Multi-collector Thermal Ionization Mass Spectrometry Research Articles

Evidence of glass bead‐making in the early Islamic Iberian Peninsula

AbstractGlass beads from two Islamic archaeological sites in the Tagus valley in central Spain were selected and analysed by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS), and a subset of samples (n = 6) was analysed for Pb isotopes by multicollector thermal ionization mass spectrometry (MC‐TIMS). The analytical and isotopic data of the beads from Ciudad de Vascos (Toledo) and Albalat (Cáceres) demonstrate beyond reasonable doubt that glass beads were produced in the Iberian Peninsula during the Islamic period using local Pb‐silica and soda‐rich plant‐ash glass. The bead workshops in al‐Andalus were evidently part of an efficient system of glass collection and recycling, and used only relatively simple bead‐making techniques such as winding and folding. At present it is unclear to what extent the Islamic bead‐makers in the Iberian Peninsula were involved in the international trade in glass beads or whether their products were mainly destined for a regional market. Despite local production, some samples show compositional and typological features that suggest the import of finished glass beads, perhaps from Central Asia.

A double-spike MC TIMS measurement procedure for low-amount Ca isotopic analysis of limited biological tissue samples.

The application of Ca isotopic analysis in biomedical studies has great potential to identify changes in Ca metabolism and bone metabolism. Reliable measurement of Ca isotope-amount ratios is challenging considering limited Ca amounts and significant procedural blank levels. In this study, Ca purification was performed using the DGA Resin, optimized for low procedural blanks and separation of Ca from matrix elements and isobaric interferences (Na, Mg, K, Ti, Fe, Ba), while maintaining quasi-quantitative recoveries which are sufficient since a 42Ca-48Ca double-spike (DS) was applied. Ca isotopic analysis was performed using multicollector thermal ionization mass spectrometry (MC TIMS). The obtained procedural Ca blank of ≤10ng enables processing of limited Ca amounts down to 670ng. Data reduction of the measured Ca isotope-amount ratios was performed using an in-house developed software solving the DS algorithm. Data quality was improved by extension of equilibration time of the sample-DS mixture and implementation of a normalization strategy for raw isotopic data. The reported δ(44Ca/40Ca)NIST SRM 915a of NIST SRM 915a processed as a sample was found to be 0.01‰ ± 0.08‰ (2 SD, n = 15). Ca isotope-amount ratios of the reference material NIST SRM 1400 (bone ash), NIST SRM 1486 (bone meal), GBW07601 (human hair), and IAPSO (seawater) were in good agreement within uncertainty with literature data. Novel data on additional reference materials for biological tissues (hair) is presented, which might indicate a potential fractionation of Ca incorporated into hair tissue when compared to the blood pool.

Isotopic composition of a sample enriched in 93Zr

A project to determine the neutron-capture cross section of long lived fission products and minor actinides has been started by using a beam-line at Japan Proton Accelerator Research Complex (J-PARC). One of the target nuclides is 93Zr, which was prepared in Oak Ridge National Laboratory. Qualitative and quantitative analyses on the sample were performed at Kyoto University. The isotopic composition of m Zr (m 90, 91, 92, 93, 94, and 96) was precisely determined by multi-collector thermal ionization mass spectrometry with <0.1 % of 2σ uncertainty. The atomic abundance of 93Zr in the sample was determined to be 18.86 ± 0.05 %.

Evaluation of the Homogeneity of the Uranium Isotope Composition of NIST SRM 610/611 by MC-ICP-MS, MC-TIMS, and SIMS

