Determination Of Isotope Ratios Research Articles

Precise Determination of Cd Isotope Ratios at 3-10 ng Level by Thermal Ionization Mass Spectrometry Using a Molybdenum Silicide Emitter.

Thermal ionization mass spectrometry (TIMS) combined with the double spike technique has excellent analytical precision for Cd isotopic ratio analysis. However, because of the low ionization efficiency of Cd by TIMS, it is still not possible to obtain high precision Cd isotope ratios for small sample size (<100 ng) due to the lack of a highly sensitive emitter for Cd. A new loading method using molybdenum silicide (MoSi2) emitter has been developed for Cd isotope ratio measurements. This emitter produces a significant enhancement in the ionization efficiency of Cd and thus significantly reduces the required sample size to the 3-10 ng level. Analyses of δ114/110Cd for the NIST SRM 3108 using 108Cd-116Cd double spike method show excellent reproducibility (2 SD) that reaches ±0.032‰, ±0.042‰, and ±0.051‰ for 10, 5, and 3 ng of Cd, respectively. This method was further verified with a suite of geological reference materials. Replicate digestions and analyses (n = 8, 2 SD) of δ114/110Cd for NIST SRM 2711a, NOD A-1, and GBW08401 demonstrated good external reproducibility with results of 0.596 ± 0.024‰ for NIST SRM 2711a, 0.150 ± 0.036‰ for NOD A-1, and -0.665 ± 0.084‰ for GBW08401. These data clearly indicate that MoSi2 is an excellent alternative for traditional silica gel to Cd isotopic measurements, especially for samples with a low content of Cd.

Innovative Determination of Zinc Isotope Ratios in Geological Reference Materials: A Combined Precipitation and Anion Exchange Resin Method by MC-ICP-MS

Innovative Determination of Zinc Isotope Ratios in Geological Reference Materials: A Combined Precipitation and Anion Exchange Resin Method by MC-ICP-MS

A multi-analytical approach for the identification of pollutant sources on black crust samples: Stable isotope ratio of carbon, sulphur, and oxygen

This study is focused on the identification of pollutant sources on black crust (BC) samples from the Monumental Cemetery of Milan (Italy), through a multi-analytical approach based on the determination of stable isotope ratios of carbon, sulphur, and oxygen. Six black crust samples, mainly developed on marble sculptures over a time span of 100–150 years, were analysed.For the first time, δ13C was measured for BC samples: δ13C values of the pulverized samples (from −1.2 to +1.3 ‰) are very close to the values obtained from the carbonate matrix, whereas after the removal of the matrix through acidification, δ13C values of BC samples from Milan range from −27.2 to −22.1 ‰, with no significant variation between samples with different ratios of organic carbon to elemental carbon. In sum, the δ13C values obtained for all BC samples fall within the range of anthropogenic emissions such as vehicle traffic, coal combustion and industrial emissions.δ34S and δ18O values of sulphate from BC samples range from −6.3 to +7.0 ‰ and from +7.6 to +10.5 ‰, respectively. Coupling the analysis of the oxygen isotope ratio with that of sulphur enables a more precise identification of the origin of sulphates: the observed isotopic composition falls in the range typical for anthropogenic emission of sulphur dioxide.Overall, in this study, C, S and O isotopes were combined for the first time to assess pollutant sources on black crust samples: this multi-stable isotope approach allowed to show that the BC formation on monuments from the Monumental Cemetery of Milan mostly results from anthropogenic emissions from fossil fuels combustion by road vehicles and factories, as well as domestic heating.

Lithium isotope ratio analysis of geological samples using atomic absorption spectrometry with improved spectral resolution

This study introduces an improved spectrometric method with enhanced precision to determine isotope ratios in geological samples without chromatographic separation. Firstly, the improvement is achieved by increasing the spectral resolution of the spectrometer applied in well-known high-resolution continuum source atomic absorption spectrometry (HR-CS-AAS). The resulting resolving power and linear dispersion of the upgraded setup, which is denoted in the following as HR+CS-AAS, is well adapted to the line widths of the Li isotope components we investigated. Secondly, our proposed method combines optical absorption spectrometry with machine learning data analysis using an extreme gradient boosting algorithm (XGBoost). This method was applied to analyze certified geological reference materials with δLSVEC(7Li/6Li) (hereafter δ7Li) values ranging from −0.5 ‰ to 4.5 ‰. With a pixel related optical resolving power of λ/∆λ ≈ 780 000, we obtain precisions in δ7Li measurements from 1.0 ‰ to 2.5 ‰. The method is validated by comparing the results with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), confirming its metrological compatibility. This work presents a fast, robust, and reliable method for δ7Li measurement in geological samples.

