An automated parallel multi-channel chromatographic system for isotopic analysis – Demonstration considering Sr

A fully automated, closed-column chromatographic system with parallel multi-channel has been developed. This system is established with seven reagent reservoirs, one multi-channel syringe pump, eight 10-port valves, forty sample tubes, 40 columns, and a fraction collection tray. Four samples can be purified simultaneously at a time, and 40 samples can be purified in one batch. Each sample can be purified by an independent channel, avoiding cross-contamination. The sample tubes can be flipped upside down for automatic cleaning, which eliminates the residue of samples. Moreover, the fraction collection tray can collect up to 104 different target components. The key performance of the system has been investigated. The results show that the sample tubes are well-cleaned, the bubble does not affect the chemical behavior of columns, the consistency of the parallel channels is excellent and the blank of the system is negligible. The system was demonstrated by the purification of Sr from reference materials (BCR-2, JB-2, JB-3, and NIST SRM 987). The recoveries of Sr are better than 89.4% and the blank of the whole procedure is less than 200 pg. The Sr isotope values agree well with the reference values.     

A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1–20 ng/g) by wet chemistry is challenging. Combustion–trapping techniques have been shown to be an appropriate alternative [1]. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O₂ stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H₂O, CO₂, SO₂, etc. The O₂ carrier gas, including combustion products and elemental Hg, is then purged into a 40 % (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO₃/1HCl (v/v), 25 mL/min O₂ flow rate, and a dynamic temperature ramp rate (15 °C/min for 25–150 and 600–900 °C; 2.5 °C/min for 150–600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81–102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80–120 %. This protocol has the advantages of a short sample processing time (～3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.     

On the necessity of organic solvent extraction for carbon isotopic analysis of α-cellulose: implications for environmental reconstructions

α-cellulose is widely used as a target substance for isotope ratio analysis in environmental reconstructions. Its preparation includes three basic steps: organic solvent extraction, delignification and alkaline hydrolysis. Recent works have suggested omission of the first step. We have made a detailed comparison in carbon isotope ratio of α-cellulose with or without organic solvent extraction using 32 consecutive tree ring and 30 subfossil peat samples. These samples were exposed to three different chemical treatments: with organic solvent extraction as the first step (Cell_OE), without organic solvent extraction (Cell_NOE), and with organic solvent extraction as the final step (Cell_NOE/OE). The third treatment is used to test if organic extractives can be completely removed or if their solubility in organic solvents has been altered by delignification and alkaline hydrolysis. In tree rings and peat, δ¹³C_{C ell NOE} was always significantly different from δ¹³C_{C ell OE}, but the trends were not the same. In tree rings, δ¹³C_{C ell NOE} was always more negative than δ¹³C_{C ell OE} by ?0.31 ～ ?0.01‰. In contrast, δ¹³C_{C ell NOE} in peat could be more negative or more positive than δ¹³C_{C ell OE} by ?3.08 ～ 0.27‰. The third chemical treatment resulted in different patterns. For tree rings, δ¹³C_{C ell NOE/OE} was still more negative than δ¹³C_{C ell OE} by ?0.36 ～ ?0.08‰. However, the differences between δ¹³C_{C ell NOE/OE} and δ¹³C_{C ell OE} for peat varied in a more narrow range from ?0.58 to 0.61‰, compared to the differences between δ¹³C_{C ell NOE} and δ¹³C_{C ell OE}. These results exposed a complex chemical evolution behaviour and an incomplete removal of lipids during delignification and alkaline hydrolysis. The mean value, long-term trend and seesaw patterns for a tree ring or peat Cell_NOE series were significantly different from those for a Cell_OE series, indicating that omission of organic solvent extraction will lead to a biased inference of past environmental conditions.     

A gamma–gamma coincidence spectrometric method for rapid characterization of uranium isotopic fingerprints

This paper reports on initial efforts for uranium isotopic analysis using gamma-rays and X-ray fluorescence coincidence. In this study, a gamma–gamma coincidence spectrometry was developed. The spectrometry consists of two NaI(Tl) scintillators and XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The developed spectrometry was optimized according to the considerations of output count rate and gamma peak energy resolution. It has been demonstrated that the spectrometry provides an effective method of assessing the content of uranium isotopes for nuclear materials. The main advantages of this approach over the conventional gamma spectrometry include the fact that ²³⁵U enrichment can be graphically characterized by its unique coincidence “fingerprints”. The method could be further developed for fast uranium isotope verification with an established gamma–gamma coincidence spectral imaging library by various nuclear materials.     

