Isotope Ratio Mass Spectrometer Research Articles

Application of environmental isotopes and hydrochemistry in the identification of source of seepage and likely connection with lake water in Lesser Himalaya, Uttarakhand, India

Oxygen (\({\updelta }^{18}\hbox {O}\)) and hydrogen (\({\updelta }^{2}\hbox {H}\) and \(^{3}\hbox {H}\)) isotopes of water, along with their hydrochemistry, were used to identify the source of a newly emerged seepage water in the downstream of Lake Nainital, located in the Lesser Himalayan region of Uttarakhand, India. A total of 57 samples of water from 19 different sites, in and around the seepage site, were collected. Samples were analysed for chemical tracers like \(\hbox {Ca}^{++}\), \(\hbox {Mg}^{++}\), \(\hbox {Na}^{+}\), \(\hbox {K}^{+}\), \({\hbox {SO}_{4}}^{--}\) and \(\hbox {Cl}^{-}\) using an Ion Chromatograph (Dionex IC-5000). A Dual Inlet Isotope Ratio Mass Spectrometer (DIIRMS) and an Ultra-Low Level Liquid Scintillation Counter (ULLSC), were used in measurements of stable isotopes (\({\updelta }^{2}\hbox {H}\) and \({\updelta }^{18}\hbox {O}\)) and a radioisotope (\(^{3}\hbox {H}\)), respectively. Results obtained in this study repudiate the possibility of any likely connection between seepage water and the lake water, and indicate that the source of seepage water is mainly due to locally recharged groundwater. The study suggests that environmental isotopes (\({\updelta }^{2}\hbox {H}\), \({\updelta }^{18}\hbox {O}\) and \(^{3}\hbox {H}\)) can effectively be used as ‘tracers’ in the detection of the source of seepage water in conjunction with other hydrochemical tracers, and can help in water resource management and planning.

Rapid and high-resolution stable isotopic measurement of biogenic accretionary carbonate using an online CO2 laser ablation system: Standardization of the analytical protocol.

The elaborate sampling and analytical protocol associated with conventional dual-inlet isotope ratio mass spectrometry has long hindered high-resolution climate studies from biogenic accretionary carbonates. Laser-based on-line systems, in comparison, produce rapid data, but suffer from unresolvable matrix effects. It is, therefore, necessary to resolve these matrix effects to take advantage of the automated laser-based method. Two marine bivalve shells (one aragonite and one calcite) and one fish otolith (aragonite) were first analysed using a CO2 laser ablation system attached to a continuous flow isotope ratio mass spectrometer under different experimental conditions (different laser power, sample untreated vs vacuum roasted). The shells and the otolith were then micro-drilled and the isotopic compositions of the powders were measured in a dual-inlet isotope ratio mass spectrometer following the conventional acid digestion method. The vacuum-roasted samples (both aragonite and calcite) produced mean isotopic ratios (with a reproducibility of ±0.2 ‰ for both δ18 O and δ13 C values) almost identical to the values obtained using the conventional acid digestion method. As the isotopic ratio of the acid digested samples fall within the analytical precision (±0.2 ‰) of the laser ablation system, this suggests the usefulness of the method for studying the biogenic accretionary carbonate matrix. When using laser-based continuous flow isotope ratio mass spectrometry for the high-resolution isotopic measurements of biogenic carbonates, the employment of a vacuum-roasting step will reduce the matrix effect. This method will be of immense help to geologists and sclerochronologists in exploring short-term changes in climatic parameters (e.g. seasonality) in geological times.

Grain-scale stable carbon and oxygen isotopic variations of the international reference calcite, IAEA-603.

