A comparison of carbon and nitrogen stable isotope ratios of fish tissues following lipid extractions with non-polar and traditional chloroform/methanol solvent systems

Stable isotope ratios act as chemical tracers of animal diet, and are used to study food web dynamics. Because carbon stable isotope values are influenced by tissue lipid content, a number of extraction methods have been used to remove lipid bias, but, in some species and tissues, extractions also alter nitrogen isotope values. We have analyzed delta(13)C and delta(15)N in Atlantic bluefin tuna liver and white muscle, and whole Atlantic herring, fish tissues covering a wide range of lipid content (bulk C:N 3.1-12.5). In order to compare delta(13)C and delta(15)N values from traditional chloroform/methanol extractions with non-polar solvent alternatives, we analyzed samples following (1) no treatment, (2) lipid removal using chloroform/methanol (2:1), and (3) Soxhlet extractions using chloroform, diethyl ether or hexane. Chloroform/methanol and chloroform extractions produced the lowest C:N values and highest delta(13)C values. In bluefin tuna, chloroform and hexane extractions significantly altered liver delta(15)N, and all methods significantly altered delta(15)N values in white muscle. Whole Atlantic herring delta(15)N was not altered by any extraction method, while the 2:1 chloroform/methanol extraction most completely removed fish tissue lipid components. Our results indicate that delta(15)N effects are not limited to common chloroform/methanol extractions and suggest that chloroform/methanol is the most effective extraction for delta(13)C correction. Given evidence for delta(15)N alteration among all tested methods, mathematical correction approaches should be further explored as an alternative to lipid correction.     

Dependence of isotope effects on conformation in decarboxylation of 3-carboxybenzisoxazoles

Conformational analysis of 3-carboxybenzisoxazole and its 4-hydroxy-substituted derivative was performed by a semiempirical molecular dynamics approach. The most stable conformers of the reactants and transition states from these simulations were used in calculations of the kinetic isotope effects of carbon, nitrogen, oxygen and deuterium. It was shown that the conformation of either reactant or transition state can significantly affect the magnitude of an isotope effect, especially for atoms involved in hydrogen bonding.     

常见炸药的稳定同位素比值分析方法研究进展

炸药的深度比对与溯源对于爆炸案事件的侦破具有重大意义,以不同地域来源的原料或不同生产工艺生产的炸药,其组成元素的稳定同位素比值具有差异,因而稳定同位素比值可作为炸药深度比对与溯源的重要指标.稳定同位素比值质谱法(IRMS)作为一种高精度的稳定同位素比值测量手段,已逐渐发展成熟,与元素分析仪、气相色谱仪、液相色谱仪等仪器...     

The potential of inorganic mass spectrometry in mineral and trace element nutrition research

Over the past two decades, new applications of inorganic mass spectrometry have been made possible by the use of stable isotopes as tracers in studies of mineral and trace element metabolism in man. Stable isotope techniques and radioisotope methods are the only reliable tools available for determination of the absorption, retention, or utilization of a nutrient by the human body. Recent developments in inorganic mass spectrometry might open new perspectives as progress in this field of research depends mainly on improving existing stable isotope techniques and on developing novel concepts. By improving precision in isotope analysis, isotope doses in experiments on man can be reduced to physiologically more meaningful levels. This will also enable reduction of the (often substantial) costs of isotopically labeling a nutrient in a test meal. Improvements in the mass spectrometric sensitivity will enable the development of new tracer techniques that have the potential to provide the information required by: 1. governmental institutions for designing food fortification programs; 2. the food industry for developing nutrient-fortified food products; and 3. public health authorities for establishing reliable dietary recommendations for intake of inorganic nutrients. In this context the current scope and limitations of thermal ionization mass spectrometry, inductively coupled mass spectrometry, accelerator mass spectrometry, and resonance ionization mass spectrometry are evaluated. Iron isotopic variations in the human body are discussed as a possible source of bias that might be a future biological limit to stable isotope-dose reduction in experiments on iron metabolism in man.     

