Continuous-flow Isotope Ratio Mass Spectrometer Research Articles

Reproducible measurements of the δ2H composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system

Non-exchangeable hydrogen-isotope (δ2Hn) measurements of complex organic samples are used in forensics to determine sample authenticity, traceability, and provenance. However, δ2Hn assays of organics are usually complicated by uncontrolled “exchangeable hydrogen” and residual moisture contamination; hence, δ2Hn assays are persistently incomparable amongst laboratories. We introduce a revised technical solution (UniPrep2) to control hydrogen-isotope exchange and for robust online sample drying and vapour equilibration. The UniPrep2 device is coupled to a high-temperature thermochemical elemental analyser and continuous-flow isotope-ratio mass spectrometer. This technical solution empowers isotope analysts to:•Conduct reproducible controlled vapour equilibrations of complex organic samples and standards to determine the δ2Hn values by controlling hydrogen-isotope exchange.•Conduct online vacuum-oven evacuation with extensive helium drying without exposure to air to reabsorb or exchange hydrogen with ambient water vapour.The protocol describes the operation of the UniPrep2 device and the step-by-step procedures needed to obtain accurate and precise δ2Hn values for a wide range of organic sample types. Two analytical approaches are described in detail; the Dual-Vapour Equilibration (DVE) approach, intended for determining δ2Hn for a complex organic environmental sample where matrix equivalent H isotope reference materials are not available, and the Comparative Equilibration (CE) approach, which is intended for routine high-throughput analyses of complex organic samples where at least two matrix-equivalent organic isotope reference materials with consensus δ2Hn values are being used. These standard operating procedures are envisioned to be a sound basis for advancing hydrogen-isotope analysis for different organic environmental matrices and studies.

Isotopic analysis of otolith carbonates using laser heating: A fast method for obtaining high-resolution climate signal.

The stable isotopic compositions of biogenic carbonates like fish otoliths (ear bones) are widely used for palaeoclimatic reconstruction. The conventional method using acid-digestion of micro-milled samples is a multi-step time-consuming process. Here we report a fast method based on laser heating of otolith carbonates to obtain accurate and high-resolution stable isotopic compositions. Otoliths of catfish from the Gulf of Kutch were analysed to check the precision, accuracy and time-resolution of the isotope ratios. The CO2 , generated by heating otoliths with a 50 W CO2 laser, was analysed for its oxygen and carbon isotope ratio [δ18 O and δ13 C, with precision: 0.12 and 0.17‰ (1σ), accuracy: 0.13 and 0.25‰, respectively] using a continuous-flow isotope ratio mass spectrometer. The effect of laser power (0.7-2W) was assessed for reproducible data. Samples were roasted and analysed to account for the effect of the inherent organic matter on the isotopic values. Roasting did not alter the δ18 O of the otoliths but increased the δ13 C slightly. High-resolution (125 μm) analysis of the right and left otolith of a fish yielded similar δ18 O and δ13 C values, suggesting the suitability of either of them for deriving the climate signal. An increase in δ18 O values from ~ -2‰ to ~ -1‰, observed across the ontogeny, is consistent with the known migratory behaviour of the catfish between freshwater and the sea. The otolith δ18 O value of an adult fish records the sea surface temperature (with ~3°C uncertainty) on a monthly scale. The otolith δ13 C values, with the knowledge of dietary δ13 C, provide the mean annual δ13 C value of dissolved inorganic carbon. The study provides a rapid method for retrieving high-resolution seasonal climate data from otoliths found aplenty in geological/archaeological records.

Cell size influences inorganic carbon acquisition in artificially selected phytoplankton.

Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume-specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2 -concentrating mechanisms (CCMs). Previous studies have focused on among-species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3-fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext ), isotopic signatures (δ13 C) and growth among size-selected lineages. Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13 C. Larger cells also achieved faster growth and higher maximum biovolume densities. We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species.

Nitrogen isotopic analysis of nitrate in aquatic environment using cadmium-hydroxylamine hydrochloride reduction.