Refinement of Pu parent–daughter isotopic and concentration analysis for forensic (dating) purposes

Plutonium (Pu) metal samples from an interlaboratory exchange exercise and simulated swipe samples were dated using plutonium–uranium (Pu–U) and plutonium–americium (Pu–Am). Metal data were evaluated for consistency and the swipe data against its source material. Metal ages based on ²³⁹Pu versus ²³⁵U and ²⁴⁰Pu versus ²³⁶U agreed to within a few percent, while the ²³⁸Pu–²³⁴U and ²⁴¹Pu–²⁴¹Am measurements had larger uncertainties. Swipe ages compared favorably with the material’s known history. Neptunium (²³⁷Np) analyses were examined in the context of the ²⁴¹Pu–²⁴¹Am–²³⁷Np system to estimate whether Np can provide insights on material from which Am, Np, and U were removed.     

Effects of retrograde-zoning of garnet on Sm-Nd isotopic dating of eclogite and oxygen isotopic disequilibrium between eclogitic minerals

The compositional zoning of the garnet in a strongly deformed eclogite from Raobazhaifoliated peridotite has been recognized. The CaO concentrations of the garnet are decreased fromthe core to the rim, while its MnO concentrations are increased, suggesting the retrograde origin ofsuch CaO-MnO zoning. The tie line of garnet+omphacite from this eclogite gives a Sm-Nd ageof (187±5) Ma, which is less significant than the Sm-Nd ages of (221±5)-(228±3) Ma and (210±6)-(214±6) Ma for ultrahigh-pressure eclogites in the southern Dabie zone and in the northernDabie zone, respectively. This younger Sm-Nd age could result from the ~(143)Nd/~(144)Nd ratio decreaseof the retrograde zone in the garnet. The δ~(80)O values of the garnet and omphacite show that theirfractionation values are less than the equilibrium fractionation value between the garnet and om-phacite at 500-900℃, which suggests an oxygen isotopic disequilibrium between them.     

Self-consistent potential energy curves for the A1Σ+ and X1Σ+ states of isotopic cesium hydrides

From the spectroscopic experimental data available in the literature we have determined the mass-reduced Dunham coefficients for the A¹Σ⁺ ↔ X¹Σ⁺ system of the isotopic species CsH and CsD. Based upon these results, for both ground and excited states of cesium hydride and deuteride we report new hybrid rotationless potential energy curves (PMO-RKR-van der Waals) up to the dissociation. As a consistency check on the accuracy of the potentials the eigenvalues were calculated by direct numerical integration of the radial Schrödinger equation and found to agree within the rms error 0.39 cm⁻¹ (X¹Σ⁺) and 0.41 cm⁻¹ (A¹Σ⁺) with the experimental vibrational energies. From the wavefunctions, the rotational constants B_υ, centrifugal distortion terms D_υ, H_υ and L_υ, Franck—Condon factors, and probability density distributions were obtained. The probability density distributions for the lowest vibrational levels of the A¹Σ⁺ show an anharmonicity associated with the anomalous behavior of that state.     

Fission track–secondary ion mass spectrometry as a tool for detecting the isotopic signature of individual uranium containing particles

A fission track technique was used as a sample preparation method for subsequent isotope abundance ratio analysis of individual uranium containing particles with secondary ion mass spectrometry (SIMS) to measure the particles with higher enriched uranium efficiently. A polycarbonate film containing particles was irradiated with thermal neutrons and etched with 6 M NaOH solution. Each uranium containing particle was then identified by observing fission tracks created and a portion of the film having a uranium containing particle was cut out and put onto a glassy carbon planchet. The polycarbonate film, which gave the increases of background signals on the uranium mass region in SIMS analysis, was removed by plasma ashing with 200 W for 20 min. In the analysis of swipe samples having particles containing natural (NBL CRM 950a) or low enriched uranium (NBL CRM U100) with the fission track–SIMS method, uranium isotope abundance ratios were successfully determined. This method was then applied to the analysis of a real inspection swipe sample taken at a nuclear facility. As a consequence, the range of ²³⁵U/²³⁸U isotope abundance ratio between 0.0276 and 0.0438 was obtained, which was higher than that measured by SIMS without using a fission track technique (0.0225 and 0.0341). This indicates that the fission track–SIMS method is a powerful tool to identify the particle with higher enriched uranium in environmental samples efficiently.     

An optimized isotopic labelling strategy of isoleucine-γ2 methyl groups for solution NMR studies of high molecular weight proteins

An efficient synthetic route is proposed to produce 2-hydroxy-2-ethyl-3-oxobutanoate for the specific labelling of Ile methyl-γ(2) groups in proteins. The (2)H, (13)C-pattern of the biosynthetic precursor has been designed to optimize magnetization transfer, in large proteins, between these important structural probes and their corresponding backbone nuclei.     

Spectroscopic studies of Lewis acid—base complexes—VI. Vibrational spectra and normal coordinate calculations for several isotopic varieties of trimethylphosphine—gallium trichloride

Raman and infrared spectra of trimethylphosphine—gallium trichloride have been obtained from microcrystalline solids, mulls and KBr discs. The data include results from the deuterated species as well as from samples prepared from ⁶⁹Ga and ⁷¹Ga. Revised assignments are proposed on the basis of the isotopic data and are supported by normal coordinate calculations.     