The new international reference material IAEA-603 (calcite) for stable carbon and oxygen isotopes (δ13 C and δ18 O values) was released in 2016 to replace the previous reference material, NBS19 (exhausted). We examined the grain-scale isotopic variations in IAEA-603 for application to microscale isotopic analysis of carbonate samples. Individual grains of IAEA-603 were analyzed with an IsoPrime100 isotope ratio mass spectrometer with a customized continuous-flow gas preparation system (MICAL3c). The individual grains of IAEA-603 were observed by optical and scanning electron microscopy, and their observational characteristics (grain color and size) were compared with their stable isotope compositions. Translucent grains (main component of IAEA-603; grain weight, 4-132μg) had homogeneous isotopic ratios, comparable with the grain-scale isotopic homogeneity of NBS 19. Their average δ13 C and δ18 O values were the same as the recommended values determined by the IAEA. Opaque (whitish) grains (1-2 per 100 grains; grain weight, 8-63μg) were significantly more depleted in 13 C and 18 O than the translucent grains. Low-abundance opaque grains (1-2 grains out of 100 grains) have lower δ13 C and δ18 O values, suggesting that these grains should be eliminated when using IAEA-603 for single-grain (microscale) isotope analysis.

Molecular distributions and isotopic compositions of organic aerosols over the western North Atlantic: Dicarboxylic acids, related compounds, sugars, and secondary organic aerosol tracers

Marine aerosols were collected over the western North Atlantic off the coast of Boston to Bermuda in August 2012 using a high-volume air sampler. Aerosol samples were analyzed for organic and elemental carbon (OC/EC), low molecular weight dicarboxylic acids and related compounds, lipid class compounds (n-alkanes, fatty acids and fatty alcohols), sugars and various secondary organic aerosol (SOA) tracers. Homologous series (C2-C12) of dicarboxylic acids (31–335ng/m3) were detected with a predominance of oxalic acid. Diacids were found to be the most abundant compound class followed by monoterpene-SOA tracers>isoprene-SOA tracers>sugars>oxoacids>fatty alcohols>fatty acids>α-dicarbonyls>aromatic acids>n-alkanes. The concentrations of these compounds were higher in the coastal site and decreased towards the open ocean. However, the abundance of diacids stayed relatively high even in the remote ocean. Interestingly, contributions of oxalic acid to total aerosol carbon increased from the coast (2.3%) to the open ocean (5.6%) near Bermuda.Stable carbon isotope ratios of aerosol total carbon and individual diacids and oxoacids were determined using an isotope ratio mass spectrometer. The stable carbon isotopic composition of oxalic acid increased from the coast (−17.5‰) to the open ocean (−12.4‰), confirming that photochemical aging of organic aerosols occurred during the atmospheric over the ocean. Stable carbon isotope ratios of bulk aerosol carbon also increased from the coast near Boston (−24.3‰) to the open ocean near Bermuda (−18.2‰), consistent with photochemical aging of organic aerosols.

Identifying Groundwater Recharge Sites through Environmental Stable Isotopes in an Alluvial Aquifer

Environmental isotope tracers have been a useful tool in providing new insights into hydrologic processes. In Mexico, there have been several studies reporting different values for δ 18 O and δ 2 H for certain geographical areas. The objective of this study is to achieve the isotopic characterization of rainfall and groundwater and to report the comprehensive understanding of groundwater flow processes around and within the Calera aquifer and, consequently, its potential recharge sites. The samples used for the stable isotope analysis ( δ 18 O , δ 2 H ) were measured using a GV-Isoprime isotope-ratio mass spectrometer at the Isotopy Laboratory of the Water Center for Latin America and the Caribbean. The δ D of precipitation ranged between −110.20‰ and 10.11‰, with a mean of −55.67‰ ± 27.81‰. The δ 18 O ranged between −17.80‰ and 2.74‰, with a mean of −9.44‰ ± 4.74‰. The δ D of groundwater ranged between −81.92‰ and −36.45‰, with a mean of −66.05‰ ± 8.58‰. The δ 18 O ranged between −18.26‰ and −8.84‰, with a mean of −12.35‰ ± 2.12‰. The local meteoric water line of the Zacatecas state is δ D = − 2.03 + 5.68 δ 18 O . The groundwater samples were clustered into four groups. The clustering of the samples led to the finding that streamflows play a significant role in the hydrological balance as a source of local recharge to the aquifer.

