Determination of rubidium by isotope dilution—inductively-coupled plasma mass spectrometry as an alternative to thermal ionization mass spectrometry

The combined techniques of inductively coupled plasma mass spectrometry (ICP-MS) and isotope dilution yield as much as a three-fold improvement in precision for trace-level rubidium determinations in geological materials over conventional isotope dilution using thermal ionization mass spectrometry (TIMS). Rubidium determinations by TIMS, precise to 0.6% (1 s.d.), are hindered by uncorrectable fractionation effects, whereas fractionation can be monitored during ICP-MS determinations, providing results as precise as 0.17% (1 s.d.). Precise rubidium data are critical for high-precision RbSr geochronology.     

Mass spectrometry of long-lived radionuclides

The capability of determining element concentrations at the trace and ultratrace level and isotope ratios is a main feature of inorganic mass spectrometry. The precise and accurate determination of isotope ratios of long-lived natural and artificial radionuclides is required, e.g. for their environmental monitoring and health control, for studying radionuclide migration, for age dating, for determining isotope ratios of radiogenic elements in the nuclear industry, for quality assurance and determination of the burn-up of fuel material in a nuclear power plant, for reprocessing plants, nuclear material accounting and radioactive waste control. Inorganic mass spectrometry, especially inductively coupled plasma mass spectrometry (ICP-MS) as the most important inorganic mass spectrometric technique today, possesses excellent sensitivity, precision and good accuracy for isotope ratio measurements and practically no restriction with respect to the ionization potential of the element investigated—therefore, thermal ionization mass spectrometry (TIMS), which has been used as the dominant analytical technique for precise isotope ratio measurements of long-lived radionuclides for many decades, is being replaced increasingly by ICP-MS. In the last few years instrumental progress in improving figures of merit for the determination of isotope ratio measurements of long-lived radionuclides in ICP-MS has been achieved by the application of a multiple ion collector device (MC-ICP-MS) and the introduction of the collision cell interface in order to dissociate disturbing argon-based molecular ions, to reduce the kinetic energy of ions and neutralize the disturbing noble gas ions (e.g. of ¹²⁹Xe⁺ for the determination of ¹²⁹I). The review describes the state of the art and the progress of different inorganic mass spectrometric techniques such as ICP-MS, laser ablation ICP-MS vs. TIMS, glow discharge mass spectrometry, secondary ion mass spectrometry, resonance ionization mass spectrometry and accelerator mass spectrometry for the determination of long-lived radionuclides in quite different materials.     

Precise and accurate isotope ratio measurements by ICP-MS

The precise and accurate determination of isotope ratios by inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) is important for quite different application fields (e.g. for isotope ratio measurements of stable isotopes in nature, especially for the investigation of isotope variation in nature or age dating, for determining isotope ratios of radiogenic elements in the nuclear industry, quality assurance of fuel material, for reprocessing plants, nuclear material accounting and radioactive waste control, for tracer experiments using stable isotopes or long-lived radionuclides in biological or medical studies). Thermal ionization mass spectrometry (TIMS), which used to be the dominant analytical technique for precise isotope ratio measurements, is being increasingly replaced for isotope ratio measurements by ICP-MS due to its excellent sensitivity, precision and good accuracy. Instrumental progress in ICP-MS was achieved by the introduction of the collision cell interface in order to dissociate many disturbing argon-based molecular ions, thermalize the ions and neutralize the disturbing argon ions of plasma gas (Ar+). The application of the collision cell in ICP-QMS results in a higher ion transmission, improved sensitivity and better precision of isotope ratio measurements compared to quadrupole ICP-MS without the collision cell [e.g., for 235U/238U approximately 1 (10 microg x L(-1) uranium) 0.07% relative standard deviation (RSD) vs. 0.2% RSD in short-term measurements (n = 5)]. A significant instrumental improvement for ICP-MS is the multicollector device (MC-ICP-MS) in order to obtain a better precision of isotope ratio measurements (with a precision of up to 0.002%, RSD). CE- and HPLC-ICP-MS are used for the separation of isobaric interferences of long-lived radionuclides and stable isotopes by determination of spallation nuclide abundances in an irradiated tantalum target.     