Novel concept for the mass spectrometric determination of absolute isotopic abundances with improved measurement uncertainty: Part 2 – Development of an experimental procedure for the determination of the molar mass of silicon using MC-ICP-MS

The isotopic abundances and thus molar mass M(Si) of a silicon crystal material with natural isotopic abundances have been measured for the first time using multicollector-ICP-mass spectrometry (MC-ICP-MS) in combination with a novel concept of a modified isotope dilution mass spectrometry (IDMS)-method. This experimental work is the further development of part 1 of this series of papers. While part 1 describes the theoretical background and the mathematical derivation of the novel concept in detail, the measurements presented here serve to validate the novel concept and give experimental proof of its capability. Moreover, the also new method for the analytical calculation of calibration factors needed in the determination of absolute isotope amount ratios has been tested successfully. Silicon isotopic abundances have been measured directly from an aqueous alkaline matrix following a new sample preparation protocol developed within the framework of this study. A molar mass of M(Si) = 28.08548(13) g/mol with an associated relative uncertainty of u_rel = 4.6 × 10^?6 (k = 1) has been measured. This is in excellent agreement with the current IUPAC value for the molar mass of natural silicon M(Si_nat) = 28.08550(15) g/mol with u_rel = 5.3 × 10^?6 (k = 1). An uncertainty budget according to the Guide to the Expression of Uncertainty in Measurement (GUM) was calculated to assess the presented results and to validate the novel concept with the help of experimental data. The development of a new experimental procedure is presented in detail and the contributions to the uncertainty are discussed in comparison to part 1 of this work.     

Condensed aromatics—XXVI. Vibrational frequencies of 13C60 isotopic buckminsterfullerene

The force-field of molecular vibrations of C₆₀ buckminsterfullerene is refined and used to calculate the frequencies of ¹³C₆₀ isotopic buckminsterfullerene. The resulting IR-active frequencies show very good agreement with experimental data from literature. It is suggested that the predicted Raman-active frequencies for ¹³C₆₀ are reliable. Calculated Coriolis coupling constants for the IR-active frequencies are given.     

Overcoming spectral overlap in isotopic analysis via single- and multi-collector ICP–mass spectrometry

For isotope ratio applications where an internal isotope ratio precision >0.05–0.1% relative standard deviation suffices, single-collector inductively coupled plasma mass spectrometry (ICPMS) is fit-for-purpose, but for detecting more subtle variations in the natural isotopic composition of a target element, only multi-collector ICPMS (MC-ICPMS) can compete with thermal ionization mass spectrometry (TIMS). While as a result of the extensive sample preparation (analyte isolation) preceding TIMS and the "softer" ionization in vacuum, spectral interferences only seldom occur with this technique, their occurrence is recognized to be the most important drawback of ICPMS. This paper discusses high mass resolution and chemical resolution in a collision or dynamic reaction cell as powerful and versatile means to overcome spectral overlap and illustrates how their introduction has led to a substantial extension of the application range of ICPMS for isotope ratio applications. High mass resolution is the most elegant and straightforward way to overcome the problem of spectral overlap. Offering the possibility to operate the mass analyzer at a higher mass resolution, while at the same time preserving the flat-topped or trapezoidal peak shape required for highly precise isotope ratio measurements, was a challenge for the manufacturers of MC-ICPMS instrumentation. It will be discussed how these apparently contradicting requirements could be fulfilled simultaneously and an overview of the current situation will be given. Chemical resolution in a collision or dynamic reaction cell is an alternative to high mass resolution for overcoming spectral overlap. Real-life examples will be given to illustrate how also this approach can be used to advantage in isotope ratio work. Despite the greater flexibility and straightforwardness of high mass resolution, some situations will be discussed where chemical resolution is to be preferred. Finally, some desires as to future instrumentation are formulated.     

Is the isotopic composition of nitrous oxide an indicator for its origin from nitrification or denitrification? A theoretical approach from referred data and microbiological and enzyme kinetic aspects

Literature data on the isotopic composition of nitrous oxide indicate a general predominance of the alpha-15N-isotopomer and a parallel 18O-enrichment in N2O from nitrification and denitrification, respectively. As the kinetic isotope effects on any individual reactions of the two processes lead to depletions of the heavy isotopes of nitrogen and oxygen in the products, the observed enrichments could mainly be caused by enzymatic reduction of NO, provided it occurs via a symmetric intermediate like hyponitrite; infrared data are in favour of large differences between the binding constants of the isotopomers and isotopologues of this compound. As a matter of fact one of the mechanisms discussed for the nitric oxide reductase from certain microorganisms implies the parallel binding of two NO molecules and the formation of a symmetrical intermediate, while that of the enzyme from other microorganisms reduces NO in a sequential mechanism. In addition, isotope effects on the reduction of N2O to N2 must contribute to the observed isotope characteristics of N2O, especially in context with denitrification. Therefore, the known enzymatic reaction pathways suggest that the alpha-15N-isotopomer preference and the 18O-signature of the produced N2O is not essentially characteristic for its origin from nitrification or denitrification, respectively, but rather from the involved population of microorganisms and the type of their nitric oxide reductases. This has to be confirmed experimentally.     