Tissue-specific turnover and diet-tissue discrimination factors of carbon and nitrogen isotopes of a common forage fish held at two temperatures.

The application of stable isotopes to foraging ecology is dependent on understanding life-history and environmental factors unrelated to diet that may influence isotopic composition. Diet-tissue discrimination factors (DTDFs) and turnover rates will increase the accuracy of isotope-based studies. Furthermore, little consideration has been given to the effects of temperature or life-history stage on isotopic ratios despite the prevalence of variation in temperature and growth rates throughout life. We measured δ13 C and δ15 N values with an elemental analyzer coupled to a continuous flow isotope ratio mass spectrometer. These values were used to estimate turnover and DTDFs for Emerald Shiners (Notropis atherinoides), a common North American freshwater forage fish. Fish were assigned to a temperature treatment, either 10°C (Low) or 20°C (High), and provided one of three diets (commercial pellet, Artemia salina, or Hemimysis anomala). At regular intervals fish were sampled and the isotopic compositions of whole body and liver tissues were determined. Tissue turnover rates for fish fed Artemia were faster for liver than for whole body, but were also influenced by temperature. Turnover occurred faster at higher temperatures for body and liver δ15 N values, but not for δ13 C values. The pellet and Hemimysis treatments were in isotopic equilibrium from the start of the experiment and estimated DTDFs based on these treatments were lower than assumed for Δ15 N (+0.6 to 2.7‰) and variable, but within expected ranges for Δ13 C (-1.9 to +1.5‰). The results for Emerald Shiners differed from commonly made assumptions for applying stable isotopes to ecological questions, possibly related to a bias in the use of juveniles in studies of turnover and DTDFs and assumptions regarding thermal-independence of isotopic relationships. The species-specific DTDF and tissue turnover estimates provided here will inform interpretations of stable isotope data for smaller fish species and improve food-web studies.

Large variability in CO2 and N2 O emissions and in 15 N site preference of N2 O from reactions of nitrite with lignin and its derivatives at different pH.

Chemodenitrification is an important N2 O source in soil; however, knowledge about the production of CO2 and N2 O from abiotic nitrite-SOM reactions, especially the N2 O isotopic signatures (intramolecular 15 N site preference (SP), and δ15 Nbulk and δ18 O values), is quite limited at present. N2 O and CO2 emissions from chemical reactions of nitrite with lignin products were determined with gas chromatography, and their response surfaces as a function of pH from 3 to 6 and nitrite concentration from 0.1 to 0.5mM were explored with polynomial regression. The intramolecular 15 N distribution of N2 O, as well as δ15 Nbulk and δ18 O values, were measured with an isotope ratio mass spectrometer coupled to an online pre-concentration unit. The variability in N2 O SP values was tested from pH3 to 5, and for nitrite concentrations from 0.3 to 0.5mM. Both CO2 and N2 O emissions varied largely with pH and the structure of lignin products. The highest N2 O emission occurred at pH4-5 in 4-hydroxy-3,5-dimethoxybenzaldehyde and 4-hydroxy-3,5-dimethoxybenzoic acid treatments, and at pH3 in the treatments with lignin, 4-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-3-methoxybenzoic acid, 4-hydroxybenzaldehyde, and 4-hydroxybenzoic acid. A wide range of N2 O SP values (11.9-37.4‰), which was pH dependent and not distinguishable from microbial pathways, was observed at pH3-5. The δ15 Nbulk and δ18 O values of N2 O were both in a similar range to that reported for fungal denitrification and bacterial denitrification. These results present the first characterization of the isotopic composition of N2 O from chemodenitrification in pure chemical assays. Chemical reactions of nitrite with lignin are pH-dependent and associated with substantial CO2 and N2 O emissions. The SP values of N2 O derived from chemodenitrification were neither distinguishable from the biotic pathways nor remained stable with varying pH. Therefore, the use of N2 O isotopic signatures for source partitioning is restricted when chemodenitrification is contributing significantly to N2 O emission.

Efficacy of passive sampler collection for atmospheric NO2 isotopes under simulated environmental conditions.