High-temperature liquid chromatography-isotope ratio mass spectrometry methodology for carbon isotope ratio determination of anabolic steroids in urine

BackgroundGas Chromatography Isotope Ratio Mass Spectrometry (GC-C-IRMS) has long been used in routine laboratories to determine the δ13C values of anabolic steroids in urine, differentiating between, e.g., endogenous and synthetic testosterone (T) in sports doping control. Until now, liquid chromatography (LC-IRMS) has not been used. The LC-IRMS setup doesn't allow organic solvents or modifiers in the mobile phase for δ13C determinations. Mid-to non-polar analytes such as steroids can be analysed in water heated to High Temperatures (HT, up to 200 °C) because at 200 °C has a similar polarity as 80/20 methanol/water at ambient temperature. In this work, we developed a method for steroids in urine, extending the application of the LC-IRMS to non-polar analytes in complex matrices. ResultAn HT-LC-IRMS method capable of determining the δ13C values of four steroids (i.e., testosterone (T), 5α-androstane-3α,17β-diol (ααβ), 5β-androstane-3α,17β-diol (βαβ) and pregnanetriol (PT)) in urine was developed and validated. Accuracy ranged from 0.23 ‰ (ααβ and βαβ) to 0.49 ‰ (T), and the detection limit was set at 10 ng mL−1 (T, ααβ+βαβ). The validation data and a comparison of authentic urine samples analysed with HT-LC-IRMS and GC-C-IRMS indicated a comparable performance between HT-LC-IRMS and GC-C-IRMS. SignificanceHT-LC-IRMS can be used to determine δ13C values of anabolic steroids, extending the applicability of both HT-LC and LC-IRMS to non-polar substances determined in a complex matrix in routine laboratory practice.

Radiological assessment of both unperturbed and agricultural soils from southern Ecuador

The radiological background in soils across various areas in Southern Ecuador, such as Vilcabamba, Loja, Palanda, Catamayo, and Taquil, was studied to understand the impact of agriculture and fertilizer usage on soil radiological composition. Areas impacted by agricultural activities alongside reference areas unaffected by human intervention were chosen, encompassing comprehensive analyses including gamma and alpha radiation measurements, isotopic ratio determinations, and assessments of radioactive decay chain disequilibrium. Key radiological parameters such as the radium equivalent index, the external gamma absorbed dose rate and the external hazard index were calculated. The external gamma absorbed dose is equal or lower than 57 nGy h−1 (mean value worldwide in the Earth's crust). The remaining indexes as well as the annual dose rate are far from the limits allowed for public. Fallout due to 137Cs is negligible and below the minimum detectable activity (MDA). Ratios 238U/232Th varies from 0.55 in Catamayo to 1.11 in Taquil. These values show disequilibrium between the two radioactive chains and it is possible to assume A (238U)∼0.64 A (232Th) (excluding Taquil, value 1.11). Furthermore, the radiological composition of commonly used fertilizers, including urea, NPK, NH4NO3, KNO3 and compost, was analyzed, identifying 40K and 210Pb as significant radionuclides. Interestingly, no correlation was found between the types of fertilizers used and the radiological composition of soils. The predominance of the radiological background provided by the parent rock remains the main factor influencing soil composition. The radiological background values for 226Ra, 228Ra, and 40K were established, with a mean value of 23 ± 5 Bq kg−1, 30 ± 4 Bq kg−1, and 450 ± 80 Bq kg−1, respectively. Finally, the distribution of 210Pb in unperturbed soils suggests a higher concentration in the top layer, which is indicative of natural deposition patterns, except in areas affected by erosion such as Vilcabamba, Loja, and Catamayo.

Determination of Δc13 and Δc18 Isotope Ratios to Predict Carbon-Water Relationship in Different Forest Stands in Yenice Forest Hot Spot

Determination of Δc13 and Δc18 Isotope Ratios to Predict Carbon-Water Relationship in Different Forest Stands in Yenice Forest Hot Spot

A rapid method for the determination of stable hydrogen isotope ratios of acetic acid in vinegar.

Vinegar is an everyday condiment made from fermented grains or fruits. It contains acetic acid which is the main organic material produced by fermentation. Vinegar suffers from the authenticity problem of exogenous adulteration due to the indistinguishability of low-cost chemical sources of synthetic acetic acid from acetic acid produced by fermentation. It is necessary to establish a simple and rapid measurement technique. Determination was according to the total acid content of vinegar diluted with acetone to a certain concentration. Online separation and determination of acetic acid δD in vinegar were carried out using gas chromatography-pyrolysis-isotope ratio mass spectrometry. An HP-Plot/U column was selected for online separation of acetic acid and water with molecular sieve characteristics. At the same time, combined with the instrument blowback function to remove water. Dilute solvent acetone was treated with a molecular sieve to remove trace water. The reproducibility of this method is less than 3‰. The long-term stability is within a reasonable error range. The accuracy correlation coefficient is greater than 0.99. The δD values of acetic acid in vinegar (-264.5 ± 20.3‰) and from chemical sources (-30.5 ± 90.8‰) were obtained. A rapid method was developed for identification of different sources of acetic acid. These different sources of acetic acid exhibited significant hydrogen isotope distribution characteristics. Additionally, it was observed that the carboxyl hydrogen of acetic acid exhibited facile exchange with water. In future investigations, we aim to mitigate this interference.

