NRC Publications Archive Archives des publications du CNRC Determination of the isotopic composition of osmium using MC-ICPMS Zhu, Zuhao; Meija, Juris; Tong, Shuoyun; Zheng, Airong; Zhou, Lian; Yang, Lu This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur. For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous. Publisher’s version / Version de l'éditeur: https://doi.org/10.1021/acs.analchem.8b01859 Analytical Chemistry, 90, 15, pp. 9281-9288, 2018-06-21 NRC Publications Archive Record / Notice des Archives des publications du CNRC : https://nrc-publications.canada.ca/eng/view/object/?id=45709299-174b-4f06-91d3-411ee9765217 https://publications-cnrc.canada.ca/fra/voir/objet/?id=45709299-174b-4f06-91d3-411ee9765217 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at https://nrc-publications.canada.ca/eng/copyright READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site https://publications-cnrc.canada.ca/fra/droits LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at [email protected]. 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Chem. 2018, 90, 9281−9288 pubs.acs.org/ac Determination of the Isotopic Composition of Osmium Using MC- ICPMS Zuhao Zhu,†,‡ Juris Meija,‡ Shuoyun Tong,∥ Airong Zheng,§ Lian Zhou,∥ and Lu Yang*,‡ †Fourth Institute of Oceanography, State Oceanic Administration (SOA), Beihai 536000, China ‡National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario K1A 0R6, Canada §College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China ∥State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China *S Supporting Information ABSTRACT: Despite its widespread applications in geology, all osmium isotope ratio measurements are either uncalibrated or rely on the veracity of the uncalibrated 1937 Nier values by adopting them as normalizing constants typically in conjunction with an exponential mass bias correction model. In this study, isotope ratios of osmium were determined in six commercial osmium materials, including the DROsS standard and a new NRC isotopic osmium reference material OSIS-1, by MC-ICPMS. We use a previously optimized and validated regression mass bias correction model to correct instrumental isotope fractionation effects which does not rely either on Nier’s values or on a strictly mass-dependent behavior of the isotopes. Deviations from mass-dependent fractionation (mass independent fractionation) were observed for osmium isotopes in MC-ICPMS with the most dramatic effect occurring for 187Os, wherein, on average, close to half-percent bias in the isotope ratio 187Os/188Os was observed as a result of imposing Russell’s law. 1. INTRODUCTION Union of Pure and Applied Chemistry is that of Völkening et 3 ’ In 1970, Riley and Delong noted that “very few comparisons of al. measured by N-TIMS which relies on Nier s values to the natural isotopic composition of osmium have ever been correct for instrumental fractionation of isotope ratios. In fact, ffi most measurements of osmium isotope ratios adopt fixed made because of analytical di culties and limited availability of ’ osmium rich samples”.1 Since then, significant improvements canonical values of nonradiogenic isotope ratios, such as Nier s value 192Os/188Os = 3.083,28,29 for mass bias correction of the in negative thermal ionization mass spectrometry (N-TIMS) ’ methods2,3 have led to numerous applications of osmium radiogenic isotope ratio. It is remarkable that Nier s measure- isotopes in geological sciences. These include the study of low- ments have not been superseded after eight decades of Downloaded via NATL RESEARCH COUNCIL CANADA on April 11, 2019 at 16:54:32 (UTC). progress in mass spectrometry. See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. and high-temperature processes such as mantle−crust interaction, sedimentation, cosmic evolution, ocean circulation, TIMS has been the traditional instrument of choice to and even industrial waste migration.4−20 The radioactive decay obtain high-accuracy osmium isotope ratio measurements, fi despite the investment of extensive sample preparation and of rhenium-187 to osmium-187 leads to signi cant variations 26,30 of this radiogenic osmium isotope. As an example, isotope ratio long measurement times. In the last several decades, 187Os/188Os varies by several orders of magnitude from 1:10 in multicollector inductively coupled plasma mass spectrometry ’ 7 21 (MC-ICPMS) has become a powerful tool for the determi- the Earth s mantle to 1:1 in seawater and 10:1 in some 26,31 sulfide ores.22 Owing to these