Variations In Isotopic Abundances Research Articles

Calcium isotope analysis by mass spectrometry

The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. The present article discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. In Sections 2 and 3, mass spectrometric methods applied to precise stable isotope analysis and to the determination of (41)Ca are described. Section 4 contains a short summary of selected applications, and includes tracer experiments and the potential use of biological isotope fractionation in medical studies, paleoclimatic and paleoceanographic, and other terrestrial as well as extraterrestrial investigations.

Feldspathic clasts in Yamato-86032: Remnants of the lunar crust with implications for its formation and impact history

Low concentrations of Th and Fe in the Yamato (Y)-86032 bulk meteorite support earlier suggestions that Y-86032 comes from a region of the moon far distant from the Procellarum KREEP Terrain (PKT), probably from the lunar farside. 39Ar– 40Ar, Rb–Sr, Sm–Nd, and Sm-isotopic studies characterize the chronology of Y-86032 and its precursors in the mega regolith. One of the rock types present in a light gray breccia lithology is an anorthosite characterized by plagioclase with An ∼93, i.e., more sodic than lunar FANs, but with very low 87Rb/ 86Sr and 87Sr/ 86Sr similar to those of FANs. (FAN stands for Ferroan Anorthosite). This “An93 anorthosite” has Nd-isotopic systematics similar to those of nearside norites. A FAN-like “An97 anorthosite” is present in a second light-colored feldspathic breccia clast and has a more negative ε Nd value consistent with residence in a LREE-enriched environment as would be provided by an early plagioclase flotation crust on the Lunar Magma Ocean (LMO). This result contrasts with generally positive values of ε Nd for Apollo 16 FANs suggesting the possibility of assymetric development of the LMO. Other possible explanations for the dichotomy in ε Nd values are advanced in the text. The Y-86032 protolith formed at least 4.43 ± 0.03 Ga ago as determined from a Sm–Nd isochron for mineral fragments from the breccia clast composed predominantly of An93 anorthosite and a second clast of more varied composition. We interpret the mineral fragments as being predominatly from a cogenetic rock suite. An 39Ar– 40Ar age of 4.36–4.41 ± 0.035 Ga for a third clast composed predominantly of An97 anorthosite supports an old age for the protolith. Initial 143Nd/ 144Nd in that clast was −0.64 ± 0.13 ε-units below 143Nd/ 144Nd in reservoirs having chondritic Sm/Nd ratios, consistent with prior fractionation of mafic cumulates from the LMO. A maximum in the 39Ar– 40Ar age spectrum of 4.23 ± 0.03 Ga for a second sample of the same feldspathic breccia clast probably reflects some diffusive 40Ar loss. Lack of solar wind and lunar atmosphere implanted Ar in the light gray breccia clast allows determination of an 39Ar/ 40Ar age of 4.10 ± 0.02 Ga, which is interpreted as the time of initial brecciation of this litholgy. After correction for implanted lunar atmosphere 40Ar, impact melt and dark regolith clasts give Ar ages of 3.8 ± 0.1 Ga implying melt formation and final breccia assembly ∼3.8 Ga ago. Some breccia lithologies were exposed to thermal neutron fluences of ∼2 × 10 15 n/cm 2, only about 1% of the fluence experienced by some other lunar highlands meteorites. Other lithologies experienced neutron fluences of ∼1 × 10 15 n/cm 2. Thus, Y-86032 spent most of the time following final brecciation deeply buried in the megaregolith. The neutron fluence data are consistent with cosmogenic 38Ar cos cosmic ray exposure ages of ∼10 Ma. Variations among differing lithologies in the amount of several regolith exposure indicators, including cosmogenic noble gas abundances, neutron capture induced variations in Sm isotopic abundances, and Ir contents, are consistent with a period of early (>∼3.8 Ga ago) lunar regolith exposure, subsequent deep burial at >∼5 m depth, and ejection from the moon ∼7–10 Ma ago.