Employing 11-Ketotestosterone as a Target Analyte for Adrenosterone (11OXO) Administration in Doping Controls.

Adrenosterone (Androst-4-ene-3,11,17-trione, 11OXO) is forbidden in sports according to the Prohibited List of the World Anti-Doping Agency. The administration of 11OXO may be detected by monitoring the urinary concentrations of its main human metabolites 11β-hydroxy-androsterone and 11β-hydroxy-etiocholanolone. Preliminary urinary concentration and concentration ratio thresholds have been established for sports drug testing purposes, but adaptations are desirable as the suggested limits would result in numerous suspicious findings due to naturally elevated concentrations and ratios. Recently, the metabolism of 11-oxo-testosterone (KT) was investigated in the context of anti-doping research, resulting in a preliminary urinary concentration threshold and a confirmation procedure based on the determination of carbon isotope ratios (CIRs). Gas chromatography coupled to isotope ratio mass spectrometry was employed to investigate the CIRs of selected steroids. As KT is also a metabolite of 11OXO, the developed protocols for KT have been tested to elucidate their potential to detect the administration of 11OXO after a single oral dose of 100 mg. In order to further improve the analytical approach, the threshold for urinary concentrations of KT was re-investigated by employing a reference population of n = 5232 routine doping control samples. Quantification of urinary steroids was conducted by employing gas chromatography coupled to triple quadrupole mass spectrometry. Derived from these, a subset of n = 106 samples showing elevated concentrations of KT was investigated regarding their CIRs. By means of this, potentially positive samples due to the illicit administration of 11OXO or KT could be excluded, and the calculation of reference population-derived thresholds for the concentrations and CIR of KT was possible. Based on the results, the urinary concentration threshold for KT is suggested to be established at 130 ng/mL.

Coprecipitation as a One-Step Se Separation for Determination of Isotope Ratios Completed with Revised Uncertainty Evaluation.

This study introduces a simplified purification method for analyzing 82Se/78Se isotope ratios in diverse natural samples using hydride generation MC-ICP-MS. Unlike the thiol resin method, which is time-consuming and sensitive to the concentrations of reagents used at individual stages, our proposed alternative is quicker, simpler, and robust. The procedure involves coprecipitation of selenium with iron hydroxide and dissolution in hydrochloric acid. Combining hydride generation and a second cleanup stage achieves sufficient purification for Se isotope ratio measurements. The method is efficient, taking 3-4 h after sample decomposition, utilizing common reagents [HCl, Fe(NO3)3, NH4Cl] without evaporation or clean lab conditions. Results on 82Se/78Se isotope ratios in various matrices are presented, comparing them with literature data. All isotopic results have been subjected to a newly proposed state-of-the-art approach to uncertainty estimation dedicated to isotope ratio measurements. The approach is based on applying Monte Carlo simulations with consideration of different samples' results normalized by the expected value. By doing that, we obtained estimated uncertainty for any Se sample with the influence of particular measurements on the final estimation included. We employ a Monte Carlo simulation-based uncertainty estimation approach for isotope ratio measurements, providing estimated uncertainty for each selenium sample.

Separation of Lipoproteins for Quantitative Analysis of 14C-Labeled Lipid-Soluble Compounds by Accelerator Mass Spectrometry.

To date, 14C tracer studies using accelerator mass spectrometry (AMS) have not yet resolved lipid-soluble analytes into individual lipoprotein density subclasses. The objective of this work was to develop a reliable method for lipoprotein separation and quantitative recovery for biokinetic modeling purposes. The novel method developed provides the means for use of small volumes (10-200 µL) of frozen plasma as a starting material for continuous isopycnic lipoprotein separation within a carbon- and pH-stable analyte matrix, which, following post-separation fraction clean up, created samples suitable for highly accurate 14C/12C isotope ratio determinations by AMS. Manual aspiration achieved 99.2 ± 0.41% recovery of [5-14CH3]-(2R, 4'R, 8'R)-α-tocopherol contained within 25 µL plasma recovered in triacylglycerol rich lipoproteins (TRL = Chylomicrons + VLDL), LDL, HDL, and infranatant (INF) from each of 10 different sampling times for one male and one female subject, n = 20 total samples. Small sample volumes of previously frozen plasma and high analyte recoveries make this an attractive method for AMS studies using newer, smaller footprint AMS equipment to develop genuine tracer analyses of lipophilic nutrients or compounds in all human age ranges.