Isotopic turnover of a submersed macrophyte following transplant: the roles of growth and metabolism in eutrophic conditions

Stable isotopic turnover with isotopic change due to growth and metabolic tissue replacement associated with a change in environmental conditions is a critical aspect of the use of stable isotope analyses as time-integrating tracers of resource-consumer interactions. However, stable isotopic turnover in plants remains poorly understood compared with those of animals, and here we used continuous flow elemental analyzer-isotopic ratio mass spectrometry (EA-IRMS) to analyse the turnover of stable carbon and nitrogen isotopes in a submersed macrophyte (Vallisneria natans) after transplantation to hypereutrophic and mesoeutrophic treatments in a field mesocosm experiment. The direction and magnitude of the isotopic shifts of V. natans were suggested to be determined by the inorganic nutrient availability and its isotopic content in the different treatments. Based on the modelling results of turnover, the contribution of growth to the isotopic turnover was as high as those observed in various aquatic ectotherms. However, the contribution of metabolism was also considerable, especially for nitrogen in the hypereutrophic treatment, which was argued to be a response, co-occurring with growth inhabitation and biochemical disorder of V. natans, to the stress induced by the eutrophication. Our results indicated that isotope turnover in a macrophyte is a feasible technique for estimating its ecophysiological conditions in the natural environment, and that it may facilitate understanding of isotopic data in field studies of food web and habitat restoration under eutrophic conditions.     

Effect of acidification on elemental and isotopic compositions of sediment organic matter and macro‐invertebrate muscle tissues in food web research

Stable isotope techniques in food web studies often focus on organic carbon in food sources which are subsequently assimilated in the tissue of consumer organisms through diet. The presence of non‐dietary carbonates in bulk samples can affect their δ¹³C values, altering how their results are interpreted. Acidification of samples is a common practice to eliminate any inorganic carbon present prior to analysis. We examined the effects of pre‐analysis acidification on two size fractions of sediment organic matter (SOM) from marine and freshwater wetlands and pure muscle tissue of a common freshwater invertebrate (Cherax destructor). The elemental content and isotopic ratios of carbon and nitrogen were compared between paired samples of acidified and control treatments. Our results showed that acidification does not affect the elemental or isotopic values of freshwater SOM. In the marine environment acidification depleted the δ¹³C and δ¹⁵N values of the fine fraction of saltmarsh and δ¹⁵N values of mangrove fine SOM. Whilst acidification did not change the elemental content of invertebrate muscle tissue, the δ¹³C and δ¹⁵N values were affected. We recommend to researchers considering using acidification techniques on material prepared for stable isotope analysis that a formal assessment of the effect of acidification on their particular sample type should be undertaken. Further detailed investigation to understand the impact of acidification on elemental and isotopic values of organic matter and muscular tissues is required. Copyright © 2010 John Wiley & Sons, Ltd.     

The potential of inorganic mass spectrometry in mineral and trace element nutrition research

Over the past two decades, new applications of inorganic mass spectrometry have been made possible by the use of stable isotopes as tracers in studies of mineral and trace element metabolism in man. Stable isotope techniques and radioisotope methods are the only reliable tools available for determination of the absorption, retention, or utilization of a nutrient by the human body. Recent developments in inorganic mass spectrometry might open new perspectives as progress in this field of research depends mainly on improving existing stable isotope techniques and on developing novel concepts. By improving precision in isotope analysis, isotope doses in experiments on man can be reduced to physiologically more meaningful levels. This will also enable reduction of the (often substantial) costs of isotopically labeling a nutrient in a test meal. Improvements in the mass spectrometric sensitivity will enable the development of new tracer techniques that have the potential to provide the information required by: 1. governmental institutions for designing food fortification programs; 2. the food industry for developing nutrient-fortified food products; and 3. public health authorities for establishing reliable dietary recommendations for intake of inorganic nutrients. In this context the current scope and limitations of thermal ionization mass spectrometry, inductively coupled mass spectrometry, accelerator mass spectrometry, and resonance ionization mass spectrometry are evaluated. Iron isotopic variations in the human body are discussed as a possible source of bias that might be a future biological limit to stable isotope-dose reduction in experiments on iron metabolism in man. Received: 9 February 2001 / Revised: 21 March 2001 / Accepted: 23 March 2001     

Calling all archaeologists: guidelines for terminology,methodology, data handling,and reporting when undertaking and reviewing stable isotope applications in archaeology

Stable isotope analysis has been utilized in archaeology since the 1970s, yet standardized protocols for terminology, sampling, pretreatment evaluation, calibration, quality assurance and control, data presentation, and graphical or statistical treatment still remain lacking in archaeological applications. Here, we present recommendations and requirements for each of these in the archaeological context of: bulk stable carbon and nitrogen isotope analysis of organics; bulk stable carbon and oxygen isotope analysis of carbonates; single compound stable carbon and nitrogen isotope analysis on amino acids in collagen and keratin; and single compound stable carbon and hydrogen isotope analysis on fatty acids. The protocols are based on recommendations from the Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) as well as an expanding geochemical and archaeological science experimental literature. We hope that this will provide a useful future reference for authors and reviewers engaging with the growing number of stable isotope applications and datasets in archaeology.     

