Concept: Isotope ratio mass spectrometry
The contamination of Japan after the Fukushima accident has been investigated mainly for volatile fission products, but only sparsely for actinides such as plutonium. Only small releases of actinides were estimated in Fukushima. Plutonium is still omnipresent in the environment from previous atmospheric nuclear weapons tests. We investigated soil and plants sampled at different hot spots in Japan, searching for reactor-borne plutonium using its isotopic ratio (240)Pu/(239)Pu. By using accelerator mass spectrometry, we clearly demonstrated the release of Pu from the Fukushima Daiichi power plant: While most samples contained only the radionuclide signature of fallout plutonium, there is at least one vegetation sample whose isotope ratio (0.381 ± 0.046) evidences that the Pu originates from a nuclear reactor ((239+240)Pu activity concentration 0.49 Bq/kg). Plutonium content and isotope ratios differ considerably even for very close sampling locations, e.g. the soil and the plants growing on it. This strong localization indicates a particulate Pu release, which is of high radiological risk if incorporated.
The carbon isotope ratio (δ(13)C) is elevated in corn- and cane sugar-based foods and has recently shown associations with sweetener intake in multiple U.S. populations. However, a high carbon isotope ratio is not specific to corn- and sugar cane-based sweeteners, as other foods, including meats and fish, also have elevated δ(13)C. This study examines whether the inclusion of a second marker, the nitrogen isotope ratio (δ(15)N), can control for confounding dietary effects on δ(13)C and improve the validity of isotopic markers of sweetener intake. The study participants are from the Yup'ik population of southwest Alaska and consume large and variable amounts of fish and marine mammals known to have elevated carbon and nitrogen isotope ratios. Sixty-eight participants completed 4 weekly 24-h recalls followed by a blood draw. RBC δ(13)C and δ(15)N were used to predict sweetener intake, including total sugars, added sugars, and sugar-sweetened beverages. A model including both δ(13)C and δ(15)N explained more than 3 times as much of the variation in sweetener intake than did a model using only δ(13)C. Because carbon and nitrogen isotope ratios are simultaneously determined in a single, high-throughput analysis, this dual isotope marker provides a simple method to improve the validity of stable isotope markers of sweetener intake with no additional cost. We anticipate that this multi-isotope approach will have utility in any population where a stable isotope biomarker is elevated in several food groups and there are appropriate “covariate” isotopes to control for intake of foods not of research interest.
The burgeoning field of ‘clumped isotope’ paleothermometry, which has broad applications in geosciences, depends almost entirely on measurements made on two types of mass spectrometer with the same ion source design. Demonstration that these measurements can be carried out on a retrofitted mass spectrometer with a different type of ion source is important to the growing community of geoscientists considering employing this technique.
The (13)C/(12)C carbon isotope ratio is a chemical parameter with many important applications in several scientific area and the technique of choice currently used for the δ(13)C determination is the isotope ratio mass spectrometry (IRMS). This latter is highly accurate (0.1‰) and sensitive (up to 0.01‰), but at the same time expensive and complex. The objective of this work was to assess the reliability of FTIR and NDIRS techniques for the measurement of carbon stable isotope ratio of food sample, in comparison to IRMS. IRMS, NDIRS and FTIR were used to analyze samples of food, such as oil, durum, cocoa, pasta and sugar, in order to determine the natural abundance isotopic ratio of carbon in a parallel way. The results were comparable, showing a close relationship among the three techniques. The main advantage in using FTIR and NDIRS is related to their cheapness and easy-to-operate in comparison to IRMS.
A need exists for a reliable method for determining the geographical and botanical origin of hops. For this study three sets of samples were collected: the first set comprised five German samples, the second set comprised samples of hops from ten of the world’s major hop growing regions while the third comprised the four main Slovenian. The samples were analyzed using Isotope Ratio Mass Spectrometry (IRMS) to obtain δ13C, δ15N and δ34S values. The δ15N (2.2 ‰ to 8.4 ‰) and δ34S (0.7 ‰ to 12.3 ‰) values were the most discriminating parameters for classifying hop according to geographical origin. ANOVA showed distinct groupings for eight out of the ten hop-growing regions. Although it was not possible to distinguish the geographical origin of hops based on δ13C (-28.9 ‰ to -24.7 ‰), in the case of botanical origin, δ13C values proved to be the most discriminative albeit with limited success.
Dissolved inorganic carbon (DIC) is one of the most important parameters to be measured in seawaters for climate change studies. Its quantitative assessment requires analytical methodologies with overall uncertainties around 0.05% RSD for clear evaluation of temporal trends. Herein, two alternative Isotope Dilution Mass Spectrometry (IDMS) methodologies (on-line and species-specific) using an Isotope Ratio Mass Spectrometer (IRMS) and two calculation procedures for each methodology have been compared. As a result, a new method for the determination of DIC in seawaters, based on species-specific IDMS with Isotope Pattern Deconvolution calculation, was developed and validated. A 13C-enriched bicarbonate tracer was added to the sample and, after equilibration and acidification, the isotope abundances at CO2 masses 44, 45 and 46 were measured on an IRMS instrument. Notably, early spiking allows correcting for evaporations and/or adsorptions during sample preparation and storage and could be carried out immediately after sampling. Full uncertainty budgets were calculated taking into account all the factors involved in the determination (initial weighs, concentration and isotope abundances of standards and final IRMS measurements). Average DIC value obtained for CRM seawater agreed very well with the certified value. Propagated precision obtained ranged from 0.035 to 0.050% RSD for individual sample triplicates. Reproducibility, assessed by three independent experiments carried out in different working days, was excellent as well (-0.01% and 0.057%, error and full combined uncertainty, respectively). Additionally, the approach proposed improves on established methods by simplicity, higher throughput (15 min per sample) and lower volume requirements (10 mL).