Comparison and influence of 1011 and 1013 ohm resistors used for MC-ICP-MS determination of isotope ratios in highly enriched silicon

Use of high ohmic feedback resistors connected with Faraday cups enables strong reduction of sample size (here: Si crystal slices enriched in 28Si) and proper signal quality while maintaining the measurement uncertainty.

Highly sensitive spectral measurement of rubidium isotopes using open multi-pass cell in tunable diode laser absorption spectroscopy

An open multi-pass cell was constructed to extend the interaction distance between the light and Rb atoms in the TDLAS measurement system. Compared with single-path direct absorption, the SNR of the system was improved by 3.8 times.

Rapid and accurate determination of chlorine isotopic ratios with ICP-MS/MS using O2 reaction gas

We report a tandem ICP-MS/MS method using O2 gas for chlorine isotopic ratio determinations, with improved accuracy and increased throughput.

In situ precise determination of stable Mo isotope ratios in molybdenite by femtosecond LA-MC-ICP-MS

We developed a new method for in situ measurement of Mo stable isotope ratios using femtosecond laser ablation coupled with MC-ICP-MS. Additionally, experiments were conducted on nine natural molybdenite samples from different ore deposits in China.

Determination of indium isotopic ratios of geostandards with different matrices by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

A new method was developed to separate In from geostandards of different matrices, and In recovery is estimated to 98% ± 2%. We measured In isotope compositions of these standards and found significant In isotopic variations in terrestrial samples.

Simultaneous determination of the oxygen isotope ratio and vola-tile composition of apatite with high lateral resolution via nano-secondary-ion mass spectrometry

Apatite is commonly used as a tracer in Earth and planetary sciences by leveraging its oxygen isotopes and volatile compo-sitions to elucidate the derivation and evolution of magma and geological...

Using Carbon Stable Isotopes to Study C3 and C4 Photosynthesis: Models and Calculations.

Stable carbon isotopes are a powerful tool to study photosynthesis. Initial applications consisted of determining isotope ratios of plant biomass using mass spectrometry. Subsequently, theoretical models relating C isotope values to gas exchange characteristics were introduced and tested against instantaneous online measurements of 13C photosynthetic discrimination. Beginning in the twenty-first century, laser absorption spectroscopes with sufficient precision for determining isotope mixing ratios became commercially available. This has allowed collection of large data sets at lower cost and with unprecedented temporal resolution. More data and accompanying knowledge have permitted refinement of 13C discrimination model equations, but often at the expense of increased model complexity and difficult parametrization. This chapter describes instantaneous online measurements of 13C photosynthetic discrimination, provides recommendations for experimental setup, and presents a thorough compilation of equations available to researchers. We update our previous 2018 version of this chapter by including recently improved descriptions of (photo)respiratory processes and associated fractionations. We discuss the capabilities and limitations of the diverse 13C discrimination model equations and provide guidance for selecting the model complexity needed for different applications.

Investigation of potential polyatomic interferences on uranium isotope ratio measurements for the LS-APGD-Orbitrap MS system

The determination of actinide (e.g., U and Pu) content and isotopics is of importance to the nuclear forensics and safeguards communities. However, in the analysis of environmental samples, such as those collected by the International Atomic Energy Agency, uranium measurements can be complicated by isobaric interferences from polyatomic variants of heavy elements (e.g., Pb). This leads to complex, time-consuming sample manipulations (i.e., separations) before determining isotope ratios. An alternative strategy to sample pretreatment is to use high-resolution mass spectrometric platforms during the analysis to fully resolve the uranium isotopes from potential polyatomic interferences, negating the need for prior chemical separation. The liquid sampling - atmospheric pressure glow discharge (LS-APGD) coupled with an Orbitrap mass spectrometer provides a high-resolution (>70,000 m/Δm at m/z 200) inorganic mass spectrometry platform. As a demonstration of the power of this instrumental platform, and indeed, the high-resolution approach in general, uranium isotope ratios were determined in the presence of elemental impurities (e.g., Pb, Pt, Ta, W) commonly encountered with environmental sample swipe analysis, without any prior treatment. Even at elemental impurity concentrations of 1000–5000× relative to uranium, no interference was observed with the 235U or 238U signal. In addition, the 235U/238U isotope ratio for the samples with the concomitants present are within 2 standard deviations of the values obtained without their addition, indicating that these impurities do not impact the determined uranium isotope ratio. These findings represent a significant first step in leveraging the high resolution of the LS-APGD-Orbitrap-MS to overcome isobaric and molecular interferences instead of relying on chemical separations.

Determination of age, isotopic ratios, and elemental impurities in nuclear materials by single quadrupole ICP-MS

Determination of age, isotopic ratios, and elemental impurities in nuclear materials by single quadrupole ICP-MS