Nitrogen oxides or NOx (NOx = NO + NO2 ) play an important role in air quality, atmospheric chemistry, and climate. The isotopic compositions of anthropogenic and natural NO2 sources are wide-ranging, and they can be used to constrain sources of ambient NO2 and associated atmospheric deposition of nitrogen compounds. While passive sample collection of NO2 isotopes has been used in field studies to determine NOx source influences on atmospheric deposition, this approach has not been evaluated for accuracy or precision under different environmental conditions. The efficacy of NO2 passive sampler collection for NO2 isotopes was evaluated under varied temperature and relative humidity (RH) conditions in a dynamic flux chamber. The precision and accuracy of the filter NO2 collection as nitrite (NO2- ) for isotopic analysis were determined using a reference NO2 gas tank and through inter-calibration with a modified EPA Method 7. The bacterial denitrifer method was used to convert 20 μM of collected NO2- or nitrate (NO3- ) into N2 O and was carried out on an Isoprime continuous flow isotope ratio mass spectrometer. δ15 N-NO2 values determined from passive NO2 collection, in conditions of 11-34 °C, 1-78% RH, have an overall accuracy and precision of ±2.1 ‰, and individual run precision of ±0.6 ‰. δ18 O-NO2 values obtained from passive NO2 sampler collection, under the same conditions, have an overall precision of ± 1.3 ‰. Suitable conditions for passive sampler collection of NO2 isotopes are in environments ranging from 11 to 34 °C and 1 to 78% RH. The passive NO2 isotope measurement technique provides an accurate method to determine variations in atmospheric δ15 N-NO2 values and a precise method for determining atmospheric δ18 O-NO2 values. The ability to measure NO2 isotopes over spatial gradients at the same temporal resolution provides a unique perspective on the extent and seasonality of fluctuations in atmospheric NO2 isotopic compositions. Copyright © 2017 John Wiley & Sons, Ltd.

Variation of δ2H, δ18O & δ13C in crude palm oil from different regions in Malaysia: Potential of stable isotope signatures as a key traceability parameter

A total of 33 crude palm oil samples were randomly collected from different regions in Malaysia. Stable carbon isotopic composition (δ13C) was determined using Flash 2000 elemental analyzer while hydrogen and oxygen isotopic compositions (δ2H and δ18O) were analyzed by Thermo Finnigan TC/EA, wherein both instruments were coupled to an isotope ratio mass spectrometer. The bulk δ2H, δ18O and δ13C of the samples were analyzed by Hierarchical Cluster Analysis (HCA), Principal Component Analysis (PCA) and Orthogonal Partial Least Square-Discriminant Analysis (OPLS-DA). Unsupervised HCA and PCA methods have demonstrated that crude palm oil samples were grouped into clusters according to respective state. A predictive model was constructed by supervised OPLS-DA with good predictive power of 52.60%. Robustness of the predictive model was validated with overall accuracy of 71.43%. Blind test samples were correctly assigned to their respective cluster except for samples from southern region. δ18O was proposed as the promising discriminatory marker for discerning crude palm oil samples obtained from different regions. Stable isotopes profile was proven to be useful for origin traceability of crude palm oil samples at a narrower geographical area, i.e. based on regions in Malaysia. Predictive power and accuracy of the predictive model was expected to improve with the increase in sample size. Conclusively, the results in this study has fulfilled the main objective of this work where the simple approach of combining stable isotope analysis with chemometrics can be used to discriminate crude palm oil samples obtained from different regions in Malaysia. Overall, this study shows the feasibility of this approach to be used as a traceability assessment of crude palm oils.

Carbonate clumped isotope analyses with the long-integration dual-inlet (LIDI) workflow: scratching at the lower sample weight boundaries.