Strontium isotope ratios (87Sr/86Sr) of tooth enamel: a comparison of solution and laser ablation multicollector inductively coupled plasma mass spectrometry methods

Strontium isotope ratios (87Sr/86Sr) in tooth enamel provide a means to investigate migration and landscape use in humans and other animals. Established methods for measuring (87)Sr/(86)Sr in teeth use bulk sampling (5-20 mg) and labor-intensive elemental purification procedures before analysis by either thermal ionization mass spectrometry (TIMS) or multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Another method for measuring 87Sr/86Sr is laser ablation MC-ICP-MS, but concerns have been expressed about its accuracy for measuring tooth enamel. In this study we test the precision and accuracy of the technique by analyzing 30 modern rodent teeth from the Sterkfontein Valley, South Africa by laser ablation MC-ICP-MS and solution MC-ICP-MS. The results show a mean difference in 87Sr/86Sr measured by laser ablation and by solution of 0.0003 +/- 0.0002. This degree of precision is well within the margin necessary for investigating the potential geographic origins of humans or animals in many areas of the world. Because laser ablation is faster, less expensive, and less destructive than bulk sampling solution methods, it opens the possibility for conducting 87Sr/86Sr analyses of intra-tooth samples and small and/or rare specimens such as micromammal and fossil teeth.     

Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS

This paper reviews the problems encountered in eleven studies of Sr isotope analysis using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) in the period 1995–2006. This technique has been shown to have great potential, but the accuracy and precision are limited by: (1) large instrumental mass discrimination, (2) laser-induced isotopic and elemental fractionations and (3) molecular interferences. The most important isobaric interferences are Kr and Rb, whereas Ca dimer/argides and doubly charged rare earth elements (REE) are limited to sample materials which contain substantial amounts of these elements. With modern laser (193 nm) and MC-ICPMS equipment, minerals with >500 ppm Sr content can be analysed with a precision of better than 100 ppm and a spatial resolution (spot size) of approximately 100 μm. The LA MC-ICPMS analysis of ⁸⁷Sr/⁸⁶Sr of both carbonate material and plagioclase is successful in all reported studies, although the higher ⁸⁴Sr/⁸⁶Sr ratios do suggest in some cases an influence of Ca dimer and/or argides. High Rb/Sr (>0.01) materials have been successfully analysed by carefully measuring the ⁸⁵Rb/⁸⁷Rb in standard material and by applying the standard-sample bracketing method for accurate Rb corrections. However, published LA-MC-ICPMS data on clinopyroxene, apatite and sphene records differences when compared with ⁸⁷Sr/⁸⁶Sr measured by thermal ionisation mass spectrometry (TIMS) and solution MC-ICPMS. This suggests that further studies are required to ensure that the most optimal correction methods are applied for all isobaric interferences.     

87Sr/86Sr measurements on marine sediments by inductively coupled plasma-mass spectrometry

The application of inductively coupled plasma-mass spectrometry (ICP-MS) is documented for the study of the strontium isotopic composition (⁸⁷Sr/⁸⁶Sr) in geological samples, i.e. in the marine lithic fraction of core sediments. Methods for the determination of the isotopic composition, its accuracy and precision are reported. The results obtained simultaneously on 11 samples by both ICP-MS and thermal ionization mass spectrometry (TIMS) reveal a very good correlation (r² = 0.955). Received: 24 February 1997 / Revised: 26 May 1997 / Accepted: 30 May 1997     

87Sr/86Sr measurements on marine sediments by inductively coupled plasma-mass spectrometry

The application of inductively coupled plasma-mass spectrometry (ICP-MS) is documented for the study of the strontium isotopic composition (⁸⁷Sr/⁸⁶Sr) in geological samples, i.e. in the marine lithic fraction of core sediments. Methods for the determination of the isotopic composition, its accuracy and precision are reported. The results obtained simultaneously on 11 samples by both ICP-MS and thermal ionization mass spectrometry (TIMS) reveal a very good correlation (r² = 0.955). Received: 24 February 1997 / Revised: 26 May 1997 / Accepted: 30 May 1997     