The nitrogen isotopic ratio of nitrate (δ15 N-NO3 - value) is a critical parameter for understanding nitrogen biogeochemical cycling in aquatic systems. Current approaches to the determination of δ15 N-NO3 - values involve time-intensive handling procedures, the use of toxic chemicals and complicated microbial incubation. A chemical reduction method for measuring the δ15 N-NO3 - values of aquatic samples was established. Nitrate was first quantitatively reduced to nitrite in a column filled with copper-coated cadmium granules, and the produced nitrite further reduced to nitrous oxide gas with hydroxylamine hydrochloride. The nitrogen isotope ratio of the produced nitrous oxide was measured using a continuous-flow isotope ratio mass spectrometer coupled with a purge and cryogenic trap system. The optimized experimental conditions were: solution acidity, H+ concentration of 0.46 M, pH = 0.34; dosage of hydroxylamine, molar ratio of NH2 OH to NO2 - of 4; reaction temperature, 45°C; and reaction time, 14-16 h. No salt effect was found for this method. The reproducibility of the δ15 N-NO3 - value for the laboratory standard was better than 0.3‰ for long-term measurements (20 nmol NO3 - requirement). This method provides a reliable approach for the determination of δ15 N-NO3 - values at natural abundance. It provides (1) high measurement accuracy, (2) ease of operation, (3) environmental-friendly procedure (less toxic regents used), and (4) suitability for both freshwater and saline water samples.

Improved method for simultaneous determination of the carbon isotopic composition and concentration of atmospheric CO2 using CF-IRMS

Determination of the concentration and isotopic composition of atmospheric CO2 is essential for the identification of sources and sinks of anthropogenic CO2 and the monitoring of various emission reduction techniques, such as geological CO2 storage. A customized and convenient method was proposed to determine the carbon isotopic composition and concentration of CO2 of air samples simultaneously using a continuous flow-isotope ratio mass spectrometer (CF-IRMS) interfaced with a GasBench II (Thermo Fisher Scientific, Bremen, Germany). Convenient sampling and isotopic analysis were achieved using 12-mL Exetainer vials with open tops, screw caps, and rubber septa for both air sampling and isotopic analysis. The proposed method differs from previously reported methods in several aspects, including the convenience of sampling and analysis, and high accuracy and precision despite small sample consumption. Combined with the Keeling plot technique, this method allows accurate determination of the isotope composition of atmospheric CO2. The proposed technique can be applied in various studies involving the isotopic composition and concentration of CO2, such as diagnosing cancer, tracing of anthropogenic CO2 and monitoring of leakage from subsurface CO2 storage.

Mobile continuous-flow isotope-ratio mass spectrometer system for automated measurements of N2 and N2O fluxes in fertilized cropping systems

The use of synthetic N fertilizers has grown exponentially over the last century, with severe environmental consequences. Most of the reactive N will ultimately be removed by denitrification, but estimates of denitrification are highly uncertain due to methodical constraints of existing methods. Here we present a novel, mobile isotope ratio mass spectrometer system (Field-IRMS) for in-situ quantification of N2 and N2O fluxes from fertilized cropping systems. The system was tested in a sugarcane field continuously monitoring N2 and N2O fluxes for 7 days following fertilization using a fully automated measuring cycle. The detection limit of the Field-IRMS proved to be highly sensitive for N2 (54 g ha−1 day−1) and N2O (0.25 g ha−1 day−1) emissions. The main product of denitrification was N2 with total denitrification losses of up to 1.3 kg N ha−1 day−1. These losses demonstrate sugarcane systems in Australia are a hotspot for denitrification where high emissions of N2O and N2 can be expected. The new Field-IRMS allows for the direct and highly sensitive detection of N2 and N2O fluxes in real time at a high temporal resolution, which will help to improve our quantitative understanding of denitrification in fertilized cropping systems.

