Ellyn S. Beary

Applications of the 190Pt186Os isotope system to geochemistry and cosmochemistry

Abstract Platinum is fractionated from osmium primarily as a consequence of processes involving sulfide and metal crystallization. Consequently, the 190Pt186Os isotope system (190Pt → 186Os + α) shows promise for dating some types of magmatic sulfide ores and evolved iron meteorites. The first 190Pt 186Os isochrons are presented here for ores from the ca. 251 Ma Norilsk, Siberia plume, and for group IIAB magmatic iron meteorites. Given the known age of the Norilsk system, a decay constant for 190Pt is determined to be 1.542 × 10−12a−1, with ±1% uncertainty. The isochron generated for the IIAB irons is consistent with this decay constant and the known age of the group. The 186Os/188Os ratios of presumably young, mantle-derived osmiridiums and also the carbonaceous chondrite Allende were measured to high-precision to constrain the composition of the modern upper mantle. These compositions overlap, indicating that the upper mantle is chondritic within the level of resolution now available. Our best estimate for this 186Os/188Os ratio is 0.119834 ± 2 (2σM). The 190Pt/186Os ratios determined for six enstatite chondrites average 0.001659 ± 75, which is very similar to published values for carbonaceous chondrites. Using this ratio and the presumed composition of the modern upper mantle and chondrites, a solar system initial 186Os/188Os ratio of 0.119820 is calculated. In comparison to the modern upper mantle composition, the 186Os/188Os ratio of the Norilsk plume was approximately 0.012% enriched in 186Os. Possible reasons for this heterogeneity include the recycling of Pt-rich crust into the mantle source of the plume and derivation of the osmium from the outer core. Derivation of the osmium from the outer core is our favored model.

Protocol for isotope dilution using inductively coupled plasma-mass spectrometry (ICP-MS) for the determination of inorganic elements

The Comite Consultatif pour la Quantite de Matiere (CCQM) endeavours to identify and carry out key activities with the objective of facilitating world-wide comparability and traceability of chemical measurements. Towards this goal, the CCQM has identified comparisons to be carried out using candidate primary methods of chemical analysis. One such method is isotope dilution mass spectrometry. In the first comparison carried out by the CCQM (Study I), the concentrations of various inorganic elements were determined in water solutions using IDMS. The results did not meet the target level of 1% maximum relative deviation from the reference values of the unknowns. It was concluded that more guidance was necessary on the execution of the IDMS method and that a detailed protocol should be developed. Participants would use inductively coupled plasma (ICP) as the ionization source. Here we present the protocol developed for use by CCQM participants in the next comparison (Study III) on the determination of the concentration of lead in water using the IDMS method with an inductively coupled plasma-mass spectrometer.

Purified reagents for trace metal analysis

Sub-boiling distillations have become a standard tool for the reduction of the inorganic analytical blank. More than 10 years of practical experience in the production of reagent acids is reviewed and a description is given of a new laboratory especially designed to permit trouble-free operation as well as ensure the continued high quality of the reagents produced.

Precise boron isotopic analysis of aqueous samples: Ion exchange extraction and mass spectrometry

Abstract This paper presents details of an effective ion exchange method for extracting and purifying boron from aqueous fluids as well as modifications to the cesium metaborate mass spectrometric method for determining boron isotopic ratios. Using these methods, natural waters and brines may be routinely analyzed with precision and accuracy on the order of 0.25%. (2 σ), as indicated by analyses of standards and samples taken through the full separation procedure. We review and compare the essential methods used previously for boron isotopic analysis and discuss factors that adversely affect analytical precision and accuracy.

190Pt-186Os and 187Re-187Os systematics of the Sudbury Igneous complex, Ontario

Abstract We measured by negative thermal ionization mass spectrometry (NTIMS) Re, Os and 186 Os/ 188 Os and 187 Os/ 188 Os in 26 samples of 18 Ni-Cu sulfide ores from the Falconbridge, McCreedy West, and Strathcona mines at Sudbury, Ontario. At McCreedy West and Falconbridge, the isochron Re-Os ages are 1835 ± 70 Ma and 1827 ± 340 Ma, and the initial 187 Os/ 188 Os ratios 0.514 ± 0.019 and 0.550 ± 0.024, respectively. The ages agree with the canonical value of 1850 ± 1 Ma for the Sudbury Igneous Complex (SIC). For Hangingwall and Deep Zone ores at Strathcona, the age of 1780 ± 7 Ma may reflect resetting by dyke activity. The high initial 187 Os/ 188 Os of 0.934 ± 0.005 in these ores is distinct from those at McCreedy West and Falconbridge. Strathcona Deep Copper Zone ores have highly radiogenic Os giving a mean model age of 1883 ± 54 Ma that is similar to ages at McCreedy West and Falconbridge, but distinct from other Strathcona sulfides. Initial 186 Os/ 188 Os in two Strathcona ores with low 190 Pt/ 188 Os average 0.119 826 ± 0.000 009 ( n = 3) and 0.119 827 ± 0.000 004 ( n = 3), respectively, with a grand mean of 0.119 827 ± 0.000 003. This ratio may be slightly lower than the chondritic value at that time. Similar ores at Falconbridge and McCreedy West show more scatter, averaging 0.119 855 ± 0.000 008 ( n = 6) and 0.119 867 ± 0.000 020 ( n = 3), respectively. These values are substantially suprachondritic. The Re-Os isotope systematics of Sudbury ores are clearly of crustal origin and may be derived from a binary mixture of Superior Province and Huronian metasedimentary rocks, with Strathcona, Falconbridge, and McCreedy West ores containing, respectively, 55%, 16%, and 12% of Os from Superior sediments. The suprachondritic 186 Os/ 188 Os at McCreedy West and Falconbridge may be due to admixture of Archean or Paleozoic mafic rocks with 190 Pt/ 188 Os ≈ 0.1. No trace of the asteroid that produced the Sudbury Structure has been reported. At the Whistle mine S-poor olivine melanorite inclusions with high Ni and Os and low 187 Os/ 188 Os may contain the signature of a magmatically fractionated asteroidal core contributing 1 to 2.5 % metal. The S-poor melanorite Ni and Os data are equally well explained by admixture of ≈40% mantle peridotite, however.

