A comprehensive view on the fate of N isotope-labeled nitrite in model systems for cured and heated sausages.

Cured and heated sausage model systems with N isotope-labeled nitrite were analyzed with headspace GC-MS, GC-IRMS and EA-IRMS. Nitrous oxide (NO) was quantified for the first time under food-relevant conditions in the gas phase. After heating at 100 °C for 90 min, simulating the conditions of full preserves, almost 20 % of the ingoing nitrite was released as NO, with the proportion increasing to up to 30 % with the addition of ascorbic acid (AS).

Stable Isotope Reference Materials and Scale Definitions-Outcomes of the 2024 IAEA Experts Meeting.

The participants of the 12 International Atomic Energy Agency (IAEA) meeting on stable isotope reference materials reached a consensus, acknowledging the existence and use of two carbon isotope delta scales: the VPDB (Vienna Peedee belemnite) scale and the VPDB-LSVEC (LSVEC - lithium carbonate prepared by H. J. Svec).

Sources and fate of dissolved sulphate, carbonate, and nitrate in groundwater of the temperate climate zone: a high-resolution multi-isotope (H, C, O, S) study in north-eastern Germany*.

Different natural and anthropogenic drivers impact the groundwater in the catchment area of the southern Baltic Sea, north-eastern Germany. To understand the sources and fate of dissolved sulphate, carbonate, and nitrate on a regional scale, in the present study, the hydrogeochemical and multi-stable isotope (H, C, O, S) composition of groundwater samples from up to more than 300 sites (depths from near-surface down to 291 m) was studied. To investigate the element sources and the water-rock-microbe interaction processes that took place along the groundwater flow path, a mass balance approach is combined with physico-chemical modelling.

Vitamin B as a source of variability in isotope effects for chloroform biotransformation by Dehalobacter.

Carbon and chlorine isotope effects for biotransformation of chloroform by different microbes show significant variability. Reductive dehalogenases (RDase) enzymes contain different cobamides, affecting substrate preferences, growth yields, and dechlorination rates and extent. We investigate the role of cobamide type on carbon and chlorine isotopic signals observed during reductive dechlorination of chloroform by the RDase CfrA.

Continuous-Flow Stable Sulfur Isotope Analysis of Organic and Inorganic Compounds by EA-MC-ICPMS.

Elemental analysis (EA) coupled to isotope ratio mass spectrometry (IRMS) is a well-established method to derive stable isotope ratios of sulfur (S/S). Conversion of sulfur to SO by EA and measurement of SO isotopologues by IRMS represents the simplest and most versatile method to accomplish isotope measurement of sulfur even in bulk samples. Yet, interferences by oxygen isotopes in SO often impair the precision and trueness of measured results.

Novel extraction methods and compound-specific isotope analysis of methoxychlor in environmental water and aquifer slurry samples.

Multi-element compound-specific stable isotope analysis (ME-CSIA) allows monitoring the environmental behavior and transformation of most common and persistent contaminants. Recent advancements in analytical techniques have extended the applicability of ME-CSIA to organic micropollutants, including pesticides. Nevertheless, the application of this methodology remains unexplored concerning harmful insecticides such as methoxychlor, a polar organochlorine pesticide usually detected in soil and groundwater.

Quantifying energy expenditure in Göttingen Minipigs with the C-bicarbonate method under basal and drug-treated conditions.

Effective treatments of obesity focusing on energy expenditure (EE) are needed. To evaluate future EE-modulating drug candidates, appropriate animal models and methods to assess EE are needed. This study aimed to evaluate the stable isotope C-bicarbonate method (C-BM) for estimating EE in Göttingen minipigs under basal and drug-treated conditions.

Determination of Stable Hydrogen Isotopic Composition and Isotope Enrichment Factor at Low Hydrogen Concentration.

Determination of stable hydrogen isotopic compositions (δH) is currently challenged to achieve a high detection limit for reaching the linear range where δH values are independent of concentration. Therefore, it is difficult to assess precise δH values for calculating the hydrogen isotope enrichment factor (ε) and for field application where the concentrations of contaminants are relatively low. In this study, a data treatment approach was developed to obtain accurate δH values below the linear range.