Carbon stock and ?13C data of sediment samples collected from a tropical seagrass meadow in Malaysia

Seagrass ecosystems are considered as major blue carbon sinks, thus contributing directly to the mitigation of climate change by storing carbon in their habitats. However, empirical data for carbon stocks in Malaysia seagrass meadow sediment remain unreported in a standardised format. This paper presents data on organic (OC) and inorganic carbon (IC) stocks, and stable isotope signatures of carbon (?13C) in bulk seagrass sediments collected from Sungai Pulai estuary (Johor, Malaysia). Within this estuary, seagrasses form shoals at Tanjung Adang and Merambong. Organic carbon and ?13C values in bulk sediment were analysed by an elemental analyser and a continuous flow isotope-ratio mass spectrometer, respectively, while sediment IC data was derived from loss-on-ignition calculations of sample mass differences. The data from these samples are presented as downcore profile of OC (values range at 0.14% to 2.49%), IC (0.16% to 5.29%), ?13C values of organic matter (-27.9‰ to -20.4‰), and cumulative carbon stocks (1.03-3.39 kg OC m-2 and 0.76-2.84 kg IC m-2) in the top 30 cm of sediments. This dataset is applicable for regional and local blue carbon studies, which would allow insights into carbon sink and carbon cycling capacity, in addition to gaining insights into the provenances of carbon stored in seagrass meadows.

Can stable isotope markers be used to distinguish wild and mass-reared Anastrepha fraterculus flies?

The availability of accurate techniques to discriminate between marked laboratory-reared flies and unmarked wild flies captured in monitoring traps is essential for programs that integrate the Sterile Insect Technique (SIT) to manage fruit flies. In this study, the feasibility of using a stable isotope marking technique for the South American fruit fly, Anastrepha fraterculus (Wiedemann), was assessed. Wild flies were collected from apple orchards, which are a target of a SIT project in southern Brazil. To verify if adult flies could be labelled by the stable isotopes from larval diets, larvae were reared on two different C4-based diets and fruits in laboratory. To evaluate the influence of the two most common attractants applied to capture A. fraterculus (grape juice and CeraTrapTM) and the most common preservation method in fruit fly collections (ethanol), laboratory-reared flies were immersed in McPhail traps containing the respective treatments for two periods of time. Samples were analyzed in an elemental analyzer coupled to a Continuous Flow Isotope Ratio Mass Spectrometer (CF-IRMS) at CENA/USP. The δ13C signatures of flies reared on artificial diets differed significantly from the δ13C of flies whose larvae were reared on fruits and from wild flies. In contrast, the δ15N values were less conclusive and the technique could not rely solely on them. In all cases considered, the δ13C and δ15N signatures from males did not differ from females. Despite the alterations caused by the attractants tested and ethanol, laboratory-flies could be distinguished from the wild ones based on δ13C signatures. This is the first comprehensive study to demonstrate that it is possible to distinguish wild A. fraterculus from flies reared on larval diets containing C4 sugar. The first experimentally derived trophic discrimination factors were also obtained for this species. Thus, intrinsic isotope labelling can serve as a backup to conventional dye marking.

Nitrogen Mass Fraction and Isotope Determinations in Geological Reference Materials Using Sealed‐Tube Combustion Coupled with Continuous‐Flow Isotope‐Ratio Mass Spectrometry

A method using a high‐temperature sealed‐tube combustion technique coupled with a continuous‐flow isotope‐ratio mass spectrometer (CF‐IRMS) was developed in this study to accurately determine the nitrogen mass fractions and δ15N of silicate rocks with a low nitrogen mass fraction of < 200 μg g−1. Analysis of reference material (HBa3) demonstrated that the nitrogen mass fraction and δ15N results using the developed method were in agreement with data obtained using classical sealed‐tube combustion coupled to a dual‐inlet MS. Given the lack of commercially accessible reference materials usable for interlaboratory comparisons, two igneous reference materials (BCR‐2 and BHVO‐2) obtained from the United States Geological Survey (USGS) were analysed for nitrogen mass fractions and δ15N using the new method. Due to their homogenous characteristics, they can potentially be used as test materials for inter‐laboratory comparisons. The sealed‐tube combustion technique yielded higher N mass fractions than the elemental analyser, suggesting that previous nitrogen mass fractions measured using EA‐IRMS were underestimated. Thus, the nitrogen mass fractions and δ15N of BCR‐2 and BHVO‐2 may not have been correctly determined using EA‐IRMS.