Study of the vibrational photochemical reation of UF_6+HCl and its isotopic selectivity

The photochemical vibrational reaction of UF_6+HCl was investigated by exciting theternary overtone of 3ν_3 of UF_6 in an intracavity CO laser system.It was found that the rateof the laser-driven reaction was much greater than that of the thermal reaction and thisphotochemical process had an isotopic selectivity.The uranium isotope enrichment factorsmeasured in experiments wore around 1,007 in a single step.     

Comparative performance study of ICP mass spectrometers by means of U “isotopic measurements”

The performance of four commercially available ICPMS instruments of three different types was compared by means of uranium “isotopic measurements”. Examined were two quadrupole sector (different generation, different manufacturer), one single detector double focusing magnetic sector and one multiple collector double focusing magnetic sector instruments. The same samples of the IRMM-072 series were used under routine conditions to measure the ²³³U/²³⁵U and the ²³³U/²³⁸U ratios which, in these samples, vary over almost three orders of magnitude from ～ 1 to ～ 2 · 10^–3. Within expanded (k = 2) uncertainties, good agreement was observed between the certified values and the data internally corrected for mass-discrimination effects. The magnitude of the evaluated uncertainties was different for each type of instrument. With the multiple collector instrument, expanded uncertainties varied from ± 0.04% to± 0.24% for the ²³³U/²³⁵U ratio, and from ± 0.08% to ± 0.27% for the ²³³U/²³⁸U ratio. They were ～ 1 to 5 times larger with the single detector magnetic sector instrument, and ～ 10 to 25 times larger with both quadrupole sector instruments. With the multiple collector instrument, repeatability of the measurements seemed to be limited by the difficulty of correcting properly for instrumental background, whereas with the single detector magnetic sector instrument the counting statistics was the only limitation (on smallest ratios). Apparent mass-discrimination was clearly found to be larger but more reproducible (and hence easier to correct for) in the case of magnetic sector instruments than for both quadrupole sector instruments. If space charge effects were the main source of mass-discrimination for all instruments, these results are in contradiction with the hypothesis of the size of mass-discrimination decreasing with the acceleration voltage. With the single detector magnetic sector instrument in particular (when operated by changing the ion energy only), our results pointed at more than only one major source of mass-discrimination, with variable size depending on the ratios measured.     

An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ11B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH)4- is the dominant spe-cies incorporated into the biogenic calcite structure. The isotopic fractionation factors α between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH)3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH)3 is attributed to the formation of Mg(OH)2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH)2 precipitated from artificial seawater shows that heavier 11B is enriched in Mg(OH)2 precipitation, which suggests that isotopically heavier B(OH)3 species incorporated preferentially into Mg(OH)2 precipitation. This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.     

Accurate time-dependent wave packet study of the Li + H₂⁺ reaction and its isotopic variants

The dynamics and kinetics of the Li + H?? reaction and its isotopic variants (D?? and T??) have been studied by using a time-dependent wave packet (TDWP) coupled-channel (CC) method on the ab initio potential energy surface (PES) of Martinazzo et al. [J. Chem. Phys. 2003, 119, 21]. Total initial v = 0, j = 0 state-selected reaction probabilities for the Li + H?? reaction and its isotopic variants have been calculated from the threshold up to 1 eV for total angular momenta J from 0 to 90. Integral cross sections have been evaluated from the reaction probabilities at collision energies from threshold (≈0.2 eV) up to 1.0 eV collision. The calculated rate constants as a function of temperature show an Arrhenius type behavior in the 200 ≤ T ≤ 1000 K temperature interval. It has been found to be a considerable large intermolecular kinetic isotope effect. The TDWP-CC results are in overall good agreement with those obtained applying the TDWP Centrifugal-Sudden (CS) approximation, showing that the CS approximation is rather accurate for the title reaction.     

The isotopic effects in the IR-multiphoton excitation of molecules with c_(2v) symmetry

Quantum dynamical calculations for the IR-multiphoton excitation of H_2O,D_2O andT_2O are presented using a generalized Hamiltonian for XY_2 molecules.The energy spectraobtained from this Hamiltonian are in good agreement with those of the experiments.Thelong time average of the transition probabilities and the isotopic effects are discussed in detail,