Investigation of active site amino acid influence on carbon and chlorine isotope fractionation during reductive dechlorination.

Reductive dehalogenases (RDases) are corrinoid-dependent enzymes that reductively dehalogenate organohalides in respiratory processes. By comparing isotope effects in biotically catalyzed reactions to reference experiments with abiotic corrinoid catalysts, compound-specific isotope analysis (CSIA) has been shown to yield valuable insights into enzyme mechanisms and kinetics, including RDases. Here, we report isotopic fractionation (ε) during biotransformation of chloroform (CF) for carbon (εC = -1.

Multi-element isotopic evidence for monochlorobenzene and benzene degradation under anaerobic conditions in contaminated sediments.

Industrial chemicals are frequently detected in sediments due to a legacy of chemical spills. Globally, site remedies for groundwater and sediment decontamination include natural attenuation by in situ abiotic and biotic processes. Compound-specific isotope analysis (CSIA) is a diagnostic tool to identify, quantify, and characterize degradation processes in situ, and in some cases can differentiate between abiotic degradation and biodegradation.

Simultaneous Compound-Specific Analysis of δS and δS in Organic Compounds by GC-MC-ICPMS Using Medium- and Low-Mass-Resolution Modes.

Compound-specific isotope analysis of sulfur (δS-CSIA) in organic compounds was established in the last decade employing gas chromatography connected to multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS). However, δS-CSIA has not yet been reported so far. In this study, we present a method for the simultaneous determination of δS and δS in organic compounds by GC-MC-ICPMS applying medium- and also low-mass-resolution modes.

Requirements for Chromium Reactors for Use in the Determination of H Isotopes in Compound-Specific Stable Isotope Analysis of Chlorinated Compounds.

There is a strong need for careful quality control in hydrogen compound-specific stable isotope analysis (CSIA) of halogenated compounds. This arises in part due to the lack of universal design of the chromium (Cr) reactors. In this study, factors that optimize the critical performance parameter, linearity, for the Cr reduction method for hydrogen isotope analysis were identified and evaluated.

Distinct nitrogen cycling and steep chemical gradients in Trichodesmium colonies.

Trichodesmium is an important dinitrogen (N)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that Trichodesmium colonies with their diverse epibionts support various nitrogen (N) transformations beyond N fixation. However, rates of these transformations and concentration gradients of N compounds in Trichodesmium colonies remain largely unresolved.

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.

Compound Specific Stable Chlorine Isotopic Analysis of Volatile Aliphatic Compounds Using Gas Chromatography Hyphenated with Multiple Collector Inductively Coupled Plasma Mass Spectrometry.

Stable chlorine isotope analysis is increasingly used to characterize sources, transformation pathways, and sinks of organic aliphatic compounds, many of them being priority pollutants in groundwater and the atmosphere. A wider use of chlorine isotopes in environmental studies is still inhibited by limitations of the different analytical techniques such as high sample needs, offline preparation, confinement to few compounds and mediocre precision, respectively. Here we present a method for the δCl determination in volatile aliphatic compounds using gas chromatography coupled with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS), which overcomes these limitations.

Compound-specific hydrogen isotope analysis of fluorine-, chlorine-, bromine- and iodine-bearing organics using gas chromatography-chromium-based high-temperature conversion (Cr/HTC) isotope ratio mass spectrometry.

Rationale: The conventional high-temperature conversion (HTC) approach towards hydrogen compound-specific isotope analysis (CSIA) of halogen-bearing (F, Cl, Br, I) organics suffers from incomplete H yields and associated hydrogen isotope fractionation due to generation of HF, HCl, HBr, and HI byproducts. Moreover, the traditional off-line combustion of highly halogenated compounds results in incomplete recovery of water as an intermediary compound for hydrogen isotope ratio mass spectrometry (IRMS), and hence also leads to isotope fractionation. This study presents an optimized chromium-based high-temperature conversion (Cr/HTC) approach for hydrogen CSIA of various fluorinated, chlorinated, brominated and iodinated organic compounds.