Clumped isotope analyses (Δ47 ) of carbonates by dual inlet (DI) mass spectrometry require long integration times to reach the necessary high precision due to the low abundance of the rare isotopologue 13 C18 O16 O. Traditional DI protocols reach this only with large amounts of sample and/or a large number of replicates as a large portion of the analyte gas is wasted. We tested an improved analytical workflow that significantly reduces the sample sizes and total analysis time per sample while preserving precision and accuracy. We implemented the LIDI (long-integration dual-inlet) protocol to measure carbonates in micro-volume mode using a Kiel IV carbonate device coupled to a Thermo Scientific 253 Plus isotope ratio mass spectrometer without the new 1013 ohm amplifier technology. The LIDI protocol includes a single measurement of the sample gas (600s integration) followed by a single measurement of the working gas (WG) with the same integration time. The Δ47 measurements of four calcite standards over a period of 5weeks demonstrate excellent long-term stability with a standard deviation of ±0.021 to ±0.025 ‰ for the final values of the individual aliquots. The Δ47 analyses of a coral, four foraminifera and a calcite precipitated in the laboratory demonstrate that 14 replicates of 90 to 120μg are sufficient to achieve an external precision of ±0.007 ‰ (1SE) or of ±0.013 ‰ at the 95% confidence level. This study demonstrates that by using a Kiel IV-253 Plus system with LIDI it is possible to achieve the same analytical precision as conventional DI measurements with at least a factor of 40 less sample material. With the new 1013 ohm resistor technology there is the potential to reduce the required sample material even more. This opens new avenues of research in paleoceanography, paleoclimatology, low-temperature diagenesis and other currently sample size limited applications. Copyright © 2017 John Wiley & Sons, Ltd.

δ15N values of atmospheric N species simultaneously collected using sector-based samplers distant from sources – Isotopic inheritance and fractionation

The nitrogen isotope ratios (δ15N) of atmospheric N species are commonly suggested as indicators of N emission sources. Therefore, numerous research studies have developed analytical methodologies and characterized primary (gases) and secondary emission products (mostly precipitation and aerosols) from various emitters. These previous studies have generally collected either reduced or oxidized N forms, and sampled them separately prior to determining their δ15N values. Distinctive isotopic signals have been reported for emissions from various sources, and seasonality of the δ15N values has been frequently attributed to shifts in relative contributions from sources with different isotopic signals. However, theoretical concepts suggest that temperature effects on isotopic fractionation may also affect the δ15N values of atmospheric reaction products.Here we use a sector-based multi-stage filter system to simultaneously collect seven reduced and oxidized N species downwind from five different source types in Alberta, Canada. We report δ15N values obtained with a state-of-the-art gold-furnace pre-concentrator online with an isotope ratio mass spectrometer (IRMS) to provide representative results even for oxidized-N forms. We find that equilibrium isotope effects and their temperature dependence play significant roles in determining the δ15N values of the secondary emission products. In the end, seasonal δ15N changes here are mainly caused by temperature effects on fractionation, and the δ15N values of only two N species from one source type can be retained as potential fingerprints of emissions.

Elucidating the Origin of Milk Products on the Chinese Market Using Multi Element Stable Isotope Technique

Preference for foreign milk products is the cause of the economically motivated adulteration of milk products on the Chinese market. The present study was done to ascertain the feasibility of utilizing δ2 H, δ18O and δ15N stable isotope techniques in elucidating the geographical origin of milk products on the Chinese market. 42 milk samples from the United States of America, Canada, Southern China, Northern China, Australia and New Zealand were analyzed. An isotope ratio mass spectrometer with a combination of a high-temperature conversion elemental analyzer, Thermo-Fisher was used. Statistical analysis was performed using one-way ANOVA. The study revealed that both δ2 H and δ18O had a wide range of mean values: 13.86 to 22.25‰ and -82.86 to -28.5‰, respectively. There was a significant difference in the δ2 H (n=7; F=20880, P=7.876E-43) and δ18O (n=7; F=1399.0; P=9.215E-29) composition of the milk samples from the different regions. It was observed that δ2 H and δ18O composition is helpful in elucidating milk products from different regions on the Chinese market (P<0.05). The range of the mean δ15N values of the milk samples was very close, 3.06 to 5.61‰, indicating a possible limitation in employing δ15N isotopic technique. The nitrogen stable isotope could not provide a clear distinction for the milk products because δ15N of an animal reflects that of the diet. Hence in cases of similar diet, it may not be possible to provide a distinction between the animals using this technique.