Influence of temporal variations in water chemistry on the Pb isotopic composition of rainbow trout ( Oncorhynchus mykiss)

Field and laboratory investigations were undertaken to determine (1) the relations between discharge, Pb concentration, and the Pb isotopic composition of the dissolved load in Richland Creek, western North Carolina, and (2) the potential influence of varying Pb water chemistry on the Pb isotopic abundances in liver and bone tissues of rainbow trout ( Oncorhynchus mykiss). Stream waters were characterized by relatively low Pb concentrations during periods of base flow exceeding 10 days in length. Moreover, greater than 65% of the Pb was derived from orchard soils located upstream of the monitoring site which are contaminated by lead arsenate. During small to moderate floods, the dissolved load exhibited Pb concentrations more than twice as high as those measured during base flow, but the contribution of Pb from lead arsenate was relatively low and varied directly with discharge. In contrast to smaller events, Pb from lead arsenate in an 8- to 10-year (overbank) event in May 2003 was minimal during peak flow conditions, suggesting that discharge-source relations are dependent on flood magnitude. The hydrologic and geochemical data demonstrate that aquatic biota in Richland Creek are subjected to short-term variations in Pb concentrations and Pb isotopic abundances within the dissolved load ranging from a few hours to few a weeks. Laboratory studies demonstrated that when rainbow trout were exposed to elevated Pb concentrations with a distinct isotopic fingerprint, the bone and liver rapidly acquire isotopic ratios similar to that of the water. Following exposure, bone retains Pb from the contaminant source for a period of months, while the liver excreted approximately 50% of the accumulated Pb within a few days and nearly all of the Pb within a few weeks. Differences in the rates of excretion resulted in contrasting isotopic ratios between the tissues. It seems plausible, then, that previously observed differences between the isotopic composition of bone and liver in rainbow trout from Richland Creek are related to their short-term exposure to Pb from soils contaminated with Pb arsenate that result from fluctuating hydrologic conditions. If these trends prove to be common in other contaminated aquatic environments, it may be possible to use the Pb isotopic composition of bone as an indicator of the long-term exposure to Pb and the liver as a biomarker for short-term Pb exposures.

Carbon-13 natural abundance as a tool to study the dynamics of lignin monomers in soil: an appraisal at the Closeaux experimental field (France)

Plant residues incorporated into soils are subjected to contrasted stabilization and biodegradation processes and may contribute to pools of soil organic matter (SOM) displaying different turnover times. Little is known about the relationship between the chemical structure of plant macromolecules and their long-term turnover in soils. Our research objective was to quantify the in situ turnover of phenols derived from lignin, which is a major component of plant tissues often considered slowly biodegradable relative to total plant organic matter. In this study, we used natural 13C labeling of SOM generated by a 9-year chronosequence of maize C4 crop ( δ 13C around −12‰) replacing the previous wheat C3 crop ( δ 13C around −27‰) at the Closeaux experimental field, in France. Here we present the combined applications of CuO oxidation and gas chromatography coupled via a combustion interface to an isotope ratio mass spectrometer (GC/C-IRMS) to follow variations in the isotopic composition of lignin-derived monomers in soils of the wheat–maize transition chronosequence. This study aimed at evaluating: (1) the precision and repeatability of this molecular-level isotopic tracer technique, and (2) its potential for computing the proportion of newly derived C in each lignin phenol. Nine years of maize cropping influenced neither the total organic carbon (OC) content nor the lignin content and biodegradation degree in soil. The total SOM after 9 years of maize cropping was significantly enriched in 13C by 1.4‰ compared to the wheat soil. In the CuO-derived lignin phenols, the variations of 13C contents after 9 years of maize cropping ranged from 4.9‰ to 10.0‰, with an average value for total lignin of 7.3‰. These variations were well above the precision of the analytical method, calculated for maize plant and soils to be in the range 0.2–0.8‰. This study thus demonstrates that the CuO oxidation technique is applicable to the determination of the natural isotopic abundance variations in lignin monomers of soils of a C3/C4 chronosequence. Finally, we could calculate the proportion of newly derived OC after 9 years of maize cropping. This proportion was 9% for total SOM and 47% for lignin, which displayed faster dynamics in this soil than total OC. This study confirms, using in situ labeling technique in combination with lignin monomers analysis after CuO oxidation, that lignin macromolecules are not stabilized as such in these soils.

