidation agent and phosphoric acid added in the interface. To determine accurate isotope ratios, a quantitative conversion of the carbon contained in the analyte to the CO2 measurement gas is a prerequisite. Oxidation efficiencies are not commonly evaluated during method development, although certain analytes are known to be difficult to be oxidized by sulfate radicals. For the assessment of the oxidation efficiency of the LC-IRMS system, three different approaches were evaluated. (1) Residual organic carbon in the eluent stream of the interface was determined to calculate oxidation yields depending on the initial analyte concentration. (2) The IRMS response was calibrated to an inorganic carbon reference material to determine oxidation efficiencies with the help of the IRMS as a detector. (3) The oxidation temperature was deliberately reduced while monitoring the δ13C and signal intensity. The common assumption that a linear relation of IRMS signal to analyte concentration is an indicator for complete oxidation in LC-IRMS could be disproved. All three approaches can be applied for future method development in LC-IRMS, monitoring of existing flow injection applications, as well as for verification of complete oxidation in established LC-IRMS methods.