Effect of Gastric By‐pass on Dietary Protein Bioavailability and Protein Anabolism in Rats

IntroductionBariatric surgery is an efficient treatment of massive obesity but it can trigger nutritional deficiencies, especially regarding vitamins and proteins. Protein wasting may be observed although there are large prevalence variations in the literature. Additionally to a low protein intake, protein malabsorption logically appears as a risk factor of protein wasting. However, there is little data on protein digestion after bariatric surgery. Our study aimed to assess the effect of gastric‐bypass (RYGB) on dietary protein bioavailability and protein status in rats.MethodsRats were fed for 3 months an obesogenic diet. Eighteen rats underwent RYGB surgery (survival: n=9) and 10 Sham (survival: n=10) served as control that were pair‐fed. For 15 d post‐surgery, dietary intake, weight and body composition were measured. After 15 d, rats were given a test meal containing 15N labeled proteins. They were sacrificed 6 h after the meal and dietary proteins were quantified in gastrointestinal segments (stomach, duodenum, jejunum, ileum, caecum and colon) by elemental analyzer coupled to isotope ratio mass spectrometer. Small intestine morphology was studied by histology. The protein Fractional Synthesis Rate (FSR) was measured in the liver, kidney, muscle and skin using a 13C valine flooding dose before sacrifice. Results (means ± SEM) were analyzed using a t test (P<0.05).ResultsCompared to baseline, RYGB decreased dietary intake by 49%. Despite pair‐feeding, weight loss was higher in RYGB than in Sham (14±2 % vs 7±0.8 %, P= 0.002), as well as fat mass loss (33±5 % vs 20±1 %, P=0.03). Lean mass loss was 7±1.5 %. in both groups. Six hours after the meal test, there was more dietary nitrogen in the caecum of Sham than RYGB but no difference was detected in other intestinal segments. Real protein digestibility was lower in Sham than RYGB (93.1±0.6 % vs 95.2±0.7%, P=0.03). Histology revealed a hypertrophy of jejunum mucosa in RYGB. The FSR of kidney protein was strongly decreased (P<0.001) in RYGB (72.2±3.2 %/j) compared to sham (98.4±3.3 %/j). Protein anabolism was similar between groups in other tissues.ConclusionWe showed that dietary protein bioavailability was paradoxically improved in RYGB, an effect that can be attributed to the jejunum mucosa hypertrophy. We also revealed that RYGB markedly lowered protein anabolism in the kidney. It will be interesting to identify which protein are involved in this effect.

Changes in stable isotope ratios in PDO cheese related to the area of production and green forage availability. The case study of Pecorino Siciliano.

No study has investigated the variations in stable isotope ratios (SIRs) of bioelements within a Protected Designations of Origin (PDO) cheese and few studies have focused on the dietary background of animals. For traceability purposes, it is important to know how and whether these issues affect SIRs in a PDO cheese. Thirty-six Pecorino Siciliano cheese samples were collected in three east-Sicilian areas in seasons in which green herbage was present or absent in the diet of the animals. The determination of C, N and S SIRs was performed using an isotope ratio mass spectrometer coupled with an elemental analyser. The H and O SIRs were measured using an isotope ratio mass spectrometer equipped with a thermal conversion elemental analyser pyrolysis unit. The C, N, H, O and S SIRs measured in defatted cheeses were subjected to a multivariate stepwise discriminant analysis to verify if cheeses could be distinguished based on their geographical origin and on the animals' feeding regimen. Sulfur and nitrogen SIRs allowed the best discrimination among the three areas (97.2% correct classification of the cheeses). The discrimination of the feeding system, to check the presence or not of fresh forage in the diet of the animals, correctly classified 86.1% of the cheeses. The C and O SIRs were the most effective parameters. This study demonstrates that the variability in C, H, O, N and S SIRs can allow discrimination between cheeses produced in a narrow geographical region within a PDO area. This may lead to the search for new tools in authentication studies such as the creation of specific isoscapes. Moreover, this study confirms that SIR determination can also discriminate cheeses obtained from animals fed in stalls from those produced when animals have access to green forage, with benefit in terms of environmental impact, animal welfare and product quality. Copyright © 2017 John Wiley & Sons, Ltd.