Sports doping requires high precision carbon isotope ratio (CIR) analysis of endogenous steroids using gas chromatography-combustion isotope ratio mass spectrometry (GCC-IRMS), however methods are relatively slow and cumbersome. A cryofocusing fast GCC-IRMS (Cryofocus Fast GCC-IRMS) was developed and optimized with minimal peak broadening using a programmable temperature vaporization (PTV) inlet and a low dead volume narrow-bore continuous capillary combustion interface to an IRMS. PTV injection, followed with cryofocusing before steroid analytes were volatilized by a hot jet, was used to initiate chromatography. Compared to ramping temperature using a conventional GC oven, cryofocusing with hot jet volatilization reduced analysis time by a factor of 3 to 4 and reduced peak widths to ∼800 ms. Well separated peak isotope ratios were measured with SD(δ13C) < 0.5‰ over a range of 10-50 ng of each steroid on column and were accurate from 2 ng to 100 ng. Characterization of the current experimental system with well characterized pure steroid isotopic standards demonstrates how the technique can be applied to steroid mixtures derived from real urine samples. Cryofocus Fast GCC-IRMS advances toward the goal of routine CIR testing of steroids in all urine samples for doping control.
Optimized slice-selective1H NMR experiments combined with highly accurate quantitative13C NMR using an internal reference method
- Journal of magnetic resonance (San Diego, Calif. : 1997)
- Published 3 months ago
Isotope ratio monitoring by13C NMR spectrometry (irm-13C NMR) provides the complete13C intramolecular position-specific composition at natural abundance. It represents a powerful tool to track the (bio)chemical pathway which has led to the synthesis of targeted molecules, since it allows Position-specific Isotope Analysis (PSIA). Due to the very small composition range (which represents the range of variation of the isotopic composition of a given nuclei) of13C natural abundance values (50‰), irm-13C NMR requires a 1‰ accuracy and thus highly quantitative analysis by13C NMR. Until now, the conventional strategy to determine the position-specific abundance xirelies on the combination of irm-MS (isotopic ratio monitoring Mass Spectrometry) and13C quantitative NMR. However this approach presents a serious drawback since it relies on two different techniques and requires to measure separately the signal of all the carbons of the analyzed compound, which is not always possible. To circumvent this constraint, we recently proposed a new methodology to perform13C isotopic analysis using an internal reference method and relying on NMR only. The method combines a highly quantitative1H NMR pulse sequence (named DWET) with a13C isotopic NMR measurement. However, the recently published DWET sequence is unsuited for samples with short T1, which forms a serious limitation for irm-13C NMR experiments where a relaxing agent is added. In this context, we suggest two variants of the DWET called Multi-WET and Profiled-WET, developed and optimized to reach the same accuracy of 1‰ with a better immunity towards T1variations. Their performance is evaluated on the determination of the13C isotopic profile of vanillin. Both pulse sequences show a 1‰ accuracy with an increased robustness to pulse miscalibrations compared to the initial DWET method. This constitutes a major advance in the context of irm-13C NMR since it is now possible to perform isotopic analysis with high relaxing agent concentrations, leading to a strong reduction of the overall experiment time.
The concentration-gradient-method (CGM) was previously introduced as a precise and accurate method for isotope ratio determination by quadrupole-based inductively coupled plasma mass spectrometry (ICP-QMS). The investigation of its potential and advantages in the analysis of analytes with a poor signal-noise ratio (S/N) is important to establish routine isotope ratio analysis industrial applications on these widely used instruments.
Stable isotope ratios (13C/12C and 15N/14N) of South African lambs from different regions were measured by isotope ratio mass spectrometry (IRMS). Homogenised and defatted meat of the Longissimus lumborum muscle was assessed. The Rûens and Hantam Karoo regions had the lowest (P≤0.05) δ13C values related to the presence of C3 plants (lucerne and Karoo bushes, respectively). The Northern Karoo, Namibia and Bushmanland had the highest δ13C values likely due to a high proportion of dietary C4 grass species. The δ15N values were highest for Central Karoo, Semi-extensive, Namibia and Hantam Karoo, while Rûens and Feedlot had the lowest nitrogen isotope values (P≤0.05). Classification of origin (Karoo vs. Non-Karoo) using discriminant analysis allowed 95% and 90% correct classification of the samples for the estimation model and validation models, respectively. The results confirm that IRMS provides sufficient discriminative power to classify lamb meat of varying origin.