As analytical and microanalytical applications employing uranium isotope ratios increase, so does the need for reliable reference materials, particularly in the fields of geochemistry, geochronology, and nuclear forensics. We present working values for uranium isotopic data of NIST 610/611 glass, collected by multicollector inductively-coupled plasma mass spectrometry (MC-ICP-MS), multicollector thermal ionization mass spectrometry (MC-TIMS), and secondary ion mass spectrometry (SIMS). The presence of depleted U, and, in this case, measureable 236U, makes NIST 610/611 an ideal candidate for a uranium isotopic reference material for nuclear materials. We analyzed multiple chips of three different NIST 611 wafers and found no heterogeneity in 234U/238U, 235U/238U, and 236U/238U within or between the wafers, within analytical uncertainty. We determined working values and uncertainties (using a coverage factor of two) using data from this study and the literature for the following U isotope ratios: 234U/238U = 9.45 × 10−6 ± 5.0 × 10−8; 235U/238U = 2.38555 × 10−3 ± 4.7 × 10−7; and 236U/238U = 4.314 × 10−5 ± 4.0 × 10−8. SIMS data show 235U/238U is reproducible to within 1% (within analytical uncertainty) in a single wafer, at a scale of 25 μm. Multiple studies have demonstrated homogeneity between wafers of NIST 610 and NIST 611, thus the data reported here can be considered representative of NIST 610 as well.

Evaluation of New Geological Reference Materials for Uranium-Series Measurements: Chinese Geological Standard Glasses (CGSG) and Macusanite Obsidian

Recent advances in high-resolution, rapid, in situ microanalytical techniques present numerous opportunities for the analytical community, provided accurately characterized reference materials are available. Here, we present multicollector thermal ionization mass spectrometry (MC-TIMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) uranium and thorium concentration and isotopic data obtained by isotope dilution for a suite of newly available Chinese Geological Standard Glasses (CGSG) designed for microanalysis. These glasses exhibit a range of compositions including basalt, syenite, andesite, and a soil. Uranium concentrations for these glasses range from ∼2 to 14 μg g(-1), Th/U weight ratios range from ∼4 to 6, (234)U/(238)U activity ratios range from 0.93 to 1.02, and (230)Th/(238)U activity ratios range from 0.98 to 1.12. Uranium and thorium concentration and isotopic data are also presented for a rhyolitic obsidian from Macusani, SE Peru (macusanite). This glass can also be used as a rhyolitic reference material, has a very low Th/U weight ratio (around 0.077), and is approximately in (238)U-(234)U-(230)Th secular equilibrium. The U-Th concentration data agree with but are significantly more precise than those previously measured. U-Th concentration and isotopic data agree within estimated errors for the two measurement techniques, providing validation of the two methods. The large (238)U-(234)U-(230)Th disequilibria for some of the glasses, along with the wide range in their chemical compositions and Th/U ratios should provide useful reference points for the U-series analytical community.

Precise analysis of Ca isotope ratios (δ44/40Ca) using an optimized 43Ca–42Ca double-spike MC-TIMS method

We used a Monte Carlo error model to optimize a 43Ca–42Ca double-spike technique for measuring Ca isotope ratios (δ44/40Ca) by Multi-Collector Thermal Ionization Mass Spectrometry (MC-TIMS). Optimization is non-unique and method-specific because errors for counting statistics and Johnson noise depend on ion beam intensities, integration times, and the total number of duty cycles, while the cumulative effects of measurement-induced Faraday collector damage restrict the double-spike 43Ca/42Ca and spike/sample ratios that can be practically employed. Factors that improve counting statistics and limit Johnson noise also accelerate collector damage and associated drift in measured δ44/40Ca values. Accordingly, better internal precision occurs at the expense of accuracy and external reproducibility. For a 20V 40Ca ion-beam implemented in a three-hop, dynamic multi-collection routine, the model predicts that a wide range of 43Ca/42Ca ratios should yield internal precisions of ±0.020–0.025‰ (2σSEM) for a runtime of 2.5h/sample, but theoretical constraints for minimizing drift exclude options having relatively high spike/sample ratios. Using a Thermo Fisher MC-TIMS (Triton), we tested 43Ca/42Ca=1 [42Ca/(42Ca+43Ca)=0.50mol/mol] and spike/sample=0.33 [Cadsp/(Cadsp+Casmp)=0.25mol/mol] by repeatedly analyzing OSIL Atlantic seawater (sw), NIST SRM 915a, NIST SRM 915b, and CaF2 over 11 sessions spanning 3 months. The average internal precision for 171 measurements is ±0.024‰, in excellent agreement with the model prediction. We adopted an experimental protocol that eliminates drift for a single measurement session (≤30 runs), thereby increasing accuracy and external reproducibility across consecutive sessions. The average δ44/40Ca values agree well with accepted values: δ44/40Casw-sw=0.000±0.005‰ (n=62), δ44/40Ca915a-sw=−1.865±0.006‰ (n=42), δ44/40Ca915b-sw=−1.134±0.006‰ (n=37), and δ44/40CaCaF2-sw=−1.392±0.008‰ (n=30). The global, long-term external reproducibility for the method is ±0.041‰ (2σSD), which represents a two- to ten-fold improvement over Ca isotope measurements made with existing double-spike MC-TIMS methods.