Trophic Dynamics and Feeding Ecology of Skipjack Tuna (Katsuwonus pelamis) off Eastern and Western Taiwan

The skipjack tuna (Katsuwonus pelamis) is a mesopredator fish species with seasonal abundance in waters off Taiwan. Regional ecological and life-history information has been historically lacking for this species. In recent years, stable isotope analysis (SIA) of carbon and nitrogen has been used to assess predator feeding ecology and broader ecosystem trophic dynamics. This study evaluated comparative skipjack feeding ecology in distinct regions off Taiwan, combining traditional stomach content analysis with SIA of individuals off western (n = 43; 2020) and eastern (n = 347; 2012–2014 and n = 167; 2020) Taiwan. The stomach content analysis showed the most important prey to be ponyfish (Photopectoralis bindus) in western Taiwan and epipelagic squids (Myopsina spp.) and carangids (Decapterus macrosoma;) in eastern Taiwan from 2012 to 2014 and epipelagic carangids (Decapterus spp.) and flying fishes (Cheilopogon spp.) in eastern Taiwan in 2020, suggesting that the skipjack tuna is a generalist predator across regions. In contrast, time-integrated diet estimates from Bayesian mixing models indicated the importance of cephalopods and crustaceans as prey, potentially demonstrating more mesopelagic feeding in less productive waters during skipjack migrations outside the study regions. Skipjack off western Taiwan had a slightly higher estimated trophic position than in the waters off eastern Taiwan, potentially driven by the varying nutrient-driven pelagic food web structures. Skipjack SI values increased with body size off eastern Taiwan but not in western waters, suggesting that opportunistic predation can still result in different predator–prey size dynamics between regions.     

Differential growth of the fungus Absidia cylindrospora on 13C/15N-labelled media

Many studies utilise enrichment of stable isotopes as tracers to follow the interactions occurring within soil food webs and methods have been developed to enrich bacteria, soil fauna and plant litter, Here for the first time we attempt to enrich a soil fungus to 99 atom% with (13)C and (15)N stable isotopes. In this study our objectives were to (a) assess whether the saprotrophic zygomycete fungus Absidia cylindrospora could grow on a medium enriched to 99 atom% with (13)C-glucose and (15)N-ammonium chloride, (b) to determine the level of enrichment obtained, and (c) to examine the change in growth rate of this fungus while it was growing on the dually enriched medium. To achieve this, the fungus was grown on agar enriched with (13)C and (15)N to 99 atom% and its growth rate monitored. The results showed that A. cylindrospora would grow on the highly labelled growth medium, but that its rate of growth was affected compared with the rate on either natural abundance media or media highly enriched with a single isotope ((13)C or (15)N). The implications of these results is that although the fungus is able to utilise these heavier isotopes, the biochemical processes involved in growth are affected, and consideration should be given to these differences when using stable isotope tracers in, for example, soil food web studies.     

Applications of stable,nonradioactive isotope tracers in in vivo human metabolic research

The human body is in a constant state of turnover, that is, being synthesized, broken down and/or converted to different compounds. The dynamic nature of in vivo kinetics of human metabolism at rest and in stressed conditions such as exercise and pathophysiological conditions such as diabetes and cancer can be quantitatively assessed with stable, nonradioactive isotope tracers in conjunction with gas or liquid chromatography mass spectrometry and modeling. Although measurements of metabolite concentrations have been useful as general indicators of one''s health status, critical information on in vivo kinetics of metabolites such as rates of production, appearance or disappearance of metabolites are not provided. Over the past decades, stable, nonradioactive isotope tracers have been used to provide information on dynamics of specific metabolites. Stable isotope tracers can be used in conjunction with molecular and cellular biology tools, thereby providing an in-depth dynamic assessment of metabolic changes, as well as simultaneous investigation of the molecular basis for the observed kinetic responses. In this review, we will introduce basic principles of stable isotope methodology for tracing in vivo kinetics of human or animal metabolism with examples of quantifying certain aspects of in vivo kinetics of carbohydrate, lipid and protein metabolism.     