variations, isotope ratios nation of isotope ratios in a variety of applications, largely involving osmium-187 are of key interest.23 due to its advantages in sample introduction and high ffi 32 Despite these advances, however, the measurement ionization e ciency. It has been noted that MC-ICPMS is technique is still not mature enough to allow for new better suited to measure osmium isotope ratios compared to 33 independent measurements of isotope ratios of osmium, and TIMS owing to the fact that ICP measures elemental ions 24−27 + − in turn, isotopic abundances or atomic weight. To this (Os ) directly whereas TIMS detects oxide ions (OsO3 ) day, most if not all osmium isotope ratio measurements are traceable (directly or indirectly) to the values published by Received: April 25, 2018 Nier in 1937.28,29 As an example, the best osmium isotope Accepted: June 21, 2018 ratio measurement currently recognized by the International Published: June 21, 2018 © 2018 American Chemical Society 9281 DOI: 10.1021/acs.analchem.8b01859 Anal. Chem. 2018, 90, 9281−9288 Analytical Chemistry Article which requires further signal deconvolution. Despite these approximately 5.6 min. Longer measurement time (17 min) advantages, however, MC-ICPMS suffers much larger was tested in our preliminary experiments, and it provided instrumental mass bias compared to that of TIMS.31 Although similar precision for osmium isotope ratios. Thus, the short the majority of the bias (if it is not caused by an interference measurement time was adopted for all subsequent work. effect) can be modeled using mass-dependent laws, mass- 2.2. Reagents and Solutions. Reagent grade nitric and independent fractionation (MIF) has been reported in MC- hydrochloric acids (Fisher Scientific, Ottawa ON, Canada) ICPMS for many elements including Nd,34−37 Ce,35 W,38 were purified before use via a sub-boiling distillation system Sr,35,39 Ge,40 Pb,40 Hg,40 Si,41 and Ba.42 Consequently, proper (Milestone Inc., Shelton CT, USA). A NanoPure mixed-bed mass bias correction is crucial when MC-ICPMS is used for the ion exchange system with reverse osmosis domestic feedwater determination of absolute isotope ratios. (Barnstead/Thermolyne Corp, Iowa USA) was used to A primary method to calibrate isotope ratio measurement prepare high-purity (18 MΩ cm) deionized water. Environ- results utilizes gravimetric mixtures of near-pure isotopes with mental grade aqueous ammonia (20−22% volume fraction) known chemical purity43 (not to be confused with the double was obtained from Anachemia Science (Montreal, Canada). spike calibration). For an element with N stable isotopes, this Aqueous ammonia (5%) and hydrochloric acid (1%) primary approach is based on measuring all (N − 1) isotope solutions were used to reduce the osmium memory effect ratios in all N isotopically enriched materials along with after each measurement session. A severe osmium memory isotopic composition measurements of (N − 1) independent effect was encountered with liquid introduction to MC-ICPMS gravimetric mixtures of any two enriched materials. This model during preliminary experiments. Commonly used rinsing has been successfully employed for many two-isotope systems solutions such as 3−5 M HCl26 and EtOH were tested (Li and C)44,45 and three-isotope systems (Si)46,47 and without much success. As suggested by Nowell et al.,26 it is recently adopted for more complex elements such as beneficial to keep osmium in a reduced or complexed state for 48 molybdenum. While this approach provides the highest a better washout. Thus, Na2SO3,NH2OH·HCl, and NH3·H2O metrological quality of isotope ratio measurements, it requires were tested. It was found that alternate use of 5% ammonia weighable quantities of all enriched isotopes in a chemically solution and 1% HCl (blank solution) was sufficient to wash pure form. As the number of isotopes increases, so does the out osmium after a session of measurement to a blank level cost of enriched isotopes, efforts to characterize their chemical within 30 min, likely due to the ability of ammonia to complex purities, as well as the complexity of mathematical calculations. osmium ions. We also rinsed the spray chamber daily with 5% Hence, cost-effective alternative approaches are often sought. ammonia, 5% HCl, and water to reduce the memory effects. The aim of this study is to provide osmium isotopic Six osmium materials were purchased from different composition measurements which are fully independent from commercial vendors as summarized in Table 1.