Elucidating the Origin of Milk Products on the Chinese Market Using Hydrogen and Oxygen Stable Isotope Technique

Preference for foreign milk products is the cause of the economically motivated adulteration of milk products on the Chinese market. 42 milk samples from the United States of America, Canada, Southern China, Northern China, Australia and New Zealand were analyzed using δ2H and δ18O stable isotope technique to differentiate the origin of milk products. An isotope ratio mass spectrometer with a combination of a high-temperature conversion elemental analyzer, Thermo-Fisher was used. Statistical analysis was performed using one-way ANOVA. The study revealed δ2H and δ18O had a wide range of mean values: 13.86 to 22.25‰ and -82.86 to -28.5‰, respectively. There was a significant difference in the δ2H (n=7; F=20880, P=7.876E-43) and δ18O (n=7; F=1399.0; P=9.215E-29) composition of the milk samples from the different regions. It was observed that δ2H and δ18O composition is helpful in elucidating milk products from different regions on the Chinese market (P<0.05).

Measurements and modeling of 16O12C17O spectroscopic parameters at 2 µm

The lack of spectroscopic measurements for rare CO2 isotopologues was the main motivation of this work. In our present study we report line intensity measurements for 16O12C17O made with a high resolution Fourier transform spectrometer (Bruker IFS-125HR) and a 21 m path cryogenic Herriott cell at Jet Propulsion Laboratory. For this, a 17O-enriched CO2 gas sample was used, which comes as a mixture of primary and several minor CO2 isotopologues. The mole fraction of the 16O12C17O isotopologue in the mixture was determined to be 0.3991 by mass spectrometry from a Stable Isotope Ratio Mass Spectrometer (SIRMS) under stochastic distribution assumption at thermal equilibrium. Since the collisional narrowing effect was observed, the Rautian molecular line shape profile was systematically adopted instead of the Voigt profile. Absolute line positions were also investigated by performing a wavenumber calibration based on CO, HCl and a few well-known 16O12C16O transitions. Finally, around 1000 transitions were studied between 4604 and 5126cm−1 involving 15 bands of the 16O12C17O isotopologue. All the measured line intensities were renormalized to be the values for 100% pure isotopologue sample. Transition dipole moments and Herman-Wallis factors were derived enabling a global comparison with theoretical calculations and predictions for the 15 bands of the 16O12C17O isotopologue. For the measured line positions, the absolute accuracy is around 2×10−4cm−1. The accuracies of retrieved line intensities are 2 – 5% for five cold and two hot bands, and 6–30% for eight other weaker hot bands. Results from this work were in a good agreement with HITRAN 2012 for positions, but showed rather significant discrepancies for line intensities. An extensive line list was generated from new experimental measurements in order to improve and validate spectroscopic knowledge of 12C16O17O isotopologue in support of atmospheric remote sensing for the Earth (e.g., OCO-2 mission), Mars and Venus.

Isotopic half-life and enrichment factor in two species of European freshwater fish larvae: an experimental approach.