A perspective on environmental models and QSARs

A general review is presented of the roles of QSARs and mass balance models as tools for assessing the environmental fate and effects of chemicals of commerce. It is argued that all such chemicals must be assessed using a consistent and transparent methodology that uses chemical property data derived from QSARs, or experimental determinations when possible and applies evaluative or region-specific environmental models. These data and models enable an assessment to be made of the key chemical features of persistence, bioaccumulation, potential for long-range transport and toxicity. The other key feature is quantity used or discharged to the environment. A taxonomy of environmental models is presented in which it is suggested that rather than develop a single comprehensive model, the aim should be to establish a set of coordinated and consistent models treating evaluative and real environmental systems at a variety of scales from local to global and including food web models, organism-specific models and human exposure and pharmacokinetic models. The concentrations derived from these models can then be compared with levels judged to be of toxic significance. A brief account is given of perceived QSAR needs in terms of partitioning, reactivity, transport and toxicity data to support these models.     

Automated interpretation of mass spectra of complex mixtures by matching of isotope peak distributions

Mass spectrometry is now firmly established as a powerful technique for the identification and characterization of proteins when used in conjunction with sequence databases. Various approaches involving stable-isotope labeling have been developed for quantitative comparisons between paired samples in proteomic expression analysis by mass spectrometry. However, interpretation of such mass spectra is far from being fully automated, mainly due to the difficulty of analyzing complex patterns resulting from the overlap of multiple peaks arising from the assortment of natural isotopes. In order to facilitate the interpretation of a complex mass spectrum of such a mixture, such as an MS spectrum of a stable-isotope-enriched ion species, we report on the development of a software application, 'Matching' (web accessible), that enables the automatic matching of theoretical isotope envelopes to multiple ion peaks in a raw spectrum. It is particularly useful for resolving the relative abundances of narrow-split paired peaks caused by enrichment with a stable isotope, such as 18O, 13C, 2H, or 15N.     

Nitrogen balance and delta15N: why you're not what you eat during pregnancy

Carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios were longitudinally measured in human hair that reflected the period from pre-conception to delivery in 10 pregnant women. There was no significant change in the delta13C results, but all subjects showed a decrease in delta15N values (-0.3 to -1.1 per thousand) during gestation. The mechanisms causing this decrease in hair delta15N have not been fully elucidated. However, since the delta15N values of dietary nitrogen and urea nitrogen are significantly lower compared to maternal tissues, it is hypothesized that the increased utilization of dietary and urea nitrogen for tissue synthesis during pregnancy resulted in a reduction of the steady state diet to a body trophic level effect by approximately 0.5-1 per thousand. An inverse correlation (R2 = 0.67) between hair delta15N and weight gain was also found, suggesting that positive nitrogen balance results in a reduction of delta15N values independent of diet. These results indicate that delta15N measurements have the ability to monitor not only dietary inputs, but also the nitrogen balance of an organism. A potential application of this technique is the detection of fertility patterns in modern and ancient species that have tissues that linearly record stable isotope ratios through time.     

A perspective on environmental models and QSARs

A general review is presented of the roles of QSARs and mass balance models as tools for assessing the environmental fate and effects of chemicals of commerce. It is argued that all such chemicals must be assessed using a consistent and transparent methodology that uses chemical property data derived from QSARs, or experimental determinations when possible and applies evaluative or region-specific environmental models. These data and models enable an assessment to be made of the key chemical features of persistence, bioaccumulation, potential for long-range transport and toxicity. The other key feature is quantity used or discharged to the environment. A taxonomy of environmental models is presented in which it is suggested that rather than develop a single comprehensive model, the aim should be to establish a set of coordinated and consistent models treating evaluative and real environmental systems at a variety of scales from local to global and including food web models, organism-specific models and human exposure and pharmacokinetic models. The concentrations derived from these models can then be compared with levels judged to be of toxic significance. A brief account is given of perceived QSAR needs in terms of partitioning, reactivity, transport and toxicity data to support these models.     

The use of ICPMS for stable isotope tracer studies in humans: a review

The use of stable isotope tracers in human studies is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation and from the better availability of mass spectrometric techniques to nutritional scientists during the last three decades. Traditionally, thermal ionization mass spectrometry (TIMS) has been the preferred technique for these studies, but the development of new inductively coupled plasma mass spectrometric (ICPMS) techniques with better isotope-ratio measurement and interference-removal capabilities (e.g. single and multi-detector ICPMS and reaction/collision cell ICPMS) has enabled broader use of ICPMS for determination of stable isotope tracers in nutritional research. This review discusses the current and future use of ICPMS in stable isotope tracer studies in humans.     