A comparison of isotope dilution mass spectrometric methods for the assay of copper in copper ore reference materials

The trend toward lower assays in the repeated determination of copper in copper ore, Standard Reference Material 332, have resulted in the withdrawal of this reference material due to material instability. Recent analyses by both isotope dilution thermal ionisation mass spectrometry (TIMS) and isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) have confirmed this change in copper assay. In this study ICP-MS was shown to be an excellent method for the determination of the concentration of copper in copper ore and therefore may be capable of relatively high precision for a number of elements in inorganic matrices. Two experiments were designed to study the relationship between the high loss of volatile components on drying and the corresponding low copper assay. The slow oxidation of CuS to CuSO4 was confirmed. The accelerated moisture study indicated that exposure to changes in temperature and relative humidity did not cause this oxidation. Microwave drying provided additional information about moisture associated with the samples that had been oxidised.

Sample preparation approaches for isotope dilution inductively coupled plasma mass spectrometric certification of reference materials

Ratio measurements can be made by inductively coupled plasma mass spectrometry (ICP-MS) with precisions approaching 0.1–0.2% relative standard deviation, under carefully controlled conditions. This capability is well suited to isotope dilution quantification, since quantitative data are based solely on ratio measurements. Conversion of the precision of isotopic ratio measurements to accuracy requires attention to both the operation of the ICP mass spectrometer and to the sample preparation procedures. The concentration of Mg, Cd, Mo and Pb were determined in synthetic samples with average precision and accuracy of <0.15%. Although more extensive chemistry was required, analytical precision was better than 0.15% for Cu and Cd in zinc ore and for Cu and Mo in domestic sludge.

Perspective. Impact of inductively coupled plasma mass spectrometry on certification programmes for geochemical reference materials

The National Institute of Standards and Technology (NIST) began using inductively coupled plasma mass spectrometry (ICP-MS) for the certification of its Standard Reference Materials (SRMs) in 1986, only a few years after instruments first became commercially available. The United States, Canadian and Ontario Geological Surveys (USGS, CGS, and OGS, respectively) also made early use of the method to provide new data for existing certified reference materials (CRMs) and other non-certified geochemical reference materials (GRMs). The application of ICP-MS extends to most elements in the periodic table. NISTs efforts have focused largely on environmentally important trace elements. However, the impact of ICP-MS analysis in geochemistry is greatest in providing certified values for the platinum group elements (PGEs) and the rare earth elements (REEs). This paper will review the growing impact of ICP-MS analyses on the certification of CRMs/GRMs. Examples include NIST SRMs 1646a Estuarine Sediment, 2709-2711 Soils, 113b Zinc Concentrate; Centre de Recherches Petrographiques et Geochemiques (CRPG) CRMs CHR-Pt+ and CHR-Bkgr; Canadian Certified Reference Materials Program (CCRMP) WGB-1 gabbro rock, TDB-1 diabase rock and three other CCRMP CRMs recently certified for the PGEs. NIST has used ICP-MS almost exclusively in conjunction with isotope dilution. This has not been the situation among other users, but is to be recommended in certification analysis for several reasons, which will be outlined.

High purity fluoropolymer materials: Trace element content and leaching

Abstract Many problems in analytical chemistry are shared by the high purity crystal growth community since both are greatly concerned with the effects of impurities either upon an analysis or upon a device. Fluoropolymers are widely used today in applications where inertness or high purity or both are needed. The behavior of these polymers in high purity solvent systems has been investigated by several analytical techniques. Both the resin from which finished parts are made as well as blow molded bottles have been evaluated to determine cationic impurities in both the resin and in leachates.

Approaches to the accurate characterization of high purity metal fluorides and fluoride glasses

Abstract The analytical challenges posed by the measurement of trace contaminants in high purity metal fluorides require that innovative chemical preparation procedures be used to enhance existing instrumental techniques. The instrumental techniques used to analyze these difficult matrices must be sensitive enough to detect extremely low levels of trace impurities, and the background interferences derived from the matrix (metal fluoride or glass) must be minimized. A survey of analytical techniques that have the necessary characteristics to analyze these materials will be given. In addition, means of controlling the chemical blank will be presented. Mass and atomic spectrometric techniques will be discussed, specifically graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma-mass spectrometry (ICP-MS). Analytical procedures using GFAAS and ICP-MS have been developed to determine sub ppb (part per billion) levels of contaminants in high purity fluoride materials.