The need for new SI-traceable magnesium isotopic reference materials

Recent measurements revealed that commercial magnesium standard solutions showed isotopic abundance variations, which cannot clearly be distinguished from each other by calibrating against the only available isotopic reference material, SRM 980, or reference materials made from SRM 980 like IRMM-009. Therefore new SI-traceable magnesium isotopic reference materials are required.

Single and mixed diets in Collembola: effects on reproduction and stable isotope fractionation

Summary Reproduction of Heteromurus nitidus (Collembola) feeding on conidial fungi, ectomycorrhizal fungi and soil algae in single and mixed diets was investigated. Feeding on mixed diets generally increased Collembola reproduction even in combinations of fungi/algae of high food quality with those of low food quality, indicating that Collembola generally benefit from feeding on mixed diets. The contribution of dietary species in mixed diets to Collembola nutrition was quantified using stable isotope methods. Incorporation of carbon from fungal/algal species into H. nitidus in mixed diets varied with food quality indicating that Collembola are able to adjust the proportion of food materials ingested to maximize fitness. Fractionation of 13C and 15N in H. nitidus feeding on single and mixed diets varied between diets and differed between juveniles and adults. The trophic structure of fungal feeding soil invertebrates cannot be inferred in a straightforward way from variations in natural abundances of stable isotopes, rather, stable isotope signatures reflect feeding guilds.

Isotope-Abundance Variations of Selected Elements (IUPAC Technical Report)

Isotope-Abundance Variations of Selected Elements (IUPAC Technical Report)

Isotope-abundance variations of selected elements (IUPAC Technical Report)

Abstract Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic-weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic-weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope-abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope-abundance variations potentially are large enough to result in future expansion of their atomic-weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope variations in materials of natural ter- restrial origin are too small to have a significant effect on their standard atomic-weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio.

Variations in the boron isotope composition of Coffea arabica beans

Significant B isotope abundance variations were found for a variety of Coffea arabica beans from a number of coffee-growing regions around the world. This may be attributed to the influence of local sources of B (including soil, water and fertilizer) each having a characteristic B isotope abundance ratio of its own. The results of this preliminary study indicate that B isotope abundance data can be used to study the biogeochemical cycle of B, an important micronutrient. In addition, the isotopic data can be employed in quality assurance programs of commercial coffee as the quality depends to a large extent on the genetic and geographic origin of the coffee.

Determination of Lead in Botanicals/Chinese Prepared Medicines by Using Microwave Digestion with Flow Injection–Inductively Coupled Plasma–Mass Spectrometry

A simple, sensitive, and rapid method was developed for the determination of lead in botanicals and Chinese prepared medicines (CPM) by using closed-vessel microwave digestion with flow injection-inductively coupled plasma-mass spectrometry. The limits of detection and quantitation for the method, based on 0.5 g digested sample, were calculated to be 0.10 and 0.61 mg/kg, respectively. A simple approach was proposed for calibration by multiple linear regression (MLR) with 207Pb, 206Pb, and 204Pb for the determination of lead in botanical and CPM samples. The results from calibration by MLR were compared with those obtained by conventional modes using 207Pb and the sum of 207Pb and 206Pb. The results obtained by the different modes of calibration were in good agreement for botanical and CPM samples. The method was found to have good accuracy for the analysis of botanical reference materials. Method precision based on analyses of different types of CPM samples by different analysts on different days for different levels of lead was between 3.0 and 8.0% (relative standard deviation, n = 6). The effect of possible matrix interference caused by nitric acid and the extent of digestion was investigated with the method of standard additions. Significant matrix interference was not observed for the CPM samples analyzed. MLR was used to examine the effect of variation in isotopic abundance, which was found to present no significant problem in the determination of lead in the botanical and CPM samples.