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

北京地区典型落叶阔叶乔木叶片含氮量和δ15N值对大气氮沉降的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 北京地区典型落叶阔叶乔木叶片含氮量和δ15N值对大气氮沉降的响应 DOI: 10.5846/stxb201511202348 作者: 作者单位: 北京林业大学,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 北京市优秀人才培养资助项目（2014000020124G073）；国家自然科学基金资助项目（41503077）；北京林业大学科技创新计划资助项目（BLX20120022） Responses and Indications of Foliar Nitrogen Contents and δ15N values to Atmospheric Nitrogen Deposition in Beijing, China Author: Affiliation: Beijing Forestry University,,,,Beijing Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究植物对大气氮沉降的响应和对这部分氮素的来源指示作用，本研究通过对北京地区198个采样点，典型落叶阔叶乔木杨属（Populus）和柳属（Salix）植物叶片进行采样，测定其叶片样品含氮量和δ15 N值。结果表明：北京地区杨属植物叶片含氮量为16.5-38.6 g/kg，平均（24.0±4.0）g/kg；柳属植物叶片含氮量为17.2-36.2 g/kg，平均（25.9±4.1）g/kg。研究区域范围内杨属、柳属植物叶片的含氮量均呈现出西北低、东南高的对角线型分布，与该区域大气氮沉降的空间变异相吻合。由于研究区域范围内气候因子无明显的变异，植物叶片的含氮量变化反应了大气氮沉降对植物元素化学计量特征的影响和植物对大气氮沉降的响应。北京地区杨属植物叶片δ15N值为-3.95‰-8.10‰，平均（1.15±2.48）‰；柳属植物叶片δ15N值为-3.04‰-9.73‰，平均（2.31±2.60）‰。杨属和柳属植物叶片的δ15N值均呈现出西北高、中部高、东南低的空间分布，与叶片含氮量空间分布趋势相反。中部城区较高的δ15N值反应了交通污染对大气含氮化合物增加的影响；西北部较高的δ15N值反应了该区域受人为活动排放源的影响较少，自然的氮循环是其较高δ15N值的主要原因；东南部较低的δ15N值则有可能是由农业活动和交通共同作用的结果。 Abstract:With 60% of the total area located in the North China Plain, Beijing suffered with very high atmospheric nitrogen (N) deposition in the south part, which was as high as 100 kg hm-2 a-1 including both organic and inorganic nitrogenous species from both wet and dry deposition. To test the responses of foliar N contents of plants, a collection of deciduous broadleaf tree leaves was conducted across Beijing areas. Typical deciduous broadleaf trees, Populus and Salix were selected at 189 sites, which were firstly designed at 5-decimal minute in latitude and longitude grid resolution and then excluded sites without Populus or Salix species. Leaf sampling collection was carried out in the end of August corresponding to annual peak-standing biomass in late summer. Five trees of every species at each site were selected, and five mature leaves of every tree were collected. All the leaf samples were over-dried at 105℃ for 10 minutes and then 65℃ for 48 hours to constant mass. Samples of each species at each site were put together and grounded with a mill to pass 1-mm sieve for N contents analysis. Foliar N was determined following Kjeldehl digestion and δ15N values were determined by continuous flow isotope-ratio mass spectrometer. The foliar N contents were (24.0±4.0) g/kg and (25.9±4.1) g/kg on average for Populus and Salix, respectively. Spatial variations of both the two genus showed similar trends, with higher foliar N contents in the southeast and lower foliar N contents in the northwest, consisting with the spatial variation of atmospheric N deposition in Beijing area. The foliar δ15N values were (1.15±2.48)‰ and (2.31±2.60)‰ on average for Populus and Salix, respectively. However, the spatial variation trends of δ15N values were contrary with the foliar N contents. Higher δ15N values were found in the city center and northwest, while lower δ15N values were found in the southeast. With the different δ15N values of potential sources, the higher δ15N values in the city center indicated the traffic emission sources, the higher δ15N values in the northwest indicated the natural N cycling, while the lower δ15N values indicated both the agricultural and traffic pollution. 参考文献 相似文献 引证文献

Hepatoblastoma Biology Using Isotope Ratio Mass Spectrometry: Utility of a Unique Technique for the Analysis of Oncological Specimens.