Determination of 206/207Pb isotope ratios by ICP-MS in particulate matter from the north sea environment

Summary The determination of lead isotope ratios can be used for source and pathway characterization of lead in the environment. The suitability of inductively coupled mass spectrometry (ICP-MS) was evaluated for the measurement of ^206/207Pb isotope ratios in several marine compartments as marine aerosols from different source regions and suspended particulate matter from the North Sea. Two different ICP-MS systems were used to carry out these investigations. First optimization studies have been performed to yield a sufficient precision (RSD <0.5%) in combination with a reasonable measuring time. This study has been carried out using the standard reference material NBS 981 with certified lead isotope ratios. Furthermore, it could be shown for marine environmental samples, that a precision of less than 0.5% RSD is attainable for counting rates of above approximately 50000 cps. As the following measurements of lead isotope ratios in marine aerosols from main source regions surrounding the North Sea demonstrated, this precision is sufficient to determine significant differences due to the origin of atmospheric lead. The analysis of aerosol samples revealed isotope ratios varying from as low as 1.10, which is close to that ratio for leaded gasoline in Europe to near background (modern lead) values of 1.20. The lead isotope ratios for the investigated suspended particulate matter ranges between 1.13 and 1.18. These values can be related to the solid discharge, the urban density and anthropogenic activity of the drainage basin.     

Inter‐laboratory comparison of elemental analysis and gas chromatography/combustion/isotope ratio mass spectrometry. II. δ15N measurements of selected compounds for the development of an isotopic Grob test

An inter‐laboratory exercise was carried out by a consortium of five European laboratories to establish a set of compounds, suitable for calibrating gas chromatography/combustion/isotope ratio mass spectrometry (GC‐C‐IRMS) devices, to be used as isotopic reference materials for hydrogen, carbon, nitrogen and oxygen stable isotope measurements. The set of compounds was chosen with the aim of developing a mixture of reference materials to be used in analytical protocols to check for food and beverage authentication. The exercise was organized in several steps to achieve the certification level: the first step consisted of the a priori selection of chemical compounds on the basis of the scientific literature and successive GC tests to set the analytical conditions for each single compound and the mixture. After elimination of the compounds that turned out to be unsuitable in a multi‐compound mixture, some additional oxygen‐ and nitrogen‐containing substances were added to complete the range of calibration isotopes. The results of δ¹³C determinations for the entire set of reference compounds have previously been published, while the δD and δ¹⁸O determinations were unsuccessful and after statistical analysis of the data the results did not reach the level required for certification. In the present paper we present the results of an inter‐laboratory exercise to identify and test the set of nitrogen‐containing compounds present in the mixture developed for use as reference materials for the validation of GC‐C‐IRMS analyses in individual laboratories. Copyright © 2009 John Wiley & Sons, Ltd.     

Applications of Thermal Analysis on the Marine Phytoplankton,Tetraselmis Suecica

Marine microalgae represent an essential link in the planktonic food web and some of them are commonly utilised in aquaculture systems as food for larval and juvenile stages of fishes, crustacea and mollusca. However, the caloric content and the biochemical composition of these microrganisms vary in relation to ageing and to several environmental conditions; so if the parameters under which phytoplankton grow are not suitable, marine microalgae can supply small quantities of energy and essential nutrients. The aim of this work was to study the effects of temperature on the marine planktonic alga Tetraselmis suecica using thermogravimetry (TG) and differential thermal analysis(DTA). Marked differences have been observed between exponentially, stationary and senescence phases probably due to both the presence of different biomolecules produced during algal growth and to the differences in the thermal properties of these intracellular molecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of formalin preservation on stable carbon and nitrogen isotope signatures in Calanoid copepods: implications for the use of Continuous Plankton Recorder Survey samples in stable isotope analyses

Preserved and archived organic material offers huge potential for the conduct of retrospective and long-term historical ecosystem reconstructions using stable isotope analyses, but because of isotopic exchange with preservatives the obtained values require validation. The Continuous Plankton Recorder (CPR) Survey is the most extensive long-term monitoring program for plankton communities worldwide and has utilised ships of opportunity to collect samples since 1931. To keep the samples intact for subsequent analysis, they are collected and preserved in formalin; however, previous studies have found that this may alter stable carbon and nitrogen isotope ratios in zooplankton. A maximum ~0.9‰ increase of δ(15) N and a time dependent maximum ~1.0‰ decrease of δ(13) C were observed when the copepod, Calanus helgolandicus, was experimentally exposed to two formalin preservatives for 12 months. Applying specific correction factors to δ(15) N and δ(13) C values for similarly preserved Calanoid species collected by the CPR Survey within 12 months of analysis may be appropriate to enable their use in stable isotope studies. The isotope values of samples stored frozen did not differ significantly from those of controls. Although the impact of formalin preservation was relatively small in this and other studies of marine zooplankton, changes in isotope signatures are not consistent across taxa, especially for δ(15) N, indicating that species-specific studies may be required.