Thermal ionization mass spectrometry of molybdenum isotopes

A simple and reliable analytical technique for molybdenum isotope abundance determinations by thermal ionization mass spectrometry, capable of realizing precise data from submicrogram amounts of material, is described. This method was specifically designed for molybdenum fission product and double-beta decay studies, for which only nanogram amounts of sample are available. The molybdenum isotope composition of a high purity molybdenum metal rod, four off-the-shelf reagents, and five molybdenites from different regions were analyzed. No significant isotope abundance variations were observed. The molybdenum isotope abundances determined were compared to current International Union of Pure and Applied Chemistry (IUPAC) isotope composition and atomic weight data.

Fractionation of hydrogen isotopes in lipid biosynthesis

Isotopic compositions of carbon-bound hydrogen in individual compounds from eight different organisms were measured using isotope-ratio-monitoring gas chromatography–mass spectrometry. This technique is capable of measuring D/H ratios at natural abundance in individual lipids yielding as little as 20 nmol of H 2, and is applicable to a wide range of compounds including hydrocarbons, sterols, and fatty acids. The hydrogen isotopic compositions of lipids are controlled by three factors: isotopic compositions of biosynthetic precursors, fractionation and exchange accompanying biosynthesis, and hydrogenation during biosynthesis. δD values of lipids from the eight organisms examined here suggest that all three processes are important for controlling natural variations in isotopic abundance. n-Alkyl lipids are depleted in D relative to growth water by 113–262‰, while polyisoprenoid lipids are depleted in D relative to growth water by 142–376‰. Isotopic variations within compound classes (e.g., n-alkanes) are usually less than ∼50‰, but variations as large as 150‰ are observed among isoprenoid lipids from a single organism. Phytol is consistently depleted in D by up to 50‰ relative to other isoprenoid lipids. Inferred isotopic fractionations between cellular water and lipids are greater than those indicated by previous studies.

Hyphenation of gas chromatographic techniques with isotope ratio mass spectrometry: Present and future

Isotope ratio mass spectrometers (IRMS) are highly specialized sector field mass spectrometers which are dedicated to a single purpose: high precision and high accuracy measurements of the variations in natural isotopic abundance of the light stable isotopes of C, O, H, N, S, (and much less frequently, Cl, Si, and Se). These mass spectrometers have a fixed array of Faraday collectors and they are built to analyze a very small range of simple molecular species (C02, N2, H2, S02, CO). The main applications were in the characterization and mass balance of the various geological cycles which couple the hydrosphere, the lithosphere, and the atmosphere. Systematic applications of stable isotope methodology to the biosphere had to await the coupling of gas chromatography (GC) with IRMS, which allowed the exquisite chemical resolving power of the GC to be hyphenated with the extraordinary precision of the IRMS.

304 韓国江原道・寧越型朝鮮累層群にみられる炭素同位体組成・希土類元素含有量の変動

304 韓国江原道・寧越型朝鮮累層群にみられる炭素同位体組成・希土類元素含有量の変動

Precision of energy expenditure (EE) measurement in pre-term infants: contribution of natural isotopic abundance (NIA) variations

Precision of energy expenditure (EE) measurement in pre-term infants: contribution of natural isotopic abundance (NIA) variations

Precision of Energy Expenditure (EE) Measurements in Preterm Infants : Contribution of Natural Isotopic Abundance (NIA) Variations. 191

Background: In very low birth weight (VLBW) infants, little is known about NIA in oxygene 18 (O18) and deuterium (D2) and influence of NIA variations on EE measurement with doubly labelled water (DLW) method. Sujects and methods: During a nutritional balance study, urine samples were collected each day during 3 to 5 days in 13 VLBW infants(post-natal age: 28.0±4.4 days, gestational age: 32.5±1.1 SA, body weight: 1509±124 g) fed human milk (n=5) or preterm formula (n=8). NIA was measured (n=54) with isotope ratio mass spectrometer (Optima®, Fisons). Results: NIA was -3.13±0.83 ∂%o for O18 and-24.56±3.63 ∂%o for D2, which is close to the adults values. The mean coefficient of variation of EE measurement in relation with NIA variations was 1.98±0.78% (0.62 to 2.98%). Conclusion: In VLBW infants the variations in NIA did not significantly influence precision of EE measurement by DLW method.