Optimization of on-line hydrogen stable isotope ratio measurements of halogen- and sulfur-bearing organic compounds using elemental analyzer-chromium/high-temperature conversion isotope ratio mass spectrometry (EA-Cr/HTC-IRMS).

Rationale: Accurate hydrogen isotopic analysis of halogen- and sulfur-bearing organics has not been possible with traditional high-temperature conversion (HTC) because the formation of hydrogen-bearing reaction products other than molecular hydrogen (H ) is responsible for non-quantitative H yields and possible hydrogen isotopic fractionation. Our previously introduced, new chromium-based EA-Cr/HTC-IRMS (Elemental Analyzer-Chromium/High-Temperature Conversion Isotope Ratio Mass Spectrometry) technique focused primarily on nitrogen-bearing compounds. Several technical and analytical issues concerning halogen- and sulfur-bearing samples, however, remained unresolved and required further refinement of the reactor systems.

Evaluation of the performance of high temperature conversion reactors for compound-specific oxygen stable isotope analysis.

In this study conversion conditions for oxygen gas chromatography high temperature conversion (HTC) isotope ratio mass spectrometry (IRMS) are characterised using qualitative mass spectrometry (IonTrap). It is shown that physical and chemical properties of a given reactor design impact HTC and thus the ability to accurately measure oxygen isotope ratios. Commercially available and custom-built tube-in-tube reactors were used to elucidate (i) by-product formation (carbon dioxide, water, small organic molecules), (ii) 2nd sources of oxygen (leakage, metal oxides, ceramic material), and (iii) required reactor conditions (conditioning, reduction, stability).

Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, L-Valines, Polyethylenes, and Oils.

An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ(2)H(VSMOW-SLAP) values from -210.

Bacterial communities potentially involved in iron-cycling in Baltic Sea and North Sea sediments revealed by pyrosequencing.

To gain insight into the bacterial communities involved in iron-(Fe) cycling under marine conditions, we analysed sediments with Fe-contents (0.5-1.5 wt %) from the suboxic zone at a marine site in the Skagerrak (SK) and a brackish site in the Bothnian Bay (BB) using 16S rRNA gene pyrosequencing.

Isotopic disproportionation during hydrogen isotopic analysis of nitrogen-bearing organic compounds.

Rationale: High-precision hydrogen isotope ratio analysis of nitrogen-bearing organic materials using high-temperature conversion (HTC) techniques has proven troublesome in the past. Formation of reaction products other than molecular hydrogen (H(2)) has been suspected as a possible cause of incomplete H(2) yield and hydrogen isotopic fractionation.

Methods: The classical HTC reactor setup and a modified version including elemental chromium, both operated at temperatures in excess of 1400 °C, have been compared using a selection of nitrogen-bearing organic compounds, including caffeine.

Multidimensional isotope analysis of carbon, hydrogen and oxygen as tool for identification of the origin of ibuprofen.

Multidimensional isotope profiling is a useful tool for the characterization of the provenance of active pharmaceutical ingredients (API). To evaluate this approach, samples of the nonsteroidal anti-inflammatory drug (NSAIDs) ibuprofen were collected from 32 manufactures and 13 countries, and carbon, hydrogen and oxygen isotope ratios were analyzed by elemental analyzer, chromium-filled elemental analyzer and high temperature conversion elemental analyzer (EA, Cr-EA and TC/EA) coupled to an isotope ratio mass spectrometry (IRMS). The range of isotope values of ibuprofen (δ(13)C: -33.

Compound-specific hydrogen isotope analysis of heteroatom-bearing compounds via gas chromatography-chromium-based high-temperature conversion (Cr/HTC)-isotope ratio mass spectrometry.

The traditional high-temperature conversion (HTC) approach toward compound-specific stable isotope analysis (CSIA) of hydrogen for heteroatom-bearing (i.e., N, Cl, S) compounds has been afflicted by fractionation bias due to formation of byproducts HCN, HCl, and H2S.