Measurement of Isotope Abundance Variations in Nature by Gravimetric Spiking Isotope Dilution Analysis (GS-IDA)

Subtle variations in the isotopic composition of elements carry unique information about physical and chemical processes in nature and are now exploited widely in diverse areas of research. Reliable measurement of natural isotope abundance variations is among the biggest challenges in inorganic mass spectrometry as they are highly sensitive to methodological bias. For decades, double spiking of the sample with a mix of two stable isotopes has been considered the reference technique for measuring such variations both by multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS) and multicollector-thermal ionization mass spectrometry (MC-TIMS). However, this technique can only be applied to elements having at least four stable isotopes. Here we present a novel approach that requires measurement of three isotope signals only and which is more robust than the conventional double spiking technique. This became possible by gravimetric mixing of the sample with an isotopic spike in different proportions and by applying principles of isotope dilution for data analysis (GS-IDA). The potential and principle use of the technique is demonstrated for Mg in human urine using MC-TIMS for isotopic analysis. Mg is an element inaccessible to double spiking methods as it consists of three stable isotopes only and shows great potential for metabolically induced isotope effects waiting to be explored.

Improvements in routine uranium isotope ratio measurements using the modified total evaporation method for multi-collector thermal ionization mass spectrometry

A new version of the “modified total evaporation” (MTE) method for isotopic analysis of uranium samples by multi-collector thermal ionization mass spectrometry (TIMS), with high analytical performance and designed in a more user-friendly and routinely applicable way, is described in detail. It is mainly being used for nuclear safeguards measurements, but can readily be applied in other scientific areas like geochemistry. The development of the MTE method was organized in collaboration of several “key nuclear mass spectrometry laboratories”, namely the New Brunswick Laboratory (NBL), the Safeguards Analytical Laboratory (SAL, now SGAS—Safeguards Analytical Services) of the International Atomic Energy Agency (IAEA), the Institute for Transuranium Elements (ITU/JRC), and the Institute for Reference Materials and Measurements (IRMM/JRC), with IRMM taking the leading role. Due to the use of the “total evaporation” (TE) principle the measurement of the “major” ratio n(235U)/n(238U) is routinely being performed with an accuracy of 0.02%. In contrast to the TE method, in the MTE method the total evaporation process is interrupted on a regular basis to allow for correction for background from peak tailing, internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, peak-centering, and ion source re-focusing. Therefore, the most significant improvement using the MTE method is in the measurement performance achieved for the “minor” ratios n(234U)/n(238U) and n(236U)/n(238U). The n(234U)/n(238U) ratio is measured using Faraday cups only with the result that the (relative) measurement uncertainty (k = 2) is better than 0.12%, which is an improvement by a factor of about 5–10 compared to TE measurements. Furthermore, the IAEA requirement for the “measurement performance”, defined here as the sum of the (absolute) deviation of the measured from the true (certified) value plus the (absolute) measurement uncertainty (k = 2), for n(236U)/n(238U) ratio measurements is 1 × 10−6, but the MTE method provides a measurement performance which is, depending on the ratio, by several orders of magnitude superior compared to this limit and to the TE method. For routine MTE measurements a detection limit of 3 × 10−9 was achieved using an SEM detector for detecting the isotope 236U. The MTE method is now routinely being used at all collaborating laboratories with the hope that more laboratories will implement this capability in the future as well. Additional applications for the MTE method are presented in this paper, e.g., for absolute Ca isotope measurements.