The North Fiji Basin basalts and their magma sources: Part II. Sr-Nd isotopic and trace element constraints

Sr-Nd isotope and trace element data are reported for basalts from the North Fiji Basin (NFB). NFB basalts are characterized by extreme variations in isotopic ratios and trace element abundances which are related to mantle heterogeneities. Values of 87 Sr 86 Sr for basalts from the northern segments, N160° and triple junction range from 0.7029 to 0.7041, whereas 143 Nd 144 Nd values vary from 0.51281 to 0.51313. Most of the basalts from these segments are characterized by strong relative enrichments in Rb, Ba, Sr, K, Nb, Ta La, Ce and Ti that are comparable to OIB components. The central segments, N15° and N-S have 143 Nd 144 Nd ratios between 0.51298 and 0.51363 and 87 Sr 86 Sr ratios between 0.7029 and 0.7033, and are depleted in large ion lithophile, light rare-earth and high field strength elements similar to N-MORB. Covariation between trace element and isotopic ratios among NFB basalts supports a model in which melts from the NFB rift system are derived by mixing of OIB-type and depleted N-MORB mantle components. The Sr-Nd isotopic and trace element variability indicates that the NFB basalt source is heterogeneous on the scale of individual melt batches.

Isotopic variations in the rock-forming elements in meteorites

Variations in isotopic abundances of the major rock-forming elements can be used as tracers for chemical processes in the solar nebula, and may also provide links to the presolar cloud from which the solar nebula was derived. Emphasis in this paper is placed on the correlation of isotopic variations between pairs of elements, both for mass-dependent fractionation effects and for nucleosynthetic effects. Variations in oxygen isotope abundances, which are ubiquitous in all Solar System matter, are decoupled from those in other elements, probably because of the effect of a large oxygen reservoir in the nebular gas. Among the metallic rock-forming elements (Mg, Si, Ca, Ti, Cr, Fe, Ni) isotopic variations are small to immeasurable in ordinary chondrites and achondrites. Large variations are observed in refractory inclusions in carbonaceous chondrites in the elements Mg, Si, Ca and Ti. Fractionation effects result from evaporation and condensation at high temperatures. The dominant nucleosynthetic effects are seen as excesses and deficiencies of the neutron-rich isotopes in the region of the iron abundance peak: 48 Ca, 49 Ti, 50 Ti, 54 Cr, 64 Ni. These effects result from mixing in different proportions of the products of different regions of a supernova. The rock-forming elements also show isotopic variations due to extinct radioactivities: 26 Mg, 53 Cr and 41 K. A local source is likely, as is heterogeneous distribution within the solar nebula.

The predicted abundances of deuterium-bearing gases in the atmospheres of Jupiter and Saturn

The first set of comprehensive thermochemical equilibrium and chemical kinetic calculations on the chemistry of deuterium-bearing gases in the deep atmospheres of Jupiter and Saturn is presented. The sensitivity of the results to variations in elemental and isotopic abundances is studied. Isotopic fractionation effects in the C-13/C12, N-15/N-14, and O-18/O-16 ratios in nonequilibrium species such as CO, CO2, HCN, and N2 are briefly considered.

Isotopic ordering and isotopic correlations as a possible new tool for geosciences

Stable isotopes in crystalline materials under certain conditions (e.g., at high pressures in interior of planets) can form ordered (in space) or correlated distributions. There are several experimental methods that can be upgraded for the search of the positional isotopic correlations (IC) and isotopic superlattices. Differences in the degree of IC in natural crystallites, if detected, could be interpreted as indicators of their formation history. Therefore, a search for IC could open a new application of isotopic geology complementary to the detection of variations of isotopic abundances in minerals, rocks and meteorites.