Stable isotope ratios of carbon and nitrogen are valuable tools for field ecologists to use to analyse animal diets. However, the application of these tools requires knowledge of the tissue enrichment factor (TEF) and half-life (HL). We experimentally compared TEF and HL in two freshwater fish larvae. We hypothesised that chub had a better growth/tissue replacement ratio than roach, due to the use of a food closer to their natural diet. We determined the isotopic HL, the TEF and the contribution of growth or metabolic tissue replacement to dynamic isotopic incorporation. After yolk sac resorption, larvae were fed for 5weeks with prey similar to their natural diet (Artemia nauplii) up to the isotopic equilibrium followed by Chironomid larvae. Stable isotope measurements were carried out using a continuous flow isotope ratio mass spectrometer coupled to an elemental analyser. Changes in isotopic composition strongly followed the predictions of exponential growth and time-dependent models. The isotopic HL varied between 8.2 and 12.6days and the TEF of nitrogen and carbon ranged from 1.7 to 3.1 ‰ and from -0.9 to 1.2 ‰, respectively. The incorporation of dietary 13 C was due more to the production of new tissue (between 56 and 79%) than to the metabolic process. Chub allocated more energy to growth than roach and the Chironomidae diet contributed more to the consumers' growth than the Artemia diet. Metabolic rates seemed lower for chub than for roach, especially when they were fed with Chironomidae. A Chironomidae-based diet would be more profitable to chub, and the high associated growth rate could increase the development of the fish larvae. The HL and TEF were in the range of those reported in the literature. These results will be helpful for field-based studies, because they can help to increase the accuracy of models. Copyright © 2017 John Wiley & Sons, Ltd.

Heart-cutting two-dimensional gas chromatography–isotope ratio mass spectrometry analysis of monoaromatic hydrocarbons in complex groundwater and gas-phase samples

Compound-specific isotope analysis (CSIA) is increasingly used to evaluate the origin and fate of petroleum hydrocarbons in the environment. However, as samples often contain a complex mixture of compounds and the method requires a full chromatographic separation, it can be challenging to obtain accurate and precise isotope values. In this study, in order to develop a method to analyze carbon isotopes in benzene, toluene, ethylbenzene, and xylenes (BTEX) in complex environmental samples, a two-dimensional heart-cutting gas chromatograph (GC) was hyphenated to an isotope ratio mass spectrometer (IRMS). The focus was placed on benzene and toluene, which are the main compounds of concern in contaminated sites. A full separation for BTEX was successfully achieved using a 60m polar column in the first dimension and a 30m non-polar column in the second dimension. Accuracy and precision of carbon isotope measurements of standards were not impacted by the new setup compared to classic one-dimensional (1D) GC-C–IRMS. For benzene and toluene, precision remained very good (≤0.2‰) for concentrations comprised between 5 and 20μg/L. A high matrix load did not influence the precision and accuracy of isotope measurements. The method was tested on several samples from two different field sites. For all samples tested, full chromatographic baseline resolution was achieved for benzene and toluene. Spatial variability of isotopes values linked to biodegradation was evidenced for one field site. This new 2D-GC-C–IRMS method will broaden the spectrum of samples suitable for isotope analysis and will be therefore able to give new insights into attenuation processes of BTEX in contaminated sites or source fingerprinting.

Detection of corn oil in adulterated olive and soybean oil by carbon stable isotope analysis

The production of olive oil and soybean oil is expensive and time-consuming, and the products have high commercial value. These make the products highly susceptible to economically motivated adulteration, especially on the Chinese market. The study was performed to elucidate the possible detection of varying adulteration levels of corn oil in olive and soybean oil using the carbon isotope technique. An elemental analyzer, which was connected to an isotope ratio mass spectrometer and operated in the continuous flow mode was utilized. Statistical analysis was performed using descriptive statistics and one-way ANOVA. The results showed that the samples of olive and soybean oil had lower δ13C values relative to corn oil samples irrespective of the origin of production. The standard error (SE) of the mean on δ13C value of olive oil, soybean and corn oil was −29.26 ± 0.14; −28.90 ± 0.35 and −15.84 ± 0.08‰, respectively. The difference in δ13C values of both olive oil and soybean oil adulterated with corn oil samples at different adulteration content (25, 50, 75, and 95%) were statistically significant (p 0.97 for both products. Therefore, the carbon stable isotope technique is a good tool for detecting both complete and partial substitution of pure olive oil and soybean oil with corn oil.

連続フロー型質量分析計による固体試料の炭素・硫黄同位体比分析 : 高精度分析のための改善点

連続フロー型質量分析計による固体試料の炭素・硫黄同位体比分析 : 高精度分析のための改善点