Determination of isotope ratios of metals (and metalloids) by means of inductively coupled plasma-mass spectrometry for provenancing purposes — A review

Since considerable time, isotopic analysis of different elements present in a sample, material or object (such as the ‘light’ elements H, C, N, O and S and ‘heavy’ elements, such as Sr and Pb), has been used in provenancing studies, as several factors — defined by “the environment” or origin of the sample — can lead to measurable differences in their isotopic composition. For the light elements, traditionally, (gas source) isotope ratio mass spectrometry (IR-MS) is used, while for a long period of time, thermal ionization mass spectrometry (TIMS) was considered as the only technique capable of detecting subtle variations in the isotopic composition of the ‘heavier’ elements. However, since the introduction of the first inductively coupled plasma mass spectrometers (ICP-MS), considerable attention has been devoted to the development of methodologies and strategies to perform isotopic analysis by means of ICP-MS. While the relatively modest isotope ratio precision offered by single-collector ICP-MS may already be fit-for-purpose under some circumstances, especially the introduction of multi-collector ICP-MS instruments, equipped with an array of Faraday detectors instead of a single electron multiplier, has lead to tremendous improvements in the field of isotopic analysis. As a result, MC-ICP-MS can be seen as a very strong competitor of TIMS nowadays, while it even provides information on the small isotopic variations shown by some elements, that are not or hardly accessible by means of TIMS (e.g., elements with a high ionization energy). Owing to these new instrumental developments, the application field of isotopic analysis by means of ICP-MS is continuously growing, also in the field of provenance determination. This paper is intended as a review of the developments in and the recent applications of isotopic analysis by means of ICP-MS in this specific research field.     

ESI-QIMS Investigation of Sr,Rb, and Crown Ether Mixture Solutions

The isotope distribution of Sr, alternatively ⁸⁷Sr/⁸⁶Sr ratio frequently reported in geologic investigations, is obtained by direct electrospray ionization of aqueous samples containing Sr(II), Rb(I) with added 18-crown-6 (18c6) [1,4,7,10,13,16-Hexaoxacyclooctadecane C₁₂H₂₄O₆ m/z 264.3]. At relatively high concentrations of Sr and Rb, we observed favorable formation of Sr²⁺(18c6)₂ and Rb⁺(18c6) rather than Sr²⁺(18c6) complexes. Significant Sr²⁺(18c6)₂ suppression observed in post column addition of samples into water solvent disappeared when formic acid was present in the carrier solvent. Electrospray ionization-quadrupole-ion trap mass spectrometry (ESI-QITMS) successfully obtained the expected isotope distribution of Sr showing no interference from Rb without chromatographic separation of ⁸⁷Sr and ⁸⁷Rb necessary in ICP-MS studies.     

Evaluation of strontium isotope abundance ratios in combination with multi-elemental analysis as a possible tool to study the geographical origin of ciders

In order to evaluate alternative analytical methodologies to study the geographical origin of ciders, both multi-elemental analysis and Sr isotope abundance ratios in combination with multivariate statistical analysis were estimated in 67 samples from England, Switzerland, France and two Spanish regions (Asturias and the Basque Country). A methodology for the precise and accurate determination of the ⁸⁷Sr/⁸⁶Sr isotope abundance ratio in ciders by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) was developed. Major elements (Na, K, Ca and Mg) were measured by ICP-AES and minor and trace elements (Li, Be, B, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Mo, Cd, Sn, Sb, Cs, Ba, La, Ce, W, Tl, Pb, Bi, Th and U) were measured by ICP-MS using a collision cell instrument operated in multitune mode. An analysis of variance (ANOVA test) indicated that group means for B, Cr, Fe, Ni, Cu, Se, Cd, Cs, Ce, W, Pb, Bi and U did not show any significant differences at the 95% confidence level, so these elements were rejected for further statistical analysis. Another group of elements (Li, Be, Sc, Co, Ga, Y, Sn, Sb, La, Tl, Th) was removed from the data set because concentrations were close to the limits of detection for many samples. Therefore, the remaining elements (Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba) together with ⁸⁷Sr/⁸⁶Sr isotope abundance ratio were considered for principal component analysis (PCA) and linear discriminant analysis (LDA). Finally, LDA was able to classify correctly 100% of cider samples coming from different Spanish regions, France, England and Switzerland when considering Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba and ⁸⁷Sr/⁸⁶Sr isotope abundance ratio as original variables.     