Hepatoblastoma is the most common primary liver tumor in children. However, it occurs rarely, with an incidence of 0.5-1.5 cases per million children. There is no clear explanation of the relationship between clinicopathologic features, therapy, and outcome in hepatoblastoma cases, so far. One of the most widely accepted prognostic factors in hepatoblastoma is histology of the tumor. The aim of the study was to determine the potential differences in biology of hepatoblastoma histological subtypes at the atomic level using the unique method of isotope ratio mass spectrometry, which is especially valuable in examination of small groups of biological samples. Twenty-four measurements of nitrogen stable isotope ratio, carbon stable isotope ratio and total carbon to nitrogen mass ratio in fetal and embryonal hepatoblastoma tissue were performed using a Sercon 20-22 Continuous Flow Isotope Ratio Mass Spectrometer (CF-IRMS) coupled with a Sercon SL elemental analyzer for simultaneous carbon-nitrogen-sulfur (NCS) analysis. A difference of about 1.781‰ in stable nitrogen isotope 15N/14N ratio was found between examined hepatoblastoma histological subtypes. The prognosis in liver tumors cases in children may be challenging particularly because of the lack of versatile methods of its evaluation. Isotope ratio mass spectrometry allows one to determine the difference between hepatoblastoma histological subtypes and clearly indicates the cases with the best outcome.

What can a multi tracer approach tell us about the ecology of two sympatric species of Globicephala genus?

What can a multi tracer approach tell us about the ecology of two sympatric species of Globicephala genus?

Accuracy of δ(18)O isotope ratio measurements on the same sample by continuous-flow isotope-ratio mass spectrometry.

The doubly labeled water method is considered the reference method to measure energy expenditure. Conventional mass spectrometry requires a separate aliquot of the same sample to be prepared and analyzed separately. With continuous-flow isotope-ratio mass spectrometry, the same sample could be analyzed sequentially for both (2)H and (18)O content and thus minimize sample requirement, reduce analytical cost, and avoid memory effect. The (2)H contents of 197 urine samples collected from 22 doubly labeled water studies were determined using a Thermo Delta V Advantage continuous-flow isotope-ratio mass spectrometer. The (18)O content of these samples was measured either using a separate aliquot of the same sample using a VG Isogas gas-isotope-ratio mass spectrometer or using the same sample following the (2)H measurements on a Thermo Delta V continuous-flow isotope-ratio instrument. The δ(18)O values using the same aliquot of samples were accurate to 0.18 ± 2.61‰ (mean difference ± standard deviation (SD); 95% CI, -0.18 to 0.55‰; P = 0.33) compared with the values based on the standard conventional method. Bland and Altman pair-wise comparison also yielded a bias of 0.18‰ with a 95% limit of agreement between -4.94 and 5.30‰. The study demonstrated that continuous-flow isotope-ratio mass spectrometry is capable of producing accurate (18)O measurements on the same sample after (2)H measurements. The method greatly reduces the analytical cost and sample size requirement and could easily be adopted by any laboratories equipped with a continuous-flow isotope-ratio mass spectrometer.

Stable isotope composition of human fingernails from Slovakia

Stable isotope composition of human fingernails has proven to be useful for documenting human dietary information and geographical patterns in archeological, forensic, anthropological and biological studies. Therefore, it is of interest to detect all factors influencing the stable isotopic composition in the certain regions in the world.Carbon and nitrogen isotope data of human fingernail keratin from 52 individuals from Slovakia were reported in this study. The online combustion and continuous flow isotope-ratio mass spectrometer Delta V Advantage was used for δ13C and δ15N analysis of fingernail keratin samples from 24 vegetarian and 28 omnivorous individuals.A group of people with frequent meat consumption showed enrichment in 13C and 15N isotopes in fingernails. A similar trend was observed with increasing seafood in an individual's diet. Moreover a significant difference was revealed between smokers and nonsmokers for both δ13C and δ15N values. These data were compared to previously published δ13C and δ15N fingernail values from across the globe.This study brings new information on the stable isotope signature of individuals from Slovakia and characterizes the Central European region for the first time. The stable isotope composition of fingernails is influenced by the frequency of meat and seafood consumption as well as smoking.