Measurement of the δ34S value in methionine by double spike multi‐collector thermal ionization mass spectrometry using Carius tube digestion

Methionine is an essential amino acid and is the primary source of sulfur for humans. Using the double spike ((33)S-(36)S) multi-collector thermal ionization mass spectrometry (MC-TIMS) technique, three sample bottles of a methionine material obtained from the Institute for Reference Materials and Measurements have been measured for delta(34)S and sulfur concentration. The mean delta(34)S value, relative to Vienna Canyon Diablo Troilite (VCDT), determined was 10.34 +/- 0.11 per thousand (n = 9) with the uncertainty reported as expanded uncertainties (U). These delta(34)S measurements include a correction for blank which has been previously ignored in studies of sulfur isotopic composition. The sulfur concentrations for the three bottles range from 56 to 88 microg/g. The isotope composition and concentration results demonstrate the high accuracy and precision of the DS-MC-TIMS technique for measuring sulfur in methionine.

Implementation of Guide to the expression of Uncertainty in Measurement (GUM) to multi-collector TIMS uranium isotope ratio metrology

The application of the GUM (Guide to the expression of Uncertainty in Measurement) to calculate standard uncertainties for routine uranium isotope mass spectrometry measurements for nuclear safeguards and nuclear metrology is introduced. The benefit of this approach is an improved coherency and transparency of the uncertainty calculation, which should include contributions from all potentially significant sources of uncertainty to the mass spectrometric measurement result. The GUM approach puts the responsibility for quantifying the uncertainty on the analyst who makes the measurements and not with the user of the data. The uncertainty budget also serves to provide a feedback to the analyst. It identifies the dominant components of the measurement uncertainty and allows for better understanding, management, and improvement of the measurement process. Detailed examples of uncertainty calculations are presented for the most common types of uranium isotope measurements by multi-collector thermal ionization mass spectrometry (TIMS), e.g., total evaporation, conventional Faraday cup measurements using internal normalization, and combined measurements using a secondary electron multiplier and Faraday cups. Various sources of uncertainty common to multi-collector TIMS, such as baseline noise, peak-tailing effects, peak flatness, detector inter-calibration, and detector linearity response are discussed with respect to the determination of their uncertainty contribution and their influence on the results. Different approaches are explained with their advantages and disadvantages.

Isotope ratio analysis of actinides, fission products, and geolocators by high-efficiency multi-collector thermal ionization mass spectrometry

A ThermoFisher “Triton” multi-collector thermal ionization mass spectrometer (MC-TIMS) was evaluated for trace and ultra-trace level isotope ratio analysis of actinides (uranium, plutonium, and americium), fission products and geolocators (strontium, cesium, and neodymium). Total efficiencies (atoms loaded to ions detected) of up to 0.5–2% for U, Pu, and Am, and 1–30% for Sr, Cs, and Nd can be reported employing resin bead load techniques onto flat ribbon Re filaments or resin beads loaded into a millimeter-sized cavity drilled into a Re rod. This results in detection limits of <0.1 fg (10 4 atoms to 10 5 atoms) for 239–242+244Pu, 233+236U, 241–243Am, 89,90Sr, and 134,135,137Cs, and ≤1 pg for natural Nd isotopes (limited by the chemical processing blank) using a secondary electron multiplier (SEM) or multiple-ion counters (MICs). Relative standard deviations (RSD) as small as 0.1% and abundance sensitivities of 1 × 10 6 or better using a SEM are reported here. Precisions of RSD ≈0.01–0.001% using a multi-collector Faraday cup array can be achieved at sub-nanogram concentrations for strontium and neodymium and are suitable to gain crucial geolocation information. The analytical protocols reported herein are of particular value for nuclear forensic and nuclear safeguard applications.