Calculation methods for direct internal mass fractionation correction of spiked isotopic ratios from multi-collector mass spectrometric measurements

It is difficult to do internal mass fractionation corrections for isotope dilution analysis by thermal ionization mass spectrometry (TIMS) or multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), especially for MC-ICP-MS. In this study, calculation methods for direct internal fractionation correction of spiked isotope analysis by TIMS or MC-ICP-MS cycle by cycle for elements having at least two internal reference isotopic ratios are presented. For TIMS, direct internal mass fractionation correction calculation methods, based on both power and exponential laws, are derived; whereas for MC-ICP-MS, due to larger mass fractionation effects, only exponential law is considered. These calculation strategies can be applied for both static and multi-dynamic measurements. For multi-dynamic measurements, the isotope fractionation effect, gain and cup efficiency effects of different collectors, as well as ion beam fluctuation effects are all simultaneously eliminated. The calculation methods were verified by Sr isotopic analyses of spiked NBS987 standard solutions by TIMS and Hf isotopic analyses of spiked geological reference materials by MC-ICP-MS. In addition, precise and accurate calibrations of isotopic ratios of the spikes, based on the calculation methods, are discussed.     

The determination and application of 87Sr/86Sr ratio in verifying geographical origin of wheat

As ⁸⁷Sr/⁸⁶Sr ratio plays a significant role in authenticating the geographical origin of foodstuff, it is important to identify where the ⁸⁷Sr/⁸⁶Sr signature in food comes from, and the methods of ⁸⁷Sr/⁸⁶Sr ratio analysis in food and environmental samples. Wheat with three genotypes, soil and groundwater samples were collected from three regions of China during harvest time of 2014. The ⁸⁷Sr/⁸⁶Sr ratios in the samples were determined by thermal ionization mass spectrometer in order to investigate the possible source of ⁸⁷Sr/⁸⁶Sr in wheat, and the concentrations of Rb and Sr in wheat and soils were also detected by inductively coupled plasma mass spectrometry and combined with ⁸⁷Sr/⁸⁶Sr ratio in order to trace the geographical origin of wheat. The ⁸⁷Sr/⁸⁶Sr ratio, the contents Rb and Sr, and Rb/Sr ratio of wheat and soil samples showed significant differences among three regions. The ⁸⁷Sr/⁸⁶Sr ratios and the concentrations of Rb and Sr in soils were higher than those in corresponding wheat. The ⁸⁷Sr/⁸⁶Sr ratio in wheat was identical to that corresponding soil NH₄NO₃ extracts (labile fraction of soil) and groundwater. Wheat uptake more Rb than Sr. 3D distribution of ⁸⁷Sr/⁸⁶Sr, Rb and Sr could identify wheat samples from different regions clearly. The ⁸⁷Sr/⁸⁶Sr ratio of wheat reflects the ⁸⁷Sr/⁸⁶Sr ratio of the associated environment including soil and groundwater. It is expected that the use the parameters of ⁸⁷Sr/⁸⁶Sr ratio, the contents of Rb and Sr will allow to trace geographical origin of wheat. Copyright © 2017 John Wiley & Sons, Ltd.     