Evidence for Proteomic and Metabolic Adaptations Associated with Alterations of Seed Yield and Quality in Sulfur-limited Brassica napus L

In Brassica napus, seed yield and quality are related to sulfate availability, but the seed metabolic changes in response to sulfate limitation remain largely unknown. To address this question, proteomics and biochemical studies were carried out on mature seeds obtained from plants grown under low sulfate applied at the bolting (LS32), early flowering (LS53), or start of pod filling (LS70) stage. The protein quality of all low-sulfate seeds was reduced and associated with a reduction of S-rich seed storage protein accumulation (as Cruciferin Cru4) and an increase of S-poor seed storage protein (as Cruciferin BnC1). This compensation allowed the protein content to be maintained in LS70 and LS53 seeds but was not sufficient to maintain the protein content in LS32 seeds. The lipid content and quality of LS53 and LS32 seeds were also affected, and these effects were primarily associated with a reduction of C18-derivative accumulation. Proteomics changes related to lipid storage, carbohydrate metabolism, and energy (reduction of caleosins, phosphoglycerate kinase, malate synthase, ATP-synthase β-subunit, and thiazole biosynthetic enzyme THI1 and accumulation of β-glucosidase and citrate synthase) provide insights into processes that may contribute to decreased oil content and altered lipid composition (in favor of long-chain fatty acids in LS53 and LS32 seeds). These data indicate that metabolic changes associated with S limitation responses affect seed storage protein composition and lipid quality. Proteins involved in plant stress response, such as dehydroascorbate reductase and Cu/Zn-superoxide dismutase, were also accumulated in LS53 and LS32 seeds, and this might be a consequence of reduced glutathione content under low S availability. LS32 treatment also resulted in (i) reduced germination vigor, as evidenced by lower germination indexes, (ii) reduced seed germination capacity, related to a lower seed viability, and (iii) a strong decrease of glyoxysomal malate synthase, which is essential for the use of fatty acids during seedling establishment.

A Hydrogen Gas-Water Equilibration Method Produces Accurate and Precise Stable Hydrogen Isotope Ratio Measurements in Nutrition Studies ,

Stable hydrogen isotope methodology is used in nutrition studies to measure growth, breast milk intake, and energy requirement. Isotope ratio MS is the best instrumentation to measure the stable hydrogen isotope ratios in physiological fluids. Conventional methods to convert physiological fluids to hydrogen gas (H 2 ) for mass spectrometric analysis are labor intensive, require special reagent, and involve memory effect and potential isotope fractionation. The objective of this study was to determine the accuracy and precision of a platinum catalyzed H 2 -water equilibration method for stable hydrogen isotope ratio measurements. Time to reach isotopic equilibrium, day-to-day and week-to-week reproducibility, accuracy, and precision of stable hydrogen isotope ratio measurements by the H 2 -water equilibration method were assessed using a Thermo DELTA V Advantage continuous-flow isotope ratio mass spectrometer. It took 3 h to reach isotopic equilibrium. The day-to-day and week-to-week measurements on water and urine samples with natural abundance and enriched levels of deuterium were highly reproducible. The method was accurate to within 2.8 o /oo and reproducible to within 4.0 o /oo based on analysis of international references. All the outcome variables, whether in urine samples collected in 10 doubly labeled water studies or plasma samples collected in 26 body water studies, did not differ from those obtained using the reference zinc reduction method. The method produced highly accurate estimation on ad libitum energy intakes, body composition, and water turnover rates. The method greatly reduces the analytical cost and could easily be adopted by laboratories equipped with a continuous-flow isotope ratio mass spectrometer.