Revised δ34S reference values for IAEA sulfur isotope reference materials S‐2 and S‐3

Revised delta(34)S reference values with associated expanded uncertainties (95% confidence interval (C.I.)) are presented for the sulfur isotope reference materials IAEA-S-2 (22.62 +/- 0.16 per thousand) and IAEA-S-3 (-32.49 +/- 0.16 per thousand). These revised values are determined using two relative-difference measurement techniques, gas source isotope ratio mass spectrometry (GIRMS) and double-spike multi-collector thermal ionization mass spectrometry (MC-TIMS). Gas analyses have traditionally been considered the most robust for relative isotopic difference measurements of sulfur. The double-spike MC-TIMS technique provides an independent method for value-assignment validation and produces revised values that are both unbiased and more precise than previous value assignments. Unbiased delta(34)S values are required to anchor the positive and negative end members of the sulfur delta (delta) scale because they are the basis for reporting both delta(34)S values and the derived mass-independent Delta(33)S and Delta(36)S values.

Comparative studies on the certification of reference materials by ICPMS and TIMS using isotope dilution procedures.

A comparison of different isotope dilution mass spectrometric (IDMS) procedures using inductively coupled plasma mass spectrometry (ICPMS) and thermal ionization mass spectrometry (TIMS) was carried out to examine the degree of equivalence between the used procedures in terms of requirements for reference material certification. The comparison was based on the measurement results and their uncertainties. The sample used in this study is a pure zinc metal to be certified by the Bureau Communie de Référence (BCR) for amount contents of different trace elements. This study focuses on cadmium and thallium. The TIMS values contributed to the certified values. To guarantee identical conditions as far as possible for the procedures under investigation, the samples were split into subsamples after spiking and digestion took place. Thus, every IDMS procedure started with an identical set of samples. In total, four different IDMS procedures and one external calibration procedure using internal standardization as an example of routine analysis were applied. The IDMS procedures divide in a group with and a group without trace/matrix separation. Multicollector TIMS (TI-MC-MS) and multicollector ICPMS (ICP-MC-MS) were used in combination with trace/matrix separation, whereas quadrupole ICPMS (ICP-QMS) and ICP-MC-MS were also applied to nonseparated samples. All IDMS results agree well within their combined uncertainties, while some results from the external calibration procedure do not. IDMS results obtained by ICPMS without separation are comparable to those obtained by TI-MC-MS with separation regarding precision and accuracy. The smallest uncertainties were achieved using ICP-MC-MS in combination with trace/matrix separation.

Improved lead isotope ratio measurements in environmental and biological samples with a double focussing magnetic sector inductively coupled plasma mass spectrometer (ICP-MS)

A method to measure lead (Pb) isotope ratios in biological and environmental samples using a single collector double focussing magnetic sector inductively coupled plasma mass spectrometer (ICP-MS) is presented. This method is intercalibrated with multicollector thermal ionization mass spectrometry (TIMS) to assess the suitability of the ICP-MS method for accurately and precisely identifying sources of environmental Pb exposure to humans. Results indicate that the external measurement precision (reproducibility) of this method, as evaluated by repeated analyses of the Pb isotope standard NBS 981 over the course of a year, was <0.1% (1σ) for 206 Pb: 204 Pb, 207 Pb: 206 Pb and 208 Pb: 206 Pb ratios. Accuracy of isotope ratio measurements by ICP-MS was evaluated by comparing analyses of whole blood (biological) and household dust (environmental) samples with the definitive TIMS analyses of the same samples. For whole blood and dust samples, the 206 Pb: 204 Pb, 207 Pb: 206 Pb and 208 Pb: 206 Pb ratios measured by ICP-MS and TIMS generally agreed to within twice the propagated standard deviation (2σ, σ=√σTIMS2+σICP-MS2)of both methods. However, a small but systematic difference between the Pb isotope ratios of blood measured with the two methods was apparent. The source of this difference remains under investigation. These data demonstrate that this ICP-MS method provides improved accuracy and precision of lead isotope ratio measurements compared to previous ICP-MS methods, and is suitable for use in studies to evaluate sources of environmental Pb exposure to children. Further, the increased samplethroughput and reduced cost of analyses using this method are substantial advantages over the more time-consuming and expensive TIMS method. Consequently, this Pb isotope methodology should prove useful as a routine tool in the investigation and mitigation of Pb exposure associated hazards.