Isotope ratio analysis of individual sub-micrometer plutonium particles with inductively coupled plasma mass spectrometry

Information on plutonium isotope ratios in individual particles is of great importance for nuclear safeguards, nuclear forensics and so on. Although secondary ion mass spectrometry (SIMS) is successfully utilized for the analysis of individual uranium particles, the isobaric interference of americium-241 to plutonium-241 makes difficult to obtain accurate isotope ratios in individual plutonium particles. In the present work, an analytical technique by a combination of chemical separation and inductively coupled plasma mass spectrometry (ICP-MS) is developed and applied to isotope ratio analysis of individual sub-micrometer plutonium particles. The ICP-MS results for individual plutonium particles prepared from a standard reference material (NBL SRM-947) indicate that the use of a desolvation system for sample introduction improves the precision of isotope ratios. In addition, the accuracy of the ²⁴¹Pu/²³⁹Pu isotope ratio is much improved, owing to the chemical separation of plutonium and americium. In conclusion, the performance of the proposed ICP-MS technique is sufficient for the analysis of individual plutonium particles.     

Isotopic analyses by ICP-MS in clinical samples

This critical review focuses on inductively coupled plasma mass spectrometry (ICP-MS) based applications for isotope abundance ratio measurements in various clinical samples relevant to monitoring occupational or environmental exposure, human provenancing and reconstruction of migration pathways as well as metabolic research. It starts with a brief overview of recent advances in ICP-MS instrumentation, followed by selected examples that cover the fields of accurate analyte quantification using isotope dilution, tracer studies in nutrition and toxicology, and areas relying upon natural or man-made variations in isotope abundance ratios (Pb, Sr, actinides and stable heavy elements). Finally, some suggestions on future developments in the field are provided.     

High-precision direct determination of the Sr/Sr isotope ratio of bottled Sr-rich natural mineral drinking water using multiple collector inductively coupled plasma mass spectrometry

We describe a precise and accurate method for the direct determination of the ⁸⁷Sr/⁸⁶Sr isotope ratio of bottled Sr-rich natural mineral drinking water using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The method is validated by the comparative analysis of the same water with and without cation-exchange resin purification. The work indicates that isobarically interfering elements can be corrected for when ⁸⁷Rb/⁸⁶Sr < 0.05 (Rb/Sr < 0.015), and that the matrix elements (Ca, Mg, K and Na) have no significant effect on the accuracy of the Sr isotope data. The method is simple, rapid, eliminates sample preparation time, and avoids potential contamination during complicated sample-preparation procedures. Therefore, the high sample throughput inherent to the MC-ICP-MS can be fully exploited.     

Investigation and analysis of Ryukyu lacquerwares decorated with wisteria vine by pyrolysis GC/MS and 87Sr/86Sr isotope ratio

Three lacquer trays decorated with wisteria vine (rattan) produced in the 18–19th century in Ryukyu Kingdom were analyzed by cross‐section, pyrolysis gas chromatography/mass spectrometry, strontium isotope ratios (⁸⁷Sr/⁸⁶Sr), radioactive carbon‐14 dating, and field emission scanning electron microscope with energy dispersive X‐ray spectrometry. One sample had only one red lacquer layer, and the other two samples had two layers with top red lacquer and a bottom layer of natural lacquer, respectively. The ⁸⁷Sr/⁸⁶Sr isotope ratios of three samples were 0.7091–0.7107, consistent with that of the Japanese mainland (<0.7110). The wood species of lacquer objects were identified as Japanese white pine, Japanese cedar, and Cunninghamia lanceolata, which grow in the Japanese islands. The carbon‐14 dating results showed that the lacquer films were about 1719–1785. In pyrolysis gas chromatography/mass spectrometry, 3‐heptylphenol (C7) and 3‐pentadecylphenol (C15) were detected in the mass chromatograms at m/z = 108 and palmitic acid and stearic acid were detected in the mass chromatograms at m/z = 60, implying that the coating material was sap collected from Toxicodendron vernicifluum lacquer tree and included a drying oil. Energy dispersive X‐ray spectrometry revealed that mainly mercury sulfide was used as red pigment in these three Ryukyu lacquerwares. Copyright © 2017 John Wiley & Sons, Ltd.     

Influence of extraction process on Cs isotope ratios for Fukushima Daiichi nuclear power plant accident-contaminated soil

Journal of Radioanalytical and Nuclear Chemistry - The influence of extraction process on Cs isotope ratios was investigated by thermal ionization mass spectrometry (TIMS) for nitric-acid (HNO3)...     