Stable carbon isotope ratio analyses on trace methane from ice samples

Measurement of the concentration and stable isotope ratios of methane from air enclosures in ancient ice can aid in understanding the temporal dynamics of methane sources and sinks. These measurements can reconstruct past atmospheric compositions on scales of tens-to-hundreds of years with adequate precision and accuracy. We present an improved micro-extraction gas-chromatography continuous-flow isotope ratio mass spectrometer (CF-IRMS) method to extract and measure the methane 13C/ 12C ratio (δ 13CH 4) of air occluded in glacial ice. The technique described uses a unique post-combustion trapping of the methane signal to produce a high amplitude sample peak increasing the signal to noise ratio of the sample. The technique requires only ca. 165 pmol of CH 4 (ca. 30–150 g of ice depending on methane concentration). The small sample requirement permits very fine temporal sampling resolution and the possibility of routine duplicate measurements from multi-parameter ice core samples. The technique was applied to atmospheric air, artificial ice samples, and samples from the GISP2 ice core. The precision of our technique was evaluated using both atmospheric air and artificial ice samples and is less than ± 0.3‰ (1σ). Our test measurements of shallow, poorer quality GISP2 ice from 225 ± 20 yr BP give a δ 13CH 4 value of − 47.37 ± 0.6‰ (corrected for gravitational fractionation and referenced to VPDB), which is in excellent agreement with other published data.

Analysis of Compound-Specific Chlorine Stable Isotopes of Vinyl Chloride by Continuous Flow–Isotope Ratio Mass Spectrometry (FC–IRMS)

A new method for determining compound-specific chlorine stable isotope was developed for vinyl chloride (VC). The analysis is carried out on a continuous flow–isotope ratio mass spectrometer (CF–IRMS) with special collectors for m/z 64 and 62. The precision of this technique is better than ± 0.16‰ (1σ) for pure phase gas injection and headspace solid phase microextraction (SPME) injection. The new methodology was tested in a confined sandy aquifer contaminated with VC located near the city of Ferrara, northern Italy. The VC isotopic signatures (37Cl and 13C) showed that the VC is not a primary manufactured compound and is a byproduct of production of petrochemicals in the Ferrara region during the 1970s and 1980s. The isotope data also suggested VC is attenuated by biodegradation along the groundwater flow system. The development of compound-specific isotope analysis (CSIA) for VC offers a new tool for fingerprinting sources and processes that affect VC in groundwater.

Oxygen isotope analysis of phosphate: improved precision using TC/EA CF‐IRMS

Oxygen isotope values of biogenic apatite have long demonstrated considerable promise for paleothermometry potential because of the abundance of material in the fossil record and greater resistance of apatite to diagenesis compared to carbonate. Unfortunately, this promise has not been fully realized because of relatively poor precision of isotopic measurements, and exceedingly small size of some substrates for analysis. Building on previous work, we demonstrate that it is possible to improve precision of delta18O(PO4) measurements using a 'reverse-plumbed' thermal conversion elemental analyzer (TC/EA) coupled to a continuous flow isotope ratio mass spectrometer (CF-IRMS) via a helium stream [Correction made here after initial online publication]. This modification to the flow of helium through the TC/EA, and careful location of the packing of glassy carbon fragments relative to the hot spot in the reactor, leads to narrower, more symmetrically distributed CO elution peaks with diminished tailing. In addition, we describe our apatite purification chemistry that uses nitric acid and cation exchange resin. Purification chemistry is optimized for processing small samples, minimizing isotopic fractionation of PO4(-3) and permitting Ca, Sr and Nd to be eluted and purified further for the measurement of delta44Ca and 87Sr/86Sr in modern biogenic apatite and 143Nd/144Nd in fossil apatite. Our methodology yields an external precision of +/- 0.15 per thousand (1sigma) for delta18O(PO4). The uncertainty is related to the preparation of the Ag3PO4 salt, conversion to CO gas in a reversed-plumbed TC/EA, analysis of oxygen isotopes using a CF-IRMS, and uncertainty in constructing calibration lines that convert raw delta18O data to the VSMOW scale. Matrix matching of samples and standards for the purpose of calibration to the VSMOW scale was determined to be unnecessary. Our method requires only slightly modified equipment that is widely available. This fact, and the demonstrated improvement in precision, should help to make apatite paleothermometry far more accessible to paleoclimate researchers.