Rapid and precise determination of Sr and Nd isotopic ratios in geological samples from the same filament loading by thermal ionization mass spectrometry employing a single-step separation scheme

Thermal ionization mass spectrometry (TIMS) offers the excellent precision and accuracy of the Sr and Nd isotopic ratio analysis for geological samples, but this method is labour intensive, expensive and time-consuming. In this study, a new analytical protocol by TIMS is presented that aims at improving analytical efficiency and cutting down experimental cost. Using the single-step cation exchange resin technique, mixed Sr and rare earth elements (REEs) fractions were separated from matrix and evaporated to dryness. Afterwards, mixed Sr + REEs fractions were dissolved and loaded onto the same Re filament using 1 μL of 2 M HCl. Then, Sr and Nd were sequentially measured without venting using TIMS. In contrast to conventional TIMS methods, the merits of this analytical protocol are its cost- and time-saving adaptations. The applicability of our method is evaluated by replicated measurements of ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd for nine international silicate rock reference materials, spanning a wide range of bulk compositions. The typical internal precision in this study is ca. 0.001% (RSE) for ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd; the analytical results obtained for these standard rocks show a good agreement with reported values, indicating the effectiveness of the proposed method.     

Determination of Am and Cm in spent nuclear fuels by isotope dilution inductively coupled plasma mass spectrometry and isotope dilution thermal ionization mass spectrometry after separation by high-performance liquid chromatography

Elemental and isotopic determination of americium and curium in spent nuclear fuels is necessary to validate neutronic calculation codes and for nuclear waste disposal purposes. Prior to mass spectrometric analysis, it is mandatory to perform separations in order to eliminate isobaric interferences between U, Pu, Am and Cm. In the spent fuels samples analyzed, a separation of U and Pu has been first realized with an anion-exchange resin. Then a rapid Am/Cm separation has been developed by high-performance liquid chromatography (HPLC) with an on-line detection using the Am and Cm α-emission. The influence of the different parameters on the chromatographic separation are described and discussed. Inductively coupled plasma mass spectrometry (ICP-MS) and thermal-ionization mass spectrometry (TIMS) have been used to measure the isotopic composition of U, Am and Cm and to determine the ²⁴¹Am/²³⁸U and ²⁴⁴Cm/²³⁸U ratios with the double spike isotope dilution method. The measurement procedures and the accuracy and precision of the results obtained with a quadrupole ICP-MS on different spent fuels samples are discussed and compared with those obtained by TIMS, used as a reference technique. Received: 30 November 1998 / Revised: 8 January 1999 / Accepted: 12 January 1999     

Determination of Am and Cm in spent nuclear fuels by isotope dilution inductively coupled plasma mass spectrometry and isotope dilution thermal ionization mass spectrometry after separation by high-performance liquid chromatography

Elemental and isotopic determination of americium and curium in spent nuclear fuels is necessary to validate neutronic calculation codes and for nuclear waste disposal purposes. Prior to mass spectrometric analysis, it is mandatory to perform separations in order to eliminate isobaric interferences between U, Pu, Am and Cm. In the spent fuels samples analyzed, a separation of U and Pu has been first realized with an anion-exchange resin. Then a rapid Am/Cm separation has been developed by high-performance liquid chromatography (HPLC) with an on-line detection using the Am and Cm α-emission. The influence of the different parameters on the chromatographic separation are described and discussed. Inductively coupled plasma mass spectrometry (ICP-MS) and thermal-ionization mass spectrometry (TIMS) have been used to measure the isotopic composition of U, Am and Cm and to determine the ²⁴¹Am/²³⁸U and ²⁴⁴Cm/²³⁸U ratios with the double spike isotope dilution method. The measurement procedures and the accuracy and precision of the results obtained with a quadrupole ICP-MS on different spent fuels samples are discussed and compared with those obtained by TIMS, used as a reference technique. Received: 30 November 1998 / Revised: 8 January 1999 / Accepted: 12 January 1999